Internal Adaptation and Fit of Auxilary Retentive Features for Chairside CAD-CAM Zirconia Crowns

Abstract

Abstract:

Background: Restoration resistance and retention are crucial for the long-term success of restorations. The tooth preparation geometry is a significant factor in the creation of mechanical retention. A clinical benefit of zirconia restorations is the physical strength of zirconia restorations provides the ability to cement them rather than adhesively bond them to the tooth. Zirconia restorations are fabricated with a computer assisted design/computer assisted machining process (CAD/CAM) that may influence the intimate adaptation of the restoration to geometric aspects of a preparation affecting the restoration retention.

Objective: The margin fit and internal adaptation will be measured for zirconia crowns with tooth preparations containing different auxiliary retentive features. The monolithic zirconia crowns will be fabricated with a chairside CAD/CAM workflow.

Materials and Methods: A master zirconia crown was prepared on a typodont tooth and scanned to print four different sets of models. A total of 48 zirconia crowns were milled and divided into four groups (n = 12) based on the auxilary retentive features: control, small buccal groove, large buccal groove, and mesial proximal box. The internal fit was evaluated using the polyvinyl siloxane (PVS) replica method, sectioned horizontally to assess the internal fit adaptation of auxilary retentive features and vertically to evaluate marginal adaptation. The cement space was then measured under a microscope from the marginal and auxiliary retentive features.

Results: Significant differences were found among groups for margin (p = .003), axial (p < .001), HorAxial (p = .009), and RetFeature (p < .001) adaptation. The box showed significantly higher margin and axial adaptation but poorer HorAxial and RetFeature adaptation values compared to other groups. No significant difference was observed for occlusal adaptation (p = .112)

Conclusion: There is a statistical difference in the margin fit and axial fit of the crowns. However, there is no clinical significance in the difference in fit since all margins are less than 120 µm. The box design group showed that it does not fit well in the retentive feature compared to other groups.