EVALUATING CAD/CAM AS AN OBJECTIVE GRADING TOOL
Derek Hou, Joshua Kristiansen, DMD, John Da Silva, DMD, MPH, ScM
Harvard School of Dental Medicine
BACKGROUND
RESULTS
DISCUSSION
Continuous feedback is integral for students
learning the skills of tooth preparations. Feedback
is generally only received verbally, which can be
diﬃcult to conceptualize for a novice practitioner.
Students are also dependent on a small number of
faculty for feedback, spending valuable class time
waiting in line to receive feedback. Furthermore,
even calibrated faculty can have a wide range of
opinions on the same preparation. As a result,
preclinical time is not being used eﬃciently and
students fail to learn the key concepts of tooth
preparations. The purpose of this study is to
evaluate if new software (prepCheck) developed
by Sirona can evaluate and provide meaningful
feedback on tooth preparations.
This study focused on evaluating reduction, taper, and undercuts. Of the twenty-six
scanned preparations, only one tooth did not show undercuts with the software. All of the
preparations showed insuﬃcient occlusal reduction (<1mm) when compared to the
unprepared tooth. For axial reduction, seven preparations showed excessive reduction
(>2mm) and nineteen preparations showed insuﬃcient reduction (<1mm). For taper, all of the
preparations showed either areas of over taper (>10°) or areas of under taper (<5°). Often, the
same preparation would show both areas of over taper and under taper.
Overall, the software was able to measure
reduction, undercut, and taper. Surprisingly, the
software identified problems with all of the
preparations. All but one of the teeth were found
to have undercut. This is likely due to the undercut
detection feature being too sensitive. Areas of
roughness or scanning artifacts were often
erroneously marked as undercut.
The taper tool often showed areas of both over
and under taper on the same tooth. The strict cut
oﬀ of over taper >10° and under taper <5° may be
too limited to have clinical significance. It is
unclear why every preparation was found to have
insuﬃcient occlusal reduction. Students typically
evaluate occlusal reduction using a putty to
compare to the unprepared tooth. Further analysis
is needed to determine if the software is correct in
measuring occlusal under reduction for all of the
preparations.
One challenge to using the software is that
multiple steps are required before the analysis can
be generated. The long setup time may prevent
widespread use among students.
The next step is to determine if grading by
calibrated faculty agree with the analysis
generated by prepCheck.
Sufficient
Excessive
Insufficient
1 (no undercut)
25 (undercut present)
-
Occlusal Reduction
0
0
26
Axial Reduction
0
7
19
Undercut
METHODS
#30 PFM crown preparations were prepared by
third year students as part of a preclinical exam
for the prosthodontics course. Twenty-six
preparations were collected and scanned into
CEREC 4.2 using Sirona’s Omnicam scanner. The
margin and path of draw were set before exporting
to Sirona’s prepCheck software. An unprepared
#30 tooth was also scanned to serve as a
comparison for reduction measurements. Analysis
was performed for reduction, undercuts, and
taper. An IRB exemption was obtained for this
non-human study.
Tracing the margins in CEREC software before
exporting scan to prepCheck
Unprepared tooth used to generate
ideal master preparation based upon
set reduction parameters
Undercut areas are identified in yellow.
Reduction analysis comparing
preparation to unprepared tooth. Green
shows areas of under reduction.
Taper analysis with red showing over
taper (>10°)
SUMMARY
Sirona’s prepCheck is a new tool to provide
feedback to students in preclinic for tooth
preparations. The software was able to measure
undercut, taper, and reduction. However, the
undercut and taper analysis may be too sensitive
to have clinical significance. Further testing is
needed to determine if the reduction analysis is
accurate. At this point, the software is not fast or
easy enough for widespread use. Future software
development may correct these issues. CAD/CAM
evaluations will likely supplement faculty
evaluations in teaching tooth preparations in the
future.