Convergence Angles of Clinical Tooth Preparations for Metal Ceramic Restorations Among Dental Students and General Practitioners

Numerous studies showed that the convergence angle (CA) of prepared teeth for fixed prosthodontics in the clinical practice is greater than the recommended values.
This cross-sectional study aimed to compare the total occlusal convergence (TOC) angles of metal ceramic fixed prosthodontics among dental students [final-year undergraduate (UG) and Master Prosthodontics (MS) students] and general practitioners (GP) in their private clinics with the recommended value (≤ 12 degrees).
The buccolingual (BL) and mesiodistal (MD) TOC of 114, 90, and 111 stone dies referred to UG, MS, and GP, respectively, were measured. These dies included incisors, premolars, and molars. One sample Wilcoxon signed rank test, Mann-Whitney U test, Kruskal-Wallis, and Fisher exact test were used for statistical analysis.
Mean values of TOC for UG were 27.8 degrees BL and 20.9 degrees MD, whereas they were 30.6 degrees BL and 18.2 degrees MD for MS. GP had TOC of 35.5 degrees BL and 24 degrees MD. GP had significantly higher TOC values than the other groups (0.001 > P value ≤ 0.007). In each group, TOC did not differ when calculated for partial fixed prosthodontic and single crown abutments (0.117 ≤ P value ≤ 0.797). Molars in general had the highest TOC values. Only 0.9%, 3.3%, and 0.9% of UG, MS, and GP, respectively, respected the TOC ≤ 12 degrees.
In all the groups, tooth preparations were inconsistent with the recommended TOC values, even among specialists in fixed prosthodontics. These results support the existing literature that the recommended values were rarely achieved and may require reconsideration.
Clinical Significance: Clinically, the CA values of prepared teeth for fixed prosthodontics exceed the recommended values in most cases, not only among general practitioners, but also among students in academic institutes. Thus, the effects of teeth preparations with CA greater than the recommended values on the longevity of the prosthodontics should be further investigated.