bluuebunny/crossref_metadata_2025 huggingface dataset:
Re-epithelialization of Human Oral Keratinocytes in vitro
Authors: Garlick J.A. , Parks W.C. , Welgus H.G. , Taichman L.B.
Published: January 2009

Re-epithelialization involves interactions between keratinocytes and the extracellular matrix upon which these cells move. It is hypothesized that keratinocytes are activated when wounded, and the resultant phenotypic change directs re-epithelialization. We have adapted organotypic cultures, in which oral gingival keratinocytes are fully differentiated, to study re-epithelialization following wounding. To elucidate keratinocyte behavior and phenotype during re-epithelialization, we have investigated this process in the presence and absence of the growth factor TGF-β1 and have monitored expression of MMP-1 (Type I collagenase) mRNA by in situ hybridization. In addition, we have followed proliferation and migration of wound keratinocytes by genetically marking these cells with a retroviral vector and by measuring their proliferative index. We found that keratinocytes grown without TGF-β1 were hyperproliferative in response to wounding, and re-epithelialization was complete by 24 h. However, 2.5 ng/mL TGF-β1 induced a transient delay in re-epithelialization, a reduction in proliferation, and fewer clusters of genetically marked cells. Keratinocytes expressed MMP-1 mRNA only when they covered the wounded surface, suggesting that the cells acquire a collagenolytic phenotype during re-epithelializaation and that contact with different ECM components may modulate keratinocyte expression of MMP-1. We conclude that the phenotype of oral keratinocytes is altered during re-epithelialization in vitro and that this process is modulated by TGF-pl. Reepithelialization occurs as keratinocytes are activated to move over the wound bed. Understanding the phenotype of wounded keratinocytes may facilitate treatment of chronic oral wounds and periodontal disease.
Enamel Defects in the Deciduous Dentition as a Potential Predictor of Defects in the Permanent Dentition of 8- and 9-year-old Children in Fluoridated Cheshire, England
Authors: Milsom K.M. , Woodward M. , Haran D. , Lennon M.A.
Published: January 2009

It is claimed that dental fluorosis in both deciduous and permanent teeth is increasing in fluoridated and non-fluoridated communities. What is unclear is whether fluoride-induced enamel opacities in the deciduous dentition are associated with the subsequent appearance of enamel defects in the permanent dentition. The aim of this study was to establish whether a relationship existed between the presence of diffuse enamel defects on the deciduous molars and permanent incisors of schoolchildren who were lifetime residents in an optimally fluoridated community in Cheshire, England. The dentitions of eight-and nine-year-old children were examined by two examiners, each unaware of the findings of the other. There was a significant increased risk of diffuse enamel defects in the permanent incisors for those children who presented with diffuse defects on their first deciduous molars (Relative Risk, 1.45; 95% confidence interval, 1.05 to 2.0) or second deciduous molars (Relative Risk, 1.86; 95% confidence interval, 1.36 to 2.54). In light of these findings, it is worth considering the potential of the presence of enamel defects in deciduous molars in children aged 1 to 3 years as a predictor of the future appearance of similar lesions in their permanent incisors.
Abnormal Enamel Development in a Cystic Fibrosis Transgenic Mouse Model
Authors: Wright J.T. , Kiefer C.L. , Hall K.I. , Grubb B.R.
Published: January 2009

Cystic fibrosis (CF) is a hereditary condition that affects cAMP-regulated chloride channels in epithelial tissues due to a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Recently, a transgenic CF mouse model was developed at UNC that exhibits no CFTR expression. Interestingly, the CF mouse demonstrates abnormal incisor enamel. Therefore, the purpose of this investigation was to characterize the enamel in this CF mouse model. Incisors from CF and normal mice were evaluated by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The enamel proteins were examined by amino acid analysis, SDS-PAGE, and Western blot. Gross examination showed that 100% of CF mice had soft, chalky white incisor enamel, while the enamel of normal mice was hard and yellow-brown. LM indicated that the ameloblasts in the CF mice underwent premature degeneration shortly after completion of the secretory phase. The CF mouse enamel appeared to be of relatively normal thickness and showed a prism structure similar to that of normal mouse enamel. However, the CF mouse enamel crystallites appeared to have a rough granular surface compared with normal enamel. SDS-PAGE indicated that mature CF enamel retained low-molecular-weight material (~ 20 kDa), whereas normal mature enamel did not. This low-molecular-weight material cross-reacted with anti-amelogenin antibodies in Western blot analysis. This investigation shows that abnormal CFTR expression in the mouse results in developmental abnormalities in the incisor enamel. Although further investigation is required to determine the mechanism leading to abnormal enamel formation, the CF mouse provides a potentially useful animal model for investigating aberrant enamel development.
A Comparison of the Ability of Intra-oral and Extra-oral Fibroblasts to Stimulate Extracellular Matrix Reorganization in a Model of Wound Contraction
Authors: Stephens P. , Davies K.J. , Al-Khateeb T. , Shepherd J.P. , Thomas D.W.
Published: January 2009

Intra-oral wounds, like wounds in children, demonstrate privileged healing when compared with adult wounds at extra-oral sites. This study investigated whether this preferential healing is related to an increased ability of oral mucosal fibroblasts to reorganize extracellular matrix (ECM) when compared with their dermal counterparts. ECM reorganization was investigated by means of a fibroblast-populated collagen lattice (FPCL) system. The effect of donor age was also investigated in this system. Differences in ECM reorganization and FPCL contraction were evident: FPCL contraction was more rapid by oral mucosal fibroblasts than dermal fibroblasts (p < 0.01). FPCL contraction was also greater in child (donor < 10 years) than adult (donor > 18 years) oral mucosal fibroblasts (p < 0.01). These differences were not related to phenotypic differences in cell viability (p > 0.5), DNA synthesis (p > 0.05), and cell number (p > 0.5) within the FPCLs, or cellular attachment to collagen (p > 0.07). FPCL contraction was not stimulated by the addition of conditioned medium from oral mucosal or dermal fibroblasts (p > 0.05). These data show that the significantly increased ability of oral mucosal fibroblasts to reorganize ECM in vitro, when compared with dermal fibroblasts, represents a distinct phenotypic contractile difference, rather than differences in their production of soluble mediators or cell attachment to ECM.
Electrophoretic Gels of Dentin Matrix Proteins as Diffusion Media for in vitro Mineralization
Authors: Wada Y. , Fujisawa R. , Nodasaka Y. , Kuboki Y.
Published: January 2009

Non-collagenous proteins of dentin and bone have important effects on mineralization which have been studied by various in vitro systems. We developed an in vitro mineralization system using electrophoretic gels as diffusion media of calcium and phosphate ions. Calcium and phosphate ions were diffused naturally or propelled by electric potential. Calcium phosphate was precipitated in the gel, and the precipitation was affected by proteins in the gel which had been separated by electrophoresis. We applied this system to analysis of non-collagenous proteins of dentin. Among the proteins, phosphophoryns promoted calcium phosphate precipitation in the natural-diffusion system. A non-collagenous protein having a molecular mass of 60 kDa inhibited precipitation. The results were different, however, in the electric-diffusion system, in which phosphophoryns had a negative effect. The present system enabled us to compare the effects of plural proteins rapidly, even using unpurified material.
Total Fluoride Intake in Children Aged 3 to 4 Years—A Longitudinal Study
Authors: Guha-Chowdhury N. , Drummond B.K. , Smillie A.C.
Published: January 2009

Several previous studies using food consumption tables or diet records have estimated that children aged 1 to 12 years resident in fluoridated (1 ppm) areas receive, on average, between 0.05 and 0.07 mg fluoride/kg body weight from foods and drinks alone. In this study, the duplicate-diet approach, which is a more accurate method of determining nutrient intake, was used to determine if levels of fluoride intake from foods and drinks are similar to those estimated from food consumption tables or diet records. Duplicate portions of all foods and drinks consumed over 24 hours by 66 children aged 3 to 4 years resident in fluoridated and low-fluoride areas of New Zealand were collected on three separate days over a period of 12 months and analyzed for fluoride. Fluoride intake from the use and ingestion of toothpastes and fluoride supplements was also determined for each child. It was hypothesized that the total amount of fluoride received by children in low-fluoride areas from diet, toothpastes, and fluoride supplements was similar to that received by children in fluoridated areas from diet and toothpastes. The mean fluoride intake from foods and drinks alone in the low-fluoride areas was 0.008 ± 0.003 mg/kg body weight (0.15 ± 0.06 mg/day; n = 34) and in the fluoridated areas was 0.019 ± 0.009 mg/kg body weight (0.36 ± 0.17 mg/day; n = 32). The mean fluoride intake from foods and drinks and toothpastes in the low-fluoride areas was 0.027 ± 0.012 mg/kg body weight (0.49 ± 0.25 mg/day) and in the fluoridated areas was 0.036 ± 0.015 mg/kg body weight (0.68 ± 0.27 mg/day). Fluoride intake from diet alone did not exceed 0.04 mg/kg body weight (0.74 mg/day), and fluoride intake from diet and toothpaste did not exceed 0.07 mg/kg body weight (1.31 mg/day). The results suggest that levels of fluoride intake from foods and drinks alone as estimated by the duplicate-diet approach are much lower than previously estimated from food consumption tables or diet records. It was calculated that if all children in the low-fluoride areas were to take currently recommended dosages of fluoride tablets, which have been based on dietary surveys and diet records, then the total fluoride intake of some children in the low-fluoride areas would exceed that of their counterparts in the fluoridated areas. The results suggest that currently recommended dosages of fluoride tablets need to be further reduced if dental fluorosis in children is to be avoided.
Form Difference Computations in Restorative Dentistry Utilizing the Macroelement Method
Authors: McAlamey M.E. , Phillips C.B. , Song D.
Published: January 2009

The comparison between the size and shape (form) of two structures or the analysis of one object under differing conditions is important in restorative dentistry. Despite rapid advances in digitizing technologies, form comparison is still mainly limited to scalar measurements. The objective of this study was to test the potential use of a newly developed tensorial morphometric difference technique, the macroelement method, in a model restorative system where the processing and materials properties are known: duplication of a denture anchor in stone via polysulfide, addition silicone, and polyether impression materials. Nine machined landmarks were utilized to construct a nine-sided element for macroelement analysis. Macroelement results compared well with the known impression materials properties of polymerization shrinkage and incomplete recovery in terms of: (1) larger die diameter, (2) smaller die (vertically), (3) horizontal direction of maximum expansion, and (4) vertical direction of maximum contraction. Also, macroelement results along boundary lines were equal to the traditional form difference measure of change in length/length of those lines. The macroelement method provided results which are superior to those of traditional methods in that both (1) the magnitude and direction of difference at any point on the structure could be determined, and (2) the graphical representation of the results provides an intuitive appreciation of how and where the forms differ. Therefore, since macroelement results: (1) compare well with known materials properties and traditional measures, and (2) have the above-stated advantages, tensorial techniques such as the macroelement method, used in conjunction with new digitizing technologies, can be used better to describe the kinematics of form difference. With the description of the kinematics provided by the technique, the dynamic cause of the form difference can be ascertained with the investigators' knowledge of materials. The investigators can then suggest changes to be made in materials and/or techniques that would enable the desired size and shape to be obtained.
Finite Element Stress Analysis of Three Filling Techniques for Class V Light-cured Composite Restorations
Authors: Winkler M.M. , Katona T.R. , Paydar N.H.
Published: January 2009

An important disadvantage of current dental resin composites is polymerization shrinkage. This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries. The objective of this study was to compare three filling techniques in terms of the transient stresses induced at the resin composite/tooth interface during polymerization. The techniques were: bulk filling (B), three horizontal increments (HI), and three wedge increments (WI). A simple Class V cavity preparation was modeled in finite element analysis. Polymerization shrinkage was simulated by a thermal stress analogy, thereby causing 1% shrinkage due to an arbitrary coefficient of thermal expansion. Interface normal and shear stresses were calculated at nine steps during polymerization, proceeding from 0% to 100% volume of cured resin. The importance of the interface transient stresses was revealed by the finding that, in most cases, their peak values exceeded the final or residual stress. Also, the WI and B techniques consistently exhibited the highest and lowest maximum transient stresses, respectively. These results from the simple model of a Class V restoration suggest that bulk filling of light-cured resin composites should be used in restorations which are sufficiently shallow to be cured to their full depth.
Microvascular Luminal Volume Changes in Aged Mouse Periodontal Ligament
Authors: Sims M.R. , Leppard P.I. , Sampson W.J. , Dreyer C.W.
Published: January 2009

Data for the microvascular bed in the aged periodontal ligament have not been established. This investigation tested the hypothesis that the luminal microvascular volume decreased in the aged ligament. Mice 35 days old and one year old were vascular-perfused and the mandibular first molar periodontal ligament processed for electron microscopy. Tissue quadrats from each circumferential third ligament region were recorded at 150-μm intervals from the alveolar crest to the apex for randomized sampling of blood vessel lumina. The data were analyzed with a generalized linear model at the p < 0.01 level for the interaction of the aging effect with differences across regions. Stereological parameters were established for vessel lumen volume, and for surface and length densities. Mean ligament width decreased from 119.9 ± 16.94 (μm ± SE) in young mice to 60.0 ± 10.58 (μm ± SE) in aged mice. The luminal volume of 8.63 ± 1.37 (% ± SE) in young ligament increased to 9.83 ± 2.14 (% ± SE) in aged ligament. Collecting venules and the combined group of arterio-venous anastomoses with terminal arterioles showed a two-fold increase in luminal volume density (p < 0.01). In aged ligament, regional shifts affected the microvascular bed distribution, but these changes were not consistent across regions, or with depth. The average cross-sectional tissue area served per capillary decreased from 2117 μm2 to 1451 μm 2 for young and old. Average ligament thickness served per capillary dropped from 52.5 μm to 27.5 μm. These reductions in average diffusion distances indicated a change in the quality of the diffusion barrier with age.
The Human Mandibular Canal Arises from Three Separate Canals Innervating Different Tooth Groups
Authors: Chávez-Lomelí M.E. , Mansilla Lory J. , Pompa J.A. , Kjær I.
Published: January 2009

The purpose of this study was to describe the prenatal formation of the human mandibular canal. Since bony canals develop in prenatal life around the nerve paths, it was assumed that the canal pattern could reflect the pattern of innervation of the dentition. Mapping of this early canal pattern does not appear to have been undertaken before. The material consisted of anthropological mandibles from the National Institute of Anthropology and History, Mexico City. A total of 302 human hemimandibles from the latter half of the prenatal period was investigated. The length, measured from the mental symphysis to the mandibular condyle, ranged from 28 to 60 mm. The dento-alveolar maturity was classified in two stages according to the appearance of alveolar sockets of deciduous and first permanent molars. The mandibles were radiographed with guttapercha points inserted into the canal openings (foramina) on the lingual surfaces of the mandibular rami. The study showed that the canal to the incisors appeared first, followed by the canal to the primary molars, and last by the one or more canals to the first permanent molars. In the most mature group, three different canals always occurred in each hemimandible. The canals were directed from the lingual surface of the mandibular ramus toward the different tooth groups. The inferior alveolar nerve presumably occurs in the mandible as three individual nerve paths originating at different stages of development. It is suggested that rapid prenatal growth and remodeling in the ramus region result in a gradual coalescence of the canal entrances that is obvious at birth. It is hypothesized that the pattern of tooth agenesis within the three groups of teeth is related to the three separate paths of innervation of the dentition.
Immunolocalization of Fibronectin during Reparative Dentinogenesis in Human Teeth after Pulp Capping with Calcium Hydroxide
Authors: Yoshiba K. , Yoshiba N. , Nakamura H. , Iwaku M. , Ozawa H.
Published: January 2009

Exposed dental pulp is known to possess the ability to form a hard-tissue barrier (dentin bridge). The exact mechanisms by which pulp cells differentiate into odontoblasts in this process are unknown. Fibronectin has been demonstrated to play a crucial role in odontoblast differentiation during tooth development. This study tested the hypothesis that fibronectin is involved in the initial stages of replacement odontoblast differentiation and reparative dentin formation. We observed its immunohistochemical localization during dentin bridge formation in human teeth, after pulp was capped with calcium hydroxide [Ca(OH)2]. One day after the capping, precipitation of crystalline structures was observed at the TEM level in association with cell debris at the interface between the superficial necrotic zone and underlying pulp tissue. This layer of dystrophic calcification showed positive reaction for fibronectin, and pulp cells appeared to be closely associated with this layer, seven to ten days postoperatively. At 14 days, an alignment of cells, some of which were elongated and odontoblast-like, was observed adjacent to the fibroriectin-positive irregular matrix. Between the cells, corkscrew fiber-like fluorescence was visible. At 28 days, the irregular fibrous matrix was followed by the formation of tubular dentin-like matrix lined with odontoblast-like cells. Therefore, it would seem that fibronectin associated with the initially formed calcified layer might play a mediating role in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis, after pulp was capped with Ca(OH)2.
Poor Oral Health and Coronary Heart Disease
Authors: Joshipura K.J. , Rimm E.B. , Douglass C.W. , Trichopoulos D. , Ascherio A. , Willett W.C.
Published: January 2009

A few recent studies have shown associations between poor oral health and coronary heart disease (CHD). The objective of this study was to examine the incidence of CHD in relation to number of teeth present and periodontal disease, and to explore potential mediators of this association, in a prospective cohort study. This study is a part of the ongoing Health Professionals Follow-Up Study (HPFS). Participants included a US national sample of 44,119 male health professionals (58% of whom were dentists), from 40 to 75 years of age, who reported no diagnosed CHD, cancer, or diabetes at baseline. We recorded 757 incident cases of CHD, including fatal and non-fatal mvocardial infarction and sudden death, in six years of follow-up. Among men who reported pre-existing periodontal disease, those with 10 or fewer teeth were at increased risk of CHD compared with men with 25 or more teeth (relative risk = 1.67; 95% confidence interval, 1.03 to 2.71), after adjustment for standard CHD risk factors. Among men without pre-existing periodontal disease, no relationship was found (relative risk = 1.11; 95% confidence interval, 0.74 to 1.68). The associations were only slightly attenuated after we controlled for dietary factors. No overall associations were found between periodontal disease and coronary heart disease. Tooth loss may be associated with increased risk of CHD, primarily among those with a positive periodontal disease history; diet was only a small mediator of this association.
Quantitative Assessment of the Efficacy of Amorphous Calcium Phosphate/Methacrylate Composites in Remineralizing Caries-like Lesions Artificially Produced in Bovine Enamel
Authors: Skrtic D. , Hailer A.W. , Takagi S. , Antonucci J.M. , Eanes E.D.
Published: January 2009

Recent studies show that methacrylate-based composites with amorphous calcium phosphate (ACP) as a filler can release supersaturating levels of calcium and phosphate ions in proportions favorable for apatite formation. These findings suggest that such composites could be effectively used as coatings for remineralizing teeth damaged by tooth decay. To examine this hypothesis, we tested composites in vitro for their efficacy to remineralize artificially formed caries-like lesions in extracted bovine incisors. Single 120-μm-thick sagittal tooth sections were placed in holders that exposed only the carious enamel surface. The exposed surfaces were coated with a 1-mm- to 1.5-mm-thick layer of the composite containing, by mass, 40% apatite, silica, or P2O74--stabilized ACP and 60% photoactivated resin comprised of Bis-GMA, TEGDMA, HEMA, and ZrM. The photocured composite-coated sections were immersed either in a remineralizing solution for 4 weeks at 37°C (static model) or cyclically immersed in demineralizing (0.5 h) and remineralizing solutions (11.5 h) for 2 weeks (dynamic model). Quantitative digital image analysis of matched 102 μm x 220 um areas from contact microradiographs taken of the sections before and after immersion showed that lesions coated with ACP-filled composites fractionally recovered 71% ± 33% of their lost mineral compared with 14% ± 13% for apatite controls in the static model and 38% ± 16% compared with -6% ± 24% in the dynamic model. The results suggest that sealants based on ACP-filled methacrylate composites have the potential to remineralize carious enamel lesions.
Palatal Displacement of Canine is Genetic and Related to Congenital Absence of Teeth
Authors: Pirinen S. , Arte S. , Apajalahti S.
Published: January 2009

The palatally displaced canine is a harmful complication of dental development. It appears in 1 to 2% of the Western population. According to our clinical experience, this anomaly is seen in families in which missing and peg-shaped teeth are common. It could be caused by the same genetic component that causes incisor-premolar hypodontia. We examined 106 patients who had been operated on and treated orthodontically for palatally impacted canine(s). The patients and their family members were examined for dental anomalies. One hundred and ten first- and 93 second-degree relatives were clinically and radiologically examined, and 35 pedigrees were constructed. Thirty-six percent of the patients had congenitally missing permanent teeth (hypodontia), which is 4.5 times the population prevalence. Hypodontia was noted in 19 to 20% of both the first- and second-degree relatives. This is 2.5 times the population prevalence. Frequency of missing teeth, analyzed by tooth groups, was of the same order as that shown for incisor-premolar hypodontia in the Western population. In six of the 35 pedigrees, a palatally impacted canine was noted in several generations of the same family. Prevalence of this anomaly was 4.9% in the studied group, which is 2.5 times the population prevalence. From the findings, we conclude that the palatally displaced canine belongs to the spectrum of dental abnormalities related to hypodontia.
Induced Hypoxia in Rat Pulp and Periapex Demonstrated by 3H-Misonidazole Retention
Authors: Baumgardner K.R. , Walton R.E. , Osborne J.W. , Born J.L.
Published: January 2009

Cellular hypoxia may be a useful indication of tissue distress in the dental pulp that could be used to investigate the early stages of pulpal responses. Tritiated misonidazole (3H-MISO) is a marker which preferentially labels cells with decreased oxygen tension (hypoxia). The experiments reported here were carried out to determine whether this agent could distinguish between hypoxic and normoxic pulp and periapical tissues. Rats were injected intra-peritoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic, hypoxic, and control groups. Normoxic animals were maintained at ambient pressure. We induced hypoxia by maintaining animals in a hypobaric chamber at 0.5 atm for 24 hrs. 3H-MISO retention was assessed by quantitative analysis of tissue autoradiographs. 3H-MISO retention rates in normoxic animals showed little variation except for increased retention in mature ameloblasts and immature odontoblasts in the continually erupting incisor. In both incisor and molar pulps, hypobaric hypoxia significantly increased 3H-MISO retention when compared with normoxic controls. Hypobaric hypoxia also resulted in intense 3H-MISO retention in cellular cementum, periodontal ligament, osteocytes, and, occasionally, in molar pulp horn odontoblasts. This study demonstrated that, with standard autoradiographic techniques, 3H-MISO can label induced hypoxic disturbances in the pulp and surrounding periodontium.
Angiogenesis in Human Dental Pulp Following Orthodontic Tooth Movement
Authors: Derringer K.A. , Jaggers D.C. , Linden R.W.A.
Published: January 2009

The pulpal response to orthodontic force is thought to involve cell damage, inflammation, and wound healing. These situations are likely to be associated with the release of angiogenic growth factors. We therefore investigated human dental pulps to determine if angiogenic changes could be detected after orthodontic force application. Fifteen premolar teeth were treated with straight-wire fixed orthodontic appliances for two weeks, and comparisons were made with 15 untreated control premolar teeth from the same subjects. The teeth were extracted and sectioned. The pulps were removed, divided into 1-mm sections, embedded in collagen, and cultured in growth media for up to four weeks. Cultures were examined daily, by light microscopy, for growth and number of microvessels. Apparent microvessels were observed within five days. Confirmation of microvessel identification was by electron microscopy for endothelial cell morphology. There were significantly greater numbers of microvessels at day five and day ten of culture in the pulp explants from orthodontically treated teeth compared with those from the pulps of control teeth. These results are consistent with the hypothesis that there is an increase in angiogenic growth factors in the pulp of orthodontically moved teeth.
Striatal D2 Receptor Binding in Sleep Bruxism: A Controlled Study with Iodine-123-Iodobenzamide and Single-photon-emission Computed Tomography
Authors: Lobbezoo F. , Soucy J.-P. , Montplaisir J.Y. , Lavigne G.J.
Published: January 2009

The neurochemical mechanisms underlying sleep bruxism are little understood at present. However, recent pharmacologic evidence suggests that the central dopaminergic system may be involved in the pathophysiology of sleep bruxism. This possibility was further assessed by means of functional neuroimaging of dopamine D2 receptors with single-photon-emission computed tomography (SPECT). Ten controls and ten patients with polysomnographically confirmed sleep bruxism were injected intravenously with 185 MBq (5 mCi) iodine-123-iodobenzamide, a specific D2 receptor antagonist radioligand, and data acquisition was performed 90 min post-injection. Following image reconstruction, it was found that striatal D2 receptor binding potential (basal ganglia/background ratio) did not differ significantly between bruxism patients and controls. However, side-to-side differences between unilateral values of the striatal D2 binding potential ("highest side" values minus "lowest side" values) were significantly larger for the bruxism patients (p < 0.001, by two-independent-samples t test with pooled variances). It was concluded that an abnormal side imbalance in striatal D2 receptor expression can be associated with sleep bruxism. This reinforces the possibility that the central dopaminergic system plays a role in the pathophysiology of this disorder.
Anatomic and Directional Variation in the Mechanical Properties of the Mandibular Condyle in Pigs
Authors: Teng S. , Herring S.W.
Published: January 2009

Stereologic studies of trabecular architecture suggest that the pig mandibular condyle is strongest when loaded supero-inferiorly, and that stress is concentrated in the antero-inferior region (Teng and Herring, 1995). To test these hypotheses, we investigated the uni-axial mechanical properties of 22 pig mandibular condyles in three loading directions at a mean strain rate of 0.14 (± 0.12)% s-1. A total of 91 rectangular beam specimens (averaging 9.0 mm x 6.0 mm x 5.0 mm) was tested. For each specimen, 5 or 6 nondestructive tests were performed before compressive failure. Strain in both longitudinal and transverse directions was measured by foil strain gauges on the central part of the specimen. Data were normalized at a strain rate of 0.1% s-1, specimen length of 9 mm, and cross-sectional area of 30.25 mm2. Generally, modulus of elasticity (E) and ultimate stress (σu) in the anterior regions of the condyle were greater than those in the posterior. E, σu, and Poisson's ratio (υ) were significantly different among the test directions, but ultimate strain (εu) was not. The highest values of E (4.04 GPa), σu (14.97 MPa), and p (0.81 g/cm3) were seen in the anterior inferior/middle region under supero-inferior loading. The lowest values (0.94 GPa for E, 2.38 MPa for σu, and 0.52 g/cm3 for p) were found in the inferior/posterior region in medio-lateral loading. Although the mechanical properties of the condyle vary depending upon location, these results verify that the condyle is strongest and stiffest under compressive loads in the supero-inferior direction, and that the anterior-inferior region is particularly strong and stiff.
Protein Characterization of Fluorosed Human Enamel
Authors: Wright J.T. , Chen S.C. , Hall K.I. , Yamauchi M. , Bawden J.W.
Published: January 2009

Despite extensive investigation, the developmental mechanism or mechanisms resulting in dental fluorosis are unknown. Several hypotheses suggest abnormal matrix synthesis, secretion, and delayed and/or defective matrix degradation with retention of enamel protein. The purpose of this study was to characterize the protein composition of fluorosed human enamel. Nine permanent moderately fluorosed (developed in a 3.2 ppm H2O area) and ten permanent normal control teeth (from individuals with < 0.2 ppm F in their drinking water) were evaluated. The enamel fluoride concentration, protein content, and amino acid composition were determined for each tooth. The enamel proteins were further characterized by gel electrophoresis and by Western blot analysis by means of polyclonal antibodies raised against recombinant amelogenin protein. Fluorotic enamel had significantly elevated (p = 0.0001) F levels compared with normal enamel (mean [F-] fluorosed = 431 ppm; mean [F-] control = 62 ppm). While there was a significantly greater protein content by weight in fluorosed enamel compared with normal enamel (mean fluorosed = 0.27%; mean control = 0.11%), the amino acid profiles were similar for fluorosed and normal enamel. Gel electrophoresis showed fluorosed enamel to have a greater diversity of primarily low-molecular-weight proteins compared with normal enamel. Western blot analysis did not indicate retention of amelogenin in either fluorosed or normal enamel. This investigation showed that the protein content of fluorosed enamel was greater than that of normal enamel; however, the amino acid compositions were similar for fluorosed and normal enamel. Furthermore, there does not appear to be retention of significant amounts of amelogenin in fully mature, moderately fluorosed human enamel. Although delayed removal of the enamel matrix proteins may play a role in the hypomineralization defects seen in fluorosed enamel, the majority of these proteins are absent in the mature tissue of these moderately fluorosed teeth.
Prediction of Secondary Caries around Tooth-colored Restorations: A Clinical and Microbiological Study
Authors: Kidd E.A.M. , Beighton D.
Published: January 2009

Caries at the margins of restorations is difficult to diagnose, and the relevance of staining and ditching around tooth-colored fillings is unclear. This clinical study questions the relevance of marginal color change and marginal ditching to the level of infection of the dentin beneath the margins of tooth-colored restorations. Clinically visible sites (197) on the tooth/restoration margin were selected in 113 teeth. The filling margin and the enamel adjacent to each site were noted as stained or stain-free, and sites were graded as intact, having a narrow ditch, or having a wide ditch. Thirty sites with frankly carious lesions were also included. Plaque was sampled at the toothrestoration margin and the filling removed. The enamel-dentin junction (EDJ) at each sample site was noted as hard or soft when probed, and the dentin was sampled. Samples were vortexed, diluted, and cultured for total anaerobic counts, mutans streptococci, and lactobacilli. There were more bacteria in the plaque over frankly carious cavities, and the dentin was soft and heavily infected. Only 38 out of 167 sites without frankly carious cavities had soft dentin at the EDJ. Both the plaque and dentin in these sites harbored more micro-organisms. However, none of the clinical criteria chosen would reliably predict the presence of this soft dentin. In this study, only a frankly carious lesion at the margin of the filling constituted a reliable diagnosis of secondary caries.
Electromyographic Heterogeneity in the Human Temporalis and Masseter Muscles during Dynamic Tasks Guided by Visual Feedback
Authors: Blanksma N.G. , van Eijden T.M.G.J. , van Ruijven L.J. , Weijs W.A.
Published: January 2009

The complex architecture of the human jaw muscles suggests regional differences in function within these muscles. This study examines the way the temporalis and masseter muscle regions are activated when free mandibular movements with various speeds and against various external loads are carried out guided by visual feedback. Electromyographic (EMG) activity was registered in six temporalis and three masseter muscle regions with bipolar fine-wire electrodes. Recordings were made during open/close excursions, protrusion/retrusion movements, and laterodeviations. During open/close excursions and protrusion/retrusion movements, an anterior and posterior temporalis part could be distinguished, whereas during laterodeviations a more complex partitioning of this muscle was observed. During the protrusion/retrusion movements and the laterodeviations, the temporalis muscle demonstrated higher EMG peak activities than the masseter muscle, and within the masseter muscle the deep masseter showed higher EMG peaks than the superficial one. In contrast to this, during the open/close excursions the masseter showed higher peak activities than the temporalis muscle, while the superficial masseter showed higher EMG peak activities than the deep masseter. Within the deep masseter, differences were also found. During open/close excursions, the anterior deep region demonstrated higher EMG peak activities than the posterior region, whereas during protrusion/retrusion and laterodeviations the posterior deep region showed higher peaks. In general, speed had a greater effect on the EMG peak activity than external load. Only during laterodeviations did speed and load equally influence peak activity in both the deep and superficial masseter. During protrusion/retrusion movements, load showed no significant effect on EMG peak activity in the masseter muscle. A general finding was that, according to task, different regions were activated preferentially. This points to a partitioning of the excitatory command of the motoneuron pool.
The Effect of Food Consistency upon Jaw Movement in the Macaque: A Cineradiographic Study
Authors: Thexton A. , Hiiemae K.M.
Published: January 2009

Variation in the form of masticatory cycles in individuals is often assumed to be limited. The contrary hypothesis, that jaw cycles vary widely but systematically with food consistency, was tested in macaques fed similar-sized pieces of monkey chow, apple, and banana. With the animals under general anesthesia, radiopaque markers were inserted into the jaw, tongue, and hyoid. Oral movements were recorded by cineradiography at 100 frames/sec in lateral projection synchronously with frontal view cinephotography (50 frames/sec). The films were examined for the events that subdivide each jaw movement cycle into its constituent phases (fast closing, slow closing, intercuspal, slow or early opening, final opening). The frame numbers at which these events occurred were used to define phase durations. The numbers of cycles preceding a swallow increased with the hardness of the ingested food item. Regardless of the test food, every feeding sequence (initial ingestion to final clearance of mouth) contained multiple swallows, each of which defined the end of a sub-sequence. When the animals were feeding on chow, the sub-sequences were initially long (20 cycles or more), but when they were feeding on banana, the sub-sequences were short (10 cycles or fewer). Although the form of individual cycles (defined by phase durations) was often unrelated to that of neighboring cycles, the general cycle characteristics in a sub-sequence typified a particular food. Chow feeding cycles were characterized by slow-closing (SC) phases of long duration with slow-opening (SO) phases of short duration; the characteristics of banana feeding cycles were the reverse. SC duration correlated directly and SO duration correlated inversely with food hardness (p < 0.001). The evidence supports the view that the centrally generated pattern of movement is highly dependent upon intra-oral sensory feedback.
Effect of Jaw Opening on the Direction and Magnitude of Human Incisal Bite Forces
Authors: Paphangkorakit J. , Osborn J.W.
Published: January 2009

The maximum bite force (MBF) appears to be different when measured at different jaw openings ( e.g., Manns et al., 1979; Mackenna and Turker, 1983; Lindauer et al., 1993). However, the change could be related to a change in the bite direction. We have measured the MBF on incisors and its direction in three dimensions for different jaw openings in ten subjects. Surface electromyography (EMG) of anterior temporalis and masseter muscles on both sides was recorded simultaneously. The results showed that: (1) the average %MBF increased as the jaw was opened, reached a plateau between 14 and 28 mm of incisal separation, and then decreased at wider jaw openings; (2) the initial forward bite direction with respect to the mandibular occlusal plane shifted backwards during jaw opening; and (3) the activity of the masseter muscles declined and that of the temporalis muscles was largely unchanged, resulting in an increase of the ratio between the activity in temporalis and masseter muscles (T/M). There was a significant correlation between bite direction and jaw opening (r = 0.51, p < 0.001) and between T/M ratio and jaw opening (r = 0.56, p < 0.001). Based on comparative data, we have calculated sarcomere lengths while the jaw is opened and hypothesize that the average %MBF reaches its maximum when the sarcomeres in the masseter muscle achieve their optimum length. A plateau continues during further jaw opening, until those of temporalis reach their optimum length while those of masseter lengthen beyond their optimum length. The change in bite direction was attributed to either a change in the relation between upper and lower bite points as the jaw was opened or the gradual decline of masseter activity at larger openings.
Short-chain Carboxylic Acid Concentration in Human Gingival Crevicular Fluid
Authors: Niederman R. , Buyle-Bodin Y. , Lu B.-Y. , Robinson P. , Naleway C.
Published: January 2009

Short-chain carboxylic acids (e.g., lactic acid, propionic acid, butyric acid) are metabolic by-products of bacterial metabolism which can accumulate in the gingival crevice. It is of no small consequence, therefore, that 1- to 5-mM concentrations of these acids exhibit significant biological activity, including the ability to alter cell proliferation and gene expression in cells of importance to the periodontium. This communication reports on the in vivo concentrations of propionic and butyric acid in the gingival crevices of periodontal subjects with severe and mild disease. The results indicated that severely diseased subjects exhibited a > 10-fold increase in the mM concentration of these acids when compared with mildly diseased subjects (mean propionic acid - severe = 9.5 ± 1.8 mM, and mild = 0.8 ± 0.3 mM; mean butyric acid - severe = 2.6 ± 0.4 mM, and mild = 0.2 ± 0.04 mM). These differences (mean ± SE) were significant (p < 0.0001). The propionic and butyric acid concentrations were below detection limits in healthy sites of mildly diseased subjects. The propionic and butyric acid concentrations also associated significantly with clinical measures of disease severity (e.g., pocket depth, attachment level) and inflammation (e.g., subgingival temperature, % of sites bleeding when probed), and with the total microbial load (all p < 0.05). Taken together, these data suggest that short-chain carboxylic acids play a mediating role in periodontal disease pathogenesis.
Effects of Collagenase on Root Demineralization
Authors: Kawasaki K. , Featherstone J.D.B.
Published: January 2009

The role of proteolytic enzymes in the root caries process remains unclear. The aim of this study was to investigate collagenase activity during tooth root demineralization and remineralization in an in vitro demineralization/remineralization pH-cycling model. Human tooth roots were subjected to pH cycling (alternating demineralization and remineralization) in one of two different time cycles for five days. Collagenase at 90, 180, or 360 μg per root was placed into either the demineralizing solution or the remineralizing solution in the pH-cycling system. The effects of additional exposure to collagenase before or after pH cycling were also studied. After the exposure, thin sections of the roots were examined histologically by polarized light microscopy. Changes of calcium and phosphate in the solutions were analyzed chemically. Surface erosion occurred only in the groups where collagenase was contained in the remineralizing solution and in which the root samples were exposed to severe demineralization. However, no differences among the control and experimental groups were found in calcium and phosphate changes in the pH-cycling solutions. These findings suggest that collagenase works during the remineralizing phase and predominantly attacks the organic matrix of the root after demineralization. Additional exposure to collagenase before or after pH cycling did not increase surface erosion except for exposure to collagenase in the absence of phosphate following pH cycling.
Surface Characterization of Amalgam Made with Hg-In Liquid Alloy
Authors: Nakajima H. , Akaiwa Y. , Hashimoto H. , Ferracane J.L. , Okabe T.
Published: January 2009

When amalgam was triturated with Hg-In liquid alloys instead of pure mercury, the resultant amalgams released a significantly smaller amount of mercury vapor during setting. To understand the mechanisms responsible for the drastic decrease in mercury evaporation from the In-containing amalgam, we used Auger Electron Spectroscopy to examine surface oxide films on amalgams made with Hg-10 wt% In or pure mercury. The surface of the In-containing amalgam was rapidly covered with both indium and tin oxide films. Greater amounts of oxygen were found on the γ1 Ag-Hg matrix in the In-containing amalgam than in the amalgam without indium. The rapid formation of the oxide film contributes to a reduction in the mercury release from the In-containing amalgam by forming an effective barrier to evaporation.
Sheathlin: Cloning, cDNA/Polypeptide Sequences, and Immunolocalization of Porcine Enamel Sheath Proteins
Authors: Hu C.-C. , Fukae M. , Uchida T. , Qian Q. , Zhang C.H. , Ryu O.H. , Tanabe T. , Yamakoshi Y. , Murakami C. , Dohi N. , Shimizu M. , Simmer J.P.
Published: January 2009

Sheath proteins designate low-molecular-weight non-amelogenin enamel polypeptides and their parent protein, which concentrate in the sheath space separating rod and interrod enamel (Uchida et al., 1995). Two porcine sheath proteins, with apparent molecular weights of 13 and 15 kDa, are characterized by protein sequencing. The primary structures of these polypeptides match a portion of the derived amino acid sequences of clones isolated from a porcine enamel organ epithelia-specific cDNA library. Sheath protein RNA messages differ by the inclusion or deletion of a 45-nucleotide segment and by the use of three alternative polyadenylation/cleavage sites. The secreted proteins are 395 and 380 residues in length, with molecular masses of 42,358 and 40,279 Daltons and calculated isoelectric points of 6.3 and 6.7, respectively. Polyclonal antibodies were raised against a synthetic peptide having the sheathlin-specific sequence EHETQQYEYSGGC. Immunohistochemistry with this antibody demonstrates that the protein encoded by the sheathlin cDNA is preferentially localized in the sheath space. We propose that the porcine sheath proteins and their proteolytic cleavage products be designated "sheathlin".