Influence of different methods of cleaning custom bases on the shear bond strength of indirectly bonded brackets

Physical and chemical mechanisms involved in adhesion of orthodontic bonding composites: in vitro evaluations

Background

Bond strength of orthodontic composite is strongly influenced by molecular and structural mechanisms. Aim of this in vitro study was to compare bond strength of light-cure orthodontic composites by measuring debonding forces and evaluating locations of bond failure. Investigations on chemical compositions clarified adhesive behaviors and abilities, exploring effects of ageing processes in this junction materials.

Methods

Twelve enamel discs, from human premolars, were randomly coupled to one orthodontic adhesive system (Transbond XT™ 3 M UNITEK, USA, Light-Cure Orthodontic Paste, LEONE, Italy and Bisco Ortho Bracket Paste LC, BISCO, Illinois) and underwent to Shear Bond Strength test. Metallic brackets were bonded to twenty-seven human premolar, with one of the adhesive systems, to quantify, at FE-SEM magnifications, after debonding, the residual material on enamel and bracket base surfaces. Raman Spectroscopy analysis was performed on eight discs of each composites to investigate on chemical compositions, before and after accelerated aging procedures in human saliva and sugary drink.

Results

Orthodontic adhesive systems showed similar strength of adhesion to enamel. The breakage of adhesive-adherent bond occurs in TXT at enamel-adhesive interface while in Bisco and Leone at adhesive-bracket interface. Accelerated in vitro aging demonstrated good physical–chemical stability for all composites, Bisco only, was weakly contaminated with respect to the other materials.

Conclusion

A similar, clinically adequate and acceptable bond strength to enamel for debonding maneuvers was recorded in all orthodontic adhesive systems under examination. No significant chemical alterations are recorded, even in highly critical situations, not altering the initial mechanical properties of materials.

Evaluation of the effects of two different indirect bonding methods on strength of the brackets in mandibular model of severe anterior crowding

An indirect bonding method was developed to solve the problems likely to be encountered during proper positioning of the brackets. The aim of this study is to compare two different indirect bonding methods on the bond strength of the brackets. A 160 extracted human lower incisors were assigned into two groups. Transparent silicone material and bioplast material were used in transfer tray preparation in groups 1 and 2, respectively. Transbond XT adhesive system was used to bond brackets to teeth in both groups. A high intensity LED light source was used for 3 s for adhesive polymerization. Brackets were subjected to shear forces with universal test machine under 0.5 mm/min crosshead speed until failure. Adhesive Remnant Index was used to assess the amount of adhesive remnant on enamel surface after shear test under 10× magnification. Two subjects from both groups were evaluated for enamel surface characteristics with scanning electron microscope (SEM). Mean shear bond strengths were found to be 5.13 ± 1.8 MPa and 5.93 ± 2.19 MPa for silicone and bioplast groups, respectively. Bioplast group showed significantly greater shear bond strength than that of the silicone group. Maximum ARI score, assessed under ×10 magnification was 3 in both groups. A score of 3 was significantly more frequent in bioplast group. Differences were seen between the groups in terms of enamel surface characteristics under SEM evaluation. It was determined that bioplast material, which is considered to be the gold standard for the indirect bonding method, has greater shear bond strength than silicone material.

Indirect Bonding Revisited

In recent years, the popularity of indirect bonding increased due to advantages such as reduction of chair time and enhancement of patient comfort. Although the indirect bonding technique has improved over the years, the literature has shown different techniques of bracket placement; furthermore, new materials were specially developed for this technique. The aim of this article is to provide a review of the literature, advantages, disadvantages, and laboratory and clinical stages of the indirect bonding technique.