Which material is the best for a dental crown?
There are a number of factors that influence the choice of material for a dental crown. A full gold crown is a metal crown that has been in use for a long period of time and therefore has a large proven record of success. In particular, in one retrospective study1 it was found that 94.1% of all the gold crowns were still in place 40 years after they were initially placed. The amount of tooth structure removal required for a full gold crown is lesser than a metal and porcelain, all porcelain crown or a zirconia crown. They have greater strength and are more resistant to fracture. In addition, they do not wear the opposing tooth to the same degree as a metal and porcelaincrown. Poor aesthetics are the main disadvantage of full gold crowns and therefore they are recommendedfor molar teeth where they wouldn’t be visible when smiling or during speech. Rarely, allergic reactions may occur to the base metals that are present in the gold alloy.
Metal and porcelain crowns, known as porcelain bonded to metal (PBM) or porcelain fused to metal (PFM) crowns combine the strength of the metal with the aesthetics of the porcelain. They are composed of a metal substructure that is overlied by a veneering porcelain. They have a record of clinical success that extends over 50 years and survival rates exceeding 95% over 10 years. The main disadvantages of metal and porcelain crowns are that their aesthetics are not as good as all porcelain or zirconia crowns, they can have grey discoloration near the gum margins and they can cause wear of the opposing tooth.
All porcelain crowns have improved significantly over the last 10-20 years and have the greatest aesthetics compared to metal, metal and porcelain and zirconia crowns.The main disadvantage of porcelain is that it is brittle and can fracture easily. Previously, the use of porcelain had been limited to veneering of stronger substructures like metal or stronger ceramics. However further developments in porcelain have resulted in the formation of lithium disilicate, also known as e.max. Lithium disilicate has increased strength and is more resistant to fracture compared to other types of porcelain and can be used as a uni-layered material (without a metal or stronger ceramic substructure) for crowns. Therefore, all porcelain crowns can be a great option for front teeth where their excellent aesthetics aredesiredbut they are not placed under heavy loads.
Zirconia crowns have recently become a popular option.The main advantages of zirconia are that it can be better matched to the colour of the natural teeth and is more aesthetically pleasing than a metal or a metal and porcelain crown. Other advantages include high strength and resistance to fracture. Disadvantages of zirconia include poorer aesthetics compared to e.max crowns and questionable bonding to the underlying tooth. This makes Zirconia a great choice for a crown on the back teeth where its strength and colour matching ability is desired but it doesn’t need to have excellent aesthetics.
1Donovan et al. Retrospective clinical evaluation of 1314 cast gold restorations in service from 1 to 52 years. J EsthetRestor Dent 2004;16(3):194-204
