Influence of Margin Designs on Crack Initiation of High Translucency Monolithic Zirconia Crowns.

PURPOSE

Zirconia crowns often crack at the margin. This study determined the loads and the times at which cracks are initiated in high-translucency monolithic zirconia crowns with different margin designs.

MATERIALS AND METHODS

A total of 90 crowns were fabricated from Zirconia blanks. The fabricated crowns had different margin thicknesses (light-chamfer, C and heavy-chamfer, C ) and collar heights (no-collar, N ; low-collar, L ; high-collar, H ). They were grouped as C N , C L , C H , C N , C L , and C H (15 crowns/group). The crowns were seated on a metal model and loaded vertically through round end punch (Φ = 10 mm) at 0.2 mm/min crosshead speed until cracks began to be seen. Videos of the crack initiation were recorded at the rate of 50 frames/second. Load-initiated cracks and durability time were compared for significant differences using analysis of variance.

RESULTS

The mean ± standard deviation values of load (N) and time (s) taken to initiate cracks were 3190 ±775, 212 ±47 for C N ; 2754 ±1109, 180 ±42 for C L ; 2887±832, 191±27 for C H ; 4082 ±896, 241 ±36 for C N ; 4180 ±1029, 220 ±28 for C L ; 4119 ±1124, 222 ±39 for C H . This indicates that the thickness of the margin has a significant influence on load-withstanding crack initiation capacity and durability time (p < 0.05). No significant impact of collar height was observed on either load-withstanding capacity or durability time (p > 0.05). No interaction was observed among these factors.

CONCLUSION

Heavy chamfer margin provided a stronger zirconia crown than the light chamfer margin, but both of them were capable of withstanding crack-initiated load higher than the theoretical maximum masticatory force. The presence or absence of a collar did not have any impact on the crack initiation. Fabrication of zirconia crowns with either a heavy or light chamfer margin and with or without the presence of a collar should be generated by considering the relevant emergence profile.