cosmetic dentistry_ beauty & science

or using inappropriate materials, is a recipe for disaster. Furthermore, aesthetic restorations are unique because they are often non-retentive, thin, delicate and fragile, requiring careful ma- nipulation to prevent breakage during the ce- mentation procedure (Fig. 13). Choice of cement The choice of permanent cement for defini- tive aesthetic restorations is either RMGI or re- sin. Although RMGIs offer chemical adhesion to dentine, they are unsuitable for aesthetic resto- rations owing to poor mechanical properties, inferior optical properties (profound opacity), making translucent silica-based ceramics appear dull, and a limited selection of shades, making accurate shade matching difficult. Furthermore, RMGIs undergo significant post-cementation dimensional changes that may fracture weaker uni-layer ceramic restorations.7 Therefore, the ideal cement for aesthetic restorations is a resin, which has superior mechanical, optical and phys- ical properties (Table I). In addition, newer resin cements also offer low film thicknesses of 8 to 21 µm,8 comparable with that of RMGI, resulting in reduced micro-leakage.9 The disadvantages of resins are hydrolytic degradation, chromatic instability over time, post-operative sensitivity and requiring adherence to a stringent adhesive technique. The next decision is choosing between AR and CR cement. The AR variety of resin cements is in- appropriate for aesthetic restoration cementa- tion owing to their limited shade availability and because the uncontrollable working time of dual- cure setting causes difficulty cleaning excess set cement. Besides, many aesthetic restorations re- quire minimal preparation and are usually fin- ished within enamel. Since self-etch ARs do not require separate enamel etching with 37 % phos- phoric acid, the higher pH primer in AR may not create an adequate enamel-etching pattern for efficacious bonding.10 For these reasons, a CR is therefore the ideal choice of cement for bonding tooth-coloured aesthetic restorations. The CR cements are recommended for uni- layered, non-retentive, silica-based ceramics (lower flexural strength of 100 to 300 MPa), of- fering increased translucency, assuming the un- derlying tooth substrate is an acceptable colour. These ceramics are amenable to etching with hydrofluoric acid (HF) for enhanced mechanical retention, and when treated with silane (Figs. 14a–c) create silica–silane chemical bonds at the cement–restoration interface. However, CR must Figs. 18a–c_OptiBond XTR incorporates an adhesive monomer and is copiously applied to the fitting surfaces of ceramic restorations, achieving chemical adhesion at the cement–restoration interface. Fig. 19_Cavity preparation for an inlay on the maxillary first molar. Fig. 20_Impression of inlay cavity using an addition silicone impression material. Fig. 21_Temporary restoration in situ. Fig. 20 Fig. 21Fig. 19 28 I I clinical technique _ bonding cosmeticdentistry 1_2012 Fig. 18b Fig. 18cFig. 18a