Abstract

Simplified dentin-bonding systems are clinically employed for most adhesive procedures, and they are prone to hydrolytic degradation. Objective This study aimed to investigate the effect of laser diode irradiation on the degree of conversion (DC), water sorption (WS), and water solubility (WSB) of these bonding systems in an attempt to improve their physico-mechanical resistance.Material and Methods Two bonding agents were tested: a two-step total-etch system [Adper™ Single Bond 2, 3M ESPE (SB)] and a universal system [Adper™ Single Bond Universal, 3M ESPE (SU)]. Square-shaped specimens were prepared and assigned into 4 groups (n=5): SB and SU (control groups – no laser irradiation) and SB-L and SU-L [SB and SU laser (L) – irradiated groups]. DC was assessed using Fourier transform infrared spectroscopy with attenuated total reflectance. Additional uncured resin samples (≈3.0 µL, n=5) of each adhesive were also scanned for final DC calculation. For WS/WSB tests, similar specimens (n=10) were prepared and measured by monitoring the mass changes after dehydration/water storage cycles. For both tests, adhesive fluids were dropped into standardized Teflon molds (6.0×6.0×1.0 mm), irradiated with a 970-nm laser diode, and then polymerized with an LED-curing unit (1 W/cm2).Results Laser irradiation immediately before photopolymerization increased the DC (%) of the tested adhesives: SB-L>SB>SU-L>SU. For WS/WSB (μg/mm3), only the dentin bonding system (DBS) was a significant factor (p<0.05): SB>SU.Conclusion Irradiation with a laser diode improved the degree of conversion of all tested simplified dentin bonding systems, with no impact on water sorption and solubility.

Highlights

  • Previous studies have indicated that an increase in temperature could enhance the mechanical properties of dentin bonding systems7,25

  • Maenosono, et al.17 (2015) showed that the use of a laser diode improved bond strength when associated with simplified dentin bonding systems (SDBSs)

  • As the laser diode promoted a variation in temperature of approximately 6°C, varying from 20.98 to 27.21°C for these SDBSs during their application, laser diodes can be more advantageous regarding biological conditions as well. Another rationale that supports the improvement of the degree of conversion (DC) and water sorption (WS)/water solubility (WSB) of dental adhesives is related to the effect of air-drying on solvent evaporation

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Summary

Introduction

Previous studies have indicated that an increase in temperature could enhance the mechanical properties of dentin bonding systems7,25 Despite these advantages, some concerns limit their clinical indications, since the heat could damage pulp tissue, thereby compromising dental vitality. Some concerns limit their clinical indications, since the heat could damage pulp tissue, thereby compromising dental vitality14,27 In this scenario, the association of lasers with dentin bonding systems has been investigated to achieve a more resistant hybrid layer. Et al. (1999) assessed Nd:YLF laser irradiation over a three-step, etch-and-rinse system prior to curing, which promoted an increase in dentin bond strength values These authors attributed this performance to the creation of a new substrate composed of recrystallized hydroxyapatite after being melted in the presence of resin monomers, resulting in a substrate that is physically more resistant. In addition to the role of the laser’s interaction with dentin, the authors emphasized the evaporation of solvents as an advantage of laser use, reducing the bond’s susceptibility to degradation over time

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