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.