Increasingly, patients are demanding dental restorations that provide excellent aesthetics and functionality. Most ceramic restorations can meet these needs, and there are many different types on the market. Achieving a successful restoration depends on the clinician’s ability to select the appropriate material and follow the right preparation and cementation protocols. Selection should be based on the ceramic’s physical properties, which include fracture resistance, strength, wear resistance, and long-term durability. One of the most popular materials is zirconia. Modern zirconia is very different from its original bone-white incarnation.
Zirconia is renowned for its strength and durability, and the latest generation of zirconia materials provide excellent aesthetics. The restorations are fabricated using CADCAM technology, and choices include monolithic restorations, which are suitable for posterior crowns and bridges, and layered zirconia restorations, which are especially suited for long-span bridges anywhere in the mouth. Zirconia’s flexural strength ranges from 590 MPA for high translucent zirconia to 1400 MPA for monolithic zirconia. Zirconia restorations can be cemented using self-adhesive resin cement or resin-modified glass ionomer cement.
If the patient expresses interest in an all-ceramic restoration, or if you feel that it’s the best material for a case, then consider the indications and the limitations of zirconia restorations. Points to think about include:
Considering these factors will help you select the right material for each case. The aesthetic zone refers to teeth in the anterior sextant. However, sometimes the aesthetic zone can extend as far back as the first molar depending on the patient’s facial musculature, their smile line, and their expectations for treatment. Functional zone teeth are typically premolars and molars, although premolars can fall into both categories. While anterior teeth are also functional, the forces they generate are typically much lower than the occlusal loading forces in the functional zone.
You must consider occlusal forces when planning indirect restorations in the functional zone. Zirconia provides an excellent alternative to more traditional PFM restorations, where limited space results in adhesive failures between the metal and porcelain. Initially, adhesive failures were reported in early layered zirconia restorations, but the preparation design has been modified, and techniques for bonding layered porcelain have improved considerably. Now, functional cusps, occlusal form, and marginal ridges may be designed in full-contour monolithic zirconia, while non-functional areas, such as non-functional cusps or buccal surfaces, are layered. Monolithic zirconia is suitable for posterior crowns and multi-unit bridges.
Zirconia restorations in the aesthetic zone must closely mimic the color and translucency found in natural teeth and need to absorb, scatter, and reflect light in a similar manner. While lithium disilicate is highly aesthetic, it doesn’t have zirconia’s strength and cannot be traditionally cemented; it must be resin bonded. One significant advantage of choosing zirconia is the ability to cement it traditionally and, with the introduction of high translucency and multi-layered zirconia, it is now possible to create restorations that closely mimic natural teeth. High quality processing improves translucency and minimizes the effects of impurities and structural defects that alter the way zirconia reflects light.
Early monolithic restorations had high opacity and high values, and, while very strong, they lacked the aesthetic qualities needed to satisfy patient demands. Now, monolithic zirconia restorations can meet the demand for excellent strength and good aesthetics and are proven to be clinically reliable. Monolithic restorations are also highly suitable for successfully masking underlying dark tooth structure. Patients who are heavy grinders and who have experienced previous restoration failures can benefit from monolithic zirconia restorations. A recent study showed that the risk of complications is low, and patient acceptance is high.
When zirconia was initially introduced, there was a concern that it could cause high wear to the opposing dentition, a view that is now challenged. Zirconia can be gentler to opposing dentition compared with traditional PFMs. Zirconia’s low wear properties are attributed to its microstructure and small grain size. The small grain size allows the surface to be highly polished, which makes it kinder to the opposing dentition. The latest generation of zirconia products being developed offers improved translucency and opalescence and can be milled with multiple shades and translucencies.
For years, titanium implants have been regarded as the gold standard, but zirconia implants are increasing in popularity. Initially, only one-piece zirconia implants were available, which were not always able to meet prosthodontic requirements. One-piece implants are immediately exposed to masticatory forces from the tongue, and implant restorations must be cemented in place. Now, two-piece zirconia implants are more readily available, allowing for custom abutments. Zirconia implants are preferable where there is risk of the titanium gray color shining through the peri-implant tissues. Moreover, any release of metal ions can discolor gingiva after implantation, leading to dissatisfaction with the long-term aesthetic results of treatment.
Approximately 0.6% of patients have a titanium allergy, and, although uncommon, zirconia implants offer a good alternative treatment and appeal to patients who would prefer metal-free dental restorations. The white color of zirconia implants will not affect appearance, even if some gingival recession occurs. Additionally, zirconia implants have shown an excellent ability to integrate with soft and hard tissues. However, zirconia dental implants are a newer product, and long-term research into their use is still very limited.
When used correctly, zirconia is a fantastic material, capable of producing high-quality outcomes and increasing patient satisfaction. Proper tooth preparation is also essential. If you would like specific advice about which material to select for a case, please talk to our technical team.
Please be reminded that our experienced technical team is here to assist you should you wish to discuss a case in more detail.
Click here to schedule a consultation with our technical team »
References:
http://decisionsindentistry.com/article/selection-guidelines-ceramic-restorations/
https://www.sciencedirect.com/science/article/pii/S0300571218300253
https://www.nadl.org/userfiles/files/Technical%20from%20JDT_2_18.pdf
https://onlinelibrary.wiley.com/doi/full/10.1111/prd.12180
https://www.tandfonline.com/doi/full/10.1080/17436753.2016.1264537