Dental crowns can be made as a ceramic fused to metal known as metal-ceramic crowns or full ceramic crowns. Ceramic fused to metal crowns are used for decades to replace missing tooth or as an anchor of the dental bridge. The core of the crown is made of metal alloy covered by ceramics. Zirconia crowns or full ceramic crowns are made out of crystalline dioxide of zirconia. Their core may be made up of zirconia with ceramic fused to the matrix or they can be made up entirely of zirconia known as monolithic zirconia crowns. There are many differences between metal-ceramic crowns and zirconia crowns and more advantages of zirconia crowns.
The main advantage of zirconia crowns is esthetics and the translucency of zirconia crowns should be considered as the most important characteristic since it is usually the first advantage of zirconia crowns that is visible for the patients. Zirconia crowns give better esthetic appearance than metal-ceramic crowns in general, but there are also fine differences between monolithic zirconia and ceramics fused to zirconia crowns. Monolithic zirconia crowns are made of single zirconia blocks and have minimal options for improvement of its esthetic characteristics while ceramic fused to zirconia crowns has a wide range of esthetical improvement by using few layers of ceramics, shading, and polishing. Monolithic zirconia lacks in translucency compared to ceramic fused to zirconia so better esthetic effects can be achieved with veneered zirconia crowns thanks to improved zirconia such as CubeX from Dental Direkt. Better translucency is what makes the more natural look of zirconia crowns in all light sources. Beside this, it is common that color of metal-ceramic crowns in the gingival area is compromised. Firstly, the crown thickness in this area makes an unnatural look of these crowns, but more importantly, the presence of metal is a greater problem in this area. During tooth preparation, so as cementation of the crown the gingiva is usually prone to bleeding. When cementation is finished ions from metal alloy may diffuse to gingiva making it darker during the time. This phenomenon is known as “metal tattoo” and it is not easy to remove. Depending on the extent of this change in gingiva, surgical procedures may be necessary. Luckily, whit zirconia crowns these problems can be avoided. Since there is no metal in zirconia crowns and with consideration of its color, gingiva keeps its natural look after cementation. Another issue related to gingival margin is the presence of metal under the gingiva in metal-ceramic crowns. The metal edge of these crowns will be visible as a “metal shadow” through the gingiva and that way change the entire esthetic impression of new crown even when the ceramic color is perfectly adapted to the present patient’s teeth.
The second issue in selecting the right type of crowns for yourself is the physical properties of the material. Definitely, the zirconia has high strength and that is exactly why it can be alternative to the metal core in metal-ceramic bridges. However, when we talk about the strength of the material it should be pointed out that there are few properties that define the strength of the material. The resistance to pressure and torsion, elasticity, and other forces that will appear during the chewing. Since chewing forces are greater in the molar area, your dentist will help you choose the best possible solution for your specific case regarding the optimum material strength and esthetics.
Besides previously mentioned differences and characteristics, another aspect that should be taken seriously when choosing the right crowns is the biocompatibility of material. Here again, the advantages go for zirconia. Biocompatibility is related to potential interactions between the dental material and human tissues. These interactions can be numerous and can lead to light irritations, to infections or even allergic reactions of different intensity. Zirconia is safe material and these interactions are very rare. When compared to metal-ceramic crowns it can be considered that the zirconia is the most biocompatible material for crowns. Previously mentioned “metal tattoo” is just one of many possible harmful effects of metal. The second most common reaction is gingivitis or inflammation of gingiva around the metal-ceramic crowns. Hypersensitivity or allergic potential to some of the elements of the metal alloy are the main causes of this condition but, not less common, the type of preparation for metal-ceramic crowns. Earlier suggestions were related to the deeper undercut of margins for future crowns. This means that dentist should cut deeper under the gingiva while preparing a tooth for the future crown which leads to extensive destruction of gingiva and a greater pressure of future prosthodontics on soft tissue around the crown, with consequent chronic gingival inflammation. Even though, current techniques in crown preparation suggest equigingival placement of crown margin this scenario is almost impossible with zirconia crowns since there is no alloy present in the subgingival area. Except this, the galvanic effect is avoided with zirconia crowns. The galvanic effect is a common problem with any metal material present in the mouth, whether old amalgam fillings are present or any kind of metal alloys as a part of dental crowns or bridges. As a result of the electrical current, the sensations of burning or pricking may be present.
Zirconia Implant abutments
When talking about zirconia crowns it is important to mention zirconia abutments. Abutments are parts of implant systems that actually connect and carry the crown on the implant. Zirconia abutments have many benefits over titanium abutments. Beside better esthetic appearance there is also better compatibility of zirconia abutments with surrounding gingival tissue which has enormous importance since the often esthetic problems with gingiva and interdental papilla around the implant, especially in esthetic zone. When we talk about zirconia abutments, it is important to mention that mesoabutment are considered as a golden standard. These abutments have a titanium base in the abutment and over that part customized zirconium .
So entire abutment consists of inner titanium part which is connected directly to implant (titanium to titanium interphase) and outer part of the abutment made of zirconia, so the future crown is connected to zirconia (zirconia to zirconia interphase). This way titanium-zirconia interphase between the implant and the abutment is avoided which favours the durability of implant-abutment interphase. There are many other benefits of zirconia abutment, such as greater biocompatibility i.e. better adherence of soft tissue around the implant and no plaque adhesion and natural look of gums around the implant with no metal shadow in this area that often is present with titanium abutments. Currently, the leading system on the market is Z-system from Switzerland.
Cad Cam Zirconia
One of the major concerns when choosing the right type of crown for you is the price. Considering the price of basic materials used for manufacturing the crown greater expenses can be expected with zirconia crowns. Beside this, for the precise and successful design of zirconia crowns special computer technology known as CAD-CAM should be used during laboratory process of production of your future crown. All of this makes zirconia crowns more expensive compared to metal-ceramic crowns. There are several types of zirconia depending on additional chemical modification in order to achieve better DDBioZX2, and DDBioZ. These cubes are different by their physical and esthetical properties and their indications may vary.
DDcubeX2 has great flexural strength, over 750 MPa and translucency of 49%, and in that way is considered as the ideal material for reduced and full contour bridges up to 3 units, especially in esthetic zone i.e. anterior teeth. DDcubeONE has an even greater flexural strength of 1000 MPa but lower translucency of 45% which makes it ideal for many different prosthodontics solutions: from veneers, inlays, overlays to full contoured and reduced bridges of 3 or more unites, so as hybrid abutment crowns. DDBioZX2 cubes with their greater flexural strength has different range of indications and may be used for full contour so as reduced crowns or bridges with more than 3 units, but also as a hybrid abutment and for bars, while DDBioZ can be used only for reduced crown or bridges of 3 or more units, but also for hybrid abutment and bars. Beside their indication based on physical properties, the esthetical properties are also of great importance in choosing the right material for your future prosthodontics, especially considering the price of these materials that is increasing exponentially with translucency. Since each type of zirconia has its own specific properties and depending on individual requirements in collaboration with your dentist you will easily choose the best one for you.