Axial Wall Height Effect on Adhesively Luted Ceramic Crown Failure

Objectives: Objectives: To analyze the significance of axial wall height in adhesively-luted CEREC e.Max CAD crown retention, and to compare failure load (N) results to calculated failure stress (MPa).
Methods: Methods: 60 recently-extracted maxillary third molars were randomly divided into 5 groups and prepared for ceramic crowns with axial wall heights of 0,1,2,3, and 4mm (n=12) all with a 15-degree total occlusal convergence (TOC). 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 24hrs and tested to failure at a 45-degree angle applied to the palatal cusp on a universal testing machine. Failure load was converted to MPa using the available bonding surface area with the mean data analyzed using ANOVA/Tukey’s (p=0.05).
Results: Results: Results are listed in the table. All groups displayed statistically similar failure stress (p=0.35), while the 2, 3,and 4mm axial height groups demonstrated significantly greater failure load (p<0.006).
Conclusions: Conclusions: Maxillary third molars restored with adhesively-luted e.max CAD crowns with 15 degree TOC demonstrated similar failure stress regardless of axial wall preparation height. The calculation of failure stress based on adhesive bonding surface area may be more discriminatory than simply recording load at failure.