Dental Adhesives for Direct Placement Composite Restorations: An Update

Dental adhesives used to bond composite resins to tooth structure have evolved over the last several decades. The earliest bonding systems required an acid-etch technique and were only compatible with enamel, and the challenge has always been to predictably bond to enamel and dentin simultaneously. There can be confusion as to what bonding agents are being described, because there are a number of different labeling categories. With a simplified, logical category description the clinician is better able to understand what each bonding agent is and how it is used. Bonding systems can in fact be differentiated into two distinct classes: etch-and-rinse and self-etch. Both classes of bonding systems work well as long as one understands which to use for different treatment conditions. There is no one universal bonding system that does it all, but recent advances in the chemistries of these adhesives allow many of them to be bonded to all intraoral substrates – to enamel; to dentin; and to all types of dental resins, ceramics and metals. The key to success is to provide your patients with materials and techniques that you can reproduce to achieve the best, longest-lasting clinical results. Introduction Important advances and innovations in restorative dental treatment that have changed the way we treat patients for the better would certainly include fluorides, local anesthesia, high-speed handpieces, dental radiography and implants. Another innovation that would be near the top of this elite list is dental resin adhesion. Little did Michael Buonocore and colleagues at the Eastman Dental Center in Rochester, New York, realize that the introduction of adhesion, first bonding to enamel, would change the way we practice dentistry. G.V. Black described the retention of restorations based upon cavity design and undercut dentin.1 Even with the caries removed, because of the limitations of the restorative materials available at the time (gold foil and dental silver amalgam), additional tooth structure needed to be removed to fulfill the requirements for retention of the restorative material. The goal of conservation of tooth structure was limited by the materials that were available up until the late 1960s, when clinical techniques with resin adhesives bonded to etched enamel were introduced using UV-light-cured resin restoratives, a resin sealant and a composite resin that utilized the acid etch technique described by Buonocore.2,3 Bonding to tooth substrates is now the standard of care for single-tooth direct placement restorations and has been the driving force in changing how we prepare and restore teeth. With the use of adhesives, minimally invasive dentistry (MID) with a more conservative, tooth-structure saving approach when treatment planning restorative dental procedures is possible. While the majority of restorations placed today are restoration replacements, minimally invasive adhesive restorative dentistry not only relates to the treatment of caries but also to these restoration replacements and to elective esthetic dentistry. There has been a significant change in the principles of cavity preparation design, from the traditional principles of “extension for prevention” described by G.V. Black to a more carious lesion-centered approach.4-6 This lesion-centered approach is possible through the advancements in adhesive restorative materials, as well as through the introduction of computer-assisted methods of caries detection, a better understanding of the role of magnification, digital radiography and caries risk assessment of the patient to allow for improved conservative caries management.7 One of the greatest benefits of a more conservative approach is that it allows the clinician to maintain as much tooth structure as possible. While enamel bonding and dentin bonding have been pursued in parallel paths, the goal has been to develop a universal adhesive that bonds to all substrates used in dentistry: enamel, dentin, metals, ceramics and composite resin. This author remembers reading an article in 1985 written by Dr. Wayne Barkmeier on the fundamental elements for an adhesive used for bonding restorative materials to tooth structure. Recently these five key prerequisites for successful adhesion to tooth structure were reiterated because they have not changed since then.8 (Table 1) Table 1. Key prerequisites for successful adhesion 1. The procedure must be safe and biologically acceptable. 2. The level of bond strength must be clinically significant to avoid discoloration at the margins and secondary caries. 3. The bond strength must be routinely achieved so that predictable results are obtained. 4. The bond must be established quickly in order to permit immediate finishing. 5. The bond must be stable in vivo for a clinically significant period of time. Since then, significant advances in the development of dental adhesives have been accomplished. The adhesives currently available offer reliable adhesion between restorative materials and tooth structure.