Original article
Bond strength of various bracket base designs

https://doi.org/10.1016/j.ajodo.2003.01.003Get rights and content

Abstract

To determine the influence of various bracket base designs on bond strength and debond interface, 6 types of metal interlock brackets of different sizes and with different base designs were evaluated. The bracket base types and mesh sizes tested were as follows: retention groove base (Dynalock, Unitek, Monrovia, Calif), circular concave base (Accuarch appliance Formula-R, Tomy, Tokyo, Japan), double mesh with 5.1 × 10−2 mm2 mesh size (Ultratrimm, Dentaurum, Ispringen, Germany), double mesh, 3.1 × 10−2 mm2 (Minidiagonali Roth, Leone, Florence, Italy), double mesh, 3.1 × 10−2 mm2 (Tip-edge Rx-I, TP Orthodontics, LaPorte Ind), and double mesh, 2.9 × 10−2 mm2 (Mini Diamond, Ormco, Glendora, Calif). The Unitek bracket is cast in 1 piece; the other brackets are welded together. Brackets were bonded to human teeth and then debonded on a testing machine. The debond interface was recorded and analyzed with scanning electron microscopy and energy-dispersive x-ray spectrometry, and the distribution of interfaces was determined. The ranking of bond strength of individual bases (kg/base) from highest to lowest was Tomy, Dentaurum, Unitek, Leone, TP Orthodontics, and Ormco. The ranking of bonding strength per area squared MPa from highest to lowest was Tomy, Dentaurum, Leone, Unitek, TP Orthodontics, and Ormco. Debond in interfaces occurred between the bracket and resin, within the resin, or between the resin and enamel. The most debonded interfaces were between the bracket and resin and between the resin and enamel. The Tomy bracket, with its circular concave base, produced greater bond strength than did the mesh-based brackets; among the mesh-based brackets, Dentaurum, with the larger mesh size, produced greater bond strength than the brackets with smaller mesh sizes. The Unitek bracket, with its 1-piece cast base with retention grooves, ranked in the midrange of bond strength.

Section snippets

Material and methods

Six types of direct-bond maxillary premolar metal brackets with mechanical interlocking bases were available in Taiwan market at the time of this study; those brackets were selected for testing. The brackets were evaluated for various design characteristics, including whether the bracket was cast in 1 piece or welded together, base size, base type (retention groove, circular concave, or mesh), and mesh size. The brackets tested were as follows: Dynalock (Unitek, Monrovia, Calif), Accuarch

Results

The overall mean bond strengths were 9.67 ± 1.79, 8.56 ± 2.15, 8.12 ± 1.94, 7.19 ± 1.68, 5.60 ± 1.00, and 3.81 ± 1.17 kg/base for the Tomy, Dentaurum, Unitek, Leone, TP Orthodontics, and Ormco brackets, respectively (Table II). The statistical analysis of bonding strength with 1-way ANOVA gave an F value of 32.65 (ie, a statistically significant difference; P < .05). The Scheffé test was chosen (α = .05) for further analysis and comparison. The F value of 2.29 showed that there were

Discussion

The results of this study indicate that the relative bonding strength for the Tomy bracket was 9.67 kg/base or 9.32 MPa. This bracket has a relatively large base (9.9 mm2) with many circular concavities that allow air to escape so that the composite resin can penetrate into the concave surfaces (Fig, B). This resulted in better retention and relatively less debonding between the bracket and resin (35.3%) than occurred with other bracket base designs.

MacColl et al19 reported that there were no

Conclusions

  • 1.

    The size and design of a bracket base can affect bond strength.

  • 2.

    The Tomy bracket, with a circular concave base design, produced greater bond strength than the Dentaurum, Leone, TP Orthodontics, and Ormco brackets, with their mesh bases.

  • 3.

    Among the brackets with mesh-type bases, the larger the mesh spacing, the greater the bond strength.

  • 4.

    The Unitek 1-piece cast bracket with a horizontal retention groove base produced moderate bond strength.

  • 5.

    Most debonding interfaces are between bracket and resin and

References (20)

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This study was supported by a grant from the National Science Council of the Republic of China (NSC 86-2314-B-016-078).

Submitted, October 2001; revised and accepted, January 2003.

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