Dental Crowns
Dental crowns, also known as dental caps, cover damaged or discolored teeth. Crowns cover the entire tooth, starting at the gum line. They are usually made of gold, porcelain, or a combination of both.
Though crowns can be used to improve the appearance of a tooth, they are not primarily cosmetic devices. Dentists recommend crowns to protect or strengthen weakened teeth, or to restore a disfigured tooth to its original shape. "Capping" a tooth requires buffing away part of a tooth to make room for the crown, so dentists often discourage it as a cosmetic method unless the teeth are damaged.
Crowns strengthen teeth by binding the sides of the weakened tooth together, much the way a splint holds together a broken bone. Large fillings taking up over a third of the tooth may weaken that tooth over time; crowns are often used in cases where such weakened teeth threaten to break.
The "capping" procedure takes place under local anesthetic. Because the crown is about two millimeters thick, the dentist first shaves this same amount off your existing tooth to avoid awkward-looking, oversized teeth. The dentist will also re-shape your tooth into a form upon which a cap can easily sit. He or she will then make a replica of your tooth by taking an impression. The impression material is usually a putty-like material. This mold is then sent to a laboratory, where the crown will be made based on a stone copy obtained by the impression mold. In the case of a porcelain crown, the dentist will choose a shade close to the color of the surrounding teeth. You will return about three weeks later to have the crown fitted and, once both you and your dentist are satisfied with the "look and feel" of the crown, cemented over your original tooth.
Gold Crowns are made from gold alloyed with many other metals. The actual gold content can range from 90% to as low as 5%. Gold in its pure state is too soft and malleable to withstand the rigors of daily chewing. Gold crowns need generally less thickness to retain their strength as compared to ceramic crowns, which means that the tooth can be prepared more conservatively. On the other hand, the esthetic considerations are its shortcomings. Gold crowns are usually placed in the upper molar areas, where their visibility is not as obvious.
Porcelain-Fused-to-Metal crowns are crowns that are contain an outer porcelain layer and an inner metal layer. This metal layer can be either a gold gold or another type of metal alloy. PFMs can provide a natural looking appearance. However, since the porcelain is fused to metal, these crowns do not have the advantage of being able to capture and reflect light like natural teeth or all-ceramic crowns can. The metal substructure of PFMs require an opaque layer underneath the porcelain. Therefore, on occasion, a darker line will become visible at the edge of the crown near the gum as the gum recedes with age. Despite this esthetic disadvantage, PFMs offer excellent strength and are the most common crowns used today. PFMs that utilize a mixture of porcelain and gold are more esthetically pleasing than those that use other metal alloys. Gold, however, reduces the overall strength of the crown somewhat as compared to PFMs using "silvery-type" metal alloys, however they are still stronger than the all-ceramic dental crowns.
This term is actually a misnomer, although it is still being used today. Since many of these crowns are now being made from reinforced resins, the correct term should be "Ceramic or Reinforced Resin Crowns", however for brevity's sake we will stick with the original terminology. All-Ceramic Crowns are generally used for the front teeth and are the most esthetically pleasing dental crowns. Mirroring the color of natural teeth, this type of dental crown has the advantages of capturing and reflecting light like natural teeth, as well as having a natural appearance with a smooth surface. However, an ideal fit where the gum meets the crown is more difficult in porcelain crowns due to its thickness. More tooth structure has to be removed and it appears that gingival inflammation is sometimes more common in All-Ceramic dental crowns, as compared to PFMs. Although these types of crowns are more likely to chip than a PFM, it is still extremely durable. It is also the recommended dental crown for patients with metal sensitivities.
Onlays are also indirect restorations (like crowns), however, they are do not cover the entire tooth. The dentist prepares the tooth by removing the damaged areas and re-shapes the tooth so that it can be fitted with an onlay. Onlays are often also referred to as "Partial Coverage Crowns". Their advantage is that they conserve tooth structure, by leaving the unaffected areas of the tooth untouched.
Onlays can either be made out of gold, or a ceramic or resin. We will not dwell again on the esthetic advantages and disadvantages of both, suffice to say that the ceramic or reinforced resin onlays enjoy a higher popularity, due to their higher esthetic value.
