[Effect of different placement techniques and curing methods on composite microhardness in class I restorations]

The polymerization of light cured composite resins is initiated from surface layer and the rate of polymerization reduces from surface to depth. The difference in hardness is in correlation with different factors such as the intensity of unit and the distance between composite and light tip. The aim of this study was to compare the effect of four different methods of filling and two light direction on microhardness of class I composite resin restorations. In this parallel interventional study, 40 intact human premolar teeth were selected. Class I cavities were prepared [4x4x4 mm]. After etching and applying Excite as a dentin adhesive, the specimens were divided into four groups [n=10] based on the filling Group l] one bulk, group 2] horizontal incremental and occlusal light curing, group 3] horizontal incremental and three directional light curing, Group 4]oblique and three directional light curing. Z100 was used for restoration of cavities. Microhardness of specimens was measured by kicker's microhardness tester in 0, 1.5, 2.5 and 3.5 mm distance from surface. Data were analyzed using ANOVA and Duncan tests [a=0.05]. The mean value of microhardness in groups 1 and 2 showed significant difference from that of groups 3 and 4 [p<0.05]. Within each group, the subsurface layer showed the highest value of hardness [P<0.05] except for group 2 that all surfaces showed a similar hardness value [p>0.05]. Based on the results of this study, incremental technique [oblique or horizontal] with three dimensional light curing is the most suitable procedure for obtaining a maximum hardness in Class I composite resin restoration

Laboratory evaluation of composite wear resistance with and without occlusal index

The polishing and finishing procedures may cause topographical changes and introduce subsurface micro-cracks in dental composite restorations. The effect of Occlusal Index on the amount of wear in the posterior composite restorations was evaluated. Likewise, a comparison was made between the wear rates of Tetric Ceram and Ideal Makoo composite resin products. A total of 40 premolars were collected and randomly divided into four groups. Occlusal Indices were prepared with a transparent acrylic resin [Duralay]. Class I cavities were prepared in all specimens. In two groups, teeth were restored with Occlusal Index. However, the restorations were completed without any Occlusal Index in the other two groups. Wear on the surfaces of these restorations were made by an oral cavity simulator and a tooth-brush machine. The vertical sections of the [pre-wear]and [post-wear] replicas were compared with a Projector Profilometer and the differences between the two sections were analyzed using two way ANOVAtest at alpha = 0.5. The results showed that the mean-wear in index groups was higher. The findings did not show any significant difference between the wear rates of the two materials used in this experimental evaluation. The uses of occlusal index dose not decrease the wear of posterior composite restorations

[ clinical and histological evaluation of human pulpal response after power bleaching]

"Power Bleaching" which is a new an in-office whitening technique with a combination of a whitening agent [peroxide] and an auxiliary [plasma-Arch light], has been claimed to be an effective and fast method in tooth bleaching. What is more important in using this method is the maintenance of the pulp health after tooth whitening. The aim of this study was to evaluate the human pulpal response after bleaching with H2o2 38% and plasma-Arc light. Eighty seven sound first premolars from 27 patients were selected and divided into 3 groups of 29, based on the time intervals of histologic evaluation. In each group 9 teeth were considered as a control. Vitality tests were done before bleaching [base line] and in four intervals of 2, 7, 30 and 60 days, but histologic evaluation was performed in three intervals 2, 7 and 60 days. Immediately after extraction, apical one third of the roots were sectioned off and each specimen was placed in 10% buffered formalin solution for pulpal fixation. EDTA was used for decalcification and sections were prepared from each specimen and stained with H and E and subsequently assessed microscopically for the following criteria: Irregularities in the odontoblastic layer, the presence of inflammatory cell, vasodilatation and pulpal fibrosis. Data was analyzed using Friedman test and Wilcoxon test [alpha= 0.05]. There were significant differences between the 2 and 60 days groups and between 7 and 60 days groups with respect to inflammatory responses and vasodilatation [p<0.05]. Comparison of the control and experimental groups of the 2 and 7 days revealed statistically significant differences in inflammation and vasodilatation [p<0.05]. No patient had experienced sensitivity, after different bleaching periods. Bleaching of teeth with H2o2 38% and plasma-Arc light might cause slight to moderate pulp reactions after 2 and 7 days confined to the coronal pulp. However, the observed histological changes did not affect the overall health of the pulp tissue permanently