What is the influence of the operator on the long-term survival of posterior partial lithium disilicate restorations in an undergraduate setting?

Objective: To evaluate the influence of the (undergraduate) operator on the survival and success rate of posterior partial lithium disilicate restorations.

Materials And Methods: Patients who received at least one posterior partial lithium disilicate restoration between 2009 and 2019 by undergraduates at the Center for Dentistry and Oral Hygiene in Groningen were included. Operator- (academic year (4th, 5th, 6th year)), patient- (presence of a nightguard, caries risk, age), tooth- (endodontic status, inlay/onlay, position of the restoration outline) and material-related factors (cement type, rubber dam use, Immediate Dentin Sealing) on the survival and success rate were analyzed using multilevel Cox regression (p < 0.05).

Results: In total, 637 restorations were placed in 373 patients. On the level of survival, 100 restorations failed during the observation period (median follow-up: 70 months, interquartile range 48-99 months): 26 extractions, 61 restoration replacements and 13 biological complications. The overall 5- and 10-year cumulative survival rates were 89.1 % (95 % CI: 86.5 %-91.7 %) and 77.6 % (95 % CI: 73.1 % - 82.5 %) respectively. Multilevel Cox regression showed a medium to high caries risk (HR: 1.57; 95 % CI: 1.21 - 2.04) and an approximal outline located within 3 mm of the bone (HR: 1.52; 95 % CI: 1.05 - 2.22) as significant risk factors for failure. The academic year had no statistically significant effect.

Conclusion: The 10-year survival and success of lithium disilicate posterior partial indirect restorations placed by undergraduates was not significantly affected by the academic year of the operator.

Clinical Significance: When a clear treatment protocol is followed, patient- and tooth-related factors rather than academic year of the operator appear to have a significant influence on the quality of posterior partial lithium disilicate restorations.