cosmetic dentistry_ beauty & science

seventh-generation DBAs. Compared with sev- enth-generation DBAs, XTR does not require se- lective etching of enamel margins owing to its profound etching pattern on both cut (prismatic) and uncut (aprismatic) enamel (Figs. 15 & 16) and is fully compatible with all dual- and self-cured resin-based composites and cements. It has an SBS greater than most self-etch systems of ap- proximately 30 MPa. Another problem with self- etch DBA is inadequate penetration of the adhe- sive into the dentine tubules following etching, which results in post-operative sensitivity and large film thicknesses. XTR overcomes this by pe- netrating deeper into dentine tubules, reducing the film thickness to less than 5 µm, SBS to den- tineof37MPa,andpost-operativesensitivity(Figs. 17a & b). Finally, XTR can be used with any CR ce- ment for bonding indirect aesthetic restorations, and in combination with Nexus NX3 achieves dentine bond strengths of nearly of 42 MPa. Cementation protocols As mentioned previously, nearly half of all risk factors relating to successful cementation de- pends on operator factors, which leaves little latitude for errors. The cementation protocol can be divided into three distinct processes: pre- treatment of the intaglio or fitting surface of the restoration, pre-treatment of the intra-oral abutment, and clinical steps for cementation. 1. Pre-treatment of intaglio surface The conditioning of the intaglio surface de- pends on the restorative material and the choice of cement (RMGI, CR, AR). The preferred method for silica-based restoration is chemical condi- tioning, using HF acid (4–10 % for 3 minutes), fol- lowed by application of warm silane or DBA, which increases the SBS between ceramics and the dentine substrate at the cement–restoration interface.11 However, prolonged etching with HF acid can excessively dissolve the glass filler parti- cles in the ceramic, making the surface smooth and negating the etching process. In addition, gross alteration to glass particles also compro- mises the strength of the ceramic. Hydrofluoric and phosphoric acids cannot be used to etch metal, alumina or zirconia, but may be used for cleansing to ensure a contamination- free intaglio surface. The surface roughness or micro-irregularities of high strength dense ce- ramics must be created during the manufactur- ing process. Air abrasion of zirconia and alumina fitting surfaces prior to cementation is contro- versial. To date, there is no long-term data to ver- ify this practice, and air abrasion of zirconia can cause transformation change from the tetrago- nal to the monoclinic phase, weakening and re- ducing the life expectancy of the restoration.12 Otherchemicalagentsincludealloyprimersortin plating for some casting alloys. Another benefit of using OptiBond XTR is that the adhesive liquid contains an adhesive mono- mer that provides true chemical adhesion for most restorative materials at the cement–resto- ration interface (Figs. 18a–c). Therefore, applica- tion of silane, or other alloy primers, to the fitting surface is superfluous. Fig. 28_Pre-treatment of intra-oral abutment: isolation with rubber dam, removal of temporary dressing and thorough cleansing cavity with pumice, rinsing and drying. The inlay is seated using water-soluble NX3 try-in pastes for verifying colour and selecting the corresponding shade of the permanent cement. Fig. 29_Pre-treatment of intra-oral abutment: OptiBond XTR primer is applied to both enamel and dentine, and continuously scrubbed for 20 seconds. This is followed by gentle drying for 5 seconds. Fig. 30_Pre-treatment of intra-oral abutment: OptiBond XTR adhesive is lightly brushed for 15 seconds, air- dried for another 5 seconds and light- cured for 10 seconds. Fig. 31_Cementation technique: the selected shade of light-cured NX3 is dispensed onto the inlay, or directly into the prepared cavity, avoiding introducing air. Fig. 32_Cementation technique: after wiping away excess cement and ensuring patent contact points, NX3 is light-cured for 10 seconds from all aspects. All occlusal checks are carried out post-cementation to avoid damaging the ceramic beforehand. Any necessary adjustments, together with the margins are polished with OptiDiscs andOpti1Steppolishingtips(bothKerr). Fig. 29 Fig. 30Fig. 28 Fig. 32 Fig. 33Fig. 31 30 I I clinical technique _ bonding cosmeticdentistry 1_2012