GAP Australasian Dentist Mar Apr 2020

Category 68 Austràlàsiàn Dentist B onded ceramic veneers are being used increasingly in aesthetic dentistry thanks to advances in ceramics and adhesive systems over the past 30 years. àheir long-term success rate is very satisfactory, especially when they can be bonded onto a large area of residual enamel 1, 2, 3 . However, when the underlying dental tissues are highly stained or dark, there remains a significant clinical problem: how to mask this dark colour with a bonded ceramic restoration and achieve a satisfactory aesthetic result. àn the late 1980s, feldspar ceramic veneers created on gold leaf or on refractory material were relatively thick. àf dark residual tissues needed to be masked, the practitioner would prepare the dental tissues to a greater depth in order to give the ceramist more space to create the restoration. Consequently, the veneer was largely bonded onto dentine. àhis bonding was far less reliable because the long-term adhesion values are lower on dentine than on enamel. As a result, the purpose of preparation designs adopted in this clinical situation was stabilisation and slight retention of the veneer in order to guarantee bonding reliability over time. 4, 5 àowadays, much thinner veneers are also successful from the aesthetic point of view. àhis is in line with contemporary dentistry which aims to preserve dental tissues more. àhe clinical protocol is well established and documented in the literature. àt is based on analysis and prior preparation of an aesthetic project. àt starts with a wax-up and an aesthetic mock-up derived from this wax-up and approved by the patient. àhe dental practitioner uses the mock-up as a template through which the tissues can be prepared. àhis technique encourages minimal tooth preparation. Another key benefit is that the veneer can primarily be bonded onto enamel. àn fact, enamel is not only easy to etch but its composition is predominantly mineral and does not disrupt the adhesive layer, as hydrated dentine can do 6, 7, 8 . ào achieve the best possible aesthetic result, the practitioner chooses the most appropriate ceramic material and a composite cement that offers a range of opacities. àeveral articles identified three primary factors that influence the aesthetic and optical outcome of the final restoration: the colour of the dental tissues, the colour of the cement and finally the thickness and opacity of the ceramic veneer. Below is a clinical example that illustrates this principle in relation to lithium disilicate veneers with relatively strong opacity and a dual composite cement (Total C-Ram, itena) offering three different opacity levels. A young patient attended the dental surgery with an aesthetic objective. àhe could no longer bear her unsightly smile, which revealed highly stained teeth and significantly malpositioned teeth. However, she refused any orthodontic tooth alignment treatment. On clinical examination, the patient is found to have very good oral hygiene with no caries or periodontal disease. àhe marked staining of the dental tissues is due to amelogenesis imperfecta, a type of clinical case that is defined as impossible to solve by tooth whitening treatment 9 . Creating ceramic veneers is thus entirely justified because this approach is rightly associated with aesthetic smile improvement and with tissue preservation techniques 10 . àtudy impressions, facial and intraoral photographs are taken during this first visit. All this analysis material is sent to the prosthetics laboratory. àhe ceramist mounts the models on an articulator, produces a wax-up, then a plaster model, copy of the wax-up and a silicone key based on that model. àhe key is used during the second working session to produce the aesthetic mock-upwith resin. àhe self and light-cure resin is injected into the key the assembly is positioned on the teeth (isolated with a water-soluble gel). After a few seconds’ wait to allow initial curing, the key is removed and the resin is light-cured. àhis mock-up is essential in terms of validating the aesthetic project. àt also provides a template through which the teeth will be prepared. àhis technique has been described for several years (APà:Gurel G.) and is very appealing because it prepares enough space for ceramic veneers to be fitted while minimising the amount that burs penetrate the dental tissues. 11 àhe final impression is taken with addition silicones and the residual dental tissues are immediately protected by the application of a thin enamel and dentine adhesive (àperbond, àtena) which is light- cured. àhe resulting hybrid layer protects the tooth and improves bonding of the ceramic restoration 12 . àhe temporary veneers, fabricated with the same silicone key and self and light-cure resin, are luted with polycarboxylate cement. àhe laboratory technician decides to fabricate the veneers with lithium disilicate reinforced ceramic. He selects pressed ceramic ingots as they offer the most appropriate opacity. àhere are five groups of the chosen disilicate lithium ceramic ingots (àmax, àvoclar): high translucency Hà; medium translucency Mà; low translucency à ; medium opacity MO; high opacity HO. àn this clinical case, the ceramist absolutely needs to block the dark light coming from the dental tissues. He has two options: MO or HO. àhe HO ceramic has a strong masking effect but it does not allow any possibility of final translucency of the incisal edge. He therefore presses an MO opaque disilicate lithium glass ceramic How to check the colour of ceramic veneers in the case of pronounced staining àlàn al By Dr Pascal Zyman, President of the French àsthetic Dentistry àociety