Artificial carious lesions were produced in human enamel using lactic acid [HL] buffers plus diphosphonate [MHDP]. Surface layer thickness was related to [MHDP], middle zone (body) and inner zone depths to [HL] and pH. Indications are that diffusion in enamel is predominantly by unionised species such as HL and CaHPO4, and dissolution by H+ and L-.

Chemical Phenomena↗

PubMedDate not supplied

Examination of the potential structure of human salivary cystatins based on computer modelling.

The cystatin family of proteins exists in both excreted and intracellular forms, and appears to be involved in protective and regulatory roles, inhibiting a variety of bacterial, viral and intracellular proteases. The amino acid sequences of several human forms of cystatin are known, but currently only the structure of chicken cystatin (approx. 40% homologous to the human forms) has been experimentally determined. The objective of this study was to use the X-ray coordinates of chicken cystatin to construct computer models of the structures of three human salivary forms (SN, S and SA). These structures were energy-minimized and subjected to dynamic simulations. The resultant structures were compared to determine conformational differences. Global root mean square deviations between equivalent atoms ranged from 1.4 A to 3.9 A. The closest structural similarity to chicken cystatin involved cystatin SN, which also showed the highest (68%) functional sequence homology. Local secondary structure was examined in more detail. In comparisons of alpha-carbon position the third beta-strand (77% functional sequence conservation) and its preceding loop (60% conserved) showed the highest structural conservation in S, while beta-strand 4 showed the highest structural conservation in SN and SA. Throughout their structures, SN and SA were more structurally similar to chicken cystatin than to salivary cystatin S. There are two regions of conserved, negatively charged residues in the salivary cystatins, which appear to be spaced so that they are capable of interaction with hydroxypatite. It is concluded that not only does structural modelling by analogy provide detailed models of salivary cystatins that can be tested by future experimentation, but also that examination of the models has revealed potential sites of interaction with hydroxyapatite.

Amino Acid Sequence↗

PubMedDate not supplied

Clinical evaluation of Fluroshield pit and fissure sealant.

A triple-blind clinical study was performed to measure the amount, rate and oral distribution of fluoride released from Fluoroshield, a commercially available, filled Bis-GMA type sealant containing 2% NaF and 1% adhesion promoter. The study also compared the retention of this sealant in vivo with its nonfluoride-containing analog, Prisma-Shield. One hundred forty-seven pairs of caries-free permanent first molars in 82 children, aged six to nine years, were sealed with the two sealant types. Samples of whole unstimulated saliva, as well as site-specific saliva samples, were collected from 20 randomly selected subjects and analyzed for fluoride content. Complete or partial coverage was observed for 274 of 275 teeth evaluated at six months and for all 199 teeth evaluated at 12 months. There were no statistically significant differences in retention between the two sealants at 6 to 12 months. The release of fluoride was intense, but of short duration. Mean whole saliva fluoride content was 2.9 ppm +/- 0.13 (S.E.), and site-specific saliva fluoride content was 11.4 ppm +/- 1.02 (S.E.) buccal to the fluoride-releasing sealant at 30 minutes; both values returned to baseline within 24 hours. It was concluded that the addition and subsequent release of fluoride in Fluroshield did not decrease its retentiveness.

Child↗