A base is a type of dental cement that is applied under a filling or crown to decrease sensitivity to heat or cold and protect the filling. Dental cements are widespread materials which can be used for multiple purposes namely as base materials. It is important to consider each cement on its own merits before choosing the correct one. The effectiveness of each cement in a given situation can be based on the following criteria.
ﾷ Chemistry of the setting reaction
ﾷ Consistency in proportion of powder to liquid ratio in mixing cements
ﾷ Maximum solubility and disintegration
ﾷ Dimensional change
ﾷ Working and setting times
ﾷ Bonding strength for their intended use
ﾷ Optimum film thickness
ﾷ Thermal and electric conductivity
ﾷ Amount of heat generated during setting
ﾷ Safety (should not be toxic carcinogenic mutagenic irritating or sensitizing)
The sealing ability of a base material is also an important feature as it may avoid the possible microleakage of the restoration.
Dental cements can be divided primarily into two types class 1 and class 2. Class I devices are composed of zinc oxide-eugenol and are intended to serve as a temporary tooth filling or as a base cement to fasten a temporary tooth filling to attach dental devices such as crowns or bridges or to be applied to a tooth to protect the tooth pulp. A class 2 cement is composed of various materials other than zinc oxide-eugenol.
Typical dental cements include zinc oxide-eugenol (class I); and zinc phosphate zinc silico-phosphate zinc-polyacrylate zinc-polycarboxylate glass ionomer resin-based silicate-based cements etc (class II).
Glass ionmomer bases are typical class 2 cements and are used mainly for small non-load bearing fillings cavity liners and cements for crowns and bridges. Glass ionmomer bases are a self-hardening mixture of fluoride containing glass powder and organic acid that forms a solid tooth colored restoration able to release fluoride. The adhesive bonding that they produce permits removing less tooth structure when being applied however a significant disadvantage of this type of base is its high wear when placed on chewing surfaces.
Other well-used class 2 bases include Resin-based cements. These tooth-coloured filling materials have reached a high degree of sophistication since their appearance on the dental scene in the early 1960s. A modern dental composite consists of a paste created by combining a mixture of dimethacrylate monomers and cross-linking agents or resins with ceramic particles that act as a filler. This composite paste is packed into a dental cavity and the dentist exposes it for about 30 seconds to intense visible blue light. This light causes the paste to become a durable solid filling.