Convergence angles for full veneer crown preparation completed by undergraduate students in a dental teaching hospital

Objectives: To determine the degree of taper and the average angle of convergence (AOC) accomplished for full veneer/coverage crowns (FVC) by supervised undergraduate students at a dental teaching hospital. Methods: One hundred and twenty-five stone dies of FVC preparations (25 full-metal [FMCs] and 100 metal-ceramic [MCCs]), prepared by dental students were included in this study. To measure AOC, standardised buccal and mesial photographs were taken when dies were mounted onto a custom silicone jig after careful positioning. 2D digital analysis software (ImageJ) was used to calculate the average mesio-distal (MD), bucco-lingual (BL) and overall AOC for each die. Differences between groups were tested for significance at 95% confidence using t-tests and analysis of variance (ANOVA). Findings were compared to the recommended 6°–15° range. Results: The average AOC was 24.2° ± 11.95°. As few as one-in-four preparations (26.4%, n = 33) complied with the recommended standards. The MD plane (24.7° ± 15.53°) was more tapered than the BL plane (23.0° ± 13.84°) (p >0.05) and FMCs preparations (34.7° ± 15.10°) more than MCCs (21.6° ± 9.38°) (p <0.001). Molars (31.6° ± 12.56°) had the greatest AOC, followed by premolars (20.7° ± 7.81°), canines (19.4° ± 6.37°) and incisors (17.0° ± 9.62°) (p <0.001). Additionally, mandibular teeth (28.8° ± 13.76°) exhibited a greater AOC than those in the maxilla (21.7° ± 10.08°) (p <0.05). Conclusion: The findings of this study suggest that within a dental school teaching environment, crown preparations completed by undergraduate students are over-tapered. Tooth type, inter and intra-arch position and crown material significantly impact taper, with mandibular molar FMCs displaying the greatest AOC. Contemporary dental school teaching should help support students in this important aspect of their clinical training.