Original article
Effect of early orthodontic force on shear bond strength of orthodontic brackets bonded with different adhesive systems

https://doi.org/10.1016/j.ajodo.2008.09.034Get rights and content

Introduction

This study was conducted to evaluate the effect of applying early orthodontic force on the shear bond strength (SBS) of orthodontic brackets bonded with 4 adhesive systems.

Methods

Eighty stainless steel brackets were bonded to the enamel surfaces of extracted premolars with 4 adhesive systems. For each adhesive, 10 brackets were bonded without application of force (groups 1, 3, 5, and 7), and another 10 were subjected to a 120-g force with a coil spring (groups 2, 4, 6, and 8). This force was applied 30 minutes after bonding and maintained for 24 hours. Groups 1 and 2 had Rely-a-bond primer and Rely-a-bond adhesive (Reliance Orthodontic Products, Itasca, Ill). Groups 3 and 4 had Transbond XT primer and Transbond XT adhesive (3M Unitek, Monrovia, Calif). Groups 5 and 6 had Transbond Plus Self Etching Primer and Transbond XT adhesive (3M Unitek). Groups 7 and 8 had RelyX Unicem (3M ESPE, Seefeld, Germany). After thermocycling, SBS testing was performed by using a universal testing machine (Type 500, Lloyd Instruments Ltd, Fareham Hants, UK). The results of SBS testing for all adhesives were analyzed by 2-way analysis of variance and the Duncan test. The unpaired Student t test was used to compare the effect of force on the SBS of each adhesive.

Results

Transbond XT primer and its adhesive had the highest values (without force, 11.2 ± 3.1 MPa; with force, 10.7 ± 2.7 MPa), and RelyX Unicem had the lowest (without force, 5.8 ± 1.5MPa; with force, 5.7 ± 1.6 MPa). Application of force yielded nonsignificant reductions in SBS for all adhesives; this reduction was less pronounced with RelyX Unicem.

Conclusions

For all studied adhesive systems, orthodontic force up to 120 g can be applied within the first hour after bonding with no deleterious effects on bond strength.

Section snippets

Material and methods

Eighty freshly extracted maxillary first premolars were collected, cleaned, and stored in a 0.1% aqueous thymol solution. The teeth selected had no cracks, caries, attrition, or restorations. They were embedded in autopolymerizing acrylic resin (Duracryl, SpofaDental, Prague, Czech Republic) poured in plastic rings with the buccal surface up. The teeth were cleaned and then polished with pumice and rubber cups. A hook made of 0.9-mm stainless steel round wire was fixed in the acrylic toward the

Results

The results of the 2-way ANOVA are given in Table II. Mean SBS values, standard deviations, and the results of the Duncan and t tests for the adhesive systems with and without application of force are shown in Table III. A graphic presentation of these values is shown in Figure 2.

Regarding SBS without application of force, Transbond XT primer and its adhesive system had the highest value (11.2 ± 3.1 MPa), whereas RelyX Unicem showed the lowest value (5.8 ± 1.5MPa). Rely-a-bond primer and its

Discussion

In clinical orthodontic practice, bonding of brackets and placement of the archwires can be done in the same visit, particularly after rebonding of debonded brackets. Hence, force could be applied to the bracket within the first hour after bonding. This force could affect polymerization of the orthodontic adhesive and subsequently its bond strength. The purpose of this study was to determine the development of bond strength of 4 adhesive systems subjected to a force similar to clinical

Conclusions

Regardless of the application of force, the Transbond XT primer and Transbond adhesive system yielded a significantly higher bond strength compared with the other studied systems. RelyX Unicem had the lowest value. Application of orthodontic force 30 minutes after bonding for 24 hours gave a nonsignificant reduction in SBS for all studied adhesive systems. However, the effect of such a force was less noticeable with RelyX Unicem. Therefore, orthodontic forces up to 120 g can be applied within

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    The authors report no commercial, proprietary, or financial interest in the products or companies described in this article.

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