Premolar Axial Wall Height Effect on CAD/CAM Crown Retention

Objective: To evaluate the significance of reduced axial wall height on retention of adhesively luted, all-ceramic, lithium disilicate premolar computer-Aided design/computeraided manufacturing (CAD/CAM) crowns based on preparations with a near ideal total occlusal convergence of 108. Methods: Forty-eight recently extracted premolars were randomly divided into four groups (n=12). Each group received all-ceramic CAD/ CAM crown preparations featuring axial wall heights of 0, 1, 2, and 3 mm, respectively, all with a 108 total occlusal convergence. Scanned preparations were fitted with lithium disilicate allceramic crowns that were luted with a selfetching resin cement. Specimens were tested to failure at a 458 angle to the tooth long axis with failure load converted to megapascals (MPa) based on the measured bonding surface area. Mean data were analyzed using analysis of variance/Tukey's post hoc test (a=0.05). Results: Lithium disilicate crowns adhesively luted on preparations with 0 axial wall height demonstrated significantly less failure resistance compared with the crowns luted on preparations with axial wall heights of 1 to 3 mm. There was no failure stress difference between preparations with 1 to 3 mm axial wall height. Conclusions: Under conditions of this study, adhesively luted lithium disilicate bicuspid crowns with a total occlusal convergence of 108 demonstrated similar failure resistance independent of axial wall height of 1 to 3 mm. This study provides some evidence that adhesion combined with an ideal total occlusal convergence may compensate for reduced axial wall height.