Effect of the applied load on surface contact fatigue of dental filling materials

Objective. The purpose of this study was to investigate the effect of the applied load in a rolling-ball device on the surface contact fatigue of two dental filling materials: a microfilled composite (FA) and a glass ionomer (GFII). Methods. Disk specimens 10 mm diameter by 1.5 mm thick were set into cavities cut in plates of PMMA. After setting, the specimens were ground and polished using wet-carborundum paper followed by 1 μm alumina and then stored for 24 h in water at 23 °C. The surface fatigue test was carried out using loads ranging from 100 to 500 gf through a ruby ball 2 mm diameter using a rolling-ball device. The ball was set to rotate at 720 rpm and a surface profile was determined on impressions recorded at regular intervals. Fatigue life was defined as the number of cycles to produce a track 5 μm deep and was determined by interpolation. Data were statistically analyzed by ANOVA and t-tests at a significance level of 0.05. Results. At loads ranging from 200 to 500 gf the fatigue life was 0.7–10.6×105 cycles for FA, and 0.7–4.8×103 cycles for GFII. For both materials the fatigue life was reduced significantly by increasing the test load (p<0.05). The surface contact fatigue life for FA was at least 100 times greater than that for GFII at all loads. Significance. The rolling ball device was confirmed as a simple and meaningful device for the study of surface contact fatigue. A microfilled composite is very much more resistant to contact fatigue than a glass ionomer.