Abstract:
Abstract: The objective of this study is to investigate the influence of veneering technique
(hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based
hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled.
Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique
(LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group
acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator.
Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature
fluctuation between 5 and 55 C. Crowns were then subjected to static load a to fracture test. Data were
statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were
observed under scanning electron microscopy to view fractured surfaces. Study results indicate
that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate.
Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at
the baseline and after fatigue (p 0.05). However, fatigue did not cause a statistically significant
reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD
crowns only and the fracture path was dierent in both LD and HL groups. According to the results,
it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly
higher fracture resistance, and better withstand clinical masticatory loads in the posterior region
compared to the hand-layered technique. Also, fatigue application and artificial aging caused no
significant strength reduction in both techniques. Clinical significance: Dierent veneering techniques
and materials (hand-layering or milling) act dierently to clinical forces and environment and may be
prone to early chipping d