bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum Shortening Velocity and Myosin Heavy-chain Isoform Expression in Human Masseter Muscle Fibers
Authors: Morris T.J. , Branden C.A. , Horton M.J. , Carlson D.S. , Sciote J.J.
Published: January 2009

While human masseter muscle is known to have unusual co-expression of myosin heavy-chain proteins, cellular kinetics of individual fibers has not yet been tested. Here we examine if myosin heavy-chain protein content is closely correlated to fiber-shortening speed, as previously reported in other human muscles, or if these proteins do not correlate well to shortening speeds, as has been demonstrated previously in rat muscle. Slack-test recordings of single, skinned human masseter fibers at 15°C revealed maximum shortening velocities generally slower and much more variable than those recorded in human limb muscle. The slowest fiber recorded had a maximum shortening velocity (V0) value of 0.027 muscle lengths ·s-1, several times slower than the slowest type I fibers previously measured in humans. By contrast, human limb muscle controls produced V0 measurements comparable with previously published results. Analysis by gel electrophoresis found 63% of masseter fibers to contain pure type I MyHC and the remainder to co-express mostly type I in various combinations with IIA and IIX isoforms. Vo in masseter fibers forms a continuum in which no clear relationship to MyHC isoform content is apparent.
Growth Hormone and Insulin-like Growth Factor I Receptors in the Temporomandibular Joint of the Rat
Authors: Visnapuu V. , Peltomäki T. , Rönning O. , Vahlberg T. , Helenius H.
Published: January 2009

While there are numerous investigations on hormonal control of long bone epiphyseal growth, corresponding knowledge is sparse concerning the condylar cartilage. We investigated the distribution of growth hormone (GH) and insulin-like growth factor I (IGF-I) receptors in the temporomandibular joint (TMJ), especially the condyle, and compared the findings with information of long bone epiphyseal plates. The localization of the receptors was examined in vivo by immunohistochemical methods in one- to 21-day-old rats. GH receptors were detected in various components of the TMJ, but not in the fibrous articular surface or in the cartilage layers of the condyle. IGF-I receptors were found in the fibrous articular surface of the condyle and particularly in the superior and posterosuperior regions of the condylar cartilage, the depth of the labeled cell layer increasing significantly with age. It is evident that the expression of GH and IGF-I receptors is area-specific in the TMJ. Early post-natal growth and development of the mandibular condylar cartilage seem to be IGF-I-dependent but not directly dependent on GH.
Three-dimensional Finite Element Analysis of the Cartilaginous Structures in the Human Temporomandibular Joint
Authors: Beek M. , Koolstra J.H. , Van Ruijven L.J. , Van Eijden T.M.G.J.
Published: January 2009

While the movability of the human temporomandibular joint is great, the strains and stresses in the cartilaginous structures might largely depend on the position of the mandible with respect to the skull. This hypothesis was investigated by means of static three-dimensional finite element simulations involving different habitual condylar positions. Furthermore, the influence of several model parameters was examined by sensitivity analyses. The results indicated that the disc moved together with the condyle in the anterior direction without the presence of ligaments and the lateral pterygoid muscle. By adapting its shape to the changing geometry of the articular surfaces, the disc prevented small contact areas and thus local peak loading. In a jaw-closed configuration, the influence of 30° variations of the loading direction was negligible. The load distribution capability of the disc appeared to be proportional to its elasticity and was enhanced by the fibrocartilage layers on the articular surfaces.
Reversal of Compromised Bonding to Oxidized Etched Dentin
Authors: Lai S.C.N. , Mak Y.F. , Cheung G.S.P. , Osorio R. , Toledano M. , Carvalho R.M. , Tay F.R. , Pashley D.H.
Published: January 2009

The mechanism responsible for hydrogenperoxide- or sodium-hypochlorite-induced reductions in dentin bond strength is unknown. This in vitro study tested the hypothesis that these oxidizing agents were responsible by attempting to reverse the effect with sodium ascorbate, a reducing agent. Human dentin was treated with these oxidants before or after being acid-etched and with or without post-treatment with sodium ascorbate. They were bonded with either Single Bond or Excite. Hydrogen peroxide reduced the bond strengths of both adhesives, while sodium hypochlorite produced reduction in adhesion of only Single Bond (p < 0.05). Following treatment with sodium ascorbate, reductions in bond strength were reversed. Transmission and scanning electron microscopy showed partial removal of the demineralized collagen matrix only by sodium hypochlorite. The observed compromised bond strengths cannot be attributed to incomplete deproteinization and may be related to changes in the redox potential of the bonding substrates.
A New Approach to Enhancement of Bone Formation by Electrically Polarized Hydroxyapatite
Authors: Teng N.C. , Nakamura S. , Takagi Y. , Yamashita Y. , Ohgaki M. , Yamashita K.
Published: January 2009

An electrical field may affect osteogenesis. Since we found that hydroxyapatite (HA) ceramics may be polarizable, we hypothesized that electrically polarized HA may foster production of new bone in vivo. Both polarized and non-polarized HA ceramics were inserted into the subperiosteum spaces at the parietal bone area of rats. After 2, 4, and 8 weeks, the implant sites were examined histologically. Morphometric analysis revealed that new bone formation was accelerated on the negatively charged surface of the polarized HA (N-surface) at 2 weeks. The newly formed bone approached maturation at 4 weeks and was thicker on the N-surface than in the controls. By 8 weeks, newly formed bone in the controls was almost the same as that on the N-surface. These findings suggest that polarized HA is biocompatible and that bone formation on the N-surface is enhanced in the early stage of bone healing.
Sleep Bruxism: An Oromotor Activity Secondary to Micro-arousal
Authors: Kato T. , Rompré P. , Montplaisir J.Y. , Sessle B.J. , Lavigne G.J.
Published: January 2009

Spontaneous rhythmic masticatory muscle activity (RMMA) during sleep occurs in relation to transient activation in the cerebral and autonomic nervous systems of normal subjects and in patients with sleep bruxism (SB). In this study, we made a quantitative assessment of the sequential changes in cortical electroencephalographic (EEG) and autonomic-cardiac activities associated with micro-arousals preceding RMMA episodes. We matched 10 SB patients with 10 normal subjects. The onset of RMMA episodes was defined in terms of the onset of activation in the suprahyoid muscles. In SB patients, an increase in cortical EEG activity was observed 4 seconds before the onset of suprahyoid activity in 79% of episodes. A significant acceleration in heart rate was initiated one cardiac cycle before RMMA onset. A clear sequence of cortical to autonomic-cardiac activation precedes jaw motor activity in SB patients. This suggests that SB is a powerful oromotor manifestation secondary to micro-arousal.
Association of Streptococcus mutans Infection and Oral Developmental Nodules in Pre-dentate Infants
Authors: Wan A.K.L. , Seow W.K. , Walsh L.J. , Bird P. , Tudehope D.I. , Purdie D.M.
Published: January 2009

Since dental caries may present soon after tooth eruption, we hypothesized that colonization of Streptococcus mutans can occur in the predentate stages. In this study, we examined S. mutans colonization and its association with oral developmental nodules (Bohn's nodules) in 60 pre-term and 128 full-term, three-month-old infants. Overall, S. mutans was cultured from 30% (56/188) of the infants, and oral developmental nodules were noted in 55% (103/188). Compared with the pre-term, full-term infants showed a higher prevalence of S. mutans (34% vs. 20%, p < 0.02) as well as developmental nodules (61% vs. 42%, p < 0.05). In both groups, S. mutans was positively associated with numbers of developmental nodules in a dose-response relationship (p < 0.001), and with maternal salivary levels of the bacteria (p = 0.03). The permanence of S. mutans infection was confirmed by repeat saliva sampling at 6 months of age. Our results thus showed that many infants have already acquired S. mutans at 3 months of age, prior to tooth eruption.
Sugared Soda Consumption and Dental Caries in the United States
Authors: Heller K.E. , Burt B.A. , Eklund S.A.
Published: January 2009

Because of the complexity of the caries process, the potential cariogenicity of specific food items is difficult to assess. The purpose of this study was to investigate the associations between sugared soda consumption and caries. Dietary and dental examination data from the 1988-94 Third National Health and Nutrition Examination Survey (NHANES III) were used. From the food frequency questionnaire and 24-hour recall data, significant associations between DMFS and soda consumption were generally seen in persons over age 25. No differences in DMFS, relative to soda consumption, were seen in persons under age 25, or in analyses of dfs for children under age 12. The observed associations could be due to the cumulative effects of the long-term consumption of sugared soda. The absence of apparent effects of sugared soda consumption in younger people may also be related to the increased use of fluorides since the 1960s.
Sonic hedgehog Regulates Epithelial Proliferation and Cell Survival in the Developing Tooth Germ
Authors: Cobourne M.T. , Hardcastle Z. , Sharpe P.T.
Published: January 2009

Shh expression is highly restricted to the future sites of tooth development during the initiation of odontogenesis. This suggests a role for Shh as a proliferative factor, as localized epithelial thickenings invaginate to form a tooth bud. We have investigated this role by blocking Shh signaling between E10.5 and E12.5 in murine mandibular processes using a 5E1 blocking antibody and the PKA activator Forskolin. This results in down-regulation of Ptc, a principle target of Shh signaling. The effects of inhibition varied with developmental time. At E10.5, tooth development was arrested as epithelial thickenings and the numbers of teeth developing were considerably reduced. Inhibition at E12.5 produced localized apoptosis in the epithelium at the tip of the tooth buds, although some teeth were able to develop. Thus, Shh has dual roles in early odontogenesis, first in bud formation by stimulating epithelial proliferation, and second in the development of cap-stage tooth germs by increasing epithelial cell survival.
Identification of Cariostatic Substances in the Cacao Bean Husk: Their Anti-glucosyltransferase and Antibacterial Activities
Authors: Osawa K. , Miyazaki K. , Shimura S. , Okuda J. , Matsumoto M. , Ooshima T.
Published: January 2009

The cacao bean husk has been shown to possess two types of cariostatic substances, one showing anti-glucosyltransferase (GTF) activity and the other antibacterial activity, and to inhibit experimental dental caries in rats infected with mutans streptococci. In the present study, chromatographic purification revealed high-molecular-weight polyphenolic compounds and unsaturated fatty acids as active components. The former, which showed strong anti-GTF activity, were polymeric epicatechins with C-4β and C-8 intermolecular bonds estimated to be 4636 in molecular weight in an acetylated form. The latter, which showed bactericidal activity against Streptococcus mutans, were determined to be oleic and linoleic acids, and demonstrated a high level of activity at a concentration of 30 μg/mL. The cariostatic activity of the cacao bean husk is likely caused by these biologically active constituents.
Experimental Gingivitis in Women Using Oral Contraceptives
Authors: Preshaw P.M. , Knutsen M.A. , Mariotti A.
Published: January 2009

Oral contraceptives (OC) have historically been considered a risk factor for gingival diseases. We set out to investigate this premise further, given that, over recent years, hormone concentrations in OC have been substantially reduced. Using a prospective, split-mouth, experimental gingivitis model, pre-menopausal women either taking (n = 14) or not taking (n = 16) OC refrained from all oral hygiene practices in one maxillary (test) quadrant while continuing to perform normal oral hygiene activities in the contralateral (control) quadrant. Mean increases in plaque index (PI), gingival index (GI), and gingival crevicular fluid (GCF) volume from days 0 to 21 were significant in test quadrants (P < 0.05) but did not differ regardless of whether subjects received OC (P > 0.05). PI, GI, and GCF volume did not vary in control quadrants over the course of the study (P > 0.05). Analysis of these data suggests that current OC formulations do not affect the inflammatory response of the gingiva to dental plaque.
Kaplan-Meier Analysis of Dental Implant Survival: A Strategy for Estimating Survival with Clustered Observations
Authors: Chuang S.K. , Tian L. , Wei L.J. , Dodson T.B.
Published: January 2009

The study's purposes were to estimate dental implant survival in a statistically valid manner and to compare three models for estimating survival. We estimated survival using three different statistical models: (1) randomly selecting one implant per patient; (2) utilizing all implants, assuming independence among implants from the same subject; and (3) utilizing all implants, assuming dependence among implants from the same subject. The cohort was composed of 660 patients who had 2286 implants placed. Due to the high success rates of implants, the five-year survival point and standard error estimates varied little among the three models. Patients at high risk for implant failure (smokers) manifested greater variation in the standard error estimates among the three models, 8.2%, 4.0%, and 5.6%, respectively. To obtain statistically valid survival confidence intervals when performing Kaplan-Meier survival analyses, we recommend adjusting for dependence when there are multiple observations within the same subject.
Analysis of Vitamin D and Fcγ Receptor Polymorphisms in Japanese Patients with Generalized Early-onset Periodontitis
Authors: Yoshihara A. , Sugita N. , Yamamoto K. , Kobayashi T. , Miyazaki H. , Yoshie H.
Published: January 2009

Early-onset periodontitis (EOP) is considered to have a genetic basis which has not been clearly defined. Genetic polymorphisms of the vitamin D receptor (VDR-B-b) and the immunoglobulin-Fcγ receptor IIIb (FcγRIIIb-NA1-NA2) are associated with bone metabolism and infectious diseases, respectively. The purpose of this study was to investigate the associations of EOP with VDR and FcγRIIIb polymorphisms. Subjects were comprised of those with generalized EOP (G-EOP, n = 42), adult periodontitis (AP, n = 52), and healthy control (HC, n = 55). VDR and FcγRIIIb genotypes were determined by allele-specific polymerase chain-reactions. Our results indicated that frequencies of the VDR-B non-carrier and the FcγRIIIb-NA2 carrier were lower in the G-EOP compared with the AP and HC groups. Furthermore, we found a strong association between G-EOP and the VDR-FcγRIIIb composite genotype (G-EOP vs. AP - OR = 5.09, p = 0.009; G-EOP vs. HC - OR = 5.93, p = 0.004). In conclusion, no correlation was found between the VDR genotype and G-EOP. However, the VDR and FcγRIIIb genotype combination may be associated with susceptibility to G-EOP.
A Community-based Caries Control Program for Pre-school Children Using Topical Fluorides: 18-month Results
Authors: Lo E.C.M. , Chu C.H. , Lin H.C.
Published: January 2009

Dental caries in Chinese pre-school children is common, and restorative treatment is not readily available. This prospective controlled clinical trial investigated the effectiveness of topical fluoride applications in arresting dentin caries. We divided 375 children (aged 3-5 yrs) with carious upper anterior teeth into five groups. Children in the first and second groups received annual applications of silver diamine fluoride solution (44,800 ppm F). NaF varnish (22,600 ppm F) was applied every three months onto the lesions of children in the third and fourth groups. For children in the first and third groups, soft carious tissues were removed prior to fluoride application. The fifth group was the control. We followed 341 children for 18 months. The mean numbers of new caries surfaces in the five groups were 0.4, 0.4, 0.8, 0.6, and 1.2, respectively (p = 0.001). The respective mean numbers of arrested carious tooth surfaces were 2.8, 3.0, 1.7, 1.5, and 1.0 (p < 0.001).
Occlusal Disharmony Affects Plasma Corticosterone and Hypothalamic Noradrenaline Release in Rats
Authors: Yoshihara T. , Matsumoto Y. , Ogura T.
Published: January 2009

Few neuro-endocrinological studies have examined the relationship between occlusal disharmony and stress. To determine the effect of occlusal disharmony on the central nervous system, we measured plasma corticosterone and extracellular noradrenaline in the vicinity of the hypothalamic paraventricular nucleus in rats both with and without incisal caps. After the caps were set, plasma corticosterone and extracellular noradrenaline levels gradually increased, reaching a peak at 8.5 and 6.5 hours, respectively, after which they decreased. Furthermore, plasma corticosterone and extracellular noradrenaline levels increased in a circadian fashion around the onset of the dark phase in rats without caps, but not in rats with caps. These results suggest that occlusal disharmony causes chronic stress in the rat.
Novel F-releasing Composite with Improved Mechanical Properties
Authors: Ling L. , Xu X. , Choi G.-Y. , Billodeaux D. , Guo G. , Diwan R.M.
Published: January 2009

In recent years, the authors have been developing novel fluoride-releasing dental composites containing ternary zirconium fluoride chelates. The aim of this study was to improve the physical and mechanical properties of these composites by improving the formulation of the monomers and photoinitiators. The hypothesis was that reduction of hydrophilic monomers and improvement of the photoinitiators could reduce water sorption and significantly increase the mechanical properties of the composite. The degree of conversion of the composites containing different compositions of photoinitiators was studied by Fourier transform near-infrared spectroscopy (FT-NIR). Ten experimental composites containing different compositions of ethoxylated bisphenol-A dimethacrylate (EBPADMA), 1,6-hexanediol dimethacrylate (HDDMA), triethylene glycol dimethacrylate (TEGDMA), and 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]-propane (BisGMA) were tested for flexural strength, viscosity, and water sorption. The experimental composite containing 20% synthesized fluoride-releasing monomer, 30% BisGMA, 30% EBPADMA, and 20% HDDMA showed significantly higher fluoride release and recharge, but physical and mechanical properties similar to those of the control composite containing 40% BisGMA, 40% EBPADMA, and 20% HDDMA.
A Compilation of Partial Sequences of Randomly Selected cDNA Clones from the Rat Incisor
Authors: Matsuki Y. , Nakashima M. , Amizukal N. , Warshawsky H. , Goltzman D. , Yamada K.M. , Yamada Y.
Published: January 2009

The formation of tooth organs is regulated by a series of developmental programs. We have initiated a genome project with the ultimate goal of identifying novel genes important for tooth development. As an initial approach, we constructed a unidirectional cDNA library from the non-calcified portion of incisors of 3- to 4-week-old rats, sequenced cDNA clones, and classified their sequences by homology search through the GenBank data base and the PIR protein data base. Here, we report partial DNA sequences obtained by automated DNA sequencing on 400 cDNA clones randomly selected from the library. Of the sequences determined, 51% represented sequences of new genes that were not related to any previously reported gene. Twenty-six percent of the clones strongly matched genes and proteins in the data bases, including amelogenin, α1(I) and a2(I) collagen chains, osteonectin, and decorin. Nine percent of clones revealed partial sequence homology to known genes such as transcription factors and cell surface receptors. A significant number of the previously identified genes were expressed redundantly and were found to encode extracellular matrix proteins. Identification and cataloging of cDNA clones in these tissues are the first step toward identification of markers expressed in a tissue- or stage-specific manner, as well as the genetic linkage study of tooth anomalies. Further characterization of the clones described in this paper should lead to the discovery of novel genes important for tooth development.
Identification of Bone-type Alkaline Phosphatase mRNA from Human Periodontal Ligament Cells
Authors: Goseki M. , Oida S. , Takeda K. , Ogata Y. , Iimura T. , Maruoka Y. , Sasaki S.
Published: January 2009

Tissue-nonspecific-type alkaline phosphatase is found in the bone, liver, kidney, and other tissues, and its gene consists of 12 exons with the coding sequence beginning in the second exon. Recently, an alternative noncoding first exon was identified in the liver message which differed from that of the previously known osteoblast-derived cDNA sequence. Although these two mRNAs produce an identical protein, they have different promoter regions. The periodontal ligament tissue expresses a high level of alkaline phosphatase activity. To identify its mRNA type, we isolated a full-length cDNA for alkaline phosphatase from a cultured human periodontal ligament cell expression library, using bone-derived tissue-nonspecific alkaline phosphatase cDNA as a hybridization probe. The size of this clone was 2.5 kb, and its 5' and 3' untranslated sequences were identical to those of the human tissue-nonspecific type isolated from osteoblastic cells but not to those of the liver type. In addition, the same fragments as in bone-derived tissue-nonspecific-type cDNA were detected by the treatment of the cDNA clone with restriction enzymes Hinc II and Pst I. The results suggest that expression of the same alkaline phosphatase isozyme in human periodontal ligament cells may be regulated by the same transcriptional mechanism as in bone.
Effect of Hydrostatic Pressure on the Diffusion of Monomers through Dentin in vitro
Authors: Gerzina T.M. , Hume W.R.
Published: January 2009

In previous work, the diffusion of monomers from composite and bonding resins through dentin was demonstrated in vitro. The monomers triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) were identified in samples from the pulp space. In the current study, we examined the effects of two levels of positive hydrostatic pressure on the passage of resin monomers through dentin in vitro from a compositeresin/bonding-resin combination to test the hypothesis that monomer diffusion is prevented by such pressure. An occlusal cavity prepared in the tooth crown was restored with the resins. Distilled water samples from the pulpal space were removed over time and analyzed for monomer content by high-performance liquid chromatography and mass spectrometry. Positive pulpal pressure reduced but did not prevent pulpward movement of diluent monomers that leach from bonding agents and from resin composites through dentin in vitro. The degree of reduction of diffusion was greater with TEGDMA than with the lower-molecular-weight monomer HEMA.
Acute Toxicity of Carbamide Peroxide and a Commercially Available Tooth-bleaching Agent in Rats
Authors: Dahl J.E. , Becher R.
Published: January 2009

Previous studies have indicated that tooth-bleaching agents contain potentially hazardous chemicals. The present study evaluates the acute toxicity of a commercially available tooth-bleaching agent and carbamide peroxide, which is the active bleaching ingredient. Rats were dosed by stomach gavage, i.e., via a stomach tube, with 5, 15, and 50 mg carbamide peroxide/kg body weight and 150 and 500 mg tooth-bleaching agent/kg body weight, corresponding to 15 and 50 mg carbamide peroxide/kg body weight. Animals were killed after either one or 24 h. Autopsies were performed, and the distal part of the esophagus and the stomach were removed and processed for light microscopy investigation. Liver and kidney were evaluated histologically in animals killed after 24 h. Carbamide peroxide gave dose-dependent ulcerations of the gastric mucosa, with the 15 mg/kg body weight as the lowest observed effect level. The lesions were clearly visible after one h and seemed to be healing after 24 h. The ulcerations of the gastric mucosa were more pronounced after exposure to the tooth-bleaching agent than those observed after a comparable dose of carbamide peroxide. This may be attributed to the hydrophobic gel and the content of a carbopol (which increases the tissue adherence and retards the release of oxygen) in the bleaching agent. No apparent injury was observed in livers and kidneys. An exposure limit based on the lowest observed effect level (15 mg carbamide peroxide/kg body weight) and a safety factor of 100 were established and utilized in a risk assessment which indicated that daily human exposure during a bleaching procedure may come close to or even exceed this limit.
Salivary PAF Levels Correlate with the Severity of Periodontal Inflammation
Authors: Garito M.L. , Prihoda T.J. , McManus L.M.
Published: January 2009

Platelet-activating factor (PAF), a potent phospholipid mediator of inflammation, has been previously identified in inflamed gingival tissues and gingival crevicular fluid. However, the role of PAF in oral pathobiology remains unknown. The purpose of the present study was to evaluate the relationship between salivary PAF levels and the severity of periodontal inflammation. PAF activity in lipid extracts of whole (mixed) saliva collected from 69 untreated subjects immediately prior to routine oral evaluation was determined by platelet bioassay. Significant positive correlations were observed between the level of PAF in saliva and measures of periodontal inflammation, i.e., the percentage of periodontal probing depths greater than 4 mm, the number of periodontal bleeding sites, and the number of histologically identified polymorphonuclear neutrophilic leukocytes (PMN) in saliva. Moreover, when subjects were subdivided into groups on the basis of periodontal probing depths, a significant correlation was observed between salivary PAF levels and the extent of periodontal disease, i.e., PAF levels in saliva progressively increased from the healthiest group to the most severely affected group. Thus, salivary PAF levels correlate with the severity of periodontal inflammation. These results support the hypothesis that this pro-inflammatory phospholipid autacoid may participate in the pathogenesis of periodontal tissue injury and disease.
Effects of Fluoride on the Calcium Phosphate Precipitation Method for Dentinal Tubule Occlusion
Authors: Suge T. , Ishikawa K. , Kawasaki A. , Yoshiyama M. , Asaoka K. , Ebisu S.
Published: January 2009

Use of the calcium phosphate precipitation (CPP) method makes possible the occlusion of dentinal tubules to approximately 10 to 15 pn from the dentinal surface, and thus shows good potential for the treatment of dentin hypersensitivity. The precipitate formed in the dentinal tubules by the CPP method is, however, not apatite [HAP; Ca10(PO4)6(OH)2], a component of tooth and bone, but dicaldum phosphate dihydrate (DCPD; CaHPO 4·2H2O). Since fluoride enhances the conversion of DCPD to HAP, we evaluated the effects of fluoride on the texture of the precipitate formed by the CPP method and on its capacity to occlude dentinal tubules in this in vitro study. CPP solution (1.0 mol/L CaHPO4·2H 2O dissolved in 2.0 mol/L H3PO4) was applied to a dentin disk and was subsequently neutralized with a post-treatment solution (1 mol/L NaOH, from 0 to 0.1 mol/L NaF). Scanning electron microscopy revealed that the precipitate occluded dentinal tubules to a depth of approximately 10 to 15 μm from the dentinal surface, regardless of the NaF concentration (from 0 to 0.1 mol/L) in the post-treatment solution. Also, dentin permeability was reduced to 15% by the CPP treatment regardless of the NaF concentration. The Ca/P molar ratio of the precipitate, measured by x-ray micro-analysis, was higher (1.25 ± 0.04) in the presence of NaF than in its absence (1.03 ± 0.01). For further identification of the precipitate formed in the dentinal tubules, the same procedure was used in glass tubes (diameter, 1 mm), so that a larger amount of precipitate would be obtained. Powder x-ray diffraction analysis and Fourier transform infrared (FT-IR) measurement revealed that the precipitate formed by the CPP method gradually changed from DCPD to apatitic as the NaF concentration increased. We concluded that the addition of NaF to the post-treatment solution with the CPP method was desirable, since it led to more apatitic precipitate formation and did not lessen the occluding capacity of the precipitate.
Scanning Transmission Electron Microscopy/Energy-dispersive Spectroscopy Analysis of the Dentin Adhesive Interface Using a Labeled 2-Hydroxyethylmethacrylate Analogue
Authors: Eick J.D. , Robinson S.J. , Byerley T.J. , Chappell R.P. , Spencer P. , Chappelow C.C.
Published: January 2009

In an attempt to compare the morphology of the dentin adhesive interface and the wetting and penetration of the adhesive in relation to the dentin surface, we studied four dentin adhesive systems using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). 2-Hydroxyethylmethacrylate (HEMA), a monomer common to many commercial dentin adhesive systems, was altered to produce a thiolated analogue (HETMA). Sulfur, traceable by EDS and STEM, was substituted for the oxygen atom in the backbone of the HEMA molecule. The resulting analogue, with solubility parameters and other wetting and physical properties very similar to those of HEMA, was applied to four sets of tooth specimens, each pre-treated with a different primer or etchant. Three separate pre-treatments-nitric acid, maleic acid, and citric acid/ferric chloride—created a demineralized zone approximately 1 to 3 μm thick at the dentin surface. The HETMA was found to permeate freely into this zone when either of the latter two pre-treatments was used. However, the band of dentin that was demineralized by the nitric acid pre-treatment appeared impermeable to the HETMA. The fourth pre-treatment, an alcohol-based solution including the phosphorus acid ester PENTA and HEMA, modified the smear layer of the tooth slightly and did not appear to demineralize the dentin. HETMA applied to the specimens pre-treated with PENTA and HEMA was clearly in intimate contact with the dentin or modified smear layer; however, it did not penetrate or diffuse into these areas. It did flow into the dentinal tubules, as was also evident with each of the other systems. It was concluded that the acid pre-treatment of the dentin greatly influenced the wetting behavior of the dentin adhesive and thus could substantially affect the resultant bond strength of the dentin adhesive systems.
Effects of Dopamine on Adenylyl Cyclase Activity and Amylase Secretion in Rat Parotid Tissue
Authors: Hatta S. , Amemiya N. , Takemura H. , Ohshika H.
Published: January 2009

Several previous studies have shown that dopamine causes amylase secretion from rat parotid tissue. However, the mechanism of this dopamine action is still unclear. The present study was designed to characterize dopamine action in rat parotid gland tissue by examining the effects of dopamine on cyclic AMP accumulation, adenylyl cyclase activity, and amylase release. Dopamine significantly enhanced accumulation of cyclic AMP in parotid slices and stimulated adenylyl cyclase activity in parotid membrane preparations. It also significantly stimulated amylase release from parotid slices. The stimulatory effects of dopamine on cyclic AMP accumulation, adenylyl cyclase activity, and amylase release were effectively blocked with propranolol, a β-adrenergic antagonist, but not by either SCH 23390, a preferential D1antagonist, or butaclamol, a preferential D2 antagonist. No substantial specific binding sites for D, receptors were detectable by [3H]SCH 23390 binding in parotid membranes. These results suggest that the stimulatory effect of dopamine on amylase secretion in rat parotid tissue is not mediated through specific D1dopamine receptors but rather through β-adrenergic receptors.
Arachidonic Acid Stimulates Intracellular Calcium Mobilization and Regulates Protein Synthesis, ATP Levels, and Mucin Secretion in Submandibular Gland Cells
Authors: Fleming N. , Mellow L.
Published: January 2009

Earlier observations that arachidonic acid inhibited the synthesis of membrane inositol phospholipids in rat submandibular acinar cells prompted the present study on whether the fatty acid may also regulate other key physiological processes in the model. Arachidonate, at concentrations above 10 pmol/L, inhibited up to 97% protein synthesis in acinar cells. The acid also lowered cellular ATP levels to 25% of control values by a ouabaininsensitive mechanism. In endoplasmic reticulum-calcium studies in permeabilized cells, arachidonic acid stimulated the mobilization of up to 73% loaded ER-45Ca2+to the cytosol, a much greater response than those caused by other calcium translocators, thapsigargin or inositol 1,4,5-trisphosphate. Additionally, arachidonate provoked the release of over 80% of total cell45Ca2+to the extracellular space in intact cells and stimulated mucin secretion in the submandibular model. The inhibitory effect of arachidonic acid on protein synthesis was duplicated by carbachol, thapsigargin, and BAPTA/AM, three agents that cause net efflux of ER-Ca2+by different mechanisms. Furthermore, comparable with the arachidonate effect on ATP, carbachol and thapsigargin also significantly reduced cellular levels of the nucleotide. It is concluded that arachidonic acid acts as a regulator of central synthetic/secretory processes in mucous acinar cells of rat submandibular gland and suggested that at least some of its effects may be secondary to its calcium-mobilizing action.
Characterization and Identification of Proteinases and Proteinase Inhibitors Synthesized by Temporomandibular Joint Disc Cells
Authors: Kapila S. , Lee C. , Richards D.W.
Published: January 2009

The adult mammalian temporomandibular joint (TMJ) disc is a fibrocartilaginous tissue that undergoes normal developmental remodeling, requiring removal of the existing extracellular matrix and its replacement by new matrix macromolecules. This remodeling is probably mediated by matrix-degrading enzymes, but to date none has been demonstrated in association with the TMJ disc. We characterized, identified, and determined the regulation of proteinases and proteinase inhibitors (PIs) synthesized by TMJ disc cells in organ and cell cultures. TMJ discs were retrieved from 14-week-old male NZW rabbits and both tissue- and disc-derived cells were cultured in serum-free medium. The conditioned media were retrieved at 12-hour intervals and assayed for proteinases and PIs in gelatin- and casein-impregnated polyacrylamide gels. Three proteinases with gelatinolytic activities at 92 kDa, 72 kDa, and 53/57 kDa and one caseinolytic activity at 51/54 kDa were detected. All were inhibited by 1,10-1 phenanthroline, thus characterizing these enzymes as matrix metalloproteinases (MMPs), most likely 92-kDa gelatinase (proMMP-9), 72-kDa gelatinase (proMMP-2), procollagenase (proMMP-1), and prostromelysin (proMMP-3). The identity of the latter two MMPs was confirmed by Western blots. Two PIs of 30 kDa and 20 kDa, probably tissue inhibitors of metalloproteinase (TIMP) and TIMP-2, were observed on reverse zymograms. TPA, a protein kinase-C agonist, increased the expression of 92-kDa gelatinase and 30-kDa PI by both explanted discs and isolated disc cells. The profile of MMPs constitutively expressed by disc cells is similar to that of synovial fibroblasts but different from that of chondrocytes. These findings implicate MMPs and Pis in the normal remodeling of the TMJ disc, and potentially in the pathologic degradation of the disc during various arthritides.
Volatile Fatty Acids, Metabolic By-products of Periodontopathic Bacteria, Inhibit Lymphocyte Proliferation and Cytokine Production
Authors: Kurita-Ochiai T. , Fukushima K. , Ochiai K.
Published: January 2009

Short-chain fatty acids are a major by-product of anaerobic metabolism and can be detected in gingival fluid from periodontal pockets. Since most T cells are present subjacent to the pocket epithelium in conjunction with the plasma cells, it is important to know how these T cells are affected by short-chain fatty acids produced by subgingival plaque. The purpose of this study is to examine the effects of extracellular metabolites from periodontopathic bacteria on the proliferation and cytokine production of mouse splenic cells as a potential mechanism of imbalance among host-microbial interactions. A low-molecular-weight, heat-stable agent present in the two-day culture filtrate of Porphyromonas gingival is, Prevotella loescheii, and Fusobacterium nucleatum significantly depressed Con A- and LPS- induced cell proliferation. To determine whether short-chain fatty acids present in the filtrate could account for the depression, we tested extracted volatile and nonvolatile fatty acids for their effects on mitogenic activity. The volatile fatty acids extracted from immunosuppressive supernatants greatly inhibited T- and B- cell proliferation. Among these volatile fatty acids, butyric, propionic, valeric, and isovaleric acids impaired cell proliferation dose-dependently. From gas-liquid chromatographic analysis data, it is suggested that immuno-inhibitory activities in culture filtrates are mainly attributable to butyric and isovaleric acids in P. gingival is, to propionic, butyric, and isovaleric acids in P. loescheii, and to butyric acid in F. nucleatum. Furthermore, these fatty acids significantly depressed interleukin 2 (IL-2), IL-4, IL-5, IL-6, and IL-10 production by Con A-stimulated splenic-T cells dose-dependently. These results suggest that the volatile fatty acids produced by periodontopathic bacteria, easily penetrating the oral mucosa, severely harm periodontal tissue, including immunoregulatory cells.
Alkaline Phosphatase Activity in the Periodontal Ligament and Gingiva of the Rat Molar: Its Relation to Cementum Formation
Authors: Groeneveld M.C. , Everts V. , Beertsen W.
Published: January 2009

Alkaline phosphatase (ALP) is a glycoprotein thought to be involved in processes leading to mineral formation in tissues like bone and cementum. In the rat molar periodontium, several regions are associated with the formation of cementum (periodontal ligament, inner part of the gingiva), whereas other areas are not ( e. g., the outer part of the gingiva just beneath the outer oral epithelium). In an attempt to establish how the spatial distribution of ALP activity relates to cementum formation, we assessed the activity of the enzyme quantitatively in the periodontium of the rat maxillary molars, by using the indoxyl-tetrazolium salt method. It appeared that the distribution of enzyme activity in the ligament was heterogeneous, indicating local variations in the phosphate household. Highest activity was found in areas related to mineralization, adjacent to the alveolar bone and cementum. Enzyme activity was higher adjacent to cellular cementum than to acellular cementum. With respect to acellular cementum, a highly significant positive correlation was found between ALP activity and cementum thickness, which indicates a close relationship between local phosphate production and cementum formation rate. An interesting observation in the connective tissue of the gingiva mesial to the first molar was a sharp demarcation between an ALP-positive inner part, adjacent to the tooth, and an ALP-negative outer part, underneath the outer oral epithelium. In the interdental gingiva, the entire connective tissue proved positive for the enzyme, suggesting that this region consists of the combined inner gingival parts of two adjacent teeth.
Genetic Covariance Structure of Incisor Crown Size in Twins
Authors: Dempsey P.J. , Townsend G.C. , Martin N.G. , Neale M.C.
Published: January 2009

Previous studies of tooth size in twins and their families have suggested a high degree of genetic control, although there have been difficulties separating the various genetic and environmental effects. A genetic analysis of variation in crown size of the permanent incisors of South Australian twins was carried out, with structural equation modeling used to determine the relative contributions of genetic and environmental factors. Maximum mesiodistal crown dimensions of maxillary and mandibular permanent incisors were recorded from dental models of 298 pairs of twins, including 149 monozygous (MZ) and 149 dizygous (DZ) pairs. The analysis revealed that: (i) an adequate fit required additive genetic and unique environmental components; (ii) augmenting the model with non-additive genetic variation did not lead to a significant improvement in fit; (iii) there was evidence of shared environmental influences in the upper central incisors of males; (iv) the additive genetic component constituted a general factor loading on all eight teeth, with group factors loading on antimeric pairs of teeth; (v) unique environmental effects were mostly variable-specific; (vi) most factor loadings on antimeric tooth pairs could be constrained to be equal, indicating a symmetry of genetic and environmental influences between left and right sides; and (vii) estimated heritability of the incisor mesiodistal dimensions varied from 0.81 to 0.91.
Long-term Exposure to Fluoride in Drinking Water and Sister Chromatid Exchange Frequency in Human Blood Lymphocytes
Authors: Li Y. , Liang C.K. , Katz B.P. , Brizendine E.J. , Stookey G.K.
Published: January 2009

The genetic toxicity of fluoride has been investigated extensively by various test systems. However, results obtained have been inconsistent. Fluoride has been reported to be non-genotoxic, genotoxic, and synergistic or antagonistic with certain mutagens. To date, there are no published human studies on the genotoxicity of fluoride. The purpose of this investigation was to determine genotoxic risks of long-term exposure to various concentrations of fluoride in drinking water in humans with normal or inadequate nutrition. Six groups of subjects with either normal or inadequate nutritional intakes were selected from areas of approximately 0.2, 1.0, or 4.8 ppm (10.5, 52.6, or 252.6 μmol/L) fluoride in water. The subjects had been continuous residents in the area for at least 35 years. Samples of drinking water, plasma, and urine were analyzed for fluoride content. Blood lymphocytes were examined to determine the frequency of sister chromatid exchange (SCE). Blood chemistry and electrolytes were also analyzed. The results showed that average daily fluoride intake as well as urine and plasma fluoride levels increased with increase in the fluoride content of the drinking water. The blood chemistry and electrolyte values were within the normal range for all populations, but several parameters were significantly different. While the numerical differences were small, the subjects with low fluoride in the water (0.11 and 0.23 ppm or 5.8 and 12.1 umol/L) had significantly higher SCE frequencies than those with higher fluoride exposures. Reasons for the reduced SCE frequency in subjects with higher fluoride exposure are unclear; however, the data demonstrated that long-term exposure to fluoride in the drinking water, even at an elevated level, does not have genotoxic effects in humans.
Fluoride Reduces Bone Strength in Older Rats
Authors: Turner C.H. , Hasegawa K. , Zhang W. , Wilson M. , Li Y. , Dunipace A.J.
Published: January 2009

In response to recent concerns about the effect of water fluoridation on hip fracture rates, we studied the influence of fluoride intake on bone strength. Four groups of rats were fed a low-fluoride diet ad libitum and received 0, 5, 15, or 50 ppm of fluoride in their drinking water. Animals were euthanized after 3, 6, 12, or 18 months of treatment. Mechanical strength of the right femur was measured by three-point bending. Fluoride content for the left femur was measured, and static histomorphometric measurements were made on a lumbar vertebra. Femoral failure load was not significantly decreased in rats treated for 3 and 6 months, but was decreased as much as 23% in rats treated 12 and 18 months at 50 ppm fluoride. Extrapolation from regression equations predicted that older rats lose 36% of femoral bone strength when bone fluoride content is increased from 0 to 10,000 ppm, while younger rats will lose only 15%. Thus, the decreased strength appeared to be due to the combined effects of fluoride intake and age on bone tissue and was not associated with a decrease in bone density or mineralization defects. There were only small effects of fluoride on bone histomorphometry. Fluoride intake at high levels had no negative effects on bone mineralization. Fluoride intake was associated with slight increases in trabecular bone volume and trabecular thickness, but these effects could not be demonstrated consistently. The mechanism by which large amounts of fluoride affect bone strength more severely in older animals is unknown.
Computer Modeling of the Effects of Chewing Sugar-free and Sucrose-containing Gums on the pH Changes in Dental Plaque Associated with a Cariogenic Challenge at Different Intra-oral Sites
Authors: Dibdin G.H. , Dawes C. , Macpherson L.M.D.
Published: January 2009

Variation in salivary access to different intra-oral sites is an important factor in the site-dependence of dental caries. This study explored, theoretically, how access is modified by chewing sugar-free and sugar-containing gums. A finite difference computer model, described elsewhere, was used. This allowed for diffusion and/or reaction of substrate, acid product, salivary buffers, and fixed-acid groups. Site-dependent saliva/plaque exchange was modeled in terms of a 100-μm-thick salivary film covering the plaque (a) flowing directly from the salivary ducts, (b) flowing from the intra-oral salivary pool, or (c) exchanging with the pool. Computed flow-velocities or rates of exchange were based on previous intra-oral measurements. The model was also tested against an in vitro study conducted by two of the authors. In addition, the three proposed models of saliva/plaque interaction were compared, and the effect of salivary film thickness investigate. Results suggested that: (1) although sugar-free gum chewed during a cariogenic challenge causes a rapid rise in plaque pH, sucrose-containing gums cause the pH, after a temporary rise resulting from increased salivary flow, to stay low for an extended period; (2) the computer model reproduced in vitro tests reasonably well; (3) although the three models of the plaque/saliva interaction start from different assumptions, two lead to closely related predictions; and (4) increasing the assumed salivary film thickness by a large amount ( e.g., from 50 to 200 μm) caused no change in modeled Stephan curves, as long as these changes were accompanied by appropriate reductions in film velocity, in accord, theoretically, with the practical clearance data.