[Effect of bleaching on the microhardness of tooth-colored restorative materials]

Bleaching agents not only affect the tooth structure, but also may later the properties of restorative materials. The aim of this in vitro study was to evaluate the effect of different bleaching regimens on the microhardness of four tooth-colored restorative materials. Eighty specimens of four restorative materials [Microhybrid resin composite [Z250 [3M, ESPE], nanohybrid composite Z350 [3M, ESPE], packable composite P60 [3M, ESPE], and resin modified glass ionomer Vitremer [3M, ESPE]] were fabricated and were polished after 24 h with Soflex discs [3M,ESPE]. Then the specimens were divided into two groups: In office bleach group, 40 specimens [10 of each restorative material] were bleached with hydrogen peroxide 37.5% for 30 min in two sessions with 7 days interval. In home bleaching group, 40 specimens were bleached with carbamid peroxide 22%, 6 h a day for 14 days. Vickers microhardness test were done before and after bleaching [baseline]. Finally data were evaluated using analysis of Variance. Two bleaching regimens were significantly decreased the microhardness values. In Z250 resin composite, the microhardness values before and after bleaching were 95.30 and 92.67 kg/mm[2], respectively. for office bleaching [P=0.011] and 95.38 and 92.39 kg/mm[2] for home bleaching [P<0.001]. In Z350 resin composite, the microhardness values before and after bleaching were 98.29 and 92.41 kg/mm[2], for office bleaching [P<0.001] and 97.35 and 93.44 kg/mm[2] for home bleaching [P<0.001] respectively. In P60 resin composite, the microhardness values before and after bleaching were 103.10 and 96.16 kg/mm[2], respectively. for office bleaching [P=0.045] and 102.61 and 98.16 kg/mm[2] for home bleaching [P=0.001]. In resin modified glass ionomer [Vitremer], the microhardness values before and after bleaching were 56.79 and 49.41 kg/mm[2], respectively. for office bleaching [P=0.004] and 54.17 and 46.50 kg/mm[2] for home bleaching [P<0.001]. There was no significant difference between two bleaching agents [P=0.365]. Dental bleaching agents decrease the microhardness of tooth-colored restorative materials

[Comparison of degree of conversion of packable and hybrid composites by fourier transform infrared spectroscopy]

Clinical performance of light cured resin composites is related to their degree of polymerization. The purpose of this study was to compare the degree of conversion of packable and hybrid composites by FTIR [Fourier Transform Infrared Spectroscopy]. In this experimental study, 40 composite disks were prepared in two groups from Z250 and P60 composites. Each group was divided into four subgroups [2mm thickness cured with QTH unit, 2mm thickness cured with LED unit, 5mm thickness cured with QTH unit, and 5mm thickness cured with LED unit]. Then samples were evaluated by FTIR to determine the degree of conversion [DC]. Data were analyzed by Kolmogorov-Smirnov and three way ANOVA. There was not a significant difference among the DC of the materials tested. LED significantly increased the degree of conversion of materials tested [P<0.001]. DC values were significantly greater in 2mm diameter samples vs 5mm ones [P<0.001]. The use of incremental technique in deep cavities restored with these composites is suggested. Also using LED is advised for curing composites because of a better result