The influence of different light-curing modes on microleakage of posterior resin composites

Abstract

This investigation evaluated the effect of various curing modes on the extent of microleakage of differently resin-based posterior composites. Box-form Class II (MO/OD) cavities (n = 8) were prepared on proximal sides of 36 human sound mandibular molars. The cavities were restored by posterior composites (Filtek™ P90, Filtek™ Z250, and Filtek™ P60). The composite was placed in horizontal layers and irradiated occlusally by Astralis™ 10 light source at three modes of continuous intensities (conventional, high intensity power, and pulse-soft start). The specimens were thermocycled for 500 cycles at 5-55°C, then immersed in 2% methylene blue solution for 4-h at 37°C. The microleakage was examined by a stereomicroscope and scored occlusally and gingivally according to the ordinal scoring criteria. The Kruskal-Wallis revealed high significant differences between microleakage medians of the posterior composites examined ( p < 0.05). However, no significant differences were noted between microleakage medians at different modes of curing intensities occlusally ( p = 0.076) and there were significant differences gingivally ( p = 0.015). Mann-Whitney U-test showed a significant difference in microleakage for cavities restored by Z250 between high power and pulse modes of cure ( p = 0.006). The highest microleakage score was identified in the cavities restored with P60, while the lowest microleakage score was found in cavities restored by P90 specifically at conventional and pulse mode of cure. The light intensity modes have no significant effect on the microleakage, while the difference in composition of posterior resin composites investigated was the main factor for such a significant difference.

Effects of light curing modes and ethanol-wet bonding on dentin bonding properties

“…Some scholars believe that the soft-start mode cannot reduce polymerization stress and microleakage, and that it has no significant effect on improving marginal adaptation in the bonding interface and degree of conversion of the resin monomer (Bouschlicher et al, 2000;Fleming et al, 2007). Too high or too low initial intensity cannot achieve a good curing effect (Marghalani, 2014), so the initial light intensity of the soft-start mode in our experiment is 400 mW/cm². Cunha et al (2007) reported that the soft-start mode did not reduce the degree of conversion, but led to lower shrinkage stress and higher bond strength, which demonstrated the correlation with shrinkage stress and bond strength.…”

“…If shrinkage stress during the polymerization process is greater than the adhesive force in the bonding interface, it will generate gaps in the bonding interface and the material inside. Thus, the polymerization shrinkage of a composite resin has a lot of negative effects on clinical applications, such as microleakage, edge color, fracture of teeth or restorative materials, post-operative sensitivity, and secondary caries (Bouschlicher et al, 2000;Marghalani, 2014). To facilitate clinical operation and shorten treatment time, high-powered light-emitting diode (LED) light units came into being.…”