Comparison Of Shear Bond Strength Of Orthodontic Resin Brackets Under Different Conditions In Vitro

objectiveThe majority of modern orthodontic patients are adults, and more oyer are female. Along with the extensive development of adults'orthodontics, special requests of occupation , patients usually hope the orthodontic appliances can remain in concealment or little outside. Hence accelerate the development and ap-plicantion of nonmetal bracket , ceramic bracket and transparent resin bracket are commonly used. The price of ceramic bracket is higher, While resin bracket is relative cheaper and slinky, which tends toward be accepted. In clinical practices, resin brackets have limitation which inadequate in adhesive strength and have high rate of bracket loss. This characteristic prevent the extensive developing of resin brackets. Resin brackets can be widely used when the problem of bond strength can be well solved, they will look after both sides the beautiful of ceramics bracket and economic advantages of the stainless steel bracket . This experiment has been divided into two parts, Experiment A;Selected to use three kinds of orthodontic adhensives; Jingjin enamel adhesive (JJ ) ; self-etch light cured composite resin adhesive (3M); single - component adhesive ( the United States BISCO; ORTHO - ONE), selected the group of the biggest strength according the results of experiment A. Experiment B: Making use of the results of experiment A , selected the group of largest strength with different treatment of bracket bases, treatment methods including sandblasting ; draw monosbonds and draw the single component (methacrylic acid methyl ester). All these three kinds of treatments on the surfaces of bracket bases were bonded under the nor-mal conditions, the shear bond strength of each group were tested for the comparison. Selected the best methods of bracket bases. Compared the ARI (adhesive remnant index) on enamel after debonding, recorded the enamel cracking of each group. The aim of this study was to find the best methods to guide the clinical practices of resin bracket.Materials and methodsSelected One hundred and twenty human premolars without caries, extracted for orthodontic reasons. All teeth were stored in 0. 5% aqueouschloramines T . The specimens were cleaned and stored at room temperature. The longest conservancy time was not more than 6 months.Experiment A; Sixty human teeth were used and divided in three groups randomly (n =20). The brackets were Edgewise, resin brackets with a cross -section 0. 022 x 0. 028 inches and with a base area 13.24mm2.Experiment A : 60 teeth were randomized into three groups (n = 20) as follows :Ⅰ Jingjin enamel adhesive group (JJ ) ;Ⅱ. self- etch light cured composite resin adhesive group (3M) ;Ⅲ single - component adhesive ( the United States BISCO; ORTHO -ONE) group,Experiment B 60 teeth were randomized into three groups (n = 20) as follows :Ⅰ no bracket controled group (the same as group Ⅲ of experiment A )Ⅱ sandblasting group;Ⅲ monosbonds groupⅣ the single component(methacrylic acid methyl ester).Adhensives of experiment B were selected according to the results of experiment A . All brackers bonded routinely according to the directions of the manufacture.Each specimen was mounted vertically in self — care acrylic so that the shear force was parallel to each other. All groups were subjected to thermal cyc-ling before debonding test. After10 minutes ,the teeth specimens were stored in artificial saliva at 37 ℃. for 24 hours. The teeth were dried after being taken out. After thennocycling the hydropuls testing machine (Shimadzu Corporation, Japan) was used to test the shear bond strength. Shear bond strength was recorded in megapascals ( Mpa ).After debonding, all teeth were examined under an optical stereo-microscope. The amount of residual adhesive was classified according to the adhesive remnant index (ARI) , which consists of a 4 - point scale with score ranging from 0 to 3. A score of 0 indicates that no adhesive is left on the tooth, A score of 1 indicates that less than half the adhesive is left on the tooth, A score of 2 indicates that more than half the adhesive is left on the tooth, and a score of 3 indicates that all the adhesive is left on the tooth, including a distinct impression of the bracket bases. Then examined the buccal enamel with naked eye and recorded the situation of the enamel cracking.Results were statistically analyzed using an analysis of variance (ANOVA) and Q - test to determine if any significant differences among groups. Chi square test was carried out to detennine if there were any significant differences between the ARI scores of all groups.Results1. Experiment A1.1 shear bond strengthThe values of shear bond strength ranged from 0.85Mpa to 7.16 Mpa . Significant difference(P <0.01) were seen among all these three groups. Q - test showed no significant difference between Jingjin enamel adhesive group and self - etch light cured composite resin adhesive (3M) group ( P > 0. 05) ; while single -component adhesive ( the United States BISCO; ORTHO - ONE) group showed highly significant difference compare with those other groups ( P < 0. 05).1.2 The ARI scoresThe ARI scores showed no significant differences among three adhesives . (...