effect of bulk depth and irradiation time on the surface hardness and degree of cure of bulk-fill composites

Statement of Problem: for many years, application of the composite restoration with a thickness less than 2 mm for achieving the minimum polymerization contraction and stress has been accepted as a principle. But through the recent development in dental material a group of resin based composites [RBCs] called Bulk Fill is introduced whose producers claim the possibility of achieving a good restoration in bulks with depths of 4 or even 5 mm

Objectives: to evaluate the effect of irradiation times and bulk depths on the degree of cure [DC] of a bulk fill composite and compare it with the universal type

Materials and Methods: this study was conducted on two groups of dental RBCs including Tetric N Ceram Bulk Fill and Tetric N Ceram Universal. The composite samples were prepared in Teflon moulds with a diameter of 5 mm and height of 2, 4 and 6 mm. Then, half of the samples in each depth were cured from the upper side of the mould for 20s by LED light curing unit. The irradiation time for other specimens was 40s. After 24 hours of storage in distilled water, the microhardness of the top and bottom of the samples was measured using a Future Tech [Japan- Model FM 700] Vickers hardness testing machine. Data were analyzed statistically using the one and multi way ANOVAand Tukey's test [p = 0.050]

Results: the DC of Tetric N Ceram Bulk Fill in defined irradiation time and bulk depth was significantly more than the universal type [p < 0.001]. Also, the DC of both composites studied was significantly [p < 0.001] reduced by increasing the bulk depths. Increasing the curing time from 20 to 40 seconds had a marginally significant effect [p

Conclusions: the DC of the investigated bulk fill composite was better than the universal type in all the irradiation times and bulk depths. The studied universal and bulk fill RBCs had an appropriate DC at the 2 and 4 mm bulk depths respectively and using the recommended curing time of 40s can led to the slightly better value of DC in both composites

Effect of flowable composite on Microleakage of packable resin composites in class II cavities

Polymerization shrinkage is one of the most common causes of microleakage in packable composites. Various methods are recommended to reduce polymerization shrinkage and the application of flowable composites is one of these methods. The aim of the current study was to evaluate the effect of flowable composite on the microleakage of packable resin composite in class II cavities. This experimental study was performed at Dental School of Shahid Sadoughi University, Yazd [Iran] in 2006. On 32 recently extracted upper premolar teeth, the mesial and distal class II cavities with the same dimensions were created. The teeth were randomly assigned into two groups: the distal surfaces of the first group were restored with P60 while in the other group restoration was accomplished with Solitaire resin composite. The mesial aspects of the teeth were filled with Filtekflow flowable composite and other composites mentioned above. After thermocycling, the samples were soaked in 2% methylene blue solution followed by sectioning in mesiodistal direction. The degree of microleakage was evaluated by stereomicroscope with 25 X magnification. Data were subjected to the chi-square and Exact tests, statistically. The flowable composite failed to reduce the degree of microleakage in axial wall and gingival floors [p>0.05]. The application of flowable resin composite caused no effect on microleakage of class II packable resin composite restorations

Effect of voltage stabilizer on the light intensity output of curing units

The success rate of light composite restorative treatments is in close relation to the light intensity of the light curing units. The purpose of this study was to evaluate the rate of light intensity of visible light curing units, before and after voltage stabilizer application. This study was performed on 82 light curing units in all clinics and dental offices of Yazd city. For evaluating light exit intensity, Hilux radiometer was used. At first, the light intensity was measured, and then by use of 220 V electrical voltage stabilizer the light exit intensity was recorded. Results were analyzed using Pearson and Spearman tests. Mean range of light intensity before and after voltage stabilizer was 241.3 and 272.6 mW/cm2 respectively. There were statistically significant differences between before and after use of voltage stabilizer [p < 0.05]. Considering the light intensity, 64.7% of the light curing units were suitable for optimum curing and 8.6% were in group that required increase light exposure time. 21.9% did not completely cure the composites, and 4.8% were in group with higher light intensity 2 [over 500 mW/Cm2]. Light intensity output of the curing units in dental clinics of Yazd city were less than expected, but by using voltage stabilizer, the light intensity was significantly increased

Comparison of microleakage in class V direct composite and ceramic inlay restorations cemented with two different resin cements

Ceramic inlays are alternative systems for restoring dental cavities with tooth colored materials. These restorations may have some benefits over direct composite restorations such as reduction in the bulk of the cured composite. The aim of this study was to evaluate the microleakage of direct composite restorations and ceramic inlays with two different resin cements. In this experimental study, 45 class V cavities [15 teeth in each group] were prepared in buccal surfaces of human extracted molars. For 30 cavities, ceramic inlays were prepared and were cemented either with Variolin k / Excite DSC or Panavia F / ED primer. Fifteen samples were restored with Excite / Heliomolar [direct composite]. Then the teeth were thermocycled and were covered with sticky wax and were immersed into the 2% Methylene blue for 48 hours. The teeth were sectioned longitudinally and dye penetration was determined. Data were statistically analyzed using nonparametric tests of Kruskal Wallis, and Mann Whitney with significance level 0.05. Enamel margins showed less microleakage than dentin margins in all groups [P<0.05]. No significant differences were observed between the materials used in this study [P>0.05]. The materials used in this study can not completely prevent microlekage. It seems that ceramic inlays can not reduce microleakage over direct composite significantly

[Evaluation of etching technique and storage on shear bond strength of two bonding agents; a self etch and a total etch]

Bonding agents are one of the most important materials in adhesive dentistry. Sixth generation bondings have more simple application than fifth generation, but despite this, it has been addressed by some articles that adhesive strength of sixth generation gradually decreases over time. The aim of this study was to compare the shear bond strength of a resin composite with application of two bonding agents [fifth and sixth generation] after three months storage in normal saline. This invitro study was conducted on 40 anterior bovine teeth. After complete removal of enamels, the samples were randomly divided into four groups based on the use of acid etch technique and the type of bonding agents [Excite or Prompt L-pop]. After applying Z250 composite resin, the samples were immersed in normal saline for 90 days and then were thermocycled and subjected to shear bond testing with Dartec universal testing machine. Statistical analysis was performed using one-way ANOVA and Tukey's test. In non-etched groups, Prompt L-pop showed significant higher bond strength than Exite, but in etched groups Excite had significantly higher bond strength [p<0.005]. There were no significant differences in Prompt L-pop subgroups with or without etching meanwhile in Excite subgroups, significant differences were found. The use of Excite with acid etching technique provide more reliable bonding than Prompt L-pop to dentin