Attractive and with character

17. November, 2019
Fig. 1 - High-esthetic zirconia restorations with an individual character

This is my protocol about the correct handling of zirconia materials such as Zolid HT+ Preshades which can be applied to all kind of esthetic restorations starting with single crowns up to implant-supported full arch cases. In this article, I will show how to individualize and characterize high-esthetic monolithic zirconia restorations in a very efficient and easy way. For this case I have chosen two show-cases. A monolithic tooth-supported full-arch 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+ Preshades.

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’ll 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 finalize 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 Characterization
To achieve an optimum esthetic 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 (Fig. 7). For this we must 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 Zolid Green State Finishing Kit (Fig. 8). 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 characterization 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 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 esthetics and the natural appearance of the restoration.

Infiltration
This stage has the least influence on the final result, but it is the most “dangerous” step. We must improve the chroma and the effects of the restoration without a real and immediate visualization of the colors we use. The final color becomes visible for the first time after the sintering process. To achieve esthetic 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 coloring 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 visualization and implementation works quite easy. For this process step I recommend the following preparation:
1. Prepare all the colors 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 behavior.
4. Apply the chroma (dentine liquid) to the intended areas, i.e. approximal, cervical and occlusal. Due to the use of preshaded zirconia, the color only needs to be reinforced in those areas.
5. Apply the effects e.g. in the incisal area.

Surface preparation and color customization
The pictures Fig. 9-12 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 behavior of zirconia. If the restoration meets all requirements after sintering, we can concentrate on the most important aspect, the esthetics. In that case I used the staining system “Ivo-color” 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 Cº to 890 Cº without harming its properties. The second reason is it’s optical behavior. This kit has three unique colors on the market: Ivocolor E22, Magenta Ivocolor E21 and Neutral Gray Ivocolor E17.  It also has 3 basic shades SD0, SD1 and SD2, that form the base of the chroma that we will need for this type of work. This system allows users to apply smaller amounts of material, saving on costs, reducing time and errors.

First stain firing
For the first firing, I apply glaze as a base. At this stage, it is possible to take advantage of the great margin of fusion that these stains have and also to apply a little chroma (SD2) to the body of the teeth and to increase depth in the approximal spaces (Ivocolor E11 Mahogany). The first bake is the most important to prepare the surface for good esthetic results, facilitating the application of the next layers, but also providing a good base for the adhesion of the ceramics used. In order to achieve high-esthetic results, a lot of attention must be paid to the consistency of the glaze. Apply small amounts of stains in each application, maintaining a smooth and uniform color. It is crucial to be careful with this detail for every firing. Keep in mind that in all firings, effects can be added and chroma can be improved (Fig. 13-16).

Second stain firing
With the next stain firing we have the opportunity to work very predictably. The anatomy, the shape and the function are done and now we can apply the necessary colors to make the work look as natural as possible. One of the great advantages of using only stains for monolithic restorations is the possibility of seeing the result of the firing before going to the furnace. The colors of the stains stay the same before and after the firing, so besides the form, we also achieve predict-ability in colors and effects (Fig. 17&18).

The ceramic firing
In this stage of the protocol, we add veneering ceramics to the surface of zirconia. Again, let’s take the advantage of all the firings to add more detail so that we can finish the job as quickly and simply as possible. Ideally, we will try to make just one our two ceramic firings. We apply the ceramic materials in the desired places and in the monolithic areas and, of course, we can also add effects and improve the chroma with stains (Fig. 19, 20&21). Thus, we reduce the thermal stress of the zirconia and ceramic, and we gain time. Remove the zirconia frames from the furnace when the temperature reaches 250 C, too high temperatures can lead to thermal stress and fractures.

Finalization
In this case, I will not go into the surface treatment any further. That would go beyond the scope here and is also very individual from technician to technician and highly dependent on personal taste. Although I would still like to give a hint. Zirconia is characterized among other things by its high biocompatibility, which demonstrates very good behavior on the contact points with the tissue if properly processed. There are already numerous studies that prove this. When zirconia is high-gloss polished, the material shows an extremely smooth surface. This prevents the excessive colonization of bacteria and significantly improves wearing comfort for the patient. So, when finishing the restoration, we have to make sure that all contact points with the gingiva are carefully polished. In addition, these areas should never be stained or veneered, as this in turn could lead to a deterioration of wearing comfort and to plaque adhesion. It is also essential to ensure a clean and gap-free connection between the titanium base and the zirconia frame. A gap can lead to the colonization of undesirable bacteria (Fig. 22-24). For monolithic zirconia restorations, the polishing of the occlusal contact points is also extremely important. Only a high-gloss polished surface prevents abrasion of the antagonist.

Conclusion
With the arrival of CAD/CAM technologies, the doors for zirconia were opened. Nowadays the great evolution of this material allows us to obtain highly esthetic results in a predictable way, by using only small cut-backs or even full-contours. Mechanically, we reduce the possibility of fractures, and if we apply this protocol to any ceramic system, we should have a homogeneous restoration with predictable results. I believe that Zolid HT+ Preshade changed the game in a lasting way. This article is based on two show- cases, where we show a characterization with a lot of effort and in the end, with a high-esthetic result (Fig. 25-28) in a simple and fast way. 

Categories: Ceramics, Software