Lee Cooper

Validation of enamel erosion in vitro

OBJECTIVES Many tools are available to quantify dental erosion, but each technique has its own inherent disadvantages. This study aims to validate the use of quantitative light-induced fluorescence (QLF) and non-contacting surface profilometry compared to the gold standard transverse microradiography (TMR) for the quantification of enamel erosion in vitro. METHODS This was an in vitro laboratory based study. 60 bovine incisors were divided into 6 groups of 10. Each tooths labial surface was completely varnished except for a window of enamel approximately 3mmx5mm. Each was baseline imaged with QLF and non-contacting surface profilometry before being subjected to an erosive solution (pH 3.4) for up to 36h. The lesions were imaged using non-contacting surface profilometry and QLF, sectioned and analysed with TMR. Correlation coefficients were calculated to assess the validity of the methods of measurement as compared to TMR. RESULTS A range of lesion severities resulted. Mineral loss measured as DeltaQ (QLF) and step height (profilometry), was recorded and confirmed by TMR. A correlation was found between DeltaZ (TMR) and profilometry lesion depth of r=0.648 (p<0.001). A poorer correlation was found between DeltaZ and DeltaQ: r=0.217 (p=0.096). CONCLUSIONS Profilometry lesion depth and DeltaZ correlated significantly. Both methods allow for quantification of erosive crater depth. QLF correlated poorly with DeltaZ, but is useful for measuring subsurface loss of mineralisation. TMR is valuable but is destructive and can only be used in vitro. Currently only QLF can be used in vivo. Advances in these technologies may allow the development of non-destructive in vivo measurements of mineral loss, combining the positive features of each measurement method.

The erosive potential of some alcopops using bovine enamel: an in vitro study.

OBJECTIVES Alcoholic soft drinks have become increasingly popular and have high concentrations of citric acid and alcohol so might have the potential to cause dental erosion. This study aimed to investigate the erosive potential of alcopops on bovine enamel in vitro. METHODS Six bovine upper incisors were prepared and sectioned to give six slabs per tooth, 4mm x 4mm each. Each slab was covered with nail varnish, leaving an exposed window (2mm x 2mm). Samples were immersed in 20ml of each of the test solutions for 20min, 1h, and 24h under gentle agitation (100rpm). Enamel surface loss was determined using Quantitative Laser Fluorescence (QLF), Non-contact Profilometry (NCP) and Transverse Microradiography (TMR). RESULTS Enamel loss occurred with all test drinks and the positive control (p<0.05), and the depth of lesion correlated with pH and time. No significant difference was observed between 20min and 1h exposure, although both times had significantly (p<0.05) greater erosion when compared with baseline. Within each alcopops group significant erosion had occurred at 24h exposure compared with the baseline and previous times. CONCLUSION All the tested alcopops resulted in significant enamel loss at 24h (p<0.001) with direct correlation between degree of enamel loss and both pH and increasing exposure time.

Effects of zinc and fluoride on the remineralisation of artificial carious lesions under simulated plaque-fluid conditions

The aim was to study the effects of zinc (Zn) and fluoride (F) on remineralisation at plaque fluid concentrations. Artificial carious lesions were created in 2 acid-gel demineralising systems (initially infinitely undersaturated and partially saturated with respect to enamel) giving lesions with different mineral distribution characteristics (high and low R values, respectively) but similar integrated mineral loss values. Lesions of both types were assigned to 1 of 4 groups and remineralised for 5 days at 37°C. Zn and F were added, based on plaque fluid concentrations 1 h after application, to give 4 treatments: 231 µmol/l Zn, 10.5 µmol/l F, Zn/F combined and an unmodified control solution (non-F/non-Zn). Subsequently remineralisation was measured using microradiography. High-R lesions were analysed for calcium, phosphorus, F and Zn using electron probe micro-analysis. All lesions underwent statistically significant remineralisation. For low-R lesions, remineralisation was in the order Fa < non-F/non-Zna < Zna, b < Zn/Fb, and for high-R lesions Fa < non-F/non-Znb < Znb < Zn/Fc (treatments with the same superscript letter not significantly different, at p < 0.05). Qualitatively, remineralisation occurred throughout non-F/non-Zn and Zn groups, predominantly at the surface zone (F) and within the lesion body (Zn/F). Electron probe micro-analysis revealed Zn in relatively large amounts in the outer regions (Zn, Zn/F). F was abundant not only at the surface (F), but also in the lesion body (Zn/F). Calcium:phosphate ratios were similar to hydroxyapatite (all). To conclude, under static remineralising conditions simulating plaque fluid, Zn/F treatment gave significantly greater remineralisation than did F treatment, possibly because Zn in the Zn/F group maintained greater surface zone porosity compared with F, facilitating greater lesion body remineralisation.

Effect of gallium on growth of Streptococcus mutans NCTC 10449 and dental tissues.

Gallium-doped phosphate-based glasses (Ga-PBG) were assessed for their impact on Streptococcus mutans and dental mineralisation, firstly by disc diffusion assays followed by biofilms grown on nitrocellulose filter membrane (NFM) and constant-depth film fermentor (CDFF). Short-time exposure (10 min) effects of Ga-PBG on S. mutans biofilm were compared with that of 0.2% chlorhexidine. The effects of Ga-PBG on bovine enamel (which was investigated under pH-cycling condition) and dentine were analysed using transverse microradiography (TMR), profilometry and inductively coupled plasma optical-emission spectrometry (ICP-OES). The disc diffusion assays showed inhibition zones of 24.5 ± 0.5 mm for Ga-PBG compared with controls (C-PBG). Ga-PBG showed statistically significant growth inhibition of S. mutans biofilms on NFM (p = 0.001) and CDFF (p < 0.046) compared with hydroxyapatite (HA) and C-PBG. The CDFF assay revealed a maximum of 2.11 log colony-forming unit (CFU) reduction at 48 h, but short-time exposure effects were comparable with that of 0.2% chlorhexidine only on older biofilms (maximum of 0.59 vs. 0.69 log CFU reduction at 120 h). TMR analyses of the enamel revealed non-significant mineral loss (p = 0.37) only in the case of Ga-PBG samples compared with controls including sodium fluoride. ICP-OES analyses indicated transient gallium adsorption into dentine by calcium displacement. The results confirmed that gallium inhibited S. mutans growth and appears to have the potential to protect the enamel surface under conditions representative of the oral environment. Further work is needed to establish whether it has an application in daily oral hygiene procedures to prevent or reduce caries.

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

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-pKa acids following exposures to sucrose. However, both conditions retained the ability for caries-like lesion formation.

A randomised controlled trial to investigate the remineralising potential of Tooth Mousse™ in orthodontic patients

Objective To investigate the remineralisation of enamel subsurface lesions treated with fluoride toothpaste (1450 ppm) or a combination of fluoride toothpaste in addition to Tooth Mousse™. Design An in situ, cross-over, randomised controlled trial. Setting Orthodontic department at Liverpool University Dental Hospital, UK. Participants: Twelve patients receiving fixed orthodontic treatment. Methods: Demineralised subsurface enamel lesions were placed in a carrier and attached onto a fixed orthodontic appliance. Interventions were either standard fluoride toothpaste or CPP-ACP paste (Tooth Mousse™) in addition to the fluoride toothpaste. Participants received both interventions in a randomised order. Transverse microradiography analysis was used to compare lesion mineral content profiles. Results Mineral loss was reduced by 15.4 and 24.6% between the fluoride and CPP-ACP groups, respectively (p = 0.023). Lesion depth was reduced by 1.6 and 11.1% between the fluoride and CPP-ACP groups, respectively (p = 0.037). Lesion width was reduced by 4.5 and 15.3% between the fluoride and CPP-ACP groups, respectively (p = 0.015). Conclusions Remineralisation occurred regardless of treatment group allocation. However, the addition of Tooth Mousse™ resulted in a significantly increased remineralisation effect, compared to fluoride alone. Tooth Mousse™ may be beneficial for patients undergoing orthodontic treatment who are at high risk of demineralisation. Trial Registration Registered on Current Control Trials http://www.controlled-trials.com/ISRCTN04899524