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Technical ceramics are used in a wide range of applications because their use can be tailored to provide specific properties that are beneficial to each application. This is due in part to the range of properties that these ceramics offer, but also the range of ceramics available across different material classes. In this article, we look at how technical ceramics are used in dental applications and the property benefits that these materials bring.
What are Technical Ceramics
Technical ceramics are a class of non-metallic inorganic-based ceramics which provide specific properties, often mechanically or thermal-based, to a given application. There are many types of technical ceramics and the choice of ceramic is usually tailored to each specific application. On the classification front, inorganic technical ceramics usually fall within two categories— amorphous glasses and crystalline materials, although there are instances where these two categories meet and a hybrid of the two is used.
Focusing in on the two general classes that are used within dental applications, glass-based technical ceramics are often composed of silica materials and can also contain some amount of alumina within their compositional makeup—i.e. they are often aluminosilicate glasses. However, a wide range of filler materials can be added to the glasses depending on the dental application. On the other hand, crystalline technical ceramics are materials formed from sintered crystals and possess a dense, air-free and glass-free structure, most of which are some form of oxide (be it zirconia oxide, aluminous-oxide, or otherwise). Many of the hybrid materials still possess a core crystalline structure but they are filled with glass-based materials, such as alumina, zirconia or hydroxyapatite.
Areas of Dentistry That Use Technical Ceramics
The main area of use is in the restoration of teeth, be it for the fillings, implants, the replacement of crowns, and even as a bonding material in root canal procedures. Within these areas, different ceramics are used in different ways, and one of the most useful advancements has been the use of computer-aided design (CAD) and computer-aided manufacturing (CAM) processes which have helped to reduce both the time and cost associated with these procedures.
The Properties Which Are Beneficial For Dentists
There is a fine line in dentistry (compared to other applications) with balancing the aesthetics of how the ceramic will look against the properties they provide. As many people care about how their teeth look, it is one of only a few applications where the materialistic properties and aesthetic look need to be balanced. So, on one hand, the glassier the ceramic is, the more translucent and aesthetically pleasing it will be. However, highly glassy ceramics tend to be weaker and are more susceptible to crack propagation. On the other hand, highly crystalline materials have much better mechanical properties, but it is often at the expense of aesthetics. Considering many people want dental treatments to be aesthetically pleasing as well as functional, dental ceramics are developed with both factors in mind.
Nevertheless, the area is well-developed and has advanced significantly over the years to the point where both aspects can be achieved with a high success by using hybrid materials (gone are the days of ‘ugly’ dental treatments). Each type of ceramic component brings something to the application, be it for using different oxides to develop the appropriate opacity of the ceramic, to using Kaolin as a binder material, or even using feldspar to better initiate the fusion of the ceramic into a solid mass. Overall, regardless of the aesthetic principles, there are a couple of key properties that are realized by using technical ceramics in dental applications. These are a high strength and fracture toughness.
Strength
Strength is a big factor for dental applications. Technical ceramics have a high fatigue strength which enables them to be used for long periods of time and are extremely durable—which is a significant benefit considering the amount of mechanical stress that they are under in the mouth. Technical dental ceramics also have a high resistance to compressive stress, which is again important as the motion of eating often imparts a large amount of compression onto the teeth. However, the strength is limited by the strength of the filler within the ceramic, but the overall strength is not the most important factor.
Fracture Toughness
The fracture toughness is the most important and beneficial property that technical ceramics bring to dental prosthetics. Fracture toughness is the ability to resist crack growth, and in dental prosthetics, this is a crucial factor as any broken ceramics would need to be replaced and this would soon get costly and time-consuming. Therefore, the technical ceramics used in dental applications have a higher resistance to cracking than many other materials.
There are three different ways that technical ceramics provide this crack resistance in dental applications—these are through crack tip interactions, crack tip shielding and crack bridging. In crack tip interaction mechanisms, particles within the ceramic impede the crack motion and deflect it into a different plane so that the ceramic is no longer subjected to the original tensile strength that caused the crack. In crack tip shielding, an internal toughening mechanism occurs, through either a transformation or microstructure blocking approach, that reduces the stress of the crack. For crack bridging, some of the particles act as ‘ligament’ which in turn makes it harder for the cracks to open. Regardless of the mechanism employed, it enables technical ceramics to be much more resistant to cracking than other materials.
Other Properties
Aside from the two main benefits, technical ceramics also possess a high biocompatibility that enables them to be used within the body without complication, they have a high surface hardness, the thermal expansion of technical ceramics nowadays is almost comparable to that of a natural tooth, and there is a high adhesion affinity between these ceramics and the natural tooth which helps to promote long-term cohesiveness and durability.
Sources and Further Reading
- Ceramic Industry: https://www.ceramicindustry.com/articles/95536-technical-ceramics-empower-medical-and-dental-advancements
- “Ceramic materials in dentistry: historical evolution and current practice”- Kelly J. R. and Benetti P., Australian Dental Journal¸ 2011, DOI: 10.1111/j.1834-7819.2010.01299.x
- “Dental ceramics: a review of new materials and processing methods”- da Silva L. H. et al, Brazilian Oral Research, 2017, DOI: 10.1590/1807-3107bor-2017.vol31.0058
- “Dental Ceramics: Part I – An Overview of Composition, Structure and Properties”- Babu P. J. et al, American Journal of Materials Engineering and Technology, 2015, DOI: 10.12691/materials-3-1-3
- “Properties and Clinical Application of Three Types of Dental Glass-Ceramics and Ceramics for CAD-CAM Technologies”- Ritzberger C. et al, Materials, 2010, DOI: 10.3390/ma3063700
- “Dental ceramics: An update”- Shenoy A. and Shenoy N., Journal of Conservative Dentistry, 2010, DOI: 10.4103/0972-0707.73379
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