cosmetic dentistry_ beauty & science

08 I I review _ ceramics and whether orthodontic treatment is required to facilitate a more conservative and aesthetic outcome. _Clinical parameters to evaluate Once the 3-D smile design has been completed, colour change assessed, and adjunctive therapy finished to create an environment that will allow the least removal of healthy tooth structure, an evaluation of each tooth is needed for ascertain- ing which ceramic system and technique are most suitable. The evaluation of individual teeth for specific material selection involves assessing four environmentalconditionsinwhichtherestoration will function. Substrate The first consideration is evaluating the sub- stratetowhichthematerialwillbeattached(Fig.1). Is it enamel? How much of the bonded surface will be enamel? How much enamel is on the tooth? Is it dentine? How much of the bonded surface will be dentine? What type of dentine will the restoration be bonded to (tertiary or sclerotic den- tine exhibits a very poor bond strength, and bond- ing to this type of dentine should be avoided when possible)? Is it a restorative material (e.g. compos- ite,alloy)?Thesequestionsshouldbeaddressedfor each tooth to be restored, since this will be a major parameter for material selection. It is generally understood and accepted that a predictable and high bond strength is achieved when restorations are bonded to enamel, given the fact that the stiffness of enamel supports and resists the stresses placed on the materials in function. However, it is equally understood that bonding to dentine surfaces, as well as composite substrates, is less predictable given the flexibility of these substrates. The more stress placed on the bonds between dentine and composite substrates and the restoration, the more damage to the restorationandunderlyingtoothstructureislikely tooccur.Therefore,becauseenamelissignificantly stiffer than either dentine or composite and much more predictable for bonding, it is the ideal sub- strate for bonded porcelain restorations. Flexureriskassessment Next is the flexure risk assessment. Each tooth and existing restorations are evaluated for signs of past overt tooth flexure. Signs of excessive tooth flexure can be excessive enamel crazing (Fig. 2), tooth and restoration wear, tooth and restoration fracture, micro-leakage at restoration margins, re- cession,andabfractionlesions.Often,theaetiology is multifactorial and controversial. However, if sev- eral of these conditions exist, there is an increased risk of flexure on the restorations that are placed, which may overload weaker materials. Evaluation of this possibility is also based on the amount of remaining tooth structure. The more intact the enamel is, the less potential there is for flexure. The amount of tooth preparation can directly affect tooth flexure and stress concentration. There is much potential subjectivity in any observational assessment of clinical conditions; however, an as- sessment of flexure potential for each tooth to be restored is needed. A subjective assignment of low, medium, or high risk for flexure is based on the evaluated parameters, as outlined below: Low risk for clinical situations in which there is low wear; minimal to no fractures or lesions in the mouth; and the patient’s oral condition is reasonably healthy. Medium risk when signs of occlusal trauma are present; mild to moderate gingival recession exists,alongwithinflammation;bondingmostlyto enamel is still possible; and there are no excessive fractures. High risk when there is evidence of occlusal trauma from parafunction; more than 50 % of dentine exposure exists; there is significant loss of enamelduetowearof50%ormore;andporcelain must be built up by more than 2 mm. Fig. 7_Pre-op image of a case for an inlay in tooth 18 and onlay in tooth 19. Fig. 8_Post-op image using non-layer IPS e.max HT. cosmeticdentistry 2_2013 Fig. 7 Fig. 8