WEAR OF HUMAN ENAMEL - A QUANTITATIVE IN-VITRO ASSESSMENT

Many factors influence the extent and rate at which enamel wears. Clin ical studies in humans are limited by difficulties in the accurate qua ntification of intra-oral wear and by a lack of control over the oral environment. The purpose of this study was to determine the wear chara cteristics of human dental enamel under controlled experimental condit ions. An electro-mechanical tooth wear machine, in which opposing enam el surfaces of sectioned, extracted teeth were worn under various cond itions, was used to simulate tooth grinding or bruxism. Enamel surface wear was quantified by weight to an accuracy of 0.1 mg, with water up take and loss controlled. The variables considered included the struct ure and hardness of enamel, facet area, duration of tooth contact, rel ative speed of opposing surfaces, temperature, load, pH, and the natur e of the lubricant. Enamel wear under non-lubricated conditions increa sed with increasing load over the range of 1.7 to 16.2 kg. The additio n of a liquid lubricant (pH = 7) reduced enamel wear up to 6.7 kg, but when the load increased above this threshold, the rate of wear increa sed dramatically. With the viscosity of the lubricant constant and pH = 3, the rate of wear was further reduced to less than 10% of the non- lubricated rate at 9.95 kg, after which the rate again increased subst antially. Under more extreme conditions (pH = 1.2, simulating gastric acids), the wear was excessive under all experimental loads. When sali va was used as a lubricant, the amount of wear was relatively low at 9 .95 kg, but rapid wear occurred at 14.2 kg and above. These results in dicate that under non-lubricated conditions, enamel wear remains low a t high loads due to the dry lubricating capabilities of fine enamel po wder. Under lubricated conditions, low loads with an acidic lubricant lead to little enamel wear, whereas very low pH results in a high rate of wear under all loads.