Objective: To examine the effect of increasing cement thickness for conventional and adhesive cementation on the fracture load of two CAD/CAM crown materials.
Methods: Eight groups were examined: two materials (e.maxCAD Li2O·SiO2, Ivoclar Vivadent or MarkII, Vident), two cementation types (adhesive or conventional) and 2 thicknesses defined by spacer layers (0 or 6 layers approximately 50 and 150 mm). A standardized molar crown was designed using the Cerec InLab (Sirona). Eighty crowns (10/group) were milled in each material using the MCXL milling-unit. The Li2O·SiO2 specimens were fired and glazed in one firing according to the manufacturer's instructions in a P500 Programat oven (Ivoclar Vivadent Inc.). The feldspathic crowns were glazed according manufacturer's instructions. The internal surfaces were then layered with die spacer to provide 2 ranges of cement thickness. The internal surfaces were filled with composite (Tetric EvoCeram, Ivoclar Vivadent) and cured. The crowns were cemented to composite preparations using either conventional cement (Fleck's zinc phosphate, Mizzy) or an adhesive cement (Multilink Automix, Ivoclar Vivadent, Inc.) and stored in 37°C water for 1 week. The specimens were loaded to failure using a 15-mm diameter steel ball at a crosshead speed of 0.5 mm/min with an Instron Universal Testing machine.
Results:
Failure Load (N) | ||||
Li2O•SiO2 | Feldspathic | |||
Cementation | Cementation | |||
# of layers | Adhesive | Conventional | Adhesive | Conventional |
0 | 2,321±422 | 2,020±240 | 1,091±274 | 675±180 |
6 | 2,296±167 | 1914±436 | 1,146±207 | 622±195 |
Conclusion: Within this study, crown material statistically affected the failure load while cementation type had a very strong effect in all cases. The increase in cement thickness did not have a statistical affect.