Effect Of Pretreating The Post Space By Er: YAG Laser On Bond Strength Of Fiber Post

Objective:To compare the cleanliness of the smear layer and the bond strength of fiber posts in different parts of the root canal under different pretreatment of post space methods including syringe irrigation,passive ultrasonic irrigation,three different parameters of 0.2W,0.3 W,and 0.35 W of Er: YAG laser SWEEPS mode.In order to provide a theoretical basis for the wider and safer clinical application of Er: YAG laser SWEEPS mode.Methods:Seventy-five single-rooted teeth extracted for orthodontic or periodontitis were selected and randomly divided into five groups after completed root canal preparation,root canal filling and post space preparation.Group A: 17%EDTA + 3%Na OCl + syringe irrigation;Group B: 17%EDTA + 3%Na OCl + passive ultrasonic irrigation by P5;Group C: 17%EDTA + 3%Na OCl + Er: YAG laser SWEEPS mode(15 Hz,20 m J,0.3 W);Group D: 17%EDTA + 3%Na OCl + Er: YAG laser SWEEPS mode(15 Hz,15 m J,0.2W);Group E: 17%EDTA + 3%Na OCl + Er: YAG laser SWEEPS mode(15 Hz,25 m J,0.35 W).One isolated tooth from each group was randomly selected to observe the cleanliness of the smear layer under scanning electron microscope.And the remaining 14 adhesive fiber posts in each group were sectioned at the root apex,middle,and crown,for thin section push-out experiments and fracture patterns analysis.Results:Observation of the cleanliness of the smear layer in each group revealed that: in group A,there were a large number of clumpy smear layers and sporadically opened dentin tubules;In group B,most of dentin tubules were open but the opening sizes were different,and the dentin wall surface was uneven;In group C,the dentin tubules were evenly open,organized and clear,and the dentin wall surface was flat without significant depression;In group D,the dentin tubules were not totally open,only shallow fissures with uniform distribution were observed,and there was a small amount of smear layer;In group E,almost no smear layer debris was observed on the dentin wall.The number of dentin tubule openings was less than that in group C and the size was uneven,but the dentin wall surface was flat.Comparison of bond strength of fiber post in each part of root: the bond strength of fiber post in group C was the largest,higher than that in the other four groups(P < 0.01);The bond strength of fiber post in group E was higher than that in group A(P < 0.05);There was no difference between group A,group B and group D(P > 0.05);There was no significant difference between group B,group D and group E(P > 0.05).The bond strength was greatest in the crown of the root,followed by the middle portion of the root,and least in the apical portion(P < 0.05).The results of fracture patterns showed that the incidence of fracture at the adhesive-dentin interface was higher than mixed fractures than adhesive-fiber post fracture rates(P < 0.01).Conclusion:1.The root canal cleaning effect of Er: YAG laser SWEEPS mode 0.3W and 0.35 W is better than that of syringe irrigation and passive ultrasonic irrigation,and they have less damage to dentin surface than passive ultrasonic irrigation.2.The bond strength of fiber post was the greatest at the Er: YAG laser SWEEPS mode 0.3 W group,which was higher than that of the other four groups;The bond strength of the fiber post was higher after irrigating by Er: YAG laser SWEEPS mode0.35 W than after the syringe irrigation.3.The bond strength of fiber post and dentin wall was the largest in the crown part of root,followed by the middle of root and the smallest in the apex.4.The incidence of fracture at the adhesive-dentin interface was the highest,followed by mixed fracture,and the incidence of fracture at the adhesive-fiber post interface was the lowest.