Abstract
Purpose: To evaluate and compare marginal adaptation and fracture resistance of vonlays restoring premolars of three different ceramics.
Materials and methods:
30 3D printed resin dies of natural premolar no. 14 prepared for vonlay restoration. Three groups (n = 10) of vonlays were categorized according to ceramic material. Group I: Zirconia. Group II: Glass ceramic. Group III: Nanohybrid ceramic. Vertical marginal adaptation was measured on the natural premolar tooth without cementation using a digital microscope (90X). Then, it was measured after adhesion of vonlays over their respective dies. Vonlays were subjected to thermomechanical fatigue for aging. Universal testing machine used for measurement of the fracture resistance. Failure mode was examined visually and microscopically. Statistical analysis was done using One- way ANOVA, LSD, and Fisher's Exact test.

Results: No statistical significance recorded in the marginal gaps of the three groups. Notable variation in fracture resistance recorded among the three groups: zirconia had the highest mean value, followed by glass ceramics, then nanohybrid ceramic. Visual inspection of the failed sections revealed that, there were 80% class II fracture mode in group I, 70% class IV in group II, and 80% class IV in group III. Stereomicroscope images of all specimens showed mixed adhesive cohesive fracture mode.
Conclusion: The three tested materials offered clinically acceptable marginal gaps. Fracture resistance of vonlays shown to be significantly variant between tested materials, it was exceeded the limit of chewing force in the premolars. Vonlays offers a reliable and cautious restoration in the premolars.