Romanian Journal of Morphology and Embryology 2005, 46(2):131136 [614855]

Romanian Journal of Morphology and Embryology 2005, 46(2):131–136
Morphological changes in dental pulp
after the teeth preparation procedure
ANCA VIȚALARIU1), IRINA-DRAGA CĂRUNTU2)
1)Department of Oral Rehabilitation, Faculty of Dentistry, “Gr. T. Popa” University of Medicine and Pharmacy, Iassy
2)Department of Oral Biology, Faculty of Dentistry, “Gr. T. Popa” University of Medicine and Pharmacy, Iassy
Abstract
The aim of this study was to evaluate the immediate changes in the pulp-dentin complex that result from crown preparation, and their
correlation with the thickness of remaining dentin and the preparation technique (with or without water spray cooling). Thirty upper intact
premolars scheduled for extraction for orthodontic reasons were high speed prepared, extracted immediately after preparation an d divided
in 5 groups. The analysis of the pulp morphology demonstrated that there are several differences according with the preparation technique.
The most severe changes appear after the profound preparation without water-cooling, the odontoblastic layer being extremely af fected.
Also, vascular reactions and inflammatory infiltrate (in the absence of bacteria) were present. Our study revealed that the his tologic
changes in the pulp and dentin following complete crown preparation occur anyway and they are considered difficult to avoid, ev en if an
adequate technique of preparation is used.
Keywords : dental pulp, odontoblast, histologi c changes, full crown preparation.
 Introduction
The dentin and the dental pulp are considered as a
biologic entity named dentin-pulp complex, with very
tight-related elements, a common mesenchymal origin, a conjugated evolution, as well as permanent
interactions. For all these reasons, some authors
refer the dentin-pulp complex as a histo-physiologic entity [1, 2].
Pulp reactions to the tooth preparation techniques
are still a major concern in restorative dentistry [3, 4].
The term “stressed pulp” used in the literature means
a bad prognosis from the beginning, because, previous
to the prosthesis, caries, old restorations, occlusal
trauma, abrasion or periodontal disease already
exhausted the pulp adaptability. For such a tooth, any additional trauma, even a small one, can cause a
degenerative process in the pulp [5].
According to many longitudinal investigations, there
is a high rate of vital teeth exhibiting typical signs of
pulp complications, while there is a significantly
increased frequency of endodontic treatments following dental preparation and crowns cementation [6-8].
Displacement of odontoblastic nuclei following the
teeth preparation is a phe nomenon taken into account
when high-speed dental engines were introduced in the
late 1950s [9, 10].
The phenomenon was described initially as
“aspiration” of the odontoblastic nuclei into the dentinal
tubules [9, 10], but the term “displacement of
odontoblasts” [3, 11] has come into common use because it does not suggest any certain mechanism for
its occurrence.
It was demonstrated that the pulp reactivity includes
also immediate vascular responses , resulted from the
grinding of dentin [12-14].
The reactivity of the dental pulp is reported in
almost all stages of the pros thetic treatment [15-20], the
pulp response being influenced by many factors: the thickness of remaining dentin, the frictional heat and
vibrations generated by high speed burs during crown preparation, the excessive dr ying of dentine, the effects
of local anesthesia and of the astringent and hemostatic
substances used for the te mporary enlargement of the
gingival sulcus, the impression and cementation
materials.
The first step, the ablation of the dental hard tissues,
is a non-biological process by its own destructive
nature. Thus, in order to rest rict the destructive effect, a
minimal removal of dental substance is performed, with the aim to preserve the pulp vitality. There is few data in
the literature about the long-term effects of the
preparation alone.
These are difficult to asse ss because the prepared
teeth will receive a permanent restoration. Thus, it is
considered [3, 21] that the histological evaluation of the
immediate structural changes in the pulp-dentin
complex resulting from crown preparation involves two
conditions.
The first condition is to extract the tooth
immediately after the preparation , because no
restorative material is 100% biologically inert and thus
it is possible to produce a certain pulp response.
The second condition is to use intact teeth from
young individuals, preferably newly eruptive teeth, the
normal structure being well-known and any deviation in
structure can be attributed to the preparation procedure.
Unfortunately, the teeth that are to receive prosthetic
therapy have or have had caries, posttraumatic fractures,
abrasions or old restorations, and in all these instances, the damages to the pulp are already produced.
The aim of this experimental study was to evaluate
the immediate changes in the pulp-dentin complex that result from crown preparation, and their correlation with
the thickness of remaining dentin (the depth of the
preparation) and the preparation technique used (with or without water spray cooling).

Anca Vițalariu, Irina-Draga C ăruntu
132
 Material and methods
For this experiment we used 30 intact upper
premolars, newly erupted, scheduled for extraction for
orthodontic reasons, from children (10-16 years old).
After anesthesia (Scandonest 3%, without vasoconstrictor), the teeth we re high speed prepared in
two different ways: half of them were superficially
prepared (0.4 mm depth) and the other half was profoundly prepared (1.5 mm depth). Every type of
preparation was made with and without water spray
cooling.
The teeth were extracted immediately after
preparation and placed in formalin (15% solution).
Based on the type of preparation procedure used, they were classified in 5 groups:
▪ gr. 1 – control (sound teeth, without preparation);
▪ gr. 2 – superficial preparation (0.4 mm) with water
sprays cooling;
▪ gr. 3 – superficial preparation (0.4 mm) without
water sprays cooling;
▪ gr. 4 – profound preparation (1.5 mm) with water
sprays cooling;
▪ gr. 5 – profound preparation (1.5 mm) without
water sprays cooling.
The extraction of the dental pulp was performed by
the guided fracture of the teeth, aiming for a minimal
dilaceration of the pulp. The biopsy fragments were
fixed in formalin and routinely processed. The specimens were stained with Haematoxylin-Eosin
(HE) and trichrome Szekelly.
 Results and discussions
1. Synoptic presentation of the morphologic
features
a) Group 1 (control – sound teeth, without
preparation)
The microscopic aspect of the pulp from the control
group was characteristic for the normal status.
The peripheral pulp presented the three typical areas:
the odontoblastic zone, the cell-free zone (Weil) and the
cell-rich zone (with Hohl cells).
The odontoblastic layer appeared continuous,
uninterrupted, with the cells placed “in palisades”. The
cells were columnar at the pulp horns, becoming later cuboidal and squamous.
The central pulp revealed a loose connective tissue,
with fibroblasts and fibrocytes. As the dental pulp was young, the collagen fibers were few and isolated,
dispersed among the cells of the pulp.
b) Group 2 (superficial preparation with water
spray cooling)
For the superficially prepar ed teeth (0.4 mm), with
water spray cooling, there were no obvious
modifications at the pulp level, the morphological
aspects resembling the normal pulp from group 1.
Although, generally, the pulp histology was normal,
there should be noted some changes in the position and orientation of the odontoblastic nuclei axis, suggesting a tendency of displacement towa rds the dentinal tubules
(Figure 1), as a result of the high speed preparation of
teeth.
c) Group 3 (superficial preparation without water
spray cooling)
The superficial preparation (0.4 mm) without water-
cooling determined important changes on the
odontoblastic zone and in the vascular field.
Thus, there were observed some disruptions and
vacuolations of the odontoblastic layer (Figure 2) as
well as the irregular placement of the cells, without the normal aspect of “palisades”. Also, the movement of the
odontoblastic nuclei towards the dentinal tubules was
more evident than in the second group (Figure 3).
At the same time, there a ppeared reactions in the
vascular field, comprising vasodilatations and small
hemorrhages in the arteriolar and capillary segment.
d) Group 4 (profound preparation with water
spray cooling)
In the fourth group, the deeper tooth preparation
(1.5 mm) produced an important ablation of the hard
tissues of the teeth and a significant decrease in the
thickness of remaining dentine. Here, even though the
preparation was performed with adequate water cooling,
the changes occurred in the dentin-pulp complex were more important than in the case of the superficial
preparation. In the peripheral pulp the clear distinction
between the three zones (odontoblastic layer, the cell-free zone and the cell-ri ch zone) disappeared.
The odontoblastic layer was interrupted and vacuolated
on large areas, with the cells in an obvious disorder. The
cell nuclei were displaced be yond the predentin layer,
deeper within the dentinal tubules (Figures 4 and 5).
Under the odontoblastic layer we noticed a
clustering of fibroblasts and fibrocytes (Figure 6), which
are not usually present at this level (cell-free zone). Although the loose connective tissue maintained its
normal aspect, this agglomeration of fibroblasts and
fibrocytes anticipates the st age of fibrosis in that
specific pulp territory.
We also observed in the cen tral pulp the existence of
some areas with an abundance of fibrocytes and collagen bundles, together with vasodilatations and important
hemorrhages of the large pulp vessels (arterioles and
venules). The small vessels were also vasodilated and showed plumped endothelial cells. Other notable features
were some microhemorrhages and pulp interstitial edema.
e) Group 5 (profound preparation without water
spray cooling)
The histologic sections from the teeth in the fifth
group showed that the modifications in the pulp from
these cases are extremely severe. Important changes appeared in the peripheral pulp, the odontoblastic layer
being completely destroyed. The brutal thermal
aggression, caused by the profound preparation without water-cooling, produced at the vascular level a rapid
vasodilatation with important hemorrhages (Figures 7
and 8) and exudate, determining an interstitial edema on large areas of the coronal pulp.

Morphological changes in dental pulp after the teeth preparation procedure 133
Figure 1 – Odontoblastic nuclei with modificated axis and
tendency of displacement towards dentinal tubules
(HE, ×400)
Figure 2 – Disrupted odontoblastic layer presenting
vacuolation and a slight vasodilatation
of the arterioles (Szekelly, ×200)
Figure 3 – Odontoblastic nuclei displaced towards
dentinal tubules (Szekelly, ×400)
Figure 4 – Interrupted and vacuolated odontoblastic layer,
odontoblastic nuclei dislocated into the dentinal tubules
(Szekelly, ×400)Figure 5 – Dentin with odontoblastic nucleus
in the dentinal tubule (Szekelly, ×400)

134 Anca Vițalariu, Irina-Draga Căruntu
Figure 6 – Fibroblasts and fibrocytes agglomeration
under the odontoblastic layer (HE, ×200)Figure 7 – Central pulp: pronounced dilatations in
arterio-venous territory (Szekelly, ×200)
Figure 8 – Interstitial hemorrhages (HE, ×200)
Figure 9 – Loose connective tissue with normal aspect (left)
and densification tendency (right) (Szekelly, ×200)Figure 10 – Accute inflammatory infiltrate detail (HE, ×400)

Morphological changes in dental pulp after the teeth preparation procedure
135
Another aspect in this group was a tendency towards
densification of the connective tissue, in wide zones of
the central pulp, alternating with loose connective tissue areas, appearing normal (Figure 9).
Although most of the times it is associated with an
infectious (bacterial) ag ent, the presence of the
inflammatory infiltrate (polymorphonuclears,
lymphocytes, macrophages) (Figure 10) could be
observed in this group, surrounded by numerous fibrocytes.
The existence of an inflammatory infiltrate in the
pulp of a recently erupted sound tooth is a proof that the
brutal thermal aggression represented by high-speed
preparation without water-cooling can determine the
apparition of an acute inflammatory process.
2. The pulp reactivity
The pulp immediate reactions to high-speed
preparation can be classified in three groups:
▪ structural changes – the most important being the
displacements of the odontoblastic nuclei into the dentinal tubules;
▪ vascular reactions – dilatations, decrease of blood
flow and/or hemorrhages on wide areas, interstitial edema, vascular stasis;
▪ inflammatory reactions even in the absence of
bacteria.
The displacement of odontoblastic nuclei and of
the tubular contents, observed in this study and reported
by some authors in the literature [3, 9-11, 22] can be produced by several mechanisms: overheating of the
dentin during the teeth preparation, evaporation of the
dentinal fluid from the prep ared surfaces, the exposure
of a high-pressure area by sectioning the tubules,
excessive drying of the dentin by air cooling,
mechanical distortion of the pulp-dentin complex during the teeth extraction.
The densification of the connective tissue and, as a
result, the pulp fibrosis is phenomena appearing in the
general context of aging. On the contrary, in the
circumstances investigat ed by our study, these
reactional changes are produced by the damages to the
pulp, consequent to the activity of aggressive external
factors [23].
The increase of pressure in the pulp, as a result of
the exudate and the interstitial edema [12], may cause
self-aggression for the pulp elements and, thus, the amplification of inflammatory phenomena.
Also, the high pulp pressure leads to compression of
the venules, followed by the slowing down of the return circulation and venous stasis, determining the
accumulation of toxic products from the metabolic
processes.
The results of our study concur with those of About
et al. [24] and Murray et al. [25] who noticed that the
preparation of the dentin produced an inflammatory response in the absence of bacteria.
The pulp changes and the degree of inflammation
corresponded with the depth of the preparation
(inversely proportional to the thickness of the remaining
dentin). 3. The thickness of the remaining dentin
Besides the utilization (or not) of water-cooling
during preparation, the severity of the immediate pulp reactions depends on the thickness of remaining dentin
as well (the depth of the preparation) [3]. Regarding the
thickness of the remaining dentin, there are several opinions stated in the literature.
Thus, according to [26, 27] a minimum of 2 mm
seems to be a critical factor in determining the pulp response and to guarantee the pulp vitality, if all the
other prophylactic measures are taken.
It was experimentally demonstrated that very small
variations in thickness of the remaining dentin have a
significant influence on pulp reactions. Other authors
consider that for the maintenance of the pulp vitality a 0.25-0.50 mm dentin thickness is appropriate [25, 28].
Zollner [5] demonstrated e xperimentally that, actually,
the critical thickness of the remaining dentin must be
ensured on the direction of the dentinal tubules opened
by the preparation.
Irrespective of the mechanism involved, the results
of this experiment showed that the displacement of
odontoblastic nuclei occurs even in the case of a superficial preparation (0.4 mm) with water-cooling.
The results of our study concur with those of
[25, 28, 29] demonstrating that high-speed teeth preparation produces immediate pulp modifications
even an adequate water-cooling is used. The severity of
the changes is dependent on the thickness of the remaining dentin (the depth of the preparation).
4. Clinico-morphological correlations
Histologic and clinical experience showed that,
although the pulp has a good regenerative potential, and
the inflammatory response will often be followed by
healing, the induced modifications can become significant on the long run [5, 22].
Thus, in the implementation of a treatment plan one
must never start from the hypothesis that an
asymptomatic tooth is a tooth with a healthy pulp. The
scars following inflammatory and reparatory phenomena alter the resistance of the pulp to future
injuries.
Regarding to the prosthetic fixed therapy, it is easy
to be seduced by the technical possibilities and to forget
the biological realities of the patient [30]. Recent
developments in dental materials offer less destructive alternatives such as veneers, inlays and resin-bonded
porcelain crowns.
The choice of a certain type of crown must be
always in the patient’s best interest and depend on the
functional requirements, strength and vitality of the
remaining tooth and the aesthetic demands, as well the individual morphological characteristics of every tooth
(the thickness of enamel and dentin layers).
Full metal crowns have the advantage of requiring a
relatively superficial tooth preparation (0.4 mm),
comparing with ceramic, composite, metal-ceramic and
metal-polymeric crowns, that require a deeper preparation
(1.5-2 mm) and thus are more destructive for the tooth
structures.

Anca Vițalariu, Irina-Draga C ăruntu
136
A minimal preparation (only the enamel) is required
in the case of resin-bonded porcelain crowns. Being the
most conservative crowns for the tooth hard tissues, these
are indicated especially in younger patients who have large, vulnerable pulp [31].
 Conclusions
1. The dental pulp shows structural changes,
especially in the odontoblastic zone, its reactivity being correlated with the depth and the technique of
preparation.
2. In spite of all technical progresses in modern
dentistry, there is no harmless, completely non-
traumatic technique for the crown preparation.
Histological changes in the underlying pulp occur anyway and are difficult to avoid as long as the crown
preparation is performed at high speed, even if an
adequate water cooling system is used.
3. Pulpal complications involving inflammation,
degradation and necrosis are the result of a series of
traumatic external injuries. So, it is the responsibility of
the restorative dentist to minimize the trauma to dentin
and pulp during all clinical procedures, especially in the tooth preparation phase.
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Mailing address
Irina-Draga C ăruntu, Professor, M. D., Ph. D., “Gr. T. Popa” University of Medicine and Pharmacy,
Faculty of Dentistry, Department of Oral Biology, Street of Univer sity no. 16, 700115 Iassy, Romania;
Phone +40232–267 801 / 145, E-mail: dicarunt@mail.dntis.ro

Received: 20 September, 2005
Accepted: 15 October, 2005