Effect of shade and light curing mode on the degree of conversion of silorane-based and methacrylate-based resin composites

Statement of Problem: The degree of conversion depends on the material composition, light source properties, distance from light source, light intensity, curing time, and other factors such as shade and translucency

Objectives: In the present study, we evaluated the effects of different light- curing modes and shades of methacrylate and silorane-based resin composites on the degree of conversion of resin composites [DC]

Materials and Methods: The methacrylate-based [Filtek Z250, 3M, ESPE] and low-shrinkage silorane-based [Filtek P90, 3M, ESPE] resin composites were used in three groups as follows: group 1-Filtek Z250 [shade A3], group 2-Filtek Z250 [shade B2], and group 3-Filtek P90 [shade A3]. We used a light-emitting diode [LED] curing unit for photopolymerization. 10 samples were prepared in each group to evaluate the degree of conversion; 5 samples were cured using soft-start curing mode, and the other 5 were cured using standard curing mode. The DC of the resin composites was measured using Fourier Transform Infrared Spectroscopy [FTIR]. The data were analyzed using Kruskal Wallis and one- way ANOVA statistical tests

Results: The degree of conversion of silorane-based resin composite was 70 - 75.8% and that of methacrylate-based resin composites was 60.2 - 68.2% [p = 0.009]. The degree of conversion of the composite with brighter colour [B2] was statistically more than the darker composite [A3]. Higher degree of conversion was achieved applying the standard curing mode

Conclusions: The results of the study showed that the colour and type of the resin composite and also the curing mode influence the degree of conversion of resin composites

[ effect of one versus two applications of self- etch primers on micro-shear bond strength to the enamel and dentin]

Self etch acidic primers may be unable to etch the enamel and penetrate the thick dentinal smear layer and as a result produce inadequate bond strength. The present study aimed to evaluate the effect of the second layer application of two self-etch primers on etching pattern and micro-shear bond strength to the enamel and dentin. In an experimental study, 104 human premolar teeth were divided into two groups. The buccal surfaces of the teeth were prepared for enamel and dentinal evaluation. Self-etch primer of clearfil SE Bond and clearfil S3 Bond were applied in one or two layers on the prepared enamel and dentin surfaces. One specimen of each prepared group was selected for SEM group evaluation. The composite resin cylinders were bonded to the rest of the specimens for micro-shear bond strength measurement. The data were analyzed using two- way ANOVA and HSD -Turkey's tests. Application of the second layer had no significant effect on micro-shear bond strength to the enamel and dentin [p>0.05]. The dentinal micro- shear bond strength values of the specimens treated by Clearfil SE Bond, were significantly higher compared to Clearfil S3 Bond [p<0.05] but no significant effect was found on enamel bond strength [p>0.05]. Application of one layer of self- etch primer produced sufficient bond strength and there is no need to apply the second layer

Comparison of micro-leakage in class V ceramic inlay restorations cemented with two different resin cements

Resin cements are usually used for bonding ceramic inlays. The aim of this study was to evaluate the micro-leakage in class V ceramic inlays cemented with two different resin cements. A total of 30 class V cavities were prepared in buccal surfaces of human extracted molars with occlusal margins in enamel and gingival margins in dentin [cementum]. Ceramic inlays were prepared for all cavities and were cemented either with Variolink / Excite DSC or Panavia F/ED primer. These teeth were thermocycled and covered with sticky wax except for 1 mm around cavities and were immersed into 2% Methylen blue for 48 hours. The teeth were sectioned longitudinally and dye penetration was evaluated using stereomicroscope. Data was analyzed using nonparametric tests. There were no significant difference between the two types of cements in dentin or enamel margins [P>0.05]. Compared with enamel margins, Panavia F showed less micro-leakage in dentin margins [P>0.05]. The resin cements under evaluation in this study can not completely prevent micro-leakage. It seems that both cements have almost the same effects regarding micro-leakage reduction