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

The Role of Microbiology in Models of Dental Caries: Reaction Paper

Models of the caries process have made significant contributions toward defining the roles of bacteria in caries. Microbiologists use a variety of in vitro systems to model aspects of the caries process. Also, in situ models in humans provide information on the microbiology of caries in vivo. These models do not involve the entire process leading to natural caries; consequently, the results from such studies are used to deduce the roles of bacteria in natural caries. Therefore, they can be described as Inferential Caries Models. In contrast, animal models and some clinical trials in humans involve natural caries and can be described as Complete Caries Models. Furthermore, these models are used in two distinct ways. They can be used as Exploratory Models to explore different aspects of the caries process, or as Test Models to determine the effects of anticaries agents. This dichotomy in approach to the use of caries models results in modification of the models to suit a particular role. For example, if we consider Exploratory Models, the in situ appliance in humans is superior to others for analyzing the microbiology of plaque development and demineralization in vivo. The chemostat and biofilm models are excellent for exploring factors influencing bacterial interactions. Both models can also be used as Test Models. The in situ model has been used to test the effects of fluoride on the microflora and demineralization, while the chemostat and biofilm models allow for the testing of antibacterial agents. Each model has its advantages and disadvantages and role in analysis of the caries process. Selection of the model depends on the scientific question posed and the limitations imposed by the conditions available for the study.

In Situ Caries Models: Reaction Paper

In situ caries models can be found in all shapes and sizes and designed for many purposes. Building on previous conferences, Dr. Zero has done a remarkable job in summarizing the many aspects of in situ models, and as such this reactor's paper will be restricted to only several aspects of the model. One of the most important steps in using in situ models involves the reporting of enough details and reasons for choices in model parameters so that the reviewer or reader can judge clinical relevance and applicability. This approach tends to broaden the field as much as restrict it to only one substrate, evaluative technique, or appliance type. Continued work needs to be done on both surface and subsurface lesions; there is a need to establish "gold standards" for model validation in areas such as salivary flow, antimicrobials, food sequencing, etc., and the clinical relevance of each model needs to be explored.

Influence of a Fluoride Mouthrinse on Mutans Streptococci in Schoolchildren

This study aimed to determine whether the long-term use of a fluoride mouthrinse affects the salivary levels of mutans streptococci. Two hundred and fifteen schoolchildren (aged 9-10 years) participated. One hundred and forty-nine of these children had used a fluoride mouthrinse since 5 years of age at nursery school, and the remaining 66 children had not. DFT (decayed and filled teeth) was recorded, and the salivary levels of Streptococcus mutans and Streptococcus sobrinus were measured using mitis salivarius bacitracin agar. The group that had used a fluoride mouthrinse had a significantly lower prevalence of both S. mutans and S. sobrinus (p = 0.038) and a significantly lower DFT score (p < 0.001) than the other group. Using logistic regression analysis including caries experience at baseline as a dependent variable, the odds ratio of carrying S. mutans alone was 8.0 (p = 0.066) and that of carrying both S. mutans and S. sobrinus was 16.5 (p = 0.022) in the group that had not used the fluoride mouthrinse. Children carrying both S. mutans and S. sobrinus had a higher caries incidence in 1 year than the others, with odds ratios of 5.73 (p = 0.067) in the group with a fluoride mouthrinse and 3.47 (p = 0.035) in the group without it. These results show that the long-term use of a fluoride mouthrinse is associated with reduced salivary levels of mutans streptococci and this bacterial reduction may partly contribute to the suppression of dental caries in children using a long-term fluoride mouthrinse.

Procedures for establishing efficacy of antimicrobial agents for chemotherapeutic caries prevention

Chemotherapeutics are presently considered for use in caries-preventive programs. The laboratory and in vivo testing of these agents, to some extent, parallels the methodology developed for the evaluation of fluoride products. However, fluoride is primarily effective by interfering with the de- and remineralization balance between enamel and the oral fluids. Antimicrobial and chemotherapeutic agents interfere with the bacterial colonization, growth, and metabolism of dental plaque. The initial selection of promising agents is done, therefore, by determination of the minimum inhibitory concentration (MIC) against a wide range of relevant bacterial species, together with tests of the effects of sub-MIC levels on the expression of virulence factors. In the hierarchy of tests proposed in this paper, studies of bacterial adhesion and enamel caries models form the next phase in the evaluation of agents. Also, mixed-culture studies are recommended to determine how a treatment perturbs a stable microflora. A final stage before clinical testing might involve intra-oral studies on limited numbers of volunteers. These should be tests of intra-oral substantivity and activity of the agents in formulated products, and in situ models of enamel caries lesion formation and remineralization. The latter type of study seems particularly appropriate to ensure that new agents do not decrease the efficacy of the other active components (e.g., fluoride) in caries-preventive products.

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.