Dental Crowns: Are Porcelain Fused To Metal Crowns Safe?

Dental crowns are used to restore the function and aesthetics of teeth that have been heavily damaged and to protect them from further damage. When a tooth has decayed, a filling can be placed if it is small. However, if the decay is large, there might not be enough healthy tooth structure to place a regular filling. This is when a crown will be better to have enough strength to protect the remaining healthy tooth structure for the long term.

If your dentist has recommended restoring one of your teeth with a crown, then you might find it difficult to choose a suitable crown material that best fits your dental needs and budgetary constraints. This article will give you an idea of the different types of crown materials available for restoring damaged teeth.

What are different types of crown materials?

Crown materials can be broadly divided into two types; metal and non-metal.

Metal Crowns

These dental crowns are prepared from different metal alloys.

Gold Crowns – Gold alloy based dental crowns have been in use for restoring damaged teeth for a long time and might have seen some actors in old movies with “gold teeth.” Gold crowns provide an excellent balance between strength, safety and durability. However, their drawback is their metallic golden appearance, which may not be acceptable nowadays. Cost is also typically high, due to the rising cost of gold.

Metal Alloys or PFM (Porcelain Fused Metal) Crowns – These crowns are typically made from a mixture of non-precious metal alloys in which the main ingredient is nickel, cobalt or chromium, that is then covered with a layer of porcelain to achieve a white appearance. The great disadvantage is that they need to be prepared in thick sections to allow space for both layers of metal and porcelain thickness. Therefore, they require extensive removal of the healthy tooth structure. This weakens the tooth further and can increase the risk of needing root canal treatment.
Although it can appear white, it is usually easily distinguished from the natural tooth. Another one of their major drawbacks of porcelain metal crowns is the appearance of a dark silver metal line beneath the ceramic layer, which is quite unpleasant for many patients. Also, as the porcelain layer wears out over time, the underlying metal can be exposed and visible on the biting surface of the crown.

Metal Free Crowns

These crowns are made from tooth-coloured materials to provide lifelike aesthetics.

Resin Crowns – These crowns are made from tooth-coloured polymer resins. They can appear similar to natural teeth. Over time, they will lose their polish and appear more matte. They also tend to be less aesthetic than their ceramic counterparts. Minor chips can be repaired immediately by the dentist. The main advantage of resin crowns is that very little or no tooth structure needs to be removed for the crown. The overall strength of the crown is lower than that of other materials but is still strong enough for normal use.

Porcelain or Ceramic Crowns – The most beautiful and natural-looking option, they possess excellent strength, durability1, and aesthetics. This is why porcelain crowns are one of the most commonly placed prostheses in the oral cavity. Ceramic crowns can be bonded onto the tooth enamel for extra strength and retention, and thus require less tooth structure to be removed. In fact, more healthy tooth structure can be conserved with ceramic crowns, instead of having to be drilled away for the crown.

Zirconia Crowns – These crowns offer the best combination of strength, aesthetic appearance, and durability. They are white in appearance and similar to natural teeth. However, they are more opaque in nature, which makes them look slightly more bright in comparison to natural teeth. Zirconia crowns are very strong; they can withstand very heavy masticatory forces generated on the molar teeth. Also, they do not require the extensive sacrifice of natural tooth structure as they can be prepared in very thin (1mm) section. 

What are the differences between conventional and 3D CAD/CAM crowns?

Previously, dental crowns were prepared in the laboratory by using the impressions and study models of the prepared teeth. However, the prepared crowns were not always perfectly fitting, as there was still room for human error. For example, dimensional changes could take place in the impressions if they were kept in the open air for too long, or the distortion of the wax pattern of the prosthesis at any step. The impression quality also can vary depending on how deep the tooth margin or surface is. Also, problems could arise with the exact colour and shade matching of the crowns with the adjacent teeth, which meant multiple visits where the crown has to be sent back to be remade. Unfortunately, these drawbacks were more prevalent in traditional crowns as they required a higher number of steps for their fabrication.