Dental crowns are made to fit over your teeth. Crowns are attached to abutments, fixed into an implant that is connected to the jaw bone, and all stay in place with the help of dental cement. Dental glue for crowns can be made from a variety of materials, including powdered glass and synthetic resins. Dental cements are also used in other dental work, particularly when attaching braces to teeth. Some are even activated with ultraviolet light.
How Dental Cements Work
Dental glue works by creating resistance and retention when compressed, and some cements also form a chemical bond. According to Gary M. DeWood, DDS, MS, the force of the compressed cement underneath the crown holds it together. Chemically bonding cements supply additional strength, and they're less likely to break down than non-bonding cements. But when a crown is in need of replacement or repair, it's more difficult to remove. Dr. DeWood suggests bonding cements are only needed in crowns whose strength depends on a chemical adhesive. In patients who grind their teeth, for example, this extra stability increases the chances that the crown will stay intact.
While you wait for a permanent crown to be fabricated, dentists usually fit a temporary crown with a cement that's fairly easy to break. Restorative Dental Materials addresses a range of dental cements, commenting that zinc oxide-eugenol cement is often used as the cement for temporary crowns. This is made from zinc oxide powder, eugenol and olive oil.
Cements for Permanent Crowns
Zinc phosphate, glass ionomer (GI), resin-modified glass ionomer (RMGI) and resin cements are some dental glues that create a semi-permanent seal. Zinc phosphate is made from zinc oxide powder and phosphoric acid liquid, according to Restorative Dental Materials. Mojdeh Dehghan, DDS and other dentists say it was one of the earliest and most reliable cements available. Newer dental glue for crowns includes GI and RMGI cement, which Dr. Dehghan explains are usually made from fluoroaluminosilicate glass powder and polyacrylic acid liquid. RMGI cement also contains hydrophilic methacrylate monomers. Meanwhile, resin cements contain synthetic resins and dimethacrylates, which affect the consistency and strength of the cement.
Dentists consider a range of factors when deciding which cement to use. For example, GI cement chemically bonds to stainless steel and other metals, but not porcelain, and it is slightly soluble in oral fluids. Robert A. Lowe, DDS explains that today's dentists often prefer RMGI cement because it is completely insoluble. However, according to Dr. Dehghan, all-ceramic crowns should not be attached with RMGI cement because they're likely to fracture.
Resin cements, on the other hand, can be used with ceramic crowns, and dentists choose between light-cured, dual-cured and auto-cured resins. Light-cured cements are useful when the crown is thin and easily accessible, whereas dual-cured cements are used when light penetration is likely to be poor. Before attaching the crown with either of these cements, dentists apply a dental bonding agent. Auto-cured cements don't require this bonding agent, and might be used where light exposure and dental preparation is difficult. Though the chemical bonding in auto-cured cements is weaker than in other resin cements.
Whichever cement a dentist uses to attach a crown, its longevity depends on good oral care. Crowns only cover teeth as far as the gumline, where bacteria can enter and cause decay. If you have a crown, brush and floss it regularly as part of your normal dental health routine, using a decay-specific toothpaste such as Colgate® Cavity Protection™.