bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Macromolecular Assembly of Enamel Matrix Proteins in Enamel Formation
Authors: Margolis H.C. , Beniash E. , Fowler C.E.
Published: January 2009

Unlike other mineralized tissues, mature dental enamel is primarily (> 95% by weight) composed of apatitic crystals and has a unique hierarchical structure. Due to its high mineral content and organized structure, enamel has exceptional functional properties and is the hardest substance in the human body. Enamel formation (amelogenesis) is the result of highly orchestrated extracellular processes that regulate the nucleation, growth, and organization of forming mineral crystals. However, major aspects of the mechanism of enamel formation are not well-understood, although substantial evidence suggests that protein-protein and protein-mineral interactions play crucial roles in this process. The purpose of this review is a critical evaluation of the present state of knowledge regarding the potential role of the assembly of enamel matrix proteins in the regulation of crystal growth and the structural organization of the resulting enamel tissue. This review primarily focuses on the structure and function of amelogenin, the predominant enamel matrix protein. This review also provides a brief description of novel in vitro approaches that have used synthetic macromolecules ( i.e., surfactants and polymers) to regulate the formation of hierarchical inorganic (composite) structures in a fashion analogous to that believed to take place in biological systems, such as enamel. Accordingly, this review illustrates the potential for developing bio-inspired approaches to mineralized tissue repair and regeneration. In conclusion, the authors present a hypothesis, based on the evidence presented, that the full-length amelogenin uniquely regulates proper enamel formation through a process of cooperative mineralization, and not as a pre-formed matrix.
Desipramine Inhibits Na+/H+ Exchanger in Human Submandibular Cells
Authors: Choi S.-Y. , Li J. , Jo S.-H. , Lee S.J. , Oh S.B. , Kim J.-S. , Lee J.-H. , Park K.
Published: January 2009

A common and significant side-effect of the antidepressant desipramine is xerostomia (dry mouth). We investigated the effect of desipramine on Na+/H+ exchanger, which is an important modulator of salivary secretion. In dissociated human submandibular acinar cells, desipramine inhibited intracellular pH recovery in a concentration-dependent manner. Likewise, 5-(N-ethyl-N-isopropyl)amiloride (EIPA), a Na+/H+ exchanger inhibitor, had the same effect as desipramine, whereas the effect of 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid (DIDS), a Na+/HCO3− co-transporter inhibitor, was not dramatic. Although desipramine is known to inhibit catecholamine re-uptake, desipramine also inhibited pH recovery in the human submandibular gland cell line, HSG cells, which lack nerve inputs. Our results suggest that desipramine directly inhibits Na+/H+ exchange in human submandibular glands without the involvement of catecholamine re-uptake, revealing the cellular mechanism of desipramine-evoked xerostomia.
Functional Adaptability of Jaw-muscle Spindles after Bite-raising
Authors: Yabushita T. , Zeredo J.L. , Fujita K. , Toda K. , Soma K.
Published: January 2009

In a previous experiment, we found that masseter muscle spindles show functional plasticity after 5 to 15 days under increased occlusal vertical dimension (iOVD). In the present study, we hypothesized that spindle function would eventually recover if longer observation periods were allowed. Therefore, in this study we investigated changes in masseter muscle spindle function over periods of 1 day to 8 weeks. Masseter muscle-spindle responses to ramp-and-hold jaw stretches were recorded from the mesencephalic trigeminal nucleus in 35 barbiturate-anesthetized female Wistar rats. The rats were previously divided into Control and iOVD groups, and those in the iOVD group received a 2.0-mm composite resin build-up to the maxillary molars. In this condition, there were no statistically significant differences in masseter muscle spindle sensitivity between Control and iOVD in the six- and eight-week subgroups. Our results further indicate a high degree of adaptability in masseter muscle spindle function following changes in OVD.
Oral Clonidine Pre-treatment and Diazepam/Meperidine Sedation
Authors: Hall D.L. , Tatakis D.N. , Walters J.D. , Rezvan E.
Published: January 2009

Clonidine has recently been used as a pre-operative medication and sedative/anxiolytic drug. Its extended duration of action makes it suitable for longer procedures. In this randomized, crossover, placebo-controlled clinical trial, we characterized the effects of oral clonidine pre-treatment on intravenous diazepam/meperidine sedation using the bi-spectral index (BIS) in 13 participants. Clonidine significantly increased the numbers of BIS-depressed readings and percent memory loss during sedation, while reducing total diazepam and post-operative analgesic dosages by 44% and 55%, respectively. Systolic, diastolic, and mean arterial blood pressures, as well as pulse rates, were reduced. Respiratory rate, oxygen saturation, end-tidal CO2, and recovery from sedation were unchanged. Participants, surgeons, and sedationists preferred clonidine over the placebo. Clonidine pre-treatment increased and prolonged sedation and amnesia and stabilized vital signs while significantly decreasing diazepam and post-operative analgesic usage. These results suggest that pre-operative clonidine administration could be a useful supplement to intravenous sedation for dental procedures of long duration.
Fluid Shear Stress Inhibits TNFα-induced Osteocyte Apoptosis
Authors: Tan S.D. , Kuijpers-Jagtman A.M. , Semeins C.M. , Bronckers A.L.J.J. , Maltha J.C. , Von den Hoff J.W. , Everts V. , Klein-Nulend J.
Published: January 2009

Bone tissue can adapt to orthodontic load. Mechanosensing in bone is primarily a task for the osteocytes, which translate the canalicular flow resulting from bone loading into osteoclast and osteoblast recruiting signals. Apoptotic osteocytes attract osteoclasts, and inhibition of osteocyte apoptosis can therefore affect bone remodeling. Since TNF-α is a pro-inflammatory cytokine with apoptotic potency, and elevated levels are found in the gingival sulcus during orthodontic tooth movement, we investigated if mechanical loading by pulsating fluid flow affects TNF-α-induced apoptosis in chicken osteocytes, osteoblasts, and periosteal fibroblasts. During fluid stasis, TNF-α increased apoptosis by more than two-fold in both osteocytes and osteoblasts, but not in periosteal fibroblasts. One-hour pulsating fluid flow (0.70 ± 0.30 Pa, 5 Hz) inhibited (−25%) TNF-α-induced apoptosis in osteocytes, but not in osteoblasts or periosteal fibroblasts, suggesting a key regulatory role for osteocyte apoptosis in bone remodeling after the application of an orthodontic load.
Streptococcus salivarius Promotes Mucin Putrefaction and Malodor Production by Porphyromonas gingivalis
Authors: Sterer N. , Rosenberg M.
Published: January 2009

Although the contribution of the oral microbiota to oral malodor is well-documented, the potential role of Gram-positive micro-organisms is unclear. In the current study, we tested the hypothesis that Gram-positive micro-organisms contribute to malodor production by deglycosylating oral glycoproteins, rendering them susceptible to subsequent proteolysis. To this end, we examined the effect of Streptococcus salivarius on Porphyromonas gingivalis-mediated putrefaction of a model glycoprotein (pig gastric mucin). Malodor was scored by two odor judges, and volatile sulfides were determined with the use of a sulfide monitor. Mucin degradation was followed by electrophoresis on SDS-PAGE. Results showed that the addition of S. salivarius or β-galactosidase promoted mucin degradation and concomitant malodor production. Addition of glycosidic inhibitors (p-APTG and glucose) inhibited this process. These results suggest that Gram-positive micro-organisms such as S. salivarius contribute to oral malodor production by deglycosylating salivary glycoproteins, thus exposing their protein core to further degradation by Gram-negative micro-organisms.
Immunogenicity and Persistence of a Targeted Anti-caries DNA Vaccine
Authors: Xu Q.A. , Yu F. , Fan M.W. , Bian Z. , Chen Z. , Fan B. , Jia R. , Guo J.H.
Published: January 2009

We have previously reported that a targeted anti-caries DNA vaccine, pGJA-P, induced accelerated and increased antibody responses compared with a non-targeted anti-caries DNA vaccine. Recently, pGJA-P/VAX, a new targeted anti-caries DNA vaccine for human trials, was constructed by replacing the pCI vector used in the construction of pGJA-P with pVAX1, the only vector authorized by the US Food and Drug Administration in clinical trials. Here, we report on our exploration of the kinetics of the antibody responses generated following pGJA-P/VAX immunization and the persistence of pGJA-P/VAX at both the inoculation site and the draining lymph nodes. Intranasal vaccination of mice with pGJA-P/VAX induced strong antibody responses that lasted for more than 6 months. Furthermore, pGJA-P/VAX could still be detected at both the inoculation site and the draining cervical lymph nodes 6 months after immunization. Thus, the persistent immune responses are likely due to the DNA depot in the host, which acts as a booster immunization.
Novel IRF6 Mutations in Chinese Patients with Van der Woude Syndrome
Authors: Du X. , Tang W. , Tian W. , Li S. , Li X. , Liu L. , Zheng X. , Chen X. , Lin Y. , Tang Y.
Published: January 2009

Van der Woude syndrome (VWS) (OMIM 119300) is a dominantly inherited, developmental disorder that is characterized by pits and/or sinuses of the lower lip and a cleft lip and/or cleft palate. Mutations in the interferon regulatory factor 6 gene ( IRF6) have been recently identified in patients with VWS, with more than 60 mutations reported. However, the VWS phenotype, IRF6 mutation genotypes, and their interrelationships in Chinese VWS patients have not been studied. Here, we report 11 Chinese families with variable clinical phenotypes of VWS and identified mutations in all patients. Of the 11 mutations, 8 appeared to be novel: CC5.6GT, T342A, 566delA, C748T, C756A, C989A, C1209G, and 1316delT. Seven mutations caused a change or loss of the IRF6 domain. The marked phenotypic variation may be caused by the action of certain modifier genes on IRF6 function. Abbreviations: VWS, Van der Woude syndrome; IRF6, interferon regulatory factor 6; CL/P, cleft lip and/or cleft palate; DBD, DNA-binding domain; SMIR, Smad-interferon regulatory factor-binding domain; Kb, kilobase; PCR, polymerase chain-reaction.
Residual Stress in Composites with the Thin-ring-slitting Approach
Authors: Park J.W. , Ferracane J.L.
Published: January 2009

During polymerization, dental composites develop residual stresses that may compromise the marginal integrity and properties of the restorative. The objective of this study was to use the thin-walled ring-slitting method to measure and compare residual stresses. The hypotheses to be tested were that composites would generate different levels of residual stress based on their specific formulations and slitting times. Rings made from composites (Z100, Herculite, and Heliomolar) were cut at different times (10 min, 1 and 24 hrs) after being light-cured, and stress was measured. Residual stress was higher at the earlier cutting times, except for Heliomolar (α < 0.05). For the 10-minute and one-hour cutting groups, stress followed this order: Z100 > Herculite > Heliomolar. Early slitting was better to capture residual stress, and the thin-walled rings showed higher values than thick-walled rings and were better able to discriminate residual stress in composites.
Efficacy and Safety of Biodegradable Osteofixation Devices in Oral and Maxillofacial Surgery: a Systematic Review
Authors: Buijs G.J. , Stegenga B. , Bos R.R.M.
Published: January 2009

The use of osteofixation devices should be evidence-based if uncomplicated bone healing is to be achieved. Numerous studies describe and claim the advantages of biodegradable over titanium devices as a bone fixation method. Here, we systematically review the available literature to determine the clinical efficacy and safety of biodegradable devices compared with titanium devices in oral and maxillofacial surgery. In addition, related general aspects of bone surgery are discussed. We conducted a highly sensitive search in the databases of MEDLINE (1966–2005), EMBASE (1989–2005), and CENTRAL (1800–2005) to identify eligible studies. Eligible studies were independently evaluated by two assessors using a quality assessment scale. The study selection procedure revealed four methodologically ‘acceptable’ articles. Owing to the different outcome measures used in the studies, it was impossible to perform a meta-analysis. Therefore, the major effects regarding the stability and morbidity of fracture fixation using titanium and biodegradable fixation systems were qualitatively described. Any firm conclusions regarding the fixation of traumatically fractured bone segments cannot be drawn, due to the lack of controlled clinical trials. Regarding the fixation of bone segments in orthognathic surgery, only a few controlled clinical studies are available. There does not appear to be a significant short-term difference between titanium and biodegradable fixation systems regarding stability and morbidity. However, definite conclusions, especially with respect to the long-term performance of biodegradable fixation devices used in maxillofacial surgery, cannot be drawn. Abbreviations: CENTRAL, Cochrane Central Register of Controlled Trials; MeSH, Medical Subject Heading; VAS, Visual Analogue Scale; and W, weight.
The Effect of Copper on Demineralization of Dental Enamel
Authors: Abdullah A.Z. , Strafford S.M. , Brookes S.J. , Duggal M.S.
Published: January 2009

Previous studies have concluded that copper might inhibit enamel demineralization in vitro. Our aim was to assess the effect of copper (Cu2+), with and without amine fluoride, on human dental enamel under cariogenic challenge in situ. In a double-blind randomized four-leg crossover trial, 14 individuals wore a removable appliance containing 2 enamel slabs, 1 containing an artificial caries lesion. During each leg, the appliance was exposed twice daily to one of the test solutions: 1.25 mM CuSO4, amine fluoride (250 ppm F), copper and amine fluoride combined, or a placebo (water). A cariogenic challenge was provided in all cases by 5 daily exposures to 10% sucrose. Slabs were assessed before and after 21 days’ exposure by Knoop microhardness and transverse microradiography. Significantly less demineralization was observed with Cu2+ and fluoride in combination than with fluoride treatment alone (p < 0.05), whereas copper alone had no significant protective effect.
Role of Alcohol in the Fracture Resistance of Teeth
Authors: Nalla R.K. , Kinney J.H. , Tomsia A.P. , Ritchie R.O.
Published: January 2009

Healthy dentin, the mineralized tissue that makes up the bulk of the tooth, is naturally hydrated in vivo; however, it is known that various chemical reagents, including acetone and ethanol, can induce dehydration and thereby affect its properties. Here, we sought to investigate this in light of the effect of alcohol on the mechanical properties of dentin, specifically by measuring the stiffness, strength, and toughness of dentin in simulated body fluid and Scotch whisky. Results indicated that chemical dehydration induced by the whisky had a significant beneficial effect on the elastic modulus, strength, and fracture toughness of dentin. Although this made teeth more resistant to fracture, the change in properties was fully reversible upon rehydration. This effect is considered to be associated with increased cross-linking of the collagen molecules from intermolecular hydrogen-bonding, where water is replaced with weaker hydrogen-bond-forming solvents such as alcohol.
Minimizing Dentinal Fluid Flow Associated with Gap Formation
Authors: Ratih D.N. , Palamara J.E.A. , Messer H.H.
Published: January 2009

The relationship between gap formation and outward fluid flow and procedures to minimize both phenomena were investigated in extracted human premolars restored in vitro with MOD composite restorations. We hypothesized that either glass-ionomer cement (GIC) liners or low-shrinkage composite could reduce fluid flow related to gap formation. Two groups restored with bonding agents with either high- or low-shrinkage resin composites, and 2 groups restored by either conventional or light-cured GIC liner plus resin composite were compared (8 teeth/group). Fluid flow was measured with an automated apparatus. Baseline fluid flow was low and unchanged after bonding, but increased sharply (though transiently) after teeth were lined with GIC. Outward flow was significantly greater with conventional than with light-cured GIC. Inward fluid flow occurred during light-curing, followed by extensive, prolonged outward flow after curing. Low-shrinkage composite or GIC liners reduced gap formation and limited outward fluid flow. GIC liners promoted outward fluid flow during their setting reactions. Abbreviations: GIC, glass-ionomer cement; CEJ, cemento-enamel junction; MOD, mesio-occluso-distal; SEM, scanning electron microscopy.
Increased Young’s Modulus and Hardness of Col1a2oim Dentin
Authors: Franco G.E. Lopez , Huang A. , Camacho N. Pleshko , Stone D.S. , Blank R.D.
Published: January 2009

Mice harboring the Col1a2 oim mutation ( oim) express dentinogenesis imperfecta. To determine the effect of Col1a2 genotype on tissue mechanical properties, we compared Young’s modulus and hardness of dentin in the 3 Col1a2 genotypes. Upper incisors were tested by nanoindentation. Genotype had a significant effect on Young’s modulus, but there was not a simple mutant allele dosage relationship. The effect of genotype on hardness did not reach significance. Hardness and Young’s modulus were greater near the dento-enamel junction than near the pulp chamber. Greater hardness and Young’s modulus values near the dento-enamel junction reflected continued mineralization of the dentin following its initial synthesis. Analysis showed the mechanical data to be consistent with Fourier transform infrared and backscattered electron microscopy studies that revealed increased mineralization in oim bone. Analysis of the data suggests that clinical fragility of teeth in oim mice is not due to deficiencies of hardness or Young’s modulus, but may be due to defects in post-yield behavior or resistance to fatigue damage.
Apparent Interfacial Fracture Toughness of Resin/Ceramic Systems
Authors: Bona A. Della , Anusavice K.J. , Mecholsky J.J.
Published: January 2009

We suggest that the apparent interfacial fracture toughness (KA) may be estimated by fracture mechanics and fractography. This study tested the hypothesis that the KA of the adhesion zone of resin/ceramic systems is affected by the ceramic microstructure. Lithia disilicate-based (Empress2-E2) and leucite-based (Empress-E1) ceramics were surface-treated with hydrofluoric acid (HF) and/or silane (S), followed by an adhesive resin. Microtensile test specimens (n = 30; area of 1 ± 0.01 mm2) were indented (9.8 N) at the interface and loaded to failure in tension. We used tensile strength (σ) and the critical crack size (c) to calculate KA (KA = Yσc1/2) (Y = 1.65). ANOVA and Weibull analyses were used for statistical analyses. Mean KA (MPa·m1/2) values were: (E1HF) 0.26 ± 0.06; (E1S) 0.23 ± 0.06; (E1HFS) 0.30 ± 0.06; (E2HF) 0.31 ± 0.06; (E2S) 0.13 ± 0.05; and (E2HFS) 0.41 ± 0.07. All fractures originated from indentation sites. Estimation of interfacial toughness was feasible by fracture mechanics and fractography. The KA for the systems tested was affected by the ceramic microstructure and surface treatment.
Effects of Systemic Fluoride and in vitro Fluoride Treatment on Enamel Crystals
Authors: Chen H. , Czajka-Jakubowska A. , Spencer N.J. , Mansfield J.F. , Robinson C. , Clarkson B.H.
Published: January 2009

Systemically administered fluoride at a concentration of 75 ppm increases the surface roughness of developing enamel crystals in rats, which may be significant in advancing our understanding of the biological mechanism of fluorosis. Thus, the aim of this study was to investigate whether the increased surface roughness may be a result of surface restructuring by the direct action of fluoride at the crystal surface. We examined the fluoride dose-dependent roughening of enamel crystal surfaces in vivo, in the rat, and whether this roughening could be mimicked by the in vitro treatment of rat enamel crystals with neutral pH fluoride solutions. Our results showed that enamel crystal surface roughness increased after treatment with increasing fluoride ion concentrations, whether applied in vitro or administered systemically. This suggests a mechanism, alongside others, for the increased surface roughness of crystals in fluorotic enamel.
Electric-current-assisted Application of Self-etch Adhesives to Dentin
Authors: Breschi L. , Mazzoni A. , Pashley D.H. , Pasquantonio G. , Ruggeri A. , Suppa P. , Mazzotti G. , Di Lenarda R. , Tay F.R.
Published: January 2009

The use of electric current during the application of etch-and-rinse adhesive systems has been recently claimed to increase bonding of etch-and-rinse adhesives by enhancing substrate impregnation. The null hypothesis tested in this study was that electrically assisted application has no effect on bond strength of self-etching bonding systems. Three self-etch adhesives (Protect-Bond, Xeno III, and Prompt L-Pop) were applied with the aid of an electric signal-generating device (ElectroBond) and tested vs. controls prepared with the same disposable sponges but without electric current. Specimens bonded under the influence of electric current exhibited increased microtensile bond strength compared with the controls (p < 0.05). High-resolution SEM analysis showed that bonding under the influence of electricity reduced interfacial nanoleakage. It is speculated that resin infiltration may be improved by the attraction of polar monomers by an electric current or by modification of the dentin surface charges, resulting in better water substitution or evaporation.
Calcium Modulates Interactions between Bacteria and Hydroxyapatite
Authors: Venegas S.C. , Palacios J.M. , Apella M.C. , Morando P.J. , Blesa M.A.
Published: January 2009

Bacterial adhesion onto hydroxyapatite is known to depend on the surface properties of both the biomaterial and the bacterial strain, but less is known about the influence of the composition of the aqueous medium. Here, the adhesion of Streptococcus mutans and 3 different Lactobacilli on powdered hydroxyapatite was shown to change with Ca2+ concentration. The effect depends on the surface properties of each strain. Adhesion of Lactobacillus fermentum and salivarius (and of Streptococcus mutans at low Ca2+) was enhanced with increasing Ca2+ concentration. Lactobacillus casei was efficiently removed by adhesion on hydroxyapatite, even without Ca2+ addition, and the effect of this ion was only marginal. The results are interpreted in terms of Ca2+-mediated adhesion, and relative to the hydrophobic properties of each strain and the electrical properties of the bacterial and solid surfaces (electrophoretic mobility).
Gingivitis Susceptibility and its Relation to Periodontitis in Men
Authors: Dietrich T. , Kaye E. Krall , Nunn M.E. , Van Dyke T. , Garcia R.I.
Published: January 2009

The objective of this cross-sectional study was to evaluate whether gingivitis susceptibility is associated with periodontitis. We analyzed data of 462 men in the VA Dental Longitudinal Study aged 47 to 92 years who had never smoked or had quit smoking 5+ years previously. Multiple logistic regression models, with tooth-level bleeding on probing at sites with attachment loss ≤ 2 mm as the dependent variable, were derived with adjustment for plaque, calculus, crown coverage, age, income, education, marital status, body mass index, diabetes, and vitamin C intake, and stratification by age (< 65, 65+ years). Periodontitis and mean attachment loss were positively associated with bleeding on probing, with stronger associations among men < 65 years old (for periodontitis, OR 2.1; 95% CI 1.5, 3.1) than men 65+ years of age (OR 1.2; 95% CI 0.9, 1.6). Our results suggest that among never and former smokers, gingivitis susceptibility is higher among men with periodontitis compared with that in men without periodontitis.
Remodeling the Dentofacial Skeleton: The Biological Basis of Orthodontics and Dentofacial Orthopedics
Authors: Meikle M.C.
Published: January 2009

Orthodontic tooth movement is dependent upon the remodeling of the periodontal ligament and alveolar bone by mechanical means. Facial sutures are also fibrous articulations, and by remodeling these joints, one can alter the positional relationships of the bones of the facial skeleton. As might be expected from the structure and mobility of the temporomandibular joint (TMJ), this articulation is more resistant to mechanical deformation, and whether functional mandibular displacement can alter the growth of the condyle remains controversial. Clinical investigations of the effects of the Andresen activator and its variants on dentofacial growth suggest that the changes are essentially dento-alveolar. However, with the popularity of active functional appliances, such as the Herbst and twin-block based on ’jumping the bite’, attention has focused on how they achieve dentofacial change. Animal experimentation enables informed decisions to be made regarding the effects of orthodontic treatment on the facial skeleton at the tissue, cellular, and molecular levels. Both rat and monkey models have been widely used, and the following conclusions can be drawn from such experimentation: (1) Facial sutures readily respond to changes in their mechanical environment; (2) anterior mandibular displacement in rat models does not increase the mitotic activity of cells within the condyle to be of clinical significance, and (3) mandibular displacement in non-human primates initiates remodeling activity within the TMJ and can alter condylar growth direction. This last conclusion may have clinical utility, particularly in an actively growing child.
Relationship between Porotic Changes in Alveolar Bone and Spinal Osteoporosis
Authors: Anwar R. Binte , Tanaka M. , Kohno S. , Ikegame M. , Watanabe N. , Ali M. Nowazesh , Ejiri S.
Published: January 2009

Epidemiological studies have shown that post-menopausal women who do not use an estrogen supplement have fewer teeth than those who do. We hypothesized that changes in the dentition of post-menopausal women might be due to alveolar bone alterations by estrogen deficiency. To clarify this, we analyzed the microstructural alveolar bone changes in ovariectomized monkeys and compared these with their lumbar bone mineral density. The % of baseline bone mineral density showed a significant decrease in the ovariectomized group as compared with the controls. The second-molar interradicular septa in ovariectomized monkeys showed a significantly decreased nodes number, cortices number, and an increased structural model index value. More pores were seen in the ovariectomized group at the top of the septa. This study demonstrated that, in such monkeys, estrogen deficiency led to fragility of the trabecular structure of the molar alveolar bone, and such fragility was inversely correlated with lumbar bone mineral density.
Chlorhexidine Preserves Dentin Bond in vitro
Authors: Carrilho M.R.O. , Carvalho R.M. , de Goes M.F. , di Hipólito V. , Geraldeli S. , Tay F.R. , Pashley D.H. , Tjäderhane L.
Published: January 2009

Loss of hybrid layer integrity compromises resin-dentin bond stability. Matrix metalloproteinases (MMPs) may be partially responsible for hybrid layer degradation. Since chlorhexidine inhibits MMPs, we hypothesized that chlorhexidine would decelerate the loss of resin-dentin bonds. Class I preparations in extracted third molars were sectioned into two halves. One half was customarily restored (etch-and-rinse adhesive/resin composite), and the other was treated with 2% chlorhexidine after being acid-etched before restoration. Specimens were stored in artificial saliva with/without protease inhibitors. Microtensile bond strengths and failure mode distribution under SEM were analyzed immediately after specimens’ preparation and 6 months later. With chlorhexidine, significantly better preservation of bond strength was observed after 6 months; protease inhibitors in the storage medium had no effect. Failure analysis showed significantly less failure in the hybrid layer with chlorhexidine, compared with controls after 6 months. In conclusion, this in vitro study suggests that chlorhexidine might be useful for the preservation of dentin bond strength.
The Epidemiology and Risk Factors of Head and Neck Cancer: a Focus on Human Papillomavirus
Authors: Ragin C.C.R. , Modugno F. , Gollin S.M.
Published: January 2009

Head and neck cancer was the eighth leading cause of cancer death worldwide in 2000. Although the incidence of head and neck squamous cell carcinoma (HNSCC) in the United States is relatively low, survival is poor and has not improved for several decades. While tobacco and alcohol are the primary risk factors for HNSCC development, epidemiological studies report a strong association with human papillomavirus (HPV) in a subset of HNSCC. More than 95% of cervical squamous cell carcinomas are linked to persistent HPV infection; evidence demonstrates that HPV is a necessary carcinogen. Not all HPV-positive HNSCC express the viral oncogenes ( E6 and E7), which suggests that HPV may function as a carcinogen in a smaller proportion of HNSCC. This review presents our current understanding of the relationship between HPV and HNSCC, and describes future research directions that may lead to a better understanding of the involvement of HPV in head and neck cancer.
Probiotics Reduce the Prevalence of Oral Candida in the Elderly—a Randomized Controlled Trial
Authors: Hatakka K. , Ahola A.J. , Yli-Knuuttila H. , Richardson M. , Poussa T. , Meurman J.H. , Korpela R.
Published: January 2009

Overgrowth of oral yeast is a common problem among the elderly. Probiotic bacteria are known to inhibit the growth of pathogenic microbes. We tested the hypothesis that cheese containing probiotic bacteria can reduce the prevalence of oral Candida. During this 16-week, randomized, double-blind, placebo-controlled study, 276 elderly people consumed daily 50 g of either probiotic (n = 136) or control cheese (n = 140). The primary outcome measure was the prevalence of a high salivary yeast count (≥ 104 cfu/mL) analyzed by the Dentocult® method. The prevalence decreased in the probiotic group from 30% to 21% (32% reduction), and increased in the control group from 28% to 34%. Probiotic intervention reduced the risk of high yeast counts by 75% (OR = 0.25, 95%CI 0.10–0.65, p = 0.004), and the risk of hyposalivation by 56% (OR = 0.44, 95%CI 0.19–1.01, p = 0.05). Thus, probiotic bacteria can be effective in controlling oral Candida and hyposalivation in the elderly.
Signaling Pathways Regulating IL-1α-induced COX-2 Expression
Authors: Ogata S. , Kubota Y. , Yamashiro T. , Takeuchi H. , Ninomiya T. , Suyama Y. , Shirasuna K.
Published: January 2009

Interleukin-1α(IL-1α) stimulates the production of prostaglandin E2(PGE2) in odontogenic keratocyst fibroblasts. However, the signaling pathways remain obscure. In this study, we investigated IL-1αsignaling pathways that regulate cyclooxygenase-2 (COX-2) expression in odontogenic keratocyst fibroblasts. IL-1αincreased the expression of COX-2 mRNA and protein, and PGE2secretion in the fibroblasts. IL-1αincreased the phosphorylation of extracellular signal-regulated protein kinase-1/2 (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK). PD-98059, SB-203580, SP-600125, and PDTC—which are inhibitors of ERK1/2, p38, JNK, and nuclear factor-κB (NF-κB), respectively—attenuated the IL-1α-induced COX-2 mRNA expression and activated protein kinase C PGE2secretion. IL-1α(PKC), and PKC inhibitor staurosporine inhibited IL-1α-induced phosphorylation of ERK1/2, p38, and JNK, and decreased IL-1α-induced COX-2 mRNA expression. Thus, in odontogenic keratocyst fibroblasts, IL-1αmay stimulate COX-2 expression both through the PKC-dependent activation of ERK1/2, p38, and JNK signaling pathways, and through the NF-κB cascade.
Polymerization Shrinkage Influences Microtensile Bond Strength
Authors: Cabrera E. , de la Macorra J.C.
Published: January 2009

Shrinkage results from a complex spatial strain network, producing movements within materials. The purpose of this study was to test whether microtensile bond strength (μTBS) of a light-curing resin composite to enamel depends on distance to the center of the curing mass. Labial surfaces of bovine incisors were ground flat, divided into 2 groups (n = 8), acid-etched, and coated with an unfilled resin bond. A resin-based composite was placed in one increment (group A) or separately at gingival, central, and incisal sites (group B), and light-cured. Teeth were sectioned, yielding stick-shaped specimens assigned to one of 9 groups according to distance to incisal edge of restoration (NDistanc). Microtensile bond strength was transformed to percentages of its maximum values within each tooth (PMPa). Comparisons within groups showed (group A) that mean PMPa decreased from central to gingival and from central to incisal (p < 0.01). Comparisons between groups showed that mean PMPa was significantly lower in group A compared with group B, only at gingival and incisal sites. Microtensile bond strength significantly decreased as the distance increased to the center of the curing mass.
Microtensile Bond Strengths of Two Adhesive Resins to Discolored Dentin after Amalgam Removal
Authors: Harnirattisai C. , Senawongse P. , Tagami J.
Published: January 2009

Studies have reported the discoloration of dentin beneath amalgam restorations. The purpose of this study was to test the hypothesis that the bond strengths of adhesive resins to this discolored dentin are lower than those to normal dentin, and are related to the presence of metallic ions or corrosion products. Amalgam-filled extracted human teeth were used. After the removal of amalgam, the discolored dentin and surrounding normal dentin were bonded with Single Bond or Clearfil SE Bond and tested for microtensile bond strengths. The bond strengths of Single Bond and Clearfil SE Bond to normal dentin were greater than to discolored dentin. Clearfil SE Bond demonstrated higher bond strength to normal dentin than did Single Bond. However, no differences were found between the bond strengths to the discolored dentin of both adhesives. Elemental micro-analysis revealed various amounts of tin in all discolored dentin.
Inflammatory Immune Responses by Water-insoluble α-glucans
Authors: Okamoto S. , Terao Y. , Kaminishi H. , Hamada S. , Kawabata S.
Published: January 2009

Water-insoluble α-glucans are synthesized from sucrose by glucosyltransferase-I of mutans streptococci and play an important role in the development of dental plaque. Several types of β-glucans in fungal cell wall components and water-soluble α-glucans from Streptococcus mutans are known to modulate innate immunity. In the present study, we investigated whether water-insoluble α-glucans also induced inflammatory innate immune responses. Our results showed that water-insoluble α-glucans synthesized by Streptococcus sobrinus activated mouse peritoneal exudate macrophages to produce pro-inflammatory cytokines. The immunological responses were not due to contamination by sucrose, water-soluble α-glucan, lipopolysaccharide, or peptidoglycan. Furthermore, human monocytes stimulated by water-insoluble α-glucans produced TNF-α and IL-8, while human polymorphonuclear cells were activated by water-insoluble α-glucans, resulting in chemotaxis and hydrogen peroxide production. The results demonstrated that water-soluble α-glucans modulate macrophage- and granulocyte-induced inflammatory immune responses, and suggest that inflammation induced by those α-glucans is associated with the development of periodontal diseases.
Functional TLRs and NODs in Human Gingival Fibroblasts
Authors: Uehara A. , Takada H.
Published: January 2009

Since human gingival fibroblasts are the major cells in periodontal tissues, we hypothesized that gingival fibroblasts are endowed with receptors for bacterial components, which induce innate immune responses against invading bacteria. We found clear mRNA expression of Toll-like receptors (TLR)1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, TLR9, MD-2, MyD88, NOD1, and NOD2 in gingival fibroblasts. Gingival fibroblasts constitutively expressed these molecules. Upon stimulation with chemically synthesized ligands mimicking microbial products for these receptors, the production of pro-inflammatory cytokines, such as interleukin (IL)-6, IL-8, and monocyte chemoattractant protein-1, was markedly up-regulated. Furthermore, the production of pro-inflammatory cytokines induced by TLR and NOD ligands was significantly inhibited by an RNA interference assay targeted to NF-κB. These findings indicate that these innate immunity-related molecules in gingival fibroblasts are functional receptors involved in inflammatory reactions in periodontal tissues, which might be responsible for periodontal pathogenesis.
Rapid Tissue Factor Induction by Oral Streptococci and Monocyte-IL-1β
Authors: Hahn C.-L. , Best A.M. , Tew J.G.
Published: January 2009

The ability of pro-inflammatory cytokines to promote coagulation prompted the hypothesis that pro-inflammatory cytokines induced by oral streptococci might play a role in the pathogenesis of viridans endocarditis. We used supernatant fluids from peripheral blood mononuclear monocyte (PBMC) cultures, stimulated for just 4–6 hrs with representative streptococcal isolates, to study cytokines that promoted endothelial tissue factor (TF) activity. Neutralizing antibodies demonstrated that interleukin-1β (IL-1β) was a major early endothelial TF inducer, and that recombinant IL-1β was comparable with the supernatant fluid in activity. IL-1β-rich supernatant fluids from oral streptococci-stimulated or lipopolysaccharide-stimulated PBMC cultures up-regulated the expression of endothelial ICAM-1 and E-selectin. These molecules could help trap TF-producing monocytes or dendritic cells bearing streptococci at the site. Thus, the rapid IL-1β-inducing capacity of oral streptococci could facilitate the early deposition of bacteria in fibrin clots and promote endocarditis.
DMP1-targeted Cre Expression in Odontoblasts and Osteocytes
Authors: Lu Y. , Xie Y. , Zhang S. , Dusevich V. , Bonewald L.F. , Feng J.Q.
Published: January 2009

Odontoblasts in dentin and osteocytes in bone contain dendritic processes. To test if their dendrites share a common feature, we compared their cellular morphology as visualized using scanning electron microscopy. Analysis of our data showed that both cells share an identical dendritic canalicular system and express extensive processes forming a complex network within the mineralized matrix. Because dentin matrix protein 1 (DMP1), an extracellular matrix protein, is highly expressed in both types of cells, we next tested, using a transgenic approach, whether a 9.6-kb Dmp1 promoter-4-kb 1st intron would be able to target Cre cDNA in these cells for expression/deletion of other genes in odontoblasts and osteocytes. We determined the specificity and efficiency of Cre activity by crossing Dmp1-Cre mice with ROSA26 reporter mice. Results showed that odontoblasts and osteocytes were specifically targeted, suggesting that this animal model will be useful for the preferential study of gene functions in both types of cells.
Fibrillin-2 Degradation by Matrix Metalloproteinase-2 in Periodontium
Authors: Tsuruga E. , Irie K. , Yajima T.
Published: January 2009

Elastic system fibers, comprised of microfibrils and tropoelastin, are extracellular components of periodontal tissue. During development, the microfibrils act as a template on which tropoelastin is deposited. However, the process of elastic system fiber remodeling is not fully understood. Therefore, we examined whether matrix metalloproteinases (MMPs) are involved in the remodeling of fibrillins (major components of microfibrils) by human gingival fibroblasts and periodontal ligament (PDL) fibroblasts. Gingival and PDL fibroblasts were cultured for 6 weeks. In some cultures, MMP inhibitor or tissue inhibitor of matrix metalloproteinsase-2 (TIMP-2) was added to the medium for an additional 2 weeks. Active MMP-2 (62 kDa) appeared as cell-membrane-associated or in extracellular matrix only in PDL fibroblast cell layers. The addition of MMP inhibitor or TIMP-2 significantly increased fibrillin-2 accumulation in PDL fibroblast cell layers, and decreased the amount of fibrillin-2 fragments, suggesting that active MMP-2 may degrade fibrillin-2, and that MMPs may play a role in the remodeling of elastic system fibers in PDL.
Nifedipine and Cyclosporin Affect Fibroblast Calcium and Gingiva
Authors: Bullon P. , Gallardo I. , Goteri G. , Rubini C. , Battino M. , Ribas J. , Newman H.N.
Published: January 2009

It has been stated that cyclosporin and nifedipine produce gingival overgrowth. However, the specific pathogenic mechanism remains uncertain. We used an experimental rat model to test the hypothesis that changes in collagen metabolism and numbers of gingival blood vessels are not mediated by intracellular calcium concentration (ratiometric Fura-2 AM measurement) in gingival fibroblasts. In the cyclosporin group, both width (364.2 ± 67.5 μm) and microvessel density (number of vessels/mm2, stained with anti-CD34 antibody) (41.6 ± 5.1) of gingiva were statistically different when compared with those in the control group (width = 184.3 ± 35.2 μm, microvessel density = 19.6 ± 2.4). The nifedipine group showed the highest content of collagen (proportion of total stroma occupied by collagen, stained with Picro-Mallory) (nifedipine group = 66.3 ± 9.4, cyclosporin group = 55.2 ± 7.9, control group = 30.1 ± 10.2). Freshly cultured fibroblasts from the cyclosporin group exhibited higher ratiometric values of fluorescence than did both the control and nifedipine groups (p = 0.03). Our results support the hypothesis that changes in gingival collagen metabolism are not mediated by calcium intracellular oscillations.
Cortical Vascular Canals in Human Mandible and Other Bones
Authors: Kingsmill V.J. , Gray C.M. , Moles D.R. , Boyde A.
Published: January 2009

The human mandible is highly mineralized. We hypothesized that this is related to the local vascularity of the bone. This could not be examined directly, but, as a surrogate, intracortical vascular canal spaces of the human mandible were studied so that we could determine possible relationships with age, gender, location, dental status, and tissue mineralization. Canal numbers, area, and volume fraction were calculated from quantitative backscattered electron images of human mandibles aged 16–96 years. Data were compared with calvaria, maxilla, lumbar vertebra, femoral neck, and iliac crest. In the mandible, the buccal aspect of the midline was the most porous, the canals being larger and more numerous. The cortical porosity in the posterior of partially dentate mandibles was significantly greater than that of either dentate or edentate mandibles, and there was a significant increase in the size of canals in the mandible with increasing age. Female mandibles had more porous cortices. No relationship was found between cortical porosity and the degree of bone mineralization.
The National Student Research Group of the AADR—An Introduction
Authors: Rogér James M. , Javarone Julie A. , Ealba Erin L. , Markiewicz Michael R. , Morlandt Anthony B.
Published: January 2009

The 2005–06 officers of the National Student Research Group (NSRG) of the American Association for Dental Research (AADR) have summarized their activities in developing the NSRG into an effective organization aimed at fostering future dental researchers. The officers have focused their efforts on establishing opportunities for the pre-doctoral dental student members of the AADR to participate in and formally present their research during dental school. In addition to the many research awards and fellowships already sponsored by the NSRG and the AADR, the NSRG has established new travel awards for students to present at specialty groups’ annual meetings. Other recent initiatives have included a contact list of all dental schools, along with local student research group (SRG) leadership contacts, advice during the creation of a new teaching fellowship opportunity, fundraising efforts to support student research and the NSRG infrastructure, and successfully pursuing a student voting position on the AADR Board. A brief addendum detailing recent activities and future initiatives is also included. The article describes membership requirements, selection of officers, and contacts for additional information. We hope that this Discovery! will serve to increase the awareness of students, researchers, and administrators regarding the role of the NSRG.
Protection Offered by Root-surface Restorative Materials against Biofilm Challenge
Authors: Yip H.K. , Guo J. , Wong W.H.S.
Published: January 2009

The prevalence of root-surface caries is increasing. We hypothesized that some restorative materials are protective against cariogenic challenge on root surfaces. Our goal was to study the effects of different restorative materials on root surfaces incubated with an oral biofilm generated in an artificial mouth. A biofilm of Streptococcus mutans, Streptococcus sobrinus, Lactobacillus rhamnosus, and Actinomyces naeslundii was co-cultured for 21 days on 24 glass-ionomer cement, resin-modified glass-ionomer cement, or resin-composite-restored root surfaces. These surfaces were then examined with Fourier transform infrared spectroscopy and scanning electron energy-dispersive spectroscopy. Only glass-ionomer restorations showed a significant increase in log calcium-to-phosphorus ratio (P < 0.01), and a significantly lower log amide I-to-hydrogen phosphate ratio on the root surface after incubation in the artificial mouth. Glass-ionomer restoratives conferred a preventive effect on the root surfaces against initial cariogenic challenge with a mixed-species oral biofilm without therapeutic intervention.
In vitro Evaluation of Corrosion and Cytotoxicity of Orthodontic Brackets
Authors: Costa M.T. , Lenza M.A. , Gosch C.S. , Costa I. , Ribeiro-Dias F.
Published: January 2009

The corrosion resistance of AISI 304 stainless steel (AISI 304 SS) and manganese stainless steel (low-nickel SS) brackets in artificial saliva was investigated. The cytotoxic effects of their corrosion products on L929 cell culture were compared by two assays, crystal violet, to evaluate cell viability, and MTT (3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide), for cell metabolism and proliferation. The atomic absorption spectroscopic analysis of the corrosion products demonstrated that nickel and manganese ion concentrations were higher for the AISI 304 SS-bracket immersion solution as compared with the low-nickel SS brackets. Scanning electron microscopy and energy-dispersive spectroscopy demonstrated less corrosion resistance for the AISI 304 SS brackets. Although none of the bracket extracts altered L929 cell viability or morphology, the AISI 304 SS-bracket extracts decreased cellular metabolism slightly. The results indicated that the low-nickel SS presents better in vitro biocompatibility than AISI 304 SS brackets. Abbreviations used: AISI, American Iron and Steel Institute; EDS, energy-dispersive spectroscopy; OD, optical density; ISO, International Organization for Standardization; MTT, (3-{4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NiSO4, nickel sulfate; SEM, standard error of the mean; WHO, World Health Organization; and TNF, tumor necrosis factor.