The effect of bleaching on enamel susceptibility to acid erosion and demineralisation

INTRODUCTION

The purpose of this in vitro study was to determine if enamel that had been bleached by carbamide (urea) peroxide gel (CPG) was at increased risk of either acid erosion or demineralisation (early caries) than un-bleached enamel.

METHODS

Human incisors were employed. The samples were randomly assigned to one of 4 groups; a) 10% CPG, b) 16% CPG, c) 22% CPG and d) 10% CPG with xylitol, fluoride and potassium. Each specimen was moistened with saliva and the appropriate formulation placed for 2 hours for a total of 40 hours of exposure. In order to ensure that bleaching had taken place, tooth shades were monitored using the Shade-Eye device. Following the bleaching process, one half of the specimen was subjected to an erosive challenge, the other to a demineralisation system with one half of each sub-sample retained as a non-bleached control. Samples were assessed longitudinally with quantitative light-induced fluorescence (QLF) and at the conclusion of the study with transverse micro-radiography (TMR).

RESULTS

Erosion was detected in all samples (DeltaQ 126+/-23.4), in both bleached and non-bleached areas. There was no statistical difference between the bleached and non-bleached areas either within the treatment groups or between them. Caries-like lesions were detected on all samples; TMR revealed sub-surface lesions on all teeth and QLF data supported this (DeltaQ 89+/-18.9). Following statistical analysis there were no differences detected between the bleached and non-bleached areas, nor between the different concentrations of the bleaching solution.

CONCLUSION

These results suggest that tooth bleaching with carbamide (urea) peroxide (using commercially available concentrations) does not increase the susceptibility of enamel to acid erosion or caries.

The use of in situ models and QLF for the study of coronal caries

OBJECTIVES

The purpose of the paper is to review aspects of the systems available to model the caries process in enamel.

METHODS

The in situ model developed in Liverpool, and the new method of quantifying mineral loss, Quantitative Light-induced Fluorescence (QLF), are described. QLF is a powerful new diagnostic tool which can be used to measure demineralisation and remineralisation in tooth surfaces in vivo; studies to optimise, validate and use QLF in different clinical situations are described.

RESULTS

Examples of the use of in situ models show that they are particularly valuable for monitoring de and remineralisation of artificial lesions in relation to product testing as alternatives to clinical trials, and present significant advances over in vitro methods. Quantification of mineral loss by Transverse Microradiography (TMR) as in the traditional Liverpool model has produced much valuable information, but the destructive nature of the method limits experimental design, and removes the system from the clinical situation. As a possible alternative, QLF has been validated and optimised. Longitudinal measures can be made on the same surface, and examples of its use are for monitoring recurrent caries and demineralisation around orthodontic brackets.

CONCLUSIONS

While current in situ models provide a major advance over earlier caries models, measurement of de and remineralisation by destructive methods such as transverse microradiography limits the design of experimental investigations. QLF offers significant time saving, reduces the cost of clinical studies, and because the measurements can be carried out longitudinally in vivo, can remove the need for intra-oral appliances carrying experimental tissues.

Quantification of dental plaque in the research environment

OBJECTIVES

To review the established and novel methods of plaque quantification employed in dental research, including a discussion of their merits and to present a new method of planimetrically measuring plaque using light induced fluorescence.

METHOD

Quantitative light-fluorescence (QLF) images were acquired from the buccal surfaces of an individual who had refrained from oral hygiene both with and without traditional plaque disclosure. Digital photographs were also taken. Images were analysed using a novel method and a percentage plaque index produced.

RESULTS

Traditional plaque indices are problematic due to their integral nature and their failure to detect small, but potentially clinically relevant changes in plaque area. The use of a fluorescent technique demonstrated good reliability although there was no correlation between red fluorescent plaque and total disclosed plaque suggesting that the auto-fluorescing plaque is not a good measure of total plaque volume.

CONCLUSIONS

The use of planimetric techniques can increase the power of plaque studies, potentially reducing the number of subjects and time required to separate therapies or products. Fluorescent methods of quantification have potential as they enable clear separation of the plaque covered and non-covered tooth surfaces.

Developments in dental plaque pH modelling

OBJECTIVES

The objectives of this review were to give a comprehensive account of the methods used to determine dental plaque pH over the last 50 years, to review how these methods have been used in dental cariology research and to give an update as to how dental plaque pH studies might be developed in the future.

DATA

Published, referred papers and abstracts of conference proceedings in the literature were reviewed.

SOURCES

A comprehensive search of the electronic databases PubMed and Medline, was undertaken. In addition, a hand search of the Index Denticus was done to identify relevant citations before 1966.

STUDY SELECTION

Relevant published literature in peer-reviewed publications was reviewed. No additional inclusion criteria were applied.

CONCLUSIONS

This comprehensive review gives an account of the background to, history of, relative merits and demerits of, applications of and future of dental plaque pH technologies.

A study to assess the efficacy of a new detergent free, whitening dentifrice in vivo using QLF planimetric analysis

OBJECTIVE

To determine the effects of a detergent-free, whitening dentifrice using an in vivo plaque regrowth model with the novel application of QLF as a planimetric analysis tool.

METHOD

A total of 20 subjects took part in a double blind, single-centre, crossover study in which slurry rinses were the only form of plaque control over a 5-day period. Following a washout and prophylaxis the subjects used 2 daily rinses in the absence of all other plaque control methods. Subjects returned to the clinic on the afternoon of day 5 when plaque was disclosed and assessed by the plaque index and area using both a photographic and novel fluorescent planimetric technique. A further 9-day washout was carried out and the rinse period repeated to ensure that each subject had used both experimental and comparator slurries.

RESULTS

Twenty subjects completed the trial. The test product showed a significant inhibition of plaque re-growth (16.9%) compared with a fluoride-matched comparator using the Turesky index (P < 0.0001), the photographic planimetric technique (17.5%) (P < 0.0001) and the novel QLF technique (18.4%) (P < 0.0001).

CONCLUSION

The results confirm that plaque inhibition capability of a detergent-free whitening dentifrice is at least as effective as a fluoride matched comparator. QLF is a promising tool for disclosed plaque quantification.

The validation of Quantitative light-induced fluorescence to quantify acid erosion of human enamel

OBJECTIVE

The purpose of this study was to validate the Quantitative light-induced fluorescence (QLF) device against transverse microradiography (TMR) with regard to the quantification of enamel erosion in vitro.

DESIGN

Longitudinal in vitro.

METHODS

Thirty previously extracted, caries free, human premolars were selected and prepared by gentle pumicing and coating in an acid-resistant nail-varnish save for an exposed window on the buccal surface. QLF baseline images were taken and the teeth then exposed to an erosive solution, 0.1% citric acid (pH 2.74). Teeth were removed at 30min intervals, air-dried and QLF images taken. At this time one tooth was randomly selected, removed from solution and sectioned through the lesion at three sites. The polished sample (100microm) was subjected to TMR and analysed for erosive mineral loss using proprietary software, with the DeltaZ values noted. QLF images were analysed by a blinded examiner with DeltaF and DeltaQ values recorded. Data were entered into SPSS and the correlation between the DeltaZ and DeltaF, and DeltaZ and DeltaQ values calculated.

RESULTS

A wide range of erosive lesions was produced, with a steady increase in both DeltaZ and DeltaF over time; DeltaZ (24.0 (S.D. 1.2)-6114.3 (S.D. 1177.57)); DeltaF (1.8-11.2), DeltaQ (2.5-202.6). The results were scatter plotted and a regression line calculated. A positive correlation between DeltaZ and DeltaF of 0.91 was found, and for DeltaZ and DeltaQ; 0.87.

CONCLUSIONS

The ability for QLF to detect and longitudinally monitor in vitro erosion has been shown. The strong positive correlation of DeltaF with DeltaZ suggests that percentage fluorescence loss as measured by QLF could be of great value in the development of a non-destructive, longitudinal tool for use in vitro, in situ and possibly in vivo.

The effect of dehydration on quantitative light-induced fluorescence analysis of early enamel demineralization

The purpose of this study was to determine the effect of hydration [distilled water (DH2O) and saliva] on lesions of varying severity and determine an optimal drying method to obtain reliable quantitative light-induced fluorescence (QLF) readings. Ten previously extracted molars were placed into a demineralizing solution for 7, 14 and 21 days. Between each demineralizing cycle the teeth were removed. To test for in vitro reliability the teeth were rinsed in DH2O for 1 min and then QLF images were taken every 10 s (control cycle with no drying employed - bench drying only). This was repeated following (i). compressed air drying for 30 s or 15 s and (ii). 30 s cotton wool roll application (CWR). To test for in vivo reliability the experiment was repeated using whole human saliva in place of DH2O. Control groups demonstrated the effect of hydration on QLF reliability; at 7 days reliable results were obtained after 370.4 s (DH2O) and 432.3 s (saliva). Air drying of both DH2O and saliva-rinsed teeth reduced reliability time to 2.1 (+/-6.0) and 3.2 s (+/-7.6), respectively. Cotton wool roll application produced reliable results in 89 s with DH2O and 110 s with saliva. As lesion severity increased [14 days mean deltaQ 115 (+/-90.2), 21 days mean deltaQ 168.0 (+/-120.7)] time to reach reliability significantly increased under control drying and CWR (P > 0.05). Time taken for compressed air-dried teeth to produce reliable results was not significantly different across the groups. Compressed air-drying for 15 s produces reliable results with both DH2O and saliva-hydrated lesions. Future in vivo experiments will be required to determine if the air-drying can be reduced further in a clinical situation.

The use of fluorescein-enhanced quantitative light-induced fluorescence to monitor de- and re-mineralization of in vitro root caries

The use of fluorescein-enhanced quantitative light-induced fluorescence (QLF) in the detection of in vitro root caries demineralization and reminerlization was investigated. Fourteen previously extracted human premolar roots were selected and determined to be caries-free. Cementum was removed and nail varnish applied leaving an exposed window. Positive and negative controls were selected. During a demineralizing regimen, roots were removed at regular intervals (12, 48, 72 and 120 h) and immersed in sodium fluorescein (0.2 mg L(-1)). Following gentle rinsing, each root was examined using QLF before being returned to the demineralizing solution. Following 120 h, each tooth was sectioned through the lesion and one-half retained for transverse micro radiography (TMR) analysis. The remaining half were subjected to a remineralizing regimen undergoing the same fluorescein and QLF examinations at 7, 28 and 36 days. Results showed that QLF effectively monitored demineralization/remineralization of root dentine as represented by fluorescein penetration. TMR analysis showed good correlations with QLF (DeltaZ/DeltaQ) after demineralization (r = 0.89) and remineralization (r = 0.84). The technique could represent an in vivo method for root caries detection and classification.

The erosive potential of commercially available mouthrinses on enamel as measured by Quantitative Light-induced Fluorescence (QLF)

DESIGN

Longitudinal in vitro.

METHODS

Previously extracted, caries free, human premolars were selected and prepared by gentle pumicing and coating in an acid-resistant nail-varnish save for an exposed enamel window on the buccal surface. Each was assigned to one of eight groups (six per group, 10 in positive control); positive control (citric acid, pH 2.7, F(-) 0 ppm), negative control (pH 7.0, F(-) 0 ppm) Listerine (pH 3.87, F(-) 0.021 ppm), Tesco Value (pH 6.05, F(-) 289.00 ppm), Tesco Total Care (pH 6.20, F(-) 313.84 ppm), Sainsbury's (pH 6.15, F(-) 365.75 ppm), Sensodyne (pH 6.12, F(-) 285.30 ppm) and Corsodyl (pH 5.65, F(-) 0 ppm). The titratable acid values (TAV) for each rinse were established using volume (ml) of 0.1 M NaOH to achieve pH 7. Fluoride values were obtained by ion selective electrode. The solutions were kept at 37 degrees C and gently agitated. Teeth were removed at hourly intervals for 15 h, air-dried and subjected to Quantitative Light-induced Fluorescence (QLF) examination by a blinded examiner and DeltaQ values recorded. At the conclusion of the study each of the positive control teeth and one from each other group were sectioned through the eroded lesion, ground and polished to 100 micrometers and subjected to transverse microradiography and DeltaZ recorded for validation.

RESULTS

TAVs were: Listerine 2.45 L > Sainsbury's 0.35 ml >Tesco Total Care 0.14 ml > Tesco Value 0.08 ml > Corsodyl 0.10 ml >Sensodyne 0.9 ml. DeltaQ increased over time for the positive control, (0 h 0.2, 10 h 95.2, 15 h 152.3). Negative controls remained stable. The increase in DeltaQ for each rinse after 15 h was Listerine (9.3(+/-7.2)), Corsodyl (1.5(+/-1.2)), Tesco Value (1.8(+/-1.2)), Tesco Total Care (1.4(+/-1.1)), Sainsbury's (3.4(+/-2.2)), Sensodyne (0.9(+/-1.6)). TMR confirmed the presence/absence of erosive lesions.

CONCLUSIONS

QLF effectively monitored erosion in the positive controls and lack of erosion in the NC. Only one mouthrinse (Listerine) caused any erosion compared to the negative control, but this was only significant after 14 h of continuous use.

Detection of in vitro demineralization adjacent to restorations using quantitative light induced fluorescence (QLF)

AIM

Quantitative light-induced fluorescence (QLF) is a technique for the detection, quantification, and longitudinal monitoring of early carious lesions. The technique is non-destructive and can be used in vivo. Using the natural fluorescence of teeth, and the loss of such fluorescence in demineralized enamel, QLF is a repeatable and valid optical caries monitor. Previously used in smooth and occlusal surfaces, the purpose of this pilot study was to determine if QLF could detect, and longitudinally monitor, demineralization adjacent to a range of restorative materials.

METHODS

Fifteen previously extracted lower third molars were selected based upon the lack of any visible demineralization. A single burr hole was placed on the buccal surface and the cavity restored with amalgam, composite, compomer, glass ionomer or a temporary filling material. The buccal surface was then coated in an acid resistant nail varnish leaving an exposed area around the restoration and also a similar sized control region. The teeth had QLF images taken at baseline and were then subjected to a demineralizing buffer, further QLF images were subsequently taken at 72 and 144 h. Transverse microradiography was used to confirm the presence of early, subsurface lesions at the completion of the cycle (144 h). QLF images were analyzed by a single blinded examiner and values for change in radiance fluorescence were computed. These values were recorded as loss of radiance fluorescence loss integrated over area of lesion and expressed as DeltaQ.

RESULTS

The appearance of each material under QLF and the change in fluorescence is described. Amalgam, glass ionomer and the temporary material all exhibited reduced fluorescence, while composite and compomer showed increased fluorescence, when compared with surrounding enamel. There was no change in fluorescence of the materials when subjected to experimental demineralizing conditions. Readings at 72 and 144 h demonstrated demineralization adjacent to the restorations and at the exposed control. Significant differences were detected between baseline, 72 and 144 h using ANOVA on all restorations with the exception of compomer where significance was noted between baseline and 144 h, p>0.05.

CONCLUSIONS

This pilot study has demonstrated the ability for QLF to detect and monitor secondary caries. Analysis techniques should be based upon the subtraction of baseline DeltaQ scores from subsequent images. Further research is required to assess the ability of QLF to detect secondary lesions in vivo.

A study to assess the effects of a new detergent-free, olive oil formulation dentifrice in vitro and in vivo

OBJECTIVE

To determine the effects of a detergent-free dentifrice containing olive oil using in vitro microbiological tests and an in vivo plaque re-growth model.

METHOD

A total of 20 subjects took part in a double blind, single-centre, crossover study in which slurry rinses were the only form of plaque control over a 5-day period. Following a washout and prophylaxis the subjects used 2x daily rinses in the absence of all other plaque control methods. Subjects returned to the clinic on the afternoon of day 5 when plaque was disclosed and assessed by plaque index and area. A further 9-day washout was carried out and the rinse period repeated to ensure that each subject had used both experimental and control slurries. In vitro microbiological experiments were conducted to examine the effects of olive oil alone and in the new dentifrice on bacterial growth and adhesion.

RESULTS

20 subjects completed the trial. The olive oil product showed a significant inhibition of plaque re-growth (17.2%) compared with a fluoride-matched control using the Turesky index (p<0.0001) and also using the planimetric technique (22.0%) (p<0.0001). Significant decreases in bacterial growth and adhesion (measured as total viable count) were detected in the presence of olive oil and the new dentifrice.

CONCLUSION

The results suggest that the experimental olive oil containing paste has potential value in the inhibition of plaque.

The in vitro detection of early enamel de- and re-mineralization adjacent to bonded orthodontic cleats using quantitative light-induced fluorescence

The purpose of this study was to determine whether quantitative light-induced fluorescence (QLF) could detect very early demineralization and remineralization longitudinally adjacent to orthodontic components in an in vitro model. Extracted human premolars (n = 13) were sectioned sagittally to produce two equal halves and an orthodontic cleat was bonded to the buccal surface of each tooth. Transparent nail varnish was placed over the remaining surface, leaving exposed enamel windows adjacent to the cleat on the coronal and gingival aspects. Each half-tooth was placed into the lid of an Eppendorf tube and randomly assigned to either control (distilled water) or experimental (lactic acid demineralizing buffer, pH 4.5) regimes. Digital photographs and QLF baseline images were taken. The tubes were mounted into a rotating holder and left for 24 hours. QLF and digital photographs were taken, the solutions refreshed and the teeth returned. This was continued every 48 hours for 288 hours. At this time the lactic acid buffer was replaced with a remineralizing solution (artificial saliva, fluoride, calcium) and the experiment continued with weekly examinations. QLF images were analysed and deltaQ at the 5 per cent threshold recorded. Analysis of the QLF images showed that both demineralization and remineralization were identified and monitored. Statistical differences between each of the timed examinations were found (P < 0.05). Analysis of the photographs demonstrated that QLF detected subclinical lesions. This initial pilot study has demonstrated the potential for QLF to longitudinally monitor de- and re-mineralization of enamel adjacent to orthodontic cleats in vitro.

Influence of abrasion in clinical manifestation of human dental erosion

The influence of abrasion from oral soft tissues on softened enamel lesion remineralization and erosion development was investigated. Using orange juice, softened enamel lesions were produced on 20 human premolars assigned randomly to 10 volunteers. Sections used as control and two test slabs were cut from each tooth. One of the two slabs from each tooth had an appliance built on it, which protected the lesion from abrasion. The two slabs (with/without appliance) were bonded to the palatal surfaces of upper right and left lateral incisor teeth of the participants who chewed sugar-free gum four times daily. After 28-day intra-oral exposure, mineral loss (Delta Z) and lesion depth (ld) in both control and test samples were quantified using transverse microradiography, and the data was analysed by paired t-test. Delta Z was significantly lower in lesions with appliance (protected), but higher in lesions without appliance (unprotected) when compared with control (unexposed). Similar pattern was observed with lesion depth. In unprotected slabs the lesions were abraded resulting in eroded enamel lesions. It was concluded that erosion observed clinically is the combined effect of demineralization of the tooth surface by an erosive agent and abrasion of the demineralized surface by surrounding oral soft tissues and through food mastication. Abrasion from oral soft tissues can contribute to site-specificity of dental erosion.

The intra- and inter-examiner reliability of quantitative light-induced fluorescence (QLF) analyses

OBJECTIVE

To assess the reliability of the analysis stage of quantitative light-induced fluorescence (QLF). The QLF analysis involves subjective input from the user and this study examines the influence of this on the reproducibility of the QLF data.

METHOD

QLF images were taken of 20 human molar teeth that had been previously subjected to a demineralizing solution (phosphoric acid 37%) to create artificial white spot lesions on their buccal surfaces. Following examination of the images, 16 were chosen to represent a range of lesion size and severity. Three copies were made of the images and each was allocated a different filename. 10 examiners in three centres were asked to analyse each of the 16 images on three occasions, with at least seven days between each attempt. Simple instructions describing the analysis procedure were supplied and examiners were asked to adhere to these directions. Examiners were asked to rate each of the 16 teeth on their first attempt both quantitatively (5 point scale) and qualitatively in terms of difficulty of analysis. Data reported were the delta Q at 5% threshold for each tooth on each of three attempts.

RESULTS

Using ANOVA and paired t-tests to detect statistical differences, the three attempts of each examiner were used to determine intra-examiner reliability. Only one examiner (a novice at the technique) demonstrated differences between all three attempts and two demonstrated difference between one attempt. When the mean scores were compared to determine the inter-examiner reliability, only one examiner's results were statistically different when compared with two others.

CONCLUSION

This study has demonstrated that the analysis stage of QLF is reliable between examiners and within multiple attempts by the same examiner, when analysing in vitro lesions. Novices at the technique should be trained before analysing experimental data.

Detection of in vitro demineralization of primary teeth using quantitative light-induced fluorescence (QLF)

INTRODUCTION

With the advent of remineralizing therapies and the new, conservative approach to restoration placement, interest in detecting and monitoring subclinical, precavitated lesions has increased. The increased understanding of clinicians about the processes of primary and secondary prevention and the detection of lesions to which these therapies may be applied, is one of the current goals in caries management. Quantitative light-induced fluorescence (QLF) is a new method for the detection of very early caries.

OBJECTIVES

To determine the ability of QLF to detect and longitudinally monitor in vitro enamel demineralization. To present the device to the paediatric community and present future in vivo uses of the device.

DESIGN

An in vitro study with combined in vivo pilot.

SAMPLE AND METHODS

Twelve previously extracted, caries free, primary molars were selected and prepared. Two teeth were randomly selected as controls. Teeth were prepared by gentle pumicing and coating in an acid-resistant nail-varnish, except for an exposed window on the buccal surface. QLF baseline images were taken and the teeth then exposed to a demineralizing solution. Teeth were removed at regular intervals (24, 48, 72, 96, 120, and 144 h), air-dried and QLF images taken. QLF images were analysed by a single, blinded examiner (to control, to length of exposure). Mineral loss, as measured by DeltaQ, was recorded.

RESULTS

Demineralization was noted in all experimental teeth by 48 h, and within 24 h in six teeth. The QLF successfully monitored the increase in mineral loss over time (P < 0.05). The detected lesions were not visible clinically until 144 h and then in only the most severe lesions. No demineralization was detected by QLF in control teeth. The device was user- and patient-friendly in vivo, detecting subclinical lesions.

CONCLUSION

Detection of very early mineral loss and subsequent monitoring of this loss is possible in primary teeth using QLF. The device is well suited to use in paediatric dentistry and offers applications for both clinicians and researchers. The determination of the status of carious lesions (active/inactive) will be possible with readings taken at recall appointments.

The effect of ambient light on QLF analyses

The use of optical methods in the diagnosis of early caries is developing rapidly. The introduction of the quantitative light-induced fluorescence (QLF) device has promised the use of a quantifiable technique in vivo. This study describes the effect that ambient light has upon the reliability of QLF analyses. Using human teeth and simulated lesions the study examined the effect of 15 different light levels on three severities of carious lesions. The study found that a light level of 88 lux could be employed in areas where QLF is to be used without significantly affecting the reported value, DeltaQ. This study impacts upon the health and safety issues surrounding QLF usage as well as ethical issues relating to working in dark environments.

The use of QLF to quantify in vitro whitening in a product testing model

BACKGROUND

Professional and consumer interest in whitening products continues to increase against a background of both increased oral health awareness and demand for cosmetic procedures. In the current legal climate, few dentists are providing 'in-office' whitening treatments, and thus many patients turn to home-use products. The most common of these are the whitening toothpastes. Researchers are keen to quantify the effectiveness of such products through clinically relevant trials.

AIM

Previous studies examining whitening products have employed a variety of stained substrates to monitor stain removal. This study aimed to quantify the removal of stain from human enamel using a new device, quantitative light-induced fluorescence (QLF). The experimental design follows that of a product-testing model.

MATERIALS AND METHODS

A total of 11 previously extracted molar teeth were coated with transparent nail varnish leaving an exposed window of enamel. The sound, exposed enamel was subject to a staining regime of human saliva, chlorhexidine and tea. Each of the eleven teeth was subjected to serial exposures of a positive control (Bocasan), a negative control (water) and a test product (Yotuel toothpaste). Following each two-minute exposure QLF images of the teeth were taken (a total of 5 applications). Following completion of one test solution, the teeth were cleaned, re-stained and the procedure repeated with the next solution. QLF images were stored on a PC and analysed by a blinded single examiner. The deltaQ value at 5% threshold was reported. ANOVA and paired t-tests were used to analyse the data.

RESULTS

The study confirmed the ability of QLF to longitudinally quantify stain reduction from human enamel. The reliability of the technique in relation to positive and negative test controls was proven. The positive control had a significantly (alpha = 0.05) higher stain removal efficacy than water (p = 0.023) and Yotuel (p = 0.046). Yotuel was more effective than water (p = 0.023).

CONCLUSION

The research community, the practicing clinician and the consumer all require sound product evaluation data. The use of human enamel specimens may offer more relevant clinical data. QLF has been designed as an in vivo device. Further development of the technique should permit in vivo clinical whitening trials.

Efficacy of sterilisation methods and their effect on enamel demineralisation

The aim of this project was to determine the effectiveness of sterilisation methods for dental enamel for use in intra-oral cariogenicity tests, and their possible effect on the degree of demineralisation of enamel. Bovine incisors were cut vertically into five portions and each assigned to one of five groups. Group 1 was used as a control while the other four groups were subjected, respectively, to gamma irradiation ( congruent with 25kGy), steam autoclaving (121 degrees C for 15 min), sodium hypochlorite (12% w/v for 24h) and povidone-iodine (7.5% w/v for 24h). Total viable counts of microorganisms remaining following sterilisation of the specimens were performed following incubation of the specimens for 24h at 37 degrees C. Caries-like lesions were produced in each specimen using an acidic buffer solution (pH4.5). Sections were cut from each specimen, ground to 80-microgram thickness, and microradiographed. Mineral loss and lesion depth were quantified using transverse microradiography. Statistical analysis was by ANOVA. Dunnett's and Tukey's tests. Microbial growth (Staphylococcus aureus and bacilli) was observed only in control specimens in both brain heart infusion broth and on blood agar plates. The sterilisation methods affected the enamel surface as follows: gamma irradiation (cream discolouration), NaOCl (bleaching), and povidone-iodine (white spot-like lesion). Compared with the control, there was no significant difference in mineral loss and lesion depth with any of the groups, but the numerical values of mineral loss and lesion depth in groups can be ranked as follows: gamma irradiation <povidone-iodine <control <autoclave <NaOCl. In conclusion, the four sterilisation methods were all effective to sterilise enamel, but gamma irradiation proved the most acceptable method for enamel to be used in cariogenicity tests having the least adverse effect.

Use of transverse microradiography to quantify mineral loss by erosion in bovine enamel

The aim of the present study was to develop transverse microradiography (TMR) in order to quantitatively assess the influence of artificial saliva and orange juice on the erosion of bovine enamel. Bovine incisors were sectioned sagittally into two equal halves. Each half was coated with acid-resistant nail varnish except for a rectangular enamel window on the labial surface of the tooth. While both halves of each tooth were immersed in pure orange juice 6 times daily for a period of 5 min at each occasion making a total of 30 min per day, one half was stored in artificial saliva and the other half in deionized distilled water between exposures to orange juice and for the remaining 12 h overnight, for 24 days making a total of 12 h of exposure to orange juice. Sections bearing intact and eroded enamel surfaces were cut from each specimen and ground to 80 microm thickness, and TMR of the sections was made. Mineral loss was quantified from the microradiographs using two-step image analysis. Mineral loss was significantly greater in those specimens cycled in orange juice and de-ionized distilled water. TMR was used successfully to quantify the mineral loss by erosion in vitro, and it is envisaged that it will be useful for specimens used in intra-oral appliances during in situ trials. Artificial saliva saturated with respect to calcium and phosphate salts can possibly remineralize an erosive lesion and may reduce the degree of erosion.

Thickness of acquired salivary pellicle as a determinant of the sites of dental erosion

Dental erosion shows a typical distribution pattern within the dental arches. Tooth protection from erosion by salivary pellicle has been shown in vitro, but the hypothesis that pellicle may differ quantitatively at sites of erosion has not been investigated. This study aimed to determine the thickness of acquired salivary pellicle within the dental arches, investigate the possible relationship of this thickness to the distribution and severity of erosion within the arches, and confirm the protective effect of pellicle against dental erosion. Eight enamel blocks were produced from each of 5 bovine incisors assigned to five volunteers. Each block was further cut into 2 slabs, producing control and experimental slabs. Pellicle developed on experimental slabs located on 8 intra-oral sites after 1 hr of exposure was stained by "sheep anti-human IgGAM-FITC". Slabs were then visualized, and pellicle thickness measured, by confocal laser scanning microscopy. Eroded enamel lesions were produced in experimental and control slabs by means of pure orange juice. The degree of erosion was quantified by transverse microradiography. Pellicle thickness varied significantly within the dental arches and among individuals. An inverse relationship (r = -0.96, p<0.001) was observed between the degree of erosion and pellicle thickness. Significant differences in erosion were observed between slabs with and those without pellicle. This study has shown that the thickness of acquired salivary pellicle varies within the dental arches, which may be responsible for the site-specificity of dental erosion, and that pellicle does protect the teeth from erosion.

The use of gamma irradiation for the sterilization of enamel for intra-oral cariogenicity tests

The dose of gamma irradiation sufficient to sterilize enamel samples to be used for intra-oral cariogenicity tests (ICT) without alteration to the structure or solubility of the enamel was determined. Each bovine incisor used was cut vertically into eight portions and each portion assigned to one of eight groups. Group 1 was used as control while other groups were subjected to respective doses of gamma irradiation from a cobalt-60 source. Following sterilization, both control and experimental groups were incubated in nutrient broth for 7 days at 37 degrees C under aerobic and anaerobic conditions. Caries-like lesions were subsequently produced in each specimen using acidic buffer solution, and mineral loss quantified using transverse microradiography. Data were analysed statistically. There was no significant difference in mineral loss between the control and experimental groups, but the numerical value of mineral loss was lower in groups irradiated with> 4080 Gy, in addition to full sterilization and enamel discoloration to cream colour observed in these groups. Microbial growth was observed in the control group and in groups irradiated with <4080 Gy but no discoloration. With 4080 Gy full sterilization without discoloration was observed. It was concluded that 4080 Gy of gamma irradiation is optimal for sterilization of enamel samples for use in ICT.

Factors influencing the development of dental erosion in vitro: enamel type, temperature and exposure time

The influence of temperature, duration of exposure, and enamel type on the development and progression of dental erosion has been determined. Three experiments were devised as follows. Eroded lesions were produced on enamel samples with orange juice: (1) at different temperatures; (2) for different lengths of time; and (3) on bovine permanent, human deciduous and human permanent enamel. Lesion parameters (mineral loss and lesion depth) were quantified using transverse microradiography. Both lesion parameters were significantly lower at 4 degrees C when compared with 20 degrees C and 37 degrees C, and at 20 degrees C when compared with 37 degrees C. Lesion parameters increased significantly as the length of exposure increased, and were positively correlated (r=0.98, P<0.05) to the exposure time. Both parameters were significantly greater in bovine enamel than human permanent and deciduous enamel, and in human deciduous than permanent enamel. Lesion progression, as measured by mineral loss, was in the ratio 2.0:1.5:1.0 for bovine:human deciduous:human permanent, and by lesion depth, 1.7:1. 3:1.0. In conclusion, the erosiveness of orange juice was less pronounced at a lower temperature, and increased with an increased exposure time. Erosion progressed twice as fast in bovine permanent than in human permanent enamel, and 1.5 times more rapidly in human deciduous than in permanent enamel.

Caries inhibiting and remineralizing effect of xylitol in vitro

This study aimed to determine the effect of xylitol on the development and remineralization of caries in vitro, and to compare this effect with that of fluoride alone and in combination. Two experiments were devised. In experiment 1, bovine incisors were each sectioned into 4 portions which were randomly assigned to 4 demineralizing agents: A) acidic buffer (x), B) x + 0.5 ppm fluoride, C) x + 20% xylitol, and D) x + 20% xylitol + 0.5 ppm fluoride. Caries-like lesions were produced in specimens. In experiment 2, carious lesions were produced in teeth. Five lesion-bearing slabs were cut from each tooth. While one was reserved as control (UN), others were randomly assigned to 4 remineralizing agents: 1) artificial saliva (y), 2) y + 0.05 ppm fluoride, (3) y + 20% xylitol, and 4) y + 20% xylitol + 0.05 ppm fluoride. Mineral loss (delta Z) and lesion depth (ld) were quantified after 4-week remineralization. In experiment 1, numerical values of delta Z and ld observed can be ranked as A > C > B > D. These differences were significant only in B and D when compared with A for delta Z, but not between any group for ld. In experiment 2, the numerical values of delta Z and ld for control UN (unremineralized) and remineralized groups (1-4) ranked as UN > 3 > 4 > 1 > 2. Compared with UN, this difference was significant in all groups with ld, but not in any group with delta Z. We concluded that tolerable levels of xylitol alone may not show a significant caries inhibiting and remineralizing effect, but may act as a caries inhibitor additively with fluoride.

Effect of sterilisation methods on the structural integrity of artificial enamel caries for intra-oral cariogenicity tests

Enamel blocks bearing artificial caries are used in intra-oral appliances for cariogenicity tests. These blocks are often sterilised to prevent the possibility of cross-infection via this route. This study therefore aimed to determine the effect of sterilisation methods on the structural integrity of artificial enamel caries used for intra-oral cariogenicity tests. Four experimental groups were devised. Ten bovine incisors were used in each group. Artificial caries was produced in each tooth which was subsequently cut into two halves. One half of each tooth was reserved as control while the other was sterilised. The four groups were subjected to respective sterilisation methods: gamma irradiation (approximately equal to 25 KGy), steam autoclaving (121 degrees C for 15 min), sodium hypochlorite (12% w/v for 24 h) and povidone-iodine (7.5% w/v for 24 h). The control and sterilised specimens in each group were examined for microbial growth after incubation in nutrient broth for up to 7 days at 37 degrees C under aerobic and anaerobic conditions. Mineral loss and lesion depth were quantified from microradiographs of sections from control and sterilised specimens using transverse microradiography. Data were analysed statistically by paired Student's t-test. Microbial growth was observed only in control specimens. Gamma irradiation and NaOCL caused cream discolouration and bleaching of the enamel surface, respectively. Autoclaving, sodium hypochlorite and povidone-iodine resulted in further demineralisation of the lesions. The four sterilisation methods were all effective sterilants for artificial caries. However, gamma irradiation appears the most acceptable method considering the more adverse effects of the other methods with regards to cariogenicity tests.

Techniques for the production of dental eroded lesions in vitro

This project firstly demonstrated an in vitro technique for the production of eroded lesions which simulates the in vivo conditions, and secondly evaluated the influence of salivary parameters on the degree of erosion in vitro. Teeth were sectioned sagitally into three equal portions. The portions were randomly assigned to one of three experimental groups (A, B and C). Lesions were produced by cycling the teeth between orange juice and either artificial saliva (A) or water (B) for a total period of 12 h, or by a single 12 h immersion in orange juice (C). Sections were prepared from each specimen and mineral loss was quantified using transverse microradiography. Mineral loss was significantly lower in group A compared with B and C. Greatest mineral loss was observed in B though not significant when compared with C. The present technique mimics the in vivo conditions with the saliva reducing the degree of erosion and possibly remineralizing the lesions.

In situ de- and remineralisation of enamel in response to sucrose chewing gum with fluoride or non-fluoride dentifrices

OBJECTIVES

Enhancement of the remineralisation of artificial enamel lesions has been observed in an intraoral model whether subjects chewed gum sweetened with a non-cariogenic sweetener such as sorbitol [1-3] or sucrose [4] after meals or snacks, and with use of a conventional (1500 ppm F) fluoride dentifrice. Since most of the clinical surveys which have shown the potential cariogenicity of sucrose chewing gum [5] were conducted before use of fluoridated dentifrices became widespread, the effect of fluoride dentifrice on de- and remineralisation of artificial lesions in enamel in response to chewing sucrose-sweetened gum has been examined with the aim of attempting to resolve this apparent discrepancy.

METHODS

Subjects wore an intraoral device bearing an enamel lesion and chewed one piece of sucrose gum for 20 min after each of three meals and two snacks daily for two 3-week periods, during which they used a dentifrice containing either 0 or 1500 ppm F in a double-blind, cross-over design. Measurement of the mineral content of the lesions was determined by microradiography or polarised light microscopy.

RESULTS

It was found that remineralisation tended to occur with 1500 ppm F dentifrice, but demineralisation with non-F dentifrice; the difference in enamel mineral content between the two periods was significant (P < 0.05).

CONCLUSIONS

The results indicate that the potential cariogenicity of sucrose-containing chewing gum may indeed be negated by the use of a conventional fluoride dentifrice.

Morphometric assessment of enamel demineralisation from photographs

OBJECTIVES

To investigate the validity and reproducibility of a method of morphometric assessment of enamel demineralisation.

METHODS

An in vitro investigation was carried out on 22 human teeth. One investigator coated the crowns of the teeth with an acid-resistant varnish, leaving a small window on the buccal surface. This was incrementally occluded by varnish over a 14-day period, during which the teeth were placed in a demineralising gel at pH 4.5. After varnish removal, a second investigator blindly quantitated the demineralised area by three methods of examination; direct visual, microscopic and from photographs. The microscopic and photographic measurements were carried out using a morphometric assessment with a 121-dot array. Photographs and assessments were repeated after 1 week. The readings were analysed using the kappa statistic, the limits of agreement and the coefficient of repeatability.

RESULTS

Photographic assessments demonstrated excellent agreement for grid positioning (kappa > 0.81) and substantial agreement for reading reproducibility (kappa = 0.61-0.80). The coefficients of repeatability were found to be the same for repeat readings of the same slide and the repeated slides (5.0 mm2). They were higher for the microscopic technique (6.8 mm2) and for the direct visual technique (7.8 mm2). The limits of agreement are presented graphically.

CONCLUSIONS

The photographic technique used was a reproducible method of measuring artificial enamel demineralisation. Measurement from photographs was more reproducible than direct measurement with the naked eye. Subjectiveness of the index leads to most variation and more objective means of assessing enamel demineralisation need to be found.

Factors affecting the development of carious lesions in bovine teeth in vitro

This study aimed to determine the effect of temperature, duration of exposure, position on enamel surface, and type of demineralization solution on the production of caries-like lesions in bovine enamel in vitro, and to establish the conditions for the formation of artificial caries in bovine enamel. Caries-like lesions were produced in incisal, middle and cervical sites on enamel samples, with either an acidified hydroxyethylcellulose gel system or a partially saturated acidic buffer solution at either 20 degrees C or 37 degrees C for 3, 4, or 5 days. Lesion variables (mineral loss/lesion depth) were quantified. Regular subsurface lesions were produced in all specimens in acidic buffer solution within 3 days at either temperature. In gel, caries-like lesions were produced in 62% of the specimens at 37 degrees C and in 49% at 20 degrees C, while the remaining specimens were either eroded or softened. Mineral loss and lesion depth were significantly greater with buffer than with gel, and with increased length of exposure in either solution. There were no significant differences in either variable with position or temperature in either solutions, though numerically both variables were greater at the cervical site, and at 37 degrees C in either solution. It was concluded that caries-like lesions can be consistently produced in bovine enamel with a partially saturated acidic buffer solution at 20 degrees C or 37 degrees C within 3 days.

The influence of xylitol and fluoride on dental erosion in vitro

The aim was to determine the effect of xylitol, fluoride and xylitol/fluoride combined on the erosion of dental enamel by pure orange juice in vitro. Freshly extracted bovine incisors were sectioned vertically into four equal portions. Each portion was then coated with an acid-resistant nail varnish except for an enamel window on the labial surface of the tooth. These were then divided into four groups with each group containing one portion of each tooth selected randomly. Four erosive agents were prepared as follows: (A) pure orange juice only; pure orange juice plus either (B) xylitol (25% w/v) or (C) fluoride (0.5 parts/10(6)) or D) xylitol/fluoride (25% and 0.5 parts/10(6) respectively). Each group was assigned to one of the erosive agents and immersed six times daily for a period of 5 min on each occasion and stored in artificial saliva between exposures and for 12 hr overnight, for 24 days making a total of 12 hr of exposure to the assigned erosive agent. Sections were cut from each enamel specimen ground to a thickness of 80 microns and microradiographed. Mineral loss was quantified by a two-step image analysis. Mineral loss was significantly lower (p < 0.05) in group D (xylitol/fluoride) only when compared with group A (pure orange juice only). The numerical values of mineral loss could be ranked as follows: group D < group C < group B < group A. It was concluded that xylitol and fluoride have an additive effect in the reduction of dental erosion by pure orange juice in vitro.

Sugar substitutes, chewing gum and dental caries--a review

The prevalent use of chewing gum has prompted interest in its dental effects. Important defining aspects are the ability to use sugar substitutes in gum manufacture and the prolonged stimulation of a protective flow of saliva. The main sugar substitutes used are sorbitol and xylitol. Because it is not fermented by oral bacteria, xylitol is considered to be non-cariogenic, and while sorbitol in solution can be fermented slowly by mutants streptococci, chewing sorbitol-sweetened gum does not cause a fall in plaque pH. Effects of chewing sugar-free gum on the ability of plaque to form acid from sucrose are equivocal, although the tendency is for the plaque acidogenicity to be reduced with the use of xylitol gum for 2-3 weeks, due to its inhibitory effects on mutants streptococci. Gum-chewing also stimulates a protective salivary flow when used after an acidogenic stimulus, and may enhance salivary function, especially in subjects with low flow rates. Sorbitol and xylitol gums have similar beneficial effects in promoting enamel remineralisation in short-term in-situ experiments. Clinical trials indicate that xylitol gum has a useful anticaries role, superior to the effects of sorbitol gum. In conclusion, both sorbitol and xylitol chewing gums are non-cariogenic in contrast to sugared gum, and exhibit beneficial anticaries properties through salivary stimulation. In addition, xylitol's antibacterial properties seem likely to lead to caries reductions superior to the more modest reductions with sorbitol gum.

Visualization of root caries lesions by means of a diazonium dye

A diazonium dye was used to visualize caries lesions in root tissue. Root caries lesions were created in vitro according to a variety of protocols based on methylcellulose gel (6% w/v) and/or lactic acid buffer (0.05 M, pH 4.5). Teeth containing lesions were soaked overnight in an alkaline solution of 2% (w/v) 2-naphthol or resorcinol, rinsed with distilled water, and immersed in a diazonium solution (prepared by titration of aniline with sodium nitrite in 1 M HCl at 5 degrees C) for up to 10 min, prior to being thoroughly rinsed with distilled water. The area of the caries lesion on the anatomical surface was clearly marked with a red/orange color following 5 minutes' incubation in the diazonium solution. The diazonium complex formed with 2-naphthol was found to be more resistant to leaching during rinsing and sectioning than that formed with resorcinol. Microscopic examination of sections taken in the apicalcoronal plane showed that the depth of area of the lesion was also marked by the red/orange coloration. Chemical changes in root mineral monitored during lesion formation showed some degree of correlation between lesion area and mineral dissolution. Visualization of coronal caries by this technique is currently under investigation. The visualization technique provides a simple means of determining the extent and severity of root caries lesions and may be a useful first step in their classification.

The establishment of a xerostomia clinic: a prospective study

The study investigated the aetiological factors and management of patients who have xerostomia. The subjects were 100 consecutive patients referred to the Oral Medicine Unit for investigation of oral dryness. A detailed case history was recorded and patients underwent a systematic examination together with sialometry, haematological, biochemical and immunological investigations. Suspected cases of Sjögren's syndrome (SS) were referred for assessment by a rheumatologist and ophthalmologist. Objective evidence of salivary gland hypofunction was found in 39 patients. A definite diagnosis of primary and secondary SS was made in 24 and 15 patients respectively, a further five cases had possible primary SS. Other causes of xerostomia were: undiagnosed diabetes (3); drug-induced (11); therapeutic radiation (3); alcohol-related (3); psychogenic (15) and idiopathic (21). Patients complaining of a dry mouth should be questioned about non-oral symptoms. In total, 40% of patients attending the dry mouth clinic had a diagnosis of SS.

Signs and symptoms in patients with salivary gland hypofunction

Salivary gland hypofunction can have a devastating effect on oral health and may be an indicator of systemic disease such as Sjögren's syndrome. This prospective study investigates the oral and non-oral signs and symptoms in 120 patients with objective evidence of salivary gland hypofunction (ie, an unstimulated whole salivary flow of < 0.2 ml/min). Patients were questioned about symptoms associated with decreased oral function; non-oral symptoms were also noted. The underlying cause of salivary gland hypofunction was established on the basis of clinical and laboratory findings and further investigations. Eighty-five per cent of patients reported symptoms of decreased oral function in addition to oral dryness. Non-oral signs and symptoms were reported by 106 patients. Fifty-three per cent of patients were diagnosed as having Sjögren's syndrome. The prevalence of the following non-oral signs and symptoms were significantly higher in patients with Sjögren's syndrome, than in those without; a history of dry/irritated eyes, salivary gland swelling, dry skin and reduced lacrimal flow. Salivary gland hypofunction is associated with a wide range of oral and non-oral signs and symptoms. Several of these are of potential value as triggers for the clinician to identify patients with Sjögren's syndrome, and should serve to prompt referral for specialist investigation.

Acid anion profiles in dental plaque following consumption of cereal-based foods and fruits

The aim of this study was to investigate the acid anions produced in plaque after chewing various cereal-based foods and fruits for one minute. Test foods were oranges, apples, bananas, Cornflakes, Branflakes, Weetabix, Alpen, white bread, wholemeal bread, rice and spaghetti, plus positive and negative controls of 10% sucrose and 10% sorbitol. 4 males and 3 females, aged 22-37 years, participated in the study .7 min from the start of chewing, 48-h plaque was collected from all accessible smooth surfaces, with no attempt to collect interproximal plaque, and centrifuged. Plaque fluid was withdrawn and analyzed by isotachophoresis for formate, succinate, lactate, acetate and propionate. At rest, acetate was the major anion present in plaque fluid, whereas following carbohydrate consumption, highest levels of lactate were detected followed by acetate. The amount of lactate only, detected in plaque fluid, was significantly correlated to the carbohydrate present in the food. It was concluded that important information regarding the acidogenicity of test foods is gained by studying the acid anion profile of plaque fluid.

Acidogenic potential and total salivary carbohydrate content of expectorants following the consumption of some cereal-based foods and fruits

The acidogenic potential of a group of popular cereal-based foods and fruits and total carbohydrate content of salivary expectorants following their consumption were assessed using an indwelling electrode with telemetry and the anthrone method. Paired t tests indicated that sorbitol did not cause the plaque pH to fall as low as any of the test foods (p <0.05) but there was no significant difference between sucrose and the test foods. Only the fruits produced less acid than sucrose. The breakfast cereals tended to yield the highest levels of total carbohydrate in the salivary expectorants although a greater percentage of original carbohydrate was retained after rice and bread. These results suggest the important effect of carbohydrate retention on plaque pH response.

Salivary gland hypofunction in elderly patients attending a xerostomia clinic

OBJECTIVES

To investigate the aetiological factors and the prevalence of salivary gland hypofunction (SGH) in patients complaining of xerostomia.

DESIGN

Prospective, clinical study.

SETTING

Xerostomia clinic in the Department of Oral Medicine at Liverpool University Dental Hospital.

SUBJECTS

100 consecutive patients, aged 60 years or older, referred for investigation of xerostomia.

INTERVENTIONS

Patients were asked specific questions concerning their complaint of oral dryness and associated orofacial symptoms. A detailed medical history was recorded and patients underwent a systematic examination of the head, neck and oral structures. All patients underwent haematological, biochemical, immunological investigations, urinalysis and sialometry. Further investigations and referrals to other specialists were undertaken when appropriate.

MAIN OUTCOME MEASURES

The causes of xerostomia were established on the basis of clinical and laboratory findings and SGH was defined as an unstimulated whole salivary flow rate of < 0.2ml/min,

RESULTS

The causes of xerostomia were identified as: Sjögren's Syndrome (40), iatrogenic (22), psychogenic (14), idiopathic (19), diabetes (1), candidosis (3) and alcohol (1). Sixty five percent of the patients studied had SGH.

CONCLUSIONS

This study has shown that 65% of patients whose presenting complaint was xerostomia had objective evidence of SGH. Several aetiological factors were identified, the most common of which was Sjögren's Syndrome. The possibility of associated systemic diseases should be considered when establishing the aetiology of SGH.

Role of saliva in caries models

The crucial role played by the actions of saliva in controlling the equilibrium between de- and remineralization in a cariogenic environment is demonstrated by the effects on caries incidence of salivary dysfunction and by the distribution of sites of caries predilection to those were salivary effects are restricted. However, of the several properties of saliva which may confer protective effects, it is not certain which are most important. A distinction can be made between static protective effects, which act continuously, and dynamic effects, which act during the time-course of the Stephan curve. Evidence implicates salivary buffering and sugar clearance as important dynamic effects of saliva to prevent demineralization; of these, the buffering of plaque acids may predominate. Enhanced remineralization of white spot lesions may also be regarded as dynamic protective effects of saliva. Fluoride in saliva (from dentifrices, ingesta, etc.) may promote remineralization and (especially fluoride in plaque) inhibit demineralization. The design of experiments using caries models must take into account the static and dynamic effects of saliva. Some models admit a full expression of these effects, while others may exclude them, restricting the range of investigations possible. The possibility is raised that protective effects of saliva and therapeutic agents may act cooperatively.

Effects of lactate dehydrogenase and nicotinamide adenine dinucleotide on human dental plaque pH and acid anion concentrations

The effect of sucrose rinses supplemented with L-LDH and NAD was investigated. When LDH or NAD were added to the sucrose rinse, the pH fall was less marked than with rinsing with sucrose alone. Significant differences (p < 0.05) in mean minimum pH and cH areas were observed when sucrose rinses were supplemented with LDH, NAD or with a combination of LDH and NAD, when compared with sucrose alone. Plaque fluid concentrations of lactate and acetate significantly decreased with all rinses when compared with sucrose alone. Phosphate levels also decreased, although not significantly, when NAD was the sole supplement. No significant decreases were observed in succinate, formate or propionate concentrations. The results confirm the beneficial effect of LDH in reducing the accumulation of lactate in plaque following a sucrose rinse. The inclusion of NAD in the rinse demonstrated the role of extracellular hydrogen acceptors in the reaction. Further work is required to identify endogenous hydrogen receptors and to clarify the fate of pyruvate resulting from the oxidation of lactate before the potential role of LDH as a cariostatic agent can be fully understood.

Interactions of fluoride and non-fluoride agents with the caries process

Fundamental to the caries process and its inhibition is an understanding of the composition and structural relationships of dental mineral. These have received greater study in recent years, leading to a better understanding of the processes involved. Fluoride has been the most successful of the anti-caries agents to date, and many studies have concentrated on this ion. The anti-caries action of fluoride has been only partially explained by the early finding that fluoride-treated mineral was less soluble, and this criterion is now less widely accepted. The dissolutive process of caries is inhibited by fluoride, monofluorophosphate, trimetaphosphate, and zinc. However, only the first three of these show anti-caries activity. The presence of fluoride during in vivo and in vitro caries is conducive to the formation of an apparently intact surface zone. Current evidence is that this zone reforms during the caries process, thus acquiring fluoride and having larger crystallites compared with sound enamel. Trimetaphosphate also favors the formation of a surface zone. There is a clear beneficial involvement of fluoride, even at low levels, in the process of lesion remineralization. It is highly probable that this process results from re-growth of residual enamel crystallites rather than de novo precipitation of calcium phosphates. Levels of fluoride found in saliva can interact with dental mineral. Although zinc has been shown to adsorb upon apatite mineral and to restrict subsequent crystal growth, it does not appear to affect the action of fluoride, including remineralization, adversely. This may be due to the fact that the uptake of zinc is reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Saliva stimulation and caries prevention

The protective role of saliva is demonstrated by the rampant caries seen in human subjects with marked salivary hypofunction, and in desalivated animals. In normal cases, however, the relationship between saliva flow and coronal or root caries experience is doubtful, and to examine the concept that stimulation of saliva might have protective effects against caries, one must look beyond a simple correlation between caries and flow rate. Protective properties of saliva which increase on stimulation include salivary clearance, buffering power, and degree of saturation with respect to tooth mineral. These benefits are maximized when saliva is stimulated after the consumption of fermentable carbohydrates, by reducing the fall in plaque pH leading to demineralization and by increasing the potential for remineralization. Plaque acid production is neutralized, and experimental lesions in enamel are remineralized, when gum is chewed to stimulate saliva after a carbohydrate intake. The pH-raising effects are more easily explained by the buffering action of the stimulated saliva than by clearance of carbohydrates. The remineralization action depends upon the presence of fluoride. These findings suggest that the protective actions of saliva can be mobilized by appropriate salivary stimulation, and that in addition to established procedures such as tooth cleaning and fluoride regimens, eating patterns which lead to saliva stimulation to increase the potential for saliva protection might be included in recommendations for caries prevention. Confirmation of this concept in clinical tests is required.

pH changes in plaque after eating snacks and meals, and their modification by chewing sugared- or sugar-free gum

Previous studies have suggested that if either sugar-free or sucrose-containing chewing gum is chewed after acidogenic meals or snacks, the plaque pH response to the latter is reduced and the potential for remineralisation of experimental white spot caries lesions is enhanced. This study has compared the effects of both gums on plaque pH (measured by the sampling technique) in 10 subjects who chewed the gums after standard acidogenic challenges (sucrose rinse, cupcake, and fried chicken dinner). The results showed that while both gums can significantly reduce the acid response, sugar-free gum appears more effective.

Extrinsic and intrinsic sugars: a review of recent UK recommendations on diet and caries

Development of caries in man is associated with dietary sugars, but the relationship between sugar contents of individual foods and their cariogenic potential is unclear. A recent report categorized dietary sugars as intrinsic (mainly fruit and vegetable) and extrinsic (mainly added sugars, milk, and fruit juices) and concluded that consumption of extrinsic sugars (except milk) should be replaced with that of intrinsic sugars. This paper examines briefly the dental consequences of the recommendations.

Saliva: its secretion, composition and functions

The secretions of the major and minor salivary glands, together with the gingival crevicular fluid, constitute the oral fluid or whole saliva which provides the chemical milieu of the teeth and oral soft tissues. The crucial role of saliva in the maintenance of dental health is demonstrated by the morbidity associated with loss of salivary gland function. In this article, the physiology of the secretory process, the reflex control of whole saliva flow rate, the composition of the fluid, the factors affecting its composition, and the functions of the organic and inorganic components are described. Finally, the clinical aspects of salivary gland dysfunction are briefly discussed.

Intra-oral models for studying de- and remineralization in man: methodology and measurement

A wide range of different methodologies and measurement techniques has been employed in laboratories around the world for the study of de- and remineralization of enamel and dentin in intra-oral systems. These different approaches are summarized and discussed in relation to the nature of the different research questions to be studied by means of the intra-oral model.

Effects of chewing gums sweetened with sorbitol or a sorbitol/xylitol mixture on the remineralisation of human enamel lesions in situ

Intra-oral remineralisation of experimental caries-like lesions in human enamel, as determined by polarised light microscopy and quantitative microradiography, was promoted to a similar extent (% fall in delta Z, 18.6 and 19.0) by chewing a sorbitol or sorbitol/xylitol (3:1)-sweetened gum for 20 min after each of three meals and two sugary snacks daily. The results suggest that reported differences in the properties of the two sweeteners do not affect their ability to enhance remineralisation due to salivary stimulation.

Interactions between fluoride and plaque in the remineralization of enamel caries-like lesions

The effect of fluoride and plaque, separately and together on the remineralization of early artificial caries lesions was studied in a group of volunteers in a double-blind randomized study design. Artificial caries lesions produced in slabs of human enamel were mounted buccally in silver bands cemented bilaterally to the mandibular first molar teeth. Volunteers wore the bands for two 2-week periods, rinsing daily with either a placebo or a 500 ppm fluoride mouthrinse. Plaque accumulation was encouraged by placing Dacron gauze over one of each pair of slabs. Sections were cut from the lesions and analyzed by microradiography followed by microdensitometry and image analysis. Microdensitometric data revealed that non-significant increases in mineralization had occurred in all of the test groups. However, the image analysis results indicated that significant remineralization had occurred in lesions after 2 weeks on the fluoride rinse regimen, with no significant remineralization in lesions exposed to the placebo. The presence or absence of plaque over the lesions had no effect on the amount of remineralization induced on the fluoride rinse regimen.