Effects Of Pulsed Nd: YAG Laser Irradiation On Resistance Of Enamel To Demineralization During Orthodontic Treatment With Fixed Appliances: An In Vitro Study

Objective: The purpose of this study was to investigate the effects of pulsed Nd:YAG laser irradiation on resistance of enamel to demineralization during orthodontic treatment with fixed appliances, and also to evaluate the influence on shear bond strength of orthodontic brackets.Methods: Part one: Effects of Nd:YAG laser irradiation on resistance of enamel to demineralization. Fifty human posterior teeth with intact enamel were collected after extraction. They were randomly assigned to 5 groups of 10 each. The stainless steel brackets were applied to the teeth by the following methos. Group A0: The brackets were bonded with jing-jin enamel adhesive , following the manufacturer s instructions. The teeth in group A1 and group A2 were lased before bracket placement . The teeth in group B1 and group B2 were lased after bracket placement . The teeth in group A2 and group B2 were daubed with enhencer before laser treatment. Then all samples were immersed in lactic acid demineralization solutions and the concentration of Ca2+ dissolved in the solution was measured. The enamel surface morphology and the interface between emamel and adhesive were observed with the scanning electron microscope.Part two: Effects of Nd:YAG laser irradiation on shear bond strength of orthodontic brackets: Sixty human posterior teeth with intact enamel were collected after extraction. They were randomly assigned to 6 groups of 10 each. The stainless steel brackets were applied to the teeth by the following methos. In group A0-A2 The brackets were bonded with jing-jin enamel adhesive , following the manufacturers instructions. In group B0-B2 The brackets were bonded with self-etching primer +Transbond . The teeth in group A1 and group B1 were lased before bracket placement. The teeth in group A2 and group B2 were lased after bracket placement. The universal testing machine was used to test the shearbond strength of each tooth. After debonding, the adhesive remnant index was scored for each tooth.Results: 1. Laser irradiation decreased the Ca2+ concentration in demineralization solution (P<.05).2. The initiator plus laser decreased the Ca2+ release of enamel samples more than the laser only group (P<.05).3. No significant differences were found between the Ca2+ concentration in the group lased before bracket placement and that in the group lased after bracket placement.4. Laser treatment altered the enamel surface morphology observed with the scanning electron microscope.5. No significant differences were found between bond strengths of brackets in the group lased before or after bracket placement and that in the control group .6. There was no statistically significant differences between the mean ARI score for the treated groups.Conclution: 1. Laser irradiation may reduce the enamel decalcification that is often seen during fixed appliance treatment. The enamel surface can be lased before or after bracket placement.2. The initiator can increase the ability of Nd.YAG laser to confer demineralization resistance on enamel.3. Nd:YAG laser irradiation of enamel before bracket bonding has no effect on subsequent bond strength.Zhuyan (Orthodontics) Directed by: Liuxinqiang...