Internal Adaptation and Margin Fit of Rapid-sintered Full-contour Zirconia Crowns

Objectives: The purpose of this in vitro study was to evaluate the margin fit and internal adaptation of full-contour zirconia crowns following a significantly shorter sintering cycle using an induction furnace (SpeedFire/Dentsply Sirona)
Methods: Three groups of crowns were fabricated from a single CEREC Omnicam (Dentsply Sirona) digital impression. Two of the groups were full contour zirconia crowns (CEREC Zirconia/Dentsply Sirona) using two fabrication techniques: dry-milled with carbide burs and wet-ground with diamonds. The zirconia crowns were subjected to a 15 minute sintering process in an induction oven. The third group was full contour nano-ceramic (Lava Ultimate/3M) crowns wet-ground with diamonds as a control. Margin fit and internal adaptation were evaluated using a replica/sectioning technique . Three buccolingual sections of each crown were evaluated by measuring five locations at 112X magnification and using a 3-dimensional measurement program (Image Pro Plus/Media Cybernetics) to record the internal adaptation and margin fit.
Results: One-way ANOVA and a boxplot revealed no significant differences in margin fit or internal adaptation between all three groups of crowns.



Conclusions: Both dry-milled and wet-ground full-contour zirconia crowns using a rapid sintering protocol had a margin fit and internal adaptation equal to nano-ceramic full-contour crowns. The heating and cooling parameters of the shortened sintering cycle did not affect the fit of the zirconia crowns. The marginal gaps and internal adaptation for all materials tested were clinically acceptable.