Implant crowns are a wonder of dentistry, used to replace missing or damaged teeth for millions across the world. But there’s a few options to choose from, with a variety of materials that differ in durability and aesthetics.
In this article, we explore the most common types of implant crowns, so that you can choose the crown that is right for you.
What are implant crowns?
An implant crown is an artificial tooth that is fixed to the jaw or cheekbone, which gives it the strength and durability of a regular tooth. Once fitted, an implant crown connects to the bone through a process called osseointegration, whereby new bone cells grow around the screw-like “post” and keep the crown secure. This is illustrated in the image below.
The structure of an implant crown. The post (screw) is secured by new bone cells that grow around it after being installed.
Implant crowns should last for a long time—30 years or more. But the abutment or crown tends to be replaced after about 10 years.
Types of crowns for implants
Solid crowns are considered the gold standard, and provide a great combination of aesthetics (the crown is the same white hue all the way through) & strength (a very durable and hard wearing material) that is desirable for both the patient and dentist alike.
Solid zirconia crowns are best used at the back of the mouth (premolar & molar regions). The zirconia material is white & comes in a number of shades but is lacking the more natural translucency of human teeth.
Therefore, when zirconia is used for the front teeth (incisors & canines) the material will be resurfaced (veneered) with a more translucent version of zirconia to make for a more natural appearance to the teeth.
The translucent zirconia whilst less durable than the solid zirconia, is supported with a framework of solid zirconia. The veneered (translucent + solid zirconia) crown makes for a very aesthetically pleasing crown, as more light is able to pass through them which makes them look closer to natural teeth, which makes them ideal for anterior (front) teeth.
Zirconia also doesn’t react with chemicals in the same way that metals do, which reduces the risk of allergic reactions.
2. Porcelain-fused-to-metal (PFM)
This type of crown was once the gold standard prior to the use of zirconia. They work well from a mechanical perspective, which means they’re able to handle tough foods for a long period of time, and they also look like natural teeth.
However, the metal base can sometimes show as a dark line along the gum line of the tooth, which detracts from their use on the anterior (front) teeth as this dark line becomes visible.
As the name suggests, these crowns are made with a metal alloy base, with metals such as gold, cobalt, nickel, and titanium. This gives them their strength. This metal base is covered with porcelain to give the crown a natural tooth-like appearance.
Emax crowns are made by Swiss dental company Ivoclar Vivadent. They have a lithium disilicate glass-ceramic base, which is very strong and provides an appearance very close to natural teeth. These crowns are half as durable as zirconia crowns. They may be suitable in patients that don’t have a strong bite (that might fracture the crown).
Emax has become popular with some dentists that use in-house mills (Cerec etc.) to produce crowns chair-side. These crowns (without the surface tinting & staining provided by an experienced dental laboratory) can be disappointing matches to the patient’s other teeth. Likewise, when used in the posterior (back) of the mouth will be more prone to fracture under bite force (in poorly selected patients).
Gold crowns are usually a combination of gold and another metal such as palladium, chromium, or nickel. Using an alloy increases the strength of the crown, and reduces the cost significantly.
Gold allows them to be incredibly strong, so they will rarely chip or break, and won’t wear down quickly. They also retain a very high polish, making them easier to clean and maintain, thus contributing to their life span.
Clearly, gold is unlikely to be chosen for anterior (front) teeth due to its unnatural appearance. Gold is expensive, but remains a very good choice for posterior (back) teeth.
5. Acrylic (PMMA) / Composite resin
Both these materials can produce very aesthetically pleasing teeth, however, the materials are not durable & therefore should be considered as short term or temporary fixes only.
PMMA (poly methyl methacrylate acrylic) is an engineered plastic. All-resin crowns are made from a mixture of plastic and glass beads.
These materials provide for the cheapest type of crowns you can buy, but wear down more easily, and are more likely to break. For this reason, they are recommended as a temporary, short-term crown if necessary.