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cosmetic dentistry_ beauty & science

22 I I clinical technique _ bonding _Most contemporary aesthetic dental treat- ment relies on resin-based aesthetic dentistry (RED). The essence of RED is achieving an effi- cacious bond to natural tooth substrate, be it enamel or dentine, for a long-lasting restoration. This is applicable to both direct and indirect aes- thetic restorations. Bonding to enamel is an established protocol, but bonding to dentine has proved more chal- lenging and undergone considerable changes. However,themajorityofcurrentdentinebonding agents (DBA) is capable of efficacious bonding to dentine, but the method for achieving this goal is still debatable. Some authorities advocate self-etch DBA, while others prefer a total-etch approach, and further research will no doubt elu- cidate the validity of these methods. Irrespective of the technique used, RED bond- ing is a quintessential requirement for success and durability of aesthetic dental restorations. It cosmeticdentistry 1_2012 Fig. 1_Cementation mechanism: two interfaces are created between the tooth and restoration— cement–tooth interface and cement–restoration interface. Fig. 1 RED bonding: Predictable cementation of indirect aesthetic restorations Author_ Dr Irfan Ahmad, UK Formulation Varieties Advantages Disadvantages Cementation mechanism: Cement–tooth Cement–restoration interface interface RMGI Polyalkenoic acid Pre-capsulated, Adhesion to dentine, Mechanically weaker Chemical adhesion Mechanicalinterlocking with addition of chemical and thin film thickness, than resins, significant a methacrylate light-cured antimicrobial, post-cementation component (e.g. fluoride releasing, dimensional changes HEMA) and fillers low solubility, adheres may fracture weak to moist tooth substrate, ceramics reduced chemical trauma to pulp CR Polymer infiltrated Chemical, light- High compressive strength, Technique sensitive, Micromechanical Chemical adhesion with filler particles and dual-cured, superior optical properties hydrolytic degradation, adhesion and/or low and high shade shift over time, chemical adhesion viscosities, shade possible post-op tints to modify colour sensitivity with poor technique AR Polymer infiltrated Dual-cured, self-etch, High compressive strength, Technique sensitive, Micromechanical Chemical adhesion with filler particles self-adhesive, superior optical properties, hydrolytic degradation, adhesion and/or with the addition of antibacterial, fluoride chemical bonding to shade shift over time, chemical adhesion an adhesive functional releasing cast-metal, alumina and lower bond strength phosphate monomer zirconia substructures compared with CR, (e.g. MPD) reduced post-op sensitivity compared with CR Table I