GAP Australasian-Dentist-Mar Apr 2019

Category AustrAlAsiAn Dentist 79 lInICal Shade selection the desired tooth shade and the existing shade of the tooth preparations were determined under daylight conditions. When photos of the teeth were taken, darker and lighter shade tabs were held against the natural teeth, the flash was turned off and all photos were taken from a similar angle. these photos were also very helpful in the fabrication of the restorations in the laboratory (Figs 7a and b). Material selection in favour of clinically proven properties the decision fell on a tried-and-tested glass-ceramic that offers long-term clinical stability along with high strength and impressive esthetics: iPs e.max ® lithium disilicate. this material is suitable for both conventional press methods and CAD/ CAM applications. it can be processed to provide fully anatomical restorations or restorations that can be customized with veneering ceramics. As this case had already taken us onto a digital route with the 2D smile design software, we decided to continue with the digital option. the situation was digitalized with a D2000 scanner (3shape). the restorations were designed in the software in line with the proportions previously established and then ground from iPs e.max CAD blocks using a Zenotec select hybrid CAD/CAM machine (Fig. 8). the iPs e.max blockswere processed in their crystalline intermediate stage (“blue” phase), which is optimally coordinated with the grinding process, providing highly accurate results. subsequently, the restorations were crystallized in a conventional ceramic furnace, in the course of which they acquired their final material properties (e.g. shade). Once crystallized, the strength of the material increases up to 530 MPa (mean biaxial strength). iPs e.max CAD blocks are available in different translucency levels, ranging from medium opaque to highly translucent (MO, lt, Mt, Ht), and in two opalescent shades. the material can be used to create frameworks for veneering or to fabricate monolithic restorations (e.g. veneers, inlays, crowns and three- unit bridges). it is also indicated for hybrid abutment restorations. iPs e.max CAD is suitable for an unrivalled wide range of indications for CAD/CAM glass-ceramics. it is even suited for minimally invasive restorations such as thin veneers (0.4 mm) and adhesive crowns (1 mm). Block selection with an app in terms of colour saturation, shade 1M2 (Vita 3D-Master) was ideal and would have come closest to the A1 shade (A-D shade guide). However, the brightness in the central third was higher than that of the iPs e.max CAD lt block in shade A1. And yet, the colour saturation of a brighter block (e.g. lt Bl4) would have been too high for the veneer. the iPs e.max CAD Ht (High translucency) blocks in the Bleach shades might have been a suitable choice. However, using highly translucent materials in restorations with slightly increased wall thicknesses always entails the risk that the restoration may be less bright and the chroma could be higher than the actual shade. For these reasons, the Ht block was not seen as ideal for the crowns on teeth ul2 and ur2. the iPs e.max shade navigation App (snA) was used to find the most suitable material. this app takes all the factors affecting the shade of a restoration into account to identify the block that is best suited to achieve the given shade. the app is fast and easy to use. You only have to enter the data pertaining to the case at hand. the app delivers an excellent result. Initial input for the crowns: u Desired tooth shade: 1M2 (= A1) u indication: crowns for ul1, ul2, ur1, ur2 u Preparation shade: nD2 u Material thickness: 1.2 mm u Material: iPs e.max CAD Based on the data entered, the app recommended an iPs e.max CAD block in shade Mt Bl4. this block was required to mask the small area of discolouration (nD4) on the ul1 and to offset the slight drop in hue and value caused by the buccal reduction and the ceramic veneering. to identify a suitable block for the veneers on teeth ul3 and ur3, “Add new restoration” was activated on the app and the following data was entered: u Desired tooth shade: 1M2 (= A1) u indication: veneers for ul3 and ur3 u Preparation shade: nD1 u Material thickness: 0.5 mm u Material: iPs e.max CAD the “Free selection” option was used to see if the shade was also suitable for the crowns. it was possible to assess if the Mt Figure 4: Crown preparations of central and lateral incisors and veneer preparation of both canines Figure 7a: Determining the shade of the lower teeth Figure 5: A deeper preparation was required in the buccal area of the upper central incisor on the right because of the pronounced dark discolouration present in that area compared with the neighbouring tooth Figure 7b: Selecting the shade of the tooth preparations using the IPS Natural Die Material shade guide Figure 6: Direct temporaries created on the basis of the smile design wax-up Figure 8: Lithium disilicate block (IPS e.max CAD) in the blue intermediate crystalline stage on the e.matrix holder (for the Zenotec select millling machine) ready for wet machining