A mixed-bacteria ecological approach to understanding the role of the oral bacteria in dental caries causation: an alternative to Streptococcus mutans and the specific-plaque hypothesis.
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For more than 100 years, investigators have tried to identify the bacteria responsible for dental caries formation and to determine whether their role is one of specificity. Frequent association of Lactobacillus acidophilus and Streptococcus mutans with caries activity gave credence to their being specific cariogens. However, dental caries occurrence in their absence, and the presence of other bacteria able to produce substantial amounts of acid from fermentable carbohydrate, provided arguments for non-specificity. In the 1940s, Stephan found that the mixed bacteria in dental plaque produced a rapid drop in pH following a sugar rinse and a slow pH return toward baseline. This response became a cornerstone of plaque and mixed-bacterial involvement in dental caries causation when Stephan showed that the pH decrease was inversely and clearly related to caries activity. Detailed examination of the pH (acid-base) metabolisms of oral pure cultures, dental plaque, and salivary sediment identified the main bacteria and metabolic processes responsible for the pH metabolism of dental plaque. It was discovered that this metabolism in different individuals, in plaque in different dentition locations within individuals, and in individuals of different levels of caries activity could be described in terms of a relatively small number of acid-base metabolic processes. This led to an overall bacterial metabolic vector concept for dental plaque, and helped unravel the bacterial involvement in the degradation of the carbohydrate and nitrogenous substrates that produce the acids and alkali that affect the pH and favor and inhibit dental caries production, respectively. A central role of oral arginolytic and non-arginolytic acidogens in the production of the Stephan pH curve was discovered. The non-arginolytics could produce only the pH fall part of this curve, whereas the arginolytics could produce both the fall and the rise. The net result of the latter was a less acidic Stephan pH curve. Both kinds of bacteria are numerous in dental plaque. By varying their ratios, we were easily able to produce Stephan pH curves indicative of different levels of caries activity. This and substantial related metabolic and microbial data indicated that it is the proportions and numbers of acid-base-producing bacteria that are at the core of dental caries activity. The elimination of S. mutans, as with a vaccine, was considered to have little chance of success in preventing dental caries in humans, since, in most cases, this would simply make more room for one or more of the many acidogens remaining. An understanding of mixed-bacterial metabolism, knowledge of how to manipulate and work with mixed bacteria, and the use of a bacterial metabolic vector approach as described in this article have led to (1) a more ecological focus for dealing with dental caries, and (2) new means of developing and evaluating anti-caries agents directed toward microbial mixtures that counter excess acid accumulation and tooth demineralization. (+info)
Orthodontic adhesives: a systematic review.
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OBJECTIVES: To evaluate which orthodontic adhesives (a). bond orthodontic brackets to teeth more reliably and (b). are more effective at preventing decalcification. DATA SOURCES: The search strategy for the literature review was carried out according to the standard Cochrane systematic review methodology. The Cochrane Clinical Trials Register and the Cochrane Oral Health Group Specialized Register were searched for randomized clinical trials and controlled clinical trials. All volumes that had not already been assessed by the Oral Health Group in the European Journal of Orthodontics, American Journal of Orthodontics, Journals of Orthodontics, and Angle Orthodontist were hand-searched. Inclusion and exclusion criteria were applied when considering the studies to be included in this review. DATA SELECTION: The primary outcome measure was the failure of the orthodontic adhesive. A secondary outcome of decalcification occurring around the orthodontic bracket was also recorded, if data were available. DATA EXTRACTION: Two randomized clinical trials and one controlled clinical trial were identified that fulfilled all the inclusion and exclusion criteria. The trials compared: (a). light- and chemically-cured composite; (b). chemically-cured composite and conventional glass ionomer cement; and (c). chemically-cured composite and light-cured compomer. DATA SYNTHESIS: Each paper was quality assessed by two people independently. A qualitative analysis of the trials in the review is presented. The data presentation, for the majority of the trials, precluded the use of suggested Cochrane Health Group statistical analysis. CONCLUSIONS: It is difficult to draw any conclusions from this review; however, suggestions are made for methods of improving future research involving orthodontic adhesives. (+info)
Quantifying enamel demineralization from teeth with orthodontic brackets--a comparison of two methods. Part 1: repeatability and agreement.
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The aim of this investigation was to compare the repeatability of measuring enamel demineralization surrounding an orthodontic bracket using two techniques: computerized image analysis from digitally converted photographic slides and quantitative light-induced fluorescence (QLF). Fifteen human molars were halved and shaped to look like incisors. The teeth were individually numbered and orthodontic brackets bonded to the buccal surface. The crowns were covered with acid resistant varnish, except for windows approximately 1.5 x 3 mm adjacent to the gingival, occlusal, mesial, and distal edges of the bracket. The windows were variously exposed to a demineralizing gel for 0, 3, 7, or 14 days, and the acid resistant varnish was removed. Standardized photographic slides and QLF images of the teeth were taken. These were repeated after 1 week. The slides were converted to grey scale digital format and analysed using Image-Pro Plus 3.0. The QLF images were stored, processed, and analysed using customized software. All images were recoded for blind analysis. The four surfaces of the bracket were inspected and only areas of suspected demineralization were analysed. This was repeated after 1 week. The limits of agreement and mean difference between repeat readings of the area of demineralization were similar for both techniques (-0.04 +/- 0.43 for photographs and -0.10 +/- 0.63 for QLF). Mean grey level (photographs) and mean loss of fluorescence from that area (deltaF) (QLF) showed acceptable limits of agreement. The Intra Class Correlation (ICC) was below 0.81 for the measurement of area from QLF, suggesting that random error needs to be reduced. There was evidence of systematic bias for the repeat readings of the grey levels from the photographs (P < 0.001). Enamel demineralization surrounding an orthodontic bracket can be measured reproducibly using these two techniques. (+info)
Quantifying enamel demineralization from teeth with orthodontic brackets--a comparison of two methods. Part 2: validity.
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This is Part 2 of an in vitro study investigating two techniques for recording and quantifying demineralization surrounding orthodontic brackets. In Part 1 the repeatability of computerized image analysis from digitally converted photographic slides and quantitative light-induced fluorescence (QLF) was explored. In Part 2 of the investigation the validity of each technique was examined. Thirty halved human molars, shaped to look like incisors and with an orthodontic bracket bonded to the buccal surface were used. A small area of each of the four edges of the bracket was variously exposed to a demineralizing gel for 0, 3, 7, or 14 days. Images of the teeth were taken and analysed using the two techniques. Repeat images and analysis were carried out blind. The sensitivity, specificity, positive, and negative predictive values were calculated. A negative result confirmed that there was no demineralization present in the majority of cases. A positive result was less reliable particularly for the occlusal and gingival regions. The 7- and 14-day demineralization patterns were detected every time using the photographic technique. The discrimination of the 0- and 3-day patterns was less reliable. The results of this study were extrapolated to allow for the prevalence of the condition following orthodontic treatment, and the implications of this for a putative clinical trial are discussed, together with the advantages and disadvantages of each method. Either technique would be applicable to use in a clinical trial. (+info)
The in vitro detection of early enamel de- and re-mineralization adjacent to bonded orthodontic cleats using quantitative light-induced fluorescence.
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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. (+info)
Relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel in vitro.
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The objective of the study was to evaluate the relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel. Four kinds of fluoride concentration of the experimental fluoride-releasing elastomers were 1.25, 2.5, 3.75 and 5.0 wt%. An enamel block was cut into two smaller enamel blocks, one of which was set with an elastomer, the other as a control not set with elastomer. A plastic block that had the same shape as the small enamel block was also set with elastomer. Fluoride release and acid resistance tests were carried out. The mineral loss of the demineralized enamel was measured by microradiography. The results showed that the fluoride-releasing ability significantly increased with the increase of fluoride concentration in the elastomer (p < 0.05). The acid resistance of the enamel appeared to be enhanced greatly, however, its change was not proportional to the fluoride concentration in the elastomers. (+info)
Development and control of caries lesions on the occlusal surface using a new in vivo caries model.
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The aim of this study was to develop a new in vivo caries model for the occlusal surface and to describe the enamel features observed before and after dental plaque control (DPC). Four volunteers (12-15 years old) participated in the experiment, each of which was due to have 2 homologous first premolars extracted for orthodontic reasons. Test surfaces did not present visible signs of demineralization, opacities or fillings. A wire mesh was used to promote dental plaque accumulation on the occlusal surface. After 4 weeks, the wire mesh was removed and DPC was performed. In Groups 1 and 2, DPC was performed by the subjects daily and, in Groups 3 and 4, DPC was performed by the subjects daily and by the professional weekly. One tooth/pair of Groups 1 and 3 was extracted after 2 weeks. One tooth/pair of Groups 2 and 4 was extracted after 4 weeks. All test surfaces showed demineralization after the wire mesh was removed. The observed re-establishment of the enamel brightness was directly related to the increase of the DPC duration. In polarized light microscopy, interindividual differences varying from pseudoisotropic areas to enamel lesions were noted in specimens submitted to 2 weeks of DPC. Specimens submitted to 4 weeks of DPC showed less tissue porosity. It was concluded that the new in vivo caries model was effective since all occlusal surfaces presented clinical and microscopic signs of mineral loss in different stages after 4 weeks of cariogenic challenge. After DPC on the test surfaces, there was a reduction of mineral loss suggesting control of demineralization on these surfaces. (+info)
Nd:YAG laser ablation and acid resistance of enamel.
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The acid resistance of Nd:YAG laser-ablated enamel surfaces was studied by evaluating crystal structure, mineral distribution, and fluorescence radiance and image in the present study. For comparison, 37% phosphoric acid etching was performed. The formation of beta-tricalcium phosphate (beta-TCP) was confirmed in the laser-ablated surface. The Ca/P ratio increased after ablation due to mineral re-distribution. In contrast, the Ca/P ratio decreased after acid etching due to mineral loss. The laser-ablated enamels showed a smaller increase of fluorescence radiances and less clear laser confocal scanning microscope images than those observed in the acid-etched enamels. The former suggests a minimized mineral loss. The Nd:YAG laser irradiation will enhance the acid resistance and retard the carious progression in enamel. (+info)