Fracture force of CAD/CAM resin composite crowns after in vitro aging

Objectives The aim of this in vitro study was to investigate the influence of material, preparation, and pre-treatment on the aging and fracture force of CAD/CAM resin composite molar crowns. Materials and methods CAD/CAM molar crowns (n = 80) were milled from four resin composites (Block HC, Shofu; Lava Ultimate, 3 M; Grandio Blocs, Voco; and Tetric CAD, Ivoclar Vivadent, with/without sandblasting). Extracted human teeth were prepared with optimal preparation (height 6-8 mm, angle 6-8 degrees) or worst-case preparation (height 3.5-4 mm, angle 10-15 degrees). Both groups were prepared with a 1-mm deep cervical circular shoulder. Crowns were adhesively bonded after corresponding tooth treatment required for the individual adhesive systems (Table 1). Specimens were aged for 90 days in water storage (37 degrees C) and subsequently subjected to thermal cycling and mechanical loading (TCML 3000 x 5 degrees C/3000 x 55 degrees C, 2 min each cycle, H20 distilled; 1.2 x 10(6) cycles a 50 N, 1.6 Hz). De-bonding and fracture force was determined. Statistics: one-way-ANOVA; post hoc Bonferroni, alpha = 0.05. Results Four crowns of Lava Ultimate with worst-case preparation de-bonded during TCML. Individual crowns without sandblasting treatment (3x Tetric CAD with optimal preparation; 1x Tetric CAD with worst-case preparation) de-bonded during water storage. One crown of Grandio Blocs with optimal preparation showed a small chipping during TCML. All other crowns survived TCML and water storage without failure. Fracture forces differed between 1272 +/- 211 N (Lava Ultimate) and 3061 +/- 521 N (Tetric CAD). All Grandio Blocs and Tetric CAD crowns revealed significantly (p <= 0.023) higher fracture forces than Block HC or Lava Ultimate crowns. No significantly different (p > 0.05) fracture forces were found between optimal or worst-case preparation/fit groups. Conclusions De-bonding during water storage and TCML was dependent on material and crown pre-treatment. Therefore, surface roughening seems strongly required. Fracture forces were not influenced by preparation but by the type of material.