bluuebunny/crossref_metadata_2025 huggingface dataset:
Staircase Assessment of the Magnitude and Time-course of 50% Nitrous-oxide Analgesia
Authors: Kaufman E. , Chastain D.C. , Gaughan A.M. , Gracely R.H.
Published: November 2010

The analgesic effect of 50% nitrous oxide and oxygen on thermal pain sensations was evaluated in a placebo-controlled, double-blind crossover design. In a session immediately before oral surgery, 20 patients used a seven-point verbal scale to rate the intensity of pain sensations evoked by three-second thermal stimuli delivered to 14 sites on the volar forearm at 20-second intervals by a 1-cm-diameter contact thermode. Subjects rated 36 stimuli while breathing room air and then two additional sets of 36 stimuli while inhaling 50% nitrous oxide and oxygen during one set and oxygen placebo during the other. Each of these two stimulus sets was preceded by a two-minute induction of the agent, and the sets were separated by a three-minute washout period. Order of administration was randomized and counterbalanced. Stimulus temperatures were adjusted continuously by an interactive computer program so that response could be maintained at predetermined levels. This method resulted in a continuous measure of analgesia in units of stimulus intensity. Results showed that, in comparison with placebo, nitrous oxide significantly increased the stimulus temperatures (mean = 0.42°C) required to make the same response [F (11,209) = 6.76, p <0.0001], indicating analgesia. This increase was one-third to one-half that observed with clinical doses of intravenous fentanyl. Analgesic effects were apparent at three min and waned 10 min after termination of nitrous-oxide inhalation. These times closely correlated with previous measures of alveolar concentration, further supporting the fast but modest analgesic action of nitrous oxide.
A Semi-empirical Model for Prediction of How Post-retained Crowns Will Fail Under Compressive Loading
Authors: Mitchell C.A. , Orr J.F. , Kennedy J.G.
Published: November 2010

The aim of this in vitro study was to determine the relative contributions to retention of the different components of the post-retained crown and the mode of failure when the crown was loaded at 50 degrees to the vertical (i.e., in an apical direction). Failure was , initiated in all the specimens as a rotation of the crown about a point on the labial surface of the root at the crown-root interface with pull-out of the post. A semi-empirical model was developed to explain this mode of failure. From experimental results, it was noted that the retention provided by the post was the most significant factor in the equation. However, large variation in the maximum forces recorded from pull-out tests on 40 posts suggested that the glass-ionomer cement was acting in the manner of a brittle composite material whose failure may be attributed to defects in the structure causing stress concentrations. The probability of survival at each ultimate strength recorded experimentally was plotted for comparison with the curve generated by the derived Weibull function. Close agreement was noted. Thus, for any given force applied compressively at 50 degrees to the vertical to a post-retained crown of known dimensions, it is possible, by use of the described equation, to calculate the force, P, applied to the post. This value of P may then be inserted into the Weibull equation to give the probability of the crown failing under that applied force.
Salivary Flow Induction by Buccal Permucosal Pilocarpine in Anesthetized Beagle Dogs
Authors: Weaver M.L. , Tanzer J.M. , Kramer P.A.
Published: November 2010

We tested whether permucosal delivery of pilocarpine nitrate could be used to elicit significant salivary secretion. Pilocarpine (pKa6.6 at 37°C) was applied as solutions (pHs 5.6, 6.6, 7.6; 15 mg/mL) to the buccal mucosa (2.8 cm2) of 6 anesthetized dogs. Saliva was collected continuously from cannulated submandibular and parotid ducts and blood sampled during and after drug administration. Plasma pilocarpine levels were determined by reversed-phase HPLC. Absorption rates were determined by use of data from separate zero-order intravenous infusions to the same dogs. Pilocarpine was buccally absorbed at a constant rate of 72.9 ± 38.5 μg/kg/h following its application at pH 7.6. At this pH of the drug solution, the time to appearance of pilocarpine in blood plasma was 0.31 ± 0.08 h, and the time to appearance of salivary flow was 0.86 ± 0.32 h. A threshold dose of 32.9 ± 7.5 ug/kg was required to induce secretion with the pH 7.6 drug, the steady-state plasma concentration was 28.9 ± 19.3 ng/mL, and the steady-state submandibular flow rate was 0.14 ± 0.11 mL/ min/gland pair. Salivary flow induction was symmetrical and reached levels as high as 0.35 mL/min/submandibular gland pair without apparent tachyphylaxis. Results at pHs 5.6, 6.6, and 7.6 were consistent with the hypothesis that pilocarpine is primarily absorbed as un-ionized drug. The data indicate that transmucosal delivery of pilocarpine, avoiding "first pass" hepatic loss, may hold promise for the treatment of xerostomia.
Fluoride Concentrations in Plaque, Whole Saliva, and Ductal Saliva After Application of Home-use Topical Fluorides
Authors: Zero D.T. , Raubertas R.F. , Fu J. , Pedersen A.M. , Hayes A.L. , Featherstone J.D.B.
Published: November 2010

It is now well-accepted that the primary anti-caries activity of fluoride (F) is via topical action. The retention of F in the mouth after topical fluoride treatment is considered to be an important factor in the clinical efficacy of F. The purpose of this study was to evaluate F levels in ductal saliva, whole saliva, and pooled plaque after treatment with topical F agents intended for home use. Ten consenting adults, mean (SD) age 31.0 (8.2) years, participated in all aspects of the study. Two days before each test, subjects received a professional tooth cleaning and subsequently abstained from all oral hygiene procedures to permit plaque to accumulate, and from the use of F-containing dental products. Treatments consisted of a placebo dentifrice (PD), fluoride dentifrice (FD; 0.24% NaF), fluoride rinse (FR; 0.05% NaF), and fluoride gel (FG; 1.1% NaF). Unstimulated whole saliva and pooled plaque were sampled at multiple points over a 24-hour period. In a separate experimental series, stimulated parotid saliva was sampled over a two-hour period after treatment. Fluoride levels generally followed the same pattern in whole saliva and pooled plaque samples, with FG > FR > FD > PD. Night-time F application resulted in prolonged F retention in whole saliva but not in plaque. Fluoride levels in parotid saliva were only slightly higher after F treatment and returned to baseline levels within two h. The results of this study indicate that the method of F delivery, the F concentration of the agent, and the time of application (daytime vs. night-time) are important factors influencing F levels in the mouth. The recycling of F in ductal saliva as a consequence of the inadvertent ingestion of home-use fluoride products does not appear to make a clinically significant contribution to F levels in the mouth.
Effect of Xylitol Consumption on the Plaque-Saliva Distribution of Mutans Streptococci and the Occurrence and Long-term Survival of Xylitol-resistant Strains
Authors: Trahan L. , Söderling E. , Drean M.-F. , Chevrier M.-C. , Isokangas P.
Published: November 2010

Since the exposure of mutans streptococci to xylitol is known to select for xylitol-resistant (XR) natural mutants, the occurrence and long-term survival of such xylitol-resistant strains was evaluated in a cross-sectional sampling of participants of the Ylivieska xylitol study four years after the original two-year experimental period. Paraffin-stimulated whole saliva was first collected, and then plaque was collected and pooled. The salivary and dental plaque mutans streptococci were enumerated after growth on TSY20B agar. The proportion of XR strains was determined by autoradiography with 14C-xylitol. A strong and significant correlation (r = 0.645 and p = 0.005) between the number of mutans streptococci in saliva and in dental plaque was observed in non-consumers of xylitol. Such a correlation totally disappeared (r = 0.098 and p = 0.612) in xylitol-exposed consumers (habitual and former xylitol-consumers). The proportion of the salivary XR mutants (35%) in non-consumers (n = 16) was significantly lower than in the xylitol-exposed consumers (79%) (n = 27), (p = 0.0001) or in former consumers (75%) (n = 13), (p = 0.0008) or in the habitual consumers (83%) (n = 14), (p = 0.004). The proportion of XR mutants in dental plaque was, on the average, much lower than in the corresponding saliva. The proportion of XR in the plaque of xylitol non-consumers was half of that of the xylitol-exposed group, but the difference was not statistically significant. Taken together, the results suggest that: (1) xylitol consumption modifies the mutans streptococci distribution between the dental plaque and the saliva; (2) once selected by the habitual use of xylitol and established in the mouth, the XR natural mutant population maintains itself for up to four years after the withdrawal of the selective agent or at least under minimal and irregular consumption of the agent; and (3) an unknown characteristic of the XR mutants allows them to be more easily shed into the saliva from the plaque than the xylitol-sensitive parental strains.
Effect of Delmopinol on the Cohesion of Glucan-containing Plaque Formed by Streptococcus mutans in a Flow Cell System
Authors: Rundegren J. , Simonsson T. , Petersson L. , Hansson E.
Published: November 2010

Glucan-containing plaque was formed by Streptococcus mutans adhering to saliva-coated glass slides in flow cells thermostated at 37°C. The substrate was Brain Heart Infusion broth containing 1% sucrose and 10% sterile saliva. During the build-up of the plaque, which lasted for 29 h, the plaque was subjected to three two-minute exposures to either 0.1 mol/L sodium acetate buffer, pH 6.0, or the same buffer containing 6.4 mmol/L (0.2%) of the surface-active anti-plaque substance delmopinol hydrochloride. The glass slides carrying the plaque were weighed, and plaques subjected to delmopinol treatment weighed only seven percent of the control plaques. The glass slides were then mounted in a beaker containing buffer, subjected to ultrasonication, and re-weighed. The delmopinol-treated plaques lost 59% of their wet weight upon sonication, while the controls lost only 19%. Control plaques having the same weight as delmopinol-treated plaques were not different from the control plaques grown for 29 h with regard to reduction of plaque weight after sonication. Transmission electron micrographs (TEM) showed a plaque dominated by globular or fibrillar matrix components in controls, while the delmopinol-treated plaque showed empty or unordered matrix areas between more densely packed cells. The TEM results were confirmed by scanning electron micrographs, which showed amorphous material associated with the bacterial cells in the control but not in the delmopinol-treated plaque. In conclusion, delmopinol reduced surface-associated glucan synthesis and lowered the cohesion of the plaque, indicating that glucan-containing plaque formed during repeated rinsings with delmopinol may be easier to remove by mechanical means than a non-treated plaque of this type.
The Fit of Gold-alloy Full-crown Castings Made with Pre-wetted Casting Ring Liners
Authors: Morey E.F. , Earnshaw R.
Published: November 2010

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured.

There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range ± 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%.

The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.
The Effect of Using Layered Specimens for Determination of the Compressive Strength of Glass-ionomer Cements
Authors: Anstice H.M. , Nicholson J.W. , McCabe J.F.
Published: November 2010

Compressive strength is widely used as the criterion of strength of glass-ionomer dental cements, despite the difficulties in interpretation of the findings. With the introduction of light-cured glass-ionomer cements, which can be used only in thin layers, the question arises of how test specimens should be prepared for the measurement of compressive strength. A suggested method has been to prepare test pieces by building them up in layers, an approach which is examined critically in the current paper. Two different conventional (acid-base) glass-ionomers were studied with the use of layered and unlayered specimens of dimensions 6 mm (height) x 4 mm (diameter) and 12 mm (height) x 6 mm (diameter). While smaller samples gave the same value of compressive strength as larger specimens, layered specimens gave significantly lower values of compressive strength for both sizes. In view of these findings, and since the layered specimens are tedious to prepare, we conclude that compressive strength is unsatisfactory as a criterion of strength for light-cured glass-ionomer cements.
Effects of Sialagogues on Ornithine Decarboxylase Induction and Proto-oncogene Expression in Murine Parotid Gland
Authors: Kawano M. , Ueno A. , Ashida Y. , Matsumoto N. , Inoue H.
Published: November 2010

The mechanism of a sialagogue-induced increase in ornithine decarboxylase (ODC) activity and the expressions of proto-oncogenes in murine parotid gland were investigated by use of isoproterenol (IPR), carbachol (CC), and methoxamine (MTX). The results were as follows: (1) The three sialagogues had similar effects on the parotid in vivo (mouse parotid after a single injection of IPR) and/or in vitro (rat parotid explants cultured on siliconized lens paper floating on 199 medium containing IPR, CC, or MTX), the order of their effectiveness being IPR > CC > MTX. (2) Northern/dot and Western blot analyses revealed that the sialagogues elevated the steady-state levels of ODC mRNA and ODC protein to maxima at two h and six h, respectively, after stimulation. The increases were roughly proportional to those in ODC activity, suggesting that sialagogue-dependent enzyme induction is regulated at the transcriptional level. (3) The mRNAs of four of nine proto-oncogenes examined showed sialagogue-dependent increases to maxima at 30 min (c-fos) or 60 min (c-jun, c-myc, and c-src) after the beginning of stimulation. These increases were all transient, with the levels returning to the control values (without sialagogue) within 60 min. (4) The IPR-dependent elevations of ODC activity and the mRNAs of ODC, c-fos, and c -jun were inhibited by monensin, but not by polymyxin B. On the other hand, the CC-dependent increases in these parameters were inhibited by polymyxin B but not by monensin. The IPR- and CC-induced increases in c-myc and c-src mRNAs were not inhibited by either monensin or polymyxin B, suggesting that the c-Fos and c-Jun proteins participate in this transcriptional control through the AP-1 site of the ODC gene.
Characterization of Fibroblast Clones from Periodontal Granulation Tissue in vitro
Authors: Hakkinen L. , Larjava H.
Published: November 2010

Connective tissues are known to be composed of heterogeneous fibroblast subpopulations. The significance of this heterogeneity in different physiological and pathological conditions is poorly understood. Granulation tissue is formed in connective tissue during wound healing, chronic inflammation, and certain pathological conditions. In this study, heterogeneity of fibroblasts from granulation tissue was investigated by cell-cloning techniques. Granulation-tissue fibroblasts (GTFs) from both chronically inflamed periodontal lesions and healing wound granulation tissue behaved similarly. GTFs showed a more pronounced decrease in proliferative capacity with increasing cumulative population doubling levels (CPDLs) and 30-40% lower cloning efficiency compared with normal gingival fibroblasts (HGFs). Morphologically, cells in GTF cultures were mainly large, whereas HGFs were mainly small in size. Both cell-line types showed heterogeneity in cell morphology. Clones composed of large stellate-like cells predominated in GTF cultures, whereas clones composed of small spindle-shaped or epithelioid cells predominated in HGF cultures. In both cell-line types, the proportion of clones composed of large cells increased with increasing CPDL. These findings show that the properties of the fibroblasts changed during their in vitro life spans. The finding that normal connective tissue and granulation tissues contain morphologically distinct fibroblast clones in different proportions suggests that local factors could stimulate local fibroblasts to differentiate into GTFs. Alternatively, local factors could select some fibroblast subpopulations to overgrow the others to form granulation tissue.
The Vascularity of Dental Pulp in Cats
Authors: Vongsavan N. , Matthews B.
Published: November 2010

The fraction of the volume of the coronal pulp of cat canines that is occupied by blood vessels was estimated by measurement of the cross-sectional areas of all the vessels in a complete transverse section of the pulp from each of four teeth. The sections were taken 0.5 mm from the pulp comu. Overall, 14.4% of the area of the pulp was occupied by vessels. In the core of the pulp, the average value was 42.9%, and superficially, near the odontoblast layer, it was between 5 and 10%. The average capillary density was 1402 /mm2, which is higher than in most other tissues.

Laser Doppler flow meters can be used for recording blood flow from the coronal pulp of intact teeth, but these instruments are linear only if the moving blood cells occupy no more than 1% of the tissue volume. The present results suggest that this figure is exceeded in pulp.
Suppressor Cell Function in Oral Lichen Planus
Authors: Sugerman P.B. , Rollason P.A. , Savage N.W. , Seymour G.J.
Published: November 2010

Oral lichen planus (OLP) is a common inflammatory condition of the oral mucous membranes which affects between one and two percent of the general population. In accordance with the protracted clinical course of OLP and its association with known auto-immune diseases, the level of self-tolerance is questionable and possibly diminished in patients with this disorder. Normal suppressor T lymphocyte function is reputedly an essential element in the maintenance of self-tolerance, and deficient cell-mediated suppressor activity is implicated in the pathogenesis of auto-immune diseases. For assessment of in vitro cell-mediated suppressor activity in OLP, peripheral blood mononuclear cells (PBMC) from ten patients with OLP and from 11 control subjects were activated with the plant mitogen concanavalin A (Con A), followed by co-culture with autologous responder cells. The ability of irradiated Con A-activated cells to suppress the proliferation of Con A-stimulated responder cells was determined. Con A-induced suppressor activity of PBMC in the OLP patients was significantly less than that in control subjects (p = 0.001). Results of the present investigation complement previous in vitro findings which provided indirect evidence of deficient cell-mediated suppressor activity in OLP, particularly a decreased proportion of circulating CD4+CD45RA+ lymphocytes and reduced Con A-stimulated PBMC proliferation. The depressed Con A-induced suppressor activity of PBMC in the OLP patients provides direct evidence of deficient in vitro cell-mediated suppressor function in OLP, and suggests that defective cell-mediated suppressor circuits and reduced self-tolerance maybe involved in the pathogenesis of this disorder.
Effect of a Pulsing Electromagnetic Field on Demineralized Bone-matrix-induced Bone Formation in a Bony Defect in the Premaxilla of Rats
Authors: Takano-Yamamoto T. , Kawakami M. , Sakuda M.
Published: November 2010

A 2-mm non-healing bony defect was prepared in the premaxilla of male Wistar rats weighing about 180 g as a simulation of an alveolar cleft, for determination of whether a pulsing electromagnetic field (PEMF) could promote regeneration of bone induced by demineralized bone matrix (DBM). The defect was either treated with 7 mg DBM or was left as a non-grafted control. The rats were exposed to a PEMF with a frequency of 100 Hz, a 10-ms-wide burst with 100 μswide quasi-rectangular pulses, repeating at 15 Hz, and magnetic field strength of 1.5-1.8 G. Alkaline phosphatase activity increased significantly from day 7 in the DBM-graft-plus-PEMF group and from day 10 in the DBM-graft group, reaching a maximum on day 14. A greater-than-two-fold rise in alkaline phosphatase activity and a three-fold rise in the amount of 45Ca incorporation in the DBM-graft-plus-PEMF group were attained compared with those of the DBM-graft group. The DBM-graft-plus-PEMF group produced more bone with almost complete osseous bridging in the defect sites than did the group treated with DBM only on day 35. The fmdings indicate that PEMF had an enhancing effect on the bone-inductive properties of the DBM through the stimulation of osteoblast differentiation induced by DBM.
Robustness of the t Test Applied to Data Distorted from Normality by Floor Effects
Authors: Sullivan L.M. , D'Agostino R.B.
Published: November 2010

In calculus, plaque, and gingivitis trials, measures are taken on subjects both prior to the use of an active treatment and after its use. When the trial is short-term, or when a cleaning of the mouth takes place after the baseline measurement, distributions of such measures (e.g., the Volpe-Manhold score or the Loe and Silness scale) are approximately normally distributed above zero but also can have a proportion of subjects who attain scores of zero. When the effects of an active treatment are compared with those of a control, the two-independent-sample t test can be applied to outcome scores or to differences between the baseline and outcome scores. Robustness of these t tests, in the presence of distributions "distorted" from normality as described, was investigated by computer simulation. In general, both t tests produced actual significance levels which were close to nominal significance levels, even in the presence of small samples and distributions in which as many as 50% of the subjects attained scores of zero.
Initial Acquisition of Mutans Streptococci by Infants: Evidence for a Discrete Window of Infectivity
Authors: Caufield P.W. , Cutter G.R. , Dasanayake A.P.
Published: November 2010

Oral bacterial levels of 46 mother-child pairs were monitored from infant birth up to five years of age so that the acquisition of mutans streptococci (MS) by children could be studied. The initial acquisition of MS occurred in 38 children at the median age of 26 months during a discrete period we designated as the "window of infectivity". MS remained undetected in eight children (17%) until the end of the study period (median age of 56 mo). The levels of both MS and lactobacilli in saliva of mothers of children with and without MS were not significantly different. Comparisons between a caries-active cohort colonized by MS (nine of 38) and children without detectable MS revealed similar histories in terms of antibiotic usage, gestational age, and birth weight. Interestingly, half of the children between the ages of one and two years who were not colonized by MS were attended by caretakers other than the mother, while all of the caries-active children during this same time period were cared for by their mothers; the difference was statistically significant. Here we report for the first time that MS is acquired by infants during a defined period in the ontogeny of a child. Support for the notion of a discrete window of infectivity comes from other sources, including animal models.
A Quantitative Study of Calcium Binding and Aggregation in Selected Oral Bacteria
Authors: Rose R.K. , Dibdin G.H. , Shellis R.P.
Published: November 2010

By means of micro-equilibrium dialysis, calcium binding capacities and affinities were measured in three different oral bacteria, and the effects of extracellular polysaccharide, pH, and aggregation were investigated. Binding capacities of 31.0 ± 2.1 (C. matruchotii), 34.7 ± 3.7 (S. sanguis), and 41.5 ± 5.4 (S. downei) μmol calcium/g wet weight of cells were found at pH 7.0, falling to 21.4 ± 0.8 μmol calcium/g wet wt. cells at pH 5.0 for S. downei. Dissociation constants were found to vary between 0.78 ± 0.24 and 1.77 ± 0.30 mmol/L (at pH 7.0, depending on species), and between 0.62 ± 0.04 and 1.77 ± 0.30 (in the pH range 5.0 to 7.0, for S. downei only). Examination suggested that at pH 7.0 calcium-facilitated bacterial association occurs in the streptococci with calcium uptake curves analogous with those of positively cooperative systems. Desorption of calcium from aggregated S. downei suggested that the mechanism of desorption differed from that of uptake. This may be an important factor in plaque formation and in the binding of cells to the surface of formed plaque. Plaque calcium forms a reservoir, readily released by a pH drop, which may increase plaque fluid saturation and reduce demineralization.
Risk Indicators and Risk Markers for Periodontal Disease Experience in Older Adults Living Independently in Ontario, Canada
Authors: Locker D. , Leake J.L.
Published: November 2010

This study examined risk indicators and risk markers for periodontal disease experience in 624 adults aged 50 years and over living independently in four communities in Ontario, Canada. The data were collected as part of the baseline phase of a longitudinal study of the oral health and treatment needs of this population. Periodontal disease experience was assessed in terms of attachment loss, measured at two sites on each remaining tooth. Bivariate and multivariate analyses were used to examine the relationship between a number of sociodemographic, general health, psychosocial, and oral health variables and three indicators of periodontal disease experience. These were: mean attachment loss, the proportion of sites examined with loss of 2 mm or more, and the probability of the subjects having severe disease, arbitrarily defined as a mean attachment loss in the upper 20th percentile of the distribution. Mean attachment loss was 2.95 mm (SD = 1.41 mm), and 76.6% of sites examined had loss of 2 mm or more. In bivariate analyses, the most consistent predictors of periodontal disease experience were: age, education, income, smoking, dental visiting, the number of remaining teeth, the number of decayed coronal surfaces, and the number of decayed root surfaces. In multivariate analyses, age, education, current smoking status, and the number of teeth had the most consistent independent effects. These data confirm the results of recent US studies indicating that periodontal disease experience is influenced by social and behavioral factors.
The Hydrolysis of Anhydrous Dicalcium Phosphate into Hydroxyapatite
Authors: Ishikawa K. , Eanes E.D.
Published: November 2010

Hydrolytic conversion of dicalcium phosphate anhydrous (DCPA; CaHPO4) to non-stoichiometric hydroxyapatite (HAP; Ca10-x(HPO4)x(PO 4)6-x(OH)2-x) was investigated under controlled-solution conditions for identification of solution factors which influence the nucleation, growth, and crystal morphology of the apatitic product phase. The hydrolysis experiments (1 mmol to 7.5 mmol CaHPO4/250 mL) were carried out under CO2-free N2 at fixed pH in the presence of 25-100 mmol/L CaCl2 by standard pH-stat techniques at 37°C. The pH values of the experimental solutions ranged from 6.35 to 9.0. The crystal size and shape of the HAP product were established by x-ray diffraction, and by scanning and transmission electron microscopy. Generally, hydrolysis times and the size of the HAP crystals attained upon completion of the conversion were inversely related to pH. However, crystal size decreased sharply below pH 6.5. Crystal morphology was also strongly affected by pH, with the most equidimensionally-shaped crystals developing at pH 7.0. Although the HAP first appeared on the surface of the DCPA, the amount of DCPA used did not affect the final HAP crystal size or the time required for the hydrolysis to be completed. These data suggest that DCPA initiated HAP formation but that nucleation density (i.e., number of nuclei/unit area DCPA surface) and subsequent growth events were controlled by solution factors.
Pulp Capping with Bioglass® and Autologous Demineralized Dentin in Miniature Swine
Authors: Oguntebi B. , Clark A. , Wilson J.
Published: November 2010

The purpose of this study was to compare the responses of mechanically exposed dental pulps which had been capped with three dissimilar materials: a bioactive ceramic (Bioglass®), autologous demineralized dentin matrix (DDM), and a calcium hydroxide product (Life®), with Teflon® discs as controls. Mechanical dental pulp exposures were made after preparation of deep buccal Class V cavities in 48 teeth in four miniature swine. The exposures were capped and the cavity preparations restored with zinc oxide-eugenol (IRM) cement. The animals were killed after 90 days, the coronal 2/3 of the teeth removed, and sections prepared for either histological or microradiographic examination. The pulpal inflammatory reactions and the degree of reparative dentin formation were assessed from demineralized serial sections. A qualitative assessment of the degree of mineralization of the reparative dentin was made from microradiographs of undecalcified sections. The observations suggest that reparative dentin formation occurs under a variety of pulp-capping materials, but the structure of the reparative dentin varies with the material and the condition of the underlying pulp.
Solubility Parameters, Fractional Polarities, and Bond Strengths of Some Intermediary Resins Used in Dentin Bonding
Authors: Asmussen E. , Uno S.
Published: November 2010

An effective bonding of resin composites to dentin is generally preceded by a conditioning of the surface of the dentin. Previous studies have indicated that the intermediary or adhesive resin should have specific wetting characteristics matching those of the conditioned dentin, in order that optimum bonding can be ensured. The wetting characteristics may be expressed in terms of solubility parameter (8) and polarity (p) of the resin. The aims of the present study were to determine these variables for a number of compounds used in adhesive resins and to investigate the effects of 8 and p on the shear bond strength to dentin. Solubility parameters were obtained according to the method of Small. Fractional polarities were calculated on the basis of measurements of refractive index and dielectric constant of the resins.

In the measurements of bond strength, Scotchprep, EDTA+Gluma, or Al 2Ox3/glycine were used as dentin conditioners in combination with intermediary resins having various 8 and p. For each conditioner, the shear bond strength (BS) could be "explained" by an exponential expression of the form BS = ea+bx, where x = (8+cp+d)2, and where a-d are constants depending on the conditioned dentin. It may be concluded that solubility parameter and polarity of the intermediary resins are important variables in the process of bonding to dentin.
Flexural Strength and Fracture Toughness of Dicor Glass-ceramic after Embedment Modification
Authors: Denry I.L. , Rosenstiel S.F.
Published: November 2010

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification.

Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside).

The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975°C. The flexural strength was significantly increased when the ceramming temperature was 1000°C.
Modified Surface-active Monomers for Adhesive Bonding to Dentin
Authors: Venz S. , Dickens B.
Published: November 2010

PMGDM, a PMDM-type adhesive monomer, was synthesized from pyromellitic dianhydride and glycerol dimethacrylate. Only the para isomer of PMDM, a solid, is used in dental adhesives. The adhesive monomer PMGDM is a liquid and consists of a mixture of para- and meta isomers.

This study shows that PMGDM has several advantages over PMDM. For example, the adhesive can be applied at a greater thickness, and additives and/or additional initiators for improved curing can be incorporated. Use of the liquid monomer PMGDM also provided a convenient means of varying the thickness of the adhesive layer between dentin and composite. The adhesive bonds were tested in both shear and tensile modes. PMDM was used as the control.

The reliability of the bonds, as judged from the Weibull modulus and Weibull characteristic strength, was improved by (1) use of more concentrated solutions of PMGDM adhesive, (2) use of an adhesive thickness of about 25 μm, and (3) modification of PMGDM with a diluent monomer which is expected to enhance the degree of cure and/or the dentin-wetting properties of the adhesive resin.
Effect of Sensory Denervation on the Response of Rat Molar Pulp to Exposure Injury
Authors: Byers M.R. , Taylor P.E.
Published: November 2010

Sensory nerve fibers that contain calcitonin gene-related peptide (CGRP) have been shown previously to sprout into inflamed tissue surrounding sites of pulpal injury. The sprouting fibers contain increased CGRP immunoreactivity (IR), and neuropeptide levels increase in the surrounding pulp. We compared denervated and innervated first mandibular molars of rats to determine whether the absence of sensory nerve fibers affected tissue survival and healing after pulp exposure. Significant differences were seen between innervated and denervated teeth six days after occlusal exposure, with more extensive necrosis in the denervated teeth, and less survival of vascular pulp. When exposures were on the side of the crown, there was no significant difference between the innervated and denervated teeth. Both the innervated and denervated teeth had begun to make reparative dentin and osteodentin by six days after tooth injury. This study shows that teeth with sensory denervation had an accelerated loss of pulp tissue following occlusal exposure compared with innervated teeth with similar injury.
Reduction of Proteolytic Degradation by Chlorhexidine
Authors: Grenier D.
Published: November 2010

The present investigation was designed to evaluate the effect of the antimicrobial agent chlorhexidine on proteolytic degradation. Chlorhexidine, at a final concentration of 0.01%, significantly (p = 0.05) affected the degradation of the general chromogenic substrate azocoll by both commercial proteases and cell-bound bacterial proteases. Reduction of proteolytic degradation was observed following pre-treatment of either azocoll or bacterial cells with chlorhexidine. Chlorhexidine was also found to prevent degradation oftype I collagen by Porphyromonas gingivalis cells. The mechanism of inhibition of proteolytic degradation appears to be related to an electrostatic chlorhexidine-protein interaction.
Comparison of Three Different Methods for Measurement of Plaque-pH in Humans after Consumption of Soft Bread and Potato Chips
Authors: Lingström P. , Imfeld T. , Birkhed D.
Published: November 2010

Three different techniques for measurement of plaque-pH—the sampling, the microtouch, and the telemetric methods-were compared after subjects had consumed different starch products. Ten volunteers, equipped with partial lower prostheses, incorporating a miniature glass pH electrode, refrained from toothbrushing for 3 days. Four products were tested: (1) soft bread, (2) potato chips, (3) 5% starch, and (4) 5% sucrose. The pH of plaque was measured for 45 min by means of all three of the methods. The results showed that the mean pH at 10 min was 1.5 units lower with the telemetric than with the sampling method and 1.0 unit lower with the telemetric than with the microtouch method. Relatively small differences were found among the effects of the four test products for all three methods, with the clearest distinctions among the pH curves being with the microtouch and telemetric methods. The main conclusions from the present investigation are: (1) that there were large differences in pH levels measured with the sampling, the microtouch, and the telemetric methods, even though they ranked the test products in about the same order, and (2) that the two starchy foods, bread and potato chips, were both easily fermented by dental plaque.
An Epidemiological Assessment of the Chronological Distribution of Dental Fluorosis in Human Maxillary Central Incisors
Authors: Evans R.W.
Published: November 2010

The objectives of this study were (1) to develop and test a new index, the Chronological Fluorosis Assessment (CFA) Index, for measuring variation in the chronological distribution and intensity of dental fluorosis, and (2) to determine whether the new index was sufficiently sensitive for detection of a decline in dental fluorosis corresponding to the reduction in the waterborne fluoride level in Hong Kong. According to the CFA Index, the cervical, middle, and incisal third divisions of the labial surface of a maxillary central incisor crown are each classified into one of six categories of an ordinal scale of fluorosis. Data from 1295 life-long resident Hong Kong Chinese children exposed to known water fluoride concentrations were analyzed. Fluorosis declined from incisal to cervical in 41% of cases, and a reverse gradient was apparent in 29%. Overall, fluorosis intensity was higher on incisal thirds than on both middle and cervical thirds. However, when tooth thirds were regrouped according to common 16-month developmental periods, in order to control for time-related variation in fluoride concentration, the incisal-middle difference was of reduced statistical significance, and both the incisal-cervical and the middle-cervical differences became insignificant. A regression analysis of CFA Index on cohort indicated a significant cohort-related fluorosis decrease, in relation to cervical, middle, and incisal tooth thirds. It was concluded (1) that fluorosed enamel which forms in chronological sequence tends toward a uniform intensity, and (2) that the new index was sufficiently sensitive for a decline to be measured in dental fluorosis in Hong Kong.
Agreement Among Dentists' Recommendations for Restorative Treatment
Authors: Bader J.D. , Shugars D.A.
Published: November 2010

Differences among dentists in their decisions to recommend treatment have been studied principally at a "macro" level by examinations of variations in dentists' treatment recommendations for individual patients, or for patients aggregated to the practice level. If reasons for these differences are to be understood, however, a "micro" level examination of differences in dentists' decisions to recommend treatment for individual teeth is necessary. Extent of agreement to recommend treatment among dentists was explored for 1187 teeth in 43 patients. Each tooth was examined by a mean of 6.6 general practitioners. A modified reliability index and distributions of raw levels of agreement were used for quantification of agreement rates across an incomplete cross-classification for practitioners and patients. Overall inter-dentist reliability in recommending individual teeth for treatment was moderate, p = 0.62. Among unrestored teeth with no clinically evident caries, as judged by an independent experienced examiner, reliability in treatment recommendations due to caries was fair, p = 0.51. Reliability was lowest for recommendations concerning previously restored teeth, p = 0.43. Among all teeth receiving at least one recommendation for treatment, only 22% received a unanimous recommendation. Over one-half of all instances of lack of agreement resulted from a single dentist's recommendation differing from those of all other dentists examining the tooth. The results suggest that much of the variation in dentists' practice profiles is due to basic differences in decisions to recommend treatment for individual teeth with specific conditions, and that the presence of previous restorations seems to magnify these differences.
The Effects of Tyramine on Salivary Flow Rate and Protein Secretion by Rat Submandibular Glands
Authors: Okina A. , Hidaka S. , Tashiro M. , Abe K.
Published: November 2010

The effects of different doses of p-tyramine injected i.v. and i.p. on salivary flow rates and proteins secreted by the submandibular glands of rats were studied with and without various types of autonomic blockers and two enzyme inhibitors. The salivary flow rates and the amounts of protein secreted progressively increased with increasing doses injected both i.v. and i.p., whereas they were dramatically reduced with all autonomic blockers except the lowest doses of β-blockers, atropine, and yohimbine. Salivation in response to p-tyramine injected i.v. and i.p. was completely abolished by simultaneous injections of both prazosin and propranolol. The concentration of protein was not dose-dependent and was not reduced by yohimbine and phenoxybenzamine at almost all doses used. However, prazosin significantly increased the protein concentration. Protease activities were dose-dependent but were significantly reduced with a-blockers other than yohimbine, and with most β-blockers. The proteins secreted in response to p-tyramine at all doses injected i.v. and i.p. were of the a-type except with the lowest dose injected i.p. However, the a-type was completely replaced by the β-type in the presence of all a-blockers except yohimbine, but not with β-blockers, atropine, or two enzyme inhibitors. Pargyline, a monoamine-oxidase inhibitor, but not disulfiram, a dopamine-β-hydroxylase inhibitor, affected all parameters except the type of protein. Thus, p-tyramine may activate both the α1- and β1adrenoceptors in the submandibular glands of rats directly or indirectly.
Effects of pH, Potassium, Magnesium, and Bacterial Growth Phase on Lysozyme Inhibition of Glucose Fermentation by Streptococcus mutans 10449
Authors: Wang Y.-B. , Germaine G.R.
Published: November 2010

The effects of physiological (saliva and plaque fluid) concentrations of potassium and magnesium and growth phase on lysozyme inhibition of glucose fermentation by S. mutans 10449 were investigated. Glucose fermentations were carried out in a pH-stat at pH 7.0 or 5.5. Cells were at least two times more sensitive to lysozyme in the early-to-middle exponential phase compared with the stationary phase. S. sobrinus 6715 exhibited three-fold greater lysozyme resistance than S. rattus BHT or S. mutans 10449. The concentration of potassium which reduced lysozyme inhibition of S. mutans 10449 fermentation by 50% was 0.2 and 10 mmol/L for stationary and exponential phase cells, respectively. Corresponding values for magnesium were ≤ 0.01 and 0.50 mmol/L. Potassium and magnesium exhibited little pH dependence in their reduction of lysozyme inhibition of fermentation by exponential- or stationary-phase S. mutans 10449. The results suggest that (i) lysozyme interaction with stationary-phase cells involves more non-inhibitory modes than with exponential-phase cells, and (ii) lysozyme may be more effective as an antibacterial agent in saliva than in plaque fluid.
Adhesion of Actinomyces Isolates to Experimental Pellicles
Authors: Steinberg D. , Kopec L.K. , Bowen W.H.
Published: November 2010

The ability of oral bacteria to adhere to surfaces is associated with their pathogenicity. Actinomyces can adhere to pellicle and cells through extracellular fimbriae. Research on adhesion of actinomyces has been conducted with use of hydroxyapatite (HA) coated with mammalian-derived salivary constituents, whereas the bacterial-derived components of the acquired pellicle have been largely ignored. The influence of the cell-free bacterial enzyme, glucosyltransferase (GTF), on adhesion of human and rodent isolates of Actinomyces viscosus was examined. Cell-free GTF was adsorbed onto parotid saliva-coated hydroxyapatite (sHA). Next, A. viscosus was exposed to the pellicle following the synthesis of glucan formed in situ by GTF. Glucans formed on the pellicle served as binding sites for adhesion of a rodent strain ofA. viscosus. Conversely, the presence of in situ glucans on sHA reduced the adhesion of human isolates of A. uiscosus compared with their adhesion to sHA. Adhesion of the rodent strains may be facilitated through a dextran-binding protein, since the rodent strains aggregated in the presence of dextrans and mutan. The human isolates were not aggregated by dextran or mutan. Pellicle harboring A. viscosus rodent strains interfered with the subsequent adhesion of Streptococcus mutans to the bacterial-coated pellicle. In contrast, the adhesion of S. mutans to pellicle was not decreased when the pellicle was pre-exposed to a human isolate ofA. viscosus. The experimental data suggest that human and the rodent isolates of A. viscosus have distinct glucan adhesion properties. Moreover, these results emphasize the role of in situ glucans in bacterial adhesion to the acquired pellicle by promoting selective adherence of bacteria or by masking potential binding sites for others.