cosmetic dentistry_ beauty & science

I 31 clinical technique _ bonding I cosmeticdentistry 1_2012 2. Pre-treatment of intra-oral abutment Pre-conditioning of the intra-oral abutment is begun by removing the temporary restoration and provisional cement, which is accomplished mechanically using hand instruments, air abra- sion, pumice paste or ultrasonic devices. Com- plete removal of the provisional cement is es- sential for avoiding compromising the bond strength between the natural tooth substrate (or artificial abutment, e.g. intra-radicular post/ cores or implant abutments) and the permanent cement. Higher SBSs are achieved when the temporary cement is removed with an effective dentine cleaner using a total-etch technique.13 Alternately, immediate dentine sealing prior to taking an impression may also enhance bond strength.14 The next stage is isolation, either with a rubber dam or intra-sulcular gingival retraction cords. A dry environment is essential for resin-based cements. A rubber dam is the ideal choice for cementing inlays in posterior teeth but may be unsuitable for anterior teeth because the retain- ing metal clamps can potentially traumatise the gingival margin, leading to recession, especially for anterior teeth with thin periodontal biotypes. A gingival retraction cord, dry or impregnated with an astringent, not only allows visualisation of the abutment margins, but also acts as a physical barrier to avoid excess cement entering the delicate gingival sulcus. However, the use of a retraction cord may be inappropriate around implant abutments because it may lacerate the friable epithelial attachment. Tooth abutment pre-treatment depends on the type of cement being used. If RMGI is em- ployed, no further conditioning is usually neces- sary, whether the abutment is dentine, enamel or artificial restorative material, e.g. a composite, amalgam, cast-metal and ceramic core or tita- nium, alumina or zirconia implant abutments. For CR cements, where the abutment is natural tooth substrate, pre-treatment involves application of a DBA, i.e. self-etch or total-etch. If an artificial abutmentispresent,theconditioningdependson the restorative material of the abutment, e.g. for composite and amalgam core build-ups, the pre- treatmentisairabrasionfollowedbyetchingwith phosphoric acid. 3. Clinical procedure After pre-treatment of the intaglio surfaces and intra-oral abutments, the next stage is dis- pensing the chosen cement. One of the major factorsthatreducescementstrengthisintroduc- tion of air into the cement, e.g. 10 % porosity can reduce strength by 55 %. Porosity is related to themethodofmixing,15 polymerisationshrinkage during the setting reaction, and disintegration of the cement owing to fatigue and thermo-cy- cling.Forthisreason,auto-mixingdispensersand pre-capsulated cartridges are ideal for a smooth, reduced porosity mix.16 Depending on the restoration, the cement is dispensed onto either the fitting surface or intra- oral abutment, and the restoration correctly locatedandseatedwithpressure,withorwithout an ultrasonic insertion technique for high vis- Fig. 33_Dento-facial view showing poor aesthetics of the maxillary central incisors. Fig. 34_Pre-op defective, discoloured and poorly contoured resin composite fillings on the maxillary central incisors. Fig. 35_The left central incisor is facially inclined and overlapping the lateral incisor. Fig. 36_Diagnostic wax-up to simulate pseudo-realignment of the left central incisor so that it is in line with the maxillary arch. Fig. 37_Transparent vacuum stent fabricated from a plaster cast of the diagnostic wax-up for intra-oral composite mock-up for gaining patient acceptance of the proposed aesthetics, and for making chairside temporary acrylic restorations. Fig. 38_Minimally invasive PLV preparations on the central incisors finished within enamel with distinct finish lines, by a healthy periodontium. Fig. 39_Chairside-fabricated acrylic temporary veneers using the vacuum stent of the wax-up. Fig. 35 Fig. 36Fig. 34 Fig. 38 Fig. 39Fig. 37