Frictional effects between natural teeth in an artificial mouth

A method for measuring frictional forces on enamel of natural teeth and restorative materials was developed using the Artificial Oral Environment. Enamel/enamel systems were tested using different oral fluids in a minienvironmental chamber capable of introducing biologic fluids between the occluding surfaces. Matched, extracted opposing human premolars mounted in physiologic occlusion under an occlusal load of 3 pounds were bruxed at approximate masticatory velocities. A load cell measured the resulting horizontal forces and an X-Y record was attained. 31 independent measurements of friction in both buccal and lingual directions were performed with the teeth dry, and with human saliva, Xerolube, and distilled water intervening. It was found that typical values for enamel/enamel coefficients of friction, μ, were in the range of 0.1-0.42. μ was independent of different fluids within any one enamel/enamel couple (coefficient of variation was typically 10%). However, the coefficient of friction of the enamel pair was highly dependent on surface texture. Roughening virgin enamel led to a 3 fold increase in μ. Conversely surfactants present in mineral oil reduced the friction of roughened enamel by 3 fold. Where the wear process is by abrasion it is likely that the reduction of the tangential forces due to friction could lead to reduced loss of contour. It is likely that finishing procedures in dentistry are important in this process. Finally, the production of low friction restorative materials are clearly indicated as a future development.