Dental Crowns (Porcelain Fused to Metal)
Crowns are a type of dental restoration that fit over that part of a tooth that lies above the gum line. For all practical purposes, once one has been cemented in place, it becomes the new outer surface for its tooth.
Making a crown for a patient involves the following steps:
1-) Tooth preparation and impression taking
The first step involves trimming the patient's tooth. Dental crowns generally need to be on the order of 2 to 3 mm thick (so they have good cosmetic and strength characteristics). That means that a tooth receiving one needs to be trimmed down by this same amount.
Once it's been properly shaped, the dentist will need to make a copy of the tooth that can be used to make its crown. In most cases, the dentist will do this using impress paste (a putty-like material that's squished over the tooth which then sets). As an alternative, the dentist may take an optical impression (a picture of the tooth that's then fed into a computer).
2-) Crown cementation
Once the crown has been fabricated, the dentist will check its fit, both on the tooth and the way it touches neighboring and opposing teeth. After making any needed adjustments, the crown is then permanently cemented onto its tooth.
Dental crowns are typically placed for the following reasons. Any one tooth may be in need of one or more of these benefits.
1) Restoring teeth to their original shape and function
Crown placement is one way a dentist can rebuild broken teeth. Crowns, above all other types of dental restoration, create a very lasting repair.
2) Strengthening teeth
Some teeth, especially back ones, may require crown placement because it is the type of dental restoration that can best withstand heavy chewing forces. Additionally, any fragile tooth, including those that have had root canal treatment, may benefit from a crown's strengthening effect.
3) Improving the appearance of teeth
Since a dental crown becomes the new outer surface of a tooth, its cosmetic appearance can be vastly improved when one is placed. This includes tooth color, shape and even apparent alignment.
Crowns - Porcelain Fused to Metal Crowns (PFM's)
Porcelain-fused-to-metal dental crowns (PFM's) can be thought of as a hybrid between their all-metal and all-ceramic counterparts.
When they're made:
▪ A thin metal thimble is fabricated that fits over the tooth (the substructure).
▪ Porcelain is then fused over this metal shell in a high-heat furnace.
Even though a substantial portion of the crown may be metal, the side that people see is covered over with porcelain so it looks white like its neighboring teeth.
PFM crowns offer good strength characteristics. And that means they make a good choice for situations where strength and durability are required (like on molars and premolars). Generally speaking, they can be considered to be stronger than all-ceramic crowns, but not as durable as metal ones.
The fact that their front surface is porcelain-covered means that they make a suitable choice for front teeth (incisors and canines), especially in applications where strength considerations are important. But in cases where perfect tooth esthetics are paramount, an all-ceramic crown may make the better esthetic choice.
Which type of dental crown makes the best choice?
It's important to understand that there's no single type of crown that always makes the best choice in every application. The right selection always varies depending on the needs of the patient's specific circumstances.
1) Front teeth -
a) Patients with high lip or smile lines.
If a person's lip line is very high, most, if not 100%, of their front teeth will constantly be on display to others. If so, it will be paramount that the crown that's placed looks as life-like as possible. If the patient has such a expectation; then we suggest the patient to consider Full Porcelain Crowns/Veneers (e-max or empress). Please visit our page about full porcelain crowns.
▪ Placing an all-ceramic crown might be a first choice for this scenario because of the superior esthetics that this type of restoration can provide.
▪ Placing a PFM might give perfectly acceptable results too. But both have their own difficulties in being able to truly mimic a natural look.
b) Patients with low lip or smile lines.
If only a portion of the person's teeth show, the aesthetic demands placed on the crown will be reduced. Possibly even to the point where other characteristics (such as strength and durability) can be given more weight in the selection process.
▪ An all-ceramic or PFM might each be considered for this type of application. The latter so in cases where the patient's situation would benefit from greater crown strength.
2) Back teeth -
Some people's molars show very little when they open their mouth. And when this is the case, the strength and durability characteristics of the type of crown selected for placement should be given primary emphasis.
▪ In cases where the appearance of a molar is a factor (like with 1st upper molars), PFM crowns have a long history of being able to provide excellent service, yet are more esthetically pleasing than all-metal ones.
▪ Ceramic zirconia crowns may make a reasonable choice for molars too.
b) Premolars (bicuspids)
Even though premolars usually hold a prominent position in a person's smile, by definition they are "back" teeth. And as such, it can be expected that they may be exposed to heavy chewing forces.
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