Crown Thickness and Debonding of CAD/CAM-Produced Composite Resin Premolar Crowns

Objectives: Computer-aided design and manufacturing (CAD/CAM)-produced composite resin (CR) crowns are used in daily clinical practice, particularly in Japan due to the medical insurance system. Some reports indicated loss of retention (debonding) of the CR crown in a short time after placement. However, the risk factors are unknown. The purpose of this study was to investigate the relationship between the CR crown thickness and the crown debonding.
Methods: CR crowns on premolars placed with adhesive resin cement in the Department of Fixed Prosthodontics at Tohoku University Hospital from April 2014 to July 2017 were investigated, and 32 crowns with available Standard Triangulated Language (STL) data were used. Crown thickness was measured for center of occlusal surface and four marginal areas (buccal, lingual, medial, distal) using a three-dimensional viewer (3Shape 3D Viewer, 3Shape AS). The thickness of the margin was taken as the average value at four marginal areas. Measured values were analyzed statistically using logistic regression analysis to estimate the odds ratios (ORs) and 95% confidence interval (CI) for the association between the crown thickness and the crown debonding.
Results: The maximum/minimum (median) measured values for the 32 CR crowns were 2.42/0.56 mm (1.11) for center of occlusal surface and 1.14/0.36 mm (0.78) for thickness of the margin. From the value of crown thickness, there was a tendency to be less than the amount of recommended preparation for abutment teeth. As results of logistic regression analysis, the center of occlusal surface and thickness of the margin were not significantly different with regard to the CR crown debonding.
Conclusions: It was suggested that the crown thickness would not be a risk factor for the CR crown debonding. To investigate the cause of the CR crown debonding, further studies are necessary to evaluate the effects of crown thickness and abutment tooth form.