The effect of base materials with different elastic moduli on the fracture loads of machinable ceramic inlays.

This study investigated the effect of two base materials with different elastic moduli (F2000 and Vitrebond) on the fracture load of machinable ceramic inlays. Standardized MOD cavities were prepared in 18 human maxillary first or second premolars. The teeth were randomly assigned to three groups of six premolars each; Group 1 (control: no base); Group 2 (base with a polyacid-modified resin composite: F2000); Group 3 (base with a resin-modified glass-ionomer cement: Vitrebond). The inlays were fabricated from Vitablocs Mark II using a Cerec II machine. After the inlays were cemented with Tetric Ceram and the Syntac adhesive system, using the Ultrasonic Insertion Technique (USI), they were stored in distilled water at 37 degrees C for 24 hours prior to fracture testing in a universal testing machine using a crosshead speed of 0.5 mm/minute. The static transverse elastic moduli of base materials were measured using a three-point bending test. The mean fracture loads and standard deviations of the Cerec inlays in Groups 1, 2 and 3 were 1.15 +/- 0.39 KN, 1.13 +/- 0.36 KN and 0.58 +/- 0.11 KN, respectively. Statistical analysis showed that the mean fracture load of Group 3 was significantly lower than that of Groups 1 and 2 (p < .05). There was no significant difference in fracture load between Groups 1 and 2. The means and standard deviations of the elastic moduli of F2000 and Vitrebond were 15.63 +/- 0.32 and 2.16 +/- 0.55 GPa, respectively. The results indicated that the fracture load increased significantly as the elastic modulus of a base material increased.