bluuebunny/crossref_metadata_2025 huggingface dataset:
Gene Expression in a Pure Population of Odontoblasts Isolated by Laser-capture Microdissection
Authors: Hoffmann M. , Olson K. , Cavender A. , Pasqualini R. , Gaikwad J. , D'Souza R.N.
Published: January 2009

Studies of odontoblast differentiation and function have been limited due to difficulties in obtaining sufficient numbers of intact cells. We describe a novel approach of laser-capture microdissection to obtain homogenous populations of pre-odontoblasts and odontoblasts from tissue sections of mouse molar cusp tips. Fixation, processing, and staining conditions were assessed for the optimal retrieval of total RNA from microdissected odontoblasts. Fluorometric assays and RT-PCR analysis of α1(I) collagen, dentin sialophosphoprotein (Dspp), and osteocalcin (OC) confirmed that the total RNA from three-day-old captured odontoblasts was sufficient in quantity and quality. Odontoblast-specific gene expression was studied by RT-PCR analysis performed in a single streptavidin-coated tube. At E15.5, Days 0 and 3, gene expression in laser-captured odontoblasts resembled that seen in vivo by in situ hybridization. The use of LCM is thus a valuable means of retrieving quality RNA from discrete populations of odontoblasts at different stages of dentinogenesis.
Crown Morphology and Pattern of Odontoblast Differentiation in Lower Molars of Tabby Mice
Authors: Lisi S. , Peterková R. , Kristenová P. , Vonesch J.L. , Peterka M. , Lesot H.
Published: January 2009

The Tabby mutation leads to abnormal crown morphology in the developing molars. To identify cusps which were altered in number, size, and position in the first lower molars of mutant mice, we analyzed the patterning of odontoblast differentiation using morphological criteria on serial sections and 3D reconstructions. In wild-type mice, polarized and functional odontoblasts were first observed in the median L2 and B2 cusps, then in the distal cusps L3 and B3, and finally in L1, B1, and 4. In Tabby mice, terminal differentiation of odontoblasts was retarded by 24-36 hours compared with wild-type mice. Polarized odontoblasts first appeared in the most mesial part of the tooth and progressively extended distally. The mesial part of the M1 in Tabby fetuses may correspond to the L2, B2 area from wild-type mice. The ante-molar dental primordium observed in some samples would thus represent remnants of cusps L1 and B1.
Acetylcholine-induced Vasodilation of Isolated Pulpal Arterioles
Authors: Yu C.Y. , Boyd N.M. , Cringle S.J. , Su E.N. , Alder V.A. , Yu D.Y.
Published: January 2009

The presence of cholinergic mechanisms in the control of pulpal microcirculation has been a controversial issue. In this study, we aimed to determine the direct vasoactive responses of isolated pulpal arterioles to acetylcholine, and to investigate whether such responses are endothelium-dependent. Using an in vitro micro-perfusion system, we isolated pig pulpal arterioles, cannulated and perfused them intraluminally, and monitored the diameter. Following equilibration, the vessels were contracted with 10-5 M noradrenaline, and the effect of increasing doses of acetylcholine was determined. The influence of the muscarinic antagonist, atropine, or the loss of endothelial cell function following saponin treatment was also determined. Acetylcholine induced a dose-dependent vasodilation, reaching 94.6 ± 1.4% (n = 22) of the uncontracted diameter at 10-4 M. The vascular relaxation effect of acetylcholine was abolished in the presence of atropine, and by saponin treatment. Analysis of these data suggests that, in the pig, the acetylcholine-induced vasodilation of incisor pulpal arterioles is endothelium-dependent and mediated by muscarinic receptors.
The Association of Bacterial Adhesion with Dental Caries
Authors: Stenudd C. , Nordlund A. , Ryberg M. , Johansson I. , KallestÅl C. , Strömberg N.
Published: January 2009

Saliva adhesion of bacteria is a key event in oral biofilm formation. Here, we used partial least-squares (PLS) analysis to correlate adhesion of cariogenic ( Streptococcus mutans Ingbritt) and commensal ( Actinomyces naeslundii LY7) model bacteria, and their agglutinin and acidic proline-rich protein ligands, respectively, with high and low caries experiences in 38 children reflecting today's skewed caries distribution. Adhesion of S. mutans was among the factors correlating strongest with high caries experience when PLS modeled together with traditional factors ( e.g., sugar intake, lactobacilli counts). Saliva phenotypes with high agglutinin levels and Db-s (an acidic PRP variant) coincided with both high caries experience and S. mutans adhesion. A. naeslundii adhesion correlated with low caries experience. Non-Db phenotypes (i.e., acidic PRP-1 and PRP-2 variants) coincided with both low caries experience and S. mutans, but high A. naeslundii, adhesion. Thus, bacterial adhesion may modulate susceptibility and resistance to dental caries.
Cell-interactive Alginate Hydrogels for Bone Tissue Engineering
Authors: Alsberg E. , Anderson K.W. , Albeiruti A. , Franceschi R.T. , Mooney D.J.
Published: January 2009

There is significant interest in the development of injectable carriers for cell transplantation to engineer bony tissues. In this study, we hypothesized that adhesion ligands covalently coupled to hydrogel carriers would allow one to control pre-osteoblast cell attachment, proliferation, and differentiation. Modification of alginate with an RGDcontaining peptide promoted osteoblast adhesion and spreading, whereas minimal cell adhesion was observed on unmodified hydrogels. Raising the adhesion ligand density increased osteoblast proliferation, and a minimum ligand density (1.5-15 femtomoles/cm2) was needed to elicit this effect. MC3T3-E1 cells demonstrated increased osteoblast differentiation with the peptide-modified hydrogels, as confirmed by the up-regulation of bone-specific differentiation markers. Further, transplantation of primary rat calvarial osteoblasts revealed statistically significant increases of in vivo bone formation at 16 and 24 weeks with G4RGDY-modified alginate compared with unmodified alginate. These findings demonstrate that biomaterials may be designed to control bone development from transplanted cells.
Kinematic Modeling of Jaw-closing Movement during Food Breakage
Authors: Yashiro K. , Fujii M. , Hidaka O. , Takada K.
Published: January 2009

It has been demonstrated that the vertical jaw movement trajectories during gum-chewing can be explained by jerk-cost minimization. However, it is uncertain whether the masticatory jaw movement in space can be predicted by the minimum-jerk model. The aims of the present study were to develop minimum-jerk models that would explain 3D masticatory jaw movements with different hardnesses of foods, and to evaluate if the models can predict the movements accurately. The 3D masticatory jaw movement during food breakage was formulated for two types of test foods. The coefficients of determination (R2) between the measured and model-based values ranged from 0.846 to 0.882. Differences were found in the kinematic parameters between the test foods. The results suggest that the models predict the 3D jaw movements during food breakage and are effective in differentiating among the kinematic features of masticatory jaw movements that are peculiar to the mechanical properties of foodstuffs.
Concise Review Biomaterials & Bioengineering: Chemical-Biological Interactions of the Resin Monomer Triethyleneglycol-dimethacrylate (TEGDMA)
Authors: Geurtsen W. , Leyhausen G.
Published: January 2009

Most dental resinous materials contain high quantities of the diluent monomer triethyleneglycol-dimethacrylate (TEGDMA). Due to its 'hydrophilic' nature, significant amounts of this substance leach into an aqueous environment, such as the oral cavity. Therefore, it is hypothesized that TEGDMA frequently interferes with oral and/or systemic tissues. In vitro studies revealed that TEGDMA is considerably cytotoxic in various cell cultures. It has also been observed that TEGDMA can easily penetrate membranes and subsequently may react with intracellular molecules. The formation of glutathione-TEGDMA adducts is of specific interest, since the nearly complete exhaustion of this molecule significantly reduces its cellular detoxifying potency. Large deletions of DNA sequences were caused by TEGDMA, resulting in high mutation frequency. In addition, TEGDMA has been identified as an important resinous sensitizer in patients and professionals. Taken together, available in vitro information, in vivo studies with animals, and clinical data as well indicate that TEGDMA may contribute considerably to local and systemic adverse effects caused by dental resins.
Oral Colonization of Streptococcus mutans in Six-month-old Predentate Infants
Authors: Wan A.K.L. , Seow W.K. , Purdie D.M. , Bird P.S. , Walsh L.J. , Tudehope D.I.
Published: January 2009

We hypothesize that S. mutans colonization occurs more frequently in pre-term children due to their relative immaturity. In this study of 172 predentate, six-month-old infants, we found that 50% of pre-term and 60% of full-term children harbored S. mutans. The colonization was confirmed by repeat sampling. Although there were minor differences, factors associated with S. mutans infection in pre-term and full-term infants were generally similar. In both groups, increased frequency of sugar was ranked the most important factor (p < 0.001), followed by breast-feeding (p < 0.001), and habits which allowed saliva transfer from mother to infant (p < 0.01). By contrast, non-colonization of S. mutans was associated with multiple courses of antibiotics (p < 0.001). Compared with pre-term children, there were higher percentages of full-term who had night feedings and consumed sugar during sleep times. Mothers with infected infants had S. mutans levels > 5 x 105 CFU/mL saliva (p < 0.001), poorer oral hygiene, more periodontal disease, and lower socio-economic status (p < 0.02) and snacked frequently (p < 0.001), compared with mothers with non-infected infants.
Periodontal Regeneration by FGF-2 (bFGF) in Primate Models
Authors: Takayama S. , Murakami S. , Shimabukuro Y. , Kitamura M. , Okada H.
Published: January 2009

We recently demonstrated that a topical application of basic fibroblast growth factor (FGF-2 ; bFGF) to alveolar bone defects in beagle dogs enhanced periodontal regeneration. The purpose of this study was further characterization of the biological effects of FGF-2 in non-human primates. Thirty-two inflamed furcation class II defects were surgically created in 4 male primates. The gelatinous carrier alone or the carrier containing 0.1 or 0.4% human recombinant FGF-2 was topically applied to the defects and compared with no treatment. Eight weeks after application, the periodontal regeneration in those defects was analyzed. In all FGF-2-treated sites, significant periodontal regeneration was dose-dependently observed in greater amounts than in the carrier-treated or non-treated sites. No instances of epithelial down-growth, ankylosis, or root resorption were observed in the FGF-2-treated sites. These results indicate that a topical application of FGF-2 can enhance considerable periodontal regeneration in surgically created furcation class II defects of non-human primates.
The Cells that Fill the Bill: Neural Crest and the Evolution of Craniofacial Development
Authors: Jheon A.H. , Schneider R.A.
Published: January 2009

Avian embryos, which have been studied scientifically since Aristotle, continue to persevere as invaluable research tools, especially for our understanding of the development and evolution of the craniofacial skeleton. Whether the topic is beak shape in Darwin’s finches or signaling interactions that underlie bone and tooth formation, birds offer advantages for craniofacial biology that uniquely complement the strengths of other vertebrate model systems, such as fish, frogs, and mice. Several papers published during the past few years have helped pinpoint molecular and cellular mechanisms that pattern the face and jaws through experiments that could only have been done together with our feathered friends. Ultimately, such knowledge will be essential for devising novel clinical approaches to treat and/or prevent diseases, injuries, and birth defects that affect the human craniofacial skeleton. Here we review recent insights plucked from avians on key developmental processes that generate craniofacial diversity.
Self-etching Increases Matrix Metalloproteinase Expression in the Dentin-Pulp Complex
Authors: Lehmann N. , Debret R. , Roméas A. , Magloire H. , Degrange M. , Bleicher F. , Sommer P. , Seux D.
Published: January 2009

In adhesive restorations, one major problem is hybrid layer degradation. At present, this deterioration is explained by the activation of the endogenous matrix metalloproteinases (MMPs) present in dentin due to the acidic property of adhesive systems. We hypothesized that self-etching adhesive should also stimulate the expression of MMPs in odontoblasts. In cultured tooth slices, we evaluated the changes in MMP-2 and proMMP-9 expression in the dentin-pulp complex after self-etching adhesive treatment on dentin cavities in immunochemistry and by zymography. The treatment resulted in increased MMP-2 expression in odontoblasts, as shown by immunohistochemistry. Zymography showed increased proMMP-9 and MMP-2 in dentin under self-etching treatment when pulp was present. These results showed that self-etching adhesive stimulates the secretion of MMPs from the dentin-pulp complex and, more precisely, by odontoblasts, suggesting that odontoblasts participate in hybrid layer degradation.
Circadian Rhythm of Osteocalcin in the Maxillomandibular Complex
Authors: Gafni Y. , Ptitsyn A.A. , Zilberman Y. , Pelled G. , Gimble J.M. , Gazit D.
Published: January 2009

The human body displays central circadian rhythms of activity. Recent findings suggest that peripheral tissues, such as bone, possess their own circadian clocks. Studies have shown that osteocalcin protein levels oscillate over a 24-hour period, yet the specific skeletal sites involved and its transcriptional profile remain unknown. The current study aimed to test the hypothesis that peripheral circadian mechanisms regulate transcription driven by the osteocalcin promoter. Transgenic mice harboring the human osteocalcin promoter linked to a luciferase reporter gene were used. Mice of both genders and various ages were analyzed non-invasively at sequential times throughout 24-hour periods. Statistical analyses of luminescent signal intensity of osteogenic activity from multiple skeletal sites indicated a periodicity of ~ 24 hrs. The maxillomandibular complex displayed the most robust oscillatory pattern. These findings have implications for dental treatments in orthodontics and maxillofacial surgery, as well as for the mechanisms underlying bone remodeling in the maxillomandibular complex.
Phosphate Regulates Osteopontin Gene Transcription
Authors: Fatherazi S. , Matsa-Dunn D. , Foster B.L. , Rutherford R.B. , Somerman M.J. , Presland R.B.
Published: January 2009

Extracellular inorganic phosphate (ePi) is a key regulator of cementoblast behavior, both in vivo and in vitro, and results in a marked increase in osteopontin expression in vitro. To examine the molecular mechanisms involved in ePi induction of osteopontin gene expression, we transfected a series of osteopontin promoter-luciferase constructs into OCCM-30 cementoblasts. Our results demonstrate that ePi can directly induce osteopontin gene transcription. The region responsive to ePi signaling was localized to a 53-bp region of the promoter between −1454 and −1401 that contains a glucocorticoid response element (GRE). Mutation of the GRE abolished the ePi response, suggesting that glucocorticoid receptor (GR) signaling is required for ePi-mediated transcription. In addition, treatment of cells with the GR antagonist RU-486 (Mifepristone) prevented promoter activation by ePi. The results presented support a model demonstrating that inorganic phosphate regulates OPN gene transcription in cementoblasts through a pathway that requires a functional GR.
Analysis of a Band 7/MEC-2 Family Gene of Porphyromonas gingivalis
Authors: Walters S. , Rodrigues P. , Bélanger M. , Whitlock J. , Progulske-Fox A.
Published: January 2009

In vivo-induced antigen technology has previously been used to identify 115 genes induced in Porphyromonas gingivalis W83 during human infection. The aim of this study was to determine if one of these genes, PG1334, was important for the virulence of P. gingivalis. Analysis of plaque samples from persons with periodontitis revealed that PG1334 was expressed in 88.0% of diseased sites, compared with 42.1% of healthy sites, even though P. gingivalis was detected in equal numbers from both sites. A mutant of PG1334 was found to adhere to and to invade better than the parent strain, but did not persist as well in human coronary artery endothelial cells. Additionally, the mutant did not persist as well in a mouse abscess model. This gene appears to be important for the virulence of P. gingivalis, both in vivo and in vitro.
Reduction of Infection-stimulated Periapical Bone Resorption by the Biological Response Modifier PGG Glucan
Authors: Stashenko P. , Wang C.Y. , Riley E. , Wu Y. , Ostroff G. , Niederman R.
Published: January 2009

Pulpal and periodontal diseases are bacterial infections which result in local connective tissue and bone destruction. Effective host resistance to these infections is primarily mediated by neutrophils and other phagocytic cells. PGG glucan (poly-β1-6-glucotriosyl-β1-3-glucopyranose glucan) is a biological response modifier which stimulates the production of neutrophils and upregulates their phagocytic and bactericidal activity. In the present studies, the effect of PGG glucan on infection-stimulated alveolar bone resorption was tested in an in vivo model. Periapical bone resorption was induced in Sprague-Dawley rats by surgical pulp exposure and subsequent infection from the oral environment. Animals were administered PGG glucan (0.5 mg/kg) or saline (control) subcutaneously the day before and on days 2, 4, 6, 9, 11, 13, 16, and 18 following the pulp exposure procedure. PGG glucan enhanced the number of circulating neutrophils and monocytes and increased neutrophil phagocytic activity approximately two-fold. PGG glucan-treated animals had significantly less infection-stimulated periapical bone resorption than control animals, as determined radiographically (-48.0%; p < 0.001) and by histomorphometry (-40.8% and -42.4% for first and second molars, respectively; p < 0.01). PGG glucan-treated animals also had less soft tissue destruction, as indicated by decreased pulpal necrosis. Only 3.3% of first molar pulps from PGG glucan-treated animals exhibited complete necrosis, as compared with 40.6% of pulps from controls. Finally, PGG glucan had no effect on either PTH- or IL-1-stimulated bone resorption in vitro. These findings support the concept that a biological response modifier which enhances endogenous antibacterial mechanisms in neutrophils can decrease infection-stimulated alveolar bone and soft tissue destruction in vivo.
Effect of Aging on Animal Response to Chronic Fluoride Exposure
Authors: Dunipace A.J. , Brizendine E.J. , Zhang W. , Wilson M.E. , Miller L.L. , Katz B.P. , Warrick J.M. , Stookey G.K.
Published: January 2009

This study was conducted to test the hypothesis that physiological changes which occur during aging increase the biological impact of fluoride and reduce the threshold of safe fluoride exposure. Four groups of rats were fed a low-fluoride diet (< 1.2 ppm) ad libitum and received 0, 5,15, or 50 ppm fluoride in their drinking water. Animals were killed after three, six, 12, or 18 months of treatment. Blood and urine were monitored for biochemical markers of tissue function, and plasma, urine, feces, and representative tissues were analyzed for fluoride. In addition, bone marrow cells from animals killed after 18 months of treatment were examined for frequency of sister chromatid exchange (SCE), a marker of genetic damage. Study results indicated that, within treatment groups, fluoride intake, excretion, and retention did not change significantly between three and 18 months. Fluoride concentration in soft tissues did not change with treatment duration in the fluoride-treated animals. Mineralized tissue fluoride concentration and the total fluoride in the carcasses increased continually as the animals aged. In spite of significant, dose-related differences in tissue fluoride levels which occurred in all age groups in this study, there were no indications that increased fluoride in the tissues caused any adverse physiological or genotoxic effects. None of the monitored clinical "wellness" markers of tissue integrity and function was altered by fluoride in a clinically significant manner. Therefore, there was no evidence from this study that aging reduces the threshold of safe chronic fluoride exposure.
Association of Free Arginine and Lysine Concentrations in Human Parotid Saliva with Caries Experience
Authors: VanWuyckhuyse B.C. , Perinpanayagam H.E.R. , Bevacqua D. , Raubertas R.E. , Billings R.J. , Bowen W.H. , Tabak L.A.
Published: January 2009

We determined the free-amino acid content of stimulated parotid (ductal) saliva from two groups of adult subjects whose caries experiences were markedly different. The levels of free arginine and free lysine in the parotid saliva of caries-free adults were significantly higher than those found in the parotid saliva of individuals with a history of dental decay. There was no correlation, however, between the levels of these amino acids and the DMFS score within the caries-susceptible groups. Microbial catabolism of dibasic amino acids contributes to the neutralization of plaque acids and may partially account for the higher resting plaque pH observed in caries-free subjects. Alternatively, the elevations observed in free levels of arginine and lysine may reflect a systemic alteration in amino acid metabolism which is common to the caries-free group of subjects.
Problems Associated with Estimation of Net Calcium Uptake During Enamel Formation Using 45Ca
Authors: Moran R.A. , Deaton T.G. , Bawden J.W.
Published: January 2009

45Ca uptake in mineralizing tissues may occur by net Ca uptake or by isotopic exchange. It is rarely possible to differentiate between these effects, making interpretation of the findings difficult. Unfortunately, this problem is not often considered, and 45Ca uptake is usually regarded as representative of only net calcium uptake. The study reported here was undertaken to estimate the extent to which 45Ca uptake in mineralizing enamel is due to net Ca deposition or to isotopic exchange, and to consider the implications.

The enamel surfaces of the lower incisors of adult rats were notched at the gingival line, and the eruption distance over 16 hours was measured. This distance was used to establish the position of a 0.3-mm-wide increment of enamel at the beginning and end of the 16-hour period, during which it passed through the early-maturation stage of enamel formation. The rate of Ca uptake was determined by chemical assay. Other rats were injected with 45Ca, mean plasma specific activity values for the experimental period determined, and the rate of Ca uptake through the same area of enamel formation was estimated. The estimates were from two- to nearly ten-fold greater than those established by chemical assay, indicating that from 50 to 90% of the 45Ca uptake occurred by isotopic exchange. 45Ca uptake may indicate more about the labile state of Ca in mineralizing enamel than about the rate of mineral deposition.
Factors Affecting the Adherence Energy of Experimental Resin Cements Bonded to a Nickel-Chromium Alloy
Authors: Asmussen E. , Attal J.-P. , Degrange M.
Published: January 2009

Reliable adherence of resin-based cements is of prime importance for the longevity of cemented restorations. The present study investigated whether a relationship exists between adherence energy to a metal substrate and the degree of cross-linking and wetting characteristics of resin-based luting agents. The adherence energies between a sand-blasted metal surface and a series of experimental resin cements were measured by means of the wedge test. The degree of cross-linking was calculated from the monomer composition of the resin cements. The measured wetting characteristics were work of adhesion and surface tension, and their dispersive and polar components. Adherence energy varied between 22 and 81 J/m2 and was influenced by the nature of the resin cements: Those with a low degree of cross-linking resulted in high adherence values. Furthermore, resin cements whose monomers were relatively polar gave rise to high adherence values. Although other metals may not behave in exactly the same way, these results may help in the formulation of new, more retentive resin cements.
The Effects of Neuropeptides (Calcitonin Gene-related Peptide and Substance P) on Cultured Human Pulp Cells
Authors: Trantor I.R. , Messer H.H. , Bimer R.
Published: January 2009

The sensory neuropeptides substance P and calcitonin gene-related peptide have been implicated in the mediation of pulpal inflammation. A possible role in healing following injury has also been suggested (Byers et al., 1990). This possibility has been investigated by an examination of a direct effect of substance P and calcitonin gene-related peptide in vitro on fibroblast-like cells derived from human dental pulp. Cells were cultured for 48 hr in Dulbecco's modified Eagle medium plus 20% fetal calf serum and antibiotics. Substance P and calcitonin gene-related peptide were added in the range from 10-12 to 10-4 mol/L. Fibroblast growth factor was used as a positive control. Effects on cell proliferation were assessed by cell counts (daily for 6 days) and [3H]-thymidine uptake (24 hr after the addition of peptides). An effect on cellular functional activity was measured by [35S]-sulfate incorporation into glycosaminoglycans, in confluent cell cultures. Both substance P and calcitonin gene-related peptide showed concentration-dependent stimulation of cell proliferation. The maximum stimulation of approximately 40% was achieved at substance P and calcitonin gene-related peptide concentrations of 10-6 mol/L, comparable with stimulation by fibroblast growth factor. By contrast, little increase in glycosaminoglycan synthesis by confluent cells could be detected. The direct effect on pulp cells is consistent with a role of the neuropeptides in pulp healing. This is exerted at the level of cell proliferation, rather than functional activity.
Combined Estimation of Mercury Species Released from Amalgam
Authors: Halbach S.
Published: January 2009

Amalgam fillings constitute, after food, the main source of exposure to mercury for the general population. Banning amalgam would incur huge costs for additional dental treatment. An evaluation of potential health risks must be based on the mercury dose released from fillings. In this study, dose is estimated by a new procedure of mercury speciation which elutes the released elemental and inorganic mercury with solvents of differing polarity. We tested the procedure by incubating spherical amalgam pellets in a mixture of light paraffin oil and saline (0.9% NaCl). Release of mercury into paraffin and saline was linear in relation to both amalgam surface area and exposure time. Measurements with this method were then extended to a group of 21 amalgam-bearing volunteers. The absorbed dose averaged 4.8 ug/day compared with 3.7 measured conventionally in intra-oral air from the same persons. With both methods, the dose was significantly correlated to the number of amalgam-covered tooth surfaces. This dose, combined with the nearly equal mercury uptake from food, is far below the acceptable daily intake limit.
Critical Issues in Periodontal Research
Authors: Page R.C.
Published: January 2009

The purpose of this paper is to highlight briefly the major achievements and the remaining critical issues in the areas of epidemiology, microbiology, pathogenesis, diagnosis, and therapy. Periodontitis affects a relatively small proportion of study populations in the United States and other countries. Prevalence may be decreasing, but that remains to be seen. The identity and characteristics of susceptible individuals and groups are not known, and risk indicators for severe disease are only beginning to be identified. A very large number of different microbial species has been implicated in the etiology. It seems unlikely that all of these are essential participants. Essential participants need to be identified and better characterized. Whether putative pathogens are members of the commensal flora or exogenous species that must be transmitted is unclear. The relationship between the presence of a pathogenic flora and disease status is obscure. Pathogenic bacterial species are essential, but insufficient to cause disease. A susceptible host and local environmental factors-for example, elevated iron concentration-may be necessary for disease to occur. Many clonal types may not be virulent, and numbers greater than certain threshold levels appear to be necessary. The pathways by which bone and connective tissues of the periodontium are destroyed are sufficiently understood to permit development of therapies aimed at their modification. Examples are the use of vaccines, topical application of anti-inflammatory drugs, and use of chemically modified tetracyclines.
Mineral Distribution and Dimensional Changes in Human Dentin during Demineralization
Authors: Kinney J.H. , Balooch M. , Haupt D.L. , Marshall S.J. , Marshall G.W.
Published: January 2009

Many bonding agents require the dentin surface to be acid-etched prior to being bonded. Understanding the stability and morphology of the etched dentin surface is important for improving bond strength and reliability in these systems. In this study, the atomic force microscope was used to quantify dimensional changes that occur to fully hydrated dentin during demineralization with a pH 4.0 lactic acid gel. A high-resolution microtomography instrument, the x-ray tomographic microscope, was also used to quantify the mineral density distribution in the dentin as a function of etching time. The intertubular dentin surface shrank by less than 0.5 μm during etching, while the peritubular dentin receded at an initially rapid linear rate. The dentin surface retained its initial morphology, although it was more porous with the removal of the peritubular dentin. Beneath the etched surface, there were three major zones characterized by mineral density differences. The first zone was a fully demineralized collagen layer, subjacent to which was a partially demineralized zone of roughly constant mineral density. Immediately following the partially mineralized layer was normal dentin. The presence of the partially mineralized layer could be explained in terms of different transport rates in the peritubular and intertubular dentin.
Cavity Preparation with the Nd:YLF Picosecond Laser
Authors: Niemz M.H.
Published: January 2009

Several laser systems for the removal of hard dental substances are currently under investigation. However, in most cases, such systems have been demonstrated to be inefficient or have led to undesirable thermal side-effects. This paper reports, for the first time, the removal of enamel and dentin by a picosecond laser system, a solid-state Nd:YLF laser. Very precise cavities can be obtained in the enamel and dentin of extracted human molars when laser pulses are distributed onto well-defined areas of the teeth. Scanning electron microscopy shows that the quality of the cavities is superior to that achieved by other laser systems. The cavity walls are very steep, and their surfaces are characterized by a sealed structure. In contrast to laser systems with longer-duration pulses, picosecond laser pulses ablate with less thermal damage to the surrounding substance. The results of dye penetration tests and polarized microscopy show that even mechanical shock-wave effects are negligible. When the Nd:YLF laser is applied to carious enamel, the ablation rate is found to be about ten times higher than for sound molars, thus making the Nd:YLF laser a caries-selective laser system.
Marginal Ditching and Staining as a Predictor of Secondary Caries Around Amalgam Restorations: A Clinical and Microbiological Study
Authors: Kidd E.A.M. , Joyston-Bechal S. , Beighton D.
Published: January 2009

Caries at the margins of restorations is difficult to diagnose. In particular, the relevance of both marginal ditching and staining around amalgam restorations is unclear. This clinical study questions the relevance of marginal ditching and color change to the level of infection of the dentin beneath the margins of amalgam restorations. Clinically visible sites (330) on the tooth/restoration margin were selected on 175 teeth. The enamel adjacent to each site was noted as stained (a grey discoloration) or stain-free. One hundred and seventy-eight sites were clinically intact, 83 sites had narrow ditches (< 0.4 mm), and at 49 sites, wide ditches were present (> 0.4 mm). Twenty sites with frankly carious lesions were also included. Plaque was sampled at the tooth-restoration margin, and the dentin was sampled at the enamel-dentin junction below each site. Samples were vortexed, diluted, and cultured for total anaerobic counts, mutans streptococci, lactobacilli, and yeasts. Plaque samples showed that margins with wide ditches (> 0.4 mm) harbored significantly more bacteria, mutans streptococci, and lactobacilli than did clinically intact margins and margins with narrow ditches. There were no significant differences in the degree of infection of the dentin beneath clinically intact restorations and those with narrow ditches, but samples associated with wide ditches and carious lesions yielded significantly more bacteria, mutans streptococci, and lactobacilli. The color of the enamel adjacent to the sample site was irrelevant to the level of infection of the dentin beneath the filling margin, provided a frankly carious lesion was not present. The results suggest that amalgam fillings where margins show wide ditches or carious lesions should be replaced. Narrow ditches and color change alone should not trigger the replacement of a filling.
Failure of All-ceramic Fixed Partial Dentures in vitro and in vivo: Analysis and Modeling
Authors: Kelly J.R. , Tesk J.A. , Sorensen J.A.
Published: January 2009

Hertzian cone cracks visible at the loading site of 20 all-ceramic fixed partial dentures (FPDs), tested in vitro, led to the hypotheses that failure was due to the propagation of localized contact damage crack systems (Hertzian stress state) and that such damage was an unlikely clinical failure mode. Fractographic analysis of the 20 laboratory-failed and nine clinically-failed all-ceramic FPDs allowed for definitive testing of these hypotheses and a comparison between in vitro and in vivo failure behavior. In all cases, failure occurred in the FPD connectors (none from contact damage), with approximately 70 to 78% originating from the interface between the core and veneer ceramics. The coincidence between failure origins provides strong evidence that the in vitro test modeled aspects of structural behavior having clinical importance. The fractographic observations, coupled with the in vitro failure load data, furnished very specific boundary conditions which were applied to constrain mathematical models of FPD connector failure. Finite element analysis (FEA) of the laboratory FPDs found that maximum principal tensile stresses would occur at locations consistent with the fractographic observations only if: (1) there were appropriate elastic moduli differences between the ceramics; and (2) a small amount of abutment rotation was allowed. Weibull failure probability (Pf) calculations, incorporating FEA stress profiles, very closely replicated the laboratory failure distribution only when: (1) the veneer ceramic was much weaker than the core ceramic; and (2) the Weibull modulus of the core-veneer interface was much lower than that for the free veneer surface (i.e., the interface is of lower quality with regard to defects). This combined fractographic and mathematical analysis of FPD connectors suggests that the core-veneer interface is an important failure source and that the veneering ceramic overwhelmingly controls load-bearing capability. Observations from failed clinical restorations provided critical guidance in validating a laboratory test and focusing a mathematical failure model.
A Quantitative Study on the Myelinated Fiber Innervation of the Periodontal Ligament of Cat Canine Teeth
Authors: Long A. , Loescher A.R. , Robinson P.P.
Published: January 2009

The periodontal ligament is richly innervated with mechanosensitive afferent nerve fibers, and the location of the mechanoreceptive terminals within the ligament is of functional significance. In this study, we have obtained quantitative information on mechanoreceptor distribution in the lower canine teeth of the cat. Using light microscopy, we quantified the number of myelinated axons in the periodontal ligament at 1 mm, 3 mm, and 5 mm from the tooth root apex. Grouped axons and axons which were isolated in the cemental half of the ligament (and therefore putative mechanoreceptors) were identified. The mean total number of axons was 1290 (n = 20) at 1 mm from the apex, 1290 at 3 mm, and 814 at 5 mm. The distribution of axons around the tooth root circumference was found to be non-uniform. Near the root apex, the highest numbers of grouped axons were located distally and mesially, and in the middle region of the root, the highest numbers were found mesially. The highest numbers of isolated axons at the apical levels were located distally, and in the mid-root region, mesially. At all levels, the lingual region was the most sparsely innervated by both groups. There was a positive correlation between the number of grouped axons and the width of the ligament in the same region, but this correlation was much weaker for isolated axons, suggesting that their distribution does not result only from the volume of tissue. Variations in the number of axons and, to a lesser extent, the dimensions of the periodontal ligament were considerable. However, these variations were less between left and right teeth of the same animal than between teeth in different animals, reinforcing the use of the contralateral tooth as a control for experiments in which these variables are quantified.
Electromyographic Heterogeneity in the Human Temporalis and Masseter Muscles during Static Biting, Open\ Close Excursions, and Chewing
Authors: Blanksma N.G. , van Eijden T.M.G.J.
Published: January 2009

The human temporalis and masseter muscles are not activated homogeneously during static bite force tasks. In this study, we studied the possible existence of regional differences in these muscles under dynamic conditions. Electromyographic (EMG) activity was recorded by means of bipolar fine-wire electrodes. Six electrodes were inserted into the temporalis muscle and three into the masseter muscle. Recordings were made during maximal-effort intercuspal and incisal static clenches, open\close excursions from both the intercuspal and incisal positions, and unilateral gum and licorice chewing on right and left sides. The EMG peak amplitudes and the peak occurrences were compared. During the static clenches and the open\close excursions, no differences could be demonstrated between the regions of the temporalis muscle. However, during the chewing tasks, the anterior and posterior regions behaved differently. Throughout almost all tasks, both superficial and deep parts could be distinguished in the masseter muscle. A further division of the deep masseter was task-dependent. In both the temporalis and masseter muscles, maximal activity (100%) was reached during intercuspal clenches. The average activity declined to 35% of the maximal activity in the temporalis muscle, to 47% in the deep, and to 86% in the superficial masseter during incisal clenches. During all chewing tasks, the EMG peak activity of the anterior temporalis and the superficial masseter muscles was higher in the working than in the balancing condition. The general finding was that different regions were preferentially activated, according to task. The detailed regional specialization previously observed during static bite force tasks could not be demonstrated in the present study.
Inhibition of Prostaglandin E2 and Interleukin 1-β Production by Low-power Laser Irradiation in Stretched Human Periodontal Ligament Cells
Authors: Shimizu N. , Yamaguchi M. , Goseki T. , Shibata Y. , Takiguchi H. , Iwasawa T. , Abiko Y.
Published: January 2009

It is well-known that orthodontic treatment usually causes some discomfort and pain to the patients. Recently, it has been reported that low-power laser irradiation is effective in reducing the pain accompanying tooth movement. However, the mechanism of such pain relief cannot be elucidated. Since high levels of prostaglandin (PG) E2 and interleukin (IL)-1β are found in the periodontal ligament (PDL) during tooth movement, and both factors are involved in the induction of pain, the effects of low-power laser irradiation on PGE2 and IL-1β production in stretched human PDL cells were studied in vitro. The PDL cells, derived from healthy premolars extracted for orthodontic treatment, were utilized for experiments. Cells were seeded in flexible-bottomed culture plates, and the bottom of each plate was elongated (18% increase) under vacuum at 6 cycles per min for 1, 3, or 5 days. The stretched cells were irradiated with a Ga-Al-As low-power diode laser (60 mW) once a day for 3, 6, or 10 min (from 10.8 to 36.0 J) for 1, 3, or 5 days. PGE2 and IL-1β levels in the medium were measured by radioimmunoassay. In response to mechanical stretching, human PDL cells showed a marked elevation in PGE2 production in a time-dependent manner. IL-1β production was also elevated, but this remained constant. The increase in PGE2 production was significantly inhibited by laser irradiation in a dose-dependent manner. The increase in IL-1β production was also significantly inhibited by laser irradiation, although the inhibition was only partial. Its inhibitory effects on PGE2 and IL-1β production suggest that laser irradiation may have great therapeutic benefits in bringing about relief of the pain that accompanies orthodontic treatment.
Infants' Fluoride Intake from Drinking Water Alone, and from Water Added to Formula, Beverages, and Food
Authors: Levy S.M. , Kohout F.J. , Guha-Chowdhury N. , Kiritsy M.C. , Heilman J.R. , Wefel J.S.
Published: January 2009

In infants, the majority of total ingested fluoride is obtained from water, formula and beverages prepared with water, baby foods, and dietary fluoride supplements. Few studies have investigated the distribution of fluoride intake from these sources among young children at risk for dental fluorosis. The purpose of this study was to assess estimated water fluoride intake from different sources of water among a birth cohort studied longitudinally from birth until age 9 months. Parental reports were collected at 6 weeks, 3 months, 6 months, and 9 months of age for water, formula, beverage, and other dietary intake during the preceding week. Fluoride levels of home and child-care tap and bottled water sources were determined. This report estimates daily quantities of fluoride ingested only from water-both by itself and used to reconstitute formula, beverages, and food. Daily fluoride intake from water by itself ranged to 0.43 mg, with mean intakes < 0.05 mg. Water fluoride intake from reconstitution of concentrated infant formula ranged to 1.57 mg, with mean intakes by age from 0.18 to 0.31 mg. Fluoride intake from water added to juices and other beverages ranged to 0.67 mg, with means < 0.05 mg. Estimated total daily water fluoride intake ranged to 1.73 mg fluoride, with means from 0.29 to 0.38 mg.
Mercury Vaporization from Amalgams with Varied Alloy Compositions
Authors: Ferracane J.L. , Adey J.D. , Nakajima H. , Okabe T.
Published: January 2009

The fact that mercury is released from dental amalgam restorations after abrasion provides a source of continued controversy over the safe use of this material. Studies have shown that the amount and rate of mercury release vary for different amalgam products. The objective of this study was to determine how alloy composition affects mercury vaporization from experimental amalgams with similar alloy particle size and shape and percent residual mercury. An hypothesis to be tested was that mercury release is dependent upon the concentration of tin in the silver-mercury matrix phase of the amalgam. Seven spherical amalgam alloys (two low-copper and five high-copper) were made by a dental manufacturer (Tokuriki Honten, Japan). Trituration conditions were adjusted so that all set amalgams had the same residual Hg (47.3%). ADAtype amalgam cylinders were aged for 14 days at 37°C, then lightly wet-abraded on #600 silicon carbide, dried, and placed into a tube through which air was blown at a rate of 750 mL/min. Mercury vaporization was monitored with a gold film analyzer (Jerome 411) for 30 min. Total Hg release was determined by integration. We analyzed polished specimens via electron microprobe to determine composition, volume fraction of silver-mercury matrix (γ 1), and amount of tin in the γ1. The results showed a strong negative correlation (r2 = 0.941) between the log of total mercury released and the amount of tin in the γ1. The effect of alloy composition, specifically the presence or absence of zinc in the amalgam, could not be definitively determined. It is concluded that the tin content in the γ1 matrix is the primary determinant of Hg vaporization from amalgam.
Efficacy of the FDA Selection Criteria for Radiographic Assessment of the Periodontium
Authors: Atchison K.A. , White S.C. , Flack V.F. , Hewlett E.R. , Kinder S.A.
Published: January 2009

The diagnosis of periodontitis is generally made on the basis of a clinical examination supported by radiographic evidence of bone loss. Recent guidelines promulgated by the US Food and Drug Administration recommend that periapical radiographs be ordered on the basis of clinical signs and symptoms indicating the probable presence of disease. This study evaluated the effectiveness of the FDA Guidelines for ordering radiographs for new adult dental patients as related to assessment of the periodontal condition of the patient. We examined 490 patients and determined the periapicals needed to supplement the posterior bitewings based upon the patient's clinical findings. We measured the reduction in the number of radiographs ordered as well as the extent of missed alveolar and furcation bone loss resulting from the use of the selected set of radiographs compared with a complete set. Four hundred thirty-three subjects had at least one clinical sign of periodontitis present in their mouths, and 264 demonstrated radiographic evidence of alveolar bone loss. Of the 460 subjects on whom periodontal probing was conducted, two-thirds demonstrated periodontal probing depths in excess of 3 mm; almost half showed evidence of bleeding upon probing. Individuals with clinical signs of periodontitis had, on average, 10 periapicals ordered-more than twice the number as those with no sign of periodontitis. Of the 2,415 teeth with radiographic findings of proximal or furcal bone loss, 152 sites of bone loss (6%) were missed when the selected set of films plus the posterior bitewings was used.