Four-year clinical evaluation of CAD/CAM indirect resin composite premolar crowns using 3D digital data: Discovering the causes of debonding

Purpose: To analyze the causes of debonding of computer-aided design/computer-aided manufacturing (CAD/CAM) indirect resin composite premolar crowns with a focus on the morphological factors of the crown and abutment teeth. Methods: The clinical courses of 109 CAD/CAM indirect resin composite crowns were observed, and the patients' background characteristics, crown locations, luting methods, types of abutments, distal-most/non-distal-most molars, and types of resin blocks were confirmed. To investigate the influence of the morphology of the crown and abutment teeth, the 1) vertical dimension of the abutment teeth, 2) taper, and 3) thickness of the crown occlusal surface during events were measured from the three-dimensional digital data. The Kaplan-Meier method and multivariable Cox proportional hazard model were used for the statistical analyses. The nonlinearity of the effect of each comparison factor was included in the model. Results: Complications included 21 debonding cases, two crown fractures, five root fractures, and two core debondings. The cumulative no-debonding and no-crown-fracture rate over 1423 days (3 years and 11 months) was 77.4%. The multivariable Cox regression analysis revealed that the abutment teeth type of tooth (first or second premolar) (P = 0.02) and luting materials (P < 0.01) significantly influenced the debonding frequency. All morphological factors (1-3) significantly influenced the debonding. The hazard ratios and nonlinear graph indicated that the crown thickness was less effective than the vertical dimension and taper. Conclusion: The combination analysis of clinical outcomes and 3D digital data revealed that preparation of the abutment is important for avoiding crown debonding.