Influence of Cutting Speed and Cutting Incidence on Microtensile Test

Objective: This study evaluated the effect of cutting incidence and cutting speed on resin cement/feldspathic ceramic bonding during the preparation of the specimens for microtensile bond strength test. Methods: Thirty two blocks (6.4 x 6.4 x 4.8 mm) of feldspathic ceramic (Vita VM7) were produced. The ceramic surfaces were etched with 10% hydrofluoridric acid gel for 60 s and silanized. Each ceramic block was placed in a silicone mold with the treated surface exposed. The dual-cured resin cement (Variolink II) was injected into the mold over the treated surface and polymerized. The resin cement-ceramic blocks were randomly divided into two conditions: a) cutting incidence – resin cement, ceramic and interface; b) cutting speed – 10000 rpm, 15000 rpm and 20000 rpm. The specimens were sectioned to achieve non-trimmed bar specimens (approximately 10 sticks/block). The microtensile bond strength test was performed in an universal testing machine (cross-head speed: 1 mm/min) and subsequently the mode of failures was examined using optical light microscope and SEM. Bond strength results were analyzed using two-way ANOVA and Tukey's test (á = 0.05). Results: The cutting incidence affected the bond strength significantly (p=0.0001) (interface > resin cement > ceramic). The cutting speed in the resin cement-ceramic block sectioned at 20000 rpm cutting speed (9.44 ± 2.89 MPa) showed lower bond strength than 15000 rpm (13.43 ± 4.97 MPa) and 10000 cutting speed (11.56 ± 4.33 MPa). All groups showed mainly mixed type of failures between the ceramic and the resin cement (75-100%). Conclusion: It can be concluded that the 20000 rpm speed presented the lowest bond strength values and the cutting incidence on the interface presented the highest bond strength values.