CDE0211

26 I I industry report _ compobonds _Besides the physical and mechanical proper- ties of dental amalgam, one of the main reasons for its success is its clinical simplicity and forgiving technique.Thederisory“drillandfill”sloganassoci- ated with dental treatment pertinently describes the provision of an amalgam restoration. The usual protocol for amalgam restorations is a single-stage procedure. Following decay excavation and tooth preparation, amalgam is placed directly into the cavity and anatomically curved and burnished. In addition, amalgam restorations are relatively tech- nique insensitive, have favourable wear resistance and high strength, are inexpensive and the post- operative expansion of the material helps “seal” cavity margins. Amalgam’s demise started in the eighties, with questions being raised about excessive tooth re- moval for creating undercuts for retention, metal corrosion products, poor aesthetics and possible mercury toxicity.1 Since then, the profession has sought suitable alternatives for this iconic and ubiquitous restorative material—the candidate: resin-based composites. The last few decades have witnessed phenomenal research and improvement ofcompositetechnology,allayingconcernsregard- ing wear resistance, retention of tooth structure, marginal adaptability and post-operative sensitivity. However, the unflagging Achilles’ heel of compos- ites is polymerisation shrinkage, which compro- mises the longevity of the restoration.2 Never- theless, newer materials have sought to overcome many of the negative effects associated with poly- merisation shrinkage. The basis for improvement has been two-fold: firstly, a better understanding and efficacy of dentine bonding; and, secondly, development of the chemical composition of resin- based composites to meet the challenges of poly- merisation shrinkage, including superior physical and mechanical properties to meet the hostile de- mands of the oral cavity. In order to appreciate the rationale for the development of compobonds, it is important to chart the scientific breakthroughs of both dentine bonding and resin-based composites. _Historical Theidealrestorativematerialshouldbeaesthetic, adhesive, abrasion-resistant and bioactive to en- courageregeneration,ratherthanrepair,oftheden- tal hard tissues. The last six decades have witnessed the introduction of many innovative materials as amalgam substitutes, and to fulfil the criteria of an ideal restorative dental material. These newer mate- rialscanbecategorisedasresinsandglass-ionomers with numerous hybrids, consisting of combinations of both materials. Resins yield a superior bond to enamel, but a less predictable bond to dentine.3 Conversely, glass-ionomers bond better to dentine by offering true chemical adhesion and releasing fluoride for bioactivity, but have inferior mechanical properties compared with resins. Numerous hybrid materials such as resin-modified glass-ionomers, compomers and giomers have sought to exploit the beneficial properties of both materials, with varying degrees of success. For example, in 2001 giomers were introduced, incorporating a pre-reacted glass filler to facilitate fluoride release from a resin-based composite.4 cosmeticdentistry 2_2011 Compobond: Evolution of a new restorative dental material Author_ Dr Irfan Ahmad, UK Fig. 1_TE DBAs involve etching (red) both enamel and dentine followed by the primer (yellow) and adhesive (green). Fig. 1