By Dr. Sepi Fatahi DMD
For many years, full porcelain restorations have been considered the most lifelike and natural looking restorations available. They are extremely beautiful and the best choice for the ultimate cosmetic result. Porcelain also does not conduct heat and cold very efficiently, so sensitivity to hot and cold foods during the initial placement period is often reduced. However, full porcelain crowns are not always the best choice for every tooth in the mouth. Here’s why:
Porcelain has the unique combination of being both strong and weak at the same time, much like an eggshell. Porcelain is harder than tooth enamel, so it can be damaging to the opposing natural teeth especially in patients who clench and grind habitually. But porcelain can also be brittle and fracture easily when it is too thin or it is habitually flexed through the forces imposed by clenching and grinding.
In order to guard against fractures related to thinness, a full porcelain crown must be thicker all around than a gold restoration. This means that more healthy tooth structure may need to be removed to allow for the porcelain to be thick enough for overall strength and durability. Additionally, full porcelain must be bonded to the teeth differently than a gold restoration. Glass ionomer cements cannot be used. Some patients are more sensitive to these bonding procedures than others, and can experience extended tooth sensitivity during the initial placement period.
Front teeth and any other tooth where an exquisite cosmetic result is the primary concern.
May not be not suitable for:
Molar restorations in patients who clench and grind; patients with sensitivities to specific bonding techniques and materials (testing is available); patients who do not have enough healthy tooth structure available to support the thickness of a porcelain restoration.
Until some of the more recent developments in the use of zirconium as a base for porcelain dental restorations, porcelain fused to gold crowns offered the best compromise between the strength and durability of gold and the cosmetic benefits of porcelain.
A porcelain fused to gold crown is made exactly as it sounds like it might be – porcelain is fused and stacked in layers on top of a high-noble gold alloy base. The porcelain offers a much better cosmetic result than a full gold crown, and the gold base not only allows for the use of glass-ionomer cements, but also acts as a protective barrier for the tooth even if the porcelain might fracture. But porcelain fused to gold crowns are not nearly as popular as they used to be.
One reason is because the gold base creates an automatic opacity in the porcelain that looks less lifelike in the mouth than full porcelain or porcelain fused to other materials like zirconium. Also, when used on the front teeth, a porcelain fused to gold crown can sometimes show a dark metal edge at the gumline when recession occurs. And certainly for any patient with metal allergies or sensitivities, any crown that contains a metal alloy base may not be a suitable choice.
Porcelain fused to gold crowns are still available, however, and they are still a useful option – especially for patients who may have several of these crowns already and are looking to match their existing dental work.
Patients who already have several porcelain fused to gold crowns and want to match them; patients who may not be good candidates for an all porcelain crown or a porcelain fused to zirconium crown, but still want a better cosmetic result than a full gold crown.
May not be suitable for:
Patients with specific metal allergies or sensitivities (testing is available); front teeth; back teeth in patients who clench and grind.
Zirconia, or zirconium dioxide, is a white crystalline oxide made from the metal zirconium. In its cubic form, it creates the simulated diamond-like stone we all know as cubic zirconia. But zirconia has also been used and studied for many years in the production of all kinds of ceramics, including dental restorations.
Zirconia is an ideal base for porcelain because the bonding process between the zirconia and the porcelain is stronger than it is with porcelain and gold. This means that the porcelain is less likely to fracture away from a zirconia base. Zirconia can also be colored to match teeth and it is translucent, mimicking the natural look of teeth far better than any crown with a gold base could.
Zirconia at its core is still derived from metal, however, and that comes with some advantages and disadvantages. Glass ionomer cements work extremely well with Zirconia based crowns, which is often a benefit for patients who are sensitive to porcelain bonding techniques. However, even though zirconia is almost never reactive as a metal in the mouth, some patients with extreme metal sensitivities may want to be tested for reactivity before placing a permanent zirconia restoration.
Any full crown restoration where a beautiful cosmetic result is desired, but extra strength and durability are required.
May not be suitable for:
Patients with specific metal allergies or sensitivities (testing is available).