T.W. Cutress

Effect of Carbonate and Fluoride on the Dissolution Behaviour of Synthetic Apatites

The initial rates of dissolution of synthetic apatites were determined using the rotating disc method. The reactivities of carbonated apatites in acidic media were directly related to their carbonate

A mechanism for dental caries based on chemical processes and diffusion phenomena during in-vitro caries simulation on human tooth enamel

Abstract Artificial carious lesions were produced in a range of lactate buffers containing disodium-methane-hydroxy-diphosphonate and the depths of the lesions were measured. The depth of the body of the lesion depended on the calculated concentration of un-ionized lactic acid (HL), and the innermost boundary depended on HL concn. and pH. Apparent diffusion coefficients of the order 10−10cm2/s were calculated from the boundary movement. A mechanism is proposed for the caries process. Diffusion, predominantly of the un-ionized chemical species HL, H3PO4, CaHPO4, Ca(H2PO4)2 and CaL2 occurs through the intercrystalline and interprismatic pores of enamel filled with water and protein. Dissolution takes place throughout the lesion by H+ and L− as HL dissociates. The outer enamel surface is partly protected by reversible adsorption of suitable chemical species.

Periodontal disease and oral hygiene in trisomy 21

Abstract The oral hygiene index and the prevalence of periodontal disease in subjects with trisomy 21 (TR) was determined on a nation-wide basis in New Zealand for subjects aged between 10 and 24 yr. Prevalence estimates were based on the examination of 223 TR subjects and compared with that of 257 other mentally retarded (MR) and 464 normal (N) subjects. TR and MR subjects were differentiated according to their residence in an institution (I) or at home (H). It was found that TRI subjects had the highest and N subjects the lowest periodontal disease scores (Periodontal Index). Although the TRI showed higher scores than MRI subjects, this difference was not so evident between TRH and MRH or between MRI and MRH subjects. It was concluded therefore that an institutional environment increased the susceptibility of TR subjects to periodontal disease. This could not be explained by differences in oral hygiene (Oral Hygiene Index) since all subject-groups showed similar correlations with periodontal scores.

Kinetics and product stoichiometry of ureolysis by human salivary bacteria and artificial mouth plaques

Ureolysis was investigated in salivary bacteria from persons with widely-differing oral ureolytic activities. Rate curves and product stoichiometry were established for urea disappearance, ammonia appearance and conversion of [14C]-urea to 14CO2. Ammonia, released stoichiometrically from urea, was best measured by a direct phenate-hypochlorite reaction. About 80 per cent of the urea-C was liberated as free CO2. Slight deviations from ammonia stoichiometry and most of the CO2 loss occurred in the first 5-10 min of reaction, when the rate of urea disappearance was constant and up to 2-fold higher than subsequently. This rate-change suggests that flux in the ureolysis pathway may be under feedback control. Ureolysis by salivary-sediment bacteria followed Michaelis-Menten kinetics with a Km of 2.5 mM; rates of end-product formation were independent of urea concentration between 25 and 500 mM. Ureolysis was inhibited 98 per cent by 5 mM acetohydroxamic acid, a urease inhibitor, and could be partly solubilized by sonication to give an enzyme preparation which, without cofactor supplementation, quantitatively hydrolysed urea. Thus urea metabolism by oral bacteria may principally involve urease-catalysed hydrolysis, rather than non-urease pathways.

pH Regulation of Urease Levels in Streptococcus salivarius

Potential mechanisms for regulation of urease levels in Streptococcus salivarius were examined, including: induction by urea, nitrogen or carbon source repression, and effects of pH and CO2 (because CO2 enrichment enhanced urease detection on urea agar plates). Regulation by either pH or CO2 was confirmed by comparison of the urease accumulation pattern during anaerobic growth under CO2 with that under N2. Under CO2, there was an initial buffering plateau at pH 6.2 and a rate of Streptococcus salivarius urease accumulation three-fold that under N2, with a pH 7.6 plateau. With both gas phases there was also an increase in the rate of urease appearance coincident with the decrease in medium pH following the pH plateau. The effects of pH, CO2, and HCO3- on urease levels and on growth were separately assessed by culture in media containing 0, 25, 100 mmol/L KHCO3 buffered at different pH levels. There was an inverse relationship between the logarithm of the urease level after 24-hour growth and the pH during growth-the urease specific activity was 100-fold higher at pH 5.5, compared with pH 7.0 and above. HCO3-/CO2 (100 mmol/L) had little effect on urease levels, but was essential for growth at pH 5.5. There was no significant urease induction by urea, or repression by ammonia or glucose. There was also evidence of pH regulation of urease levels in some staphylococci, Klebsiella pneumonia, and Corynebacterium renale, but not in Actinomyces naeslundii and several other species. We conclude that the external pH is a major factor regulating urease levels in S. salivarius and possibly some other species-a mechanism equivalent to urease repression by OH-.

The bacteria responsible for ureolysis in artificial dental plaque.

The origin of ureolytic activity in artificial-mouth plaques was established by assessing the contribution to plaque ureolytic activity of the isolated bacteria. To overcome losses of ureolytic activity caused by the unstable presence of urease in oral bacteria, ureolytic bacteria were isolated from an exceptionally active plaque (1 mumol NH3/min per mg protein) in which 63 per cent of the flora was ureolytic. After their ability to metabolize urea was stabilized, 13 ureolytic bacteria remained: seven strains of Streptococcus salivarius, one Streptococcus bovis, two Staphylococcus epidermidis and three Staphylococcus haemolyticus. Their urease activity, measured after growth into stationary phase, was reproducible and strain specific with a 20-fold range within each genus. The mean ureolytic activity of each species, when weighted by its calculated incidence in the original plaque, accounted for 40 per cent of the total plaque ureolytic activity. However, these values for urease levels were only a small fraction of the bacterial ureolytic potential. Urease per mg cell protein measured during the growth cycle of a selected Strep. salivarius, and Staph. epidermidis, varied 10-fold, and reached much higher activities (i.e. 6-8 mumol NH3/min per mg of cell protein) than under the growth conditions that were used to assess the contribution of these species to total plaque ureolysis. Thus urea metabolism in artificial plaque was due mainly to Strep. salivarius, with a small contribution from Staph. epidermidis. The presence of further unidentified species of ureolytic oral bacteria need not be invoked.

The inorganic composition and solubility of dental enamel from several specified population groups

Abstract The solubility in lactate buffer (pH 4.5) and the inorganic composition of intact enamel surfaces of 234 teeth obtained from eleven specified and diverse sources including trisomic 21 subjects, were studied. The solubility was determined at conditions approximating to equilibrium and the surface and two succeeding enamel layers (each approx. 30 μm thick) analysed. Significant differences in solubility and composition were found between some groups but trisomic enamel was not considered unusual in these respects. Enamel groups could be ranked in order of solubility; all deciduous enamel groups were more soluble than permanent enamels. For most enamels, the solubility was inversely correlated with enamel fluoride concentrations and directly correlated with carbonate concentrations and the ratio of these two components. Fluoride concentrations in the acid buffer correlated with the solubility and fluoride level in the respective enamel groups. It was concluded that environmental factors present during or following enamel maturation influence enamel composition and solubility.

Differential Diagnosis of Dental Fluorosis

Differentiating between fluorotic and non-fluorotic defects of dental enamel is an important diagnostic decision in epidemiology and public health dentistry. The commonly accepted diagnostic criteria for fluorosis discriminate between non-discrete symmetrical and asymmetrical distributions of opacities of dental enamel. These criteria appear to identify most cases of dental fluorosis. However, it is not yet confirmed that the pattern and distribution of dental fluorosis are a unique phenomenon. Metabolic, physiological, other trace elements, and malnutrition have been reported to induce bilateral symmetrical developmental enamel opacities. Misdiagnosis of non-fluoride-induced opacities remains a possibility. Reports of unexpectedly high population prevalence and individual cases of fluorosis, where such diagnoses are incompatible with the known fluoride history, indicate the need for a more precise definition and diagnosis of dental fluorosis. A more discriminating diagnostic procedure is recommended. This calls for a positive identification of the levels of fluoride available to communities and individuals before a diagnosis of fluorosis is confirmed. We believe a more critical approach to the diagnosis of fluorosis will be helpful in the rational use and control of fluorides for dental health, and in the identification of factors associated with inducing developmental defects of enamel.

Dental caries in trisomy 21.

Abstract The prevalence of dental caries in subjects with trisomy 21 (TR) was determined on a nationwide basis in New Zealand for subjects aged 5–24 yr. Caries prevalence was based on the examination of 416 TR subjects, and compared with that of 432 other mentally retarded (MR) and 697 normal (N) subjects. Subjects resident in institutions had a lower caries prevalence in permanent and deciduous dentitions than those resident at home. TR subjects in institutions had a lower DMF score than MR subjects in institutions but this difference was smaller between TR and MR subjects living at home. However, TR subjects had fewer and later erupted permanent teeth than MR and N subjects and when caries scores of groups living within similar environments were adjusted for these factors the differences in caries scores were small and not significant.

The source of variation in ureolysis in artificial plaques cultured from human salivary bacteria

Artificial-mouth plaques were cultured for 7 days from the saliva of two individuals, one with high and one with low salivary ureolytic activity. There was a 7.5-fold range in the resulting plaque ureolysis rates (per mg of protein), and the composition of the flora varied widely. The average rate of ureolysis of artificial plaque was similar to that in natural plaques but higher than in salivary sediment (after correction of sediment rates for the presence of 50 per cent non-bacterial protein). The average rate of ureolysis per ureolytic bacterium was 2.5 times higher in the artificial plaques than in saliva. Although the saliva inocula were from subjects with a 3-fold difference in salivary ureolysis rate, this difference was not reflected in the ureolytic activity of the artificial plaques. Neither was this difference evident in the ureolytic activity of the corresponding natural plaques. The established hypothesis that plaque ureolysis is derived mainly from an unidentified active segment of the total ureolytic flora was tested in the artificial plaques by analysis of variance to determine the contribution of the known ureolytic bacteria. Plaque ureolysis rates were almost entirely explained (r2 = 86 per cent) by the percentage of total detectable ureolytic bacteria in the plaque flora. The plaque bacteria giving strong ureolytic reactions on agar plates were all Gram-positive cocci and in 6 of the 9 plaques were streptococci only. Therefore, in artificial plaques the physiologically significant bacteria comprise a high proportion of the total ureolytic flora and are Gram-positive cocci, mainly streptococci.