Dental Crowns Part II
In my last blog I was presenting about crowns (or caps). At the end of the last blog, I mentioned about the four major types of dental crowns:
- Gold alloys – These crowns are made with a mix of gold, copper, palladium, platinum, and silver etc. They are strong, nor do they crack or chip. They are kind to your natural teeth as they are not coarse and abrasive to the opposing teeth during chewing and grinding.
Ceramic — These are used for restoring front teeth and are popular in this area for their ability to blend with your natural tooth color. There are different kinds of ceramic with different physical and aesthetic properties. They are generally strong but brittle. Therefore, they can be chipped and fractured off under excessive stress or prolonged wear.
- Porcelain-fused to metal (PFM crowns) – These crowns intend to provide a mixture of strength of metal and beauty of porcelain. However, the porcelain can still be chipped off from the metal substructure. The other drawbacks are the difficulty in matching the chroma, value and translucency of a natural tooth with a PFM crowns.
- Base metal alloys – These crowns are made up of non-noble metals that are highly resistant to corrosion and make for a very strong crown. It also requires the least amount of healthy tooth to be removed prior to fitting.
The four main types each has its own unique physical properties, colours (shade, chroma, and translucency), costs and tooth preparation requirements. Before you dentist prepares the tooth for a crown (after it has been decided that it is the best treatment for the tooth), he or she needs to know what kind of crown the tooth is going to be before the treatment.
1. Gold crowns
Gold crowns are strong and durable. However, they are not the best choice for front teeth because of their golden metallic colour. They are mainly selected for the molars where both strength, durability and/or preservation of natural tooth structures are important.
The main advantages of gold crowns are:
- They are strong and resistant to fracture/crack
- They last a long time if properly cared for
- Less reduction of your natural tooth is needed
- They wear down like the enamel of natural teeth such that they preserve the enamel of the opposing natural tooth during chewing and grinding
- They are ideal for posterior restorations (back teeth), especially second molars
The main disadvantages of gold crowns:
- Poor aesthetics due to the metallic appearance
- Potential allergic reactions to one of the metals in the gold alloy
- The cost of gold crowns is generally high especially when the gold is expensive nowadays
2. Ceramic Crowns
They are generally white or tooth colour and so they are definitely the most popular type of crown used nowadays. Ceramic materials include porcelain (feldspathic porcelain, derived from the natural mineral feldspar), zirconia (zirconium dioxide, combined with some other metal oxides) and EMAX glass (lithium disilicate). There are some combinations of the different ceramic materials to achieve high strength and esthetic. For examples, a layered zirconia crowns has a layer of translucent porcelain baked onto the zirconia crown.
The main advantages of ceramic crowns are:
- Porcelain or ceramic crowns provide the best and most natural look. They match your surrounding teeth in shape, size, and color.
- The best option for front teeth restorations.
- They are exceptionally biocompatible.
- The zirconia crowns are also suitable for posterior molars because of the high strength and good resistance to fracture.
- Some of the ceramic crowns can be milled chairside with a CAD/CAM machine. Therefore, you can have the crown in one sitting instead of two.
The main disadvantages of ceramic crowns are:
- They are not as strong as metal crowns. Porcelain crowns can last a long time, but they have to be well taken care of.
- Both porcelain and EMAX lithium disilicate crowns can prone to fracture.
- The zirconia crowns are difficult to adjust if the contacts are high.
- Once adjustments are done to the zirconia crowns, the adjusted surfaces are very difficult to be smoothed and polished. The adjusted zirconia crowns can be more abrasive and also prone to microfracture.
- Patients who suffer from bruxism should not consider ceramic crowns as the first choice for their teeth at the back like molars or premolars
3. Porcelain Fused-to-Metal Crowns (PFM)
Porcelain fused-to-metal (PFM) crowns are another widely used type of dental crowns. They provide both strength (due to their metal structure inside) and aesthetics (the porcelain coat outside).
The main advantages of PFM crowns are:
- They provide great aesthetics and durability
- They’ve been around for over 50 years. We know they work well.
The main disadvantages of PFMs include:
- The metal in these crowns may cause a grey line at the gumline.
- The crowns are white or tooth coloured, but they do not have the 100% aesthetic look that all porcelain crowns provide (because the porcelain coats are thin and the underlying metal structures are generally dark).
- For people who clench their teeth, this type of crown may wear down more easily against the opposing teeth.
- The porcelain can be chipped off and revealing the underlying dark metal.
4. Base Metal Crowns
The alloys used are mainly base metals. Their noble metal content is less than 25% (they may have none). They often contain large percentages of nickel, cobalt, chromium or beryllium.
The main advantages of base metal crowns are:
- They are generally hard and highly resistance to corrosion.
- They generally require the least amount of healthy tooth to be removed prior to fitting.
- The costs are generally low.
The main disadvantages of base metal crowns are:
- They are not aesthetic due to the metal colour.
- Some of the metals have been shown to trigger an allergic reaction with some patients. Nickel, chromium, palladium and cobalt have all been implicated.
At Affinity Dental Care, we provide different type of crown and bridge treatments to our patients based on the needs and best option criteria. We always put our patients’ health and well-being in the forefront.