Effects Of Light-curing Units On Microleakage And Shear Bond Strength Of Light-curing Orthodontic Adhesives

Objective:Evaluate the effect of quartz-tungsten-halogen light(QTH) and LED curing systems on the microleakage and shear bond strength of resin adhesive (3M) and resin-modified glass ionomer adhesive (GC). The aim of this study was to provide evidences for clinical chose of curing lights and Orthodontic Adhesives.Methods:96 freshly-extracted human premolars were divided to A and B group(n = 48/group),each group was randomly assigned into 4 bonding groups (n = 12/group): group A1, resin adhesive (3M),QTH cured 40s; groupA2, resin adhesive (3M),LED cured 20s; groupA3, resin-modified glass ionomer adhesive (GC), QTH cured 40s; groupA4, resin-modified glass ionomer adhesive (GC) , LED-cured 20s. The teeth were kept in distilled water for 4 weeks, and subjected to 2000 thermal cycles(from 5℃to 55℃). Then, specimens were sealed with nail varnish, stained with 0.5% basic fuchsin for 24 hours, sectioned, and photographed under a low power stereomicroscope.Microleakage was scored with regard to the adhesive-tooth interface and the bracket-adhesive interface at both incisal and gingival margins. Statistical analysis was accomplished by Kruskal-Wallis and Mann-Whitney U-tests with Bonferroni correction ( SPSS 12.0 ) .At last the interface of enamel- adhesive was obsvered under high power stereomicroscope and SEM. groupB were assigned as A, The teeth were kept in artificial saliva for 4 weeks, Specimens were thermocycled 2000 times and the shear bond strength of the adhesive system was evaluated with an Universal testing machine . Adhesive remnant index (ARI) scores were determined after bracket failure. The data were submitted to statistical analysis ( SPSS 12.0 ) , using t-test and Mann-Whitney analysis .the surface of enamel was obsvered under high power stereomicroscope and SEM after debonding the bracket.Results:1.GC results in more microleakage than 3M in both tooth-adhesive and bracket-adhesive interfaces. A significant difference was observed.2.When 3M was used, QTH displayedy more microleakage than LED in both tooth-adhesive and bracket-adhesive interfaces, significant difference was observed.3.When GC was used, QTH displayedy more microleakage than LED in both tooth-adhesive and bracket-adhesive interfaces, no significant difference was observed.4.The gingival sides in all groups exhibited higher microleakage scores compared with those observed on occlusal sides for both adhesive interfaces in each group.5.The shear bond strength and ARI of 3M was significant lager than GC.6.No matter which adhensive was used .No significant difference was found in shear bond strength and ARI between the LED and QTH.Conclusions:1.Using the conventional resin adhesive (3M) in orthodontics practice safer than using resin-modified glass ionomer adhesive (GC) as it show less microleakage.2.LED not only save the manipulative time but also lead much lower microleage under backet.3.The gingival sides in all groups exhibited lager microleakage compared with those observed on occlusal sides.4.Probably there is correlation between microleakage and the shape of enamel- adhesive interface.5.Both two kinds of light curing adhensives can satisfy the clinic need of orthodontics. Resin-modified glass ionomer adhesive significantly less incidences of enamel failure.6.Orthodontic adhesives cured with LED was statistically equivalent to those cured with a QTH. LED can save the time and be suggested for the polymerization of orthodontic bonding adhesives.