Effect of different photoactivation techniques on the bond strength of a dental composite

Abstract

Using the push-out test, this study evaluated the bond strength of the composite resin Z250 (3M/ESPE) photoactivated with the XL2500 (3M/ESPE) quartz-tungsten-halogen light-curing unit with different curing protocols: soft-start (150 mW/cm² for 2 s (S2), 3 s (S3), 5 s (S5), 10 s (S10) or 15 s (S15), followed by 700 mW/cm² for 15 s; pulse-delay (150 mW/cm² for 2 s (P2), 3 s (P3), 5 s (P5), 10 s (P10) or 15 s (P15), with a 1-min delay, followed by 700 mW/cm² for 15 s. After storage at 37°C ± 1 for 24 h ± 1, the specimens were ground, polished and subjected to a push-out test in a universal test machine (Instron) with a cell load of 500 N at a crosshead speed of 0.5 mm/min. The data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. There were no statistically significant differences (p>0.05) among the groups photoactivated using the soft-start mode. For the pulse-delay mode, P5 promoted the highest bond strength (p<0.05). Groups photoactivated with the pulse-delay mode (except for P2 and P15) presented significantly higher bond strength than those photoactivated with the soft-start. It may be concluded that the influence of initial exposure time was curing method-dependent, with the best results obtained using the pulse-delay method with 5 s in the first photoactivation cycle.

Effect of light sources and curing mode techniques on sorption, solubility and biaxial flexural strength of a composite resin

“…The use of low initial intensity followed by high intensity light with an interval between them seems to create a uniform polymerization of the composite resin, providing its best adaptation to cavity walls and possibly the least polymerization contraction stress 10,17,30 . In the delay period, little amount of free radicals and double bond conversion are produced and the composite resin has more time to molecular rearrangement and stress relief 10 .…”

“…In the delay period, little amount of free radicals and double bond conversion are produced and the composite resin has more time to molecular rearrangement and stress relief 10 . In the PD cure, there was reduced gap formation without any mechanical properties being compromised, which can be considered as an indicative that composite has the same quantity of remaining double bonds 3 .…”

“…In this technique, there is a short period (about 1-3 min) between initial exposition and final cure 10 . The interval between both pulses, an initial pulse with low energy density and a final pulse with high light irradiation, increases the composite resin pre-gel phase improving its flowability and relieving the stress generate by composite shrinkage.…”

Influence of storage temperature on vickers microhardness of resin composite

“…29,47 Preheating of resin-based materials prior to their use, will lower their viscosity and help in the handling properties, this will lead to better adaptation to cavity walls. 48 The results of the present study of the mean hardness ratio of bottom and top surface among the three levels of storage temperature (23°C, 5°C and 37°C) not considering the type of material, shows that the best hardness ratio was obtained with the refrigerated samples at 5°C (85.1%), which has a highly statistically significant difference from the other groups (F=43.292, p<0.0001). A possible justification for the improvement of hardness of refrigerated resin composites is that samples were less affected by the heat generated by the curing unit, generating less stress during its polymerization.…”

Effect of different surface penetrating sealants on the roughness of a nanofiller composite resin

“…Since the introduction of bonding systems and composite resins, wear and microleakage were the primary clinical limitations, mainly in posterior restorations (1)(2)(3)(4)(5)(6)(7)(8). The relative porosity of the restorative and absorption/adsorption of oral fluids may also allow staining agents to penetrate the material (9).…”