Objectives:
To evaluate the microtensile bond strength (µTBS) and failure mode of Cerec CAD/CAM all-ceramic crowns bonded to dentine using different surface treatments and luting cement.
Methods:
Thirty-six human premolars were prepared for all-ceramic crowns. Occlusal dentine was cut flat and polished using 600 grit carbide paper. Thirty-six all-ceramic crowns were fabricated using Cerec ceramic blocs and CAD-CAM system (Sirona GmbH, Germany). The fitting surfaces were treated with either (1) 9% hydrofluoric acid etchant (N=18) or (2) 9 % hydrofluoric acid followed by silane coupling agent (N=18). Each group was subdivided into a group of six for cementation with three different types of cement (i) Calibra, (Dentsply/Caulk, USA) (ii) RelyX U200 (3M/ ESPE, USA) (iii) Fuji Plus (GC, Japan) respectively. After 24h of water storage at 37°C, all specimens were thermocycled 500 times in a bath of distilled water at 5 to 55°C. Each crown was then sectioned to produce two 1 mm2 microbars. The microbars were subjected to a microtensile load testing using a universal testing machine (Shimadzu, Japan) at crosshead speed 1mm/min. Debonded specimens were examined by stereomicroscope and SEM to determine the mode of failure. The Kruskal-Wallis test was used to detect overall significance, followed by Mann-Whitney U tests for multiple pairwise comparisons (P=.05).
Result:
The significant difference in µTBS was found within HF groups (p= 0.04). Mann-Whitney U test showed significant differences between RelyX U200 and both Calibra and Fuji Plus (p=0.003, p=0.006 respectively). In the HF+ silane groups, there was no significant difference in µTBS between groups (p=0.903). More adhesive failure at the ceramic-cement interface and no cohesive failure were observed in all groups. Conclusion: Within the limitation of this study, Calibra and Fuji Plus produced significantly higher microtensile bond strength compared to RelyX U200 when Cerec all-ceramic crowns were treated with HF acid. Calibra luting cement produced significantly higher microtensile bond strength when Cerec all-ceramic crowns were etched with HF acid than using HF acid +SA. All specimens produced adhesive failure, mostly at ceramic-cement interfaces.
