Bracket Failure With a Novel Etchant Paste. A Randomized Clinical Trial

Acid etching of tooth surfaces to promote the bonding of orthodontic attachments to the enamel has been a routine procedure in orthodontic treatment since the 1960s. Various types of orthodontic etchants and etching techniques have been introduced in the past five decades. Michael G Buonocore in revolutionized dentistry with his historical paper: "A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces" depicting the advantage of etching and bonding of acrylic to enamel. It forever changed the practice of dentistry. Buonocore and Silverstone led the profession in acid etching and bonding of resin to etched enamel surfaces. These developments allowed orthodontists to bond brackets reliably and apply forces to move teeth without banding every tooth or having brackets deboned. Buonocore reported that 85% phosphoric acid etchant significantly increased the adhesion of acrylic resin to enamel. Since then, a variety of etchants have been used with different concentrations and etching times. These include hydrofluoric acid, citric acid, hydrochloric acid, maleic acid, nitric acid, and phosphoric acid in a variety of concentrations. Suggested etching times can vary from 15 to 60 seconds. The tooth enamel surface is known for its low-energy and hydrophobic properties, with its outermost layer being rich in fluoride. Enamel etching with phosphoric acid (PA) removes the fluoride-rich layer, dissolves enamel mineral, creates micro- pores, and renders a high-energy and hydrophilic enamel surface to permit wetting by an adhesive; yet at the expense of increased surface porosity, susceptibility to staining, caries, more remnant adhesive and enamel loss. Fixation of brackets to teeth involves joining of two different solid substrates or adherents through an intervening adhesive layer. Bracket bases are currently provided with mesh designs that ensure robust mechanical interlocking between the bracket and adhesive, whilst research is ongoing to improve enamel conditioning strategies that can attain clinically successful bond strengths yet maintain an unblemished enamel surface. Alternative methods to conventional enamel etching with phosphoric acid have been sought aiming at decreasing the bond strength to reduce the incidence of enamel damage. The use of glass ionomer cements for orthodontic bonding decreased the occurrence of enamel damage, yet at the expense of clinically unacceptable bond strengths. On the other hand, the use of laser etching and self- etch primers resulted in bracket shear bond strengths comparable to the conventional etch-and-rinse approach, but could not eliminate enamel damage. In 2019, Ibrahim et al developed a new bioactive orthodontic etchant paste made of calcium-phosphate (CaP), which could alleviate subsurface enamel demineralization in comparison with the traditional phosphoric acid etchant and the pre-clinical viability assessment using in vitro studies showed exemplary advantages. The new low-pH CaP paste etchant application is a clinically viable bracket bonding method with steps similar to PA application that yielded adequate bond strength with the advantages of minimal adhesive remnants and no enamel chipping or cracking on deboning of the bracket.