Effect of a self-etch primer/adhesive on the shear bond strength of orthodontic brackets.

Conventional adhesive systems use 3 different agents (an enamel conditioner, a primer solution, and an adhesive resin) during the bonding of orthodontic brackets to enamel. A unique characteristic of some new bonding systems in operative dentistry is that they combine the conditioning and priming agents into a single product. Combining conditioning and priming saves time and should be more cost-effective to the clinician and, indirectly, to the patient. The purpose of this study was to determine the effects of the use of a self-etch primer on the shear bond strength of orthodontic brackets and on the bracket/adhesive failure mode. Brackets were bonded to extracted human teeth according to 1 of 2 protocols. In the control group, teeth were etched with 37% phosphoric acid. After the sealant was applied, the brackets were bonded with Transbond XT (3M Unitek, Monrovia, Calif) and light cured for 20 seconds. In the experimental group, a self-etch acidic primer (ESPE Dental AG, Seefeld, Germany) was placed on the enamel for 15 seconds and gently evaporated with air, as suggested by the manufacturer. The brackets were then bonded with Transbond XT as in the first group. The present in vitro findings indicate that the use of a self-etch primer to bond orthodontic brackets to the enamel surface resulted in a significantly (P = .004) lower, but clinically acceptable, shear bond force (mean, 7.1 +/- 4.4 MPa) as compared with the control group (mean, 10.4 +/- 2.8 MPa). The comparison of the adhesive remnant index scores indicated that there was significantly (P = .006) more residual adhesive remaining on the teeth that were treated with the new self-etch primer than on those teeth that were bonded with the use of the conventional adhesive system.

Evaluation of nonrinse conditioning solution and a compomer as an alternative method of bonding orthodontic bracket.

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 are an aim of current research. The purpose of this study was to compare the effects of using two enamel conditioners and adhesives on the shear bond strength and bracket failure location. Forty freshly extracted human molars were pumiced and randomly divided into two groups of 20 teeth. Metal orthodontic brackets were bonded to the enamel surface by one of two protocols: 37% phosphoric acid with a composite adhesive (Transbond XT) or a nonrinse conditioner with a compomer adhesive (Dyract flow). The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 24 hours. A Zwick Universal Testing Machine was used to determine shear bond strengths in MegaPascals. The residual adhesive on the enamel surface was evaluated using the Adhesive Remnant Index. Student t-test and chi2-test were used to compare the two groups. Significance was predetermined at P < or = .05. The results of the t-tests indicated that there were significant differences between the two adhesive systems (t = 11.18 and P = .001) with the nonrinse conditioner/compomer system having lower shear bond strength (X = 1.7 +/- 0.9 MPa) than the phosphoric acid/composite adhesive (X = 10.4 +/- 2.8 MPa). The results of the Chi Square test evaluating the residual adhesives on the enamel surfaces also revealed significant differences between the two groups (chi2 = 7.62, P = .022). In conclusion, a nonrinse conditioner used with a compomer adhesive had significantly lower shear bond strength than a phosphoric acid/composite adhesive system.

Effect of using a new cyanoacrylate adhesive on the shear bond strength of orthodontic brackets.

During bonding of orthodontic brackets to enamel, conventional adhesive systems use three different agents: an enamel conditioner, a primer solution, and an adhesive resin. A unique characteristic of some new bonding systems is that they need neither a priming agent nor a curing light to bond brackets. Such an approach should be more cost-effective for the clinician and indirectly also for the patient. The purpose of this study was to determine the effects of using a cyanoacrylate adhesive on the shear bond strength of orthodontic brackets and on the bracket/adhesive failure mode. The brackets were bonded to extracted human teeth according to one of two protocols. Group 1: Teeth were etched with 37% phosphoric acid. After applying the primer, the brackets were bonded with Transbond XT (3M Unitek, Monrovia, Calif) and were light-cured for 20 seconds. Group 2: Teeth were etched with 35% phosphoric acid. The brackets were then bonded with Smartbond (Gestenco International, Göthenburg, Sweden). The present in vitro findings indicated that the use of the cyanoacrylate adhesive to bond orthodontic brackets to the enamel surface did not result in a significantly different (P = .24) shear bond force (mean = 5.8 +/- 2.4 MPa) as compared to the control group (mean = 5.2 +/- 2.9 MPa). The comparison of the Adhesive Remnant Index scores indicated that there was significantly (P = .006) less residual adhesive remaining on the tooth with the cyanoacrylate than on the tooth with the conventional adhesive system. In conclusion, the new adhesive has the potential to be used to bond orthodontic brackets while reducing the total bonding time.

Effect of altering the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer adhesive.

The purpose of this study was to determine the effects of changing the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer within half an hour after bonding the bracket to the tooth. 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 4 groups according to the enamel conditioner/etchant and adhesive used: group I, teeth were conditioned with 10% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group II, teeth were conditioned with 20% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group III, teeth were etched with 37% phosphoric acid and the brackets were bonded with a resin-reinforced glass ionomer adhesive; group IV, teeth were etched with 37% phosphoric acid and the brackets were bonded with a composite adhesive. The results of the analysis of variance comparing the 4 experimental groups (F = 24.87) indicated the presence of significant differences between the groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups etched with 37% phosphoric acid. This was true for both the resin-reinforced glass ionomer (X = 6.1 +/- 2.7 MPa) and the composite (X = 5.2 +/- 2.9 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the two groups conditioned with polyacrylic acid. The bond strength of the resin-reinforced glass ionomer adhesive conditioned with 10% polyacrylic acid (X = 0.4 +/- 1.0 MPa) was significantly lower than the group conditioned with 20% polyacrylic acid (&xmacr; = 3.3 +/- 2.6 MPa). The present findings indicated that the bond strength of the resin-reinforced glass ionomer adhesive can be significantly increased in the initial half hour after bonding if the enamel is etched with 37% phosphoric acid instead of being conditioned with either 10% or 20% polyacrylic acid. The clinician needs to take these properties into consideration when ligating the initial archwires.

Effect of changing enamel conditioner concentration on the shear bond strength of a resin-modified glass ionomer adhesive.

The purpose of this study was to determine the effects on shear bond strength of changing the concentration of the enamel conditioner used with resin-reinforced glass ionomer. Shear bond strength was measured within 30 minutes after bonding. Forty-six freshly extracted human molars were collected and stored in a solution of 0. 1% (weight/volume) thymol. The teeth were cleaned and polished, then randomly separated into 2 groups. In group I, enamel was conditioned with a 10% polyacrylic acid solution before bonding. In group II, the enamel was conditioned with a 20% polyacrylic acid solution. The results of t test comparisons of the 2 experimental groups (t = 4.9) indicate significant differences (P =.001). Shear bond strength was significantly greater in the group conditioned with the 20% polyacrylic acid concentration (X = 3.3 +/- 2.6 MPa) than in the group conditioned with the 10% concentration (X = 0.4 +/- 1.0 MPa). The present findings indicated that the lower initial shear bond strength of resin-reinforced glass ionomer adhesive can be improved more than 8-fold when the concentration of the polyacrylic acid enamel conditioner is increased from 10% to 20%. The clinician needs to take these properties into consideration when ligating the initial archwires.

Comparisons of two approaches for removing excess adhesive during the bonding procedure.

The purpose of this study was to compare the effects on shear bond strength of removing excess adhesive from around the bracket base at 2 time periods: (1) immediately after placing the bracket on the tooth, and (2) after subjecting the adhesive to 5 seconds of light curing to initially secure the bracket in its proper position. The debonding forces were evaluated at 2 times; within half an hour after bonding and after storing for 24 hours in water at 37 degrees qC. These comparisons will help determine the most advantageous time for the clinician to remove excess adhesive from around the brackets during the bonding process. The teeth were randomly divided into 4 groups according to: (a) the time of removal of the excess adhesive from around the bracket base namely; immediately after placing the bracket or after 5 seconds of light cure and (b) the time of debonding the brackets, namely within half an hour or after 24 hours. Shear bond strength was measured using a Zwick test machine and calculated in Megapascals. The results of the analysis of variance (F = 35.05) comparing the 4 experimental groups indicated the presence of significant differences between all 4 groups (P = .0001). In general, the shear bond strengths were significantly larger for the 2 groups debonded after 24 hours, whether they were light cured for a total of 40 seconds (X = 8.8 +/- 3.6 MPa) or 45 seconds (X = 6.9 +/- 3.4 MPa). On the other hand, the shear bond strengths was significantly lower in the 2 groups debonded within half an hour from their initial bonding, whether light cured for 40 seconds (X = 0.4 +/- 1.0 MPa) or 45 seconds (X = 3.4 +/- 2.7 MPa). In conclusion, the additional 5 seconds of light cure significantly increased the initial shear bond strength. On the other hand, removing excess adhesive after 5 seconds of light cure significantly decreased the shear bond strength at 24 hours.

Effect of light-cure time on the initial shear bond strength of a glass-ionomer adhesive.

With the introduction of photosensitive (light-cured) restorative materials in dentistry, various methods were suggested to enhance the polymerization of these materials including layering and the use of more powerful light-curing devices. The purpose of this study was to determine the effects of increasing the light-cure time on the initial shear bond strength (in the first half hour) of a resin-modified glass-ionomer adhesive. Eighty-six teeth were divided into 4 groups according to either; (1) the adhesive system used, namely resin, reinforced glass ionomer, or composite, and (2) the light-cure time for the glass ionomer adhesive, namely 40, 45, and 50 seconds. The bonding approach followed the manufacturer's instructions unless otherwise specified. The results of the analysis of variance comparing the 4 experimental groups (F = 19.4) indicated the presence of significant differences between the groups (P =. 0001). In general, the shear bond strength was greater for the composite adhesive system (¿x(-) = 5.2 +/- 2.9 MPa), followed by the 2 groups bonded with the resin-reinforced glass-ionomer adhesive and light cured for 50 seconds (¿x(-) = 3.8 +/- 1.1 MPa) and 45 seconds (¿x(-) = 3.4 +/- 2.7 MPa). On the other hand, the shear bond strength was significantly lower for the group bonded with the glass ionomer adhesive and light cured for 40 seconds only (¿x(-) = 0.4 +/- 1.0 MPa). The present findings indicated the following: (1) the resin-reinforced glass-ionomer adhesive has a significantly lower shear bond strength in the first half hour after bonding when compared to a composite resin adhesive; (2) the initial bond strength of the glass-ionomer adhesive was significantly increased by increasing the light-cure time for an additional 5 to 10 seconds; (3) the mean increase in the shear bond strength between 5 and 10 seconds of additional light curing was not significant but the variability was less with the longer cure time.

The effect of repeated bonding on the shear bond strength of a composite resin orthodontic adhesive.

One of the problems clinicians face during treatment is bracket failure. This is usually the result either of the patient's accidentally applying inappropriate forces to the bracket or of a poor bonding technique. As a result, a significant number of teeth have to be rebonded in a busy orthodontic practice. The purpose of this study was to evaluate the effect of repeated bonding on the shear bond strength of orthodontic brackets. Fifteen freshly extracted human molars were collected and stored in a solution of 0.1% (wt/vol) thymol. The teeth were cleaned, polished, and etched with a 37% phosphoric acid gel. The brackets were bonded with the adhesive and light cured for 20 seconds. The teeth were sequentially bonded and debonded 3 times with the same composite orthodontic adhesive. At each time, all 15 teeth were debonded within a half hour after bonding to simulate the clinical condition at which a newly bonded bracket is attached to the arch wire. The results of the analysis of variance comparing the shear bond strength at the 3 debonding attempts indicated the presence of no significant differences among the 3 groups (P = .104). However, when the overall change in shear bond strength within each tooth was evaluated between debonding sequences 1 and 3, 10 teeth had a significant (P = .001) decrease (mean +/- SD, -4.6+/-2.5 MPa) in bond strength, whereas 5 teeth had a significant (P = .02) increase (mean +/- SD, 2.8+/-1.6 MPa). The present findings indicated that in general, the highest values for shear bond strength were obtained after the initial bonding. Rebonded teeth have significantly lower and inconsistent shear bond strength; ie, bond strength may further decrease or increase after the second debonding, and the changes in bond strength may be related to the changes in the morphologic characteristics of the etched enamel surface as a result of the presence of adhesive remnants.

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.