A ROLLING-BALL DEVICE FOR PRODUCING SURFACE FATIGUE AND ITS APPLICATION TO DENTAL MATERIALS

A new method of producing and evaluating surface fatigue using a rolli ng-ball device has been developed. The method involves constraining a rolling ruby ball between the ''v'' groove of a rotor and the test spe cimen. The ball applies a compressive stress to the surface of the tes t material whilst it rolls in a circular pattern across the specimen s urface. The fatigue life is defined as the time taken for surface degr adation to begin to occur. The method is simple and reproducible and a llows fatigue data to be gathered using a relatively small number of s pecimens. A series of model dental composites having varying filler fr actions (23.7-66.4 vol%) were used to assess the potential of the meth od. The pattern of material loss as well as scanning electron microsco py examination of the damaged surfaces of test specimens confirmed tha t a fatigue mechanism was responsible for material loss. The fatigue l ife varied markedly with filler volume fraction being optimized at val ues in the range 30-50 vol%. Lower and higher volume fractions reduced the fatigue life. Filler silanation significantly improves fatigue li fe. The results suggest that the rolling ball device will prove useful in comparing the properties of different materials and in the develop ment of improved products.