Influence of the curing method on the post-polymerization shrinkage stress of a composite resin

Abstract

The aim of this study was to evaluate the effect of different curing methods on the stress generated by the polymerization shrinkage of a restorative composite in two moments: immediately after light exposure and after 5 min. Photoactivation was performed using two different light sources: (1) xenon plasma arc (PAC) light (1,500 mW/cm2 – 3s) and (2) a quartz-tungsten-halogen (QTH) light with three light-curing regimens: continuous exposure (40 s at 800 mW/cm2 – CL); soft-start (10 s at 150 mW/cm2 and 30 s at 800 mW/cm2 - SS) and intermittent light [cycles of 4 s (2 s with light on at 600 mW/cm2 and 2 s of light off), for 80s – IL]. The composite resin was applied between two 5-mm diameter metallic rods, mounted in a servohydraulic machine. The maximum stress was recorded immediately after light exposure (FF) and after 5 min (5F). The results were submitted to ANOVA and Tukey's test (5%). For each method, the results obtained in FF and 5F were, respectively: CL (3.58 and 4.46 MPa); SS (2.99 and 4.36 MPa); IL (3.11 and 4.32 MPa) and PAC (0.72 and 3.27 MPa). The stress generated by the polymerization shrinkage during light exposure can be associated with the photoactivation method used. A significant increase in the stress level was observed during the post-curing period up to 5 min, for all evaluated methods.

Marginal microleakage of class II composite resin restorations due to restorative techniques

“…In addition, cavity-wall gap formation may cause marginal staining, postoperative sensitivity and secondary caries (4,6), although for Lima et al (12) microleakage and surface roughness did not influenced caries lesion formation. The adaptation of the material to the cavity depends essentially on their thermal expansion and dimensional changes during the process of polymerization (2,13,14). Differences in the coefficient of linear thermal expansion between the dental restorative materials and structures are largely responsible for the leakage (2), which justifies the use of thermal cycling in this work (11,15).…”

The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements

“…This finding may be associated with the photoinitiator content of Panavia F and the broad spectral range of QTH light that can reach alternative photoinitiators better than the second-generation LED used in this study, even though the latter emits a higher irradiance for the same curing time than the QTH light. For conventional camphorquinone-based resin composites, no difference has been observed in the development of physical properties, such as the degree of conversion, when LED and QTH units are compared [13,31]. The argon ion laser has been described as a promising light source for curing resinous materials [21].…”

“…Traditionally, quartz-tungstenhalogen (QTH) lights have been widely used in dental practice. They have a spectral wavelength in the range 400-500 nm and an irradiance in the range 300-1,000 mW/cm 2 [12,13]. However, they have some drawbacks, such as gradual reduction in irradiance over time, the need for filters for wavelength selection, limited depth of cure, and considerable heat generation [14,15].…”

Influence of enamel acid-etching on mechanical properties and nanoleakage of resin composite after aging

“…Composite shrinkage can cause adhesive failure and loss of marginal sealing 1 , resulting in post operative sensitivity, marginal staining, and secondary caries 2 .…”

“…The resulting composite exhibits less than 1% shrinkage 3 , which leads to better marginal integrity 4 and less microleakage compared to methacrylate composites 5 . In addition to the monomer composition, factors that influence the stresses created by polymerization include the photo initiator, number and type of filler, c-factor, restorative technique, and light source 1,6 .…”