Effect of Fast High-Irradiance Photo-Polymerization of Resin Composites on the Dentin Bond Strength

Abstract

This study investigated the influence of conventional (10 s at 1160 mW/cm2) and fast high-irradiance (3 s at 2850 mW/cm2) light curing on the micro-tensile bond strength (μTBS) of bulk-fill resin composites bonded to human dentin. Sixty-four extracted human molars were ground to dentin and randomly assigned into eight groups (n = 8 per group). After application of a three-step adhesive system (Optibond FL), four different bulk-fill composites (two sculptable and two flowable composites) were placed. Of these, one sculptable (Tetric PowerFill) and one flowable (Tetric PowerFlow) composite were specifically developed for fast high-irradiance light curing. Each composite was polymerized with the conventional or the fast high-irradiance light-curing protocol. The specimens were cut into dentin-composite sticks, μTBS was determined and failure modes were analyzed. Statistical analysis was performed using t-test for independent observations and one-way ANOVA. A statistical difference between the curing protocols was only found for Tetric PowerFlow, where the conventional protocol (23.8 ± 4.2 MPa) led to significantly higher values than the fast high-irradiance light-curing protocol (18.7 ± 3.7 MPa). All other composite materials showed statistically similar values for both polymerization protocols. In conclusion, the use of fast high-irradiation light curing has no negative influence on the μTBS of the investigated high-viscosity bulk-fill composites. However, it may reduce the dentin bond strength of flowable bulk-fill composite.

Effect of Polywave and Monowave Light Curing Units on the Microtensile Bond Strength and Failure Types of Different Bulk-Fill Resin Composites: An in vitro Study

“… 2 , 5 In this sense, the degree of conversion depends on the type of monomers present in the organic matrix, as well as on the number of radicals generated in the activation stage of the polymerization reaction, thus becoming a crucial factor in determining the mechanical properties of the materials and their biocompatibility. 2 , 5 , 8 , 24 , 25 …”

“… 8 , 20 , 27 The remarkable variation in filler particle size and monomer blends among the tested composites must be considered when analyzing parameters related to polymerization. 25 , 27 …”

“…Therefore, such reasoning cannot be considered a general rule. 5 , 8 , 24 , 25 The composition of the bulk-fill resin composite and the depth of cure are factors that should be considered because they may influence the mechanical properties of the composite. 33 , 37 It is also important to consider the large shrinkage stresses that are generated within the resin composite and at the dentin-composite adhesive interface because they can affect the bond strength.…”

“…33 , 37 It is also important to consider the large shrinkage stresses that are generated within the resin composite and at the dentin-composite adhesive interface because they can affect the bond strength. 25 , 41 , 42 If the stress resulting from polymerization contraction exceeds the bond strength of the composite to the cavity walls, failures may occur at the marginal bonds. However, if the bonding interface resists and remains intact, residual stress could be transferred to adjacent tooth structures, possibly resulting in fractures of the enamel or dentin.…”

“… 22–25 However, recent studies have revealed that rapid curing with high-irradiance light can create large shrinkage stresses within the composite material and at the dentin-composite adhesive interface, which can affect the bond strength. 25–27 …”