Premolar Axial Wall Height Effect on CADCAM Crown Retention

Objectives: Objective: To evaluate bicuspid axial wall height effect on retention of adhesively-luted, all-ceramic CADCAM crowns with a 15-degree total occlusal convergence (TOC).
Methods: Methods: Recently-extracted premolars were randomly divided into 4 groups (n=12) with all-ceramic crown preparations accomplished using a high speed handpiece inserted into a milling device. Preparations contained a 15-degree TOC with each group consisting of axial wall heights of 0,1,2, and 3 millimeters. Completed preparation surface area was determined using a digital measuring microscope (Hirox). Scanned preparations (CEREC) were fitted with e.max CAD crowns and luted with RelyX Unicem after HF acid etching and silanation. All manufacturer recommendations were followed. Specimens were stored at 37C/98% humidity for 24hours and tested to failure at a 45-degree angle on a universal testing machine. Failure load was converted in MPa using the available bonding surface area with mean data analyzed using ANOVA/Tukey’s (p=0.05).
Results: Results: Results are listed in the Table.
The 3mm and 2mm preparation height samples displayed significantly stronger failure stress than the 0- and 1 mm samples. There was no difference between the 2mm and 3mm groups.

Conclusions: Conclusions: Under this study’s conditions, bicuspids restored with adhesively-luted, CADCAM eMax CAD crowns with a 15-degree TOC displayed significantly greater failure stress with 2- and 3mm axial than preparations with 0- and 1mm wall height. Evidence is presented that adhesion may compensate for less axial wall height in all-ceramic premolar preparations with a 15 degree taper.