Dental Asia November/December 2022

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BEHIND THE SCENES Attractive and with character With sophisticated techniques, DT Luís Manuel Rocha Saraiva presents a step-by-step guide to high-aesthetic zirconia restorations. This is my protocol about the correct handling of zirconia materials such as Zolid HT+ Preshades which can be applied to all kind of aesthetic restorations starting with single crowns up to implant-supported full arch cases. In this article, I will show how to individualise and characterise high-aesthetic monolithic zirconia restorations in a very efficient and easy way. For this case, I have chosen two cases. A monolithic tooth-supported fullarch bridge which is only stained and an implant-supported bridge with monolithic teeth and a veneered gingiva (Fig. 1). Both cases are made using Zolid HT+ Pre-shades. DIGITAL DESIGN For the design of the crowns, we usually follow the digital workflow which is given by our CAD Software. Because this article relates more to the manual processing of zirconia, we will go through it quickly. But there are some very important rules you should always consider in your design: 1. Use an Artex articulator before the digital design for all preparations of the models and use the digital articulator to finalise the functional design. 2. Never start the digital workflow without using an approved wax-up or test model. 3. Use the approved wax-up or test model as a pre-op scan (Fig. 2). 4. Always remember the basics of a dental restoration: we are trying to imitate nature, so never forget the importance of shape and anatomy. 5. Always follow the manufacturer’s instructions and the given indications of the material. GREEN STATE CHARACTERISATION To achieve an optimum aesthetic result, we need to remember the basics of tooth: anatomy and shape. In the second phase, it is necessary to use our knowledge in anatomy and dental morphology. For this we must Fig. 1: High-aesthetic zirconia restorations with an individual character Fig. 2: Pre-op scan Fig. 3: Working model scan Fig. 4: Matching process, pre-op scan and working model Fig. 5: Final CAD design tooth-supported bridge Fig. 6: Final CAD design implant-supported bridge 44 DENTAL ASIA NOVEMBER / DECEMBER <strong>2022</strong>
BEHIND THE SCENES prepare ourselves accordingly and I would recommend the following actions: 1. Always use tools that are suitable for zirconia finishing in the green state. I use the Amann Girrbach Green State Finishing Kit, it contains all the tools I need. 2. The speed specifications of the tools should always be observed. 3. Zirconia in the green state is very sensitive, never use too high pressure and/or blunt tools. 4. Always keep in mind that the zirconia shrinks by almost 20%. Due to that fact, the surface characterisation should be a bit deeper, but never make notches in areas under tensile stress. 5. Use gloves and a mask and work cleanly, milling dust must be completely removed before sintering. We should always should bear in mind that although we infiltrate the zirconia with liquids for shading, we still apply stains, glazes and veneering ceramics later. Of course, we want to keep the microstructure even if these ceramic materials are applied. We should also take this into account in this phase, too. The microstructure we create in the green state is later decisively involved in the aesthetics and the natural appearance of the restoration. INFILTRATION This stage has the least influence on the final result, but it is the trickiest step. We must improve the chroma and the effects of the restoration without a real and immediate visualisation of the colours we use. The final colour becomes visible for the first time after the sintering process. To achieve aesthetic results, we must understand the principle of the white and porous zirconia foundation. I therefore recommend to people who do not have a lot of experience with the application of colouring liquids to always start with tests on blank leftovers or practice restorations, to take photos of the last results and to record everything you do. If the principle is once understood, the mental visualisation and implementation works quite easy. For this process step, I recommend the following preparation: 1. Prepare all the colours to be used and follow the instructions for the materials. 2. Clean the zirconia surface with compressed air, milling dust needs to be fully removed. 3. Carefully start infiltration with small brushstrokes and small amounts of liquid. The zirconia in this stage has a high absorption behaviour (Fig. 12). 4. Apply the chroma (dentin liquid) to the intended areas, i.e., approximal, cervical and occlusal. Due to the use of preshaded zirconia, the colour only needs to be reinforced in those areas. 5. Apply the effects e.g., in the incisal area. SURFACE PREPARATION AND COLOUR CUSTOMISATION Figures 13-16 show the results after sintering. Despite all the work, the excellent quality of this material is evident. It is only possible with a material like Zolid HT+ Preshades to have such results after sintering and to perceive the excellent optical behaviour of zirconia. If the restoration meets all requirements after sintering, we can concentrate on the most important aspect, the aesthetics. In that case, I used the staining system Ivocolor from Ivoclar Vivadent. This has two reasons. The first is the wide range of possible firing cycles, I am able to choose a temperature between 700-890ºC without harming its properties. The second reason is its optical behaviour. This kit has three unique colours on the market: Ivocolor E22, Magenta Ivocolor E21 and Neutral Gray Ivocolor E17. It also has three basic shades SD0, SD1 and SD2, that form the base of the chroma that we will need for this type Figs. 7-8: Initial situation after milling Fig. 9: Manual re-work of zirconia in the green state Figs. 10-11: Final restoration after manual re-work, ready for sintering Fig. 12: Application of the colouring liquid DENTAL ASIA NOVEMBER/ DECEMBER <strong>2022</strong> 45
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Dental Asia November/December 2022

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