ORTHODONTIC BONDING AGENTS By Paul Gange and ADHESIVES Bonding materials are ideal to bond metal, ceramic and plastic appliances to all surfaces in the mouth. Proper technique in handling these materials and conditioning of these surfaces is mandatory. No adhesive is foolproof. The dental offices that experience the least amount of bond failure are the offices with the best technique. Chemical cure or light cure, direct or indirect—they all can produce desired results if handled properly. rthodontic bonding has experienced more advances in the last 10 years than during the previous two and a half decades. Wet field adhesives, enamel protective sealants, atypical enamel adhesives and self-etching primers are a few of the recent product developments that have made plac-ing appliances more dependable. Orthodontic appli-ances are bonded with chemical and light cure systems that can be equally successful if their inherent variables are controlled. This is the key to reducing bond failures: control the variables. Bonding success or failure starts with the tooth surface. The proper conditioning of the surface of the tooth, whether it is enamel, composite, porcelain or metal, is a variable that must be controlled when bonding a bracket with adhesive. A surface that is not conditioned properly or one that becomes contami-nated cannot produce satisfactory bond strength regardless of adhesive type. Worldwide, chemical cure and light cure systems are about equal for full fixed appliance placement, but the light cure system gains market share each year. Let’s take a closer look at the adhesive systems available. O Therefore, to mix the paste and primer properly and achieve maximum strength, the bracket base must fit the tooth surface flush. A thin (as opposed to a thick) coat of primer must be applied to the enamel and the bracket base. 2 The primed/pasted bracket is placed on the tooth and pressed to place when in the desired position. To summarize, the variables with a no mix system are: ᕡ Bracket base must fit the tooth surface flush. ᕢ Thin coat of primer on tooth surface. ᕣ Thin coat of primer on the bracket base. ᕤ Thin layer of paste on the bracket base. The mix adhesive, the most popular of the chemical cure systems, requires the mixing and application of two liquids (bonding resin) to the enamel and the mixing and application of two pastes to the bracket base. As long as the operator thoroughly mixes the two pastes and does not place brackets after the working time has expired, maximum strength can be achieved consistently. The mix system has the fewest number of variables of any adhe-sive type. With all chemical cure systems, archwires should not be ligated for at least five minutes, preferably ten minutes, after the placement of the last bracket. Light cure composites have become very popular for bracket placement because they offer the follow-ing benefits: ᕡ Unlimited working time to position bracket and clean up flash. ᕢ Immediate archwire placement. ᕣ More efficient utilization of staff. Adhesives The two types of chemical cure systems used to bond attachments are “no mix” and “two paste mix”. The no mix system has two components: a single liquid primer (catalyst) and a single paste. The primer is applied to the etched, dried enamel and the bracket base. The paste then is applied to the bracket base and the bracket is placed on the tooth. The primer serves as the catalyst for the paste and therein rests the variability with this system. Even though it is termed “no mix”, this system actu-ally mixes the paste and primer directly on the tooth. 16 May/June 2011 JAOS
Journal of the American Orthodontic Society May-June 2011: Page 16
