An in vitro study:The effects on enamel tissue of different adhesive systems used in orthodontic bracket bonding

The aim of this in vitro study was to evaluate the effects of 4 adhesive systemsand surface preperation methods on demineralization and microleakage thatmay occur on the enamel surface around and beneath the bracket.This study has 2 main parts. First part consists of quantitative assessment ofcalcium loss conducted on ninety exracted human premolars. The teeth wererandomly divided into 2 groups according to the surface preperation methodand then were randomly allocated to 4 sub-groups. The adhesive systemsapplied in these groups are as follows: (1) Clearfil Protect Bond (KurarayDental, Osaka, Japan) + Transbond XT Light-Cure Adhesive (3M/Unitek,Monrovia, Calif), (2) GC ORTHO Conditioner + Fuji ORTHO LC Capsule (both,GC Corporation, Tokyo, Japan), (3) Transbond Plus Self-Etching Primer(3M/Unitek) + Transbond XT Light-Cure Adhesive, (4) 37% phosphoric acid(3M/ESPE, St Paul, Minn) + Transbond XT Primer (3M/Unitek) + Transbond XTLight-Cure Adhesive (3M/Unitek). Besides, a control group of teeth with enameluntreated enamel surface was formed. In the second part, 40 exracted humanpremolars were used for microleakage evaluation. The teeth were randomlydivided into 2 groups according to the surface preperation and then these twogroups were divided into 4 groups in which the adhesive systems mentionedabove were used. Thermal and pH-cycles were applied to all specimens exceptfor the control group. Two sections were taken from all teeth. A randomlyselected cross-section from each tooth was analyzed with energy dispersive xrayspectroscopy (EDS) for elemental evalution. Each section wasphotographed under a stereomicroscope and dye penetration method was usedfor assessment of microleakage. Images were transferred to a computer andmicroleakage was evaluated quantitatively via image analysis program.The difference between surface preperation methods was statisticallyevaluated by Mann Whitney U test. The difference between adhesive systemswas evaluated by One-Way ANOVA or Kruskal Wallis and then post hoc Tukeyviiior non-parametric multiple comparison tests. The comparisons within groupswas done with Friedman and then Wilcoxon Sign Rank tests .None of the adhesive groups demonstrated any significant difference whencompared with the control group regarding the amount of calcium on theenamel surface under the bracket. Difference in amount of calcium betweenthe adhesive systems was observed only in Group B (unprotected surface), onthe enamel surface under the bracket. The self-etch adhesive system (ClearfilProtect Bond and Transbond Plus Self-Etching Primer) showed higher amountsof calcium under the bracket . Among all the evaluated enamel regions, thehighest calcium loss occurred on the enamel surface under the brackets. Theleast amount of microleakage was found beneath the bracket while thecervical region showed highest amounts of microleakege. Deminerilazationoccured on the enamel surface beneath the brackets and surface protection didnot have any benefit in prevention of calcium loss. Clearfil Protect Bond whenapplied without any surface protection reduced the loss of calcium. Adhesivesystems evaluated in this study, may be preferred by clinicians to minimizecalcium loss of the enamel surface and microleakege beneath the bracket thatis formed with fixed orthodontic treatment.Key Words: White spot lesion, demineralization, microleakage, energydispersive x-ray spectroscopy (EDS), image analysis program