Development of an intra-oral single-section remineralization model

Remineralization of Early Enamel Lesions with Apatite-Forming Salt

OBJECTIVES

This study sought to evaluate the remineralization of ex vivo human teeth using commercially available artificial saliva, SalivaMAX®, a supersaturated calcium phosphate rinse (SSCPR).

METHODS

early enamel lesions were artificially induced on ex vivo human teeth by chemical means. The teeth were exposed to the SSCPR for two minutes (experimental) or dH2O (control) four times per day for a total of 35 days. At time points of 0, 2.5, 21, and 35 days, micro-CT was utilized to determine the mineral density profile across the lesion and evaluate lesion depth. The relative percent remineralization was calculated from the initial lesion depth (Time 0) at each evaluation time. Student's t-test was used to compare the extent of remineralization between the SSCPR and control groups for statistical significance at each time. To evaluate the changes in percent remineralization over time, a two-way ANOVA was used.

RESULTS

At Time 0 and 2.5 days, there was no difference in the percent remineralization between the SSCPR and control groups (p > 0.05). After 21 days, the teeth exposed to the SSCPR remineralized 56.7 ± 3.7%, while the control only remineralized 10.7 ± 11.0% (p < 0.0001). At day 35, the remineralization was 73.7 ± 5.4% and 18.2 ± 10.8% (p < 0.0001) for the SSCPR and control groups, respectively.

CONCLUSIONS

A marked increase in remineralization occurred with the use of the SSCPR. Notably, the remineralization of the SSCPR occurred deep within the tooth and progressed toward the surface over time.

Effects of fluoridated milk on artificial enamel carious lesions: a pH cycling study

OBJECTIVE

To investigate the relationship between concentration of fluoride in milk and its re-mineralizing efficacy, and to test whether increasing the volume of fluoridated milk has any effect on its re-mineralizing efficacy.

METHODS

Third molars were painted leaving a 1 mm window on the buccal and/or lingual surfaces. Artificial carious lesions were induced using a de-mineralizing solution. The teeth were then sectioned longitudinally. Specimens were randomly assigned to 15 groups according to different concentrations and volume; i.e., 2.5 ppm, 5 ppm, 7.5 ppm, 10 ppm, 15 ppm, 20 ppm, and 250 ppm of fluoride with 25 ml/section and 50 ml/section. De-ionized water and plain milk were used as controls. Sections were subjected to pH cycling for 20 days. Polarized light microscopy and micro-radiography were utilized to record the lesion characteristics before and after pH cycling.

RESULTS

Mean lesion depths decreased significantly in all the fluoride groups, and increased significantly in the control groups. There were no differences in percentage of lesion depth decrease when the volume was doubled for the same fluoride concentration. There were also no statistically significant differences between percentages of decrease in lesion depth when the concentration of fluoride in milk was increased.

CONCLUSION

Fluoridated milk demonstrated a remineralization efficacy on early enamel carious lesions. A 2.5 ppm fluoride milk concentration provided similar remineralization potential to that of higher fluoride concentration in milk.

Fluoride and the caries lesion: interactions and mechanism of action

AIM

To review the mechanisms of action of fluoride (F).

METHODS

Narrative review of the literature.

FINDINGS

Fluoride can reduce tooth mineral solubility by exchanging for hydroxyl groups and reducing carbonate content. Thus its presence in solution facilitates mineral precipitation or reprecipitation by lowering solubility products of precipitating calcium phosphates. While sound enamel tends to lose fluoride with age, it accumulates at stagnation sites where caries lesions develop indicating this as a site of action. Fluoride in the lesion will encourage remineralisation [Robinson et al., 2000] such that penetration of the lesion by fluoride is pivotal. Access from plaque, however, is limited due to restricted penetration.

CONCLUSIONS

Maintaining a very thin plaque layer is thus important in delivering fluoride to the lesion.

In vitro remineralization of enamel by polymeric amorphous calcium phosphate composite: quantitative microradiographic study

OBJECTIVE

This study explores the efficacy of an experimental orthodontic amorphous calcium phosphate (ACP) composite to remineralize in vitro subsurface enamel lesions microradiographically similar to those seen in early caries.

METHODS

Lesions were artificially created in extracted human molars. Single tooth sections a minimum of 120microm thick were cut and individually placed in holders exposing only the carious enamel surface. The exposed surfaces were either left untreated (control) or coated with a 1mm thick layer of the experimental ACP composite (mass fraction 40% zirconia-hybridized ACP and 60% photo-activated resin), or a commercial fluoride-releasing orthodontic cement. The composite-coated sections were then photo-cured and microradiographic images were taken of all three groups of specimens before the treatment. Specimens were then cyclically immersed in demineralizing and remineralizing solutions for 1 month at 37 degrees C to simulate the pH changes occurring in the oral environment. Microradiographs of all specimens were taken before and after treatment.

RESULTS

Quantitative digital image analysis of matched areas from the contact microradiographs taken before and after treatment indicated higher mineral recovery with ACP composites compared to the commercial orthodontic F-releasing cement (14.4% vs. 4.3%, respectively), while the control specimens showed an average of 55.4% further demineralization.

SIGNIFICANCE

Experimental ACP composite efficiently established mineral ion transfer throughout the body of the lesions and restored the mineral lost due to acid attack. It can be considered a useful adjuvant for the control of caries in orthodontic applications.

Effect of an alcohol-free, 1% chlorhexidine gel as an adjunct to a fluoridated dentifrice using an intraoral crown model

BACKGROUND/AIMS

The use of chlorhexidine as a topically applied oral antiseptic is well documented; however, clinical studies examining the effects of chlorhexidine gel on in situ dental caries are limited. This study utilized an in situ caries model and a modified crossover design to examine whether the addition of a biweekly topical, alcohol-free, 1% chlorhexidine digluconate gel to a daily fluoridated dentifrice inhibited artificial caries in dental tissues better than the fluoridated dentifrice alone when compared to a nonfluoridated placebo dentifrice.

METHODS

Thirty patients were recruited based on their need for a mandibular, full crown. Artificial caries lesions were created in extracted human teeth and enamel and root tissue sections 100 mum in thickness were characterized using polarized light microscopy. The sections were fixed in the crown and placed on the prepared tooth. The participants were assigned a placebo toothpaste, a toothpaste with 1,100 ppm F or a 1,100 ppm F toothpaste followed by 1 ml of 1% chlorhexidine gel at day 1 and day 14 (chlorhexidine+). Patients were instructed to brush twice daily for 4 weeks. Following each round, the sections in the crown were replaced with new sections. The sections were recharacterized and the mean changes were compared using ANOVA at alpha = 0.05.

RESULTS

The chlorhexidine + Fdentifrice and the F dentifrice alone significantly reduced lesion area in enamel tissue when compared to the placebo dentifrice. Both treatments also inhibited lesion progression and initiation in root tissue better than control in this model system. Although the chlorhexidine+ group enhanced remineralization and inhibited lesion progression better than the F(-) dentifrice alone for all outcomes measured, the differences were not significant.

CONCLUSIONS

The chlorhexidine, in conjunction with a fluoride dentifrice, was no more effective than the fluoride dentifrice alone. Further study is needed before this 1% alcohol-free chlorhexidine gel should be recommended as an adjunct to a fluoride dentifrice in the treatment of dental caries.

The effects of child formula toothpastes on enamel caries using two in vitro pH-cycling models

AIMS/OBJECTIVES

To compare, using two pH-cycling models, the de/remineralisation effects of children's toothpastes on primary teeth.

DESIGN

In vitro single-section and pH-cycling models.

METHODS

Primary teeth were placed in demineralising solution for 96 hours to produce artificial carious lesions 60-100 microm deep. They were cut into 100 microm thick sections and assigned to 6 groups. Sections in Groups A and D were exposed to a non-fluoridated toothpaste, those in Groups B and E to half-pea-sized (0.16g) and those in Groups C and F to pea-sized portions (0.32g) of a 500ppm F toothpaste. pH-cycling Model I (Groups A, B, C), without added fluoride, ran for 7 days, while Model II (Groups D, E, F), with 0.25ppm F, ran for 10 days.

OUTCOME MEASUREMENTS

Lesions were evaluated using polarised light microscopy and microradiography.

RESULTS

Lesions in Groups B and E progressed by 64% and 61%, respectively, while those in Groups C and F progressed by only 19% and 23% respectively.

CONCLUSIONS

Both 10-day and 7-day pH-cycling models were suitable for studying carious lesion progression in primary teeth (the demineralising and remineralising solutions of the 10-day cycling model contained 0.25ppm F). A pea-sized portion (0.32g) of 500ppm F toothpaste slowed down the demineralisation progression better than a half-pea-sized portion.

[Effect of sucrose-containing gum and fluoridated dentifrice on in situ remineralization of artificial caries]

The aim of this study was to evaluate the remineralization of incipient carious lesions in bovine enamel in situ. Artificial carious lesions were produced and fixed in removable lower appliances in the region of the lingual surfaces of first molars, in six volunteers with ages between 18 and 22 years, who were subjected to 3 distinct experimental periods of 1 week each. In the first period (control group), patients brushed their teeth with a non-fluoridated dentifrice 4 times a day (after meals), and, in the second period (group I), patients used a dentifrice containing 1,500 ppm of fluorine (in the form of MFP). In the third period (group II) volunteers brushed their teeth with non-fluoridated dentifrice and used chewing gum containing 60% of sucrose during 20 minutes, 4 times a day (after meals). Before and after each treatment, the specimens underwent Vicker's hardness test (200 g of load), and the remineralization percentage (alpha) was calculated. The control group showed 2.78% of demineralization, and groups I and II showed 3.36 and 5.21% of remineralization, respectively. Statistical analysis (with Kruskal-Wallis and Miller's tests) showed significant difference (p < 0.05) between the control and experimental groups (I and II). Group II showed greater alpha than group I, but this difference was not significant. These results suggest that the use of sucrose-containing chewing gum and fluoridated dentifrice has a considerable effect on the remineralization of incipient carious lesions and may be a valuable alternative for their prevention.

The effect of different commercial dentifrices on enamel lesion progression: an in vitro pH-cycling study

AIMS/OBJECTIVES

To evaluate and compare the de/remineralization effects of dentifrices manufactured locally in some developing countries.

DESIGN

Utilisation of the in vitro single-section and the pH-cycling model.

SETTING

Laboratory. TEST MATERIALS: Dentifrices: Maxam DFP, Maxam Tartar Control, First, Tianqi Medicated from China; Vicco Vajradenti from India; Colgate MFP2, Crest Tartar Control from USA; and one non-fluoride dentifrice as control.

METHODS

Sound molars were painted, leaving a 1 mm wide 'window' on the buccal and/or lingual surface and placed in a demineralisation solution for 96 h to produce artificial caries lesion approximately 80-100 mm deep. The teeth were then longitudinally sectioned (approximately 100 mm thick), and randomly divided into 8 groups (22 sections/group). The pH cycling model was utilised for 10 days.

OUTCOME MEASURES

Polarised light microscopy and microradiography were used to evaluate the lesion progression before and after treatment.

RESULTS

The control group showed an increase in lesion depth of 70 per cent and was statistically different from some test groups which ranged from -2 per cent to 68 per cent (P < 0.01, t-test). Statistically significant differences were also observed among some of the fluoride containing groups.

CONCLUSIONS

This study suggests that, when compared to 'multinational dentifrices', Chinese and Indian dentifrices manufactured locally failed to show 'healing' efficacy even though they claimed to contain varying levels of fluoride.

Experimental intra-oral caries models in fluoride research

The use of experimental intra-oral caries models has increased in fluoride research. This paper focuses on the pre-clinical intra-oral models, the in situ and in vivo models, the various types, their benefits and disadvantages. Both preparation and sterilization of the hard tissue substrates can affect the substrates and therefore the results. Care needs to be taken that dentine samples are not exposed to drying and consequently shrinking during preparation and evaluation. Sterilization by gamma-radiation is at present the least tissue-damaging method. The most realistic experimental model is the in vivo model, followed by the in situ model using specimens with natural surfaces. The most accurate and direct evaluation technique for demineralization and remineralization studies is quantitative transversal microradiography, whereas confocal laser scanning microscopy (CLSM) is the most sensitive qualitative evaluation technique. Other evaluation techniques discussed are microhardness testing and the iodine permeability test. In light of the present skewed caries situation in western countries we suggest that fluoride research focuses on experimental caries models that can mimic severe cariogenic challenge. Testing of fluoride combinations and dosages that can prevent lesion development rather than promote remineralization would then be a practical consequence.

Morphology of initial lesions of enamel treated with different commercial dentifrices using a pH cycling model: scanning electron microscopy observations

The aim of this study was to evaluate and compare the 'calcium fluoride-like reaction products' formed, both on the surface and in the subsurface caries-like lesions of enamel, from different commercial dentifrices manufactured locally from developed and developing countries. The experiment was conducted by using the in vitro single-section technique under the pH-cycling system used for 10 days. The tested dentifrices include; Maxam DFP Maxam Tartar Controls, First, Tianqui Medicated (China); Vicco Vajradenti (India); Colgate MFP2. Crest Tartar Control (USA); and a non-fluoride dentifrice, Jie Yin (China) used as control. The surface and subsurface of the lesions, before and after treatment, were examined using scanning electron microscopy. Varying degrees of fine globular patterns of calcium fluoride-like material were observed on the enamel surfaces of five out of eight groups and in the subsurface of four groups. Two treatment groups showed a 'similar appearance' compared with the control and untreated groups. This study suggests and supports that, when compared with 'multinational dentifrices', some Chinese and Indian dentifrices manufactured locally failed to induce the typical morphological appearance of globules as seen with fluoride dentifrices.

Evaluating the effects of fluoride-releasing dental materials on adjacent interproximal caries

BACKGROUND

The authors examined several restorative materials to evaluate their ability to inhibit demineralization and enhance remineralization of incipient carious lesions on the interproximal enamel of teeth adjacent to those restored with the materials.

METHODS

Twenty-one subjects in need of a crown on a mandibular molar and a Class II inlay on an adjacent tooth took part in this six-phase study. Artificial enamel lesions were created and positioned within the interproximal portion of a crown. Lesions were photographed with polarized light microscopy and characterized before and after 30-day intraoral exposures. Each phase included the placement of a new section in the crown model and a new Class II inlay restorative material in the adjacent tooth.

RESULTS

Results demonstrated that nonfluoridated resin composite, fluoridated resin composite and resin-modified glass ionomer restorative materials, when placed in subjects who brushed with a fluoridated dentifrice, demonstrated significantly (P < .05) less enamel demineralization than the nonfluoridated resin composite control placed in subjects who brushed with a nonfluoridated dentifrice. The resin-modified glass ionomer cement, however, even when brushed with a nonfluoridated dentifrice, exhibited significantly (P < .05) less demineralization than the nonfluoridated resin composite control brushed with a nonfluoridated dentifrice.

CONCLUSIONS

Resin-modified glass ionomer cement appears to significantly inhibit demineralization of interproximal enamel of teeth adjacent to those restored with the material.

CLINICAL IMPLICATIONS

Resin-modified glass ionomer cement restorations can enhance prevention of enamel demineralization on adjacent teeth.

Reproducibility of TMR for the determination of longitudinal mineral changes in dental hard tissues

Transverse microradiography (TMR) of thin sections is the principal method for determining mineral changes in experimental lesions. Because it has become also the standard by which newly-developed methods are validated, demands on all steps of the procedure are high. Thin sections of enamel and dentin require high-precision cutting or lapping to preserve surface structures, but their different brittleness and elasticity preclude a uniform procedure. Image analysis permits the measurement of fine details at a micron scale, but because most studies are aimed at overall mineral changes, they are usually lost on broadening of the scan areas and averaging of experimental groups. Small errors in repositioning of the scan areas for repetitive measurements may yield distorted lesion profiles, while quantitative data such as the integrated mineral loss are hardly influenced. A major reason for "irreproducibility" of TMR are the different definitions of the lesion parameters as used by various research groups. We recommend that these definitions be agreed on if the full potential of TMR as an international standard is to be utilized.

In situ caries models

By using in situ models, we have the potential to study both fundamental aspects of the caries process as well as more applied research problems such as the effect of food on dental caries and the role of fluoride in caries prevention in human subjects without actually causing caries in the natural dentition. The key experimental parameters that need to be considered in the development of an in situ model are the characteristics of the subject panel, the physical design of the model, the type of hard tissue substrate and the method of assessing mineral status, and the study design and clinical protocol. Each parameter must be carefully considered in relation to the objectives of the research, study design requirements, ethical considerations, impact on clinical relevance, and impact on the control of variation. The major source of variation associated with in situ models should be of biological and not experimental origin. The design and conduct of proper in situ model studies require a clear understanding of the caries process, sound analytical support, and a knowledge of how to work with research subjects to achieve a high level of compliance. Given the complex nature of caries, a combination of hard tissue substrates--including sound, surface-softened lesions and subsurface lesions--may be necessary to model all aspects of caries progression and prevention successfully. Internal validation of in situ models using fluoride dose-response controls is considered to be necessary for studies evaluating the efficacy of new fluoride dentifrice formulations.

Human experimental caries models: intra-oral environmental variability

In situ caries models serve purposes other than just being a simpler way to obtain data than running a clinical trial. However, variation in information obtained not only among individuals but also, in particular, depending on different locations of the models within the oral cavity have so far been given little attention. In the present review, the aim has been to characterize the different designs of in situ caries models and to describe some important factors which may vary within the oral cavity and thus influence the outcome of the way the different in situ models are used. Advantages and disadvantages of in vivo models vs. in situ models are discussed. In the latter case, the distinction is made between dental appliance models and so-called "single tooth" models. The review concludes that in situ models differ distinctly with regard to their "biological potential". Because of regional differences in salivary film velocity, pH, and composition of the microflora, results obtained by the various models are not likely to be immediately comparable. Moreover, local factors in relation to specimen environment, such as degree of "protection" and plaque thickness, may further add to the differences. It is suggested that these observations are important in considerations of the relevance of substituting clinical trials with in situ studies. Because of the pronounced intra-oral variation in certain parameters thought to be important for caries lesion development, we conclude that no in situ model can, by itself, fulfill the role as the "model of choice". Finally, although in situ models are useful adjuncts in attempts to estimate the relative effects of new anticaries methods or compounds on caries initiation, the selection of in situ study model design will strongly depend on the aim and purpose of the study.

A single-section model for enamel de- and remineralization studies. 1. The effects of different Ca/P ratios in remineralization solutions

A prerequisite for the accurate measurement of differences between pre- and post-experimental mineral profiles in single sections by quantitative microradiography is a high degree of reproducibility of the analytical procedures. We have determined the reproducibility of both the production and analyses of microradiographs. Lesions were made in seven single bovine enamel sections and radiographed three times. Each microradiograph was then analyzed on three different occasions by use of an image analysis system. This resulted in only small standard deviations in the lesion parameters. The method was used to determine the sites of mineral deposition in lesions in single sections during remineralization in three different solutions, one of which contained 1.5 mmol/L Ca and 0.9 mmol/L PO4 (standard solution); the other two solutions were low in either Ca or PO4, but all three had the same degree of supersaturation. The mineral profiles and lesion parameters were determined after lesion formation and after remineralization for 4 days, 1, 2, and 3 weeks. The decrease in IML (integrated mineral loss) in the lesions remineralized in the standard solution was greatest during the first week. Lesion profiles revealed that, under non-standard conditions, mineral deposition was retarded in the deeper part of the lesion, in contrast to the even distribution of mineral deposition from the standard solution. Differences in IML changes and lesion profiles between these bovine enamel experimental groups diminished when remineralization continued for 2 and 3 weeks. Possibly, the reactivity of mineral surfaces in newly made lesions affected the diffusion of remineralizing ions from low concentration solutions to the lesion front.

The comparative sensitivity of intra-oral, in vitro, and animal models in the 'profile' evaluation of topical fluorides

The development of predictive and rapid methods for the assessment of the anticaries activity of topical fluorides has been a long-standing objective of caries researchers. These methods can provide useful benefits in a number of applications, ranging from the identification of novel agents to progress into clinical testing to the regulatory screening of commercial product variations. In the latter applications, combinations of test methods (so-called profiles) are used by manufacturers to prove that changes in formulations do not alter the efficacy of the products. Historically, combinations of in vitro and animal models have been used for basic research as well as for profile testing purposes; however, in recent years, the use of intra-oral or in situ models has increased. In this paper, in vitro, animal, and in situ methods are reviewed in terms of the historical basis for their development, protocols currently used in testing, and the primary advantages and limitations of each as applied to 'profile' applications. Recommendations are provided concerning circumstances for the appropriate use of modern test methods in formulation screening.

Patient selection and appliance design in intra-oral models

The conclusions derived from in situ studies are influenced by the choices made with respect to parameters of the intra-oral model systems. In an attempt to reach a consensus, this paper considers the variables (a) selection of panelists and (b) appliance design. On both topics, a short review of available systems is given. The objectives of the intra-oral study may vary from the determination of oral physiological parameters to assessment of the effects of caries-preventive treatments. This objective is a factor influencing the choice of experimental conditions. Recommendations for panelist selection and appliance design are given for different types of studies. It is concluded that relatively little information is available about the effects of individual parameters on the performance of a model. Therefore, for an assessment of caries-preventive effectiveness, an intra-oral model should be validated against clinical trials. In addition, conditions should be chosen such as to limit the degree of artificiality of the model.

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.

Demineralization and remineralization evaluation techniques--added considerations

Methods used for the analysis of tooth de- and remineralization include techniques with various degrees of sophistication and quantitative capabilities, ranging from direct measures of mineral gain/loss (e.g., microradiography) to indirect measures (e.g., iodide permeability) of changes in tooth mineral properties. In all instances, the capabilities of methods for accurate determination of changes in tooth mineral properties are affected by procedures used in the preparation of specimens for analysis, the magnitude of change taking place in the test (vs. the detection limits of the techniques), and protocols for specimen analysis. In specific instances, such as in the case of dentin, unique specimen-handling and analysis procedures must be used to prevent artifacts. The choice of techniques for the assessment of de- and remineralization depends strongly upon study protocols and laboratory capabilities; however, 'quantitative' measures of mineral gain and loss are possible only if direct chemical or radiographic techniques are used. Either radiographic, cross-sectioned microhardness or polarized light can be used for the determination of lesion depth. Porosity, light-scattering, and surface microhardness are indirect techniques which complement direct measures of mineral gain and loss. Whatever methods are used in the analysis of de- and remineralization, researchers must take care to differentiate accurately among the quantitative capabilities of techniques used in analysis.

Comparison of fluoride profiles by SIMS with mineral density of subsurface enamel lesions treated intra-orally with a fluoride-releasing device

A variety of intra-oral model systems has evolved which allows for the study of remineralization of coronal and/or root-surface lesions following application of topical fluoride (F) agents. The problem of interpretation of the results has led to a variety of analytical methods (i.e., microhardness, F biopsy, microradiography, and polarizing light microscopy), each of which provides important but limited information related to the overall understanding of remineralization. Microhardness measures change in mineral content which is more precisely localized by microradiography and polarized light microscopy. F biopsy allows for assessment of the F uptake of lesions, but does not suggest the chemical state of the F. Previous work has demonstrated that patterns of mineral deposition during remineralization do not necessarily parallel the F uptake profiles, and fluoridated apatites cannot be distinguished from non-specifically-adsorbed F (Clark et al., 1988). Because artificial lesions demonstrate variations in depth and mineral content, complementary analytical methods that demonstrate profiles of both F content and mineral density curves on the same section are needed so that the process of remineralization can be more clearly understood. This study used secondary ion mass spectrometry (SIMS) for F profiles and quantitative microradiography for assessment of mineral deposition on the same section. These state-of-the-art methods demonstrate the precision with which information about remineralization can be obtained. Subsurface lesions in human enamel specimens were developed by immersion in 0.1 M lactate buffer with 1% CMC at a pH of 4.5 for 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of model parameters in the assessment of intra-oral remineralization

Since the introduction of the Intra-oral Cariogenicity Test by Koulourides et al. (1974), many groups around the world have been developing and using intra-oral models to test new caries-preventive products, as well as to study physiological processes in the oral cavity. In spite of the large numbers of papers reporting these methods, very little research has been done to determine the importance of the many variable parameters which influence the performance of these models. Among these, the following can be identified: (a) panelist criteria, (b) the use of sound vs. pre-demineralized enamel of human or bovine origin, (c) the use of gauze or a recess to accumulate plaque, (d) the method to create incipient lesions, (e) the duration of the experiment, (f) the number of panelists required for statistical significance to be obtained, (g) the assessment techniques for mineral and/or fluoride uptake/loss, and (h) the choice of contralateral, 'cross-over', or 'monadic' experimental designs. Our results, supported by data from the literature, indicate that the choices made with respect to these parameters are of paramount importance in determination of the outcome of the respective study.

Hard-tissue substrates for evaluation of cariogenic and anti-cariogenic activity in situ

Hard-tissue substrates include primarily human and bovine enamel and human dentin. They have been used for in situ studies in a natural or sound condition, as well as flattened or containing an in vitro-formed caries-like lesion. Human enamel and dentin are generally the substrates of choice for studies of coronal and root-surface caries, respectively, but bovine enamel appears to offer a suitable alternative for many studies of enamel caries. Substrates with caries-like lesions will respond more rapidly to changes in the intra-oral mineral equilibrium and will allow both demineralization and remineralization to be determined. Findings from some studies suggest that caries-like lesions may respond somewhat differently, depending upon the degree of mineralization of the surface layer. Because in vitro findings with dentin show it to be significantly more soluble in acid than enamel, results from a study that used dentin may not be directly applicable to enamel. Both enamel and dentin substrates can be used in thin-section models. Hard-tissue substrates can also differ, depending upon their intra-oral location. Locations that result in the accumulation of plaque will behave differently from those that are plaque-free. So that plaque would accumulate, substrates have been placed approximally, beneath a fabric or steel mesh, in a protected trough, beneath a metal band or within a depression on the buccal surface. For studies requiring a determination of both demineralization and remineralization, human enamel or dentin containing a surface-softened caries-like lesion and covered with a uniform natural plaque are the substrates of choice.

Reduction of intra-oral demineralization of enamel after single exposures to sodium fluoride

Studies demonstrated the effects of single rinses with low concentrations of NaF on the intra-oral demineralization of enamel. Blocks of bovine enamel were covered with Streptococcus mutans IB1600, mounted in palatal appliances, and worn in the mouths of volunteers for specified times. Subjects rinsed with solutions of NaF, with or without sucrose. Demineralization was determined as changes in iodide penetrability (delta Ip) of the enamel, while the pH and F of the streptococcal plaque, and enamel F, were determined with ion-specific electrodes. Delta Ip was reduced by about 80% (from 14.5 +/- 2.7 to 2.8 +/- 2.3 units) when 250 micrograms F/mL was added to the sucrose rinse. Corresponding plaque pH's were 4.1 +/- 0.5 and 4.2 +/- 0.3, consistent with a lack of effect on bacterial acidogenesis. Protection against mineral loss was concentration-dependent. Administration of sucrose at different times after NaF revealed that the effect of F persisted for at least 60 min. Analyses of plaque F demonstrated an initial elevation and concentration within the cells, followed by a drop to stable, baseline values. Enamel F increased slowly to almost 500 micrograms/g enamel after 105 min. The protective effect of F appeared to be manifested in two stages, the first related to a high plaque F and the second to F that became incorporated into the enamel. Analysis of the data suggested that F was transferred from plaque to enamel during the experimental period.

An intra-oral single-section demineralization/remineralization model

This paper reviews the use of our intra-oral crown single-section model for the evaluation of in situ demineralization and remineralization. The model uses normal, healthy adults who are in need of a gold crown. A slot is placed in the working crown which can hold 3-4 single sections. A typical experiment would use an enamel lesion, root lesion, and sound root section which are characterized with polarized light microscopy and/or microradiography prior to insertion in the crown. After the experimental regimen, the sections are removed and re-characterized for any changes. The model has been used to evaluate mineral changes from the use of fluoride dentifrices and rinses, chewing gum, and food sequencing. The advantages of the model system are the before-and-after measurements on the same section, a natural plaque formation, interaction with saliva, episodic demineralization and remineralization, no bulky appliances, and the use of reasonable time frames. This model, therefore, reduces the artificiality of the in situ study to a great extent and appears to be a useful predictor of demineralization/remineralization interactions.

A review of quantitative methods for studies of mineral content of intra-oral caries lesions

Modern prospective caries studies require the measurement of small changes in tooth mineral content. Quantitative measurements of changes in mineral content in a single caries lesion is desirable. Quantitative methods can be either destructive or non-destructive. The latter type permits longitudinal studies to be conducted. Various methods available for the analysis of lesion parameters are reviewed. The basic principle of each method is summarized, and its characteristics are discussed. For each method, the correlation between the measured parameter and mineral loss, the useful range of mineral loss, the discrimination threshold, and the repeatability, are presented. Where such quantities were not available in the original papers, they were calculated from literature data. A comprehensive table of specifications of all methods is given.

The effect of plaque thickness on progression of artificial caries lesion formation in situ

Eighty thin enamel sections with artificially-formed caries lesions were implanted in the buccal surfaces of molars (in the removable partial dentures of ten subjects) and covered with a steel mesh for plaque accumulation to occur. The mesh was placed in contact with the enamel surface in half the lesions and 0.5 mm above the lesions in the other half, thus facilitating formation of thin and thick plaque samples. Following two-week use of a non-fluoride dentifrice, the lesions were analyzed for mineral change by quantitative microradiography. Significant mineral was lost from lesions in both groups, but the loss was twice as large in the thick-plaque group. These findings are important to in vivo remineralization models, since they show that plaque thickness should be controlled for minimization of variation.

Effects of fluoride on caries development and progression using intra-oral models

This paper reviews the use of intra-oral model systems to help elucidate the role of fluoride and its mechanism of action in caries prevention. The intra-oral models currently in use were found to be of three general types. The most widely used system has consisted of a removable appliance that relies on the use of dacron gauze or a recessed sample to enhance plaque formation. Similarly, the banding model of Ogaard requires the presence of orthodontic band material to produce a plaque accumulation niche for demineralization, while the crown single-section technique relies mainly on placement of the sections in plaque-retentive areas (below contact points). In general, the models may be used for the assessment of food cariogenicity, an evaluation of de- and re-mineralization, and measurement of fluoride incorporation into enamel or root substrates. On evaluation of lesion initiation and progression in vivo, it is apparent that few non-destructive in vivo techniques are available that offer the sensitivity of laboratory-based analysis. Thus, the use of intra-oral models that allow lesion formation and progression to occur in the oral environment, but can be measured with the sensitivity of in vitro techniques, has been extremely important. Although the magnitude of the fluoride dose, the longevity of fluoride in the oral environment, and the time required for remineralization are different from those found in vitro, it is apparent that the presence of fluoride in the aqueous phase is now thought to be of primary importance. Mechanistically, the presence of fluoride will both inhibit demineralization by acid and promote remineralization under more neutral conditions. Thus, one of fluoride's major contributions is to affect the rates of lesion formation and progression. It was concluded that low-concentration fluoride agents with a high frequency of application would best fulfill the above needs.

A method of semi-quantitative microradiographic analysis of root surface lesion remineralization

The purpose of this study was to present a modified photometer based digital analysis system for image enhanced microradiographic semi-quantitation of reactions of demineralization and remineralization of root surface lesions. The system was used to determine effects of fluoride on abraded root surface dentin in vitro. Lesions of 30-40 micron depth were produced during 18 h exposure of 180 micron thick single sections in solution of 3 mM Ca (Ca/P 1.67) and 30 mM lactic acid at pH 5.1. Mean mineral content of the lesions was 32% relative to adjacent sound dentin. Exposure of 20 h in the same acid with 5 mM Ca (Ca/P 1.67) and 0.12 mM NaF at pH 6.1 restored the mean mineral content to 76% of normal and increased the resistance of the lesions to demineralization. Remineralization and subsequent demineralization characteristics indicated the growth of fluorapatites on residual minerals in the dentin lesions. The microradiographic analysis system proved to be sensitive and critical in these studies.