August 18, 2014
Crowns in general are tooth shaped restorations that are used for improving the general appearance of teeth. Crowns serve their purpose by completely covering the tooth surface that is visible. These crowns are made from various types of materials but we shall focus on the porcelain fused to zirconia crowns (PFZ). This crown has become one of the favourite choice for both dentists and their patients. The reason for this preference is because this type of crown combines strength, durability and aesthetics.
Porcelain fused to zirconia crowns are formed by porcelain being combined with zirconium oxide. The zirconia base has a white shade and is layered with porcelain to match final restoration. The porcelain fused with zirconia crowns are designed and milled using computer aided design or computer aided manufacturing technology. Crowns are used for restorative purposes improving the functional and aesthetic qualities. Porcelain fused to zirconia crowns unlike metal based crowns allow more light to pass through them and this makes them more suitable to be used on anterior teeth.
Zirconium is also preferred by dentists since this material does not produce any chemical reaction in the mouth (ZiO2 is biocompatible). This is an important factor since some reactions would damage the crown or cause allergic reactions in the long run. Zirconia is an element to fuse with porcelain since the bonding process between the porcelain and the zirconia is stronger than it is with other materials such as gold. PFZ crown is also less likely to fracture as compared to porcelain fused with gold.
Having too many restorations in the mouth exposes you to the risk of having a number of metal alloys with different electric potentials. Since the saliva can act as a conductor, minor electricity can run in between the metal restorations. Such condition is known as oral galvanism or electrogalvanism.
There are other alternatives to porcelain fused zirconia crowns such as the porcelain fused to metal (PFM). The PFM crowns consist of porcelain being fused to metal alloys. The advantage of this type of crown is that the underlying metal fused with the porcelain provides great strength and stability. The disadvantage associated with it is that it does not allow much light to pass through unlike the porcelain fused to zirconia crown and if some gum recessions appear the edge of the crown will look darker than the other part of the PFM crown.
The process of putting a porcelain fused with zirconia crown includes examining the patient and making an assessment of the tooth. Secondly the dentist preps the tooth and takes impressions which he sends to the dental laboratory. A temporary crown should be made in order to protect the tooth, restore mastication and prevent the overeruption and migration of the adjacent teeth. After the dental crown is back from the dental lab the dentist fits it in. The crown fit appointment is quick and does not require anaesthesia. The dentist removes the temporary crown, cleans the temporary cement and glues the permanent crown in. The patient is then provided with information as how to take care of the crown. This would include aspects such as daily flossing, brushing and having his dental checks regularly.
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Great piece here. Really enjoyed the points about Zirconium. We just finished a blog up the other day about crowns as well if you wanna check it out http://blog.hospitaldentalgroup.com/what-is-a-crown/
20 August 2014
Thanks for sharing, Matt Hersee. It is surprising that we, as dentists, still got questions like 'What is a crown?' or 'How does a crown look like?'. Therefore posting basic educational articles do make sense for the wide audience.
20 August 2014