Demineralization in enamel and hydroxyapatite aggregates at increasing ionic strengths

The purpose of this study was to determine whether or not the dual constant-depth film fermenter (dCDFF) is able to produce caries-like enamel lesions and to ascertain further information regarding the performance of this fully functional biological caries model. Conditions were defined by the continuation (CF) or cessation (FF) of a saliva-type growth medium supply during 50-mM sucrose exposures (8 times daily). Hydroxyapatite (n = 3) and bovine enamel (n = 3) substrata were included within each condition and samples extracted after 2, 4, 8, and 16 days. Community profiles were generated for fastidious anaerobes, Lactobacillus spp., Streptococcus spp., mutans streptococci (MS), and Veillonella spp. using selective culture techniques and enamel demineralisation assessed by transverse microradiography. Results demonstrated that the dCDFF model is able to produce caries-like enamel lesions with a high degree of sensitivity where reduced ionic strength within the FF condition increased surface layer mineral deposition. Between conditions, biofilm communities did not differ significantly, although MS in the biofilms extracted from the FF condition rose to a higher proportion (by 1.5 log₁₀ units), and Veillonella spp. were initially greater within the CF condition (by 2.5 log₁₀ units), indicating an enhanced ability for the clearance of low-pK_a acids following exposures to sucrose. However, both conditions retained the ability for caries-like lesion formation.

Section: Discussionmentioning

confidence: 99%

Evidence of an in vitro Coupled Diffusion Mechanism of Lesion Formation within Microcosm Dental Plaque

Owens

Lynch²,

Hope³

et al. 2017

“…Details of the SMR technique have been given elsewhere [Anderson et al, 2004;Kosoric et al, 2010;Shah et al, 2011;Mohammed et al, 2013]. The SMR cells containing the samples were mounted on the X-Y stage, which can be moved and repositioned with high precision (±0.5 μm) under computer control.…”

Section: Smr Experimentsmentioning

confidence: 99%

“…However, there is a paucity of data regarding reductions in demineralisation effected by zinc in the literature. Scanning microradiography (SMR) is a real-time X-ray absorption technique which enables directly quantitative, continuous and precise measurements in enamel mineral mass at fixed local positions Elliott, 1985, 1992;Anderson et al, 2004;Shah et al, 2011]. Comparisons of SMR with other measurement techniques have been made elsewhere [Mohammed et al, 2013], but in brief, SMR can be used to continuously measure the physical changes in bulk enamel concentration during the process of demineralisation, in a non-destructive fashion.…”

mentioning

confidence: 99%

Inhibitory Effects of Zinc Ions on Enamel Demineralisation Kinetics in vitro

Mohammed

Lynch²,

Anderson³

2015

Metal ions including zinc have the ability to influence enamel demineralisation. However, there is a paucity of data regarding reductions in demineralisation effected by zinc ions (Zn²⁺) in the literature. Therefore the aim was to measure the effects of zinc ion concentration ([Zn²⁺]) on the real-time in vitro demineralisation of enamel, during exposure to caries-simulating conditions, using scanning microradiography (SMR). Human enamel blocks were fixed in SMR environmental cells, through which acidic solutions (0.1 M acetic acid, pH 4.0) were circulated for periods of 50 h. SMR was used to quantitatively measure continuous mineral mass loss. Subsequently, the effects of sequentially increasing [Zn²⁺] (0.1-3,565 ppm) in the acidic solutions were measured on the rate of enamel demineralisation. This study demonstrated that Zn²⁺ even at low concentrations significantly reduces enamel demineralisation. There was a log-linear relationship between the mean percentage reduction in demineralisation and increasing [Zn²⁺] up to 3,565 ppm, i.e. the change in the overall percentage reduction in demineralisation was greater at lower concentrations than at higher concentrations, with 60% reduction at 36 ppm increasing to 90% at 3,565 ppm. In conclusion, SMR demonstrated the ability of Zn²⁺ to reduce the rate of enamel demineralisation under real-time in vitro acid conditions simulating dental caries. The results suggest that Zn²⁺ in the oral fluids could protect against enamel demineralisation during an acidic challenge. The log-linear relationship between [Zn²⁺] and demineralisation suggests that the reduction in enamel dissolution is limited by the saturation of surface sites on the enamel surface.

“…It was not possible to confirm directly the occurrence of subsurface demineralisation because the X-ray beam was oriented parallel to the direction of acid attack. However, demineralisation of permeable HAP blocks under similar conditions has been shown to result in subsurface demineralisation, including the retention of an apparently intact surface [Anderson et al, 2004], so it is very likely to occur in the present study at least for the longest switching periods. Whether this also applies to shorter switching periods requires further experiments.…”

Section: Discussionmentioning

confidence: 90%

Demineralisation of Permeable Hydroxyapatite with Alternating Water and Acidic Buffer: Scanning Microradiographic Study of Effect of Switching Period

Bollet-Quivogne¹,

Anderson²,

Dowker³

et al. 2007

Permeable hydroxyapatite (HAP) blocks were exposed for equal times alternately to pH 4.0 buffer and water for 237 h. Rates of HAP loss with time (determined from changes in X-ray attenuation) were measured as a function of switching period τ (the time for a complete cycle) from 0.5 to 6 h and with a continuous buffer flow. The mean rate of HAP loss decreased markedly as τ increased, and for large τ was about half the rate for continuous buffer flow. We propose that demineralising conditions through the depth of the HAP are influenced by the extent of retention of buffer within its pores which will depend on τ. A mathematical model with parameters R₀ and Δt was developed, where R₀ is the rate of demineralisation for continuous flow, and Δt a time added to each τ/2 buffer exposure to account for its retention in the HAP pores. Experimental data fitted the model with Δt ∼8 to ∼10 min and with R₀ close to the rate observed for continuous buffer flow. The model predicts that the rate decreases and approaches R₀/2 as τ → ∞, as was found experimentally to be the case. This type of study could potentially give information about subsurface porosity and transport processes during acidic dissolution of permeable solids, for example in dental caries and dental erosion.