Premolar Axial Wall Height Effect on CADCAM Crown Retention

Objectives: Objective: To evaluate the significance of bicuspid axial wall height with retention of adhesively-luted, all-ceramic CAD/CAM crowns.
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 10-degree taper 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 and tested to failure after 24 hours 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 post hoc test (p=0.05).
Results: Results: Results are listed in the Table.
Crowns with axial walls of 1 – 3mm in height failed at a significantly greater stress than preparations with no axial wall. There was no failure stress difference between preparations with 1 – 3 mm axial wall height.
Conclusions: Conclusions: Under the conditions of this study, bicuspids restored with adhesively-luted, CAD/CAM fabricated, IPS e.max CAD crowns with axial wall heights of 1,2, and 3mm demonstrated similar failure resistance. This study provides some evidence that adhesion may compensate for less axial wall height in all-ceramic premolar preparations with a 10 degree taper.