Dental cements are hard, brittle materials formed by mixing powder and liquid together. They are either resin cements or acid-base cements. In the latter the powder is a basic metal oxide or silicate and the liquid is acidic. An acid base reaction occurs with the formation of a metal salt which acts as the cementing matrix. Dental cements are used for a variety of dental and orthodontic applications, including use as luting agents, pulp-protecting agents or cavity-lining material. Furthermore, they are used to form an insulating layer under metallic or ceramic restorations, and protect the pulp from injury. This helps in sealing or fixing and casting inlays, onlays or any such substance to both dentin and enamel.  Dental cements which contain an acid component may have an intense sour taste.
Composition and classification
Cements are classified on the basis of their components. Generally, they can be classified into categories:
- Water-based acid-base cements: zinc phosphate (Zn3(PO4)2), Zinc Polyacrylate(Polycarboxylate), glass ionomer (GIC). These contain metal oxide or silicate fillers embedded in a salt matrix.
- Non-aqueous acid-base cements: Zinc oxide eugenol and Non-eugenol zinc oxide. These contain metal oxide fillers embedded in a metal salt matrix.
- Resin-based: Acrylate or methacrylate resin cements, including the latest generation of self-adhesive resin cements which contain silicate or other types of fillers in an organic resin matrix.
Cements can be classified based on the type of their matrix:
- Phosphate (zinc phosphate, silico phosphate)
- Polycarboxylate (zinc polycarboxylate, glass ionomer)
- Phenolate (Zinc oxide–eugenol and EBA)
- Resin (polymeric) 
The requirements for dental cements are that they should:
- Be non irritant to pulp and gingiva (gums) and should not support the growth of secondary caries. (This last property is called cariostatic or anticariogenicity).
- Form a strong bond with enamel and dentin.
- Provide good marginal sealing to prevent marginal leakage.
- Be resistant to dissolution in saliva, or in any oral fluid.
- Have good aesthetics and good thermal and chemical resistance. (Opacity to X-rays is also preferred for diagnostic purposes).
- Be translucent.
3. Acid-base Cements (1993) A. D. Wilson and J.W. Nicholson