Notching of orthodontic bonding resin to facilitate ceramic bracket debond--an ex vivo investigation

Current Products and Practice

Due to an increasing demand for superior aesthetics during fixed appliance treatment, the use of aesthetic brackets has grown in popularity over recent years. Although often requested by patients, aesthetic brackets are not without their disadvantages. This article presents the currently available plastic and ceramic brackets and discusses the potential problems associated with each. Recent advances, introduced by manufacturers in an attempt to overcome their clinical disadvantages, are described.

Effects of different debonding techniques on the debonding forces and failure modes of ceramic brackets in simulated clinical set-ups

INTRODUCTION

The objectives of this study were to evaluate the effects of different debonding techniques on the in-vitro mean debonding forces and failure modes of ceramic brackets bonded to enamel with clinically simulated setups.

METHODS

Three kinds of ceramic brackets (Clarity; 3M Unitek, Monrovia, Calif; Inspire and Inspire Ice; Ormco, Orange, Calif) were bonded to extracted premolars with the same bonding system. Thirty ceramic brackets, 10 of each type, were removed by hand; 60 ceramic brackets, 20 of each type, were tested on a universal testing machine with the pliers according to the manufacturers' recommendations. To simulate clinical debonding conditions, specially designed setups were used to debond the ceramic brackets. Debonding forces and failure modes were investigated. Fractographic evaluations were performed by using scanning electron microscopy.

RESULTS

Most brackets failed at the bracket-adhesive interface. Cohesive bracket fractures were noted in all 3 types of ceramic brackets (debonded by hand: 70% of Inspire, 20% of Inspire Ice, and 10% of Clarity; debonded by machine: 75% of Inspire, 30% of Inspire Ice, and 25% of Clarity). The cohesive ceramic fractures of the Clarity brackets were located at the junction between the wings and the body, and at the slot. However, for the Inspire and the Inspire Ice brackets, the cohesive ceramic fractures were located at the occlusal aspect of the base. The mean debonding forces of Inspire, Inspire Ice, and Clarity brackets were 25.72 +/- 11.98, 17.92 +/- 5.03, and 76.89 +/- 23.47 N, respectively. No enamel damage was found after the brackets were removed.

CONCLUSIONS

The results of the failure modes showed that the new designs with a ball reduction band in the Inspire Ice bracket and the vertical debonding slot in the Clarity bracket significantly reduced the risk of ceramic bracket fracture during debonding. The force required to debond the Inspire Ice bracket was significantly lower than that of the Inspire bracket.

An ex vivo study to investigate bond strengths of different tooth types

This study aimed to identify the presence and pattern of differences in ex vivo shear bond strength between tooth types when bonding orthodontic brackets using Right-On, and took the form of a prospective laboratory study of bond strength on different tooth types, at the Newcastle University Dental School Materials Science Laboratory, 1997-1999. Ex vivo bond strength testing was undertaken using the technique described by Fox et al. (BJO 18, 125-130, 1991) on a total of 120 extracted incisor, canine, and premolar teeth of each dental arch. Analysis was by one-way ANOVA with Tukey's pairwise comparisons, and by Weibull Analysis. Shear stress to failure (measured in MPa) was recorded on Instron 5567 universal testing machine. Significant differences in mean bond strength existed between different tooth-type series. Canine (upper 12.3, lower 12.1) and premolar (upper 11.9, lower 10.9) teeth exhibited higher strengths than incisors (upper 6.9, lower 9.0). The results of this study confirm that ex vivo bond strength is not uniform across all teeth.