| Objective To compare the difference of etching morphology and bonding strength between low-energy erbium-doped:yttrium aluminum game(Er:YAG)laser irradiation and conventional phosphoric acid etching pretreatment on the root surface tissue of isolated premolars,and to preliminarily explore whether Er:YAG laser can replace phosphoric acid treatment as a new mild and efficient root surface pretreatment method,so as to provide reference for strengthening the clinical application and related research of root surface bonding restoration.Methods 160 extracted premolars were selected and the root surfaces were polished for use.Part Ⅰ:80 experimental teeth were randomly selected,and 1/3 of the roots were cut to make 80 root patches,which were divided into 5 groups according to different surface pretreatment methods(n=16),group A:untreated group,group B:phosphoric acid group,group C:30mJ Er:YAG laser irradiation group,group D:50mJ Er:YAG laser irradiation group,and group E:70mJ Er:YAG laser irradiation group.The microscopic morphological differences of each group were analyzed by histological hematoxylin-eosin staining,scanning electron microscope observation and atomic force microscope nano-roughness detection.Part II:The remaining 80 experimental teeth were designed with pretreatment area at the root 1/3,and were randomly divided into 4 groups according to different surface pretreatment methods(n=20,group A:phosphoric acid treatment group,group B:30mJ Er:YAG laser treatment group,group C:50mJ Er:YAG laser treatment group,and group D:70mJ Er:YAG laser treatment group),coated with Single bond 2 adhesive,bonded with light-cured composite resin Z350.Low speed cutter was used for all samples to prepare 160 microtensile test strips.The microtensile bond strength of each group was detected by microtensile dynamometer,and the fracture mode was analyzed by stereomicroscope,all results were statistically analyzed.Results Part I:Histological results of hematoxylin-eosin staining showed that the phosphate group demineralized and the etching depth reached the cementum layer;In the laser groups,there were pit-like defects in different degrees,some of which reached the dentin layer,and deepened with the increase of laser energy.The results of scanning electron microscopy showed that the morphology of the root surface was different after phosphoric acid treatment and laser irradiation.The surface of untreated group was flat and covered with a large number of smear layers.Many ridge-like protrusions interweaved into a net and a hole structure appeared on the surface of phosphoric acid group,accompanied by a small amount of smear layers residue;There was no smear layer on the surface of each laser group,showing a clean and irregular rough morphology,while dentinal tubules and collagen fibers were exposed to varying degrees.Atomic force microscope results showed that phosphoric acid and laser treatment had different coarsening effects.Comparing with the flat surface of the untreated group,the surface treated with phosphoric acid had hill-like structure and the roughness was increased.The values of Ra and Rq were statistically different from those of the untreated group(p<0.05).Gully structure appeared on the treated surface of 30mJ,50mJ and 70mJ Er:YAG laser groups,and the surface roughness was significantly improved,which was statistically different from that of untreated group and phosphoric acid group(p<0.05),but there was no statistical significance between 50mJ group and 70mJ group(p>0.05).Part Ⅱ:The microtensile bond strength test results showed that 50mJ laser irradiation(30.40±10.79MPa)and 70mJ laser irradiation(27.49±7.14MPa)could significantly improve the bond strength of root surface compared with phosphoric acid treatment(20.77±8.17MPa),and the difference was statistically significant(p<0.05).However,there was no statistical significance between the 50mJ laser group and the 70mJ laser group(p>0.05).The fracture mode composition ratio of each group was similar,and there was no statistical significance between groups(p>0.05).Conclusion The pretreatment method of Er:YAG laser etching with specific energy could effectively coarsen the root tissue and obtain higher bonding strength than phosphoric acid etching,which was beneficial to the close bonding between the root tissue and composite resin.To some extent,Er:YAG laser etching pretreatment method can replace phosphoric acid treatment as a new root surface pretreatment method.In clinical operation,50mJ Er:YAG laser energy is recommended as the energy parameter of root surface pretreatment,so as to achieve the purpose of high efficiency,comfort and safety. |
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