RESUMO
The purpose of this study was to evaluate the effects of filler incorporation in the adhesive materials i.e., unfilled, microfill and nanofill adhesives, on their shear bond strength to dentin and the chemical nature of the hybrid layer using the micro-Raman spectroscopy
Materials and methods: For bond strength test, the buccal surfaces at a total of 60 freshly extracted non-carious human molar teeth were ground flat. Teeth were divided into three group [n=20] according to the adhesive systems used; prime and Bond 2.1 [unfilled], Optibond Solo [microfill] and XenoIII [nanofill]. The composite resin was applied to the bonded surfaces and light cured. Shear bond strength test was performed using the universal testing machine. For the Raman spectroscopic examination, the occlusal surfaces of a total of 30 freshly extracted human molar teeth were ground flat. Teeth were divided into three groups [n=10] according to the grouping system mentioned before. The adhesive systems were applied to the occlusal surface, and then thee composite resin was applied to the surface and light cured. The specimens were sectioned parallel to the dentinal tubules, the sectioned surfaces of the cut halves were polished with silicon carbide papers. The prepared specimens were examined using the Raman spectroscopy
Results: The results of the present study revealed that the nanofill adhesive system revealed the highest mean shear bond strength values and the lowest values of Residual Double Bond RDB. The microfill adhesive system revealed the lowest mean shear bond strength values and the highest values of RDB. The unfilled adhesive system revealed intermediate results in-between the nanofill and the microfill
Conclusion: Within the limits of the present study it was evident that; Addition of fillers with nanometer particle size to the adhesive system will enhance excellent bonding and sealing of restoration to dentin. Addition of fillers with nanometer particle size to the adhesive system will enhance excellent bonding and sealing of restorations to dentin. Addition of fillers with micron particle size to the adhesive system will impair bonding and sealing of restorations to dentin. The shear bond strength test when combined with microscopic analysis of the adhesive tooth interface can provide useful information regarding the bonding mechanisms of adhesives. The laser Raman spectroscopy is a useful analytical technique for studying the bonding structure of specimens and determining their composition. Further studies are needed to determine the relationship between the amount of residual double bonds and bond strength durability
RESUMO
New light -activation units equipped with blue light emitting diodes [LEDs] have recently been proposed as a replacement for halogen units to polymerize composite resins. This study investigated the effectiveness of composite curing by Quartz tungsten halogen [QTH] and light emitting diode [LED] light curing units [LCUs] on the microhardness, depth of cure and flexural strength of nanofilled composite [Filtek Supreme]
Methods: A digital microhardness tester was used to evaluate the Vickers hardness number [NHN] of the top and bottom surfaces of the 1mm and 2mm thick composite disc specimens. All specimens were irradiated for 40 seconds exposure time with 1] QTH light in standard continuous mode and 2] in "soft start mode" as well as with 3] LED LCU. 10 specimens were evaluated for each of these conditions with two different thicknesses making a total of 60 specimens. Bottom to top B/T hardness ratio was calculated to determine the percentage of cure. Depth of cure was also evaluated for 6 specimens 4 mm diameter. 6mm depth for each condition using a penetrometer method. Flexural strength was determined for the same conditions according to the ISO specification 4049. Groups were compared using one way ANOVA and Fisher's LSD as well as student's test
Results: Significant differences in VHN in specimens cured with either LCUs at the top of the 1 and 2mm specimens, were observed with lower values when using the LED LCU. Higher hardness values were recorded on the top surfaces of all specimens compared to the bottom surfaces. The depth of cure of shade A3 composite cured using the conventional halogen LCU in both standard and soft start modes was significantly deeper [5.16, 5.06 mm] respectively [p<0.05] than the LED LCU [3.74 mm]. The flexural strength of specimens cured using the LED was significantly lower [p< 0.04] than that cured with the halogen LCU used with either modes. However the results obtained with both units exceeded the minimal requirements described in the ISO 4049
Conclusions: The differences in the irradiances of the two light curing units used in this study reflected significant differences in the microhardness, depth of cure and flexural strength properties of the composite resin