Effect and correlation of testing load and specimen’s thickness on the hardness and percent depth of cure of condensable composite resins

Background : Dental condensable composite resins were used as a substitute for dental amalgam to restore posterior teeth. They were be condensed as dental amalgam, which made it easier to produce an accurate proximal teeth contact. Objectives: The aim of this study was to measure the top and bottom hardness of two condensable composites at different thicknesses (2,3,4 and 5 mm) at different loads (25,50 and 100 gf). Percent depth of cure was calculated for both materials at the different thicknesses. The correlation between the hardness and percent depth of cure was calculated. Materials and methods : The materials used were Glacier and SureFil condensable composite resins. 120 specimens were prepared from both composite resins, 60 specimens each using transparent Perspex molds of 4mm diameter and thicknesses of 2,3,4,5 mm. Specimens of each composite resin were divided into 4 groups corresponding to the different thicknesses, 15 specimens for each thickness. Specimens for each thickness were further divided into 3 subgroups, 5 specimens for each load applied during hardness testing (25, 50 and 100gf). The hardness was measured using a universal micro hardness testing machine for the top and bottom surfaces of each specimen. Percent depth of cure was calculated by dividing the bottom hardness value by the top hardness value and multiplied by 100. Also, the correlation between the hardness and percent depth of cure was calculated . Results : The results indicated that, the top hardness values were greater than that of the bottom hardness values for both composite resins. Glacier composite showed that, the hardness was increased by increasing the testing loads and decreased by increasing the thickness, except at 3 mm thickness of Glacier, which showed higher hardness than 2 mm thickness. Also, SureFil composite resin showed increased hardness values by increasing the testing loads and decreased by increasing the thickness. The hardness of 3mm thickness was greater than that of 2mm thickness. The percent depth of cure in 2mm and 3mm thicknesses were more than 80%, while the other thicknesses showed percent depth of cure less than 80%. Both materials showed high positive correlation between the hardness and percent depth of cure . Conclusions : The top hardness was greater than that of the bottom hardness. The hardness of 3mm thickness was greater than that of 2mm thickness. The hardness was increased by increasing the testing loads and decreased by increasing the thickness. The percent depth of cure was decreased by increasing thickness. There was high positive correlation between the hardness and percent depth of cure .