What is a Porcelain Fused to Metal Crown (PFM Crown / POM Crown)
Porcelain-fused-to-metal crowns have long been considered the gold standard for the repair of damaged teeth. This type of fabrication design has been and continues to be the most common type of crown or bridge done in dentistry for 35 years. Porcelain fused to metal crowns are cast metal crowns which have a porcelain covering over it. The tooth colored ceramic is baked on top of a metallic alloy substructure called a coping for the ultimate in strength. The metal sublayer is thin, strong, and fits perfectly over the prepared teeth. The dentist will choose what type of metal to use depending on the quality level of the office. High noble gold alloys (greater than 12 caret) are the highest quality choice due its accurate fit and biocompatability. The baked on porcelain layer is 1.5 mm to 2 mm thick and is fashioned to have the same anatomy and optical characteristics as a natural tooth. The porcelain layer is tough, and withstands chewing forces very well. You could look at them as a hybrid between all porcelain and all metal crowns.
Although all-porcelain crowns are strong, there are many circumstances when a PFM version is a better choice. The PFM crown is stronger and more versitile in many clincal situations. It is often used when destructive night grinding is a problem or when long span bridges are needed. This type of crown can take more chewing force than all porcelain versions. The longevity and esthetics of these restorations can vary significantly depending on the quality level of the dentist and laboratory technician team that makes it. Absolutely fabulous esthetic results can be achieved with PFM crowns if your dentist works with a true ceramic artist.
Advantages of porcelain fused to metal crowns
- They can save your tooth!
- They are stronger and often more durable. The underlying metal support makes your crown stronger and more stable.
- They have a very high rate of success in the long run. The track record for these crowns is 70 years.
- PFM or POM (porcelain fused to metal is the same as porcelain on metal) is a preferred choice when long bridges are required and night grinding is a problem.
- PFMs made with a high noble metal substructure are very biocompatible. When the dentist chooses gold as the metal substructure, it is totally non-reactive and does not irritate gum tissue or bone. As long as the fit is good, the tissue will be very healthy.
- They can be cemented even when the tissue is unhealthy. The delivery process is much less complicated and usually can be done without novacaine. Porcelain crowns require bonding with gum tissue management. If the tissue is unhealthy, it is difficult to get a perfect seal.
- Fewer issues with sensitivity after they are delivered into the mouth
Disadvantages of porcelain fused to metal crowns
- A high quality metal based crown is more costly because the laboratory fee is higher to get the same level of esthetics as an all-porcelain crown. The popularity of PFMs is declining in favor of the all porcelain types of crowns. Porcelain crowns without metal substructures are easier to make pretty at a lower lab fee price point.
- A PFM crown is totally opaque to light. It will not trans-illuminate light down the root of the tooth. When a patient has thin gum tissue, the illuminated root of a non-restored natural tooth will brighten the gum tissue color. When there is a PFM is on the tooth crown, no light is able to illuminate the gum area and the resulting darker gum can be very visible in some patients smile.
- The porcelain from the PFM crowns can chip off when you bite on very hard foods.
- When a dentist prepares (drills down) a tooth for a PFM, at least 2mm of enamel has to be removed over the entire exposed surface of the tooth. The more natural tooth structure you have remaining the better.
QUALITY LEVELS and COSTS of PFM or POM CROWNS: Non-precious vs. high noble gold
Depending on what market niche your dentist operates in determines what your porcelain-on-metal restoration will look like. The average American dentist will contract with a laboratory to construct a PFM for about $155. This cost is usually hidden and rolled into the fee for service that the dentist charges you. An average crown will have a medium quality ceramic fused or baked over a base metal (non-precious alloy or low noble) coping. It will approximate the shape and coloration of a natural tooth. The dark metallic coping will be exposed at the margin or edge yielding a dark or black line at gum. For $60 more, the dentist could request a “porcelain-butt-joint-margin” so if or when the gum receeds, an exposed metal margin will not appear. Because all the lab costs are rolled into the price of the service, patients are rarely informed of what their dentist is selecting and prescribing for them. An inexpensive dental office might pay as little as $35 as a total fee for a mass production laboratory which is often offshore to make your restoration. At this level of quality, the coping will be an inexpensive non-precious alloy and the ceramic will be more opaque. Cheaper alloy does not cast well and will not fit as intimately and has less biocompatibility. Dr. Fondriest uses 14+ carat gold alloys (high-noble alloys primarily containing gold, platinum, palladium) under the veneering ceramic of his restorations. High carat gold’s warm color is easier to mask with the ceramic layers and less tooth reduction is required to make it attractive. High noble gold alloys will cast better producing a much better marginal fit and it is far more biocompatible. High quality laboratories charge the dentist over $600 for a PFM but if your particular case has complexity or many teeth are being done at the same time the laboratory costs to the dentist can rise to $1500 for each restoration. At this level of quality, PFMs can mimic nature’s beauty.