INTRODUCTION

Direct bonding of orthodontic brackets has resulted in an improved oral environment1–8 by enhancing the ability for plaque removal by the patient, minimizing soft tissue irritation and hyperplastic gingivitis,5–9 and eliminating the need for separation. In addition, direct bonding benefits include the absence of posttreatment band spaces, facilitated application of attachments to partially erupted teeth, minimized danger of decalcification with loose bands,910 easier detection and treatment of caries, as well as providing the patient with a more esthetic orthodontic appliance.2

Bounocore¹¹introduced the acid-etched technique in 1955 by bonding acrylic resin to the enamel surface pretreated with 85% phosphoric acid for 60 seconds.11 Since this initial report, various investigators have evaluated the technique to determine the factors that might affect the strength of the mechanical bond including the type of enamel conditioner,11–14 acid concentration,15–21 and length of etching time.1921–24

Phosphoric acid has remained the primary etchant since its initial introduction by Bounocore. Studies indicated that a phosphoric acid concentration of between 30% to 40% results in the most retentive etching pattern.1617 For most current clinical phosphoric acid applications, a 37% acid concentration is used.

Orthodontists use the acid-etch bonding technique as a primary means of attaching brackets to the enamel surface. Maintaining a sound unblemished enamel surface is a primary clinical concern when debonding the brackets after orthodontic treatment. Enamel fracture and cracks have been reported at the time of bracket debonding.2 It is possible that the depth of the etched enamel surface created by phosphoric acid may be a contributing factor to the incidence of enamel fracture.25–27 Therefore, to minimize the extent of enamel surface damage, alternative conditioners, such as maleic acid, have been used to obtain clinically useful bond strengths by decreasing the depth of enamel dissolution.

With the introduction of the new acid-etch primers that combine both the acid etchant and the primer or adhesive, it became possible for the clinician to both eliminate one of the steps during the bonding procedure and minimize the amount of enamel lost during etching.27

This is because the new acid-etch primers do not penetrate or dissolve the enamel surface to the same depth as conventional systems that use phosphoric acid.27

The acid-etch primer should be light cured during its application. When the bracket with the adhesive is placed on the tooth, the light curing needs to be repeated. It might be of interest to clinicians to determine whether it is possible to apply the curing light only at one time, ie, to cure both the acid-etch primer and the adhesive at the end of the bonding procedure, thereby saving chairside time.

The purpose of this study was to evaluate the effect on the shear bond strength of light curing the self-etch primer and the bracket adhesive in one step.

MATERIALS AND METHODS

RESULTS

The descriptive statistics for the shear bond strengths of the three groups are presented in Table 1. The results of the analysis of variance (F = 1.658) indicated that the shear bond strengths of the three groups were not significantly different (P = .203). The teeth debonded after 24 hours of storage in water at 37°C had a mean shear bond strength of 6.0 ± 3.5 MPa, whereas the group that was debonded within half-;an-;hour after two light exposures had a mean shear bond strength of 5.9 ± 2.7 MPa, and the mean for the group with only one light cure exposure was 4.3 ± 2.6 MPa.

TABLE 1. Descriptive Statistics (in MPa) and Results of the Anal ysis of Variance Comparing the Three Groups Tested^a

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DISCUSSION

The direct bonding of orthodontic brackets has revolutionized and improved the clinical practice of orthodontics. However, the reported incidents of enamel fracture during debonding ceramic brackets has raised concerns regarding the effects of phosphoric acid on enamel.2829

In the process of bonding orthodontic brackets to enamel, most conventional adhesive systems use three different agents: an enamel conditioner, a primer solution, and an adhesive resin. Acid conditioning of enamel with 35–37% phosphoric acid has been the most effective method for enhancing the bonding of adhesive resin composite restorative materials to enamel.17 Acid etching results in microporosities in the enamel surface, into which the adhesive can penetrate to produce micromechanical retention of the restoration and increase the bondable surface area.15–17 In addition to creating microporosities, the conditioner agent removes the organic film from the tooth surface so that a more direct contact is established at the tooth restorative interface.

As a result, there is a need to improve our ability to maintain clinically useful bond strength while minimizing the amount of tooth destruction, whether by fracture or by decalcification. A unique characteristic of some new bonding systems in operative dentistry is that these systems combine the conditioning and priming agents into a single acidic primer solution for simultaneous use on both enamel and dentin.2530 Current data suggest that the new self-etch adhesive systems have comparable bond strength with those of conventional systems, resulting in a strong and predictable bond to the tooth surface. Therefore, the introduction of these new tooth preparation technologies, along with the development of new simplified one-step self-etching adhesive systems, may result in more efficient and conservative ways of achieving predictable bonding to tooth structure.27

Aljuburi et al26 calculated the time it took to bond 30 premolar teeth in the laboratory using conventional bonding as compared with bonding with a self-etch primer. They found that with conventional bonding, the time was 170 seconds, whereas using an acid-etch primer bonding, the time was 111 seconds. The difference of 59 seconds was statistically significant. On the other hand, the cleaning time after debonding was not different between the two approaches.

In the present study, by light curing both the self-etch primer and the adhesive simultaneously, the clinician can potentially achieve an additional 10-second reduction in the bonding time for each tooth. During routine bonding procedures involving 20 teeth, such reduction in working time would amount to at least 200 seconds or 3+ minutes per patient.

CONCLUSIONS

The findings from the present study indicate that light curing the acid-etch primer together with the adhesive after placing the orthodontic bracket did not significantly affect the shear bond strength when compared with light curing the acid-etch primer and the adhesive separately. This approach eliminates one step in the bonding procedure and could potentially save the clinician chairside time.