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ePaper created 2016-04-05, 13:01:42 | version 1.38.0
research | 15 1 2016 laser mation in all the samples and the presence of resin tags with lateral branches. A gap along the inter- face between the VF and the dentin surface was seen in two of the samples (Figs. 4 and 5). Group 3 In the dentin surface of the samples of Group 3, it was possible to observe what seems to be melted dentin, with a few open dentinal tubules, and a gap along the interface (Fig. 6). In a sample, it was not possible to observe resin tags in the dentinal tu- bules, there was almost no hybrid layer and a big gap along the interface between the VF and the dentin surface was observed (Fig. 7). The samples of this group seemed to have a smoother dentin surface than those in Group 2, but rougher than the samples of the Control Group (Figs. 6 and 7). Discussion There are already several studies about adhesion in dental surfaces prepared with laser, but mostly with Er:YAG and enamel, and fewer about self-ad- hesiveflowableindentin,especiallywithEr,Cr:YSGG laser. Several factors can influence the adhesion to dentin, such as the dentin substrate itself, the treatment and the dentin conditioning.13,14 The ad- hesion to dentin was always a greater challenge because of the water and collagen content.15 The dentin hybridisation is the accepted mechanism to explain the resin-dentin bond, which consists in demineralised dentin with infiltrated monomers and its polymerization.8 Several articles showed that dentin surfaces pre- pared with Er,Cr:YSGG laser appear with open den- tinal tubules looking cuff-like, irregular and rough, and are without smear layer.9 These features of lased dentin theoretically should have better con- ditions for adhesion.15 The comparison presented by Beer et al., between dentin surface prepared with Er,Cr:YSGG laser and self-etch system and a dentin surface also prepared with Er,Cr:YSGG laser and etched with 37 % phosphoric acid, showed better SBS with the first system.16 The application of acid in the dental surface prepared with laser dissolves the intertubular dentin, altering the sur- face produced by laser, and leading to unknown dentin-demineralised depths, which could inter- fere with the monomers diffusion.17–19 Therefore, theoretically we do not need acid etching prior the adhesive to accomplish an ade- quate adhesion in lased surfaces. Despite the ad- vantages of the dentin surfaces prepared with Er,Cr:YSGG in adhesion,15 several studies have demonstrated a lower SBS when compared with surfacestreatedwithconventionalmethods.9, 15, 20, 21 However, this subject is still treated controver- sially.22, 23 Group 2 presented higher mean values of bond strength (4.76 ± 3.99 MPa), followed by the Control Group (1.87 ± 1.61 MPa). A lower adhesion result was observed in Group 3 (0.81 ± 0.93 MPa). The high standard deviation presenting in Group 2 shows that probably there was more variability in the sample than expected. The age of the dentin samples could be a factor with an impact on the Shear Bond Strength,24 that was not controlled in this study, and also the sample probably should be higher. None of the SBS differences between the three groups were statistically significant (p > 0.05), so neither of the null hypothesises were rejected. The settings used in Group 2 resulted in a surface without smear layer, which was rougher than the ControlGroup.Theabsenceofsmearlayerandopen dentinal tubules promotes a better surface for ad- hesion, leading to a better infiltration of the resin tags, which were observed in the SEM micrographs of this study.25 A study performed by Yazici et al., comparing the Shear Bond Strength of the VF in human dentin lased with Er:YAG and unlased sur- faces, also showed better results in the lased ones.3 Moreover, the manufacturer of VF claims that the acidic phosphate group etches the dental sur- Fig. 6: SEM of the dentin surface pre-treated with Er,Cr:YSGG laser from Group 3, showing the micromorphological aspects of the bonding region produced by Vertise™ Flow. The formation of a gap along the interface was observed (x 500). Fig. 7: SEM of the dentin surface pre-treated with Er,Cr:YSGG laser from Group 3, showing the formation of a gap along the interface (x 500). Fig. 6 Fig. 7 12016