Effects Of Various Conditioning Methods On The Bond Strength Of Rebonded Ceramic Brackets With Different Base Designs

Objective The purposes of this study was to evalute the effects of various surface conditioning methods on shear bond strength (SBS)of rebonded ceramic brackets with different base designs.Methods 219 human premolars extracted for orthodontic purpose were collected and divided randomly into two parts:one part(120 teeth)for the bond strength test;the other part(99 teeth) for getting debonded ceramic bracksts. For experimental part:120 human premolars were divided randomly into three groups(40 teeth in each group) according to different base designs:(A) round pits base,(B) microcrystalline lock base,(C) polymer mesh base. Then each test group was divided into four groups(10 teeth in each group)according to different treatment conditions:new brackets as controls (N),burning treatment (B),sandblasting (SB),silica coating (SC).33 teeth were selected respectively from three different base designs of ceramic brackets and were bonded to unetched and slightly wet tooth surfaces,then separated from the tooth surface easily with a tweezer with light pressure.Then different base designs of debonded brackets were divided to three groups with different kinds of treatments: burning treatment (B), sandblasting (SB), silica coating (SC).After that,a silane coupling agent was applied to different groups of bases.The teeth in each group were treated by conventional treatment,then were bonded with new brackets,burned brackets,sandblasted brackets,or siliac coated brackets. After 30 minutes,the samples were stored in distilled deionized water for 24 hours at 37°C in an incubator. Shear force test was performed and then the shear bond strength and the adhesive remnant index(ARI) were measured. Observe the change of the bracket base and the slot base by using SEM.Results 1.There were statistically significant differences in the shear bond strength of ceramic brackets with different base designs(P<0.01). There were statistically significant differences in the shear bond strength of ceramic brackets with different treament(P<0.01). There was an interactive relation between different base designs and different treament(P<0.01).2. Comparison of different treatment of the shear bond strength,the shear bond strength of burning group and sandbliasting group were significantly lower(P<0.01), the shear bond strength of silica coating group was significantly higer than that of burning group and sandbliasting group(P<0.01), the shear bond strength of silica coating group was close to new brackets group ,but there were no statistically significant difference between them(P>0.05).In all groups,the shear bond strength of polymer mesh base ceramic brackets with burning treament was lower than the minimum bond strength required.3. Comparison of different base designs of the shear bond strength:in new bracket group and burning group, the shear bond strength of round pits base and microcrystalline lock base were significantly higher than polymer mesh base (P<0.01).In sandblasting group, the shear bond strength of round pits base and microcrystalline lock base were significantly higher than microcrystalline lock base and polymer mesh base (P<0.05). There were no statistically significant difference between microcrystalline lock base and polymer mesh base(P>0.05).In silica coating group, there were no statistically significant difference between round pits base ,microcrystalline lock base and polymer mesh base (P>0.05).4. The score of ARI in all groups was between 2.2-3, There were no statistically significant difference among all groups (α>0.05).5.The results of SEM showed that some micro-structural changes of debonded ceramic brackets bases could be observed after different treament on debonded ceramic brackets with different base designs.Conclution:1.Silica coating is suitable for rebonding ceramic brackets with different base designs.Silica coating applications on debonded ceramic brackets base can produce bond strengths comparable with new brackets.2.After sandblasting,the shear bond strength of rebonded ceramic brackets with different base designs decreased, but was higer than the minimum bond strength required.In three cersmic brackets with different base designs, round pits base and microcrystalline lock base were more suitable for sandblasting treament.3.After burning, the shear bond strength of rebonded ceramic brackets with different base designs also decreased,but was higer than the minimum bond strength required,except for ceramic brackets with polymer mesh base.Burning on debonded ceramic brackets base can't be recommended for ceramic brackets with polymer mesh base.4.In the initial bonding, the shear bond strength of ceramic brackets wih round pits base and microcrystalline lock base was higer than that with polymer mesh base.