Introduction Direct bonding of orthodontic attachments to enamel surface has a significant impact on clinical orthodontic treatment.1 Conservation of arch length, ease of placement and esthetic superiority are some of the advantages of direct bonding. Direct bonding procedure requires de-bonding at the termination of active treatment. Great consideration should be given to de-bonding procedures and the effect that these procedures have on the enamel surface underlying the bonded attachments. The primary consideration lies in returning the enamel surface to as near its original state as possible following removal of bonded orthodontic attachments.2 The term debonding refers to removal of orthodontic attachments and all the residual adhesive from the enamel surfaces and restore as closely as possible to its pretreatment condition without inducing iatrogenic damage. The color similarity between present adhesives and enamel does not allow for complete removal of remaining adhesive which discolors with time and creates an esthetic problem.3 A variety of mechanical methods have been designed to achieve satisfactory composite removal with minimal damage to the enamel surface. With the advent of ceramic brackets, debonding of these brackets have caused enamel fractures and cracks.4 Although new techniques including thermal, electro-thermal and chemical aids to mechanical debonding, ultrasonic, lasers and intra-oral sandblasting have been advocated, mechanical debonding of both stainless steel and ceramic brackets remain the technique of choice.5 The amount of resin left and up-to which extent enamel surface is restored to its original texture is not known. Scanning electron microscopic evaluation permits a better understanding of what happens to treated enamel. Also till date there are no studies comparing the different de-bonding techniques in Bangalore urban population. Thus the purpose of the present study was to examine microscopically the enamel surface structure subjected to different de-bonding techniques using the Scanning Electron Microscope (SEM) and to develop a technique for residual adhesive removal that restores the enamel surface as closely as possible to natural enamel surface. MATERIALS AND METHOD Forty premolar teeth were collected from patients undergoing extractions for orthodontic treatment purpose. All the teeth were divided at random into four groups of 10 teeth each. The teeth were dried and mounted in improved plaster in color coded metal cups to ensure firm support during the de-bonding procedures. The buccal surfaces of all the forty premolars were cleaned with pumice, rubber wheel and cup. Etchant, primer and resin used were light cure composite (TRANSBOND XT, 3M Unitek) The straight wire twin brackets (Gemini,3M Unitek ) were bonded to the teeth. All the teeth were bench cured for 10 minutes and later stored in distilled water for 24 hours. The brackets were removed with direct bonding bracket remover (Balaji dental products,Chennai) and the remaining resin on the enamel surfaces was removed by one of the four de-bonding procedures described below. Procedure1: Remaining resin on enamel of 10 teeth was removed with hand scaler (SU15/80-HuFriedy, USA) Procedure2: Remaining resin on enamel of 10 teeth was removed with ultrasonic scaler (Cavitron,09306 Dentsply Ltd,UK) Procedure3: Remaining resin on enamel of 10 teeth was removed with plain fluted tungstun carbide bur at high speed (NO.7803, SS White, Lakewood NJ) Procedure4: Remaining resin on enamel of 10 teeth was removed with green stone (Shofu Composite kit, California) All the teeth from each procedure were finally polished with rubber wheel, cup and slurry of pumice and water. After finishing, it was completely satisfied that the enamel surface appeared clean and free of resin remnants by visual inspection as well as tactile sensation under operating light and dental probe. Enamel surface of each specimen was studied using scanning electron microscope(JOEL JSM840 JAPAN). Photographs were obtained at x200 magnification for all the specimens treated with the four procedures after polishing.The photomicrographs were studied for the nature of the enamel surface and graded according to the modified surface roughness index (table 1) originally proposed by Howell and Weekes in the form of grades and modified by Hong and Lew7 to numerical form to facilitate statistical analysis. TABLE 1 MODIFIED SURFACE ROUGHNESS INDEX SCORE 1 2 3 4 CONDITION OF ENAMEL SURFACE. Acceptable surface, fine scattered scratches Mildly rough surface, denser fine scratches with some coarser scratches. Rough surface, numerous coarse scratches over the entire surface. Very rough, deep, very coarse scratches over the entire surface RESULTS: An acceptable clinical appearance of all the tooth surfaces was achieved with all the four debonding procedures. The scanning electron photomicrographs taken were qualitatively examined for the nature of the enamel surface. All the four procedures failed to remove the adhesive resin completely. Most surfaces showed the characteristic perichymata. Though no detectable resin remnants were seen clinically the photomicrographs showed resin remnants scattered here and there. All treatments left occasional scratches, depressions or a few gouges on the enamel surfaces. Final polishing left the surfaces considerably smoother though it did not completely remove the resin remnants which were true with all the four procedures. Table 2 shows the scores obtained from photomicrographs for each removal procedure for surface roughness Index. Statistically significant differences were detected between different finishing procedures using chi-square test. Because calculated value of X2 is 30.857 which is greater than table value of X2= 16.919, we reject the hypothesis of the four procedures being homogeneous with respect to SRI scores. It concludes that there is significant difference between the four procedures. The tungsten carbide bur was superior in terms of enamel smoothness to all other finishing procedures showing greater score 1(photomicrograph1). Ultrasonic scaler came next with larger proportion of score 2(photomicrograph2) which was slightly superior to hand scaler (photomicrograph3) which showed equal proportion of scores 2and 3.Green Stone had a larger proportion of score 3(photomicrograph4). None of the finishing procedures showed score 4 although all the four procedures left some amount of resin remnants with scratches and gouges even on final pumicing. The teeth surfaces finished with tungsten carbide bur came closest to resemble natural enamel (photomicrograph5). TABLE 2 Scores of different de-bonding procedures obtained from Scanning Electron Microscopic photomicrographs DEBONDING PROCEDURES SCORE 1 SCORE 2 SCORE 3 SCORE 4 Hand scaler Green stone Ultrasconic scaler 0 0 2 5 3 6 5 8 2 0 0 0 Tungsten carbide bur 8 2 0 0 DISCUSSION Post de-bonding scarring of enamel is a disadvantage of orthodontic bonding. However, there is no doubt that the advantages outweigh the disadvantages. The clinician therefore must accept enamel scarring and then methodically attempt to return the enamel surface to as near its original condition as possible. 7-9 There is a wide range of opinion as to the best method of debonding. Restoration to a relatively smooth surface while preserving the topographic qualities of enamel is the key to a successful debonding procedure. For all practical purposes the final enamel appearance after debonding should be comparable to the adjacent enamel surface, dry as well as wet. A variety of debonding techniques have been introduced in order to achieve a satisfactory finishing of the enamel surface. Seong-Sik et al10 found that intra- oral sand blasting technique of de-bonding to be similar to that after resin removal with a low-speed hand-piece. There were significant greater temperature changes in the low-speed hand-piece than in the sand blasting group. Sandblasting for resin removal did not cause pulpal damage. In terms of time taken for resin removal sandblasting group was significantly slower than low-speed group but the vibration of low-speed hand-piece caused discomfort for the patient.However the disadvantages of intra-oral sand blasting are it is a highly complex procedure and various factors including sandblasting pressure, duration of sandblasting, particle size, type of particle and protection for operator and patient should be considered. At bracket removal bond failure can occur at the resin-enamel interface (adhesive failure) or resin-bracket interface (cohesive failure). Cohesive failure is safer than adhesive failure but with adhesive failure less adhesive is left on the enamel and less time is spent on clean-up. It can also lead to enamel loss and depend largely on the bracket material, type of resin used and the method of bracket removal. The preferred site of failure is controversial.6 Previous studies have reported undesirable enamel cracks and bracket fracture with ceramic brackets.4,11-14 It can lead to poor esthetics and costly treatment and even compromise the long –term prognosis of the affected tooth. Also conventional debonding techniques have reported bracket fractures occurring 10%-35% of the time. Because metal brackets are routinely used, the risk is reduced. Because ceramic material do not bond chemically with resin, they derive their bond strength from the use of silane coupling agent on the base of the bracket through mechanical retention or both. Mechanically retained brackets have adequate bond strength and and cause minimal enamel damage. Chemical retention results in an extremely strong bond that stresses the enamel-adhesive interface during debonding.5, 15 In order to overcome the drawbacks in debonding ceramic brackets, lasers came to be used to debond the ceramic brackets without risk of enamel fractures eg. C02 and YAG Lasers. Ezz Azzeh and Paul J. Feldon18 in their review article highlight the advantages of laser debonding of ceramic brackets. These cause debonding of the brackets by thermal softening of the adhesive and resin contraction. Debonding occurs at the resin-bracket interface, where much of the resin remains on the enamel surface. Light microscope and scanning electron microscope showed no enamel or bracket damage in any sample. The term DEBONDING refers to removal of bracket and the residual adhesive from the enamel surface and restore the surface as closely as possible to its pretreatment condition. Lasers bring about only removal of the brackets and much of the resin remains on the surface of the enamel .The risk of enamel damage and bracket fracture is significantly reduced with lasers but necessitates the removal of more residual adhesive after bracket removal. It is always better to get a cohesive failure where most of the resin remains on the enamel surface and damage to the enamel is also less during bracket removal. Various studies on the type of bond failure of metal and ceramic brackets have reported a cohesive failure.5,15,16 In one of the study to determine the amount of resin remnants on the enamel surface with three kinds of adhesives, a smaller portion of resin-modified glass ionomer was left behind than the resin based adhesives. They also concluded that it was during final enamel clean-up that most enamel surface loss occurred.16 The purpose of this study was to evaluate four different techniques of debonding for restoring the enamel to a superior quality after removal of directly bonded metal brackets. Residual resin was removed using tungsten carbide bur, ultrasonic scaler, greenstone and hand scaler and finally polishing the enamel surfaces. In the earlier work, tungsten carbide bur clean-up was considered the gold standard for residual resin removal against which other methods could be compared. 17,18 In our study, of the four instruments used, tungsten carbide bur at high speed proved to be the fastest and most efficient method of residual resin removal. It received score of 1 for the surface roughness index. Most of the surfaces exhibited a cobble stone effect, which is a reflection of the prisms exposed during etching of enamel prior to bonding. This infers that the tungsten carbide bur clean up did not remove enamel beyond that penetrated by the etchant. Fitzpatrick and Way19 in an SEM study of the effects of wear, acid etching and resin removal on human enamel showed that tungsten carbide bur at high speed removed an average of 55 microns of surface enamel or approximately the entire thickness of the etch. This was in agreement with studies done by Retief and Denys,17 Campbell,2 Hong and Lew,8 Bertrand Marshall and Cooley. 7 The time required for residual resin removal was also less with tungsten carbide bur at high speed .But studies by Zachrisson and Arthun,20 Hannah and Smith 21and Ingrid et all 22 found that tungsten carbide bur at low speed was most effective in removal of residual resin. Ingrid et al22 found that using self-etching primer rather than conventional acid-etching technique caused less enamel loss. The ultrasonic scaler clean up in our study also produced a considerable smooth surface which was in accordance with Burapavong,20 Krell,Courey and Bishara.23 But time taken for resin removal was long. The enamel surface appeared superior to that of green stone finishing. This finding is of particular interest since the task of this procedure can be thought in terms of delegating to the hygienist. With additional training a hygienist can be transformed into an expanded dental auxiliary. The ultrasonic cleanup received a large number of scores of 2 for the surface roughness index which comes nearest to being acceptable. Ingrid Hosein et al 22 found that ultrasonic finishing caused a great degree of enamel loss. The other two instruments tested i.e the hand scaler and the green stone left surfaces which were rough and left rougher and deep cuts which were not removed with pumicing which was in agreement with Gwinnet and Gorelick.24 Even Retief and Denys17 and Oliver and Griffiths25 do not advocate the use of hand scaler. Even though the hand instrument could pop adhesive almost entirely in many instances and should be tried first, they must be used cautiously if the adhesive offers resistance. Burapavong20 found a satisfactory enamel surface after resin removal by hand scaler and was superior to that achieved after finishing the enamel with green stone. Green stone left unnecessary roughness which could not be removed even with polishing. He found hand scaler and ultrasonic scaler to be useful for initial resin removal. Irrespective of the procedure, however, small amounts of resin are bound to remain on the enamel as seen in this study and others. Casperson26 found that SEM could disclose presence of acrylic islands, flakes or diffuse membranes. The finding in this study and those of others indicated that all rotating instruments effective in removing resin remnants, introduced some abrasion to enamel surface. Enamel surface is a heterogeneous tissue, composed of sub- microscopic crystallites embedded in a sparse organic matrix. Its microscopic characteristics predisposes it to many and varied abrasion anomalies. It is necessary to be cautious in using de-bonding instruments when approaching enamel. Another problem associated with cleanup is heat. Retief and Denys17 recommend air cooling whereas Campbell 2 and Rouleau et al 7 and Torun et al6 insisted on water cooling. In this study water cooling was preferred with highspeed hand-piece, even though it has the disadvantage of masking the resin remaining on the enamel surface making it difficult for the operator to differentiate between the resin and enamel. Perhaps the enamel surfaces after de-bracketing can be subjected to a disclosing medium, which allows better contrast of the tooth coloured adhesive remnants and the enamel making resin clean up easy. Burapavong,20 Hong and Lew,8 Zarrinnia ,Eid and Kehoe9 and many others found that final pumicing bettered the appearance of enamel surface. Even though Casperson 26 found that pumicing was ineffective in removing the remnants of adhesive, it was effective in smoothening the rough enamel surfaces. Although pumice is a mild abrasive, it apparently is capable of smoothening most of the roughened areas left by different procedures. Only the deep gouges, cuts and depressions are not removed by pumice prophylaxis. In addition enamel surface is subjected to normal wear with age that reduces these artificial marks together with other factors such as tooth brushing and nature of diet. Final pumicing is a necessary step in debonding. CONCLUSION The results of this study indicates that removing resin during de-bonding using a high speed tungsten carbide bur followed by pumice polishing produced significantly more acceptable surfaces than the other procedures, coming closest to resemble untreated natural enamel. With additional training a hygienist can be delegated the task of ultrasonic clean-up of enamel surfaces since the procedure produced surfaces which come nearest to being acceptable. REFERENCES. 1. Al Shamsi AH, Cunningham JL, Lammy PJ, Lynch E. Three dimensional measurements of residual adhesive and enamel loss on teeth after debonding of orthosontic brackets: an in vitro study. 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Effects on shear bond strength and the enamel surface with an enamel bonding agent. Am J Orthod Dentofacial Orthop. 2010;137:375-378. 13.Bishara SE, Oslen ME, Vonwald L, Jacobson JR. Comparison of debonding characterists of two innovative ceramic bracket designs. Am J Orthod Dentofacial Orthop. 1999;116:86-92. 14.. Kitahara-cela FMF, Mucha JN, Santos PAMD. Assessment of enamel damage after removal of ceramic brackets. Am J Orthod Dentofacial Orthop. 2008;134:548-555. 15.Theodorakopoulou LP, Sadowsky L, Jacobson A, Lacefield W. Evaluation of debonding characteristics of two ceramic brackets: an in vitro study. Am J Orthod Dentofacial Orthop. 2004;125:329-339. 16.Lee YK, Lim YK. Three dimension quantification of adhesive remanants on teeth after debonding. Am J Orthod Dentofacial Orthop. 2008;135:556562. 17.Retief DH, Denys FR. Finishing of enamel surface after debonding of orthodontic attachments. Am J Orthod Dentofacial Orthop.1979; 49: 1-10. 18.Zachrisson BU, Arthum J. Enamel surface appearance after various debonding techniques. Am J Orthod Dentofacial Orthop. 1979;75: 121-137. 19.Fitzpatrick DA, Way DC. The effects of wear, acid etching and bond removal on human enamel. Am J Orthod Dentofacial Orthop. 1977;72: 671680. 20.Burapavong V, Marshall GW, Apfel DA, Perry HT. Enamel surface characteristics on removal of bonding orthodontic brackets. Am J Orthod Dentofacial Orthop. 1978;74: 176-187. 21.Hannah CM, Smith GA. The surface finish of composite restorative material. Br Dent J. 1973;135: 483-488. 22.Hosein I, Sherriff M, Ireland AJ . Enamel loss during bonding, debonding, and cleanup with use of a self etching primer. Am J Orthod Dentofacial Orthop. 2004;126: 717-24. 23.Krell KV, Courey JM, Bishara SE. Orthodontic bracket removal using conventional and ultrasonic debonding techniques, enamel loss, and time requirements. Am J Orthod Dentofacial Orthop. 1993;103: 258-265. 24.Gwinnett AJ, Gorelick L. Microscopic evaluation of enamel after debonding: clinical application. Am J Orthod Dentofacial Orthop. 1977;71: 651-665. 25.Oliver RG, Griffiths J. Different techniques of residual composite removal following debonding-Time taken and surface enamel appearance. Br J Orthod. 1992;19: 131-137 26.Caspersen IVAR. Residual acrylic adhesive after removal of plastic orthodontics brackets; A scanning electron microscope study. Am J Orthod Dentofacial Orthop. 1981;70: 500-522. LEGENDS OF FIGIRES photomicrograph 1: Enamel surface debonded with tungsten carbide bur. photomicrograph 2: Enamel surface debonded with ultrasonic scaler. photomicrograph 3: Enamel surface debonded with hand scaler. photomicrograph 4: Enamel surface debonded with green stone. photomicrograph 5: Normal Enamel surface.