Computer-Aided Measurement of Total Occlusal Convergence of Teeth Preparations for All-Ceramic Crowns by Dental Students

Abstract

Objective: This study was based on the evaluation the degree of total occlusal convergence of teeth prepared
for all-ceramic crowns which is the main factor that retention and resistance form of indirect restorations
depended on. Teeth preparation done by 3rd year dental students at Al-Esraa university collage, Iraq in 2019.
Materials and method: Eighty typodont teeth, maxillary central incisor(n=40) and first premolar teeth
(n=40) were prepared for all-ceramic crowns by preclinical dental students under examination condition.
The prepared teeth were scanned and digitized using the laser scanner 3Shape D710 (SculptCAD, Texas,
USA). The datasets were evaluated using inspection software (shaper 3D zrt. Hungary, 2020) that used for
the assessment of the total occlusal convergence. Each tooth was virtually sectioned by four vertical planes:
buccopalatal, mesiodistal, mesiobuccal–distopalatal and distobuccal– mesiopalatal and for each plane the
total occlusal convergence angle (degree) was measured by drawing lines along the two opposing axial
walls from the finish line extended coronally. The data were analyzed with appropriate statistical tests using
analysis of variance (ANOVA) and unpaired t-tests. Differences between groups were tested for significance
at 95% confidence interval.
Results: The results revealed that the students prepared the central incisor teeth with average TOC values
of 11.46° ± 6.81°, 9.91° ± 4.92°, 10.54° ± 7.05° and 12.06° ± 6.71° respectively, from the buccopalatal,
mesiodistal, mesiobuccal–distopalatal and distobuccal– mesiopalatal planes. Concerning first premolar
teeth, students prepared them with average TOC values of 12.03° ± 6.63°,11.57° ± 6.34°, 14.3° ± 6.94° and
12.55° ± 6.6° respectively.
The findings revealed that the approximated average TOC values for all the measured planes were
greater than the optimal TOC range 4 to 6 ° but stayed within the TOC acceptable range 4 to 14 °.
Ordinary one-way ANOVA test showed no significant (P >0.05) differences in the average TOC between
the different four planes within each tested group of teeth. The average value of overall total occlusal
convergence (TOCs) in the first premolar teeth= 12.61°± 6.63°was higher than for the central incisor teeth=
10.99°±6.4°. Unpaired t-test for the two tested groups revealed significant (p < 0.05) differences.
Conclusions: The presented study found that about 85%, 65.83% respectively of upper central incisor
and first premolar teeth prepared for all-ceramic crowns by pre-clinical dental students with acceptable
recommended convergence angle range 4-14°.