Marc E. Olsen

Evaluation of a new light-cured orthodontic bonding adhesive

The purpose of this study was to compare a new light-cured bonding system that used a hybrid adhesive containing a resin reinforced glass ionomer (Fuji Ortho LC, GC America, Inc.) with a more traditional light-cured bonding system (Transbond, 3M Unitek) that contained resin material only. Seventy-five recently extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were randomly separated into five groups of 15 molars each: Group I--using Transbond adhesive system with the enamel etched and dried before bonding. Group II--using Fuji Ortho LC (FOLC) adhesive system with no etch and the enamel wet with water before bonding. Group III--using FOLC adhesive system with the enamel etched and wet with water before bonding. Group IV--using FOLC adhesive system with no etch and the enamel wet with saliva before bonding. Group V--using FOLC adhesive system with the enamel etched and wet with saliva before bonding. The shear bond strength was performed after thermal cycling between 5 degrees +/- 2 degrees C and 50 degrees +/- 2 degrees C for a total of 2000 cycles with the Zwick test machine (Zwick Gm bH & Co.). After debonding, the teeth and brackets were examined under x10 magnification to evaluate the site of bond failure and the presence of residual adhesive. The analysis of variance was used to determine whether significant differences existed between the various groups. The findings indicated that there were no statistically significant differences among the three experimental groups I, III, and V that had the enamel surface etched before bonding, regardless of the adhesive used or the enamel surface contamination with water or saliva. On the other hand, the two experimental groups that did not have the enamel etched before bonding (II and IV) had significantly lower bond strengths. In conclusion, etching the enamel surface is a critical variable that affects shear bond strength as well as bond failure location when using the new adhesive system.

Effect of time on the shear bond strength of glass ionomer and composite orthodontic adhesives

The purpose of this study was to compare the effects of time on the shear bond strength of a resin-reinforced glass ionomer and a composite adhesive system specifically (1) within half an hour after bonding the bracket to the tooth and (2) at least 24 hours from the time of bonding when the adhesive has achieved most of its bond strength. Ninety-one freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into four groups: Group I, glass ionomer adhesive debonded within 30 minutes from initial bonding; Group II, glass ionomer adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; Group III, composite adhesive debonded within 30 minutes from initial bonding; Group IV, composite adhesive debonded after 24 hours immersion in deionized water at 37 degrees C. The results of the analysis of variance comparing the 4 experimental groups (F = 59. 3) indicated the presence of significant differences between the 4 groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups debonded after 24 hours. This was true for both the resin-modified glass ionomer (x = 8.8 +/- 3.6 MPa) and the composite (x = 10.4 +/- 2.8 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the 2 groups debonded within 30 minutes of their initial bonding. The bond strength of the resin-modified glass ionomer adhesive (x = 0.4 +/- 1.0 MPa) was significantly lower than that for the composite (x = 5.2 +/- 2.9 MPa) adhesive. The present findings indicated that the resin reinforced glass ionomer adhesive has a significantly lower initial bond strength but increased more than 20-fold within 24 hours. In comparison, the composite adhesive has a significantly larger initial bond strength that doubled within 24 hours. The clinician needs to take these properties into consideration when ligating the initial arch wires.

EVALUATION OF SCOTCHBOND MULTIPURPOSE AND MALEIC ACID AS ALTERNATIVE METHODS OF BONDING ORTHODONTIC BRACKETS

Damage to the enamel surface during bonding and debonding of orthodontic brackets is a clinical concern. Alternative bonding methods that minimize enamel surface damage while maintaining a clinically useful bond strength is an aim of current research. The purpose of this study was to compare the effects on bond strength and bracket failure location of two adhesives (System 1+ and Scotchbond Multipurpose, 3M Dental Products Division) and two enamel conditioners (37% phosphoric acid and 10% maleic acid). Forty-eight freshly extracted human premolars were pumiced and divided into four groups of 12 teeth, and metal orthodontic brackets were attached to the enamel surface by one of four protocols: (1) System 1+ and phosphoric acid, (2) Scotchbond and phosphoric acid, (3) System 1+ and maleic acid, and (4) Scotchbond and maleic acid. After bracket attachment, the teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 72 hours. A Zwick universal testing machine (Zwick GmbH & Co.) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The analysis of variance was used to compare the four groups. Significance was predetermined at p < or = 0.05. The results indicated that there were no significant differences in bond strength among the four groups (p = 0.386). The results of the Chi square test, evaluating the residual adhesives on the enamel surfaces, revealed significant differences among the four groups (mean 2 = 0.005). A Duncan multiple range test revealed the difference occurred between the phosphoric acid and maleic acid groups, with maleic acid having bond failures at the enamel-adhesive interface. In conclusion, the use of Scotchbond Multipurpose and/or maleic acid does not significantly effect bond strength, however, the use of maleic acid resulted in an unfavorable bond failure location.

Comparison of shear bond strength and surface structure between conventional acid etching and air-abrasion of human enamel.

Recently, air-abrasion technology has been examined for potential applications within dentistry, including the field of orthodontics. The purpose of this study was to compare the traditional acid-etch technique with an air-abrasion surface preparation technique, with two different sizes of abrading particles. The following parameters were evaluated: (a) shear bond strength, (b) bond failure location, and (c) enamel surface preparation, as viewed through a scanning electron microscope. Sixty extracted human third molars were pumiced and divided into three groups of 20. The first group was etched with a 37% phosphoric acid gel for 30 seconds, rinsed for 30 seconds, and dried for 20 seconds. The second and third groups were air-abraded with (a) a 50 microm particle and (b) a 90 microm particle of aluminum oxide, with the Micro-etcher microabrasion machine (Danville Engineering Inc.). All three groups had molar stainless steel orthodontic brackets bonded to the buccal surface of each tooth with Transbond XT bonding system (3M Unitek). A Zwick Universal Testing Machine (Calitek Corp.) was used to determine shear bond strengths. The analysis of variance was used to compare the three groups. The Adhesive Remnant Index (ARI) was used to evaluate the residual adhesive on the enamel after bracket removal. The chi square test was used to evaluate differences in the ARI scores among the groups. The significance for all tests was predetermined at p < or = 0.05. The results indicated that there was a significant difference in shear bond strength among the three groups (p = 0.0001). The Duncan Multiple Range test showed a significant decrease in shear bond strength in the air-abraded groups. The chi square test revealed significant differences among the ARI scores of the acid-etched group and the air-abraded groups (chi(2) = 0.0001), indicating no adhesive remained on the enamel surface after debonding when air-abrasion was used. In conclusion, the current findings indicate that enamel surface preparation using air-abrasion results in a significant lower bond strength and should not be advocated for routine clinical use as an enamel conditioner at this time.

EVALUATION OF DEBONDING CHARACTERISTICS OF A NEW COLLAPSIBLE CERAMIC BRACKET

A new collapsible ceramic bracket designed with a metal-lined arch wire slot has been recently introduced. The bracket also incorporates a vertical slot designed to help create a consistent bracket failure mode during debonding. The new bracket is thought to combine the esthetic advantages of ceramics and the functional advantages of debonding metal brackets. The purpose of this study was to compare (1) the shear bond strength of the new collapsible bracket with a traditional ceramic bracket, (2) the compressive force required to debond the new bracket from the enamel surface with that needed to debond a traditional metal bracket, and (3) the bond failure location when debonding the new bracket and a traditional ceramic bracket when pliers are used. Sixty-one Clarity collapsible ceramic brackets, 41 Transcend 6000 brackets, and 21 Victory Series metal brackets were bonded to the teeth with the same bonding system. The Zwick Universal Test Machine was used to determine the shear bond strength of 21 teeth bonded with the new bracket and 20 teeth bonded with the Transcend brackets. The same testing device was used to determine the compression force levels needed to debond 20 collapsible brackets and 21 metal brackets. Pliers were used to debond both the new ceramic brackets and Transcend brackets to determine the mode of bond failure. After debonding, all teeth and brackets were examined under 10x magnification. Any adhesive remaining after bracket removal was assessed according to the Adhesive Remnant Index (ARI). The findings indicated that the shear bond strength of the new Clarity ceramic bracket was comparable to that of a conventional ceramic bracket. Similarly, there were no significant differences in the results of the compression tests comparing the magnitude of forces needed to deform and debond both the new ceramic and metal brackets. The ARI scores for both the shear and compression tests indicated a similar bond failure pattern when the new collapsible brackets were compared with either the conventional ceramic or metal brackets. On the other hand, the chi-square test results indicated that, when debonding pliers were used, there was a significantly greater incidence of an ARI score of 1 with the collapsible brackets. This indicated that, when debonding the new brackets with the Weingart pliers, there was a greater tendency for most of the adhesive to remain on the enamel surface. In conclusion, the main advantage of the Clarity ceramic brackets is that they can be debonded in the same manner as metal brackets. When the new ceramic brackets are debonded with the Weingart pliers, most of the residual adhesive remained on the enamel surface, a pattern that is similar to the one observed with metal brackets. The failure at the bracket-adhesive interface decreases the probability of enamel damage but necessitates the removal of more residual adhesive after debonding.

Effect of varying etching times on the bond strength of ceramic brackets

Damage to the enamel surface when debonding orthodontic ceramic brackets has been a clinical concern. Ideally, bond failure at the bracket-adhesive interface should occur without damaging the enamel surface. The purpose of this study was to determine the shear bond strength and debonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time interval of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid. Ceramic orthodontic brackets were bonded to each etched tooth by using the same orthodontic bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The results of the analysis of variance indicated that there were significant differences in bond strengths between the various etching times (p=0.0001). The Duncan multiple range test revealed that the 5-second and no etch group exhibited significantly lower bond strengths. The results of the Chi square test evaluating the residual adhesives on the enamel surface also revealed significant differences (p=0.0001). However, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p=0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect either bond strength or the site of bond failure.

COMPARISONS OF SHEAR BOND STRENGTH OF PRECOATED AND UNCOATED BRACKETS

In an attempt to save chairside time during bonding, orthodontists are using ceramic and metal brackets that have been precoated with the adhesive material. The adhesive used on the precoated brackets is similar in composition to that used for bonding uncoated brackets; the difference is essentially in the percentages of the various ingredients incorporated in the material. The purpose of this study is to determine whether these changes in composition affect the shear bond strength and the site of bond failure when precoated and uncoated ceramic and metal brackets are used. Eighty-five recently extracted human molars were bonded according to the manufacturers instructions and mounted in phenolic rings. An occlusogingival load was applied to the bracket, producing a shear force at the bracket-tooth interface with a Zwick Universal Test Machine. After debonding, all teeth and brackets were examined under 10x magnification. Any adhesive remaining after bracket removal was assessed with the Adhesive Remnant Index (ARI). The current findings indicated that: (1) Precoated ceramic brackets that used a slightly modified adhesive have similar shear bond strengths as that provided by Transbond XT adhesive on uncoated brackets; (2) precoated metal brackets that used the same adhesive have significantly lower shear bond strength than those obtained with Transbond XT on uncoated brackets. The differences in the bond strength between the ceramic and metal brackets were attributed to the combined effects of the changes in the composition of the adhesives used and in the retention mechanisms incorporated in the bracket bases of the different types of brackets; (3) all bracket/adhesive combinations tested provided clinically acceptable shear bond forces.

Comparison of the debonding characteristics of two innovative ceramic bracket designs

Two new ceramic brackets-one designed with a metal-lined arch wire slot and the other with an epoxy resin base-have been recently introduced. The new brackets are thought to combine the esthetic advantages of ceramics and the functional advantages of debonding metal brackets. The purpose of this study was to compare the following: 1) the shear bond strength of the 2 brackets, and 2) the bond failure location when the brackets are debonded with pliers. Sixty-one Clarity (3M Unitek) collapsible ceramic brackets and 66 MXi (TP Orthodontics, Inc) brackets were bonded to the teeth with the same bonding system. The Zwick Universal Test Machine (Zwick Gm bH & Co) was used to determine the shear bond strength force levels needed to debond the brackets. The appropriate pliers also were used to debond both types of brackets to determine the mode of bond failure that will be encountered clinically. After debonding, all the teeth and brackets were examined with 10x magnification. Any adhesive that remained after the bracket removal was assessed according to the Adhesive Remnant Index. The findings indicated that the shear bond strength of the Clarity ceramic brackets was significantly greater than that of the MXi ceramic brackets. However, both brackets exhibited forces that were adequate for clinical use. The Adhesive Remnant Index scores for both the shear test and the plier debonding indicated a similar bond failure pattern when the 2 ceramic brackets were compared with each other. This suggests that, when these brackets are debonded with the Weingart (Ormco) and ETM (Ormco) pliers, there was a greater tendency for most of the adhesive to remain on the enamel surface. In conclusion, the most efficient method to debond the MXi ceramic bracket is by placing the blades of the ETM 346 pliers between the bracket base and the enamel surface. On the other hand, the most efficient method of debonding the Clarity bracket is by using the Weingart pliers and applying pressure to the tiewings. When the 2 ceramic brackets were debonded as recommended here, most of the residual adhesive remained on the enamel surface, a pattern similar to the one observed previously with metal brackets. The failure at the bracket-adhesive interface decreases the probability of enamel damage but necessitates the removal of more residual adhesive after debonding.

Effect of applying chlorhexidine antibacterial agent on the shear bond strength of orthodontic brackets.

The purpose of this study was to determine whether the application of chlorhexidine as an antibacterial agent affects the shear bond strength and debonding failure modes of orthodontic brackets. Thirty-six recently extracted human premolars were cleaned and randomly assigned to one of three groups: prophylaxis with pumice only prophylaxis using a 13,500 ppm fluoridated pumice, and prophylaxis with pumice followed by application of 0.12% chlorhexidine paste. All teeth were etched with a 37% phosphoric acid gel and metal orthodontic brackets were bonded to each tooth using the same bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 72 hours. A Zwick Universal Testing Machine was used to determine shear bond strengths. The residual adhesive on the enamel surfaces was estimated using the Adhesive Remnant Index. The analysis of variance was used to compare the various groups. Significance was predetermined at P < 0.05. The results indicated that there were no significant differences in bond strengths between the chlorhexidine-, fluoride-, and nonfluoride-treated teeth (P = 0.233). The Chi-Square test evaluating the residual adhesive on the enamel surfaces also showed no significant differences (P = 0.456) between the various groups. In conclusion, the use of chlorhexidine and/or fluoride prophylactic pastes does not significantly affect shear bond strength nor bond failure location of orthodontic brackets.

Bond strength following the application of chlorhexidine on etched enamel.

The purpose of this study was to determine whether the application of chlorhexidine to etched enamel affects the shear bond strength and bracket/adhesive failure modes of orthodontic brackets. Forty recently extracted third molars were cleaned divided into two groups of twenty. The first group was etched with a 37% phosphoric acid gel, and a sealant was applied containing a chlorhexidine varnish. Stainless steel orthodontic brackets were bonded using the Transbond XT bonding system (3M/Unitek). Teeth in the second group were etched and bonded using the same bonding system but without chlorhexidine. A Zwick Universal Testing Machine was used to determine shear bond strengths. There were no significant differences in bond strengths between the chlorhexidine treated teeth (= 11.8 +/- 2.1 MPa) and the controls (= 12.4 +/- 3.1 MPa) (p = 0.129). The Chi Square test evaluating the residual adhesive on the enamel surfaces showed no significant differences (P = 0.136) between the two groups evaluated. The use of a primer containing chlorhexidine does not significantly affect shear bond strength nor the fracture site (bond failure location).