For many years the industry standard for fixed bridges were porcelain fused to metal, often called “PFM bridges.” These restorations provided good aesthetics and are resistant to wear. However, since technology and research has progressed, newer all-ceramic materials have been introduced, some of which were ideal for restorations within the aesthetic zone. Unfortunately, they lack the strength and durability required for posterior restorations. For example, lithium disilicate, is generally only suitable for anterior restorations. Sometimes, depending on circumstances, these dental ceramics will fail in the connector area. Therefore, Increasing the connector size could affect aesthetics and functionality.
The introduction of zirconia has conquered these problems, by combining excellent strength with aesthetics. The ability to use smaller connectors is preferable for periodontal health because the connector size is comparable to PFM bridges. Zirconia is strong enough to allow the thickness of the core material to be reduced, which can be helpful from an aesthetic point of view. Zirconia has been carefully studied for its biocompatibility and has been found to have good compatibility with tissues. It is an attractive material for people who would prefer to have metal-free bridges because of metal allergies. Although allergies and sensitivities to dental alloys are quite rare, it is still something that should not go unnoticed. In this case, a zirconia bridge is a great biocompatible and highly aesthetic choice.
The characteristics of zirconia make for a good posterior bridge as well as an anterior bridge. Studies have shown the survival rates for zirconia bridges have held up quite well over a five-year period. The only recorded complaint was of the veneer material fracturing. This could be due to bond failure between the veneer material and the zirconia substructure, especially in posterior regions and where it is subjected to stronger mastication forces, particularly in patients with bruxism. Manufacturers have responded to this problem with the introduction of solid or monolithic zirconia, which is stronger and more suited to patients with bruxism. One issue with these studies is that they are still short-term because applications for zirconia usage are still relatively new.
When selecting zirconia for a bridge, it is important to choose the correct form for the clinical requirements of the patient. Choices include, solid zirconia, layered zirconia and high-translucent zirconia.
Solid zirconia is monolithic and made from pure zirconia. This material has a high flexural strength of 1200 MPa while still maintaining lifelike translucency. It also has a natural opalescence. Solid zirconia is extremely strong and is an ideal material for patients who may have bruxism. Solid zirconia is particularly good for posterior bridges or where the tooth preparations are discoloured or have been endodontically treated. Due to the higher opacity of solid zirconia, it is not recommended for anterior bridges.
With 720 MPa, high-translucent zirconia has a higher flexural strength than PFM restorations, yet they can maintain a natural translucency, closely replicating the vibrancy of existing teeth. The material is perfect for anterior and posterior bridges of up to 3 units and aesthetics are superb. High translucent zirconia may not be ideal in certain situations where orthodontic situations cannot be corrected using restorative methods.
Zirconia can be the ideal choice for bridge restorations provided the proper selection and preparation is followed. These CAD/CAM-generated restorations provide an excellent and very precise marginal fit which when combined with exceptional aesthetics can help to increase patient satisfaction.
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References:
https://www.dentalaegis.com/cced/2012/01/evaluation-indicates-zirconia-bridges-acceptable-alternative-to-pfms
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3935908/