with the invention of bonding of orthodontic brackets to enamel over 30 years ago , orthodontics as a specialty has changed dramatically.1 prior to the introduction of the acid - etch bonding technique by buonocore , every tooth was banded in preparation for orthodontic treatment . the ability to bond orthodontic brackets has reduced patient chair time , reduced band space that would need to be closed later , improved esthetics , and aided in improvement of hygiene.2 today , with the introduction of newer bonding materials , orthodontics continues to evolve . in addition , the development of self - etching primers has further contributed to the ease of the bonding process.3 these primers eliminate the need to acid - etch the tooth surface prior to addition of the adhesive , thus reducing the number of steps involved in the bonding process . although ease of bonding has significantly improved due to direct bonding techniques and the availability of self - etching primers , the formation and prevalence of white spot lesions throughout orthodontic therapy continues to be a major area of concern for orthodontists . decalcification of enamel and ensuing white spot lesions are common around orthodontic brackets.4 gorelick et al found that 5% of patients undergoing fixed appliance therapy had at least one white spot lesion after treatment , irrespective of whether teeth were bonded or banded.5 these lesions can develop as early as 1 month into treatment,6,7 and remain an esthetic concern 5 years after removal of the appliances.8,9 during the bonding process , it is not uncommon to leave excess bonding adhesive around bracket margins unknowingly . this problem is exacerbated by the fact that many bonding adhesives are similar in shade to enamel in order to improve esthetics , but make identification of adhesive remnants more difficult.10,11 after completion of orthodontic treatment , a primary consideration is to return the enamel to its original state . during debonding it can be difficult to delineate the enamel  adhesive interface , causing potential enamel loss and/or damage during its removal . many studies have investigated the amount of enamel loss after debonding , with results in the range of 5150 m.1114 various orthodontic companies have manufactured color - changing adhesives to help remove excess adhesive before light - curing during bonding and after debonding . transbond  plus is a color - change orthodontic bonding adhesive manufactured by 3 m unitek ( monrovia , ca ) which claims excellent bond strength of the adhesive with both metal and ceramic brackets.15 the pink indicator incorporated in transbond plus becomes activated when it is exposed to light , both with ambient light and through curing . the color change of the adhesive is not an indication of a complete cure or polymerization , but rather facilitates acceptable esthetics during the course of treatment.15 the initial pink color is intended to facilitate removal of excess adhesive flash during bracket bonding ( prior to curing ) that can become a potential site of bacterial colonization and lead to enamel decalcification.1618 furthermore , remaining adhesive can also act as a mechanical irritant to the gingiva.17 gloo is a dual color - change adhesive developed by ormco corporation ( glendora , ca ) which claims an optimized formulation for esthetic brackets . at cooler temperatures the adhesive possesses a blue color , which then changes to a translucent color when the adhesive increases to warmer body temperatures . this color - change property allows for removal of excess adhesive during bracket placement and identifiable cleanup of the adhesive remnants after debonding once the adhesive is cooled with air or water.19 grngloo ( ormco corporation ) is a similar dual color - change adhesive manufactured specifically for metal brackets . according to the ormco website,20 grngloo polymerizes faster than other light - cured orthodontic bonding adhesives , providing a higher proportion of total bond strength at initial force loading . it is also designed to have up to 118% greater impact resistance for reducing bond failures from traumatic impact . its patented chemical formula has an affinity for metal brackets which helps to ensure reliable bond strength . the green color of the adhesive at lower temperatures during bonding facilitates the removal of excess adhesive . as the adhesive warms to body temperature , the color disappears , remaining clear throughout treatment . after debonding , a short blast of cool air or water is enough to lower the surface temperature and return the adhesive to its original green color for easy removal of adhesive remnants.20 a study by duers et al compared the bond strengths of different color - change adhesives ( transbond plus , gloo , and grngloo ) relative to a conventional light cure adhesive ( transbond xt ) used for orthodontic bonding . the study used 35% phosphoric acid etch and traditional primer to prepare the tooth surface prior to the addition of the adhesive and orthodontic bracket . although the average shear bond strengths varied among the adhesives at two time points ( 15 minutes and 24 hours after bonding ) , all measurements were still within the recommended bond strength range for orthodontic bonding . 21 as trends towards using self - etching primers increase in the field of orthodontics , it is important to evaluate the bond strengths of color - change adhesives when used in conjunction with a self - etching primer . the introduction of new materials that are capable of helping clinicians to achieve better results has always been intriguing . the addition of color - changing adhesives to orthodontic bonding is very promising , and therefore an evaluation of their bond strength is required to gain knowledge of their clinical success . the purpose of this study was to compare the bond strength of two different color - change adhesives formulated for optimal use with metal brackets . the color - change adhesives were compared with a conventional light - cure adhesive while using a self - etching primer . the conditions were tested at 15 minutes , 24 hours , and 1 week in order to investigate longevity . one hundred and eighty extracted bovine incisors ( animal technologies inc , tyler , tx ) were obtained . these incisors were previously mounted in acrylic resin cylinders ( samplkwick fast - cure acrylic resin , buehler ltd , lake bluff , il ) . the roots of the incisors were shortened with a slow - speed diamond saw to facilitate mounting . exposed facial surfaces of the enamel were ground using an ecomet 6 variable speed grinder - polisher ( buehler ltd ) to obtain an appropriate surface area for bonding of the orthodontic brackets . prior to bonding , the teeth were randomly divided into three groups of 60 specimens each . each group represented one of the three light - cured orthodontic bonding adhesives to be tested , ie , transbond plus , grngloo , and transbond xt . transbond plus and grngloo were the color - change light - cured adhesives , while transbond xt was the conventional light - cured adhesive used as a control . each of the three adhesive groups were then further divided into three subgroups of 20 specimens each , for a total of nine subgroups . the subgroups represented the three different time points to be tested , ie , 15 minutes , 24 hours , and 1 week . prior to bonding , the primer used was transbond plus self - etching primer ( 3 m unitek ) . the manufacturer s instructions were followed to ensure proper use of the self - etching primer . the tip of the applicator was dipped into the mixture and rubbed onto each tooth for 5 seconds while applying some pressure . a gentle air burst for 12 seconds the applicator was redipped into the reservoir to saturate the tip prior to rubbing it onto the next specimen . the orthodontic adhesive being tested was placed on the bracket base ( 3 m unitek victory series low profile 0.022 mandibular incisor brackets ) . the bracket was then seated and positioned on the bovine teeth , after which excess adhesive was removed using a scaler . the adhesive was then light - cured for 5 seconds on each side of the bracket base ( mesial , distal , incisal , gingival ) for a total of 20 seconds per tooth . all specimens were then tested under shear load using a universal instron testing machine ( model 4454 ; instron corporation , canton , ma ) at a crosshead rate of 1.0 mm / minute . the subgroups that were to be debonded at 24 hours and at 1 week were placed in containers with distilled water and stored at 37c to simulate the oral environment prior to testing . the data were analyzed using two - way analysis of variance and with fisher s protected least - significant difference multiple comparisons test at the 0.05 level of significance . after debonding , each specimen was evaluated for its adhesive remnant index ( ari ) . the ari was developed by artun and bergland22 in 1984 as a four - point scale to assess the amount of adhesive remaining on the tooth surface after debonding . an ari of 0 signifies 0% of adhesive remaining on the tooth , ari 1 signifies 50% of adhesive remaining on the tooth , ari 2 signifies > 50% of adhesive remaining on the tooth , and ari 3 signifies 100% of adhesive remaining on the tooth with a distinct impression of the bracket mesh pad . sixty teeth were bonded using each orthodontic bonding adhesive for a total sample size of 180 teeth . each adhesive group was subdivided into three groups to test three debonding times of 15 minutes , 24 hours , and 1 week . transbond plus at 1 week had the highest mean shear bond strength at 14.7 mpa , grngloo tested at 24 hours had the lowest mean shear bond strength of 11.3 mpa , and the mean shear bond strengths for the remaining seven groups had a range of 12.014.5 mpa ( table 1 ) . overall , there were no significant differences in shear bond strength for the main effects of time , ie , 15 minutes , 24 hours , and 1 week ( p = 0.43 , table 2 ) . however , there were significantly different effects in shear bond strength among the adhesives ( p = 0.04 ) . more than 80% of grngloo samples presented with an ari score of 1 at all times . fewer samples from grngloo had ari scores of 2 and 3 , but none presented with a score of 0 . interestingly , both transbond groups had > 50% of samples with ari scores of 3 . twenty - five percent of the transbond xt samples had an ari of score of 0 only at 24 hours , which may indicate potential enamel damage at the time of debonding ( table 3 ) . since the development of direct orthodontic bonding , various new developments have been made to help improve the technique . these developments have focused on improving bond strength , decreasing bonding time , reducing the number of bonding steps , and decreasing adhesive remnants . all these advances have worked towards creating the most efficient bonding protocol while maintaining enamel health during treatment and after debonding . as newer and more efficient products are marketed , we must also evaluate their interactions with other orthodontic products available to practitioners , as well as their effects on enamel . this study compared shear bond strengths of two color - change adhesives ( transbond plus and grngloo ) with a conventional light - cured adhesive ( transbond xt ) when using a self - etching primer ( transbond plus self - etching primer ) . the shear bond strengths were measured at 15 minutes , at 24 hours , and at 1 week after bonding . , these three time periods were specifically included to compare the immediate , 24-hour , and slightly longer follow - up stages . previous research has compared the bonding characteristics and strengths of human enamel and bovine enamel . the results of these studies have indicated similar physical properties , composition , and bond strength between human and bovine enamel . it has been concluded that bovine enamel is an adequate substitute for human enamel.2326 therefore , it was decided to use bovine enamel in this study . it is important to note that the bond strengths of all the adhesives after bonding with transbond plus self - etching primer ranged from 11.3 mpa to 14.7 mpa . these values were higher than the 68 mpa previously reported as an adequate bond strength for routine orthodontic treatment.27 higher bond strengths can mean a greater risk of enamel fracture upon debonding . of the three adhesives tested , this difference in mean shear bond strength may be attributed to differences in material composition . transbond xt mostly contains silane - treated quartz particles , with smaller amounts of bisphenol , a diglycidyl ether dimethacrylate ( bisgma ) and bisphenol - a bis ( 2-hydroxyethyl ether ) dimethacrylate . transbond plus has similar ingredients , including silane - treated quartz and bisgma , although to a smaller extent . half of the filler content of transbond plus is glass - reacted with hydrolyzed silane . grngloo , on the other hand , is made of inert fillers and pigments , with very small additions of glycidyl methacrylate and phenylbis ( 2,4,6-trimethylbenzoyl)-phenylphosphine oxide . therefore , the similarity in shear bond strength of transbond xt and transbond plus over time may be explained by the similar components of these materials . in orthodontics , the location of bond failure is significant because an effort is made to maintain a sound and intact enamel surface posttreatment . thus , in order to minimize the risk of enamel fracture , it is more desirable for bond failure to occur at the bracket  adhesive interface or within the adhesive than at the adhesive  enamel junction . however , a smaller adhesive remnant can mean less chair time for removal of the adhesive remaining after debonding . the ideal bonding system would leave a healthy enamel surface without large amounts of adhesive to remove . when evaluating the ari scores of the three adhesives , grngloo bonded with self - etching primer demonstrated a similar trend for all three time periods . less than 50% of the remnant adhesive was observed on the tooth surface in > 80% of the samples . this may be because of the ideal property of the material as there was no indication of potential enamel fracture . transbond xt , transbond plus , and grngloo all had higher shear bond strengths than necessary for routine orthodontic treatment when used in combination with transbond plus self - etching primer . their results indicated no significant difference in mean shear bond strength between the transbond plus and grngloo adhesives . furthermore , according to our results , their mean shear bond strength values are also very close to each other , and are well above the suggested range of shear strength in orthodontics . the main difference between these adhesives is the color - change characteristics of transbond plus and grngloo . both color - change adhesives facilitate excess adhesive removal at bonding and decrease the risk of enamel decalcification and white spot lesions . however , grngloo also has the ability to return to its initial green color after debonding when exposed to cooler temperatures . these properties can help clinicians delineate what areas are adhesive remnants needing removal and what areas are enamel . shear bonding tests involve numerous variables and are technique - sensitive , so the same bonding study can have varying results under different experimental conditions or when performed by different operators . an in vitro bonding environment factors such as saliva contamination and the patient s enamel composition can cause the same bonding study to yield different results when performed intraorally . it may be of interest to test the color - change adhesives further by bonding them directly to the enamel surface ( without a metal bracket ) . in this way , bond strength at the enamel  adhesive interface can be evaluated without the added variable of the bracket  adhesive interface . time had no significant interaction in this comparison of mean shear bond strength for transbond xt , grngloo , and transbond plus adhesives . although there was a significant difference in the mean shear bond strength for the three groups , all three adhesives demonstrated adequate bond strength to withstand orthodontic forces throughout the experiment .
backgroundthe purpose of this study was to compare the shear bond strengths of two color - change adhesives with a commonly used conventional light - cure adhesive while using a self - etching primer , and to compare any changes in shear bond strengths over time.methodsone hundred and eighty extracted bovine incisors were randomly divided into nine groups of 20 teeth each . 
 the teeth were prepared with a self - etching primer ( transbond plus ) metal lower incisor brackets were bonded directly to each tooth with two different color - change adhesives ( transbondplus and grngloo ) and a control ( transbond xt ) . 
 the teeth were debonded at three different time points ( 15 minutes , 24 hours , 1 week ) using an instron at 1.0 mm / min . 
 the teeth that were to be debonded at 24 hours and 1 week were stored in distilled water at 37c to simulate the oral environment . 
 the data were analyzed by two - way analysis of variance and with fisher s protected least - significant difference multiple comparisons test at the p < 0.05 level of significance . 
 adhesive remnant index ( ari ) scores were calculated for each debonded tooth.resultstransbond plus at 1 week had the highest mean shear bond strength ( 14.7 mpa ) . 
 grngloo tested at 24 hours had the lowest mean shear bond strength ( 11.3 mpa ) . 
 the mean shear bond strengths for the remaining seven groups had a range of 1214.5 mpa . 
 grngloo had > 80% samples presenting with an ari score of 1 at all times . 
 interestingly , both transbond groups had ari scores of 3 in more than 50% of their samples.conclusiontime had no significant effect on the mean shear bond strength of transbond xt , grngloo , or transbond plus adhesive .