As increasing use of laser technology in dental practice, many studies examined the effects of different types of laser. Cavity preparation by Er,Cr:YSGG laser has many advantages in caries removal in pediatric dentistry. The creation of open dentinal tubules without the presence of a smear layer, which is suitable for the formation of resin tags, is among the benefits of this method 
Unlike conventional bur drilling, laser irradiation does not produce any sound and vibration, does not need local anesthesia. In addition, it is less painful to be useful in people with dental anxiety, especially children who are potentially cooperative [6, 14]. The application of resin restoratives is an important challenges which facing in pediatric dentistry. For instance, their high technical sensitivity is one of these challenges.
A successful restoration is dependent on an appropriate isolation, which means the control of moisture, and bleedings at the gingiva margins. This issue has specific problems in pediatric dentistry. Accordingly, choosing a proper bonding system is one of the essential requirements in this field . Generally, washing and drying steps eliminated with using self-etch bonding agents. Therefore, using them saves chairside time, which is important in pediatric dentistry and reduces procedural errors 
Composite restoration in primary tooth has In this study, the amount of microleakage of resin restorations was compared between the cavities prepared by Er,Cr:YSGG laser and air turbine dental drilling.
Considering the results of the present study, the use of Er,Cr:YSGG lasers reduced microleakage in the studied groups. It seems that the use of laser causes a slight increase in the temperature of the bonding agent, an enhancement of its penetration, and reduced microleakage [17, 18]
This result was in contradiction with that of Ghandehari's study, which did not show a decrease in the microleakage of the teeth restoration in the primary teeth using Er:YAG laser. This inconsistency might be due to different restorative material used in the class V cavities. Ghandehari et al. used glass ionomer cement for the restoration In addition, Rossi et al., who used glass ionomer cement in class V cavities, did not see any reduction in the marginal microleakage of the cavities prepared by Er,Cr:YSGG laser compared to those prepared by conventional bur 
Borsatto and Kohara studied the effect of Er:YAG laser on the marginal microleakage of class V restorations in permanent molars compared to conventional handpiece. Inconsistent with our results, Borsatto utilized flowable composite restorations after acid etching and demonstrated more microleakage in the laser group. This difference might be due to the greater laser ablation, which is stated in the studies below.
Furthermore, regarding the results of the studies conducted by Khan and Niu, there was no significant difference between the marginal microleakage of resin restorations after the preparation of cavity by the Er:YAG laser and bur preparation [21, 22]In the study carried out by Gutknecht et al., high microleakage was observed in the composite restorations of permanent teeth prepared with Er,Cr:YSGG laser without acid etching 
However, in line with our results, Kohara restored the cavities with composites without using acid eching, the marginal microleakage in the laser group was significantly higher than the other groups [24, 25] The margins of cavities prepared by laser are irregular, but there is no smear layer, which reduces microleakage.
Furthermore, the findings of Shahabi et al., who showed less marginal microleakage using Er,Cr:YSGG laser in the composite restorations of permanent posterior teeth in comparison with conventional bur cavity preparation was consistent with our result 
Self-etch adhesives that have acidic monomers do not need to wash, which simultaneously provide conditioning and priming of the enamel. In this type of bonding, the speed of process increases and its technical sensitivity decreases due to eliminating of rinsing step. It can be useful for resin restoration of primary teeth because by saving chairside time, the probability of losing a child's cooperation diminishes 
In this study, three different generations of bonding agents (sixth, seventh, and eighths generations) were used. All of them were self-etch and there was no significant difference in their microleakage without considering the way of cavity preparation.
Baghalian et al. compared microleakage of Er:YAG laser and bur cavities preparation in a primary teeth restored with two kind of self-etch resin adhesive. They observed significantly higher microleakage scores only at the gingival margins for teeth restored with resin composite and one-step self-etch adhesive in the group prepared by laser compared with that of bur preparation. Nonetheless, microleakage scores in both occlusal and gingival margins of the teeth restored with composite and two-step self-etch adhesive, followed by Laser prepared cavity was significantly less than the bur prepared cavity 
In our study, both one-step (using 7th and 8th generations of bonding agent) and two-step self-etch bonding (using 6th generation) were applied on primary teeth. However, in all types of bonding, the amount of microleakage in both occlusal and gingival margins of Er,Cr:YSGG laser prepared cavities was less than bur prepared cavities.
Moldes et al compared microlaekage of composite resin performed by Er:YAG / Er,Cr:YSGG lasers and burs associated with two different adhesive systems on permanent teeth. They found that the self-etching adhesive system significantly had a lower microleakage score at dentine margins for cavities prepared by lasers with than the etch-and-rinse two-step adhesive system . In another study Hoseinifar et al. evaluated microleakage of one and two step self-etch adhesive systems in permanent teeth and compare them with the low shrinkage composites in Class V cavities. there were no significant differences in microleakage among two-step and one-step SE adhesive systems on both the occlusal and gingival margins so two-step SE adhesive did not provide better marginal seal than the one-step SE adhesive systems .
In the present study, class V cavity, which has a high C factor, was used to evaluate the ability of sealing margins by resin restoration. The other advantage of these cavities was the possibility of simultaneous evaluation of enamel and dentin margins The enamel is highly mineralized and more than 90% of its composition is hydroxyapatite; nevertheless, dentin consists of water and organic matter and a dense network of tubules that run into the pulp.
The adhesion and bond strength to dentin are affected by the remaining dentin thickness and its tubular structure. This tubular structure is not seen in the enamel, which leads to the difference in bond strength in the enamel and dentin. This result confirmed our result, which demonstrated that the amount of microleakage in the gingival margin was more than the occlusal one