Porcelain Fused to Metal Crown

What is a porcelain fused to metal crown?

A Porcelain Fused to Metal (PFM) crown is a type of dental crown consisting of a metal base and a tooth-colored porcelain layer that are fused together. The crown is made with a metal framework that serves as the inner core and is covered with porcelain on the outside to blend in with natural teeth. PFM crowns have been successfully used in restorative dentistry for decades and can be used for both anterior and posterior teeth, though newer materials such as Zirconia and all-ceramic crowns are gaining in popularity in cases where the highest aesthetic demands are sought.

The design of a porcelain fused to metal crown.

There are two components to a PFM crown:

• Metal coping (inner layer): Durable and helps to provide biting and chewing surface.
• Porcelain coating (outer layer): Represents the color, shape and translucency of a natural tooth.

The porcelain is permanently bonded to the metal by a high-temperature firing process to make a strong, long-lasting restoration.

When to use a PFM Crown?

A dentist can suggest porcelain fused to metal crown if you suffer from:

• A tooth with significant tooth decay.
• A broken or chipped tooth.
• A tooth that has been compromised due to root canal treatment.
• A large filling which is no longer able to support the tooth.
• A worn down tooth due to grinding.
• Aimed at the dental implant that needs a crown to be fit on its top.
• A dental bridge that requires a long-lasting base.

The advantages of a Porcelain Fused to Metal Crown include:

• Tough and hard wearing as a result of using a metal base.
• Natural-looking tooth-colored appearance
• It can be used on both the front and back teeth.
• Representative of a class of restorations that are more affordable than many all-ceramic restorations.
• Can withstand moderate to heavy chewing forces
• The long clinical success and decades of proven performance

Porcelain fused to metal crown materials

A Porcelain Fused to Metal (PFM) crown consists of two main components: metal framework (coping) for strength and the dental porcelain for a natural appearance. These materials are used together, offering PFM crowns durability and aesthetics, which remain a popular option for restoring damaged teeth.

Metal Framework (Inner Core)

The inner coping provides the crown with strength and support. Depending on the patient's need and budget there may be various types of metal alloys used.

High Noble Alloys

• The alloys are made with the noble metals and contain 40% or more of gold.

Common metals include:

• Gold
• Platinum
• Palladium

Advantages:

• Excellent biocompatibility
• Resistant to corrosion.
• Precise fit
• Not irritating to opposing teeth
• Long-lasting durability

Noble Alloys

• These are at least 25% noble metals, the main ones are palladium, platinum, or gold.

Advantages:

• Good corrosion resistance
• Strong and durable
• The low noble alloys are cheaper than high noble alloys
• Reliable long-term performance

Base Metal Alloys

• With little or no precious metals, these alloys are the most common type.

Common metals include:

• Nickel-Chromium (Ni-Cr)
• Cobalt-Chromium (Co-Cr)
• Chromium-based alloys

Advantages:

• High strength
• Lightweight
• Cost-effective
• Excellent resistance to wear

Considerations:

• Patients with nickel allergies may not be able to tolerate nickel-containing alloys.
• For patients who are metal sensitive, cobalt-chromium alloys are frequently used.

An outer layer of Dental Porcelain

The PFM crown is composed of dental porcelain (also called ceramic veneering porcelain) on the outside and a metal alloy that contains these special Grade 12 alloys on the inside. It is carefully placed on top of the metal coping and fired at high temperatures to ensure it bonds to the coping.

The properties of Dental Porcelain are:

• Tooth-colored appearance
• Translucent for a natural appearance.
• Stain-resistant
• Smooth surface
• Resistant to discoloration
• Has the ability to be customized to match adjacent teeth
• To replicate the color, translucency and texture of natural enamel, dental technicians employ several different shades and layers of porcelain.

Bonding between Metal and Porcelain

A PFM crown is dependent on the good bonding of the metal coping and the porcelain. During fabrication:

• The metal structure is molded and formed.
• An opaque glaze of porcelain is placed over the metal colour.
• Several glazes are applied.
• Crown is fired at high temperature in a porcelain furnace.
• The restoration is polished and glazed so that it has a realistic appearance.
• This process forms a strong connection which resists chewing pressure.

Material Selection Factors

There are a number of factors that influence the choice of PFM crown materials by dentists:

• Location of the tooth
• Bite force
• Aesthetic requirements
• Patient's budget
• The presence of metal allergies.
• Bruxism (teeth grinding)
• Overall oral health

Porcelain fused to metal crown preparation

Porcelain Fused to Metal (PFM) crown preparation involves reshaping a tooth to allow for space for the metal coping and porcelain veneer. Correct preparation guarantees a proper crown fit, natural appearance and chewing longevity for many years.

The purpose of PFM Crown Preparation

The goals of tooth preparation are to:

• Maintain as much healthy tooth structure as possible.
• Allow adequate space for the metal and porcelain.
• Provide good retention and resistance.
• Establish an accurate finish line for an accurate fit.
• Preserve pulp and peridontium.
• Provide good aesthetics and function.

Steps in Porcelain Fused to Metal Crown Preparation:

Clinical Examination

The dentist will do the following before preparing the tooth:

• Looks at the tooth and surrounding gums.
• Takes x-rays when necessary.
• Assesses the bite (occlusion).
• Decides if extra procedures, like a root canal or core buildup are needed.

Local Anaesthesia

• To make the procedure comfortable and painless, local anaesthesia is given.

Tooth Reduction

• A controlled amount of enamel and dentin are removed to provide space for the crown.

Typical reduction guidelines:

• Occlusal (biting surface): 1.5–2.0 mm
• Dental arch restraints: Up to 6.0 mm
• Axial reduction: 1.2–1.5 mm
• Lingual metal-only surface (posterior teeth): 0.5 – 1.0 mm (if applicable)
• Incisal edge (anterior teeth): 2.0 mm
• These reductions are sufficiently thick for the metal coping and porcelain, and ensure strong bonding of the two.

Porcelain fused to metal crown disadvantages

• Over time, a dark thin metal line can show around the gum.
• Porcelain might chip or crack when given too much stress.
• Needs more tooth preparation than newer crown materials.
• Not as translucent as all-ceramic or E-max crowns.
• Very rarely, sensitive people can develop metal allergies.

Conclusion

A Porcelain Fused to Metal (PFM) crown is a dental restoration that's been tried and proven to provide a good strength, durability and aesthetic outcome. PFM crowns are those that have a strong material structure and are covered with a natural-looking porcelain outer layer that restores broken, weakened or heavily decayed teeth and are capable of providing a reliable chewing function and a pleasing appearance. They are still used very much today, especially for posterior teeth and where long-lasting durability is desired. While there are a few disadvantages to PFM crowns, they still provide desirable long-term success. When maintained properly, with good oral health, routine dental visits and care, porcelain fused to the metal can last 10–15 years or more which is a reliable and affordable way to restore your smile. Your dentist will be able to assess whether or not a PFM crown will be suitable for you, depending on your oral health, cosmetic objectives, and finances.

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FAQ

What is the lifespan of porcelain fused to metal Crown?

• A PFM crown generally lasts for 10-15 years with the right oral care and periodic visits at the dentist's office. Patients can live 20 years or longer with good care.

Which is stronger, porcelain fused to metal crown or an all-ceramic crown?

• Yes. The metal framework provides high strength and fracture resistance to PFM crowns making it ideal for the teeth under heavy forces in chewing. Contemporary zirconia crowns, however, are as strong, if not stronger than the traditional zirconia.

Can porcelain fused to metal crown chip?

• Yes. The metal coping will not fail but the outer porcelain could crack or chip from trauma, grinding teeth or chewing on hard foods. Small fractures can sometimes be fixed and large fractures might need crown replacement.

Can porcelain be fused on to metal crowns for anterior teeth?

• Yes. The porcelain for PFM crowns is a good match for the natural tooth color allowing PFM crowns to be used for the front teeth. All-ceramic or zirconia crowns are frequently chosen for front teeth because of their excellent translucency and aesthetics though.

What is the reason for the dark line close to my PFM crown?

• If the gums recede with the passage of time, a dark line or grey line close to the gum area may be noticed due to the exposure of the metal base of the teeth underneath the porcelain. 

Does porcelain fused to metal crowns require special care?

• PFM Crown Care is the same as natural teeth care. Brush twice a day, floss around the crown, don't chew on hard objects such as ice or hard candy and get regular check-ups and professional cleanings from your dentist.

Is it possible for someone with metal allergy to get a PFM crown?

• Allergic to some metals (especially nickel) patients should notify their dentist prior to treatment. In these instances, a high noble alloy or zirconia/all-ceramic crown may be suggested.

What is the amount of tooth structure that is lost when you have a PFM crown?

• Generally, between 1.5 and 2 mm of tooth tissue is taken off to provide sufficient space for the metal coping and the porcelain to fit and look natural.