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Objectives: Fixed appliance therapy in orthodontics relies on the effective bonding of brackets to surface enamel. Bracket de-bonding during treatment is both inconvenient and costly to both dentist and patient. Factors which control the efficacy of the bond are not fully understood. For example, there has never been a study to determine the efficacy of bonding to different teeth in the dentition. The aim of this study was to investigate the possible differences in bond strength to acid etched enamel on the different teeth of the dentition., Methods: Two hundred and forty extracted sound human teeth were collected from white Caucasian subjects between the age of 10 and 22 years. Approximately 20 teeth of each tooth type were bonded using a standard acid etch technique with 'A company' stainless steel brackets using a light cured composite (Transbond, 3M Unitek). Shear bond strength (24 h) was measured using an Instron testing machine., Results: Tooth type was found to have a significant effect on bond strength (p<0.001). The greatest mean bond strength was found on the lower first molar teeth, and the lowest on the upper first molar teeth. In the upper arch, bond strength was greater on anterior teeth than posterior teeth (p<0.001). In the lower arch bond strength was weaker on anterior teeth than posterior teeth (p<0.001)., Significance: The results have profound implications for bond strength testing of dental composites to enamel as well as to the expectations of bond reliability in orthodontic therapy. The findings suggest that, in order to achieve meaningful comparisons, enamel bond strength measurements should be made using the same tooth type, or that appropriate stratification of groups of test teeth should be used. These findings may also explain, in part, variability in enamel bonding efficacy despite the best efforts of the dental practitioner.

Equilibrium dialysis was used to investigate the binding capacity and affinity of lipoteichoic acid (LTA) from the Gram-positive bacterium Streptococcus sanguis for calcium and magnesium by a competitive method. LTA was shown to bind approx. 1 mol of either calcium or magnesium per mole phosphate. Calcium and magnesium dissociation constants were found to be 8.39 +/- 0.31 mmol/l and 15.01 +/- 2.01 mmol/l respectively, indicating that S. sanguis LTA will preferentially bind calcium. LTA may act as a calcium buffer by reducing the free calcium concentration to which the cell is exposed. The capacity to produce large quantities of LTA could thus be as important as aciduricity in selection of species at caries-prone sites.

Calcium-binding by surface components of oral bacteria may have important effects on remineralization/demineralization phenomena and plaque cohesion. Additionally, some species export large quantities of lipoteichoic acid, possibly as a protective measure. Measurement of calcium-binding can facilitate prediction of how this will effectively buffer plaque fluid calcium concentration and affect these processes. Using equilibrium dialysis, we measured calcium-binding capacities and affinities at pH 7.0 in isolated cell walls of Streptococcus downei, S. sanguis, and purified lipoteichoic acid (LTA) of S. sanguis. Mean binding capacities were: 56.5 mumol Ca/g wet weight for S. downei cell walls and 47.2 mumol Ca/g wet weight for S. sanguis cell walls, and 1.11 mol Ca/mol LTA phosphate were found. Mean dissociation constants (mmol/L) for cell wall calcium binding were 2.16 mmol/L (S. downei) and 2.69 mmol/L (S. sanguis). These constants were not significantly different from those for whole cells of the same species (Rose et al., 1993), but the dissociation constant for LTA (7.82 mmol/L) was significantly higher and suggested a different mode of binding. At neutral pH, at the known calcium concentration of plaque fluid, whole cells and cell walls are likely to be completely saturated with calcium, whereas free LTA is only 30% saturated. The large amounts of LTA exported by some sucrose-grown streptococci may therefore act as a calcium buffer and so protect the organisms against high local concentrations of calcium produced during demineralization.

Extraction of Streptococcus mutans with the detergents HECAMEG and lauroyl sarcosinate preferentially extracted antigen D, previously identified as a low molecular mass wall-associated protein. Western blotting with specific antisera was used to demonstrate that this antigen is the HPr component of the sugar-phosphotransferase transport system. Non-denaturing electrophoresis indicated that HECAMEG selectively extracted only one of the two forms of HPr. It is suggested that this form of HPr may have a specific cell surface location.

The number of non-sugar sweeteners that are approved for use in foods and drinks is increasing and manufacturers are using these as alternatives to cariogenic sugar. These non-sugar sweeteners are generally classed as non-cariogenic. The most frequently used non-sugar sweetener is sorbitol, and concern has been expressed that the oral flora may adapt to sorbitol so that it looses its 'safe for teeth' property. The purpose of this review is to describe the mechanisms whereby oral microorganisms, and mutans streptococci in particular, might metabolize sorbitol and to summarize published research into changes in plaque acid production and changes in plaque flora after exposure to sorbitol. Finally, the possibility that some groups of people may be especially 'at-risk' from adaptation of oral microorganisms to sorbitol is considered. It is concluded that frequent or long-term use of sorbitol is unlikely to present any increased risk of dental caries in normal people, but that frequent use of sorbitol may present a small cariogenic risk in people with low salivary flow.

Plaque is generally accepted as the prime agent in the aetiology of gingivitis and caries. However, it has been estimated that the oral microbial load must be reduced by some 99.9% in order to produce a significant effect on plaque formation--and mechanical tooth cleaning alone is unlikely to achieve this. Considerable effort has therefore been put into researching chemical means of controlling plaque. In the final article of this eight-part series, the author reviews the efficacy and modes of action of the chemical agents currently available.

[3H]-Glycerol-labelled lipoteichoic acid (LTA) was extracted from Streptococcus sanguis cells using aqueous phenol. Chemical analysis of the LTA yielded phosphate:glycerol:glucose:fatty acids in the mole ratio 1.0:0.97:0.76:0.03. The LTA inhibited the interaction between Strep. sanguis cells and a high mol. wt blood-group-reactive glycoprotein (BGR-glycoprotein) isolated from human saliva and reduced Strep. sanguis-mediated haemagglutination activity. Purified LTA from Strep. mutans strains OMZ61 and HS6, which have been shown not to interact with the BGR-glycoprotein, also inhibited the BGR-glycoprotein mediated aggregation of Strep. sanguis, as did an antiserum prepared against Lactobacillus casei LTA. It is proposed that the binding of the salivary glycoprotein to Strep. sanguis cells in achieved through LTA associated with bacterial surface fibrils.

Artificial pellicles were prepared by coating hydroxyapatite beads with whole saliva. Radiolabelled lipoteichoic acid was isolated from Streptococcus sanguis NCTC 7863 by phenol extraction. Various concentrations of radiolabelled lipoteichoic acid were mixed with saliva-coated hydroxyapatite in the presence and absence of high ionic strength phosphate buffer, bovine serum albumin, gelatin, unlabelled lipoteichoic acid, Tween 20 and Triton X-100. The amount of lipoteichoic acid binding was measured by counting the residual radioactivity of the saliva-coated hydroxyapatite after thorough washing. In one experiment the binding was measured in the presence of a mucinous glycoprotein isolated from human saliva. The data were analysed by means of Scatchard and double reciprocal plots of the bound and unbound fraction of lipoteichoic acid. The lipoteichoic acid interacted hydrophobically with the saliva-coated hydroxyapatite; the interaction was complex with multiple binding sites exhibiting a range of affinities. The mean association constant was 1.1 x 10(9) M-1 and the minimum number of binding sites was 3.9 x 10(12)/mm2 of artificial pellicle. The salivary mucin competitively inhibited the interaction, which suggests that this may be one of the salivary components involved.

An enzyme linked immune sorbent assay (ELISA) was developed to measure bacterial surface lipoteichoic acid (LTA). Numerous strains of oral streptococci belonging to the 'viridans' group were examined on three separate occasions. The results show that, under these cultural conditions, oral streptococci do not normally express LTA on the cell surface. Occasionally strains produced amounts of LTA detectable using the ELISA but this was not a reproducible phenomenon.

Fibronectin-coated hydroxyapatite (FnHA) beads were used in a model adhesion assay to isolate the lipoteichoic acid (LTA) mediated adhesion of oral streptococci. Representative strains of the commonly isolated viridans streptococci were incubated with FnHA beads in the presence and absence of exogenous LTA. The LTA inhibited the adhesion of all strains to a greater or lesser extent, but only a very few strains were inhibited by more than 90%. Strains of Streptococcus sanguis Type II and Streptococcus mitis which synthesize an amphiphile other than LTA were also inhibited. The findings provided circumstantial evidence for the involvement of LTA in the adhesion of this group of oral bacteria.