Failure load effect of molar axial wall height with CAD/CAM ceramic crowns with moderate occlusal convergence

To evaluate the significance of axial wall height (AWH) in molar fracture resistance involving CAD/CAM adhesively bonded, all-ceramic full coverage restorations on preparations with moderate total occlusal convergence (TOC) (16°).

60 newly extracted maxillary third molars were divided into 5 groups (n = 12). Specimens were prepared for full-coverage, all ceramic restorations with occlusal cervical AWHs of 4, 3, 2, 1 as well as a flat preparation (0 mm AWH) with all preparations with AWH containing a moderate 16° TOC. Scanned preparations were fitted with a lithium disilicate restoration with a self-adhesive resin luting agent after intaglio surface preparation with hydrofluoric acid and silanation. Specimens were stored at 37°C/98% humidity for 24 hours and tested to failure at a 45° angle applied to the palatal cusp on a universal testing machine. Mean results were analyzed using ANOVA/Tukey's (P = .05).

Preparations containing 2, 3, and 4 millimeters of AWH demonstrated similar and higher resistance to fracture than the 1 and zero millimeter AWH groups.

Under the conditions of this study, results suggest that adhesive CAD/CAM technology may compensate for reduced axial wall height. However, more definitive results depend on fatigue testing.

These in vitro results suggest that adhesive CAD/CAM technology may compensate for less than optimal AWH.