Enamel Demineralization Around Orthodontic Brackets Bonded With Light-cured Resin-reinforced Glass Ionomer Cement

Part one: Enamel demineralization around orthodontic brackets bonded withlight-cured resin-reinforced glass ionomer cement:an in vitro studyObjective To investigate the light-cured resin-reinforced glass ionomer cement forinhibition of enamel demineralization around orthodontic brackets under aPH cycling experiment, and to compare the demineralization on deferentarea of enamel surface around brackets.Methods 40 human premolars extracted in orthodontic treatment were used in thestudy. Twenty teeth were bonded with Fuji Ortho Lc glass ionomercement and 20 with composite resin. All samples were under the PHcycling experiment each day for 30 days. The concentration of calciumion dissolved in the lactic acid solution was evaluated with automaticbiochemical analyzer. The element content of calcium and phosphor onenamel surface around the brackets was analyzed with SEM-EDAX. Allthe data were analyzed statistically with SPSS12.0.Results 1. The concentration of Ca²⁺ in the experimental group and the controlgroup was 1.58mmol/l and 1.85mmol/l, respectively. There wassignificant difference between the two groups.2. There was no significant difference of element content of calcium andphosphor on different area of enamel surface, whether in the experimentalgroup or the control group.3. There was significant difference of element content of calcium andphosphor between the two groups.Conclusion 1. The application of light-cured resin-reinforced glass ionomer cement tobonding can be encouraged because it can decrease the enameldemineralization around orthodontic brackets.2. There is no difference about demineralization on different area ofenamel surface around brackets. Part two: Shear bond-strength of orthodontic brackets bonded withlight-cured resin-reinforced glass ionomer: An in vitro studyObjective To study the shear bond strength of light-cured glass ionomer cement onorthodontic brackets.Methods 50 human extracted premolars were randomly and evenly divided into 5groups. Group 1: The enamel was etched with 35ï¼…phosphoric acid for 30seconds, rinsed with tap water and dried. The brackets were bonded withcomposite resin. Group 2,4: The enamel was etched with 35ï¼…phosphoricacid for 30 seconds, rinsed with tap water and left moist, the brackets werebonded with Fuji Ortho Lc glass ionomer cement, group 3,5: The enamelwas not conditioned and left moist; the brackets were bonded with FujiOrtho Lc glass ionomer cement. The 1,2,3 groups were tested for shearbond strength after24h;the 4,5 groups were tested in 30min.Results The shear bond strength of the five groups were 8.20±2.99, 10.69±3.17,7.38±2.25, 6.99±2.29 and 4.66±1.52, respectively. The shear bond strengthof group 2 was significant higher than that of group 3, 4 and 5.There was nostatistically significant deference among group 1, 3 and 4. The adhesiveremnant index was significant deference among the 5 groups.Conclusion 1.The 24h shear bond strength of Fuji Ortho Lc glass ionomer cement isadequate for clinical use whether it is etched or not.2. The 30min shear bond strength of Fuji Ortho Lc glass ionomer cement isadequate for clinical use only when it is etched.3. The shear bond strength of Fuji Ortho Lc glass ionomer cement isstronger when it is etched than not.4. The shear bond strength of Fuji Ortho Lc glass ionomer cement is enoughfor clinical use when the enamel surface is rinsed.