Objectives:
The aim of this study was to compare the in vitro performance and marginal adaptation of additively fabricated resin-based composite molar crowns.

Materials and methods:
Molar crowns (n = 8 per group, 9 groups) were 3D-printed from materials for temporary or permanent application. Milled resin based composite crowns were used as a reference. All crowns were adhesively bonded on prepared extracted human molars. Thermal cycling and mechanical loading (TCML) were performed and fracture force was determined. Marginal adaptation was evaluated before and after TCML based on images of the cement gap. Statistics: one-way ANOVA, Bonferroni post-hoc-test (α = 0.05).

Results:
All crowns survived TCML without failures. Fracture forces of the additively manufactured crowns varied between 1707.9 ± 470.2 N and 2839.6 ± 682.1 N (Reference: 3121.8 ± 557.1 N). Statistical analyses revealed significant (p ≤ 0.004) individual differences. Fracture pattern was characterized as a fracture of the crown, partially combined with a fracture of the tooth. No visible differences were found in the assessment of margin quality before and after chewing simulation. Signs of wear and scratches were visible at the contact points, but the transitions between the contact points and the crown surface showed no cracks or defects. The perfect margin of the additively manufactured crowns varied between 97.8 % and 100.0 %, before TCML, and between 92.3 % and 99.0 % after TCML.

Conclusion:
3D-printed molar crowns provided sufficient to good in vitro performance and fracture force. Good marginal adaptation was not negatively influenced by in vitro aging.

Clinical relevance:
Additively manufactured resin molar crowns on human teeth show adequate fracture resistance, moderate wear, and acceptable marginal adaptation, indicating potential suitability for posterior restorations.