Friction and wear behaviors of dental ceramics against natural tooth enamel

The friction and wear behaviors of dental ceramics against the natural tooth enamel were investigated. In this study three dental ceramics, namely zirconia with both polished and rough surfaces, hot-forged lithium disilicate glass ceramics and silicates based veneer porcelain were involved with two metallic materials, gold–palladium alloy and Nickel–chromium alloy, as references. The tribological tests were carried out under artificial saliva lubrication condition by using freshly extracted natural teeth and samples with controlled surface roughness. The frictional coefficients versus reciprocating cycles were recorded. Scanning Electron Microscopy was used to observe the topography of worn teeth enamel surfaces and antagonists. The frictional coefficient of enamel against gold palladium alloy or Nickel–chromium alloy was the smallest. The frictional coefficient of enamel against polished zirconia or porcelain was between that of metal and glass-ceramic. Upon surface polishing, frictional coefficient between zirconia and enamel was radically decreased. Furrows and granular debris were observed on the worn surfaces of enamel while sliding against the rough zirconia or glass ceramic, indicating a abrasive wear mechanism. While chipping flake and pit-like structure after stripping and crack were observed on the enamel surface while sliding against polished zirconia or Nickel–chromium alloy, indicating a type of fatigue wear. It appeared that the friction and wear performances of zirconia could be improved significantly by adequate surface polishing. This observation indicated that attention must be paid to carefully design proper occlusal surface contours and correctly choose dental materials in clinical practice.