Dental Restoration Materials - Polycarboxylate Cements, Zinc Phosphate Cements

Dental cements like polycarboxylate cements are materials used to keep a tooth restoration

or dental appliance in place in the mouth and also seal the space between the tooth and the restoration. Sometimes they are used in combination with other substances and are called bases. They can be of two types:

Temporary (Zinc Polycarboxylate)

Permanent (Zinc Oxide Eugenol, Zinc Phosphate cements)

The material is chosen based on certain criteria such as low solubility, high compressive and tensile strength, erosion, shear strength, setting time, sensitivity to moisture, compatibility with other restorations, its effect on the tooth pulp and its radio-opaqueness. Some materials such as Zinc Polycarboxylate cement and resins can be used both for short term and final use.

Zinc Oxyphosphate/Zinc Polycarboxylate

Both these have been used in dentistry for a long time. They have an acid component that tends to etch the tooth, demineralizing the dentin, although not in an even way.

Zinc Phosphate cement or ZPC results in more demineralization than Zinc Polycarboxylate cement. Its consistency is rubber-like when it sets and the extra material is removed when it completely set to avoid it from being pulled out. Since ZPC has cupric oxide, it has a brownish colour and is not always suitable for ceramic restorations.

The ZPC has to be carefully manipulated as any variation in the powder to liquid proportion can affect the working and setting time, the consistency of the mix and flow, along with its level of solubility, strength and thickness.

Temporary cements

Calcium hydroxide, Zinc Oxide Eugenol and non-Zinc Oxide Eugenol, are used as temporary material and harmless to the tooth. Calcium Hydroxide is available in the dentin and ivory shade and is harder than Zinc Oxide Eugenol. It can be easily trimmed away from the resin margins and crowns. Since it is not Eugenol based, it has no problem with the resin as the final material.

Zinc Oxide Eugenol and non-Eugenol version is effective as a seal but it tends to interfere with resin. Where resin is used as the final restoration, the non-Eugenol version of Zinc Oxide is usually used. Resin is also ideal as temporary material for its retention and aesthetic characteristics, except that it can sometimes be tough to remove and also result in a discoloured tooth after removal.

Permanent cements

Some examples are Zinc Oxide Eugenol, Zinc Oxyphosphate, Zinc Polycarboxylate, glass ionomers and resins. As mentioned earlier, Zinc Oxide Eugenol has its disadvantages. Glass ionomers have been found sensitive to moisture and bond permanently. While the advantage is the ability to fill any gaps when exposed to moisture, the inherent disadvantage is the risk of fracture.

Zinc Polycarboxylate cements make good cavity liners and luting material and come in a powder and solution combination. They set quickly and are the most popular choice for fixing crowns and inlays and cavity lining, especially before restorations are applied and after a root canal treatment.

In dentistry, liners, bases and ZPCs are used to restore and save teeth. Choosing the one that is most compatible with healing is critical.

by: Mark Mulholland

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