Objective: A comparative study of Er:YAG laser and high speed handpiece effect on the shear strength of the composite resin dentin after treatment of primary teeth.Methods: Collecting 124 mandibular primary teeth that are in accordance with the standard, burring in super hard plaster separately whose size is 3cm×5cm.
And randomly dividing into 4 groups: A, B, C, D, Each group has 31 teeth. Group A and group B with the Er:YAG laser (Power is 2W) exposure of primary teeth labial dentin, group C and group D with high speed handpiece exposure labial dentin of primary teeth. Selecting a sample from each group randomly and observing by scanning electron microscope and comparing, and then group A and group C were acid etched. The rest 120 samples will be tested and statistically analysis shear strength after filling composite resin. Results: SEM showed that primary teeth dentin surface uneven Er:YAG laser processing, the appearance is rough and has fish squamous, wavy, the surface is cleaning without smear layer, dentin tubule is clear, peritubular dentin is the intertubular dentin protrudes out of the surface, a large number of opened dentinal tubules were "cuff" appearance. Tooth surface which is treated by high speed handpiece leaves stripes, section is relatively flat,smear layer surface covered with a layer of dense, and accompanied by obvious cracks,dentin structure is not clear, dentin sections occasionally appear opened dentinal tubules.The analysis of shear strength of group A is（11.45±3.79）Mpa, group B is（9.78±3.35）Mpa, group A and group B have not statistically difference (P>0.05), it is not considered that shear strength of group A and group B have difference. Group C is（8.97±4.03）Mpa,group D is（5.90±3.29）Mpa, group C and group D have statistical significant differences (P<0.05), it can be considered that the shear strength of group C and group D were different. Group A and group C were statistically significant difference (P<0.05), it can be considered that the shear strength of group A and group C were different. group B and group D have statistical significant differences (P<0.05), it can be considered that the shear strength of group B and group D were different. Conclusion: Primary teeth dentin surface use power of Er:YAG laser treatment of 2W, whether it is combined with acid etching can increase the shear strength with composite resin. High speed handpiece combined with acid etching of primary teeth dentin can increase the shear strength of composite resin.
Keywords: Er:YAG laser; High speed handpiece; Primary teeth; Shear strength; Dentin