bluuebunny/crossref_metadata_2025 huggingface dataset:
Incidence and Characterization of Staphylococcus aureus from the Tongues of Children
Authors: Miyake Y. , Iwai T. , Sugai M. , Miura K. , Suginaka H. , Nagasaka N.
Published: November 2010

Three hundred and seven children who had no diseases other than dental disease were examined for their oral carriage of Staphylococcus aureus, the most common persistent human pathogen. Eighty-four percent of them were positive for staphylococci, and 33% were positive for S. aureus. Among the 100 strains of S. aureus isolated, 40 strains produced enterotoxin, and 19 strains produced exfoliative toxin. Their susceptibility to antibiotics was also investigated: Six strains demonstrated resistance to methicillin (MIC ≥ 12.5 μg/mL), and 50% of the isolates were borderline resistant (MIC of 3.13 to 6.25 μg/mL) to the drug. These data suggest that the mouths of children could be reservoirs of pathogenic S. aureus.
Development of Low- and High-serum Culture Conditions for Use of Human Oral Fibroblasts in Toxicity Testing of Dental Materials
Authors: Liu Y. , Arvidson K. , Atzori L. , Sundqvist K. , Silva B. , Cotgreave I. , Grafström R.C.
Published: November 2010

With the aim of establishing conditions applicable to the testing of dental materials in human target cells, fibroblastic cell lines have been derived and grown from explants of human oral mucosa. Both a high-serum medium (termed "HSM") (CMRL 1066 supplemented with 10% fetal bovine serum) and a low-serum medium (termed "LSM") (a 1:1 mixture of M 199:MCDB 153 supplemented with 1.25% serum) supported radial outgrowths of cells from oral explants, as well as the subsequent transfer and growth of the cells in mass culture and at clonal density. Cells were typically fibroblastic in that they expressed vimentin uniformly, but did not express immunocytochemical markers of epithelial or endothelial cells. Cells derived in either LSM or HSM showed significantly higher colony-forming efficiency and clonal growth rate when transferred in LSM, as compared with HSM. Because cell migration occurred to a lesser extent in LSM, microscopic scoring of colony formation was also markedly facilitated. In both LSM and HSM, cellular low-molecular-weight thiols constituted about 30% of the total amount of sulfhydryls. Glutathione was present in about six- to seven-fold-higher amounts than cysteine-glutathione primarily in its reduced form and cysteine primarily in its oxidized form. A corrosion product of dental amalgam, i.e., Hg2+, decreased cell survival measured as colony-forming efficiency in a dose-dependent manner following either an acute (one h) exposure or continuous exposure (seven days). These studies demonstrated that human oral fibroblasts could be cultured at about one-tenth of the serum content that is commonly used. It is concluded that human oral fibroblasts grown at low-serum conditions provide a highly sensitive and easily applicable in vitro model for toxicity studies of dental materials.
Masseter Muscle Thickness Measured by Ultrasonography and its Relation to Facial Morphology
Authors: Kiliaridis S. , Kälebo P.
Published: November 2010

The aims of this study were to evaluate ultrasonography as a method for measuring masseter muscle thickness, to quantitate the normal range of the ultrasonically measured thickness of the masseter in adults, and to test whether the variation in the thickness of the muscle is related to the variation in the facial morphology in different individuals. In 40 healthy, fully-dentate young adults, 20 men and 20 women, the masseter thickness was measured bilaterally by a real-time ultrasound imaging technique. The measurements were performed under both relaxed conditions and with maximal clenching. Standardized facial photos of the subjects were taken so that their facial morphology could be determined. The measurement error of the thickness of the masseter was found to be small, not exceeding 0.49 mm. Under relaxed conditions, the mean thickness (± S.D.) of the muscle in men was 9.7 (± 1.5) mm, and under contracted conditions, 15.1 ( ± 1.9) mm. In women, the respective measurements were 8.7 (± 1.6) mm and 13.0 (± 1.8) mm. The thickness of the masseter muscle was found to be related to the facial morphology, mainly in women, but not in men; the women with a thin masseter had a proportionally longer face. Ultrasonography was found to be a reliable and accurate method for study of the thickness of the masseter muscle. There was a large variation in the thickness of the muscle between individuals, and the thickness of the masseter was related to facial morphology in women.
Bonding Efficacy of Erythritol Methacrylate Solutions as Dentin Primers
Authors: Manabe A. , Katsuno K. , Itoh K. , Wakumoto S. , Miyasaka T.
Published: November 2010

The bonding efficacy of aqueous solutions of two kinds of erythritol methacrylates as dentin primers was examined by measurement of the polymerization contraction gap of a light-activated resin composite in a cylindrical dentin cavity and the tensile bond strength of the composite to the flat dentin surface. The dentin surface was cleaned with neutralized 0.5 mol/L EDTA and pre-treated with a meso-erythritol or penta-erythritol methacrylate solution, followed by application of a commercial dentin bonding agent (Clearfil New Bond) and a resin composite. Among the tested primers, a 40% meso-erythritol methacrylate solution was shown to be the most effective because, in contrast to the other primers, contraction gap formation by the composite was prevented in all tested specimens.
The Surface Roughness of Enamel-to-Enamel Contact Areas Compared with the Intrinsic Roughness of Dental Resin Composites
Authors: Willems G. , Lambrechts P. , Braem M. , Vuylsteke-Wauters M. , Vanherle G.
Published: November 2010

The purpose of this study was to determine the surface roughness of enamel-to-enamel contact areas in order to provide a standard for comparison with surface characteristics of commercially available composite restorative materials. In addition, the inherent surface roughness of resin composites was evaluated profilometrically after a toothbrush abrasion procedure. A one-sided t-test analysis was performed to outline significant differences between the surface roughness value of enamel facets and that of the respective composite samples. A surface roughness of 0.64 ± 0.25 μm (mean ± S.D.) was found for the enamel-to-enamel contact areas.
Physical Properties of Stainless-steel and Silver-reinforced Glass-ionomer Cements
Authors: Kerby R.E. , Bleiholder R.F.
Published: November 2010

The purpose of this study was to compare specific physical properties of an experimental stainless-steel-reinforced glass-ionomer cement with those of two commercially available silver-reinforced cements. Properties evaluated were compressive and diametral tensile strengths (one and 24 h), percent solubility in 0.01 mol/L lactic acid over 23 h, and working and setting times. Cylindrical specimens 6 mm (diameter) x 12 mm were prepared and maintained in distilled water at 37 ±2°C and then tested on an MTS mechanical testing machine with a cross-head displacement rate of 0.5 mm/min for the diametral tensile strength test and 1.0 mm/min for the compressive strength test. ANOVA and Tukey's Studentized Multiple Range Test indicated significant differences between the experimental and commercially available cements for both compressive and tensile strengths at one and 24 h (p<0.01). The experimental stainless-steel-reinforced cement appeared to be significantly stronger in both tensile and compressive strengths than either of the commercially available cements. Working and setting times-as well as acid solubility of the experimental cement-also compared favorably with those of the commercial cements. Results suggest that the stainless-steel-reinforced glass-ionomer cement possesses strength properties that should lead to a stronger, more fracture-resistant restorative filling material when compared with those presently available.
Clinical Trial in Adults of an Antimicrobial Varnish for Reducing Mutans Streptococci
Authors: Sandham H.J. , Brown J. , Chan K.H. , Phillips H.I. , Burgess R.C. , Stokl A.J.
Published: November 2010

An abbreviated treatment with a chlorhexidine-containing varnish was compared with a similar treatment with a placebo varnish and with a prophylaxis alone for its effects on the numbers of detectable salivary mutans streptococci in 51 adults. The varnishes, applied once weekly for four weeks, were held in place with a covering layer of either of two polyurethane sealants (FluorProtectorR or Adhesit R). On the first appointment, the varnish-sealant combination was applied to all tooth surfaces, but on succeeding appointments only the occlusal and approximal surfaces were covered. The chlorhexidine varnish, covered with either sealant, reduced the salivary mutans streptococci by an average of 3 logs (99.9%) in all of the 20 subjects treated, and below detectable levels for at least four weeks in nine of them. In the groups receiving placebo varnish-sealant combinations, the mean log number of mutans streptococci of the subjects was reduced only by approximately 0.5 log (32%), and none of the subjects experienced loss of their detectable mutans streptococci for four weeks, although one subject did so for three weeks. No significant difference between the effects of the two polyurethane sealants was observed. Treatment with a single prophylaxis had no effect on mutans streptococcus levels. Subjects treated with chlorhexidine varnish also experienced an increase in S. sanguis and a small decrease in yeasts. Loss of detectable mutans streptococci did not cause changes in the numbers of other micro-organisms examined, beyond those observed with chlorhexidine varnish treatment alone.
Electromyographic-force Characteristics in the Assessment of Oral Function
Authors: Lindauer S.J. , Gay T. , Rendell J.
Published: November 2010

The purpose of this investigation was to examine the utility of EMG-force characteristics as reliable and valid parameters by which to assess oral function. Masseter-muscle activity was recorded during controlled isometric biting exercises performed at various bite openings and force levels on two separate occasions. Measured muscle-activity levels, as well as the EMG-force characteristics of slope and y-intercept, were compared between bite openings and experimental trials. Sensitivity, assessed as the ability to detect statistically significant differences in muscle function due to changes in muscle length, was found to be acceptable for all measurements, except the y-intercept parameter, and during production of minimal forces. Reproducibility, evaluated as the correspondence between values recorded at different experimental sessions, was best for the EMG-force parameter of slope and during production of higher forces. The results from this study support the following conclusions : (1) Substantial variations in muscle function exist between individuals; (2) acceptable reliability and sensitivity of quantitative EMG values can be achieved, especially at higher muscle-activity levels, by rigidly controlling and quantifying functional activities during experimental trials; (3) the slope of an EMG-force curve is a reproducible, quantitative, and functionally sensitive measurement for assessment of muscle function; and (4) the EMG-force y-intercept is not a reliable quantity by which muscle-function characteristics may be studied.
Cytotoxic Effects of Resin Components on Cultured Mammalian Fibroblasts
Authors: Hanks C.T. , Strawn S.E. , Watahai J.C. , Craig R.G.
Published: November 2010

The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 μmol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 μmol/L, while the ID 50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 μmol/L. The concentrations to which the cells and tissues are exposed in uiuo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.
Changes in Acid-phosphate Content in Enamel Mineral during Porcine Amelogenesis
Authors: Shimoda S. , Aoba T. , Moreno E.C.
Published: November 2010

The present study was undertaken to investigate changes in the acid-phosphate content of porcine enamel mineral during its development and to assess separately the HPO42- pools in labile and stable forms. Enamel samples at the secretory and maturing stages of amelogenesis were obtained from the permanent incisors of five- to six-month-old slaughtered piglets. Human enamel from erupted, extracted teeth, synthetic hydroxyapatite, and carbonatoapatite containing acid phosphate were included as references. The acid-phosphate content of each sample was determined chemically through its pyrolytic conversion to pyrophosphate. The assessment of HPO42- in labile forms was made by analysis of samples pre-equilibrated with solutions containing 3 mmol/L phosphate at pH 11 1 (to de-protonate the HPO42- species on crystal surfaces). The analytical results of porcine enamel samples showed that: (a) the outermost secretory (youngest) enamel contained the highest HPO42-, corresponding to about 16% of the total phosphate; (b) the acid-phosphate content decreased gradually to 10% in the inner (older) secretory and to 6% in the maturing tissue; (c) a substantial part of the HPO42- in developing enamel tissue (50-60% of the HPO42- for the secretory enamel) was in labile forms; and (d) the pool of the labile HPO42- decreased with the growth of enamel mineral. In parallel studies with mature human enamel, it was ascertained that the total acid phosphate was only about 3% of the total phosphate, much lower than in developing porcine enamel, and that the labile pool of HPO42- was also small, corresponding to about 15% of the total acid phosphate determined. The overall results indicate that acid phosphate is one of the major constituents of the early enamel crystals formed during amelogenesis and that the surfaces of the growing enamel crystallites are rich in HPO42-.
The Elastic Modulus of the Temporomandibular Joint Disc from Adult Dogs
Authors: Tanne K. , Tanaka E. , Sakuda M.
Published: November 2010

The present study was designed to measure the elastic properties of temporomandibular joint (TMJ) discs from six adult dogs. Each disc was divided mediolaterally into medial, middle, and lateral parts. Under tension, the articular disc exhibited a non-linear stress-strain relationship, which could be represented as two lines (two moduli of elasticity) connected at a point of stress around 1.5 MPa. These two elastic moduli of the disc were approximately 44 MPa and 92 MPa in the lower- and higher-_stress regions, respectively. Elastic moduli of the articular disc in the middle area were significantly different from that in the lateral area of the disc. The reaction to external force appeared to be different in the medial, middle, and lateral regions of the disc.
The Effect of Local Application of 1,25-Dihydroxycholecalciferol on Osteoclast Numbers in Orthodontically Treated Rats
Authors: Takano-Yamamoto T. , Kawakami M. , Kobayashi Y. , Yamashiro T. , Sakuda M.
Published: November 2010

Orthodontic tooth movement requires remodeling of periodontal tissues, especially alveolar bone. 1,25-(OH)2D3, the active form of vitamin D 3, is known to be a potent stimulator of osteoclastic bone resorption. The purpose of this study was to investigate the effect of local application of 1,25-(OH)2D3 on osteoclast numbers induced by experimental tooth movement. A piece of orthodontic elastic band was inserted between the first and second upper molars of male Wistar rats weighing about 200 g each. Twenty μL of 1,25-(OH)2D3 (10-12-10 -7 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). The number of osteoclasts was counted in a 700 x 1050 μm2 area of the interradicular septum. The local injection of 1,25-(OH)2D3 caused a dose-dependent increase in osteoclast number. The effect of 1,25-(OH)2D3 reached a response plateau at 10-10 mol/L when greater than a threefold rise in osteoclast number was attained compared with the PBStreated controls. While the insertion of a piece of elastic band for three days induced a significant increase in osteoclasts in the alveolar bone, daily injections of 20 μL of 10-10 mol/M 1,25-(OH)2D 3 for three days markedly stimulated the numbers of osteoclasts induced by the insertion of an elastic band. 1,25-(OH)2D3 was apparently synergistic with mechanical stimuli, resulting in enhancement of the numbers of osteoclasts induced by mechanical stimuli alone. These findings suggest that the local application of 1,25-(OH)2D 3 acted directly to increase osteoclast number and to potentiate osteoclastic bone resorption induced by mechanical stimuli.
Factors Affecting Blood Mercury Concentrations in Practicing Dentists
Authors: Chang S.-B. , Siew C. , Gruninger S.E.
Published: November 2010

It has been suggested that mercury vapor may be transformed into highly toxic organomercury compounds by micro-organisms in the oral cavity and gastrointestinal tract. If this hypothesis is correct, practicing dentists might be expected to have concentrations of organic mercury in their blood higher than that found in non-dentists. Blood mercury concentrations of practicing dentists and non-dentists were determined by means of cold-vapor atomic absorption spectrophotometry. Potential sources of mercury exposure were identified in both dentists and non-dentists through a questionnaire completed at the time of sampling. Concentrations of total and inorganic blood mercury were significantly higher in dentists than in non-dentists. The organomercury concentrations of the two groups were not statistically different (p ≥0.05). The high concentration of inorganic mercury in the blood of dentists was not related to the organomercury level, suggesting that biotransformation of inorganic mercury to organomercury does not occur in vivo. However, the concentration of blood organomercury was positively correlated with the frequency of fish consumption. There was no correlation between the number of amalgam restorations and the concentration of inorganic blood mercury for both groups. Accidental mercury spills in the dental operatory may contribute most to the concentration of inorganic blood mercury in the blood of dentists.
Neutrophil Elastase and its Inhibitors in Human Gingival Crevicular Fluid during Experimental Gingivitis
Authors: Giannopoulou C. , Andersen E. , Demeurisse C. , Cimasoni G.
Published: November 2010

The relative concentrations and absolute amounts of neutrophil elastase and its two inhibitors, α2-macroglobulin (α2-M) and alantitrypsin (α1-AT), were determined in gingival crevicular fluid (GCF) collected from six dental students who refrained from brushing the upper left or right quadrant during three weeks. Plaque and gingival indices and flow of GCF were measured before, during, and after the three weeks of no brushing. Functional elastase, representing the enzyme complexed with a2-M, was measured by use of a low-molecular-weight fluorogenic substrate. Elastolytic activity in GCF was also assayed by use of elastin as substrate. Antigenic elastase, representing the enzyme complexed with a 1-AT, as well as the inhibitors a2-M and al-AT were measured by ELISA. After three weeks of plaque accumulation, the concentrations of both functional and antigenic elastase increased by a factor of about 3, whereas the concentrations of the inhibitors increased in a much higher proportion. No free elastase could be detected in GCF, as evidenced by the Sephadex G-75 elution profile of GCF, by the negative results obtained when elastin was used as substrate, and by the demonstration that pure enzyme kept its activity against the low-molecular-weight substrate after being saturated by a2-M.
Immunohistochemical Localization of Types I, V, and VI Collagen in Human Permanent Teeth and Periodontal Ligament
Authors: Lukinmaa P.-L. , Waltimo J.
Published: November 2010

Types I, V, and VI collagen were immunohistochemically localized in frozen and paraffin sections of human permanent teeth, periodontal ligament, and alveolar bone, by means of polyclonal antibodies. Hyaluronidase was effective in exposing epitopes of the various collagen types.

The expression of type I collagen in predentin was strong in frozen sections, whereas the dental pulp stained relatively weakly. Staining intensity in the dentin matrix decreased toward enamel and cementum. Reactivity in the periodontal ligament was moderate, and it was weaker in the alveolar bone and also in cementum, which stained more intensely in paraffin sections. Staining for type V collagen was strong in the pulp. Weak reactivity in predentin became uniformly evident in frozen sections only, and dentin was negative. The periodontal ligament stained with moderate intensity, and a weak staining reaction was seen in cementum and bone. Staining for type VI collagen in the pulp and periodontal ligament was strong, whereas predentin and dentin were negative. The alveolar bone stained moderately, and non-uniform reactivity was present in cementum.

In non-mineralized dental tissues, the use of frozen material enabled good immunohistochemical localization of the distinct collagen types to be carried out. Their distribution patterns in dental tissues not only differed, but the relative staining intensities for each collagen type in the pulp and predentin were inversely related. However, differences may exist in the exposure of the epitopes of collagen(s) between soft and mineralized tissues.
Evaluation of Smear Layers on Serial Sections of Human Dentin by Means of Electrochemical Impedance Measurements
Authors: Levinkind M. , Vandernoot T.J. , Elliott J.C.
Published: November 2010

The alternating current impedance characteristics of a uni-directional porous glass membrane and serial sections of dentin from unerupted human third permanent molars (with and without smear layers) were measured. The membrane was equilibrated at 20 ± 1°C in a range of concentrations of unbuffered KCI, and the tooth sections were equilibrated in 0.1 mmol/L unbuffered KCI. Each section's impedance was measured for a 50-mV (rms) alternating potential difference applied over 1 Hz to 65 kHz. By means of complex non-linear least-squares regression analysis, the dc resistance of each specimen was determined. Scanning electron microscopy and subsequent image analysis enabled the cross-sectional area of the pores in the membrane and dentin tubule surface-openings to be measured. The results showed that the measured cross-sectional area of pores in the membrane was in good agreement with that calculated from the measured dc resistance and solution resistivity over the range of electrolyte concentrations. In dentin, the presence of smear layers on the cut surfaces increased the measured resistance. The resistance of the smear layer varied, suggesting that its thickness changed across the surface of the dentin. This was superimposed on regional variations in resistance of smear-free dentin which were found to be related to alterations in the number of tubules present and their cross-sectional area. The resistivities of the dentin tubule contents and smear layer material were generally lower than that of the hydrating electrolyte. It is postulated that this could be due to ions from partial dissolution of the mineral in the dentin.
Measurement of Water Sorption by Resin Composite Adhesives with Near-Infrared Spectroscopy
Authors: Diaz-Arnold A.M. , Arnold M.A. , Williams V.D.
Published: November 2010

Spectroscopic methodology was used to follow the water uptake of disks of two resin composite luting agents during long-term storage. Fourier-transform near-infrared (FT-NIR) spectroscopy was used for collection of spectra over the 4200-6500 cm -1 spectral region. The 5200-cm-1 absorption band of water was monitored initially, at 24 h, seven days, two weeks, and then monthly over a period of 12 months. The disks were stored in water, air, and desiccated conditions. Disks were also subjected to two alternate cycles (two weeks each) of hydration and desiccation. A spectral manipulation program was used for quantitation of the area under the water absorbance band.

Area ratios demonstrated similar water-uptake patterns for the two adhesives. Rapid water uptake was seen within the first two weeks of storage. Alternate hydration and desiccation of the samples showed that water uptake by the filler/polymer network was partially reversible. The desiccant was unable to remove all the water from the samples, which indicated that some water was tightly held within the sample matrix. FT-NIR spectroscopy is recommended as an effective method for study of the equilibration of resin composites in water.
In vivo Fluoride Concentrations Measured for Two Hours After a NaF or a Novel Two-solution Rinse
Authors: Vogel G.L. , Mao Y. , Carey C.M. , Chow L.C. , Takagi S.
Published: November 2010

The concentrations of fluoride in various samples from the oral environment were measured at timed intervals after a novel rinse or a NaF rinse, both containing a total of 12 mmol/L (228 ppm) fluoride. The novel rinse consisted of two solutions mixed just before application: Part A contained calcium chloride and sodium acetate; part B contained a hydrolyzable source of fluoride (sodium hexafluorosilicate) and sodium phosphate. Samples were obtained as follows: Single-site plaque-fluid samples were obtained by centrifugation of first-molar plaque; pooled whole-plaque samples were collected from second molars; centrifuged, pooled whole-saliva was collected by vacuum. All samples were analyzed by micro-analytical methods. Results showed that, compared with NaF, the two-solution rinse produced significantly higher salivary fluoride concentrations, plaque-fluid fluoride concentrations, and acid-extractable fluoride in the whole plaque by factors of about 4, 2, and 6, respectively, at 120 min. The results of this study suggest that the new rinse may provide a greater cariostatic effect at the same fluoride dosage than does a NaF rinse.
Silica-induced Precipitation of Calcium Phosphate in the Presence of Inhibitors of Hydroxyapatite Formation
Authors: Damen J.J.M. , Ten Cate J.M.
Published: November 2010

The promotion and the inhibition of hydroxyapatite formation by various substances were determined by measurement of the induction time of spontaneous precipitation (t) from supersaturated solutions. Silica was found to decrease t. in Hepes-buffered (pH 7.2) supersaturated solutions with a wide range of calcium-to-phosphate ratios and concentrations. Also, in suspensions of the oral bacteria S. mutans or C. matruchotii in 1 mmol/L calcium, 7.5 mmol/ L phosphate, and 50 mmol/L Hepes (pH 7.2), silica was capable of stimulating precipitation. Macromolecules derived from these bacteria by freezing and thawing appeared to be strong inhibitors of calcium phosphate precipitation. In the presence of silica, the effects of these bacterial inhibitors could be partially overcome, which supports the idea that silica in dental plaque is a promoter of calculus formation. In contrast, inhibition of calcium phosphate precipitation by a low-molecular-weight inhibitor, pyrophosphate, could not be counteracted by silica.
A Computer Simulation of the Influence of Selection and Breakage of Food on the Chewing Efficiency of Human Mastication
Authors: Van Der Bilt A. , Van Der Glas H.W. , Bosman F.
Published: November 2010

The reduction of food particle sizes during mastication is considered to be the composite result of a selection and breakage process. The chance of a food particle being selected between the teeth was assumed to increase as a power function of the particle's size, whereas the breakage of food particles was described by a cumulative distribution function. The selection and breakage functions were combined with matrix algebra, resulting in a matrix model. By use of this model, particle-size distributions could be calculated after various numbers of chewing cycles. From these distributions, the decrease of the median particle size was determined as a function of the number of chewing cycles. The calculations were performed for various sets of physiologically relevant selection and breakage variables. The number of chewing cycles, N1/2, needed for the initial particle size to be halved was taken as an indication of chewing efficiency. This number varied approximately inversely with both the selection coefficient and the breakage variable. The initial particle size appeared to have the largest influence on N1/2. The theoretical results from the simulation study were also compared with data obtained from experiments on human chewing efficiency.
Adhesion of Mutans Streptococci to Glass With and Without a Salivary Coating as Studied in a Parallel-plate Flow Chamber
Authors: Busscher H.J. , Doornbusch G.I. , Van Der Mei H.C.
Published: November 2010

Deposition and adhesion to glass with and without a salivary coating in a parallel-plate flow chamber were studied with four strains of mutans streptococci. Stationary-state adhesion of the strains to uncoated glass ranged from 0.3 x 106 cm-2 (Streptococcus rattus HG218) to 12.7 x 106 cm-2 (Streptococcus sobrinus HG1025) and generally decreased after saliva coating of the glass. The poor adhesion found for S. rattus HG218 to both uncoated and saliva-coated glass could be due to its relatively high negative surface-charge. Deposition efficiencies of all strains were ≥ 1 for uncoated glass and decreased greatly after saliva coating of the glass. Possibly, adhesion to a saliva coating is less efficient and more time-consuming than that to uncoated glass, because stereochemical groups in the pellicle and on the cell surfaces may have to re-arrange before an effective interaction can occur. Desorption rates, measured 1000 s and 5000 s after the start of an experiment, decreased by a factor often upon a five-fold increase in contact time, indicative of a two-phase adhesion process. Of the four strains studied, only Streptococcus cricetus HG737 showed a minor positive cooperativity on saliva-coated glass, possibly mediated by surface appendages observed by transmission electron microscopy on negatively-stained cells. Retention of adhering bacteria was strain-dependent on uncoated glass, but was identical for all strains on saliva-coated glass, which suggests that the structure and composition of the pellicle may be more important with respect to the retention of adhering cells than the cell-surface properties themselves.
Fatigue Behavior of Direct Post-and-core-restored Premolars
Authors: Huysmans M.C.D.N.J.M. , Van Der Varst P.G.T. , Schäfer R. , Peters M.C.R.B. , Plasschaert A.J.M. , Soltesz U.
Published: November 2010

Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 104, 105, and 106 cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10 4, 105, and 106 cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 106 cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.
The Effects of Sucralose, Xylitol, and Sorbitol on Remineralization of Caries Lesions in Rats
Authors: Bowen W.H. , Pearson S.K.
Published: November 2010

The purpose of this study was to determine whether ingestion of sucralose, xylitol, sorbitol, or distilled water alone could enhance remineralization of early caries lesions in rats. Rats were infected by Streptococcus sobrinus, fed diet 2000 (Ziegler Brothers, Gardners, PA) ad libitum for two weeks, and, in addition, were offered drinking water sweetened by sucrose (10% w/v). A group of rats terminated at this time displayed significant levels of sulcal and smooth-surface caries. The remaining animals, for the ensuing three weeks, either continued on the same cariogenic challenge or received their essential nutrition by gavage and drank water, sweetened by one of the agents listed above, ad libitum. At the end of the additional three-week period, animals receiving sucralose, xylitol, sorbitol, or distilled water had fewer lesions than did the animals terminated after the two-week cariogenic challenge. The results show that removal of the cariogenic challenge allowed remineralization to occur and that no sweetening agent was superior to another in this respect.
An Immunohistochemical Study of the Distribution of Immunocompetent Cells, Especially Macrophages and Ia Antigen-expressing Cells of Heterogeneous Populations, in Normal Rat Molar Pulp
Authors: Okiji T. , Kawashima N. , Kosaka T. , Matsumoto A. , Kobayashi C. , Suda H.
Published: November 2010

The precise distribution of various immunocompetent cells in rat molar pulp was immunohistochemically examined by use of seven anti-rat monoclonal antibodies. It was demonstrated that rat molar pulp contained many 0X6 (anti-la antigen-positive cells and a large number of ED1 (anti-monocytes, macrophages, and dendritic cells)-positive, ED2 (anti-tissue macrophages)-positive, and/or OX35 (anti-macrophages and CD4+ lymphocytes)-positive cells, Macrophage-like cells predominated in the central portion of the pulp, while cells of dendritic appearance usually existed in the periphery of the pulp. Double-immunaperoxidase staining revealed that these cells showed some heterogeneity, but the majority could be classified as ED1+/0X6-/ED2+ cells, which may be Ia histiocytes. Findings also suggested that true dendritic cells may be included in the ED1+/0X6+/ED2- category of cells. A small number of T lymphocytes and plasma cells were also detected. These results suggest that the normal dental pulp contains a variety of immunocompetent cells, with macrophages as the most dominating. Following the exogenous invasion of pathogenic stimuli in the pulp, these cells may participate in the defense reaction by acting as phagocytes or antigen-presenting cells, which are essential for the initiation of immune responses.
Iron in the Enameloid of Perciform Fish
Authors: Suga S. , Taki Y. , Ogawa M.
Published: November 2010

It is known that a high concentration of iron is deposited in the enameloid of some teleostean fish. Previously, Suga et al. (1989) pointed out that the iron concentration in the enameloid is related to the phylogeny of fish rather than to the feeding habits, according to the results of quantitative iron analyses on the teeth of marine teleost fish of the Tetraodontiformes. In the present study, in order for the previous idea to be verified, quantitative iron analysis was made with an electron microprobe on the enameloid offish belonging to the Perciformes, which is the largest group of teleostean fish in the world and consists of both marine and freshwater species. The enameloid of all the fish examined (57 species) contained high iron concentrations ranging from 0.2% to 10.2% at the surface or middle layer, whereas that of an advanced suborder, Tetraodontoidei, of the Tetraodontiformes was very low in iron, at a level which could not be discriminated from the background value of the emission intensity. The distribution pattern of iron in the enameloid was classified into at least two types, namely, type A, in which a high iron concentration was observed mainly in the surface layer, and type B, in which iron was deposited throughout the entire layer, although there were differences in concentration. There were some differences in the concentration and distribution of iron in the enameloid for the families; for example, those of the Scaridae had a type A distribution, with about 0.2% iron only at the surface layer, whereas those of the Cichlidae, Centrarchidae, and Acanthuridae, which showed a type B distribution, contained iron ranging from 2.9% to 10.5% at the surface or middle layer of enameloid. Such differences seemed to be associated with the difference in timing of the commencement of the iron deposition into the developing enameloid, which is probably related to the phylogeny of fish. There was no evidence to support the idea that the iron concentration in the enameloid is associated with the feeding habits offish, as proposed by previous investigators.
Site-specific Expression of Collagen I and XII mRNAs in the Rat Periodontal Ligament at Two Developmental Stages
Authors: Karimbux N.Y. , Rosenblum N.D. , Nishimura I.
Published: November 2010

In mammals, the periodontal ligament (PDL) is a highly specialized tissue which facilitates tooth eruption and lends mechanical support to the tooth once in occlusion. The PDL extracellular matrix fibers play a major role in such functions. During its development, the spatial arrangement of the PDL extracellular matrix undergoes rapid changes. So that it could be determined whether the structural alteration in the PDL is associated with changes in the expression of collagenous proteins with different functional properties, the transcriptional patterns of collagens I and XII were examined. The maxillary dento-alveolar segments, each containing three molars, from 25-day-old and 40-day-old Sprague-Dawley rats were selected as being representative of developing and matured tissues, respectively. Rat a2(I) collagen cDNA and rat al(XII) collagen cDNA were used as molecular probes for identification of the corresponding mRNAs by RNA transfer blot analysis, RNase protection assay, and in situ hybridization. The results showed that a2(I) collagen mRNA was expressed in both developing and matured tissues. However, the level of expression decreased with maturity. In contrast, the expression of al(XII) collagen was increased in the matured tissue as compared with the developing tissue. In situ hybridization in these tissues indicated that the expression of al(XII) collagen mRNA was limited to the mature stage of PDL development. It is suggested that collagen fibril arrangement during PDL development may be related to the expression of collagen XII.
The Influence of Denture-wearing and Age on the Oral Microflora
Authors: Marsh P.D. , Percival R.S. , Challacombe S.J.
Published: November 2010

The effects of denture-wearing and age on the prevalence of selected bacteria of dental significance and on the carriage of opportunistic pathogens in molar plaque and whole saliva were determined in 120 healthy subjects, 41 of whom wore partial dentures. The subjects were divided into four age groups: 20-39 years (group A), 40-59 years (group B), 60-79 years (group C), and ≥ 80 years (group D). The proportions, mean loglo viable counts, and isolation frequency of yeasts and lactobacilli in saliva and plaque were consistently higher in partial-denture wearers. The proportions of staphylococci and mutans streptococci were also raised in denture wearers, but these differences did not reach statistical significance. When the data were analyzed for age effects, both yeasts and lactobacilli were found to be increased in saliva with age, but statistically significant differences were generally found only between denture wearers in group D and subjects in the control group A. The isolation frequency of yeasts from plaque was also significantly higher in denture wearers of the oldest age group (D) compared with those in group A. A. viscosus predominated over A. naeslundii in the older age groups, regardless of the presence of dentures. Enterobacteria were isolated occasionally but only from the saliva of denture wearers in group D. Spirochetes and black-pigmented anaerobes were generally found in lower numbers in denture wearers. Collectively, the data show that components of the oral microflora in adults can be independently influenced by both age and the wearing of partial dentures.
The Effects of Cleaning on the Kinetics of in vitro Metal Release from Dental Casting Alloys
Authors: Wataha J.C. , Craig R.G. , Hanks C.T.
Published: November 2010

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution us. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions. Auger analyses of alloy surfaces after exposure to medium showed the presence of organic films up to 50 nm thick. This study demonstrated the importance of consideration of the cleaning method and kinetic release pattern when in vitro tests which assess the cytotoxicities of these alloys are planned.
Delivery of Antiplaque Agents from Dentifrices, Gels, and Mouthwashes
Authors: Cummins D. , Creeth J.E.
Published: November 2010

Antiplaque agents delivered from toothpastes, gels, or mouthrinses can augment mechanical oral hygiene procedures to control the formation of supragingival plaque and the development of early periodontal disease. Clinically effective antiplaque agents are characterized by a combination of intrinsic antibacterial activity and good oral retention properties.

The overall oral retention of an antiplaque agent is determined by the strength and rate of association of the agent with its receptor sites and the accessibility of these sites. The substantivity of an antiplaque agent and its clearance from the oral cavity are determined by the rate of dissociation of the agent from the receptor sites and the salivary composition and flow rate. Positively charged and non-charged organic molecules, metal ions, enzymes, and surface-active agents have all been considered as antiplaque agents. To exert clinical antiplaque activity, an antimicrobial agent must be formulated in a chemically compatible delivery vehicle to give optimal release and uptake to the sites of action in a biologically active form during its time of application.

In principle, antiplaque activity may be enhanced by combining antimicrobial agents with broadly similar, but complementary, modes of action. Alternatively, the activity of a single agent may be increased by use of a retention aid to enhance oral substantivity. Substantial evidence exists to demonstrate the validity of the first approach. However, there are few data, as yet, to support the effectiveness of the second.

The oral mucosa is the bulk retention site for all clinically proven antiplaque agents. Plaque, the pellicle-coated tooth surface, and saliva are probably all sites of biological action. A detailed understanding of the interactions between agents and the various receptor sites, and of the importance of these receptor sites to biological activity, is generally lacking.
Agents for the Management of Plaque and Gingivitis
Authors: Ciancio S.G.
Published: November 2010

Numerous chemical agents have been evaluated for the supplementation of patient-dependent mechanical plaque control and thus the reduction or prevention of oral diseases. Agents discussed in this paper are those most frequently evaluated in recent studies and include chlorhexidine, essential oils, triclosan, sanguinarine, fluorides, oxygenating agents, quaternary ammonium agents, prebrushing rinses, enzymes, and antibiotics. Of the agents discussed, the greatest effect on the reduction of plaque and gingivitis can be expected from chlorhexidine, essential oils, and triclosan-containing products. These chemical agents vary in dosage form and include mouthrinses, gels, and dentifrices. Some may also be of value as irrigants. Adverse effects vary according to the chemical agent and include poor taste, burning sensation of oral tissue, staining of teeth and soft tissues, excess supragingival calculus, oral lesions in young patients, and allergic reactions. When a product is selected for a patient, consideration should be given to necessity, efficacy, adverse effects, and cost-effectiveness.
Subsurface Demineralization in Dental Enamel and Other Permeable Solids During Acid Dissolution
Authors: Anderson P. , Elliott J.C.
Published: November 2010

Subsurface demineralization of dental enamel during acid dissolution has been reported many times, but its cause remains obscure. At first, the phenomenon was thought to result from the physical structure of enamel. More recent studies have shown that subsurface demineralization occurs in other permeable solids, indicating that there must be more fundamental factors involved in this curious effect. In order for this phenomenon to be investigated, dissolution experiments were carried out by means of real-time scanning microradiography in various systems, including enamel, or aggregates of hydroxyapatite (calcium, strontium, or barium), or hydroxides (calcium or magnesium). These were chosen to discriminate between effects of structure and composition. It was found that it was not possible for the demineralization observed in these systems to be attributed to a common feature. From this, it is concluded that subsurface demineralization in enamel and other mineralized tissues should not be ascribed to a single cause.