cosmetic dentistry_ beauty & science

review _ ceramics I _Treatment philosophy A treatment philosophy based on current stan- dards of care that consider the patient’s aesthe- tic requirements is a prerequisite to making any decision regarding the use of a material or tech- nique. More importantly, this philosophy should be aimed at maintaining the long-term biological and structural health of the patient in the least destructive way. Restorative or aesthetic dentistry should be practised as conservatively as possible. The use of adhesive technologies makes it possible to preserve as much tooth structure as feasible while satis- fying the patient’s restorative needs and aesthetic desires.5 The philosophy today is not to remove any healthy tooth structure unless absolutely neces- sary. This will reduce dentists’ frustration when orthodontics would have been the ideal treatment. With restorations, clinicians should choose a mate- rialandtechniquethatallowsthemostconservative treatment in order to satisfy the patient’s aesthetic, structural, and biological requirements, and that meets the mechanical requirements to provide clinicaldurability.Eachoftheserequirementscould be the topics of individual articles. There are four broad categories or types of ceramic systems: 1. powder/liquid feldspathic porcelains; 2. pressed or machined glass-ceramics; 3. high-strength crystalline ceramics; and 4. metal ceramics. Category1 Porcelains—the most translucent—can be used the most conservatively, but are the weakest.3, 6 Category2 Glass-ceramics can be very translucent too but require slightly thicker dimensions for workability and aesthetics than porcelains do. Categories3and4 High-strength crystalline ceramics and metal ceramics, although demonstrating progressively higher fracture resistance, are more opaque and, therefore, require additional tooth reduction and are thus a less conservative alternative. Based on the treatment goal of being as con- servative as possible, the first choice will always be porcelains, then glass-ceramics, followed by high-strength ceramics or metal ceramics. The decision will be based on satisfying all the treat- ment requirements, that is, if the more-conser- vative material meets all the treatment require- ments then that is the ideal choice. The article will identify the clinical conditions in which treatment requirements dictate the use of a specific category of ceramics. _Space required for aesthetics The first consideration is the final 3-D position of the teeth, that is, smile design. There are several resources available for smile design.7, 8 The second consideration is the colour change desired from the substrate (tooth), since this will dictate the restoration thickness. In general with porcelains, a porcelain thickness of 0.2–0.3 mm is required for each shade change (A2 to A1 or 2M1 to 1M1). For example, A3 to A0 would require a veneer of 0.6–0.9 mm in thickness. Glass-ceramics have the same space require- ments as porcelain for effective shade change; however, the authors find it difficult to work with this category and produce the best aesthetic re- sultswhenthematerialislessthan0.8mminthick- ness. High-strength all-ceramic crowns require a thickness of 1.2–1.5 mm, depending on the sub- strate colour, and metal ceramics need a thickness ofatleast1.5mmtocreatelifelikeaesthetics.With that in mind, a diagnosis based on tooth position and colour change will direct treatment planning, aswellasthefinaldecisionregardingtoothprepa- ration design (i.e. total tooth structure reduction) Fig. 4_Image of preparation with poor substrate and subgingival margins where maintaining seal would be difficult. High-strength ceramics or metal ceramics would be indicated. Fig. 5_Image of minimal preparations prior to receiving bonded porcelain. Fig. 6_Two-year post-op image of very conservative Category 1 bonded porcelain restorations, using VITA VM porcelains. I 07cosmeticdentistry 2_2013 Fig. 4 Fig. 5 Fig. 6