Abstract
Smoothness of discs of human dental enamel brushed with dentifrice abrasives was estimated from transparent replicas in an instrument comprising a laser beam passing through a replica, an opaque disc to block the direct beam, and a converging lens to focus the diffused light on a photometer. Diffused light was read as millivolts. The instrument was calibrated against replicas made from surface finish standards. The logarithm of nanometer finishes was proportional to the probability function (probit) of the percentage of the maximum light diffused. When seven abrasives were compared in a randomized blocks design, calcium carbonate, plastic spheres, CaHPO 4·2H 2O and a mixture of the latter with Al(OH) 3 all left the enamel surface indistinguishable from a water brushing, whereas calcium pyrophosphate, Al(OH) 3 and insoluble metaphosphate produced significantly greater degrees of roughness ( p < 0.05). The mean values for the abrasives were 34, 30, 29, 28, 44, 41 and 47 nanometers respectively. The merits of the method are speed, reproducibility and objectivity.
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