bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbachol-induced Oxygen Consumption in Slices from Developing Rat Submandibular and Parotid Glands
Authors: Stojic D.
Published: January 2009

In contrast to the submandibular gland, the developing rat parotid gland shows refractoriness to cholinergic secretagogues until 2 wks of age. To assess the underlining mechanism of this refractoriness, I investigated changes in oxygen consumption as a function of animal age in slices from rat submandibular and parotid glands, measuring both basal and carbachol-stimulated levels. The oxygen consumption was determined by a direct manometric method in the Warburg apparatus. Carbachol-induced oxygen uptake in submandibular gland slices was observed by 1 day of age and reached the adult level of stimulation by 3 wks of age. In the parotid gland, carbachol failed to stimulate oxygen uptake in the early post-natal period, and the first response was detected at 2 wks of age, reaching the adult level at 4 wks of age. Para-fluorohexahydro-siladiphenidol (pFHHSiD), a selective M3 antagonist, inhibited carbachol-induced oxygen uptake in both glands, while pirenzepine, a selective M1 antagonist, had no effect, suggesting that the M3 muscarinic receptors are involved in this process. The respiratory effect of carbachol, in both glands, was inhibitable by ouabain and, to a lesser extent, by furosemide, indicating that carbachol-enhanced oxygen uptake is due to Na,K-ATPase and that the furosemide-sensitive co-transport of Na+ entry is underdeveloped in immature cells. The ouabain-sensitive Na,K-ATPase activity in the parotid gland increased from birth until 28 days of age. At the time of parotid gland refractoriness to carbachol, Ca2+ionophore A23187 caused an increase of oxygen uptake only in the presence of extracellular Ca2+. In the presence of carbachol, the effect of ionophore was significantly higher than that of ionophore alone. These results raise the possibility that the refractoriness of the parotid gland to carbachol is due to the inability of carbachol to increase Ca2+uptake rather than to the lack of distal limb, which resides on the pathway from receptor stimulation to Na,K-ATPase activation.
Potassium is Involved in Apatite Biomineralization
Authors: Wiesmann H.-P. , Plate U. , Zierold K. , Höhling H.J.
Published: January 2009

The biogenetic formation of mineral crystals, one aspect of biomineralization, is a multistep process of apatite formation throughout the growth of dentin tissue. An important step is the transformation of the non-mineralized predentin matrix to mineralizing dentin matrix and its biological control. In this study, the high capacity of elemental mapping is combined with single x-ray point measurements to elucidate whether special elements are involved in initiation or regulation of mineral nucleation. Directly at the mineralization front, micro-areas with a strong co-enrichment of phosphorus ( e.g., as phosphate) and potassium are found. During the beginning of the calcium enrichment and the subsequent apatite mineral formation in the characteristic micro-areas, the content of potassium decreases significantly. These findings indicate that potassium is involved in the process of dentin mineralization.
Commensal Communism and the Oral Cavity
Authors: Henderson B. , Wilson M.
Published: January 2009

The world we live in contains unimaginable numbers of bacteria, and these and other single-celled creatures represent the major diversity of life on our planet. During the last decade or so, the complexity and intimacy of the interactions which occur between bacteria and host eukaryotic cells during the of infection have begun to emerge. The study of such interactions is the subject of the new discipline of cellular microbiology. This intimacy of bacteria/host interactions creates a major paradox. The average human being is 90% bacteria in terms of cell numbers. These bacteria constitute the commensal or normal microflora and populate the mucosal surfaces of the oral cavity, gastrointestinal tract, urogenital tract, and the surface of the skin. In bacterial infections, much of the pathology is due to the release of a range of bacterial components ( e.g., modulins such as Hpopotysaccharide, peptidoglycan, DNA, molecular chaperones), which induce the synthesis of the local hormone-like molecules known as pro-inflammatory cytokines, However, such components must also be constantly released by the vast numbers of bacteria constituting the normal microflora and, as a consequence, our mucosae should constantly be in a state of inflammation. This is patently the case, and a hypothesis is forwarded to account for this ''commensal paradox", namely, that our commensal bacteria and mucosal surfaces exist in a state of bio-communism, forming a unified "tissue" in which interactions between bacteria and epithelia are finely balanced to ensure bacterial survival and prevent the induction of damaging inflammation. Evidence is emerging that bacteria can produce a variety of proteins which can inhibit the synthesis/release of inflammatory cytokines. The authors predict that such proteins are simply one part of an extensive signaling system which occurs between bacteria and epithelial cells at mucosal surfaces such as those found in the oral cavity.
The Riddle of the Large Loss in Bite Force after Fast Jaw-closing Movements
Authors: Slager G.E.C. , Otten E. , Nagashima T. , van Willigen J.D.
Published: January 2009

In unloading experiments (in which the resistance to a forceful static bite is suddenly removed), it is shown that the residual bite force (when the jaw system is arrested shortly after the unloading) is remarkably small. For example, of a 100-N initial bite force, only 18 N is left after a jaw travel distance of 5.0 mm. The present experiments were designed to study whether the magnitude of the low residual bite force is dependent on the initial bite force, the initial degree of mouth opening, and the distance of jaw travel. Furthermore, we analyzed whether the low magnitude of the residual force can be attributed to reflex events of the jaw muscles or to the force-length properties of the jaw-closing muscles. It was found that the residual forces are largely dependent on the distance of jaw travel and are barely sensitive to variations in initial mouth-opening. The relative residual forces are independent of the magnitude of the initial bite force. The maximum residual forces are on the order of 25% of the initial bite force after a jaw travel of 4.5 mm. The low values of the residual forces cannot be attributed to reflex events, because it took about 80 ms for the masseter muscles to decrease their force to a 50% level after their excitation was switched off. Furthermore, it was shown that the force-length properties of the jaw-closing muscles are not responsible for the small values of the residual forces, since over the trajectories used in the present experiments, the sarcomere lengths of the jaw-closing muscles were beyond their optimum. It is suggested that the low residual forces are brought about by (1) a non-uniform sarcomere behavior of the jaw-closing muscles when contracting, or (2) a long-lasting change in the myofilament system of the closing muscles induced by the sudden shortening of muscle fibers.
cDNA Cloning of S100 Calcium-binding Proteins from Bovine Periodontal Ligament and Their Expression in Oral Tissues
Authors: Duarte W.R. , Kasugai S. , Iimura T. , Oida S. , Takenaga K. , Ohya K. , Ishikawa I.
Published: January 2009

The periodontal ligament (PDL) is a unique tissue that is crucial for tooth function. However, little is known of the molecular mechanisms controlling PDL function. To characterize PDL cells at the molecular level, we constructed a cDNA library from bovine PDL tissue. We then focused on the isolation of S100 calcium-binding proteins (CaBPs), because they mediate Ca2+ signaling and control important cellular processes such as differentiation and metabolism. We screened the PDL cDNA library with a mouse S100A4 cDNA, and cloned the bovine cDNAs of two S100 CaBPs (S100A4 and S100A2). In Northern blotting analysis, the highest expression of S100A4 was detected in PDL from erupted teeth (PDLE). PDL from teeth under eruption (PDLU) showed a lower expression of S100A4, and its expression in gingiva was faintly detectable. S100A4 expression was also high in the pulp tissue followed by the dental papilla of the tooth germ. S100A2 expression was high in PDLE and gingiva. Interestingly, only PDLE exhibited a high expression of both S100A4 and S100A2. PDLE also expressed the highest level of β-actin, a target cytoskeletal protein for S100A4. It is conceivable that the high expression of S100A4 in PDLE is a result of the maturation of the PDL and/or a response to mechanical stress generated by mastication. Since there was a marked difference of S100A4 expression between PDL and gingiva, we propose that S100A4 could be a useful marker for distinguishing cells from these two tissues.
Expression of Transforming Growth Factor-beta 1 (TGF-β1) in the Developing Periodontium of Rats
Authors: Gao J. , Symons A.L. , Bartold P.M.
Published: January 2009

Transforming growth factor-beta 1 (TGF-pl) has been reported to be expressed within several tissue compartments of developing molar crowns and therefore is implicated in tooth development. Additionally, TGF-β1 may also play a crucial role in tissue repair and regeneration. The aim of this study was to determine the distribution of TGF-β1 in the developing periodontal attachment apparatus (cementum, periodontal ligament, and alveolar bone) in Lewis rats. Animals aged 3, 6, and 12 wks were killed, their mandibles removed, fixed, demineralized, and processed in paraffin. The localization of TGF-β1 in tissues was detected by polyclonal goat antibodies against human TGF-pl by means of immunoperoxidase techniques. TGF-β1 messenger RNA was detected by in situ hybridization with a cocktail oligonucleotide probe. Cell counts were determined for analysis of the percentage of cells stained positive for TGF-β1. Results revealed that TGF-β1 was expressed in the developing alveolar bone, periodontal ligament, and cementum at all stages of tissue development studied. Staining was stronger at sites of cementum and alveolar bone compared with the periodontal ligament. Intensity of the positive staining, based on 3 grades, indicated a similarity between the tissues obtained from different ages, but varied between several cell types. Cementoblasts and osteoblasts stained more strongly than fibroblasts. Large numbers (- 90%) of the osteocytes in developing bone expressed TGF-β1; however, in mature bone, fewer osteocytes stained for TGF-β1. The percentages of positively stained cementoblasts, osteoblasts, and fibroblasts in the periodontal space were greater at the apical portion than at the cervical portion of the root. TGF-β1 mRNA was expressed in osteoblasts, some bone marrow cells, cementoblasts, and fibroblasts. This study indicates that TGF-β1 may play an important role in the modulation of tissue formation and development of the periodontium.
Morphometric Studies of Collagen and Fibrin Lattices Contracted by Human Gingival Fibroblasts; Comparison with Dermal Fibroblasts
Authors: Lorimier S. , Hornebeck W. , Godeau G. , Pellat B. , Gillery P. , Maquart EX , Laurent-Maquin D.
Published: January 2009

Cell shape variations and substratum re-organization during contraction of floating collagen and fibrin lattices seeded with human gingival fibroblasts were determined by computerized image analysis of light and scanning electron microscopic images. Data were compared with those obtained with lattices populated with human dermal fibroblasts. The extent of collagen lattice contraction was similar with both cell types, resulting in a two-fold decrease in the area fractions occupied by collagen fibers. Fibroblasts exhibited a rounded shape (form factors equal to 0.8 and 0.7 for gingival and dermal cells, respectively) at day 1 of culture; they possessed a more elongated appearance (with form factors equal to 0.3 and 0.15 for gingival and dermal cells, respectively) at day 7. Continuous (gingival) and discontinuous (dermal) layers of cells were evidenced at the cortex of lattices. Contractions were associated with a significant reduction of the diameters of collagen fibers. Re-organization of substratum, as analyzed by the "Rose of Directions" technique, was evidenced only at the vicinity of filipodia where fibers ran parallel to these protrusions. Several lvsed matrix cavities were observed when fibrin lattices were populated with gingival but not dermal fibroblasts at day 5 of culture. Although cells in fibrin lattices exhibited morphometric parameters comparable with those in collagen lattices, no fibroblast layers could be demonstrated at gel peripheries. Fibrin matrices consisted of an isotropic network of entangled fibrin filaments from the start of culture, and only a slight reduction of the diameters of fibrin fibers could be evidenced in dermal fibroblast-populated lattices. Fibrinolysis at the vicinity of gingival fibroblasts led to an entire re-organization of substratum toward the formation of larger fibers. The differential behavior of gingival vs. dermal fibroblasts inside fibrin but not collagen matrices could therefore partly explain the increased rate of remodeling of gingiva as compared with dermis.
Relationship between Growth and the Pattern of Tooth Initiation in Alligator Embryos
Authors: Osborn J.W.
Published: January 2009

The temporal and spatial patterns in which teeth are initiated in the growing jaws of embryos are constant for a species but different for different species. The sources of the patterns have been explained in two ways. First, they are the outcome of reactions between molecules created at stationary targets and those which diffuse through embryonic tissues (e.g., Edmund, 1960). Second, Osborn (1978) supposed that the patterns mirror the way a (mixed) population of parent cells, the tooth clone, grows. Westergaard and Ferguson (1986, 1987, 1990) concluded, from their observations of the sequence of tooth initiation in alligators, that the complicated sequences in which 20 teeth are initiated in each tooth quadrant could not be explained by jaw growth. The present study attempts to refute this criticism by means of measurements made from the raw data published by Westergaard and Ferguson. These data reveal that new teeth, here called primary teeth, are added at a constant rate at the back of the jaw. Interstitial growth of the cells between primary teeth creates space for secondary teeth in secondary regions. The secondary regions increase in length exponentially with time. The sequence in which teeth are initiated in the growing secondary regions was found to be the same in every part of the upper and lower jaws. It was accurately reproduced by a computer program based on a linear contraction rate of inhibitory zones and exponential growth of secondary regions. The results suggest that the posterior progress zone in alligator embryos grows about 125 μm a day. Newly initiated tooth germs are surrounded by an inhibitory zone about 250 μm in diameter. These zones contract from 20 to 30 μm a day until they are about 170 μm in diameter. The sequences in which tooth positions are initiated in embryos may be more the result of the pattern in which cells escape from molecules that inhibit induction rather than the pattern in which cells create molecules that initiate induction.
Interfacial Characteristics of Resin-modified Glass-ionomer Materials: A Study on Fluid Permeability Using Confocal Fluorescence Microscopy
Authors: Sidhu S.K. , Watson T.E.
Published: January 2009

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.
Cytotoxicity of Dental Alloy Extracts and Corresponding Metal Salt Solutions
Authors: Schmalz G. , Langer H. , Schweikl H.
Published: January 2009

Adverse tissue reactions of the gingiva and the periodontium close to dental cast alloys may be caused by the effects of released metal elements. Tissue reactions depend upon the amounts of elements available which are a function of corrosion rates. Since pH values of standard corrosion solutions are as low as 2.3, such extracts are a priori not biocompatible. In the present study, elements released from dental cast alloys into cell-culture media were determined, and the cytotoxicity of these medium extracts was compared with the effectiveness of metal salt solutions prepared according to the metal elements found in extracts. The elements Ag, Cu, Ni, and Zn were detected in extracts of dental alloys and copper (positive control) by inductively coupled plasma atomic emission spectrometry (ICP-AES). Medium extracts of dental alloys were non-toxic in mouse fibroblasts (L929 cells). However, the amounts of elements found in these extracts were weakly cytotoxic when tested as salt solutions prepared from chloride (Cu2+, Zn 2+, Ni2+) or sulfate (Ag1+) salts. When the test specimens were heat-treated before extraction, extracts were clearly cytotoxic in a dose-related manner. Again, the amounts of elements that caused 50% cell death (TC50) were slightly lower in corresponding salt solutions than in extracts. In general, cytotoxicity of medium extracts consistently proved to be slightly less than that of the corresponding salt solutions, probably due to the limitations of the chemical analysis of extracts. This should be taken into account if salt solutions are used instead of the medium extract.
Autoregulation of Periodontal Ligament Cell Phenotype and Functions by Transforming Growth Factor-β1
Authors: Brady T.A. , Piesco N.P. , Buckley M.J. , Langkamp H.H. , Bowen L.L. , Agarwal S.
Published: January 2009

During orthodontic tooth movement, mechanical forces acting on periodontal ligament (PDL) cells induce the synthesis of mediators which alter the growth, differentiation, and secretory functions of cells of the PDL. Since the cells of the PDL represent a heterogeneous population, we examined mechanically stress-induced cytokine profiles in three separate clones of human osteoblast-like PDL cells. Of the four pro-inflammatory cytokines investigated, only IL-6 and TGF-β1 were up-regulated in response to mechanical stress. However, the expression of other pro-inflammatory cytokines such as IL-1β, TNF-a, or IL-8 was not observed. To understand the consequences of the increase in TGF-β1 expression following mechanical stress, we examined the effect of TGF-β1 on PDL cell phenotype and functions. TGF-β1 was mitogenic to PDL cells at concentrations between 0.4 and 10 ng/mL. Furthermore, TGF-β1 down-regulated the osteoblast-like phenotype of PDL cells, i.e., alkaline phosphatase activity, calcium phosphate nodule formation, expression of osteocalcin, and TGF-β1, in a dose-dependent manner. Although initially TGF-β1 induced expression of type I collagen mRNA, prolonged exposure to TGF-β1 down-regulated the ability of PDL cells to express type I collagen mRNA. Our results further show that, within 4 hrs, exogenously applied TGF-β1 down-regulated IL-6 expression in a dose-dependent manner, and this inhibition was sustained over a six-day period. In summary, the data suggest that mechanically stress-induced TGF-pl expression may be a physiological mechanism to induce mitogenesis in PDL cells while down-regulating its osteoblast-like features and simultaneously reducing the IL-6-induced bone resorption.
PDGF-α Receptor Subunit Expression Down-regulated by IL-1β in Human Periodontal Ligament Cells
Authors: Oates T.W. , Xie J.-E. , Clinton S. , Hoang A.M. , Graves D.T. , Cochran D.L.
Published: January 2009

The responses of cells to the distinct PDGF isoforms have been correlated directly to the relative numbers of specific PDGF receptor subunits on the cell surface. The modulation of PDGF-a receptor subunits, the major subunit expressed in human periodontal ligament (PDL) cells, by cytokines present in the periodontal wound site, such as interleukin-1 (IL-1), may be an important factor influencing regenerative outcomes. The purpose of the present study was to examine the effects of IL-1β on PDGF-a receptor subunit expression in human PDL cells. Primary cultures of human PDL cells were treated with IL-1β over a range of concentrations. We assessed PDGF-a receptor subunits by examining the mitogenic responses of cells to PDGF-AA, specific binding of 125I-labeled PDGF-AA, immunofluorescent analysis of PDGF-a receptor subunits, and PDGF-a receptor subunit mRNA levels using Northern blot analysis. The results demonstrate a significant concentration-dependent decrease in 3H-thymidine incorporation in response to PDGF-AA following IL-1β treatment (p < 0.001). This decreased response correlated directly with IL-1-induced decreases in 125I-labeled PDGF-AA binding (p < 0.01), the numbers of immunolabeled PDGF-a receptor subunits, and in PDGF-a receptor subunit mRNA levels. However, when combined with TGF-β, IL-1β did not show additional down-regulation in proliferative response to PDGF-AA or PDGF-a receptor subunits beyond that achieved with these factors individually. These experiments identify IL-1 (3, along with TGF-β, as significant inhibitors of PDGF stimulation in human PDL cells, acting through the down-regulation of PDGF-a receptor subunit expression.
In situ Phosphorylation of Bone and Dentin Proteins by the Casein Kinase II-like Enzyme
Authors: Suzuki Y. , Yamaguchi A. , Ikeda T. , Kawase T. , Saito S. , Mikuni-Takagaki Y.
Published: January 2009

Our previous studies suggested the possibility of extracellular phosphorylation of matrix phosphoproteins into more phosphorylated forms by mature odontoblasts and osteocytes (Mikuni-Takagi et al., 1995; Satoyoshi et al., 1995). To elucidate such phosphorylation of bone and dentin proteins, we developed a histochemical method using frozen sections to determine the sites of enzymatic processing by the casein kinase II-like enzyme. It was observed that proteins in bone, dentin, and predentin are phosphorylated by the endogenous enzyme when the tissue slices were incubated with [γ-32P] GTP, suggesting that there are both substrates and the enzyme in these matrices. In vivo, phosphate donors, ATP and GTP, may be supplied through dentinal canals and osteocyte canaliculi. Immunohistochemical analysis of frozen sections showed that the extremely intense staining of phosphoserine residues by anti-phosphoserine antibodies appeared in dentin only after demineralization of the tissue samples. It implies that these phosphoserine residues become bound to mineral as soon as the phosphorylation is completed, thereby being inaccessible to the antibodies without demineralization. The data support our notion that the extracellular phosphorylation of dentin/bone proteins, regulated by the developmental stages of bone and dentin cells, occurs prior to matrix mineralization.
Cyclic ADP-ribose Induces Ca2+ Release from Caffeine-insensitive Ca2+ Pools in Canine Salivary Gland Cells
Authors: Yamaki H. , Morita K. , Kitayama S. , Imai Y. , Itadani K. , Akagawa Y. , Dohi T.
Published: January 2009

Cyclic ADP-ribose (cADPR), a novel putative messenger of the ryanodine receptor, was examined regarding its ability to mobilize Ca2+ from intracellular Ca2+ stores in isolated cells of parotid and submandibular glands of the dog. cADPR induced a rapid and transient Ca2+ release in the digitonin-permeabilized cells of salivary glands. cADPR-induced Ca2+release was inhibited by ryanodine receptor antagonists ruthenium red, ryanodine, benzocaine, and imperatoxin inhibitor but not by the inositol 1,4,5-trisphosphate (IP3)-receptor antagonist heparin. Thapsigargin, at a concentration of 3 to 30 μM, inhibited IP3-induced Ca2+ release, while higher concentrations were required to inhibit cADPR-induced Ca2+release. Cross-potentiation was observed between cADPR and ryanodine or SrCl2, suggesting that cADPR sensitizes the Ca2+-induced Ca2+ release mechanism. Cyclic AMP plays a stimulatory role on cADPR- and IP3-induced Ca2+release in digitonin-permeabilized cells. Calmodulin also potentiated cADPR-induced Ca2+ release, but inhibited IP3-induced Ca2+release. Acetylcholine and ryanodine caused the rise in intracellular free Ca2+ concentration ([Ca2+]i) in intact submandibular and parotid cells. Caffeine did not produce any increase in Ca2+release or [Ca2+]irise in any preparation. ADP-ribosyl cyclase activity was found in the centrifuged particulate fractions of the salivary glands. These results suggest that cADPR serves as an endogenous modulator of Ca2+release from Ca2+ pools through a caffeine-insensitive ryanodine receptor channel, which are different from IP3-sensitive pools in canine salivary gland cells. This system is positively regulated by cyclic AMP and calmodulin.
Force Vectors of Single Motor Units in a Multipennate Muscle
Authors: Turkawski S.J.J. , Van Eijden T.M.G.J. , Weijs W.A.
Published: January 2009

The masseter muscle of the rabbit has a complex architectural design. Restricted motor unit territories in the muscle provide an anatomic basis for accurate control of the force vector through selective activation. In addition, the muscle shows regional differences in fiber type composition. The main objective of the present study was to measure the force vectors of single motor units within the rabbit masseter muscle by a direct mechanical approach to test the hypothesis that: (1) motor units within the masseter muscle are capable of generating different force vectors; and (2) different motor unit types are distributed heterogeneously throughout the muscle. We used a force transducer, capable of measuring both the magnitude and the position of the line of action of a force in a single plane. Motor units in the masseter muscle showed a large range of twitch contraction times and force magnitudes. There was also a large variation in the direction and moment arm of the lines of action. The variation of the lines of action was (almost) as large as the range of fiber directions found inside the muscle. Largest forces, with relatively slow contraction velocities, were produced by motor units in the anterior masseter. Smaller forces and fastest twitch contractions were produced by motor units in the posterior deep masseter. In addition, motor units in the anterior masseter showed more variability in force production than in the posterior masseter. Our results support the idea that the masseter muscle is divided into functionally different parts.
Bite Forces with Mandibular Implant-retained Overdentures
Authors: Fontijn-Tekampl EA , Slagter A.P. , van't Hof M.A. , Geertman M.E. , Kalk W.
Published: January 2009

Sensitivity or pain of the mucoperiosteum covering the mandibular edentulous ridge is often thought to limit bite forces in complete-denture wearers. Therefore, bite forces with mandibular implant-retained overdentures may depend on the degree of implant support. This study analyzed the effects of different degrees of support for the mandibular denture on bite forces measured four years after denture treatment as part of a randomized controlled clinical trial. All subjects had received new maxillary dentures and (1) mainly implant-borne overdentures on a transmandibular implant (TMI), (2) mucosa-borne overdentures on two cylindric permucosal IMZ implants, or (3) new conventional dentures in the mandible. Fifty-three women and 15 men (mean age, 59.1 yrs; range, 41 to 77) participated in this trial. Both unilateral and bilateral bite forces were recorded at different positions with a miniature strain gauge transducer and a mechanical bite fork, respectively. The subjects were asked to bite at three force levels. Results indicated that women had significantly lower maximum bite forces than men. Persons with mandibular implant-retained overdentures had significantly higher unilateral and bilateral maximum bite forces than complete-denture wearers. However, bite forces did not differ between the mainly implant-borne (TMI) and mucosa-implant-borne (IMZ) implant systems. Therefore, it appears that differences in support for the mandibular overdenture by dental implants are not reflected in bite force capabilities.
Effects of N-methacryloyl Amino Acid Applications on Hybrid Layer Formation at the Interface of Intertubular Dentin
Authors: Suzuki K. , Nishiyama N. , Nemoto K. , Torii Y. , Inoue K.
Published: January 2009

To understand the role of NMAA in the bonding of composite resin to a dentin surface, we investigated the effects of N-methacryloyl amino acid (NMAA) application on the expansion of aggregated collagen fibers, formation of a hybrid layer, and the tensile bond strength between composite resin and dentin. Four NMAA derivatives-N-methacryloyl-a-glycine (NMGly), N-methacryloyl-γ-amino n-butyric acid (NMBu), N-methacryloyl-a-hydroxyproline (NMHPro), and N-methacryloyl-a-glutamic acid (NMGlu) -were prepared and applied to dentin surfaces which had been etched with 40% by mass H3PO4 and air-blown. The shrunken collagenous layer expanded by approximately 50% to 70% by volume of the original collagenous layer thickness after application of the NMAA primers. Application of the bonding agent and composite resin after NMAA treatment resulted in the formation of a hybrid layer. The thickness of the hybrid layer was somewhat smaller than the collagenous layer formed by the NMAA treatment only, regardless of the type of NMAA used. The thickness of the hybrid layer was approximately ten times larger than that formed without NMAA treatment. Although all NMAA primers formed hybrid layers of similar thickness, higher tensile bond strengths, from 13 to 15 MPa, were obtained when etched and air-blown dentin was treated with NMBu, NMGly, or NMGlu. NMHPro gave only 6.6 MPa, a value similar to that obtained when no NMAA was used. We concluded, therefore, that formation of the hybrid layer is a necessary but insufficient condition for high bond strength.
Expression of Fos in the Rat Forebrain Following Experimental Tooth Movement
Authors: Yamashiro T. , Satoh K. , Nakagawa K. , Moriyama H. , Yagi T. , Takada K.
Published: January 2009

Orthodontic tooth movement is known to cause pain and discomfort to patients. Mechanically induced inflammatory responses in the periodontium are assumed to be related to the mechanism of pain sensation. An immediate-early gene, c-fos, that is expressed within some neurons following synaptic activation, is widely used as a marker for neuronal activity following noxious or innocuous stimulation. We have recently demonstrated that experimental tooth movement produced Fos induction in the ipsilateral trigeminal subnucleus caudalis and in the bilateral lateral parabrachial nucleus, which is known to be involved in the transmission of nociceptive information. As a further step, we investigated the distribution of Fos-like immunoreactive neurons in the upper brain regions. Twenty-four hours after the commencement of the experimental tooth movement, the Fos-like immunoreactive neurons appeared in the central nucleus of the amygdala (Ce), paraventricular nucleus of the hypothalamus (PVH), and paraventricular nucleus of the thalamus (PV) of the experimental rats. The numbers of the labeled neurons were significantly increased by 639% (P < 0.001) and 644% (P < 0.001) in the ipsilateral and contralateral sides of the Ce, respectively, by 292% (P < 0.001) and 307% (P < 0.001) in the ipsilateral and contralateral sides of the PVH, and by 264% (P < 0.0001) in the PV with respect to sham control rats. These results suggest that nociceptive information caused by experimental tooth movement might be transmitted and modulated in several regions of the forebrain.
Loading of a Unilateral Temporomandibular Joint Prosthesis: A Three-dimensional Mathematical Study
Authors: van Loon J.-P. , Otten E. , Falkenström C.H. , de Bont L.G.M. , Verkerke G.J.
Published: January 2009

The load on the prosthetic side and the influence of the design on the remaining natural contralateral TMJ must be known before a unilateral temporomandibular joint (TMJ) prosthesis can be developed. The aim of the present study was to determine the maximum loading of the TMJ prosthetic side and the natural contralateral TMJ and to investigate the influence of the location of the center of rotation of the prosthesis on the maximum loading. For this purpose, a mathematical model of the mandible with a unilateral TMJ prosthesis with a fixed center of rotation (CR) was developed. The location of the CR of the TMJ prosthesis was varied from the middle of the natural mandibular condyle to 15 mm inferior to this location. Although the maximum joint reaction forces changed as a result of a unilateral TMJ prosthesis, the trend of the loading curves was similar to that of an intact mandible. A unilateral TMJ prosthesis resulted in a 50% higher loading of the prosthetic side, while the load on the natural contralateral TMJ remained within normal limits. The maximum load on the prosthetic side occurred during molar bites and could reach 100 N in the cranial direction, 30 N in the ventral direction, and 25 N in the medio-lateral direction. The location of the CR did not have a significant influence on the loading of the TMJ prosthesis and the natural contralateral TMJ. Key words: temporomandibular joint, temporomandibular joint prosthesis, models, biomechanics, bite force, computer simulation.
Wear of Human Enamel: A Quantitative in vitro Assessment
Authors: Kaidonis J.A. , Richards L.C. , Townsend G.C. , Tansley G.D.
Published: January 2009

Many factors influence the extent and rate at which enamel wears. Clinical studies in humans are limited by difficulties in the accurate quantification of intra-oral wear and by a lack of control over the oral environment. The purpose of this study was to determine the wear characteristics of human dental enamel under controlled experimental conditions. An electro-mechanical tooth wear machine, in which opposing enamel surfaces of sectioned, extracted teeth were worn under various conditions, was used to simulate tooth grinding or bruxism. Enamel surface wear was quantified by weight to an accuracy of 0.1 mg, with water uptake and loss controlled. The variables considered included the structure and hardness of enamel, facet area, duration of tooth contact, relative speed of opposing surfaces, temperature, load, pH, and the nature of the lubricant. Enamel wear under non-lubricated conditions increased with increasing load over the range of 1.7 to 16.2 kg. The addition of a liquid lubricant (pH = 7) reduced enamel wear up to 6.7 kg, but when the load increased above this threshold, the rate of wear increased dramatically. With the viscosity of the lubricant constant and pH = 3, the rate of wear was further reduced to less than 10% of the non-lubricated rate at 9.95 kg, after which the rate again increased substantially. Under more extreme conditions (pH = 1.2, simulating gastric acids), the wear was excessive under all experimental loads. When saliva was used as a lubricant, the amount of wear was relatively low at 9.95 kg, but rapid wear occurred at 14.2 kg and above. These results indicate that under non-lubricated conditions, enamel wear remains low at high loads due to the dry-lubricating capabilities of fine enamel powder. Under lubricated conditions, low loads with an acidic lubricant lead to little enamel wear, whereas very low pH results in a high rate of wear under all loads.
Reactivity of Fluoride-containing Calcium Aluminosilicate Glasses Used in Dental Glass-ionomer Cements
Authors: De Maeyer E.A.P. , Verbeeck R.M.H. , Vercruysse C.W.J.
Published: January 2009

The glass component critically determines the properties of glass-ionomer cements (GIC). However, the exact relationship between the composition of the glass and these properties is not yet fully understood. To investigate this relationship, we studied the reactivity of glasses used in commercial GIC in acetic acid solutions, using a pH-stat method. Qualitative differences in the leaching behavior of these glasses can be explained by different pre-treatments. Acid-washing and silanization modify the surfaces of the glass particles, thus inducing a delay of the leaching process, whereas untreated glasses exhibit a fast initial leaching, but their acid reactivity slows very soon. Quantitative differences in acid reactivity can be correlated with the mean chemical composition of the glasses. In this respect, the leaching tends to increase with an increasing ratio of network-dwelling cations to Al 3+ ions. These results provide a fundamental basis for the explanation, prediction, and control of cement properties as a function of glass characteristics.
Forty-five-year Tooth Survival Probabilities among Men in Oslo, Norway
Authors: Hujoel P.P. , Löe H. , Anerud A. , Boysen H. , Leroux B.G.
Published: January 2009

Changes in tooth survival probabilities over a person's lifetime have remained largely unexplored. The goal of this study was to evaluate changes in the 45-year tooth survival probabilities in a cohort of 565 Norwegian males who were examined in 1969 as young adults, and followed up into mid-life (examination years and sample sizes (n): 1971 (n = 381), 1973 (n = 292), 1975 (n = 245), 1981 (n = 228), 1988 (n = 202), and 1995 (n = 223). The results indicated that the tooth survival probabilities varied considerably both (i) among teeth within individuals, and (ii) over time. The 45-year survival probabilities for the 28 teeth fell into the following ranges: larger than 95% for incisors and cuspids; between 84% and 92% for premolars; and between 59% and 96% for molars. Over the first 4 post-eruptive decades, the tooth mortality risks (excluding orthodontic extractions) were: 1st decade, 2.0% (from 1.7 to 2.4%); 2nd decade, 0.2% (from 0.1 to 0.4%); 3rd decade, 0.6% (from 0.4 to 0.8%); and 4th decade, 1.1% (from 0.8 to 1.5%). The tooth mortality risks in the 2nd, 3rd, and 4th decades were probably somewhat underestimated (due to dropout bias), suggesting that the true underlying tooth mortality hazard function may have been V-shaped. The conclusions were that the tooth mortality hazard during the first 4 post-eruptive decades was bathtub-shaped and that it varied considerably among teeth within individuals.
Contribution of Jaw Muscle Size and Craniofacial Morphology to Human Bite Force Magnitude
Authors: Raadsheer M.C. , van Eijden T.M.G.J. , van Ginkel F.C. , Prahl-Andersen B.
Published: January 2009

The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometries and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalometric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.
Activation of Excitatory Amino Acid Receptors in Bovine Dental Pulp Evokes the Release of iCGRP
Authors: Jackson D.L. , Hargreaves K.M.
Published: January 2009

The activation of excitatory amino acid (EAA) receptors within the central nervous system is associated with numerous centrally mediated phenomena, including hyperalgesia. However, relatively little is known about the peripheral mechanisms which these receptors may regulate when activated. This research evaluated the hypothesis that EAA receptors in bovine dental pulp activate a population of peptidergic sensory neurons as measured by the release of immunoreactive calcitonin gene-related peptide (iCGRP), a neuropeptide associated with neurogenic inflammation. In vitro superfusion of bovine dental pulp was used to evaluate the regulation of iCGRP secretion by the EAA receptor agonists AMPA, kainate, NMDA, and L-glutamate. Both AMPA and kainate stimulated the release of iCGRP in a concentration-dependent manner (AMPA EC50= 0.27 ± 3.3 nM; kainate EC50= 3.2 ± 1.1 μM). Pre-treatment and coadministration of the AMPA/kainate receptor antagonist CNQX significantly reduced the iCGRP release evoked by either of these agonists. In contrast, neither NMDA nor L-glutamate induced any consistent changes in iCGRP release. These results suggest that the activation of AMPA and kainate receptors in dental pulp may contribute to peripheral release of vasoactive neuropeptides which mediate a neurogenic component of inflammation.
Direct Interaction between Gingival Fibroblasts and Lymphoid Cells Induces Inflammatory Cytokine mRNA Expression in Gingival Fibroblasts
Authors: Murakami S. , Hino E. , Shimabukuro Y. , Nozaki T. , Kusumoto Y. , Saho T. , Hirano F. , Hirano H. , Okada H.
Published: January 2009

In inflamed periodontal lesions, dense infiltration of lymphocytes is usually observed in the extravascular periodontal connective tissue, adjacent to gingival fibroblasts. Our previous study revealed that activated lymphocytes can adhesively interact with gingival fibroblasts in vitro. In the present study, we investigated whether gingival fibroblasts are activated through direct interaction with lymphoid cells by monitoring the expression of inflammatory cytokine mRNA in human gingival fibroblasts (HGF). Co-culture with various human lymphoid cells in vitro resulted in a marked increase in the expression of IL-la, IL-1β, and IL-6 mRNA by the HGF. In addition, expression of the mRNA of the IL-1β-converting enzyme (ICE), which is essential to produce the mature form of IL-1β, was constitutively observed in the HGF, suggesting that mature IL-lp is produced by these cells. When HGF were cultured with the culture supernatant of the lymphoid cells, the increase in the inflammatory cytokine mRNA expression was not observed. Similarly, when HGF and lymphoid cells were cultured in the same well but separated by a membrane which prevented direct contact between the cells, no increase in inflammatory cytokine mRNA expression was observed. These results strongly indicate that direct interaction between these heterotypic cell types transduces activation signals into HGF that induce an increase in inflammatory cytokine mRNA expression. Furthermore, IL-1β mRNA expression in the HGF was synergistically increased when HGF directly interacted with lymphoid cells in the presence of exogeneous IL-1β. The present study demonstrates that direct interaction between HGF and lymphoid cells stimulates HGF to increase inflammatory cytokine mRNA expression, and raises the possibility that heterotypic cell-cell interaction may facilitate local inflammatory reactions.
Ion Distribution in Matrix Parts of Glass-Polyalkenoate Cement by SIMS
Authors: Maeda T. , Mukaeda K. , Shimohira T. , Katsuyama S.
Published: January 2009

The microstructure of the set glass-polyalkenoate cement has not been undertaken beyond a study where an Electron Probe Micro Analyser was used. The purpose of this investigation was to determine the ion distribution in matrix parts of the set cement by means of Secondary Ion Mass Spectrometry (SIMS). Among the techniques for surface and microscopic analysis, SIMS is said to be the one with the highest sensitivity. O2+ ions were used as the beam probe to detect silicon, aluminum, calcium, sodium, and carbon. The scanning images showed a clear difference among these elements in their distribution. A large amount of aluminum was found throughout the matrix area, with only a slight concentration gradient, while silicon appeared to be concentrated on the surface of the undissolved glass core. The distribution pattern of calcium was not as clear as that shown by aluminum and silicon. A comparatively higher content of carbon was found closer to the glass surface. These results indicate that aluminum plays an essential role in the setting of the matrix and the surface of the glass dissolved by acrylic acid and changed into the siliceous gel.
A Cross-cultural Study of Oral Health Values
Authors: Allison P. , Locker D. , Jokovic A. , Slade G.
Published: January 2009

The Oral Health Impact Profile (OHIP) is a measure of oral-health-related quality of life developed in Australia but being used increasingly in other populations. In view of the culturally specific nature of peoples' perceptions of health, if we are to make between-population comparisons of oral-health-related quality of life, cross-cultural equivalency of the relevant instruments needs to be verified. A study was therefore undertaken to compare item weights generated by an Australian sample with those generated by a sample of English-speaking Canadians and another of French-speaking Canadians. In addition, within-group comparisons by age were performed. The items and subscales used for the 2 Canadian samples were identical to those developed in Australia, although a formal French translation was used for the French-speaking sample. The method used for the generation of weights was Thurstone's paired-comparison technique, based on the judgments of convenience samples of subjects drawn from each of the three cultural settings. Comparisons were made by means of intra-subscale weight rankings and magnitude. Spearman's rank correlations of r ≥ 0.6 were found for 16/21 between-group comparisons and for 12/21, 19/21, and 8/21 within-group comparisons made by age in Australia, Ontario, and Quebec, respectively. Comparisons of the magnitudes of weights found that, even when items were ranked similarly, magnitudes could be quite different. These results suggest a reasonable degree of cross-cultural consistency, and hence validity, for the OHIP.