Cement plays a major role in dentistry as a luting and filling material. Very different materials are used for this purpose. The most commonly used dental cement to date is made of zinc phosphate.
What is cement?
The use of cement in dentistry guarantees full functionality of the dentition even with destroyed teeth and in old age. Already the living tooth naturally forms a cement, which encloses the tooth root as root cement. The root cement serves to secure the tooth in the periodontium and consists of 60 percent hydroxyapatite, 23 percent organic components and 12 percent water. Hydroxyapatite is the same material that bones are made of. It is calcium phosphate. Materials are also used for the artificial fixings of dental components, dentures, root fillings and dental fillings in general, which must have strong adhesion properties to be able to fix the teeth, crowns, dentures or inlays. Ideal materials should have good adhesion to the tooth and dentures, high tensile and compressive strength, low solubility in water and acids, rapid loading capacity, and good biocompatibility.
Shapes, types and grades
Depending on the intended use of dental cements, different materials are used. The actual dental cements contain inorganic components to a large extent. In most cases, they are zinc phosphates. Some cements have an organic resin matrix which is filled with inorganic fillers. Glass ionomer cements, in turn, are made from a mixture of organic polymers and a calcium aluminum silicate glass. Zinc phosphate cement, or phosphate cement for short, is the most widely used dental cement to date. It is used for fixing crowns, for underfilling and for temporary dental filling. It also acts as a thermal and chemical insulator. A zinc oxide-eugenol cement has been used since the 19th century. This consists of a mixture of zinc oxide and eugenol (clove oil). It is used particularly for cementing temporary restorations or root canal fillings. Eugenol causes the typical odor at the dentist. Furthermore, a so-called glass ionomer cement is used. Glass ionomer cement is produced on the basis of organic polymers of polyacrylic acid and calcium aluminum silicate glass. It is used for fixing crowns, for underfilling and for making fillings in deciduous teeth. Composites are again materials which are often used for fillings. However, they are also a suitable material for cementing crowns, roots and ceramic restorations. A mixture of glass ionomer cements and composites forms so-called compomers, which are used as filling materials.
Structure and mode of operation
The individual cements consist of different materials, which, however, have good overall bonding properties to the tooth. Due to the inorganic components such as zinc phosphate, zinc oxide or calcium aluminum silicate, they are not adhesives but cements. While adhesives have flow properties and high viscosity, cements are solids with high compressive and tensile strength. Cements with an organic resin content, however, also require a certain plasticity, although the strength factor dominates. The cement most commonly used in dentistry is still phosphate cement. It is mixed from a cement powder and a liquid shortly before use. The cement powder consists of up to 90 percent zinc oxide. The remainder is composed of magnesium oxide, calcium fluoride, silicon dioxide and aluminum oxide in decreasing amounts. The liquid represents a 45-64 percent phosphoric acid. These two components are stirred together on a non-corrosive base. The mixing ratio is chosen so that a creamy consistency is obtained. After application of this paste, the cement sets quickly and secures the crown or forms a stable dental filling. The zinc-eugenol cement, again, as already mentioned, consists of a mixture of zinc oxide and clove oil. It hardens very quickly and exhibits good flow properties. However, since eugenol dissolves acrylics, this cement should never be used for cementing acrylic restorations. The glass ionomer cement is produced by the reaction between polyacrylic acid with calcium aluminum silicate in distilled water.This produces a calcium-aluminum carboxylate gel, which hardens quickly. Its adhesive properties result from the strong bond between the carboxy group and the tooth structure. Composites represent another class of materials. They consist of a plastic matrix mixed with inorganic bodies. Compomers are again modified composites to which glass ionomer cements have been added. Both are mainly used as an alternative to amalgam, gold or ceramic fillings. Composites are also used in the cementation of crowns, ceramic restorations and root posts.
Medical and health benefits
The use of cement in dentistry guarantees full functionality of the dentition even in the case of destroyed teeth and in old age. Many teeth that are no longer alive can still be preserved for a long time with the help of crowns and root fixations, thus supporting the chewing function. Even complete dentures always require cement with materials that adhere well for cementation. Phosphate cement has proved particularly suitable for all applications. It combines all the properties required for a good cement. The material has a high adhesive capacity to the tooth, is characterized by high compressive and tensile strength and is biocompatible. Although a strong acid is used in the production of phosphate cement, it does not damage the tooth. Glass ionomer cement also has good adhesive properties and is even more pressure resistant than phosphate cement. However, its moisture resistance is lower. In addition, it is not suitable for use in decayed teeth, as it requires moisture to function. Devitalized teeth, however, are no longer supplied with moisture and therefore cannot provide it. Only in vital teeth does glass ionomer cement offer an alternative to phosphate cement. For devitalized teeth, an individual choice can be made between phosphate cement and composite. Compomers are only suitable for fillings.
