Surface roughness resulting from wear of lithia-disilicate-based posterior crowns

The objective of this study was to determine the surface roughness that occurred as a result of wear of all-ceramic crowns after 2 years of intraoral service. The ceramic material used in this study was a lithia-disilicate-based all-ceramic core ceramic and a glass-phase veneer ceramic. Posterior bilayer crowns were made for 30 subjects, who were recalled annually. At each recall time, the quality of crowns and adjacent gingival tissues were examined for acceptability, and impressions were made for replica models. The occlusal contacts of each ceramic crown were identified and surface roughness (R_a) measurement was performed on the replica model using a contact profilometer. Mean surface roughness values were analyzed using a repeated measure ANOVA. The wear patterns of contact surfaces were also characterized using a scanning electron microscope. From 30 ceramic crowns, 12 premolars and 13 molars were used for surface roughness measurements. For molar crowns, the surface roughness (R_a) at baseline was 1.76±0.43μm and the roughness significantly increased after 1 year and 2 years (p<0.05). For premolar crowns, the increase in roughness values was significantly different only after 2 years from 1.49±0.22 to 1.9±0.44μm (p<0.05). Roughening of ceramic surfaces was observed over the entire occlusal area, especially in the contact zones. Loss of superficial ceramic material as a result of microfracture was the reason for surface roughening. In conclusion, the surface roughness of ceramic crowns was significantly increased after 2 years. The increase in surface roughness indicated the degradation of the ceramic crown surfaces over time that resulted from the wear process.