What is a dental crown?
A dental crown is a tooth-shaped ‘cap’ that is placed over a tooth to cover the tooth to restore its shape, size, strength and at the same time improving its appearance.
What does a dental crown do?
A dental crown may be needed in the following situations:
- To protect a weak tooth (for instance, from decay, where more than 50% of healthy tooth substance has been lost) from breaking
- To restore an already broken tooth or a tooth that has been severely worn down
- To cover and support a tooth with a large filling when there isn’t a lot of tooth left
- To hold a dental bridge in place
- To cover mis-shapened or severely discolored teeth
- To cover a dental implant
- To make a cosmetic modification
- Cover a tooth that has had root canal treatment
What are dental crowns made of?
A few materials are currently available in the market. Each has its own advantage and drawbacks, listed below.
Gold was the most common material used for crowns before other materials were developed. Because pure gold is too soft for crowns, dentists use an alloy. Gold still offers plenty of advantages over other materials:
- Thinness. Other crown types typically need to be thicker to provide proper support. Because gold is malleable, less of the tooth has to be filed away to fit the crown.
- Durability. Some people need crowns because they have damage from clenching or grinding their teeth. Other crown types are less forgiving, so gold is the best option, especially for molars. Gold crowns can last for decades without replacement.
- Lower reactivity. One of the reasons dentists use gold instead of other metals is because gold is the least likely to cause irritation to the delicate tissues in your mouth.
The obvious downside of gold crowns is the color—they are not the best choice for a uniform smile. However, if only one of your back teeth needs to be capped, don’t be so quick to dismiss gold. It is one of the most accurately fitting types of crowns with the longest lasting results. They are also the least abrasive on your other teeth.
Metals used in crowns include alloys that have a high content of gold or platinum, or base-metal alloys (for example, cobalt-chromium and nickel-chromium alloys). Metal crowns withstand biting and chewing forces well and probably last the longest in terms of wear down. Also, metal crowns rarely chip or break. The metallic color is the main drawback. Metal crowns are a good choice for out-of-sight molars.
Porcelain Fused to Metal (PFM)
Some crowns are made with porcelain fused to metal. These were the result of trying to combine the beauty of porcelain with the functionality, strength and longevity of metal (i.e. gold alloy, cobalt-chromium etc.)
The lower layers of the crown are metallic, while the final layer is made with porcelain. This helps to offset the blatant appearance of an all gold/metallic crown. These crowns are very durable, but there are some drawbacks. The metal layer beneath the porcelain can stain the gum line to look dark gray or black. The metal layer will also give the crown a more opaque look. Due to this reason, PFM crowns are less commonly used in the anterior teeth region.
These combination crowns are most suitable for patients who still have trouble with grinding their teeth but who really don’t like the idea of an all-gold cap, or for those who have several gold-based crowns already and need a replacement to match to the others.
There is nothing like an all porcelain crown when it comes to full cosmetic effect. A nicely crafted porcelain crown is a work of art, and offers these benefits:
- Realistic. It matches the shape and size of your original tooth exactly. Porcelain has the semi-transparent appearance of real teeth.
- Strong. Porcelain is a strong material, so it takes a good deal of force to damage the crown.
- Glazed surface. The highly polished and glazed surface mimics the natural gloss of our teeth, with the added benefit of not picking up stains.
Unfortunately, there are some downsides to porcelain. Porcelain is actually harder than your natural enamel, so when you chew or grind your teeth, the porcelain crown can damage opposing teeth. This is why porcelain crowns, while beautiful, are not the best option for those who have trouble with bruxism and clenching.
Porcelain crowns are also thicker than metal gold caps, requiring that more of your original tooth be filed away to make room for the fitting. If your tooth is already unstable, a different material may be needed. They can also be more expensive because of the artistry involved in their creation.
Porcelain crowns may eventually need to be replaced in your lifetime, as they typically last from 5 to 15 years. You can extend their life by chewing carefully, avoiding hard foods like ice and brittle candy, and not using your teeth to chew fingernails or open packaging.
Zirconia is one of several newer ceramic-like materials that combine the strength of metal with the aesthetic appeal of porcelain.
Zirconia has some distinct advantages as a material for crowns:
- It can be matched to the color of existing teeth.
- It is extremely strong, eliminating the need to use a metal base for strength.
- It can be layered with porcelain, further improving its aesthetic appearance.