Лако-красочные материалы — производство

Although covered as a separate group (M2) in the FDI classification, the endodontic cements are to a large extent similar to the luting materials covered in Section II. B. One of the most frequently used cements is based on the ZOE system (see Section II. B.3) for reasons of simple and conventional application techniques and good setting properties. The irritating effects of the eugenol constituent are generally tolerated. Modified ZOE products containing various additives for consistency or setting time control dominate the market. Related sealer materials based on zinc oxide and ketone-type Zn-chelating agents, sometimes further modified with vinyl polymers, are also commercially available, as are certain retarder-modified calcium hydroxide-zinc oxide-salicylate combinations similar to the calcium hydroxide cavity-lining materials of Section IV. B.1. With a different class of sealing agents, which contain acrylate monomers resulting from epoxy-bisphenol A addition reactions, good dimensional stability and sealing capacity are attained, although irritation caused by acrylic monomers diffusing into soft connecting tissue may be problematic.

Among the newer materials advocated for root canal sealing and reviewed by Chow et al. [16] is an apatitic calcium phosphate cement formed under ambient conditions from calcium hydrogen phosphate and a tetracalcium phosphate formally composed of equi­molar quantities of CaO and Ca3(PO4)2:

CaHPO4 • 2H2O + Ca4(PO4)2O ! Ca5(PO4)3OH + 2H2O

Being hydroxyapatitic in structure, cements of this type are particularly tissue-compatible, and fluoride can be introduced (OH replaced by F) to provide protection against caries. Compressive strengths of these phosphates are in the relatively low range of 30 to 50 MPa, depending on formulation and application details. Increased strength and reduced setting time are achieved by compounding the phosphates with polyalkenoic acids, such as poly(- acrylic acid).

For the most part, the sealer cements used at present exert bonding effects to adja­cent surfaces of points or dentinal tooth structure by the micromechanical mode. Only the polyalkenoic acid-modified cements are likely to undergo additional weak retention through chemical bonding involving the carboxyl functions and apatitic hydroxyl groups of the dentin.