bluuebunny/crossref_metadata_2025 huggingface dataset:
Are Current Models for Preventive Programs Sufficient for the Needs of Tomorrow?
Authors: Bowen W.H.
Published: January 2009

We can be proud of our accomplishment in the prevention of dental caries. Many children in developed countries are now caries-free; however, by age 50, fewer than 5% of the population is caries-free. The drop in the prevalence of caries among specific age groups is undoubtedly due to widespread exposure to fluorides. However, caries protection by fluorides is not absolute; if caries attack continues throughout life, the prevalence of caries will increase. All available evidence strongly suggests that ambient levels of fluoride in the mouth play a critical role in protection against caries. It is clear that novel methods of delivery, such as sustained-release technology, will be developed to enhance the protective effect of fluoride, utilizing amounts of fluoride significantly less than those currently in use. The problems of preventing dental caries in developing countries are much more severe than those facing Western countries. The prevalence of caries appears to be increasing in no small measure due to the introduction of Western diets. Administration of fluoride through conventional routes is either impractical or inordinately expensive. It appears sensible, therefore, to direct preventive measures through dietary constituents associated with caries. Fluoridation of sugars appears to be a highly practical and safe way to reduce the prevalence of caries in such communities. Fluoride and iodide are currently added to salt in many parts of the world. If we are to reduce the prevalence of caries effectively in all countries and in all age groups, current methods of prevention will have to be greatly enhanced, and/or effective additional approaches will need to be developed.
Strategies for Application of Scientific Findings in Prevention
Authors: Wei S.H.Y.
Published: January 2009

Dental research in the last 50 years has accomplished numerous significant advances in preventive dentistry, particularly in the area of research in fluorides, periodontal diseases, restorative dentistry, and dental materials, as well as craniofacial development and molecular biology. The transfer of scientific knowledge to clinical practitioners requires additional effort. It is the responsibility of the scientific communities to transfer the fruits of their findings to society through publications, conferences, media, and the press. Specific programs that the International Association for Dental Research (IADR) has developed to transmit science to the profession and the public have included science transfer seminars, the Visiting Lecture Program, and hands-on workshops. The IADR Strategic Plan also has a major outreach goal. In addition, the Federation Dentaire Internationale (FDI) and the World Health Organization (WHO) have initiated plans to celebrate World Health Day and the Year of Oral Health in 1994. These are important strategies for the application of scientific findings in prevention.
Animal Caries Models for Evaluating Fluoride Dentifrices
Authors: Stookey G.K. , Warrick J.M. , Miller L.L. , Greene A.L.
Published: January 2009

Abstract—To determine the ability of animal caries models to evaluate the cariostatic potential of fluoride dentifrices, we examined four different coronal caries models. These currently used rat caries models were: Francis' hypomineralized area model, Gaffar's CARA rat model, the Connecticut model, and the Indiana model. Available data indicated that all of these models were capable of detecting significant cariostatic benefits from clinically proven fluoride dentifrices. For the most part, these animal models were also able to demonstrate a response to increasing concentrations of fluoride, particularly if the fluoride was provided in an ionic rather than a complexed form. Data were also presented which indicated the potential for animal caries models to be used to predict the clinical benefits of non-fluoride systems as well as the utility of fluoride systems for the prevention of root-surface caries. It is concluded that animal caries models play a significant role in the development and evaluation of fluoride and other systems for the clinical prevention of dental caries.
Salivary Factors in Caries Models
Authors: Hay D.I.
Published: January 2009

Consideration of salivary factors in caries models rarely extends beyond viewing saliva as a sink or diluent for plaque metabolic products, or as a source of buffering, for neutralizing plaque acids. In reality, saliva has a complex chemistry and a wide range of biochemical activities that may significantly affect plaque chemistry and microbiology. Thus, saliva is a major source of microbial nutrients, without which bacterial acid production is diminished. Buffering by salivary bicarbonate, and base production from urea and basic amino acids and peptides, significantly affect Stephan curves. Saliva is supersaturated with respect to basic calcium phosphate salts and contains novel inhibitors of calcium phosphate precipitation, while specific salivary proteins bind calcium. It seems important to consider if this system is reflected in plaque. Saliva, with contributions from serum and bacterial constituents, provides most of the precursors for the acquired enamel pellicle, which acts to slow demineralization during caries attack. Pellicle constituents appear to influence initial bacterial colonization of tooth surfaces and, therefore, may affect the microbial composition of plaque. There are several potent antibacterial systems in saliva which appear to influence the bacterial composition of plaque, but their detailed effects on plaque are poorly understood. Microbial adaptations to the anti-bacterial systems also seem important but are poorly investigated. Thus, saliva possesses an array of activities that have substantial actual or potential impact on plaque and, therefore, merit consideration for inclusion in systems intended to model dental caries.
The Role of Microbiology in Models of Dental Caries
Authors: Marsh P.D.
Published: January 2009

Models of dental caries (laboratory, animal, and human in situ models) vary markedly in their microbiological complexity. Laboratory models range from mono-cultures of cariogenic species providing an acidic challenge to enamel, to the development of diverse mixed cultures growing on a habitat-simulating medium in an artificial mouth or chemostat. The latter systems are of value in determining either mechanisms of action or cause-and-effect relationships-e.g., between dietary components or antimicrobial agents and the microflora. Laboratory models have also shown that the sensitivity of oral bacteria to inhibitors is markedly reduced when growing in biofilms such as dental plaque. Animal models have proved unequivocally that caries is an infectious and transmissible disease. Their use has enabled comparisons to be made of (a) the cariogenic potential of different bacterial species, (b) the role of the diet, and (c) the effects of potential anti-caries agents. It has been claimed that no caries-protective agent currently in use has failed a rodent test. In situ human models have been designed to permit the development of "natural" plaque on standardized enamel surfaces freely exposed to the human oral environment. The microflora that develops on unadulterated surfaces is similar in composition to that found at comparable sites on vital teeth. Demineralization can be accelerated by the inoculation of additional cariogenic bacteria coupled with either intra- or extra-oral sucrose rinses. The increased realism associated with the transition from laboratory to human in situ models is countered by a reduced ability to control or manipulate the system for experimental purposes. Thus, a hierarchy of tests is needed for the study of anti-caries agents, each requiring a varying degree of microbiological complexity.
Statistical Considerations in Caries Models: Reaction Paper
Authors: Kingman A.
Published: January 2009

This discussion paper focuses on validity and reliability concerns associated with the PCK methodology. Examples of subtle validity issues from the product-testing arena are presented to illustrate the importance of validity issues, even with use of the strongest of all experimental designs, the randomized controlled clinical trial. Findings from two specific profile models are presented to illustrate the need for validating that a surrogate marker for dental caries is indeed a marker. Careful use of the two-stage PCK testing procedure is recommended, but only for intra-oral model response measures which are bona fide surrogate markers for dental caries in humans.
Statistical Considerations in Caries Models: Reaction Paper
Authors: Raubertas R.F.
Published: January 2009

In his conference presentation, Proskin discussed the concepts of validity and reliability of caries models, and reviewed the Proskin-Chilton-Kingman procedure for using models to assess the clinical efficacy of a therapeutic agent. He presented a generally positive view of caries models as substitutes for clinical studies under certain conditions. In this reaction paper I propose a stronger definition of validity, and discuss conceptual and practical requirements that caries models must meet before they can be used in place of clinical studies. Meeting these requirements may depend on obtaining new clinical data; making greater use of existing clinical data; and a willingness to adopt a limited set of standardized models for demonstrating clinical efficacy.
The Application of in Situ Models for Evaluation of New Fluoride-Containing Systems
Authors: Faller R.V.
Published: January 2009

Many in situ models have assessed the anticaries potential of fluoride-containing systems (Stookey et al., 1985; Mellberg et al., 1986, 1992a,b; Corpron et al., 1986; Featherstone and Zero, 1992; Ogaard and Rolla, 1992; Stephen et al., 1992). Several models have reportedly been validated according to guidelines proposed by Proskin et al. (1992). The proposed guidelines cover only dentifrices containing sodium fluoride (NaF) or sodium monofluorophosphate (SMFP) as active ingredients. These compounds are the most widely used sources of fluoride in dentifrices, and dose-response clinical standards are available for both.

Other fluoride compounds, such as amine fluoride (AmF) and stannous fluoride (SnF2), have also been proven effective in reducing caries (Muehler et al., 1957, 1958; Marthaler, 1968; Lu et al., 1980; Cahen et al., 1982). Profile standards for these fluorides were not included in the proposed guidelines, primarily due to the lack of clinical data necessary to establish a dose response for these ingredients. Criteria for demonstrating the efficacy of these ingredients, along with methods to assess new fluoride compounds, need to be established.

In situ models are used to evaluate the anticaries potential of new compounds added to mouthrinses, gums, slow-release devices, etc. (Creanor et al., 1992; Manning and Edgar, 1992; Lamb et al., 1993; Toumba and Curzon, 1993; Wang et al., 1993). Ingredients are often added to dentifrices previously proven effective against caries in order to provide additional benefits of gum health, tartar control, cleaning, etc.

Proposals are made regarding the in situ testing of new dentifrices containing clinically proven fluoride compounds other than NaF and SMFP, as well as alternative delivery systems, in order to assist in their evaluation.
Models for Evaluating New Fluoride-Containing Systems: Reaction Paper
Authors: Duckworth R.M.
Published: January 2009

The type and number of control formulations to be used in model studies to evaluate new fluoride systems require careful consideration. While many controls may be justified on the grounds of scientific interest, some models can handle only small numbers of treatments without the statistical power of studies being compromised. In those cases, the results of more than one study may need to be combined.

Current models for evaluating fluoride products have most often been developed with systems containing ionic fluoride in mind. To test new types of delivery vehicles or formulations which contain new fluoride agents, model protocols may need to be revised in order to account properly for differences in modes of action-for example, in rates of reaction with enamel or site specificity of active ingredient delivery in the mouth.
Role of Models in Assessing New Agents for Caries Prevention—Non-Fluoride Systems
Authors: Roberts A.J.
Published: January 2009

While fluoride is an effective anti-caries agent, the search for more effective alternative therapies continues. A wide range of non-fluoride anti-caries agents has been postulated, and this paper reviews some of the pre-clinical models that have been utilized in their evaluation and some of the pitfalls that must be avoided. Using data on the potential anti-caries efficacy of phosphopeptides obtained from casein, the caution that must be applied in extrapolating laboratory data to predict clinical performance is discussed. Evaluation strategies that focus on only one potential mode of action (e.g., inhibition of demineralization) may overestimate the true clinical efficacy which may arise from a combination of two or more effects (e.g., inhibition of demineralization and stimulation of remineralization). Although laboratory and in situ data predict anti-caries efficacy for sodium trimetaphosphate in combination with fluoride, this was not found in three-year clinical trials. A possible reason for this, the lack of suitable calibration methods, is discussed. Finally, some comments on the appropriateness of laboratory evaluation strategies are made.
Surface Changes of Fluoride-Releasing Composites: a Comparison of in Vivo and in Vitro Results
Authors: Dijkman G.E.H.M. , De Vries J. , Jongebloed W.L. , Arends J.
Published: January 2009

Fluoride-releasing composites lose fluoride very slowly over time. An interesting question is the possible change in mechanical properties related to the F release. If this happens, it might be expected that the mechanical properties of the outer surface of a fluoridating composite are affected first. The purpose of this study was to investigate in vivo and in vitro the changes in surface microhardness and surface structure of three fluoride-releasing composites and a non-F-containing control after 28 days. In the in vitro experiment, the composites were stored in tap water at 37°C. The results show that all composites stored in water were significantly softened after 28 days.

In vivo, however, a very different picture emerged: The surface microhardness of the fluoride-releasing composites did not change significantly. In vitro, the data indicate that the amount of softening of the fluoridating composites is related to the amount of fluoride released. No relation was found between the amount of F released in one month in vitro and the microhardness changes in vivo. SEM micrographs of fluoridating composites do not reflect the microhardness changes mentioned.
Gingival Reactions Around and Plaque Formation on Resin Composites and Glass-Ionomer Cements
Authors: Van Dijken J.W.V. , Sjostrom S.
Published: January 2009

This review covers plaque growth on and gingival reactions adjacent to composite resin and glass-ionomer cement restorations. Despite large variations in surface roughness and chemical composition of the restoratives, no clinically measurable differences in the presence or development of plaque and gingivitis were seen. However, more pronounced signs of subclinical gingivitis adjacent to resin composites, compared with non-filled surfaces, were shown by an increase of crevicular fluid levels. This can be explained by the chemical composition of the composites and/or by clinical, not visible, small amounts of dental plaque, which increase the rate of recolonization on these surfaces. The faster recolonization can imply a higher risk for periodontal disease in susceptible patients, especially when resin composites are used more frequently in the more-difficult-to-clean posterior cavities. The effect of fluoride leaching of glass-ionomer cement on the growth of cariogenic micro-organisms is reviewed. Initially, with the still-high fluoride leaching, a lower frequency of mutans streptococci was seen on glass ionomer and glass ionomer cermet cements, compared with amalgam, resin composites, or enamel. After longer periods, this difference disappeared, explained by a too-low level of fluoride leaching from the cement, which had no effect on the micro-organisms. Contrasting results were found for the cermet restorations, where the antibacterial effects of silver ions also can contribute to the inhibition of growth.
Review of Fluoride Release and Secondary Caries Reduction by Fluoridating Composites
Authors: Arends J. , Dijkman G.E.H.M. , Dijkman A.G.
Published: January 2009

Secondary caries is one of the main reasons to replace restorations. Due to the pressure to eliminate or reduce the number of amalgam restorations in many countries, fluoride-releasing composites have gained in importance. This review limits itself to information relevant to secondary caries near fluoride-releasing anterior or posterior composites. Although many parameters are very important in composite functioning, a weak spot near a filling is always the interface and the locally present interfacial gap between the composite and the hard tissues, where secondary caries takes place due to plaque action. Relevant parameters such as the amount of fluoride released in vitro in μg.cm-2, the rate of fluoride release, and the period of fluoride release are compared for several composites. In vitro F release has been measured for some fluoridating composites for more than five years. Unfortunately, F release in vivo or in situ cannot be measured adequately.

The fluoride released by the composites considered is partly taken up by the surrounding tissues, partly released to the saliva, and partly efficacious in possible marginal gaps and defects. A major part of this paper pertains to in vitro, in situ, and in vivo secondary caries reduction experiments. In vitro caries reductions in the order of 40% from F-releasing composites vs. controls have been found. In in situ model investigations under plaque and saliva conditions, secondary caries reduction percentages of between 40 and 50% have been experimentally measured in gaps in enamel near F composites.
Fluoride Modulates the Inhibition of in Vitro Hydroxyapatite Crystal Growth by Small Dentin Proteoglycan: Relevance to Dental Calculus
Authors: Hall R.C. , Embery G. , Shellis R.P.
Published: January 2009

Glycosaminoglycan constituents of the periodontium have been detected in supragingival and subgingival dental calculus. They are polyanionic heteropolysaccharides containing -COOH and SO3H residues. The non-sulfated hyaluronan is present in supragingival calculus, whereas chondroitin sulfate, dermatan sulfate, and heparan sulfate are detected in subgingival calculus. They are implicated in both ectopic and endogenous mineralization, and have been used in the present study to investigate seeded hydroxyapatite crystal growth, and the influence of fluoride on the process. All glycosaminoglycans examined inhibited crystal growth, with chondroitin-4-sulfate and dermatan sulfate being more effective than the hyaluronan. Fluoride alone enhanced growth and reduced the inhibitory influence of the glycosaminoglycans and the parent proteoglycan, which is a potent inhibitor. The results yield important information on the role of fluoride and proteoglycan in ectopic mineralization.
Immunity at Mucosal Surfaces
Authors: Brown T.A.
Published: January 2009

The mucosae form a barrier between our bodies and a hostile external environment. Diseases and extrinsic factors which impair mucosal function may lead to serious consequences. The mucosal immune system is the primary mediator of specific immunity at mucosal surfaces. As such, it is responsible for maintaining homeostasis and for defense against both overt and opportunistic pathogens. For this reason, it is also the target of many new vaccine strategies for the induction of mucosal immunity. This brief review will examine the mucosal immune system, its role in maintaining the integrity of the mucosa, and some of the strategies aimed at enhancing specific immunity.
Type I Insulin-Dependent Diabetes Mellitus: a Model for Autoimmune Polygenic Disorders
Authors: Winter W.E.
Published: January 2009

Insulin-dependent diabetes mellitus (IDD) affects between one in 250 and one in 500 Americans. The inheritance of IDD is non-Mendelian and polygenic. Genetic susceptibility predominantly results from specific alleles in the HLA complex and insulin gene region. Autoimmune destruction of pancreatic beta cells leads to profound insulinopenia (Atkinson and Maclaren, 1990). Without insulin treatment, fatal diabetic ketoacidosis results. Even with insulin treatment, after 10 to 20 years of IDD, devastating micro- and macrovascular complications lead to significant morbidity and premature mortality (Rosenbloom, 1983). In order to prevent this catastrophic disease and its consequences, we must understand the pathogenesis and immunogenetics of insulitis (the histologic lesion characteristic of IDD), whose ultimate expression is beta cell necrosis (Cudworth, 1978; Cahill and McDevitt, 1981; Eisenbarth, 1986). Current advances include recognition of new IDD-autoantigens (e.g., glutamic acid decarboxylase), susceptibility genes (e.g., HLA-DQB 1 *0201 and 0302), and the development of trials to prevent IDD through tolerization to IDD-autoantigens (e.g., insulin) (Maclaren, 1993; Winter et al., 1993). Unlocking the genetic mechanisms responsible for IDD can also reveal more general mechanisms involved in other organ-specific autoimmune diseases.
Differential Diagnosis of Dry Eye Conditions
Authors: Pflugfelder S.C.
Published: January 2009

The pre-ocular tear film is a complex biochemical structure produced by the lacrimal glands and epithelial cells on the ocular surface. Clinical syndromes of ocular irritation may result from deficiencies in one or more of these layers. At a recent dry eye workshop at the National Eye Institute, dry eye conditions were classified into those with adequate aqueous tear production and those with aqueous tear deficiency. The majority of patients with aqueous adequate dry eye suffer from meibomian gland dysfunction that results in lipid tear deficiency. Aqueous tear deficiency can be subclassified into non-Sjogren's syndrome and Sjogren's syndrome (SS) groups. Patients with non-Sjögren's aqueous tear deficiency have less-severe symptoms and ocular surface disease than those with SS. The etiology of non-Sjögren's aqueous tear deficiency has not been established, but it appears to be multifactorial. In SS, immune-mediated destruction of the lacrimal gland results in severe aqueous tear deficiency. Aqueous tear deficiencies lead to ocular surface disease, termed keratoconjunctivitis sicca (KCS). KCS results from abnormal terminal differentiation of the ocular surface epithelia and is associated with marked reduction in mucin production by these cells. Clinical features helpful in differentiating the various dry eye syndromes are reviewed.
Albumin Gene Expression During Mouse Odontogenesis
Authors: Yuan Z.A. , Mcandrew K.S. , Collier P.M. , Koyama E. , Chen E. , Sandgren E.P. , Gibson C.W.
Published: January 2009

Albumin protein is present in developing teeth of several species. Oligomer primers and cRNA probes specific for albumin were designed to perform RT-PCR, and for in situ hybridization, respectively. In situ hybridization failed to reveal albumin expression in any tooth cells, however, albumin PCR products were amplified from tissues adhering to the roots of developing teeth from four-week-old mice. It is concluded that this source is not the primary source of albumin protein found in developing enamel, because of the location and level of expression of albumin mRNA in periodontal tissue.
Transient Accumulation of Proteins At Interrod and Rod Enamel Growth Sites
Authors: Nanci A. , Hashimoto J. , Zalzal S. , Smith C.E.
Published: January 2009

Conceptually, there should be a brief interval in time when newly secreted proteins "pile up" at secretory sites just outside the membrane of ameloblasts. Indeed, previous cytochemical studies have suggested that glycosylated and/or sulfated glycoproteins accumulate at enamel growth sites. Colloidal gold lectin cytochemistry and immunocytochemistry with antibodies to enamel proteins and phosphoserine, combined with cycloheximide and brefeldin A to inhibit protein synthesis and secretion, were applied to characterize the distribution of newly formed proteins at enamel interrod and rod growth sites. Although enamel growth sites show a "rarefied" appearance, the results indicate that one or more subclasses of enamel proteins accumulate near the cell surface at sites where elongation of enamel crystallites contributes to thickening of the enamel layer. These proteins are glycosylated and/or phosphorylated and, at least in the case of the glycosylated ones, are rapidly processed after they are released extracellularly. In contrast, immunolabeling for amelogenins is generally weaker near the cell surface and more intense at a short distance away from the site where crystallites elongate. The data suggest that the enamel proteins accumulating at growth sites likely belong to the non-amelogenin category and play a transient role in promoting the lengthening of crystallites. It is concluded that areas near the ameloblast membrane where certain enamel proteins accumulate in fact constitute the equivalent of a mineralization front.
The Rat Amelogenin Gene-Some Aspects of Evolution and Expression
Authors: Bonass W.A. , Brookes S.J. , Kirkham J. , Shore R.C. , Robinson C.
Published: January 2009

This study presents data to support the hypothesis that a major portion of the coding sequence of the amelogenin gene may have arisen by tandem duplication of internal sequences which as a consequence has introduced several additional potential RNA splice acceptor sites into the sequence. This duplication of splice sites has led to an increase in the heterogeneity of amelogenin forms found in developing enamel. By screening a rat enamel organ cDNA library for alternatively spliced products, it appears that as much as 20% of the amelogenin mRNA molecules may be alternatively spliced forms.
Expression Patterns of RNAs for Amelin and Amelogenin in Developing Rat Molars and Incisors
Authors: Fong C.D. , Hammarström L. , Lundmark C. , Wurtz T. , Slaby I.
Published: January 2009

We have recently identified a novel RNA sequence in ameloblasts, coding for amelin (Cerny et al., 1996). In the present paper, its expression has been compared with that of amelogenin in developing incisors and molars of rats, by means of in situ hybridization of paraffin sections. The RNAs for both amelin and amelogenin were highly expressed in secretory ameloblasts. The expression of RNA for amelogenin gradually decreased in the post-secretory ameloblasts. In contrast, the RNA expression for amelin remained high in post-secretory ameloblasts up to the stage of fusion between dental and oral epithelia at the time of tooth eruption. We suggest that amelin might be involved in the mineralization of enamel or in the attachment of ameloblasts to the enamel surface. The whole-mount in situ hybridization procedure is described for the first time in dental research. It proved to be a useful method and confirmed the results of the conventional in situ hybridization.
Toward Understanding the Function of Amelogenin Using Transgenic Mice
Authors: Ibaraki-O'Connor K. , Nakata K. , Young M.F.
Published: January 2009

The purpose of this study was to establish transgenic mouse lines as a tool to investigate the function of amelogenin during mineralization by causing ectopic production of amelogenin and studying its effect. The mouse amelogenin (mAme) was cloned from a 16-day-old whole mouse embryo cDNA library and was determined to be "full-length" mouse amelogenin (with a complete coding region) by comparison with the mouse amelogenin reported previously by Snead et al. (1985) and Lau et al. (1992). The overexpression construct contained: (1) the rat osteocalcin (OC) promoter (1.8 kb); (2) the adenovirus splicing casettes, including introgenic (Int) sequence (0.3 kb); (3) the full-length mAme cDNA (0.8 kb); and (4) the polyadenylation signal sequence from the pSG5 mammalian expression vector. Both Southern blotting and polymerase chain-reaction (PCR) analyses were performed, by means of a specific probe and a pair of oligodeoxynucleotides to OclntmAme(A)+, respectively. The animals which showed transgene-positive in both analyses were further used to establish F1 animals. Heterozygocity was confirmed with F1 animals by PCR analysis of DNA from the F0 x FVB/N pups. Three independent transgenic F1 heterozygous lines (640t, 706t, and 708t) have now been established. The generation of F2 homozygous lines is under way. The heterozygous transgenic animals are currently being analyzed for alterations in the morphology and structure of various bone tissues.
Magnesium and Carbonate in Enamel and Synthetic Apatites
Authors: Legfros R.Z. , Sakae T. , Bautista C. , Retino M. , Legeros J.P.
Published: January 2009

This study aimed to: determine the Mg and C03 distribution in the outer (surface), middle, and inner (closest to the enamel-dentin junction, EDJ) layers of human enamel; and determine the factors affecting the incorporation of Mg into synthetic apatites and the consequence of such incorporation on the properties of the apatites. Results demonstrated that the concentrations of Mg, C03, and organic components increased from the surface to the inner layers close to the EDJ and a difference in crystallinity from the outer to the inner layers. Initial results indicated that the extent of dissolution of the inner layer enamel is greater than that in the outer or surface enamel. Results on synthetic apatites showed the following: (1) Limited Mg incorporation into apatite was dependent on solution [Mg/Ca] molar ratio, temperature, pH, and the presence of C03 or fluoride (F); (2) incorporation of Mg causes reduction in crystallinity and an increase in the extent of dissolution of the apatite: (3) the negative effect of Mg on the properties of apatites is synergistic to that of C03 and antagonistic to that of F; and (4) exposure to acid of Mg-containing apatites causes the dissolution of Mg-rich apatite and precipitation of Mg-poor apatite. The observed decrease in the [Mg/Ca] of enamel and synthetic apatites after acid exposure may explain the observed 'preferential loss' of Mg and C03 in the initial stages of caries.
Quantitative Immunocytochemistry of Ca2+-Mg2+ ATPase in Ameloblasts Associated With Enamel Secretion and Maturation in the Rat Incisor
Authors: Zaki A.E. , Hand A.R. , Mednieks M.I. , Eisenmann D.R. , Borke J.L.
Published: January 2009

Our previous studies revealed intense membrane-associated labeling for Ca2+-Mg2+ ATPase (Ca2+-pump) in secretory and maturation ameloblasts in the rat incisor, both by enzyme cytochemistry and by immunohistochemical techniques. The purpose of the present study was to map the distribution of Ca2+-pump protein at the cellular and subcellular levels by means of a Ca2+-pump-specific monoclonal antibody and electron microscopic immunogold cytochemistry. Tissue specimens were dissected from secretory, early, and late enamel maturation zones. We quantified results by comparing gold particle densities over ameloblast lateral and distal plasma membrane regions, supranuclear cytoplasm, regions of the ruffled borders, and nuclei. The highest concentration of gold particles was seen over the distal membranes of early-maturation ameloblasts relative to those in late-maturation and secretory stages. Cytoplasmic labeling was less than that of the distal and lateral membranes, and gold particles located over nuclei were considered to be due to non-specific binding. These results are consistent with our earlier findings and suggest a role for the plasma membrane Ca2+-pump in the regulation of calcium availability to mineralizing enamel.
Analysis of Gene Expression in Streptococcus Mutans in Biofilms in Vitro
Authors: Burne Robert A. , Chen Yi-Ywan M. , Penders Jana E.C.
Published: January 2009

The purpose of this study was to develop methods for the consistent production of biofilms of S. mutans containing reporter gene fusions, and to examine the expression of genes involved in sucrose metabolism in adherent populations of this organism. Three strains of S. mutans harboring reporter gene fusions to the gene promoter regions of the gtfBC genes, ftf, and scrA were grown in a Rototorque biofilm fermenter in a tryptone-yeast extract-sucrose medium. Quasi-steady-state levels of reporter gene activity were measured after the biofilms were grown for either 48 hrs or 7 days. Also, induction of gene expression by the addition of sucrose to biofilm cells was monitored. Reporter gene activity was measurable from all gene fusion strains. This study (i) establishes the feasibility of doing detailed molecular and physiologic studies on immobilized populations of S. mutans, (ii) demonstrates that the polysaccharide synthesis machinery of S. mutans is differentially expressed in biofilms, and (iii) opens the way for a more detailed analysis of the environmental signals and signal transduction pathways governing the regulation of gene expression by S. mutans cells that are immobilized on a solid surface.
Artificial Dental Plaque Biofilm Model Systems
Authors: Sissons C.H.
Published: January 2009

Difficulties with in vivo studies of natural plaque and its complex, heterogeneous structure have led to development of laboratory biofilm plaque model systems. Technologies for their culture are outlined, and the rationale, strengths, and relative uses of two complementary approaches to microbial models with a focus on plaque biodiversity are analyzed. Construction of synthetic consortia biofilms of major plaque species has established a variety of bacterial interactions important in plaque development. In particular, the 'Marsh' nine-species biofilm consortia systems are powerful quasi steady-state models which can be closely specified, modified, and analyzed. In the second approach, microcosm plaque biofilms are evolved in vitro from the natural oral microflora to the laboratory model most closely related to plaque in vivo. Functionally reproducible microcosm plaques are attainable with a biodiverse microbiota, heterogeneous structure, and pH behavior consistent with those of natural plaque. The resting pH can be controlled by urea supply. Their growth patterns, pH gradient formation, control of urease levels by environmental effectors, and plaque mineralization have been investigated. Microcosm biofilms may be the only useful in vitro systems where the identity of the microbes and processes involved is uncertain. Together, these two approaches begin to capture the complexity of plaque biofilm development, ecology, behavior, and pathology. They facilitate hypothesis testing across almost the whole range of plaque biology and the investigation of antiplaque procedures yielding accurate predictions of plaque behavior in vivo.
Methods for Microscopic Characterization of Oral Biofilms: Analysis of Colonization, Microstructure, and Molecular Transport Phenomena
Authors: Singleton S. , Treloar R. , Warren P. , Watson G.K. , Hodgson R. , Allison C.
Published: January 2009

Assessment of the role of biofilm microstructure in biofilm-specific activities requires non-destructive measurement techniques for parameterization of structural characteristics in parallel with relevant biochemical and physiological data. This paper briefly reviews some current methods for biofilm structural analysis, with emphasis on new developments in optical imaging and mathematical modeling methods. Fluorescence imaging studies of bacterial colonization events occurring on exposed model tooth surfaces indicated that bacterial adhesion to sessile organisms was of central importance to the early colonization process and that this occurred in a non-random manner. Structural studies of mature biofilms by confocal microscopy demonstrated the spatial distribution of individual species using fluorescent antibodies. Biofilms grown under different physiological conditions exhibited differences in structure, and methods were developed for parameterizing the spatial orientations of the bacteria. Diffusive processes within biofilm microstructures were studied using a random walk model in both 2-D and 3-D. Modeling of convective flow within biofilm microstructures was achieved by application of lattice Boltzmann methodology.
Biofilm Susceptibility to Antimicrobials
Authors: Gilbert P. , Das J. , Foley I.
Published: January 2009

Microbial biofilms, where organisms are intimately associated with each other and a solid substratum through binding and inclusion within an exopolymer matrix, are widely distributed in nature and disease. In the mouth, multispecies biofilms are associated not only with dental plaque and tooth decay but also with soft tissues of the buccal cavity and with most forms of periodontal disease. Organization of micro-organisms within biofilms confers, on the component species, properties which are not evident with the individual species grown independently or as planktonic populations in liquid media. While many of these properties relate to the establishment of functional, mixed-species consortia within the exopolymeric matrices, others relate to the establishment of physico-chemical gradients, within the biofilm, that modify the metabolism of the component cells. A consequence of biofilm growth that has profound implications for their control in the environment and in medicine is a markedly enhanced resistance to chemical antimicrobial agents and antibiotics. Mechanisms associated with such resistance in biofilms will form the substance of the present review. While some aspects of biofilm resistance are yet only poorly understood, the dominant mechanisms are thought to be related to: (i) modified nutrient environments and suppression of growth rate within the biofilm; (ii) direct interactions between the exopolymer matrices, and their constituents, and antimicrobials, affecting diffusion and availability; and (iii) the development of biofilm/attachmentspecific phenotypes.
Specific Inhibitors of Bacterial Adhesion: Observations From the Study of Gram-Positive Bacteria that Initiate Biofilm Formation on the Tooth Surface
Authors: Cisar J.O. , Takahashi Y. , Ruhl S. , Donkersloot J.A. , Sandberg A.L.
Published: January 2009

Oral surfaces are bathed in secretory antibodies and other salivary macromolecules that are potential inhibitors of specific microbial adhesion. Indigenous Gram-positive bacteria that colonize teeth, including viridans streptococci and actinomyces, may avoid inhibition of adhesion by host secretory molecules through various strategies that involve the structural design and binding properties of bacterial adhesins and receptors. Further studies to define the interactions of these molecules within the host environment may suggest novel approaches for the control of oral biofilm formation.
In Vitro Models That Support Adhesion Specificity in Biofilms of Oral Bacteria
Authors: Ellen R.P. , Lépine G. , Nghiem P.-M.
Published: January 2009

Adhesion to adsorbed pellicles and interspecies co-adhesion to form plaque biofilms involve selective interactions of bacterial adhesins with specific receptors. Our laboratory has devised in vitro assays for co-adhesion between Actinomyces naeslundii and Streptococcus oralis or Porphyromonas gingivalis on saliva-coated mineral and hexadecane droplet substrata. P. gingivalis structures significant for co-adhesion with A. naeslundii include surface vesicles and fimbriae. A family of arginine-specific cysteine proteinases in vesicles may be involved in adherence to bacteria, to host cells, and to matrix proteins. New research from several laboratories has found that such proteinases are processed from genes encoding polyproteins containing both proteinase and hemagglutinin domains. In addition to enzyme-substrate recognition, bacterial adhesion is often determined by specific protein-peptide and lectin-carbohydrate recognition. A. naeslundii - salivary proline-rich protein, S. gordonii - salivary a-amylase, and Treponema denticola - matrix protein recognition are examples of the former. Co-adhesion of A. naeslundii and S. oralis is an example of the latter. Lactose can selectively desorb A. naeslundii cells from mixed biofilms with S. oralis, a demonstration of the significance of specificity. Although non-specific forces are probably secondary to stereochemical fit in determining the selective range of surfaces that bacteria have evolved to recognize and bind, they probably help stabilize non-covalent bonds within aligned, complementary domains.
Bacterial Attachment To Uro-Epithelial Cells: Mechanisms and Consequences
Authors: Connell Hugh , Hedlund Maria , Agace William , Svanborg Catharina
Published: January 2009

Microbial attachment to mucosal surfaces is a first step in mucosal infection. Specific interactions between microbial surface ligands and host receptors influence the distribution of microbes in their sites of infection. Adhesion has often been regarded as a sufficient end point, explaining tissue tropism and bacterial persistence at mucosal sites. Adherence, however, is also a virulence factor through which microbes gain access to host tissues, upset the integrity of the mucosal barrier, and cause disease. The induction of mucosal inflammation is one aspect of this process. Bacterial attachment to mucosal surfaces activates the production of pro-inflammatory cytokines that cause both local and systemic inflammation. Epithelial cells are one source of these cytokines. The binding of fimbrial lectins to epithelial cell receptors triggers transmembrane signaling events that upregulate cytokine-specific mRNA and increase cytokine secretion. P fimbriae that bind the globoseries of glycolipids cause the release of ceramides and activation of the ceramide signaling pathway which contributes to the IL-6 response. Spread of cytokines and other pro-inflammatory mediators from the local site contributes to the symptoms and signs of infection.
Bacterial Metabolism in Dental Biofilms
Authors: Carlsson J.
Published: January 2009

Dental biofilms could have a structure which, in sections, looks like tissue. The internal structure of the dental biofilm could be the result of interbacterial adhesion mechanisms in combination with nutritional conditions characterized by multiple nutrient starvation. The preservation of the structure of the biofilm over time may also involve the ability of the bacteria to withstand environmental stresses such as starvation, reactive oxygen products, and acid. The present review will describe, first, the regulation of the metabolic defense against environmental stresses and then focus mainly on the energy metabolism of dental biofilms.
Nutritional Influences on Biofilm Development
Authors: Bowden G.H.W. , Li Y.H.
Published: January 2009

The amounts and types of nutrients in the environment influence the development and final bacterial and chemical composition of biofilms. In oligotrophic environments, organisms respond to nutrient stress by alterations in their cell morphology and cell surfaces, which enhance adherence. Little is known of the responses to stress by bacteria in the animal oral cavity. The environment in the oral cavity is less extreme, and saliva provides a constant source of nutrients. Catabolic cooperation among oral bacteria allows carbon and nitrogen from salivary glycoproteins to be utilized. Modification of growth environments of oral bacteria can influence their cell surfaces and adhesion. Studies in experimental animals have shown that feeding either glucose or sucrose diets or fasting has little effect on the initial stages of development of oral biofilms. However, diet can influence the proportions of different bacterial species later in biofilm development. Studies of competition among populations in communities of oral bacteria in vitro and in vivo have shown the significance of carbon limitation and excess and changes in environmental pH. Relatively few studies have been made of the role of a nitrogen metabolism in bacterial competition in biofilms. In keeping with biofilms in nature, oral biofilms provide a sequestered habitat, where organisms are protected from removal by saliva and where interactions among cells generate a biofilm environment, distinct from that of saliva. Oral biofilms are an essential component in the etiologies of caries and periodontal disease, and understanding the biology of oral biofilms has aided and will continue to aid in the prevention and treatment of these diseases.
Ethnicity, Aging, and Oral Health Outcomes: A Conceptual Framework
Authors: Andersen R.M. , Davidson P.L.
Published: January 2009

An expanded version of Andersen's Behavioral Model of Health Services Utilization is used as the theoretical and analytical framework for the International Collaborative Study of Oral Health Outcomes (ICS-II). The conceptual framework for understanding determinants of oral health is based on a "systems" perspective. The framework posits that characteristics of the external environment, the dental care delivery system, and the personal characteristics of the population influence oral health behaviors. The expanded behavioral model conceptualizes health behaviors (oral hygiene practices and dental services utilization) as intermediate dependent variables, which in turn influence oral health outcomes (evaluated, perceived, patient satisfaction). The framework is presented with an increased focus on the effects of race-ethnicity and age cohort, the major exogenous variables used in this study for systematic assessment of the differences in the multitude of factors influencing oral health. The framework can be applied by policy analysts and health services managers to help describe, predict, and explain population-based health behaviors and health outcomes.
Oral Health Policy and Programmatic Implications: Lessons From ICS-II
Authors: Andersen R.M. , Davidson P.L. , Nakazono T.T.
Published: January 2009

The conceptual model used in the ICS-II USA Ethnicity and Aging project helps to identify who among the elderly should be targeted for oral health promotion initiatives and the kinds of initiatives most likely to promote positive oral health outcomes. Outcomes have been measured in this study as perceived by the individual and as clinically assessed by the oral epidemiologists. For policy purposes, achieving both types of outcomes is important. A typology of oral health promotion priorities is used to rank the diverse racial-ethnic groups. In the analysis, groups with both low perceived and low evaluated oral health status receive highest priority. By these criteria, the older Native American populations have the highest priority, followed, in order, by Hispanics. African-Americans, and non-Hispanic Whites. Policy implications of the empirical analyses presented in earlier articles are discussed by use of the conceptual model and the typology of oral health promotion priorities. Having a usual source of care and/or regular dental visits appears to be a promising avenue for the promotion of better-perceived oral health status among most older ethnic groups. Improved oral hygiene practices, as represented by both regular toothbrushing and dental floss use, promote better clinically evaluated oral health status among many older ethnic groups.