INTRODUCTION

The established procedure for bonding brackets to enamel with composite resin requires a series of preparatory steps. First, the surface of the enamel is polished with a glycerin-free polishing paste before being etched with 37% phosphoric acid for 15–30 seconds. Then, the surface of the enamel is rinsed with water and dried until the surface of the enamel appears chalky. A primer is applied to the enamel, and composite resin is applied to the bracket base. Finally, the bracket is positioned on the tooth and cured.

One of the main objectives of research into bonding procedures is to seek ways of reducing chair-side time. To do this, we made an evaluation of these procedures introducing alternative products. The use of polishing pastes to clean the enamel surface before acid etching does not influence bond strength.1

Research has been carried out into the possible nonuse of primers, but there appears to be some contradiction in the existing literature.2 As an alternative to the traditional acid-etch technique, the use of nonrinse conditioners has been introduced. In a previous study, we observed that one of these products provided a bond strength that could be compared with the strength obtained when using phosphoric acid.3

Recently, the use of self-etching primers has been proposed as a way of providing etching and priming simultaneously. In a previous in vitro study, it was observed that there were no significant differences in bond strength between brackets bonded with conventional techniques and those bonded with self-etching primers.4–7

In a recent in vivo study, it was observed that the use of self-etching primers significantly reduced bracket bonding time in comparison with traditional bonding techniques without generating significant differences between the overall bond failure rates of the two bonding systems over a period of 6–12 months.8

Precoated brackets (APC, 3M Unitek Dental Products, Monrovia, CA) were introduced in 1992.9 They provide a more uniform adhesive thickness and a reduction in the number of bonding procedures.10 The properties of precoated brackets have improved. The recent introduction of the APC Plus system (3M Unitek Dental Products) has provided greater tolerance to humidity than have its predecessors, and the adhesive also releases fluoride.11 The use of self-etching primers together with precoated brackets might provide an important saving of chair-side time by reducing the number of intermediate steps in bracket bonding procedures.

The aim of this study was to compare the shear bond strength and adhesive remnant on the tooth after debonding for APC Plus precoated brackets and uncoated brackets bonded with Transbond XT adhesive resin (3M Unitek Dental Products) using the self-etching primer Transbond Plus Self-Etching Primer (TPSEP) (3M Unitek Dental Products). Scanning electron microscope (SEM) observations of enamel surfaces treated with TPSEP were also carried out.

MATERIALS AND METHODS

RESULTS

Bond strength values appear in Table 1. The Student's t-test for two independent samples did not detect significant differences between the groups evaluated (P = .12).

Table 1. Shear Bond Strength (MPa)*

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The percentage of area of adhesive remaining on the tooth showed significant differences when using the Mann-Whitney U-test (P = .01) (Table 2). SEM observations of enamel surfaces treated with TPSEP showed a porous and potentially retentive surface (Figure 1).

Table 2. Percentage of Tooth Area Occupied by Adhesive*

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DISCUSSION

To our knowledge, no studies comparing the bond strength of APC Plus and Transbond XT and using TPSEP as a conditioner have been carried out.

The bond strength values achieved by the two groups were higher than those minimum values put forward by Reynolds14 as sufficient for clinically effective bonding. No significant differences were detected between the bond strengths provided by TPSEP/ Transbond XT and TPSEP/APC Plus.

Regarding the percentage of area of adhesive remaining on tooth, TPSEP/APC Plus left significantly less adhesive than did TPSEP/Transbond XT. This implies a reduction in chair-side time spent on adhesive removal after debonding. APC Plus system needs no application because each bracket is coated with the adhesive by the manufacturer, so there is less opportunity for bracket contamination during the bonding procedure; therefore, the adhesion between the adhesive and the bracket is more effective than in the conventional procedure in which the clinician has to apply the adhesive onto the bracket base.

SEM observations of the enamel treated with TPSEP showed a porous and potentially retentive surface. Some studies show that, with unground enamel, the etching pattern provided by self-etching primers is comparable with the pattern produced by phosphoric acid.315

According to our results, the use of TPSEP with APC Plus reduces chair-side time without compromising bond strength. Furthermore, some characteristics of APC Plus could prove highly favorable for clinical use. This new system contains hydrophilic monomers that improve tolerance to humidity in comparison with Transbond XT or other systems that contain mainly BisGMA or other similar hydrophobic monomers.11 In addition, the release of fluoride aimed at preventing decalcification of the enamel adjacent to the brackets is advantageous. In vitro bonding tests are highly important for initial evaluations of adhesive systems. However, in vivo research must be carried out to confirm in vitro results.

CONCLUSIONS

1. The portion of the hypothesis that states there are no significant differences in the shear bond strength between precoated brackets and uncoated brackets bonded with an adhesive resin using a self-etching primer is accepted.

2. The portion of the hypothesis that states there are no significant differences in the percentage of area of adhesive remaining on the tooth between precoated brackets and uncoated brackets bonded with an adhesive resin and a self-etching primer is rejected.