612 Journal of Dental Education ș Volume 74, Number 6The Chamfer Finish Line: Preclinical Student Performance Using Different Bur Designs Michael A…. [603446]

612 Journal of Dental Education ș Volume 74, Number 6The Chamfer Finish Line: Preclinical Student: [anonimizat], D.D.S., M.S.; Hatem A. Abdulkarim, B.D.S.; Walid R. Thabet,
B.D.S.; Stephan J. Haney, D.D.S.
Abstract: The primary purposes of this investigation were to evaluate sophomore dental student: [anonimizat]—a round-ended bur and a torpedo-shaped bur—and to gain student: [anonimizat], each of whom prepared the buccal surfaces of two
mandibular molar typodont teeth, producing chamfer finish lines. Students prepared both teeth in the same laboratory session
and were randomly assigned to two groups that were required to prepare the first of the two molars with a specific bur type. The
prepared chamfer finish lines were scored and the data analyzed using the Wilcoxon signed-rank test. Student: [anonimizat]=0.005). Student: [anonimizat] “Overall, was one bur type better?”
58 percent of the students preferred the round-ended bur for creating a chamfer finish line. The most frequent write-in comment,
made by twelve of the fifty students, criticized the torpedo-shaped bur for creating finish lines that were too shallow or too long.
Dr. Mansueto is Associate Professor and Head, Fixed Prosthodontics Division, Dental School, University of Texas Health Science
Center at San Antonio; Dr. Abdulkarim is a Periodontal Prosthesis Resident, School of Dental Medicine, University of Pennsylva –
nia; Dr. Thabet is a Postgraduate Resident in Advanced Education in General Dentistry, MetroHealth Medical Center, Cleveland,
Ohio; and Dr. Haney is Assistant Professor, Department of Prosthodontics, Dental School, University of Texas Health Science
Center at San Antonio. Direct correspondence and requests for reprints to Dr. Michael A. Mansueto, Department of Prosthodon –
tics (7912), Dental School, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX
78229-3900; 210-567-3644 phone; 210-567-6376 fax; [anonimizat].
Keywords: dental education, student: [anonimizat], diamond burs, chamfer, tooth preparation, finish line, complete veneer crown
Submitted for publication 10/17/09; accepted 2/9/10
The chamfer is considered the ideal finish line
for complete veneer preparations for metal
crowns.1-7 The chamfer is easy to produce,
provides space for an adequate bulk of restorative
material, allows for a slip-joint effect, and is distinct
and readily identifiable to both the dentist and the
laboratory technician. More than possessing sound
mechanical properties, the chamfer finish line design
exhibits low stress levels in photoelastic studies,8
which may reduce stress-induced cement failure.1 A
drawing of a classic chamfer finish line can be seen
in Figure 1.
For decades, instruction in tooth preparation
called for the creation of chamfer finish lines with
round-ended, tapered diamond burs.3,4,9-12 Y ears later,
others advocated the use of torpedo-shaped, pointed
burs for the fabrication of the chamfer.5,13-15 The
torpedo bur design was believed to be less likely
to create a “butt joint,”1 the undesirable outcome of
overpreparation with round-ended burs.
Bur types used in tooth preparation are often a
matter of operator preference. Research scientifically
supporting the use of either the round-ended or tor –
pedo bur types for the preparation of chamfer finish
lines is lacking. Over time, some respected authori -ties have changed their published bur preferences,
but again without evidence to support the change.5,9
The purposes of this investigation were to
evaluate sophomore dental student performance in
the production of a chamfer finish line using two dia –
mond bur types—a round-ended bur and a torpedo-
shaped bur—and obtain student feedback about bur
type preferences. Performance results may support
the preferential use of one bur type for the production
of chamfer finish lines.
Materials and Methods
Fifty sophomore students from the Univer –
sity of Texas Health Science Center at San Antonio
(UTHSCSA) Dental School participated in the
study. All participants volunteered, were modestly
financially compensated for their time from a grant
received from Brasseler USA (Savannah, GA), and
received no grading or coursework consideration for
their involvement. The study was completed in one
laboratory session in 2008 that followed the end of
a regularly scheduled course. Prior to tooth prepa –
ration, the participants received individual verbal

June 2010 ș Journal of Dental Education 613instructions on the study’ s methods and were given
an instruction sheet to read. This sheet contained a
review of the testing methods, a description of the
ideal chamfer and its location with regard to the free
margin of the gingiva, a drawing of an ideal chamfer
for a mandibular molar shown in cross-section, and
a photo of a prepared molar showing a chamfer fin –
ish line being assessed with the use of a periodontal
probe (Figure 2).
Each student prepared the buccal surfaces of
two #30 melamine typodont teeth (Kilgore Interna –
tional, Coldwater, MI). The tooth was screwed in
place in a fourteen-tooth, complete-arch typodont
(Kilgore International, Coldwater, MI), and the
preparations occurred on the laboratory bench top.
Teeth were reduced only axially, creating cham –
fer finish lines. For a randomly selected group of
twenty-five students, the first tooth preparation was
completed using a round-ended, medium grit, tapered
diamond bur (856.31.016, Brasseler USA, Savannah,
GA) (Figure 3). The second #30 was inserted into
the typodont directly following the first prepara –
tion. The second preparation was completed with a
torpedo-shaped, medium grit, parallel-sided diamond
bur (878.31.012, Brasseler USA, Savannah, GA)
(Figure 3). The preparation sequence was reversed
for the second set of twenty-five students: the first
Figure 1. Shape of a classic chamfer finish line
Source: Reprinted with permission from Shillingburg HT, Hobo S, Whitsett LD, Jacoby R, Brackett SE. Fundamentals of fixed prosth –
odontics. 3rd ed. Carol Stream, IL: Quintessence Publishing Co., 1997.
Figure 2. Assessment of a chamfer finish line
Note: A photographic example of chamfer finish line assess –
ment was given to each participant in the study prior to tooth
preparation.

614 Journal of Dental Education ș Volume 74, Number 6preparation was completed with the torpedo-shaped
bur, and the second preparation was accomplished
with the round-ended bur. Only high-speed dental
handpieces were used to prepare the teeth. The burs
were new, used directly following package opening.
No time limits were imposed, but all students com –
pleted both preparations and the required survey in
thirty minutes or less.
Following tooth preparation, participants com –
pleted a four-question survey and were provided the opportunity to offer additional written feedback about
their experiences with both burs. Completion of the
survey was a required element of the experiment;
provision of additional feedback was optional.
Results
Prepared teeth were collected and scored
independently by two calibrated evaluators. Both
evaluators were dentists with less than five years of
Figure 3. Burs utilized in study
Note: The medium-grit diamond burs used in this study were 856.31.016 (round-ended, tapered) on the left and 878.31.012 (torpedo-
shaped, parallel-sided, pointed) on the right.

June 2010 ș Journal of Dental Education 615experience who were enrolled in a preceptorship in
prosthodontics at UTHSCSA. Scoring was accom –
plished using the standards shown in Table 1. Each
evaluator’ s data were analyzed using the Wilcoxon
signed-ranks test; no combination of evaluators’
scores occurred. The histograms in Figure 4 show
the scores assigned by each evaluator. Student per –
formance with the round-ended bur was statistically
better (p=0.005).
Table 2 displays the results of the students’
survey responses. Fifty-eight percent of the students
indicated that it was easier to make a chamfer with
the round-ended bur. Students’ responses to the other
Table 1. Chamfer finish line scoring criteria
The finish line will be scored on a three-point scale: 1, 2, or 3, with “3” representing the ideal outcome.
A score of “1” will be awarded when the finish line:
• at mid buccal is a knife-edge design.
• at mid buccal is a “heavy” chamfer design, measuring 1 mm or greater in axial reduction.
• at mid buccal is a shoulder design, measuring 1 mm or greater in axial reduction.
• within 1.5 mm to the mesial or distal of the mid buccal, is distinctly irregular with a fluctuation(s) of 0.5 mm
or greater.
A score of “2” will be awarded when the finish line:
• at the mid buccal is a thin chamfer design, axially deeper than a knife edge, but less than 0.3 mm in axial depth.
• at mid buccal is a “heavy” chamfer, measuring greater than 0.6 mm to less than 1 mm in axial depth.
• is a shoulder design, measuring less than 1 mm in axial depth.
• within 1.5 mm to the mesial or distal of the mid buccal, is distinctly irregular with a fluctuation(s) less than 0.5 mm.
A score of “3” will be awarded when the finish line:
• is a chamfer design, measuring 0.3 mm to less than 0.6 mm in axial reduction.
• within 1.5 mm to the mesial or distal of the mid buccal, is regular with no significant fluctuations.
questions revealed no clear preference for one bur
over the other.
Optional statements from the students sup –
ported the use of the round-ended bur. Thirty-eight
students wrote comments, which were categorized
into seventeen topic areas. Ten students submitted
multiple statements. Table 3 provides a summary of
the most frequently provided comments organized
into categories. A majority of the students’ responses
dealt with the difficulty in properly shaping the
chamfer while using the torpedo-shaped bur. Students
perceived that the torpedo-shaped bur was more
prone to damage the gingiva apical to the finish line.
Figure 4. Scores given on student performance
Note: The histograms show the scores assigned by each evaluator for each bur type. Via analysis using the Wilcoxon signed-ranks test of
both evaluators’ scores, student performance with the round-ended bur was statistically better (p=0.005).

616 Journal of Dental Education ș Volume 74, Number 6Discussion
Because there is little scientific support for the
bur type used to create the chamfer finish line in tooth
preparation for complete veneer metal crowns, the
bur type selected is usually the operator’ s preference.
Hooper et al.16 reported that this situation also exists
in dental schools in the United Kingdom. Though
bullet (round-ended) and torpedo-shaped burs were
used in student instruction for the creation of chamfer
finish lines, there was no consensus in their study on
the optimal bur type among the fifteen UK dental
schools.
Early-in-training, first-semester sophomore
dental students were selected as test subjects in
our study. Since there are no fixed prosthodontics
or tooth-preparation hand skills courses offered in
the first-year curriculum at the UTHSCSA Dental
School, selection of sophomores at this stage in
their training attempted to minimize bias based on prior tooth preparation experiences and/or prolonged
exposure to the preparation philosophy espoused at
the university. However, the bur used in the prepara –
tion of the chamfer finish lines at the UTHSCSA
Dental School is a round-ended diamond. Though
efforts were made to minimize biasing effects, the
school-endorsed methods could have impacted stu –
dent performance.
The participants were randomly divided into
two groups by the sequence of their volunteering to
participate in the study. Each group was assigned a
different bur type to use for the first tooth preparation.
Though not statistically analyzed, this alternating
preparation method attempted to minimize effects re –
sulting from practice, repetition, etc. during the study.
The two bur types used in this study were dis –
similar in their taper: the torpedo-shaped bur was
parallel-sided. Bur taper could be a significant factor
in the preparation’ s outcome if complete axial or oc –
clusal reductions were elements in the experimental
design. Since this study only measured chamfer finish Table 2. Survey results: sophomore dental students’ perceptions of using round-ended and torpedo-shaped burs for
creating a chamfer finish line during tooth preparation, by number and percentage of total respondents
Question Round-Ended Torpedo-Shaped No
Number Question Bur Better Bur Better Difference
1 Was it easier to make a chamfer with one bur type? 29 18 3
(58%) (36%) (6%)
2 Did one bur type make more regular finish lines? 25 21 4
(50%) (42%) (8%)
3 Did one bur type cut more smoothly (less chatter)? 13 23 14
(26%) (46%) (28%)
4 Overall, was one bur type better? 25 19 6
(50%) (38%) (12%)
Table 3. Optional statements: summarized student statements more frequently cited undesired outcomes when the
torpedo-shaped bur was used
Summary of Optional Statements Frequency
1 Torpedo-shaped bur: hard to make a chamfer, too thin/long of an outcome 12
2 Torpedo-shaped bur: greater risk of damaging the gingiva 6
3 Torpedo-shaped bur: difficult to tell where the chamfer would terminate 6
4 Torpedo-shaped bur: nice finish line 6
5 Torpedo-shaped bur: easier to control 5
6 Torpedo-shaped bur: works great 3
7 Round-ended bur: works great 3
8 Torpedo-shaped bur: chamfer created was too steep 3
9 Round-ended bur: easier to use since tip contacts the tooth 2
10 Round-ended bur: too easy to make a shoulder finish line 2

June 2010 ș Journal of Dental Education 617line placement, not axial wall reduction, dissimilar
bur taper was not believed to be an impacting factor.
Since the bur’ s tip is used in chamfer preparation,
bur-tip diameter is important in comparisons of
chamfer placement techniques. The burs selected for
this study, therefore, had similar bur-tip diameters.
Chamfer finish lines were assessed at one
point per preparation: the mesio-distal middle of
the buccal surface. A matrix was used to identify
the location where each evaluator was to assess the
student’ s preparation. The relative smoothness and
regularity of the finish lines were also assessed by
the evaluators over a 3 mm length, 1.5 mm on each
side of the midpoint.
Chamfer scoring was accomplished using
techniques commonly employed to evaluate student
preparations both preclinically and clinically. In addi –
tion to dental loupes magnification of 2.5 power, the
primary measurement tool was a periodontal probe
with 1 mm markings and of known diameter at the
probe’ s tip. In addition to the evaluators, students
were instructed to use similar periodontal probes to
support the proper sizing of the chamfer during this
study. The probe’ s tip makes a quick reference for
assessment of chamfer size and shape. Without so –
phisticated measurement methods, it was anticipated
that small differences in evaluator’ s scores would be
encountered. Two evaluators were thus used, and no
combination of evaluator data was attempted. Statisti –
cal analysis indicated that the assessments of the two
evaluators were not significantly different.
Conclusions
Within the context of this study, student per –
formance in the preparation of a chamfer finish line
was statistically better (p=0.005) when a round-ended
bur type was used compared to results attained with
the use of a torpedo-shaped diamond bur of similar
bur-tip size. Fifty-eight percent of the students indi –
cated that it was easier to make a chamfer with the
round-ended bur. Optional write-in comments by
thirty-eight of the fifty students also tended to sup –
port the use of the round-ended bur for the creation
of chamfer finish lines.Acknowledgments
The authors are thankful for the financial
and product support received from Brasseler USA,
especially from Mr. Kenneth Allen and Mr. Dennis
Steward. The authors are thankful to Mr. Chong
Fang Zhu for his support with the statistical analysis
reported in this article.
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