GRIGORE T. POPA UNIVERSITY OF MEDICINE AND PHARMACY OF IAȘI [309440]

GRIGORE T. POPA "UNIVERSITY OF MEDICINE AND PHARMACY" OF IAȘI

FACULTY OF DENTAL MEDICINE

SPECIALITY DENTAL MEDICINE

DISCIPLINE IMPLANT PROSTHODONTIC REHABILITATION

THESIS

Implant rehabilitation therapy in maxillary

Kennedy class I edentulism

ADVISOR GRADUATE STUDENT: [anonimizat]. STAMATIN OVIDIU ŐZSOY EMRAH

IAȘI

2016

TABLE OF CONTNENTS

Introduction ……………………………………………………………………………………………………………… 3

Synthesis of Literature ………………………………………………………………………………………………. 4

I. Pre-operative evaluation ……………………………………………………………………………………………. 4

I.1. Anatomical and physiological considerations ……………………………………………………………. 4

I.2. Clinical and paraclinical examination protocol ………………………………………………………….. 9

II. Prosthetic options in Kennedy class I maxilla edentulism …………………………………………… 19

II.1. [anonimizat] …………………………………………………………………………… 19

II.2. Long-term skeletal prosthesis ……………………………………………………………………………….. 20

II.3. Implantology prosthetic options …………………………………………………………………………….. 21

III. Clinical cases ……………………………………………………………………………………………………….. 30

Discussions ………………………………………………………………………………………………………………..40

Conclussions ……………………………………………………………………………………………………………. 51

Bibliography ……………………………………………………………………………………………………………. 53

INTRODUCTION

Implant dentistry has evolved as a highly predictable clinical procedure in routine cases where the local anatomical configuration is favorable for this type of rehabilitation. [anonimizat] 1986 [anonimizat], if considered to be the most successful and reliable prosthodontic option for missing tooth replacement and also as a retainer of the loose dentures.

[anonimizat], immediate implant restoration, "All-on-4" and "All-on-6" concepts etc. to provide a desired level of implant treatment to the patients and achieve better short and long term success rates. However, a favorable local and general biological status is not met by all of our patients. [anonimizat]. As a [anonimizat] a larger field of research and those elements were followed by a greater success of the implant therapy in the patients with crestal ridge deficiency, infrabony defects or unfavorable soft tissue thickness.

Dental implant placement in the edentulous posterior maxilla area can present difficulties because of a horizontal, vertical, or combined alveolar ridge resorption caused by different etiologic factors such as periodontal disease, premature tooth loss due to odontal lesions, or increased pneumatization of the maxillary sinus. The posterior maxilla has been known by many clinicians as one of the most difficult problematic areas for implant dentistry, requiring a maximum of knowledge and attention to achieve a successful therapy.

This thesis aims to present a complete clinical and paraclinical examination of the patients with class I Kennedy maxilla edentation, followed by all options of hard and soft tissue options in order to prepare the local area for implant therapy.

SYNTHESIS OF LITERATURE

I. PREOPERATIVE EVALUATION

I.1. ANATOMICAL AND PHYSIOLOGICAL CONSIDERATIONS

Upper maxillary anatomical configuration

Hard and soft tissue healing after tooth extraction will lead to complex local anatomical changes wich has a maximum importance especially in implant dentistry if we want to achive clinical success. Maxillary bone structure, innervation and vascularisation have a very important act in the predictability of the implant restorations. Every inserted implant must be preceded by a proper evaluation of the bone offer in terms of density and volume, the type of soft tissue which will be around the implant (thick or thin gingival biotype) and also the relationship with the surrounding anatomical elements. [10]

The maxillary bones are one of the largest bones of the viscerocranium and within their medial suture form upper maxilla. The shape of this bone is pyramidal, with two sides (external and internal), four margins wich describe four angles. Inside the body of this bone, it can be found another pyramidal structure wich hosts the maxillary sinus. [19]

The maxillary sinus is the only sinus presented at birth and it`s volume varies between 9cm³ – 24cm³. The size of the sinus will increase with age by pneumatization wich varies from individual to individual and from site to site. The subanthral dimension can be diminished also after extracting the maxillary teeth wich have the roots placed in or very close to the sinus. The inner walls of this anatomical element is lined with the Schneiderian membrane. This membrane consists of respiratory multistratified epithelium formed by ciliated cells resting on the basement membrane. The membrane is continuous and connects to the nasal epithelium through the ostium in the middle meatus. In sinus bone augmentation we must be very careful with the volume of bone substitute because we don't want to obliterate the meatum. Also, any signs of sinus inflammation need to be evaluated and treated before any dental procedures because they represent a high risk of the additive therapy failure.[10,18]

Nervous branches which supply the sinus are derived from the posterior-superior alveolar branch of the maxillary division of the trigeminal nerve.

The blood circulation of the maxillary sinus and the posterior maxilla region is primarily obtained from the postero-superior alveolary artery and some branches from the infraorbital artery, both coming from the maxillary artery. Many anastomoses are described by different authors between these two arteries in the lateral antral wall. This fact has a very important clinical significance because accidental sectioning of a vascular branch can lead to hemorrhage and it will require all the effort from the clinician to stop the bleeding rapidly. A predictable way to evaluate abnormal artery anastomoses in the lateral antral wall is by carefully evaluating the anatomical area within the preoperative Cone-Beam Computed Tomography. [27]

Physiological considerations

In 1986 PI Branemark defined the osseointegration of the implant as "direct structural and functional connection between ordered, living bone and the surface of the load-carrying implant". In the same year SG Steinemann stated this phenomenon as "the direct contact between bone and implant surface".26]

Immediately after the implant loading into the maxilla bone, the periodontal tissue surrounding the implant passes through different stages of histological changed in order to reach the final stage of osseointegration of the implant with the peri-implant bone. The clinician must know and take account of these microscopic changes because all these can be deciding factor in the choosing of the rehabilitation protocol, whether we refer to conventional two-stage to one-stage implant treatment protocol, early or immediate loading of the implant. [8]

Several studies have been performed among time to find an optimal surface treatment to provide a better osseointegration process. There are scientific evidence that a roughened titanium implant surface improves bone anchoring compared to conventionally machined titanium surfaces. It has been demonstrated that a rough surface facilitates migration of osteogenic cells to the implant surface in order to encourage local osteogenesis. Also, the mechanical environment provided by this type of implant surface influences cellular proliferation and differentiation which leads to tissue synthesis. In fact, the rough-surface implants show increased removal forces, higher and earlier bone implant contact percentage, and improved osseointegration.[26]

After implant insertion, synthesis of new bone begins simultaneously at the prepared osteotomy wall and the implant surface. The contact osteogenesis begins at the implant surface but there is also a distant osteogenesis which begins at the same time at the osteotomy wall. Completion of both osteogenesis processes results in complete new bone formation at the local site and this phenomenon can describe the best as the implant osteointegration with the maxilla. [19,21]

Osseointegration is a term commonly used when we discuss implant therapy. This process means that there is no relative movement between the implant and the surrounding bone. Some researchers believe that there is a chemical integration between the bone and the surface of the titanium implant, and not only the physical integration wich represents the mechanical fixation of the implant in the bone. Osseocoalescence refers specifically to the chemical integration of the implants in bone tissue. The term is directed connected with bio-reactive materials such as bioactive classes, calcium phosphates, which undergo reactions that lead to a possible molecular bonding between bone and the biomaterial. With these type of materials the tissue effectively coalesce with the implant body. Osseocoalesced implant showed resistance to both tensile and shear loads. Unfortunately, the term has not found a widespread usage and osseointegration still is often used to describe the interaction phenomena between the bone and biomaterials. The main difference between osseocoalescence and osseointegration is that chemical integration provides good resistance to both shear and tensile forces but mechanical integration provides only good resistance to shear forces but poor resistance when it comes to tension [11,19] (Figure 1).

Osseointegration requires bone resorption, apposition and synthesis on the implant surface without any micromovement of the load. During the implant insertion, according to different parameters, the stability that the implants archives is completely mechanical and it is called primary stability. During the healing period, in a manner of months (4-6 months according to different studies), the biological processes of osseointegration change in order to achieve a mixture between a mechanical and a biological stability (secondary stability). The surrounding bone physiologically changes during the biological processes of osseointegration described by multiple phases of bone resorption and apposition over the implant surface. In this period, any micromovement of the implant may lead to a failure of implant osseointegration within the maxillary bone. We can note that the primary stability changes to secondary or biological stability one the osseointegration process of the implant is completed.[11]

Soft tissue integration around the implant structures like can be defined as a "biological process that occurs during the formation and maturation of the structural relationship between the soft tissues and the transmucosal implant superstructures". Long-term survival of implant restorations implies an adequate zone of attached and keratinizes soft tissue with intimate adaptation to the implant superstructures. Those tissue elements (epithelial and connective) are organized in order to form a protective soft tissue sealing around the implant structures with will serve to mechanical and chemical (mainly bacterial) challenges encountered in a contaminated oral cavity. The clinician must be very careful when manipulating and preserving the existing amount of soft tissue in order to achieve long-term implant therapy success. If the local area is devoided of attached and keratinized soft tissue, the clinicians must perform soft tissue grafting procedures in order to regenerate a healthy attached, thick and keratinized zone of marginal soft tissue around the implant superstructure, with a minimum of 3mm. [11,18,19]

Comparative anatomy and physiology of the tooth and the osseointegrated implant

Although the dental implant intraorally may look like a crown of a natural restored tooth, the peri-implant tissues show several biological differences between the implant surface and its superstructures compared to the natural tooth (Figure 2). [11]

The maintaining therapy and prevention of periodontal diseases are different in those two different situations and both the clinician and the patient must be aware of them in order to achieve a predictable implant therapy with a long-term maintenance. It is well known that the natural tooth possesses a periodontal ligament wich provides nutrient supply to the periodontal surrounding tissues necessary for their maintenance and long-term survival but also it serves as an efficient shock absorber against different force intensities applied over the tooth during the mastication or different parafunctions. High intensive forces will lead to an increase of the thickness of the periodontal ligament with thicker collagen fibers and also there are some bone (lamina dura) condensations described as adaptative changes. From this point of view, the implant retention and protection is inferior. The implant gets directly osseointegrated with the bone and does not have any structure like the periodontal ligament. It only possesses limited sources of nutrient supply to the perio-implant tissue and also transverses all the occlusal forced directly to the bone. This is a common fact which can explain bone resorption around the implant the rough forces are applied.[6,18,21]

Another difference which the clinician must know is that the periodontal soft tissue around the implant does not show any connective tissue attachments to the implant collar and its superstructure like the natural tooth, and any mechanical or chemical injury to the internal epithelial of the sulcus may directly affect the crestal bone with bone resorption as a consequence. For this reason, deliberate peri-implant gingival probing some authors don't recommend. Last but not least, the peri-implant tissue (crestal bone and soft keratinized soft tissue) receive blood supply only from the periosteum and from the basal bone. In this case, the blood supply from the periodontal ligament is absent and as a consequence, the peri-implant with limited thickness may find it difficult to survive and may get affected by resorption. [6]

Table I. Comparative features between periodontal and peri-implant tissue. [19]

I.2. CLINICAL AND PARACLINICAL EXAMINATION PROTOCOL

Any patient with an edentulous space is a candidate for mobilized or fixed prosthodontic treatment options. Studies concerning endosseous implants suggest a success rate between 90% to 95% that can be expected in healthy patients with good soft and hard tissue offer and normal healing capacity. [21]

Clinical examination

Local evaluation of potential crestal sites for implant placing and prosthetic restorability is an essential part of determining what type of prosthodontic rehabilitation suits best. Determining whether the patient is a good candidate for implant therapy is an important aspect decided after a comprehensive evaluation process. This aspect includes the doctor ability to identify all the local or systemic factors that might increase the risk of inter- / post- operative failures, as well as determining if the patient`s expectations are reasonable or not.[8,21]

A pretreatment evaluation is absolutely required for any patient who is being considered for dental implant therapy or other prosthodontic rehabilitation options. The assessment should evaluate all aspects of the patient's current systemic health status which also includes a review of the patient's medical history, chronical medication and all medical treatments which he has benefited from. [19]

A thorough medical history is absolutely required for any patient in need of dental treatment. This history should be noted in writing by the patient in a questionnaire completion before the clinical examination followed by a dialogue with the clinician. The patient's health status is very important because there are many systemic conditions which increase the risk for adverse reactions or postoperative complications. [6,8]

In order to benefit from a surgical therapy for placement of dental implants the patient's health status must be reasonably good under certain parameters established by common agree of a representative committee who is responsible to inform all practitioners about the guidelines. Any disorder that may interfere with the physiological wound-healing process and particularly the osseointegration must be carefully considered as a possible risk factor or contraindication to the dental therapy needed by the patient. [8]

A comprehensive physical examination is necessary if the clinician has any doubts about the current health and biological status of the patient. Routine psyhical examination implies:

▪ Appropiate laboratory blood tests (BT, INR, Platelet count, PT, aPTT, TT) if there are suspected bleeding disorders;

▪ Fasting glucose, glucose tolerance test, glycohemoglobin in case of diabetes;

▪ Cardiological consult (blood preasure reading, EKG) in case of cardio-vascular diseases

▪ Allergy testing for local anesthetics or other drugs if patient reports allergic episodes;

A review of patient's past dental experiences can be a valuable part of the evaluation process. Some oral phenomena may indicate a systemic condition that the general appearance of the patient didn't reflect. For example, the chronic periodontal disease with sever bone loss and many other periodontal complications (frequent abscesses) may indicate a susceptibility to infections which can be described in HIV/AIDS or diabetes. The patient's previous experiences with dental therapy whether surgical or prosthodontic should be discussed. An individual may have some difficulties with the implant therapy and long-term maintenance of the restoration if he declares that he had numerous problems and difficulties sustaining a proper dental care. It`s a priority before establishing a treatment plan to identify the past problems the patient confronted with and to elucidate any contributing factors. The doctor must assess the patient's dental knowledge and it is responsable to explain to the individual all the sides of the proposed treatment plan in a way that he will understand and comply with it. Generally, patients react more quickly when the edentulous space is in a frontal area because of the esthetic concerns. Class I Kennedy edentation is characterized by biterminal edentation which affects the patient's masticatory functions. In case that the general health status of the patient doesn't permit surgical therapy or the cost of the implant therapy is not affordable, partial removable dentures must be taken into account. [8,18,21]

Extraoral examination (cervico-facial) is performed by inspection (frontal and lateral, static and dynamic) and also by supperficial and deep palpation of the maxillo-facial anatomical structures. [8]

The intraoral examination is performed in order to evaluate the current health of existing teeth, as well as to assess the biological parameters of the oral soft and hard tissues. It is an absolute requirement that there should not be any pathologic condition present in any of the tissues of the oro-maxillo-facial regions. Any oral lesion, especially infections or tumoral, should be diagnosed and treated before the dental therapy. Some of the premalignant oral lesions that are an absolute contraindication for dental treatment are angular cheilitis, hyperplastic chronic candidosis, submucous fibrosis, discoid lupus erythematosus, oral lichen planus, oral leukoplakia and congenital dyskeratosis.[8]

The examination of the tooth units must reveal the degree of any coronal lesions, their implantations axis and stability. Also, the clinician must evaluate the periodontal status, if there is any gingival inflammation or alveolisis (vertical, horizontal or combined) and tooth mobility.

Oral hygiene status is a very important element which dictates the implant therapy predictability. The doctor is responsible to teach the patient an appropriate brushing techniques and oral health measures especially if an implant therapy is proposed. Poor oral hygiene is correlated with high risk of failure or any type or oral restorative treatment option. [6]

Occlusion evaluation must be assessed by static and dynamic. In class I Kennedy edentation there is a loss of the lateral occlusal contacts and it will lead eventually to dental vertical and horizontal migration, fenomena which will make the oral rehabilitation case more difficult to treat.[8]

In terms of prosthodontic oral rehabilitation, the doctor must assess all the parameters of the edentulous space in order to plan the treatment scheme which is suited for the particularities of the case. Therefore, after a thorough extraoral and intraoral evaluation, the doctor must examine the potential implant sites. All sites should be clinically evaluated to measure the available space in the bone for the placement of the implants and, also, in the dental space for prosthetic replacement of the tooth's crown. [8]

The limits of the potential prosthetic site:

▪ Widh (the bucco-lingual dimension of the edentulous space)

▪ Lenght (the mesio-distal dimension of the edentulous site)

▪ Height (the crestal-occlusal dimension of the edentulous site)

All those three parameters that describe the potential prosthetic site can be approximated with a periodontal probe or other calibrated measuring instrument.There should be also noted the orientation of adjacent teeth and their roots because there is the possibility that there may be enough space in the coronal area for the crown but not enough space in the apical region for the endosseous implant if the roots are in or near the bone area of interest. We can notice that there may be adequate space between the roots, but the coronal aspects of the teeth may be unfavorable for emergence and restoration of the implant.[6,14]

For safe endosseous implant placement it's recommended at least 1.5 – 2 mm of bone width around all surfaces of the implant. Regarding the interocclusal space, it`s dimension vary slightly depending on the type of abutment and the implant-restorative interface. Therefore, many authors recommend a generic average of interocclusal space of 7 mm. [18,19,26]

Paraclinical examination

Diagnostic casts (study models) have a critical importance in establishing a proper diagnostic and the best suitable prosthodontic treatment plan. Missing teeth have consequences like continued bone resorption and dentition changes, factors which the doctor must take into account before therapy. Study models are valuable also for research purposes and forensic information as they represent a precise stone reproduction of the dental arch and some of the surrounding area. Use of stone casts can be very effective in the patient’s education process because they provide comparable morphological data of the initial local status and the changes that have taken place over time. [26]

One of the biggest advantages of the diagnostic casts is that enables the practitioner to evaluate several prosthodontic criteria while the patient is absent from the medical center. Therefore the study models can permit an open dialogue of treatment with other doctors and dental technicians for consultation. Diagnostic casts are created by laboratory technicians after they receive the impression from the doctor. [8,26]

Study models mounted using an accurate record of the maxilo-mandibular relationships in terms of occlusion on an articulator provide much information that can influente the final treatment plan. Some of the factors which are important to evaluate on study models are:

▪ Edentulous ridge configuration;

▪ Edentulous ridge relationship with adjecent and opposing teeth;

▪ Edentulous ridge soft tissue parameters (lenght, width, angulation, muscle attachments);

▪ Jaw tuberosities or other exostosis;

▪ Occlusal centric position (freedom in centric, long centric, wide centric);

▪ Premature occlusal contacts, presence of working or balancing contacts;

▪ Tooth morphology and integrity;

▪ Position and the structure of the potential abutments;

▪ Force direction at the future implant site;

▪ Interarch space.

The impression can be taken with a variety of materials, but in the last years, digital impressions increased their popularity among the practitioners. Digital imaging impression can also be used to create stone study models, which can reproduce highly accurate the jaws, teeth, periodontal tissue and palatal area. This technique requires certain equipment and instructed medical personnel but it represents a method with many advantages compared to traditional impression techniques. [23]

Study models can also be used for designing surgical templates. A surgical template is a union of guiding cylinders and a contact surface. The contact surface, made from acrylic resins, can be placed on the patient’s gingiva or they can be directly fixed on the patient’s jaws with special screws, the last method is used predominantly in complex cases of full denture rehabilitation. The cylinders within the drill guides assist in transferring the plane by orienting the practitioner's osteotomy drill in the desired location and direction. It’s a predictable way to place implants and surgical templates are very recommended to any unexperienced surgeon due to the fact that it eliminates many possible insertion errors. [26]

The intraoral camera represents a video camera which allows clinicians to capture images inaccessible to direct view. Nevertheless, the images captured with this device are primarily used for patient’s chairside education but they can also be stored on a hard drive within the patient's medical records. The most important requirements for this device is to be as small as possible in order to get access to any intraoral situs and to capture high quality images. [8]

Of course, the clinical identification is just the first step. The doctor’s responsibility is to inform the patient and make him understand the issue before he consents to treatment. The intraoral camera is one of the best tools to use in order to get the patients emotionally involved with their oral health care. The usage of this gadget in implant dentistry is limited and it’s valuable traits can be used before prosthetic rehabilitation while detecting lesions which affect the remaining arch teeth. [8]

The radiographic evaluation of the denture assists in determining the presence of decay, inflammatory apical lesions, and periodontal bone loss. Dental films can be used to assess the periodontal disease severity in terms of bone loss but it cannot indicate the presence or absence of the disease process. [6,21]

The main anatomical elements which must be examined are:

▪ The bone crest morphology, it’s quality and it’s volume (vertical hight);

▪ The lamina dura (thick / thin, present / absent);

▪ Periodontal space (width);

▪ The distance from the crestal bone to the cemento-enamel junction;

▪ The integrity of adjecent teeth.

Nowadays most practitioners use digital radiography techniques. Some of their advantages are that it allows a better visualization of the bone low-density area, radiation exposure is less than the one from the conventional techniques and last but not least, the images can be edited (contrast, brightness) in order to get more precise details of the local biological configuration.

Dental implants do not decay nor they develop endodontic inflammatory lesions. Though, the crestal bone area is often affected by periodontal conditions orchestrated by microbial pathogens influenced by an unfavorable systemic health status. Therefore, radiological examination is one of the most accessible tools for practitioners to use to evaluate the marginal bone loss. However, this method has certain limitations because a radiograph can illustrate only the septum crestal level because it’s two dimension ability. The radiograph is less diagnostic when it comes to vertical buccal or palatal V-shaped defects around the implant, regardless the technique used to capture the hard tissue configuration (Figure 3). [21,26]

Figure 3. Example of periapical radiographs usage during the

implant insertion protocol. [21]

A peri-implant radiolucency often indicates a reason that the doctor should worry about because it’s one of the first signs of implant failure. The decision to try to save the implant or to explant it may depend on it’s mobility, evaluated with Periotest or similar devices. On rare situations, an apical radiolucency has been observed on a non-mobile implant. This fact is probably a perforation of one of the cortical plates of the bone. If the apical radiolucency is expanding or is accompanied by a fistula, surgical correction is absolutely necessary. In this case, if the implant is or gets mobile, it will be explanted. [13,24]

Periodically the implant and surrounding area’s health must be evaluated depending on the clinical and radiological observations. Therefore, a baseline radiograph will be obtained at the initial delivery of the restoration. By this time the biological width and influence of the implant crest module design have contributed to its influence on a possible bone loss. Because of the fact that crestal bone changes often occur during the first 12 months of loading, preventive maintenance appointments are recommended to be scheduled every 3 months and periapical or bitewing radiograph should be taken at 6 months to compare with the baseline in case of suspicious abnormal probing depths or other sign of inflammation. If no changes are pointed, the radiographic exam of the implant and it’s restoration should be scheduled for every 3 years. [13,19]

Occlusal radiographs are planar high-resolution radiographic images. They produce an oblique and distorted image of the maxillary bones which is of little use in implant dentistry. The mandibular occlusal radiographs use Donovan incidence while for the maxilla is needed Belot incidence. However, this type of radiological exam shows the widest width of the bone compared to the width of the crest, where the diagnostic data is most needed. The degree of the trabecular bone mineralization cannot be determined, therefore the spatial relationship between critical anatomical structures and the implant site are not relevant. Consequently, the occlusal radiograph is rarely indicated for diagnostic preprosthetic purposes in implantology. [24]

Cephalometric radiographs are oriented lateral radiographs of the cranium. This type of radiological exam is characterized by a cross-sectional image of the alveolus in the midsagittal plane which demonstrates the relationship between occlusion and esthetics. Frequently used in orthodontics, it assesses length, width, angulation and geometry of the alveolus and it can be accurate for bone quantity determination. Some facts that the clinician must take notice is the loss of vertical dimension, skeletal arch interrelationship, anterior crown-implant ratio and the anterior tooth position in the prosthesis. Therefore, this radiological exam is a useful tool for developing a treatment plan, especially for the completely edentulous patient. However, this technique is not useful when it comes to evaluating the bone quality. Moreover, some authors affirm that the image resolution is less when compared to intraoral radiographs. [8,13,24]

Panoramic radiographs have been widely used in dentistry because they offer an overview of many structures of the viscerocranium which can’t be observed with standard apical radiographs. Some of this structures are the temporomandibular joint, the coronoid process of the mandible, the shape and structure of the mandibular condyle, the maxillary sinuses and the nasal fossa. Digital panoramic radiographs replace the film-based image with a two-dimensional array of pixels. There are many studies investigating the precision and quality of this type of radiographic exam and most of them conclude that the digital system is a bit more superior to the conventional type. [26,27]

The panoramic radiograph offers an overview of the maxilla’s topography, showing useful data regarding the bone structure, information very important in establishing the local biological status which can indicate or not the implant therapy, but also can give information about the mesiodistal implantation axis of a possible implant. [8]

Using this type of paraclinical exam allows the clinicians to acquire a preliminary evaluation of the alveolar crests and their bone density based on the opacity shown by the intertrabecular spaces. This the accuracy of this evaluation depends on the technique used to capture the X-ray image and the mineralization degree of the compact bone which can sometimes hide a spongious bone radiolucency. There are four macroscopic structures of the bone, described by Carl Misch, located in different edentulous areas of the maxilla and mandible (Table II). [13,19]

Table II. Misch’s bone density classification[19]

The evaluation of the bone morphology in the posterior maxilla situs on a class I Kennedy edentation and it’s configuration near the maxillary sinus is also a very important step before the surgery procedures. The insufficient subantral bone volume may indicate the clinician if there is need of sinus lifting procedures with bone augmentation or he can choose to place a shorter but wider implant. However, the panoramic radiograph exam can supply only orientation data in a two-dimensional way, while the computer tomography exam is considered a must and the key to preoperative evaluation and treatment planning when it comes to implant dentistry. [7,19]

Periapical or panoramic radiographs are not very useful when it comes to determining bone density because the external cortical plates often obscure the trabecular bone density. Therefore, the bone density map may be more precisely determined by tomographic radiographs, especially computerized ones. [8]

Computed Tomography is a digital, modern, imaging technique that creates tomographic sections in a three-dimensional way. This radiological exam produces axial images of the patient’s anatomy which are perpendicular to the long axis of the body. The reformatted image data which CT provides are used to create the sectional tomographic images of a possible implant site in a digital manner. The thickness of the sections captured by the CT can be by 1 pixel (0.25mm) and an in-plane resolution of 1 pixel by scan spacing (0.5 – 1.5mm) producing a similar geometric resolution of a planar imaging. Each axial image has almost 280.000 pixels and each pixel has a CT number (Hounsfield unit) related to the density of the tissue within the pixel. Therefore, a higher CT number represents a denser tissue. Carl Misch stated that there is a correlation between Hounsfield units and density at the time of surgery. His classification can be evaluated on the computed tomography images by correlating to a range of Hounsfield units. Another thing to notice is that the clinician should know that the strength of the bone is directly related to it’s density, as in Figure 4. [13,19,28]

Table III. CT Determination of bone density[19]

One of the most notable advantages of the CT paraclinical exam is that it can serve the entire clinical management of the medical procedure (from diagnostics to post-op evaluation) because if gives certain data which no other radiological exam can offer with such an accuracy. For example, CT can be used for:

– Accurate localization of the vital anatomical structure near the implant site;

– Accurate measure of the crestal bone width, height, and the surface state;

– Useful data to determine whether bone grafting therapy is necessary or not;

– Choosing the appropriate implant dimensions for the edentulous site;

– Creating a digital simulation of the possible implant placement within the bone.

Generalization for treatment planning should be made in a cautious manner, based on the location of the possible implant situs. The bone density by location method is one of the most accessible ways for the doctor to estimate the bone density in the implantation site, data which can guide him in developing an appropriate treatment plan.[19]

Magnetic resonance imaging (MRI) is a paraclinical exam which used to image the protons of the body by employing magnetic fields, radio frequencies, electromagnetic detectors, and computers. This is a three-dimensional radiological technique with an electronic image acquisition process and a resulting digital image. Digital magnetic resonance imaging is described by voxels with an in-plane resolution measured in pixels and millimeters (2 to 3 mm) with the purpose of obtaining high-resolution images. Resulting images are in antithesis of CT images with cortical bone appearing dark and fat or water appearing bright or white.. [13]

As same as the computed tomography, MRI is a quantitatively accurate technique with exact tomographic sections of the tissue and no distortion. The usage of MRI in implantology is for the purpose of imaging the posterior mandible and maxilla to make a differentiation between critical structures (maxillary sinus for example) and the proposed implant site. Hence, MRI is not useful when it comes to bone mineralization determinations. [13]

A very important tip to notice is that there are no contraindications having a MRI done on a patient which has dental implants. Typically, dental implants are made from titanium which is not magnetic. Although, this is a notable concern among many patients because of the fear that their implant will be displaced during the imaging procedure or if the implant would heat up. To conclude with, a wiser decision would be for the patients and the dentists to consult with the technician performing the MRI and make them aware of the situation. [13]

II. Prosthetic options in Kennedy class I maxilla edentulism

When designing partially removable or fixed dentures, one of the most commonly used classification system is the one introduced by Edward Kennedy in the 1920s.

Kennedy class I describes a patient who has bilateral terminal edentulism. This class can also have modifications (multiple edentulous areas presented in different areas of the arch). When it comes to a complex oral rehabilitation of a class I Kennedy edentated patient the practitioner should take account of all local and systemic elements (which were pointed out in the previous chapter) in order to establish what options can be considered from a prosthodontic point of view. II.1. Acrylic resin removable partial dentures[8]

An acrylic resin removable partial denture is distinguished from other types of removable partial dentures by an all-acrylic resin base which is supported by the edentulous region of the tooth arch and by the hard palate. There can also be found simple wire retainers (0.6-0.8mm diameter) and the most common used for Kennedy class I edentulism is the cervical-alveolar retainer pointed to the edentulous space.

Nowadays, this type of prosthesis is considered to have a temporary (or palliative) nature. Due to the economical factors, all-acrylic resin removable partial dentures are indicated for young patients whose skeletal growth isn’t finished yet, but also to individuals with poor oral hygiene.

Contraindications for usage are represented by patient with psychological pathology or severe chronic diseases, acute or chronic local infections (tuberculosis, actinomycosis etc.), premalignant oral lesions or even an unfavorable edentulous ridge which needs surgical correction.

When compared to another type of removable partial dentures, the economic aspect is the main advantage of this type of dental prosthesis. Some of the disadvantages are, according to many authors, related to an increased risk of denture stomatitis, alveolar bone reduction, gag reflex triggering and the fact that the acrylic base it can easily fracture because it’s low resistance.

It is necessary to point out that for the patients allergic to acrylic resins there is available the acrylic flexible prosthesis. Those type of removable partial dentures are manufactures by an injectable acrylic resin which make them homogeneous , flexible, fact that assures a greater biological compatibility.

II.2 Skeletal removable partial denture[8]

A skeletal removable partial denture represents a long-term prosthodontic option for rehabilitation Kennedy class I edentulous patients. The difference from the all-acrylic removable partial dentures results in a more complex designing and manufacturing process with having solved almost all disadvantages of the traditional removable dentures.

The structure of a maxilla skeletal removable prosthesis is represented by:

ᴑ Major connector: – Anterior-Posterior palatal strap (very useful in cases with a torus)

– Full palatal plate (large surface area of contact with improved retention)

– Palatal strap (bar)

– Anterior palatal plate (U-Shaped)

ᴑ Minor connectors which connect other components (e.g. retainers) to the major connector

ᴑ Direct and indirect, special or conventional retainers (R.P.I, Ackerman’s retainer)

ᴑ Denture basis

Whenever is possible, the doctor should select a design that fits the local biological configuration, rather than choosing one that requires surgical intervention. When the minimal tooth recontouring is required, the surface roughness is minimized and the teeth will be less susceptible to caries. Also, minimal preparation and soft tissue management may provide an economic advantage to the patient (e.g. if crowns are not required).

The goal in designing skeletal removable partial dentures is to avoid unnecessary preparations. A prosthesis design should be chosen with the purpose to enable the partial denture to be adapted in every edentulous situs. Soft tissue anatomy such as frenum attachments, brides, and vestibular depth can affect the choice of the major connectors and direct retainers. Undercuts and tissue compressibility of attached mucosa may also affect the design. These aspects of the oral cavity need to be identified intraorally because they cannot be determined in an accurate manner only on the basis of a diagnostic cast.

The usage of this type of partial removable dental prosthesis in the maxilla is indicated in the cases where the systemic health status of the patient doesn’t allow surgical interventions for implant therapy or from economical reasons.

II.3 Implantology prosthetic options

Fixed prosthodontics in Kennedy class I maxilla can be achived only with implant dentistry. An endosteal implant represents an alloplastic material surgically inserted into a edentulous bony ridge. The usage of dental implants in the treatment of partial edentulism has become an integral treatment modality in restorative dentistry and has become a routine method to replace missing teeth. [19]

The dental implants used biomaterials which can be classified in three classes of biological compatibility:

I. Biotolerated materials (stainless steel, Cr-Co-Mo allies etc.)

II. Bioinert materials (titanium)

III. Bioreactive materials (ceramics)

Nowadays, the most used biomaterial in implantology is the titanium because it’s compatibility and physical traits. Most of the bioceramics have a poor mechanical resistance which makes them susceptible to fractures. For this reasons, they may be indicated in the frontal area, while the posterior edentulous situses of the arches are reserved for titanium implants. [11]

The most common root form design has a separate implant body and abutment, which permits only the implant body placement during the bone healing. A second procedure is required to attach the implant abutment. The design and surgical philosophy is to achieve clinical rigid fixation that corresponds to osseointegration. [12,19]

The design of the body of the implant can be cylinder, screw or combination. Cylinder root form implants depend on a coating or surface condition to provide microscopic retention to the bone. Most often the surface is either coated with a rough material (e.g., hydroxyapatite) or a macro retentive design. Cylinder implants are usually pushed or tapped into a prepared bone site. They can be a paralleled wall cylinder or a tapered implant design. Screw root forms are threaded into a slightly smaller prepared bone site and have the macroscopic retentive elements of a thread for initial bone fixation. They may be machined, textured, or coated. Combination root forms have acroscopic features from both the cylinder and screw root forms. The combination root form designs also may benefit from microscopic retention to the bone through varied surface treatments (machined, textured, and the addition of coatings). As a general rule, the combination implant designs have a press-fit surgical approach (as the cylinder implants) and a macroscopic implant design for occlusal loads (as a series of plateaus or holes in the body). Root forms also have been described by their means of insertion, healing, surgical requirements, surface characteristics, and interface. [20,26]

Regarding the dimensional parameters of the implant, a large diameter determines a favorable distribution of the stress at both bone and implant structure. It has been shown that the stress within the cortical bone decreases when the stress on the implant increases. However, choosing the highest diameter available implant doesn’t necessary mean that it’s a better choice. In some morphological limits, there is an optimal dimension when choosing an endosteal implant with the purpose of gaining a balance between the bone stress and the one which will affect the restoration. Generally, short implants are not recommended because it’s believed that occlusal forces must be dissolved on a larger surface of the implant in order to conserve the bone structure. The forces which characterize parafunctions like bruxism are considered to be the most dangerous and it’s recommended that in those cases to increase the number of the implants placed under the restoration and also their dimensional parameters. [19,26]

Regarding a long-term success, diameter and length of the implant depend on the quantity and the quality of the support bone structure. The support tissue for the implants frequently is found to be unfavorable when it comes to implant therapy and requires specific surgical additive or substractive interventions in order to obtain a situs which can serve a perfect osseointegration and long-term maintenance of the implant and it’s restoration. [26]

Additive therapy refers to bone and soft tissue enhancement.

Bone additive therapy is represented by specific surgical protocols which uses different type of biomaterials in order to gain the local bone offer. Bone grafts can be classified in four groups: ᴑ Autografts

ᴑ Allografts

ᴑ Xenografts

ᴑ Alloplastic grafts

Autografts are bone grafts harvested from the same individual but from a different donor site. In order to gain adequate bone volume, autologous bone grafts use intraoral or extraoral situses. For example, bone grafts from the iliac crests are indicated when a large amount of graft material is needed. Cortical as well as cancellous bone may be collected in sufficient amounts to restored severely resorbed maxillae included bilateral sinus lifting. Another advantage (as in almost any extra-oral potential donor situses) is the possibility of harvesting the bone block graft and also a particulate bone of the desired shape and volume. Due to the anatomy of the tibia and the cancellous nature of the bone, a limited volume of graft bone is available for additive procedures. This technique is indicated in unilateral sinus lift procedures or as onlay grafting. [3,6]

Harvesting chin grafts is an accessible technique for many practitioners but, due to the limited amount of available bone, this grafting procedure is mostly indicated for use as onlay grafting for the widening of a thin edentulous crest. A more accessible technique represents the one which uses the mandibular ramus anterior area as a donor site. There are certain limitations to the size of graft although more bone quantity is available than from the chin. It is useful in a block as well as in particulate form, although almost no cancellous bone can be harvested by this technique. Bone grafts from the maxillary tuberosity area are indicated for a very limited grafting procedures with no need for cortical bone. Usually, this donor site provides bone grafts used to fill minor defects and sometimes to cover the implant threads. [9,12]

Onlay grafting procedures are a group of methods of increasing bone volume which uses small amounts of bone material collected with a bone trap. The bone particles are harvested with certain rotary instruments especially from mandibular sites are they are placed over the infrabony defect with or without covering membrane. In the majority of cases, onlay block grafts or cortical bone are indicated where is a need to improve the width of the thin alveolar process or in order to increase it's height. Usually, cortical bone is best used as onlay while particulate bone can be used as filler around it. [4,12]

Allografts are grafts harvested from a different individual of the same species. Allograft bone is taken from cadavers that have donated their bone so that it can be used for patients who are in need of it; it is typically sourced from a bone bank. The use of allografts for guided tissue regeneration often requires sterilization and deactivation of proteins normally found in healthy bone because of the risk of a possible viral contamination (HIV). Contained in the extracellular matrix of bone tissue there can be found tissue growth factors (CGF), proteins, and other bioactive molecules necessary for osteoinduction and successful bone healing. The desired factors and proteins are removed from the mineralized tissue by using a demineralizing agent. The mineral content of the bone is degraded, and the osteoinductive agents remain in a demineralized bone matrix. [4,6,12]

Alloplastic grafts are made from biomaterials which have osteoinduction properties. alloplastic grafts may be made from hydroxyapatite (HA), a naturally occurring mineral, made from bioactive glass. Hydroxyapatite is a synthetic bone graft, which is the most used now due to its osteoconduction, hardness, and acceptability by bone. Some synthetic bone grafts are made of calcium carbonate, which starts to decrease in usage because it is completely resorbable in a short time and makes the breaking of the bone easier. Finally used is the tricalcium phosphate in combination with hydroxyapatite and thus giving effect of both, osteoconduction and resorbability. [4,12]

Xenografts are bone grafts from a species other than human, such as bovine and are used as a calcified matrix. There is a wide spread usage of this materials because of their biodisponibility and their osteoinductive properties. However, bovine bone has a reduced level of hydroxyapatite and for this purpose, in order to get high-quality bone formation, many authors recommend the usage of a 50-50 xenograft / autograft mixture. [4,6,19]

The implant body may be divided into a crest module (cervical geometry), a body, and an apex. Each section of an implant body has features that are of benefit in the surgical or prosthetic application of the implant (Figure 5). [11]

An implant body is firstly designed for either surgical ease or prosthetic loading to the implant–bone interface. A round implant permits round surgical drills to prepare the bone. A cylinder or combination implant allows the implant to be pressed or tapped into position, similar to a nail into a piece of wood. A tapered cylinder fits into the top section of the osteotomy before engagement of the bone for further ease of placement. [19,26]

The crest module of an implant body is that portion designed to retain the prosthetic component in a two-piece implant system. It also represents the transition zone from the implant body design to the trans-osteal region of the implant at the crest of the ridge. The abutment connection area usually has a platform on which the abutment is seated and it can offer physical resistance to axial occlusal loads which occur on the implant. An anti-rotation feature also is included on the platform (external hex) or extends within the implant body. Whereas the implant body has a design to transfer stress and strain to the bone during occlusal loads, the crest module often is designed to reduce bacterial invasion. Its smoother dimension varies greatly from one system to another (0.5–5 mm). [19,26]

The implant apex portion is often tapered to permit ease of initial placement into the osteotomy. An anti-rotational feature of an implant may also be included, which has flat sides or grooves along the apical region of the implant body or an apical hole. When bone grows against the flat or groove regions or within the hole, the bone is placed in compression with rotational loads. In Figure 6 is illustrated the implant components, listed from bottom to top in the order of use. [19,23]

Figure 6. Generic termes of implant components listed from bottom to top in the order of use. This language permits improved communication between reffering doctors and laboratories, which often must be familiar with several different systems. [11]

The position of the implant will be been established after the clinical and paraclinical examination, the direction/inclination of the implant in the jaw (buccolingual and mesiodistal) must be determined. If possible the implants should be placed in tooth position. This means that in the normal case the long axis of the implant should be directed through the occlusal surface of the final restoration. Regarding the buccolingual dimension , the long axis for the implants placed in the maxilla should be towards the buccal cusps of the premolars or molars of the mandible (Figure 7). If the starting point of the implant sites in the maxilla is located close to the top of the crest, and if a concavity on the buccal side of the ridge is present, there is a risk that the surgeon leans the long axis of the implants too far buccally. [18,26]

In addition, the inclination of the implants to be inserted will depend on the existing maxillo-mandibular relation. In the case of angle class I jaw relation, the implants should be placed rather vertically in both jaws. In angle class II, the implants should often be placed vertically in the maxilla and slightly buccally in the mandible. In angle class III relations, the implants are inclined buccally in the maxilla and more lingually in the mandible. If the relation between the jaws is markedly adverse, orthognathic surgery may be considered to correct the abnormal maxillary relation. [18,19,26]

Figure 7. Implant placement axis in the posterior maxilla area.[26]

At the time of insertion of a two-stage implant body, a first-stage cover screw is placed on the top of the implant in order to prevent hard, soft tissue or even debris from invading the abutment connection area during the healing period.

According to early protocols, the healing time following installation of implants with a turned surface was 3–4 months. For the maxilla and occasionally in the posterior areas of the mandible the healing time was 5–6 months, as the bone is normally more cancellous in these portions of the jaws. After the healing period, there is need of a second-stage procedure in order to expose the implant or to attach the abutment. The abutment is a permucosal extension attached transepithelial to the body of the implant. The abutment is available in multiple heights in order to accommodate soft tissue variation. It can also be straight, flared or anatomical self-made in order to assist the initial contour of the soft tissue healing. This permucosal extension supports a metal framework that attaches to the implant abutments in order to provide either retention for a fixed prosthesis. [18,19]

There are two types of abutments regarding the method which the superstructure is retained: an abutment for screw retention, for cement retention or for attachment. Each of the three abutment types may be further classified as straight or angled abutments, describing the axial relationship between the implant body of the abutment. An abutment for screw retention is recommended by many authors and it uses a hygiene cover screw placed over the abutment in order to prevent debris or calculus from internal invading. [26]

The implant abutment may be restored as a natural tooth restoration. The abutment (usually prefabricated) is inserted into the implant body. A stone cast is poured, and an individual die of the abutment is trimmed. The restoration is fabricated very similar to a tooth. This prosthetic approach may be called a direct prosthetic option. [26]

The advantages of the direct prosthetic option are:

1. Familiar to restoring dentists;

2. No laboratory analog components are required;

3. splinting crowns together is less complicated because manufacturer precision for analogs is not required and transfer of components is not required;

4. Reduced cost because analogs and laboratory fees for abutments are eliminated.

The disadvantages of the direct prosthetic option are:

1. The abutments are prepared in the mouth;

2. A different transitional restoration is often fabricated than the option during implant body healing because the abutment is inserted.

Two basic indirect implant restorative techniques are used to make a master impression, and each uses a different design transfer coping based on the transfer technique performed. [26]

An impression is necessary to transfer the position and design of the implant body or abutment to a master cast for prosthesis fabrication. A transfer coping may be used in traditional prosthetics to position a die in an impression. Most implant manufacturers use the terms transfer and coping to describe the component used in the implant body for the final impression. Therefore, a transfer coping is used to position an analog in an impression or cast and is defined by the portion of the implant it transfers to the master cast, either the implant body transfer coping or the abutment transfer coping. [26]

Impressions of natural teeth and implants are differentiated. The objective of making an impression in implant therapy is to accurately relate an implant abutment to other structures in the dental arch. This process describes an impression coping which is attached to the implant or it's abutment. This impression coping is incorporated in an impression as a metal framework. It is critical for the impression material to respect the dimensional stability and the fidelity of the prosthodontic site. Small imperfections can lead to difficulties when the restoration will be fabricated. When impressions are required for multi-implant restorations, the precision of the impression is even more critical. This fact is strictly related with the fact that frameworks are manufactured from the master cast and possible mis-fits at this level can lead to stress applied to the implants while screwing down the framework. This fact will undoubtedly lead to peri-implant bone loss and even loss if the implant's integration and maintenance. Most practitioners use as impression material elastomeric ones represented by polyethers and polyvinyl siloxanes. When using polyvinyl siloxane as impression material the practitioner must use vinyl gloves in order to prevent the interaction of latex gloves with the material. [1,18,19,26]

The impression coping takes two general forms, one type is retained intraorally when the set impression is removed. This type of impression coping is known as the transfer type impression coping. The other type is incorporated in the impression and is removed from the mouth together with the set impression and is known as a pick up type impression coping. [1]

The transfer type impression coping remain in the mouth on removal of the set impression and the analogue is attached to the impression coping after removal. For this type of impression no custom tray is needed. Finally, this assembly is replaced in the identation left on the set impression. The pick-up type impression coping are removed from the mouth together with the set impression. They require access to the retaining screw in order to allow the release of it prior to removal of the impresion coping. The analogues are attached to the impression copings while they are embedded in the impression tray. In this case is required a custom tray with access to the impression coping screws. [1,26]

Thus, there are some indications to use of the transfer type impression coping. If the patient has a limited mouth opening, they can't be used as there because it may not be sufficient space for access to the screws retaining pick-up type impression copings with the impression in place. Another situation is represented by the patients with an exaggerated gag reflex, when the impression has to be removed as quickly as possible.[1,26]

III. CLINICAL CASES

CASE I [16 ]

A common reconstruction today is one in which there are missing teeth, the remaining natural teeth are in need of restorations due to structural inadequacies, and the edentulous areas are restored with implant supported restorations. In this case, the maxillary edentulous areas are restored with implants and the mandibular with fixed partial dentures. Clinical judgment will help the dentist decide whether the edentulous areas should be restored with dental implants or tooth – supported fixed partial dentures. Attached keratinized tissue needs to be augmented in several areas. The case was provisionalized prior to the periodontal surgery and dental implant placement.

Summary of examination and diagnosis:

▪ Dentition : all teeth are structurally weak or worn but all appear to be predictably restorable;

▪ Periodontium: generalized recession but healthy; pockets under 3mm; areas of minimal attached keratinized tissue;

▪ TMJ: both can be superiorly compressed without discomfort;

▪ Muscles: sight lateral pterygoid palpation tenderness;

▪ Occlusion: lost of posterior support;

▪ Aesthetics: upper incisal edge position short, unacceptable aestetic form of teeth;

Figure 9. Preoparative condition, frontal view[16]

Figure 10. Preoperative condition buccal, lingual and occlusal view[16]

Figure 11. Preoperative articulated diagnostic casts. [16]

Figure 12. Preoperative radiographs. [16]

Summary of treatment (appointments and treatment sequence):

1. Provisionalize upper arch, lower posterior and lower anterior with composite resins;

2. Implant therapy (5 implants)

3. Healing and integration follow-up with monitor and maintain provisionals

4. Impression for lower posterior crowns/bridges and anterior veneers

5. Place crowns/bridges and bond lower anterior veneers

6. Place upper implant abutments; Abutment preparation and impressions; New provisionals

7. Place upper restorations

Figure 13. Diagnostic blueprints frontal and buccal views[16];

Figure 14. Diagnostic blueprint, occlusal view. The tipped molars were prepared for full crowns on the cast to “ upright ” them and get a better idea of the edentulous space between the abutments. The lower, right cuspid is replaced with a mesial cantelever pontic. [16]

Figure 15. Provisional restorations prior to periodontal surgery and implant placement. [16]

Figure 16. Occlusal, buccal and palatal view after 5 implant placement[16]

Figure 17. Posttreatment facial, palatal and occlusal view[16]

CASE II[14]

A 50-year-old male patient referred to clinic with atrophy of the alveolar rim in the posterior maxilla, which had inadequate width and height for implant placement (Figure 18). A pre-operative computerized tomographic (CT) scan revealed 2.5-3 mm of bone weight and height of the molar area was 5.64 mm between the alveolar crest and maxillary sinus (Figure 19). The practitioners planned segmental split osteotomy, socket lifting and three dental implant placement at the same section without using any graft materials.

Figure 18. Pre-operative radiograph of the left posterior edentulous maxilla[14]

Figure 19.Preoperative CBCT scan[14]

The surgical procedure was performed under local anesthesia. Full thickness muco-periostal flap was elevated with vertical and crestal incisions. Ridge splitting was applied with osteotome 8 mm, after the crest being prepared with surgical diamond disc in straight high speed handpiece (Figure 20). One centimeter penetration of the osteotome blade in ridge crest would automatically expand the ridge. Since osteotome thickness increases from tip toward shaft further the osteotome penetrates, more the ridge will expand. Slight buccolingual movement of the osteotome increases the expansion. 3.5×12 mm implants were placed in the canine and first premolar region into the ridge splitted crest (Figure 21). Mucoperiostal flap were sutured primerly by using 3.0 silk suture.

The present study reports that the clinical results of narrow ridge splitting. Post-operative CT scan (Figure 22) showed there was not any complications around the implants and the maxillary sinus. Five months after surgery, final fixed prosthetic restorations were accomplished.

Figure 20. Crestal exposure and spplited with rotary osteotomes.

Figure 21. Implant placement.

Figure 22. Post-operative CBCT scan.

CASE III[19]

Patient was reffered to prosthodontist in order to rehabilitate the right posterior maxilla area. After a cautious clinical and paraclinical exam it has been planned a lateral sinus lift following by placement of two implants. The panoramic radiograph shows oblique inferior sinus borders and a residual bone height between 3 and 6 mm in the position of 25 (Figure 23).

The surgical protocol consisted in:

• A presurgical rinse with chlorhexidine 0.1% performed for a period of 1 minute.

• Local anesthesia is delivered buccal and palatal to the surgical area.

• The initial incision is midcrestal extending well beyond the planned extension of the osteotomy. The incision is carried on forward Figure 23. Preoperative radiograph.

beyond the anterior border of the maxillary sinus. Releasing incisions are made anteriorly extending into the buccal vestibulum to facilitate reflection of a fullthickness mucoperiosteal flap.

• A mucoperiosteal flap is raised slightly superior to the anticipated height of the lateral window.

• After the lateral sinus wall has been exposed, a round carbide bur in a straight hand piece is used to mark the outline of the osteotomy

When the bone has been trimmed down to a thin bony plate, the preparation is continued with a round diamond bur (Figure 24) in a straight hand piece until a bluish hue of the sinus membrane is observed (Figure 25).

Three methods for handling the buccal cortical bone plate have been proposed. The most common one is the thinning of the buccal bone to a paper-thin bone lamella using a round bur, and removing it prior to the elevation of the sinus membrane.

The second method is to fracture the cortical bony plate like a trap-door and use it as the superior border to the sinus compartment, leaving it attached to the underlying mucosa. Since the cortical bony plate is resistant to bone resorption this may protect the graft.

The third method proposed is to remove the cortical bony plate during sinus floor elevation and replace it on the lateral aspect of the graft at the end of the grafting procedure. The rationale for this method was the notion that the lateral window would not completely heal without replacement of its cortical plate. However, healing of the lateral window by bone apposition has been demonstrated to occur without replacing the cortical bony plate.

The next step will be chosen according to the technique used. If the buccal wall is eliminated, the sinus membrane is elevated directly with blunt instruments (Figure 26). On the other hand, gentle tapping is continued until movement of the bony plate is observed if the “trap-door” technique is used. Then, in combination with the elevation of the sinus membrane in the inferior part of the sinus, the bony plate is rotated inwards and upwards to provide adequate space for grafting material (Figure 27). Care should be taken not to perforate the sinus membrane.

Figure 24. The buccal bony plate is trimmed to Figure 25. After removal the buccal bony

a paper-thin lamellawith a round diamond bur. place, the bluish hue of the sinus membrane

becomes clearly visible.

Figure 26. The exposure of the sinus membrane and careful elevation using a blunt instrument. To avoid penetration, it is essential to keep contact with the underlying bone all the time.

Figure 27. The buccal cortical plate was factured Figure 28. Before placing the implants,

and moved upwards and inwards like a "trap-door". grafting material has to be inserted into the

The cortical bony plate is delineating the superior medial part of the sinus compartment.

border of the maxillary sinus compartment.

Figure 29. Two implants have benn installed Figure 30. The rest of the sinus compartment

after filling the medial part of the sinus being filled with a 1:1 mixture of particulate

compartment. autogenous and xenograft bone.

Figure 31. The lateral window has been

covered with a double layer of collagen membrane.

In order to minimize post-operative complications, first of all, surgical handling should be as atraumatic as possible. The clinician must take certain precautions in order to avoid perforation of the flap or even the Schneiderian membrane. The bone should be kept moist during the surgery and a tension-free primary flap closure will be essential. The pain experienced by patients is mostly limited to the first days after surgery and the intensity is low to moderate. Swelling and bruising of the area considered some post-operative sequelae. Often those type of complications extend from the inferior border of the orbit to the lower border of the mandible. In order to reduce swelling, it is important for the patient to cool the area with cooling pads at least for the first post-operative hours. The patient must be told that occasionally, minor bleeding may arise from the nose. It is important to inform the patients that also some irritation in the nasal area may be expected. In the event of the need for sneezing, the nose should not be covered so that air pressure is allowed to escape. After the surgery, patients are placed on antibiotic therapy. Furthermore, antiseptic rinses with 0.1–0.2% chlorhexidine twice daily are indicated for the first 3 weeks after surgery. [10,19]

When performing sinus floor elevation, the risk of complications must be considered and the appropriate treatment foreseen. The most common intra-operative complication is perforation of the sinus membrane. Presence of maxillary sinus septa and root apices penetrating into the sinus may increase the risk of membrane perforation. In the event of a membrane perforation, it is recommended to elevate the membrane in the opposite direction to prevent further enlargement

of the perforation. Smaller perforations (5mm) may be closed by using tissue fibrin glue, suturing or by covering them with a resorbable barrier membrane. In cases of larger perforations, larger barrier membranes, lamellar bone plates or suturing may be used either alone or in combination

with tissue fibrin glue to provide a superior border for the grafting material. In instances of

larger perforations, where a stable superior border cannot be achieved the grafting of the axillary sinus must by aborted and a second attempt at sinus floor elevation may be performed 6–9 months later. [19,26]

Other complications that were reported during surgery included excessive bleeding from the bony window or the sinus membrane, and wound dehiscences. Iatrogenic complications include injury of the infraorbital neurovascular bundle from deep dissection to free the flap

from tension or blunt trauma due to the compression of the neurovascular bundle during retraction. Implant migration, hematoma, and adjacent tooth sensitivity have also been

reported. [10,19]

Infection of the grafted sinuses is a rare complication. However, the risk for infection increases with a membrane perforation. Hence, it is recommended to avoid sinus grafting and simultaneous implant placement in situations of membrane perforation. Infection of the grafted sinuses is usually seen 3–7 days post surgically and may lead to a failure of the graft. Possible complication secondary to infection may involve a parasinusitis with the spread of the infection to the orbita or even to the brain. For these reasons, infected sinus grafts must be treated

immediately and aggressively. Surgical removal of the entire graft from the sinus cavity

and administration of high doses of antibiotics are essential. [10,19]

DISCUSSIONS

Restorative therapy performed on an implant placed in a fully healed and non-compromised crestal ridge has clinical success ant notable survival rates. However, implants are also being placed in sites wish ridge defects of various dimensions, fresh extraction sockets or even the area of the maxillary sinus. Although some of this clinical procedures were first described many years ago, their application has only recently become common.

Hard tissue defects resulting from different etiological factors as trauma, infection or tooth loss as a complication of periodontal disease often lead to an unfavorable anatomy of the maxillary and mandibular alveolar crest. As a result for those inconvenient, the development of bone augmentation and soft tissue management procedures had open a larger field of research and those elements were followed by a greater success of the implant therapy in the patients with crestal ridge deficiency, infrabony defects or unfavorable soft tissue thickness.

As a general rule in the maxilla posterior region, one implant for each missing tooth is indicated. Implants should always be splinted together to reduce stresses to the bone. If stress factors are magnified, two implants for each missing buccal root of the molar are suggested. [18,19]

Dental implant placement in the edentulous posterior maxilla area can present difficulties because of a horizontal, vertical, or combined alveolar ridge resorption caused by different etiologic factors such as periodontal disease, premature tooth loss due to odontal lesions, or increased pneumatization of the maxillary sinus.

The posterior maxilla has been known by many clinicians as one of the most dificult problematic area for implant dentistry, requiring a maximum of knowledge and attention to achive a successful therapy. Therefore, the local anatomical morphology of the edentulous alveolar ridges in the posterior maxilla area may be unfavorable for implant placement. In many situations, the available alveolar bone height is lost in the posterior maxilla as a result of periodontal disease before tooth loss. Moreover, the maxillary molar regions have distal furcation involvement frequently, because the furca is directly under the distal contact and has no facial or palatal access for hygiene. The furca is also narrower than many dental curettes, and it is difficult to eliminate calculus after it has formed. As a result, periodontal disease is common and is associated with loss of bone height before tooth loss. The dentate maxilla has a thinner cortical plate on the vestibular compared with the mandible. In addition, the trabecular bone of the posterior maxilla is finer than other dental arch regions. [18,23]

The loss of maxillary posterior teeth results in an initial decrease in bone width at the expense of the palatal bony plate. It has been observed that the width of the posterior maxilla decreases rapidly than in any other region of the maxillary arch. The resorption phenomena are accelerated by the loss of vascularization of the alveolar bone and the existing fine trabecular bone type. However, because the initial residual ridge is so wide in the posterior maxilla, even with a high percentage decrease in the width of the ridge, adequate-diameter root form implants usually can be placed. [8,19]

The clinical examination should include assessment of color and texture alterations of the mucosa and the thickness of the soft tissues. The recipient site should also be palpated in order to estimate the volume of the tissues available in the edentulous region of the jaw. It must be realized, however, that both the mucosa and the bone of the edentulous region are included in this clinical measure. Hence, the clinician must realize that palpation may overestimate the volume of hard tissue present at the site. The radiographic examination will provide more detailed information on the amount and quality of the bone available at the recipient site. Lekholm and Zarb (1985) proposed that the edentulous jaw should be classified regarding its shape and quality. Thus a grading into five groups was used to describe the shape of the jaw (Figure 32) while four groups were used to describe the quality of the bone tissue. [18]

Figure 32. A. Schematic drawings showing residual crestal shape classification; B. Alveolar bone quality according to Lekholm and Zarb (1985). [18]

The crown height space should be carefully evaluated before implant placement because within tooth loss there can be observed an extrusion of the antagonist denture. After the occlusal plane is properly restored, the crown height space ideally should be greater than 7-8 mm. When less clinical space is available for prosthodontic reconstruction, a gingivectomy as a first surgical therapeutical option is considered, because it is common for excess tissue thickness to be present in this region. Moreover, tuberosity soft tissue hyperplasia is can appear in the cases where the patient wore removable partial dentures which did not have anatomically shaped margins. However, if tissue reduction cannot correct the clinical crown height problem, osteoplasty, or vertical osteotomy of the maxillary posterior alveolar process are recommended in order to restore the correct ridge parameters before implant therapy. [20]

A key to long-term success of posterior maxillary implants is the presence of adequate anterior teeth or implants. Therefore the treatment plan should provide for the maintenance or restoration of healthy anterior teeth in the premaxilla for implant placement. A minimum of a healthy natural canine tooth or implant abutments in the canine region for each posterior quadrant are required before posterior implants are considered. [19,20]

A rule in traditional prosthetics is that a fixed prosthesis is contraindicated when the canine and two adjacent teeth are missing. Therefore when the canine and both premolars are missing, a fixed restoration is contraindicated. A removable prosthesis that has no movement under function is considered a fixed prosthesis and therefore should follow the rules of treatment planning for a fixed prosthesis in relation to implant number and position. [18,19]

When it comes to implant therapy in extended posterior edentulous segments confined mesially and distally by remaining teeth, the question about the optimal number, size, and distribution of implants has to be raised again. Among the key parameters to be addressed during the decision-making process is the mesiodistal dimension of the edentulous segment, the precise alveolar bone crest volume (including bone height and crest width in an orofacial direction), the opposing dentition (premolars or molars), interarch distance and specific occlusal parameters, as well as the periodontal, endodontic, and structural conditions of the neighboring teeth. [20]

The treatment plan of a posterior maxilla should provide for the maintenance or restoration of healthy anterior teeth or adequate bone in the premaxilla for root form implant placement. A minimum of a healthy natural canine tooth or an implant abutment in the canine region is required before posterior implants are considered in the quadrant.

The clinician must reserve time to plan for a restorative prosthodontic therapy regarding a Kennedy class I edentation and the decision must also be made whether the implants should be placed immediately after the tooth extractions or if there is a needed a certain number of months in order to achieve hard and soft tissue healing with or without guided tissue regeneration therapy. The decision regarding the immediate implantation after the tooth extraction must be based on a proper understanding of the morphological changes that occur in the alveolar process following the loss of the teeth . Currently, it is not possible to draw conclusions concerning exclusion and inclusion criteria for immediate loading, threshold values for implant stability that allow immediate loading, the bone quality needed for immediate loading, and the relevance of immediate functional loading and immediate non-functional loading. In most of the studies on immediate loading, good bone quality has been mentioned as an important prognostic factor for the success of the procedure. Although this conclusion seems reasonable, the level of evidence that supports the assumption is low. There are, in fact, no controlled studies that have been especially designed to compare immediate loading of oral implants placed in the bone of varying density. The same is true for the lengths and diameters of implants that should be used for immediate loading. In one controlled study, moderately rough implant surfaces appeared to improve the survival rate of immediately loaded implants. In this study, however, the difference between the moderately rough as opposed to the machined-surface implants was not significant. [18,19,20,23]

The evaluation of the bone morphology in the posterior maxilla situs on a class I Kennedy edentation and it’s configuration near the maxillary sinus is also a very important step before the surgery procedures. An insufficient subantral bone volume may indicate the clinician if there is need of sinus lifting procedures with bone augmentation or he can choose to place a shorter but wider implant. However, the computer tomography exam is considered a must and the key to preoperative evaluation and treatment planning when it comes to implant dentistry. The usage of this type of paraclinical exam allows the clinicians to acquire a preliminary evaluation of the alveolar crests and their bone density based on the opacity shown by the intertrabecular spaces. This the accuracy of this evaluation depends on the technique used to capture the X-ray image and the mineralization degree of the compact bone which can sometimes hide a spongious bone radiolucency. There are four macroscopic structures of the bone, described by Carl Misch, located in different edentulous areas of the maxilla and mandible. (Table IV) [18,20]

Table IV. Comparative features regarding Misch's bone density classification.

Generally, the bone quality is lowest in the edentulous posterior maxilla compared with any other intraoral region. Bone strength is directly related to its density, and the poor density bone of this region is often weaker in comparison to bone found in the anterior mandible. Bone densities directly influence the percent of implant-bone surface contact, which accounts for the force transmission to the bone. The bone-implant contact is least in D4 bone compared with other bone densities. The stress patterns developed in poor bone density migrate farther toward the apex of the implant. As a result, bone loss is more pronounced and occurs also along the implant body, rather than only crestally as in other denser bone conditions. Type D4 bone also exhibits the greatest biomechanical elastic modulus difference when compared with titanium under load. [18]

In the posterior maxilla, the deficient bony structures and an absence of cortical plate in some situations on the crest of the ridge is a risk factor for further compromise the initial implant stability at the time of insertion. The palatal cortical plate is thin and the ridge is often wide. As a result, the lateral cortical bone-implant contact to stabilize the implant is often insignificant. Therefore initial healing of an implant in Type IV bone is often compromised, and clinical reports indicate a higher initial healing success than with D2 or D3 bone. [18,19]

The general indications for using a bone graft are when there is a need to replace missing bone volume and/or to enhance bone formation, in order to restore form and function. Many types of biomaterials have been used among time and tested to replace bony defects during the last century, for example, rephrigerated banked bone (allografts; bone from individuals within the same species), xenografts (bone derived from individuals belonging to other species), ceramics such as hydroxyapatite, corals and plastics. Nowadays, fresh autogenous cancellous and cortical bone remain the most widely indicated and used biomaterials and are still considered the ‘gold standard’ by many authors in bone grafting and other surgical regenerative procedures. [18,19]

Autografts are bone grafts harvested from the same individual but from a different donor site. In order to gain adequate bone volume, autologous bone grafts use intraoral or extraoral situses. For example, bone grafts from the iliac crests are indicated when a large amount of graft material is needed. Cortical as well as cancellous bone may be collected in sufficient amounts to restored severely resorbed maxillae included bilateral sinus lifting. Another advantage (as in almost any extra-oral potential donor situses) is the possibility of harvesting the bone block graft and also particulate bone of the desired shape and volume. Due to the anatomy of the tibia and the cancellous nature of the bone, a limited volume of graft bone is available for additive procedures. This technique is indicated in unilateral sinus lift procedures or as onlay grafting. [18,20]

Harvesting chin grafts is an accessible technique for many practitioners but, due to the limited amount of available bone, this grafting procedure is mostly indicated for use as onlay grafting for widening of a thin edentulous crest. A more accessible technique represents the one which uses the mandibular ramus anterior area as a donor site. There are certain limitations to the size of graft although more bone quantity is available than from the chin. It is useful in block as well as in particulate form, although almost no cancellous bone can be harvested by this technique. Bone grafts from the maxillary tuberosity area are indicated for a very limited grafting procedures with no need for cortical bone. Usually this donor site provides bone grafts used to fill minor defects and sometimes to cover the implant threads. [12,15]

Onlay grafting procedures are a group of methods of increasing bone volume which uses small amounts of bone material collected with a bone trap. The bone particles are harvested with certain rotary instruments especially from mandibular sites are they are placed over the infrabony defect with or without covering membrane. In the majority of cases, onlay block grafts or cortical bone are indicated where is a need to improve the width of the thin alveolar process or in order to increase it's height. Usually, cortical bone is best used as onlay while particulate bone can be used as filler around it. [10,12]

Allografts are grafts harvested from a different individual of the same species. Allograft bone is taken from cadavers that have donated their bone so that it can be used for patients who are in need of it; it is typically sourced from a bone bank. The use of allografts for guided tissue regeneration often requires sterilization and deactivation of proteins normally found in healthy bone because of the risk of a possible viral contamination (HIV). Contained in the extracellular matrix of bone tissue there can be found tissue growth factors (CGF), proteins, and other bioactive molecules necessary for osteoinduction and successful bone healing. The desired factors and proteins are removed from the mineralized tissue by using a demineralizing agent. The mineral content of the bone is degraded, and the osteoinductive agents remain in a demineralized bone matrix. [6,10,12]

Alloplastic grafts are made from biomaterials which have osteoinduction properties. alloplastic grafts may be made from hydroxyapatite (HA), a naturally occurring mineral, made from bioactive glass. Hydroxyapatite is a synthetic bone graft, which is the most used now due to its osteoconduction, hardness, and acceptability by bone. Some synthetic bone grafts are made of calcium carbonate, which starts to decrease in usage because it is completely resorbable in a short time and makes the breaking of the bone easier. Finally used is the tricalcium phosphate in combination with hydroxyapatite and thus giving effect of both, osteoconduction and resorbability. [12,15]

The majority of bone grafts available involve ceramics, either alone or in combination with another material (e.g., calcium sulfate, bioactive glass, and calcium phosphate). The use of ceramics, like calcium phosphates, is calcium hydroxyapatite which is osteoconductive and osteointegrative, and in some cases, osteoinductive. [12]

Bioactive glass (bioglass) is a biologically active silicate-based glass, having high modulus and brittle nature; it has been used in combination with polymethylmethacrylate to form bioactive bone cement and with metal implants as a coating to form a calcium-deficient carbonated calcium phosphate layer which facilitates the chemical bonding of implants to the surrounding bone. Different types of calcium phosphates are tricalcium phosphate, synthetic hydroxyapatite, and coralline hydroxyapatite; available in pastes, putties, solid matrices, and granules. [10,12]

While using bone additive therapy there is a must for the clinician to use certain barriers in order to protect the grafted area. Therefore, the usage of protective membrane is correlated with almost any guided tissue regeneration procedure. Membranes are biomaterials which can be classified in resorptive and non-resorptive. Non-resorptive membranes are made from titanium, ePTFE or latex and they present the main advantage that it offers the grafted site a superior protection to any external factors. Thus, a big disadvantage is that the removal of the membrane requires a second surgical intervention. Resorptive membranes are made especially from collagen, polylactic acid, vycril, or even periosteum. They resorp within 5 to 6 weeks. [10,12]

The success of a bone grafting procedure is correlated with many local and systemic factors. One of these is the inherent biological activity of the graft, described by the number of living cells and their cellular products, including certain proteins and growth factors stored within the matrix. The second factor is the capability of the graft to elicit an osteogenic response in the tissues at the recipient situs. A third consideration should be the ability of the graft to support and promote in-growth of new bone derived from the surrounding tissues at the recipient bed of the host. A non-vascularized graft is also completely dependent on the surrounding tissue at the recipient bed for its revascularization. [12,15]

Another important factor which the practitioner must take into account is the mechanical properties at the recipient bed. Actions at the interface between the graft and the host tissues may jeopardize it's subsequent revascularization. Taken together, the success of grafting is dependent on a sequence of cellular, biochemical and bio-mechanical events that follow a rather predictable schedule. Graft incorporation will not occur if there is a problem with any of these events or with the order in which they occur. [10,25]

When it comes to root-form endooseous implants, it became obvious that many possible posterior maxillary reception beds for implants were deficient in vertical crestal height and width. The augmentation of the alveolar ridge itself was a possible method of correcting this deficit, but in many situations the antrum also required bone grafting. Various practitioners then undertook different surgical techniques to enter the antrum to elevate the sinus membrane and to place various types of bone grafts. [10]

Sinus grafting and the placement of root-form implants has also led to the review of the anatomic characteristics of resorption of the alveolar ridge following the loss of teeth. It has been observed that the edentulous areas of the posterior maxilla tend to lose bone buccally so that the central portion of the residual resorbed ridge is more palatally displaced. The placement of implants in the midportion of the ridge in such patients often results in the apical end of the implant being positioned in the nasal wall of the antrum or in the nasal floor itself, which has been shown by examination of cadaver material. This observation is important because it points out again the need for adhering to presurgical and pregrafting diagnostic criteria to determine the correct area to be grafted for maximal support of the implant system being used. [10,15]

The most frequently used donor site for bone harvest in additive therapy techniques is the iliac crest. Generally, this site can supply enough both cortical and cancellous bone volume for different reconstructive purposes in the maxillo-facial region. Moreover, there are other sites that can be used, although less commonly, like the tibia, fibula, and the ribs. In implant therapy of Kennedy class I edentulism are more frequently used intraoral situses. Although only a small amount of bone can be harvested (from the chin or the mandibular ramus), the harvesting techniques are more accessible rather than extraoral ones and the surgical procedure is more tolerated by the patient. However, intraoral sites contribute only with compact bone. [10,19]

The posterior maxilla's dentition is characterized by the largest diameter teeth from human's dental arch, the greatest number of roots and root surface area. These can be all considered biomechanical advantages for sustaining higher occlusal forced. Therefore, implant treatment plans should attempt to simulate local status from natural denture. It's well knowen that stress is the major cause of implant treatment complications or failure. In implantology and other prosthodontic therapies, the biomechanical concept looks forward to minimizing occlusal force's local destructive effects . The number of proposed implant can be an excellent method to decrease overall masticatory stresses. Generally, at least one implant for each missing tooth in the posterior area is indicated by almost all researchers and practitioners. When occlusal forced are higher than usual, one implant for each buccal root may even be required. Implants are splinted together to biomechanically reduce stress to the periodontium. [20,25,26]

Another biomechanical parameter which can reduce local occlusal stress is represented by the surface area of a root form implant. Most implant manufacturer provides implants in variable lengths. The use of the longest possible implant is recommended in order to maximize the implant's contact area with the bone. It also allows the engagement of the opposing cortical plate, a dense region which can provide implant immobilization during the trabecular bone interface. However, in the posterior maxilla, there can be found only D3 or D4 bone density and no dense opposing cortical plates in order to engage the implant. When sinus lifting techniques are applied, longer implants may be used, but the functional surface area may not be improved. Therefore, functional surface area rather than total surface area should be addressed. Different authors admit that the most stresses to the implant-bone interface are located in the crestal 1/3 of the implant. This fact is a critical area for stress distribution and may be a risk of peri-implant bone loss. Longer implants, although of greater total surface area, may transfer very little stress to the apical regions and do not minimize stress in the most critical crestal regions. [20,25]

Implant dentistry has evolved into a greater understanding of biomechanics and the importance of stress reduction to minimize the risks of crestal bone loss and early implant failure. However, conventional implants limit themselves to implant length and diameter which are much less effective surface area enhancers than thread designs. Modified implant designs with increased functional surface area allow shorter implants with greater surface areas to be used in all regions of the mouth. This is most important in the posterior maxillary regions, where forces are greater and bone strengths are reduced, and available bone height is often less than in the anterior regions. [18,19]

Strategic choices to increase bone contact are suggested in the posterior maxilla to offset the poor strength and decreased bone density. Hydroxyapatite (HA) coating on the implant has been shown to increase the rate of osseous adaptation to implants, given greater initial rigid fixation, increase the surface of bone contact, increase the amount of lamellar bone,and give relative greater strength of the coronal bone around the HA-coated implants when compared with titanium implants. The space or gap between the bone and implant at initial placement is greatest in the soft bone of the posterior maxilla compared to the other regions. Gap healing may be enhanced by HA coatings. Therefore, HA coatings are strongly suggested in the D4 softest bone category, where the aforementioned benefits outweigh the potential problems associated with HA coating technology. [12,15]

In the past, force reduction and surface area were difficult to balance in the posterior regions of the mouth. Studies clearly demonstrate forces are often 300% greater in the posterior compared to the anterior regions of the mouth. Bone densities and strengths are 50% to 200% weaker in the posterior region. Yet, the implants with the greater surface area were inserted in the anterior regions. It is known that natural teeth do not have longer roots in the posterior regions of the mouth, where stresses are greater. Instead, increased surface area is achieved by an increase in diameter and a change in root design. [19,25]

In order to combat all anatomical unfavorable elements which the clinicians are faced with in a Kennedy class I edentulous maxilla is required a maximum knowledge and attention to achieve a successful therapy. The reports found in the Literature offer a variable surgical options which the practitioners can choose in order to restore complex cases. However, further research on this theme is required in order to minimize the post-operative complications and to rehabilitate with maximum efficiency an edentulous posterior maxilla well known for it's difficult problematics regarding implant dentistry.

CONCLUSSIONS

• The posterior maxilla has been known by many clinicians as one of the most difficult problematic areas for implant dentistry, requiring a maximum of knowledge and attention to achieve a successful therapy;

• The support tissue for the implants frequently is found to be unfavorable when it comes to implant therapy and requires specific surgical additive or substractive interventions in order to obtain a situs which can serve a perfect osseointegration and long-term maintenance of the implant and it’s restoration;

• Chemical integration provides good resistance to both shear and tensile forces, mechanical integration provides only good resistance to shear forces but poor resistance when it comes to tension;

• Fixed prosthodontics in Kennedy class I maxilla can be achieved only with implant dentistry;

• A provisional pretreatment acrylic prosthesis can be used to improve bone quality in D3 or D4 bone-supporting implants before the fabrication of the final restoration;

• The diameter and length of the implant depend on the quantity and the quality of the support bone structure;

• Diagnostic casts, periapical, panoramic radiographs, and computed tomography have a critical importance in establishing a proper diagnostic and the best suitable prosthodontic treatment plan;

• CBCT is one of the most accessible ways for a practitioner to estimate the bone density and morphological status in the implantation site, data which is absolutely necessary in order to establish a proper treatment plan;

• A key determinant for clinical success is the diagnosis of the bone density in a potential implant site;

• Whenever is possible, the doctor should select a design that fits the local biological configuration, rather than choosing one that requires surgical intervention;

• The position of the implant will be been established after the clinical and paraclinical examination, the direction/inclination of the implant in the jaw (buccolingual and mesiodistal) must be determined;

• The increase of the functional surface area of implants is warranted in the posterior regions since the implants which are placed in weaker bone types must support greater force;

• Imperative to treatment planning is to consider the biomechanical aspects of implant design and local occlusal status;

• The most used biomaterial in implantology is the titanium because it’s compatibility and physical traits;

• The implant placement requires a position at least equivalent to it's maximum deviation in order to achieve a successful final outcome;

• The use of surgical guides offers a safe positioning of implants with optimal use of the available bone;

• A biomechanical-based treatment plan reduces complications after implant loading with the prosthesis;

• Additional implants are the solution of choice in order to decrease stress, along with an increase in implant width or height;

• The amount of support required for an implant prosthesis should initially be designed similar to traditional tooth-supported restorations;

• Most authors recommend a screw-retained prosthesis instead of a cemented one;

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