Dental Asia Nov/Dec 2019

Clinical Feature DENTAL ASIA NOVEMBER / DECEMBER 2019 36 By Dr. George Freedman DDS, DiplABAD, FIADFE, FAACD Following up from Dr. Freedman’s 7 th Generation bonding agent article on our previous MarchApril 2019 issue, this issue looks at the development of new 8 th Generation bonding agents. B onding agents were tentatively introduced in the early 1970s. Since then, the evolution of adhesive techniques has transformed the scope of dental practice. Arguably, the high impact of bonded, appearance-transforming dental restoratives has propelled the dental profession into its greatest prominence in history. In fact, most direct and indirect restorations are adhered to natural tooth structure rather than cemented or mechanically retained. For more than 30 years, highly competitive research and aggressive product development have improved adhesives, initiating, and then fueling, patient demands for conservatively improved oral appearance. The widespread demand and universal use of dental adhesives has largely been a function of two factors: Composite restorations are more aesthetic than their precursors, and the adhesivemargin is clinicallymore predictable than a non-bonded interface. The rapid and intensive development of better and easier dental adhesives has focused on simplifying the clinical procedure; decades ago, resin practitioners were faced with a veritable chemistry set of materials to mix and match, in very specific sequences, in order to develop a suitable micromechanical bond between the tooth and the restoration. Adhesion, as defined by most current materials, is micromechanical attachment, not chemical bonding, to enamel and dentin. Dentists were inundated by successive “generations” of adhesive materials in relatively rapid succession. While there is no scientific basis for the term “generation” in dental adhesives, and the classification is to some extent, arbitrary, it has served a very useful purpose in the organisation of hundreds of commercially available products into a small number of more comprehensible and readily manageable categories. Generational designations assist in classifying the specific adhesive chemistries involved. They are also very useful in predicting the strengths of the dentinal bond and the ease of clinical use. Generational classification benefits both dentist and patient by simplifying the clinician’s chairside tasks and workflow. The last disruptive advance in adhesive generations (7 th generation iBond) was introduced in 2002. Since then, many competitive and innovative bonding agents have been developed, ranging from 4 th to 7 th generation. The vast majorities of these adhesives perform well, and can be used confidently, regardless of their generation; the only major trend is that higher generations offer fewer components, fewer steps, and better chairside predictability (Fig. 1). In order to best envisage the future of dental adhesives, it is essential to briefly outline their past evolution and their current state. Bond strength parameters Adhesion: Past, Present and Future Fig. 1: Bonding agents evolve to fewer components, fewer steps, and better chairside predictability Fig 2: Less than 17 MPa adhesion: polymerisation forces cause resin to contract towards composite centre pulling restorative material away from cavity walls. (Courtesy Dr. Ray Bertolotti.) Fig. 3.: More than 17 MPa adhesion: polymerisation contraction causes shrinkage of composite towards cavity walls. (Courtesy of Dr. Ray Bertolotti.) Bonding interface strength is a critical consideration in selecting an adhesive. Some of the basic parameters are conclusively established and well accepted. Munksgaard in 1985 and Retief in 1994 found that 17 MPa was the minimum required for successful adhesion to tooth structure. This figure represents the composite resin polymerisation contraction force. If adhesion to either enamel or dentin is less