Effects of ultramorphological changes on adhesion to lased dentin—Scanning electron microscopy and transmission electron microscopy analysis

Abstract

Dentin irradiation with erbium lasers has been reported to alter the composite resin bond to this treated surface. There is still a lack of studies reporting the effect of erbium lasers on dentin organic content and elucidating how laser treatment could interfere in the quality of the resin-dentin interface. This study aimed to evaluate the effect of erbium laser irradiation on dentin morphology and microtensile bond strength (μTBS) of an adhesive to dentin. Seventy-two dentin disks were divided into nine groups (n = 8): G1-Control (600-grit SiC paper); Er:YAG groups: G2- 250 mJ/4 Hz; G3- 200 mJ/4 Hz; G4- 180 mJ/10 Hz; G5- 160 mJ/10 Hz; Er,Cr:YSGG groups: G6- 2 W/20 Hz; G7- 2.5 W/20 Hz; G8- 3 W/20 Hz; G9- 4 W/20 Hz. Specimens were processed for cross-sectional analysis by scanning electron microscopy (SEM) (n = 3), transmission electron microscopy (TEM) (n = 2), and adhesive interface (n = 3). Forty-five dentin samples (n = 5) were restored and submitted to μTBS testing. ANOVA (α = 5%) revealed that G1 presented the highest μTBS values and irradiated groups did not differ from each other. TEM micrographs showed a superficial layer of denatured collagen fibrils. For SEM micrographs, it was possible to verify the laser effects extending to dentin subsurface presenting a rough aspect. Cross-sectional dentin micrographs of this hybridized surface revealed a pattern of modified tags with ringlike structures around it. This in vitro study showed that erbium laser irradiation interacts with the dental hard tissue resulting in a specific morphological pattern of dentin and collagen fibrils that negatively affected the bond strength to composite resin.

Bond strength of composite resin to enamel and dentin prepared with Er,Cr:YSGG laser

“…Dentin surfaces prepared by Er:YAG laser is denatured by heat, which in turn shows a decrease in adhesion efficacy to composite resin 9) . The same finding has been reported in several other studies using Er,Cr:YSGG laser [10][11][12][13][14] . In clinics, it is recommended that the heat-denatured layer be removed using excavation or low-speed cutting with round steel bur 9) .…”

Long-term effect of Er:YAG laser on adhesion to caries-affected dentin

“…Horizontal microcracks in the peritubular dentin and modified resin tags were observed in all interfacial SEM photomicrographs of irradiated sound dentin specimens, as observed in previous studies [26]. These cracks are different from the ones observed in non-irradiated sound dentin, which presented tubules without microcracks [26].…”

“…These cracks are different from the ones observed in non-irradiated sound dentin, which presented tubules without microcracks [26]. These cracks result from the increased pressure in the dentin subsurface due to water vaporization and subsequent ejection of organic material due to the ablation process [27].…”

Impact of Er:YAG laser pulse duration on ultra-structure of dentin collagen fibrils

“…These alterations restrict the resin diffusion into dentin and jeopardize the hybridization [27] resulting in significantly lower bond strengths [26,28,29].…”