Proteoglycan: Relevance to Dental Calculus Fluoride Modulates the Inhibition of in Vitro Hydroxyapatite Crystal Growth by Small Dentin

Glycosaminoglycan constituents of the periodontium have been detected in supragingival and subgingival dental calculus. They are polyanionic heteropolysaccharides containing -COOH and SO3H residues. The non-sulfated hyaluronan is present in supragingival calculus, whereas chondroitin sulfate, dermatan sulfate, and heparan sulfate are detected in subgingival calculus. They are implicated in both ectopic and endogenous mineralization, and have been used in the present study to investigate seeded hydroxyapatite crystal growth, and the influence of fluoride on the process. All glycosaminoglycans examined inhibited crystal growth, with chondroitin-4-sulfate and dermatan sulfate being more effective than the hyaluronan. Fluoride alone enhanced growth and reduced the inhibitory influence of the glycosaminoglycans and the parent proteoglycan, which is a potent inhibitor. The results yield important information on the role of fluoride and proteoglycan in ectopic mineralization. Key words, calculus, proteoglycan, fluoride, hydroxyapatite, crystal growth. This paper was presented at "Interaction between Dental Materials, Dental Tissues, and Oral Fluids", a workshop sponsored by the Council of Europe on October 26-30, 1994, at Leidschendam, The Netherlands. T he mechanisms by which the organic matrix of dental plaque mineralizes to form the ectopic deposit dental calculus are not fully understood. Unlike the mineralization of bone and dentin, the formation of dental calculus is outside normal cellular and hormonal control. As such, there is no remodeling or homeostatic mechanism operating. The control of dental calculus has been the subject of much commercial targeting of dentifrice products with the potential to limit the growth of both supragingival and subgingival calculus. There has been a wide range reported in the prevalence of differing mineral phases occurring in human dental calculus, when examined by x-ray diffraction (Tovborg Jensen and Dan0, 1954; Rowles, 1964; Schroder and Bambauer, 1966; Gr0n et al, 1967). However, differences between supraand subgingival calculus are consistently reported. Subgingival contains more whitlockite while supragingival calculus contains more apatite and brushite (Sunberg and Friskopp, 1985). Whitlockite occurs as bulk crystals and octacalcium phosphate (OCP) as platelet-shaped crystals, often epitactical to platelet-shaped apatite. In addition, needle-shaped crystals of brushite and apatite occur (Schroder and Bambauer, 1966; Sunberg and Friskopp, 1985). Brushite and OCP have a higher prevalence and content in the calculus of younger samples. Brushite decreases or disappears altogether with increasing age, whereas OCP is still detected in older calculus (Schroder and Bambauer, 1966; Kaufman and Kleinberg, 1973). It has therefore been proposed that OCP and brushite are formed as precursor phases in the initial stages of the calcification of dental plaque, and then are gradually hydrolyzed and transformed to apatite and/or whitlockite (Kani et al., 1983). Fluoride is known to enhance crystal growth (Barone and Nancollas, 1978; Varughese and Moreno, 1981). A wide variety of chemical inhibitors of crystal growth has been tested for their clinical efficacy; among these, pyrophosphate, ethane hydroxydiphosphonate, and zinc salts in the form of zinc citrate have been widely studied and reviewed extensively (Featherstone et al, 1989; Stookey et al, 1989). The balance among factors which enhance crystal growth, such as fluoride, those which tend to inhibit crystal growth, such as zinc citrate and pyrophosphate, and naturally occurring macromolecules such as lipoteichoic acid, a component of bacterial cell walls, isolated from Lactobacillus casei (Damen et al., 1994), is important to calculus growth. 433 at PENNSYLVANIA STATE UNIV on February 23, 2013 For personal use only. No other uses without permission. adr.sagepub.com Downloaded from 434 HALL ET AL. ADv DENT RES DECEMBER 1995