A Novel Etchant System for Orthodontic Bracket Bonding

Abstract

Orthodontic treatment is widely used to correct irregular teeth and/or jaw discrepancies to improve oral function and facial aesthetics. However, it is frequently associated with enamel damage that include chipping, demineralisation, and white spot formation. So far, current bonding systems that can maintain shear bond strengths (SBS) suitable for clinical performance are unable to limit enamel demineralisation, adhesive remnants and damage caused on removal of brackets after treatment. This study reports a novel “safe enamel etch” clinically viable procedure that was accomplished via application of novel etchant pastes developed with β-tricalcium phosphate and monocalcium phosphate monohydrate powders mixed with citric acid (5 M) or phosphoric acid (37% PA) to yield BCA and BPA etchants respectively. Although enamel etched with clinically used PA gel yielded higher SBS than the BCA/BPA etchants, it exhibited greater adhesive remnants with evidence of enamel damage. In contrast, the experimental etchants resulted in unblemished enamel surfaces with zero or minimal adhesive residue and clinically acceptable SBS. Furthermore, the BPA etchant caused lower enamel decalcification with extensive calcium-phosphate precipitation. The study conclusively showed that BPA facilitated in vitro enamel adhesion without detrimental effects of the aggressive PA gel with potential for remineralisation and saving time at the post-debonding step.

In vitro bond strengths post thermal and fatigue load cycling of sapphire brackets bonded with self-etch primer and evaluation of enamel damage

“…It has been reported that the risk of enamel damage upon debonding increases as the bracket bond strength exceeds 14 MPa since excessive bond strengths entail extra force application to debond a bracket, increasing the chance of damage to the enamel (7,8). This agrees with a recent recommendation to keep the maximum bond strength below the mean tensile strength of enamel (17), reported to be nearly 14.5 MPa with a range of 10-25 MPa according to the orientation of enamel prisms (29). While the conventional EaR method is based on micro-mechanical retention between the adhesive and enamel, the SEP approach involves an additional chemical interaction between functional monomers and tooth substrate components.…”

“…The CLSM can provide evidence about the enamel etching effects induced by acids depending on the degree of image fluorescence, which increases with the greater loss of organic matrix and exposure of enamel prisms (26). This is achieved through the use of fluorescent dyes which promote certain emission wavelengths when they are excited by laser with specific wavelengths, hence can be traced at their locations in a material and/or tissue at dilute concentrations (17). The CLSM images showed that enamel treatment with the PA gel or SEP resulted in a visible increase in fluorescence, evidenced by the more apparent honeycomb morphology, which was more discernible with an apparently greater loss of organic matrix in areas where the etched enamel prisms were clearly exposed.…”

“…-Confocal laser scanning microscopy (CLSM) samples CLSM was carried out to compare the etch-pattern produced by the self-etch primer to 37% PA gel. Five extracted, non-cracked and caries-free human molars were used for obtaining flat, wide buccal enamel surfaces following a previously described protocol (17). Before enamel etching, 0.1 wt.% Rhodamine B dye (Sigma-Aldrich, UK) was added to the control 37% PA gel and the self-etch primer to obtain fluorescent etchants.…”

Resistance of bonded premolars to four artificial ageing models post enamel conditioning with a novel calcium-phosphate paste

“…Teeth were examined under stereomicroscope (x10 magnification) for selecting intact buccal enamel surface without cracks and caries, with no history of previous orthodontic or bleaching treatments (2). Equimolar amounts of beta-tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM) powders (Sigma-Aldrich, UK) were mixed with 37% phosphoric acid solution (Sigma-Aldrich, UK) in a powder-to-liquid ratio of 0.8:1 for preparing acidic CaP etchant pastes (5). The assigned powder and liquid were mixed using a stainless steel spatula on a glass slab for 30 seconds until a homogenous workable paste was obtained.…”

“…Recently, a novel etchant system for orthodontic bracket bonding (International Patent: WO 2018/011338 A1) was developed to reduce the bracket bonding iatrogenic effects such as enamel demineralization and/or enamel damage encountered at bracket debonding step following the completion of treatment. Etchant pastes made of calcium-phosphate (CaP) powders mixed with 37% phosphoric acid were developed for the first time to simultaneously etch and re-mineralize the enamel surface before bracket bonding (5). This approach facilitated the preferable bracket debonding failure at the enamel-adhesive interface, with no or minimal adhesive remnants after debonding, thus saving chair-side time and cost at the post debonding clean-up stage.…”