CNC milling and CAD/CAM software are revolutionising the use of machinable glass ceramics in dentistry.
The outstanding mechanical and chemical properties of machinable glass ceramics have made them the materials of choice for dental prosthetics, whether as implants or crowns. They are usually based on composites of magnesium oxide and alumina and silicon dioxide. In recent years, lithium disilicate is also used for bridges and copings as well as crowns and implants.
Dentistry materials need to have very special characteristics – in particular, their mechanical properties. They must have hardness, strength and a high fracture toughness. Even the slightest micro-fracture in dental materials will allow ingress of infection into the jaw and could cause serious illness.
So the dentistry materials have to have a high tolerance to corrosion and scratches, be very durable and last for many years – even decades.
The dental prosthetics must also look natural and match the patients’ natural teeth – a characteristic that should be taken into account during their formulation.
The machinable glass ceramics used in dentistry are really crystalline materials. This property is achieved through melting a glass composite followed by a controlled resolidification. The resulting crystal boundaries provide the ceramic with its machinability.
Now digital technologies such as computer-aided design (CAD) and computer-aided manufacturing (CAM) have become important factors in tooth replacement. Not only have specialist milling machines been developed to create new prostheses, but many clinics and even individual dentists are able to have these in-house.
The result is that not only are the prostheses completed over a faster period, but the dentist is able to control the process. This saves both time and expense for the medical practitioner and the patient.
Some milling machines have been developed to tackle different materials. They combine both dry and wet milling procedures and so eliminate the need to have separate devices and avoid the inconvenience involved in changeover when manufacturing complicated prostheses.
These technological achievements have led to the expansion of dental tourism. Countries such as Hungary and Costa Rica have become important dental tourist centres by offering treatments at far lower rates than the average dental cost in North America or Western Europe. However, the disadvantage has been that patients would need to wait for extended periods for their treatments to be completed. The CAD/CAM dentistry techniques allow treatment to be completed over a more reasonable period.
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