Showing papers in "Journal of Dental Research in 1993"

Initial Acquisition of Mutans Streptococci by Infants: Evidence for a Discrete Window of Infectivity

Abstract: 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 mo...

Assessment by Nano-indentation of the Hardness and Elasticity of the Resin-Dentin Bonding Area

Abstract: The hardness and Young's modulus of the successive layers across a resin-dentin bonding area were determined by nano-indentation for four commercially-available dentin adhesive systems, of which two were also applied with a different conditioning agent. With a computer-controlled nano-indentation technique, minute triangular indentations were made within a small area of a few micrometers' diameter at a load of a few milli-Newtons. The load and displacement of the indenter were continuously monitored during the loading-unloading sequence, so hardness and Young's modulus could be computed as a function of the indenter geometry and the applied load. The hardness of the resin-dentin interdiffusion zone was significantly lower than that of unaltered dentin. A gradient of moduli of elasticity was observed from the rather stiff dentin over a more elastic resin-dentin interdiffusion zone and adhesive resin layer to the restorative composite. That gradient was more substantial in those systems that produced relatively thick adhesive resin layers or supplementally provided a filled low-viscosity resin as an intermediate layer between the adhesive resin and the bulk restorative composite. Such an elastic bonding area might have a strain capacity sufficient to relieve stresses between the shrinking composite restoration and the rigid dentin substrate, thereby improving the conservation of the dentin bond and, as a consequence, the marginal integrity and retention of the restoration.

A Multiple Logistic Regression Analysis of the Risk and Relative Odds of Temporomandibular Disorders as a Function of Common Occlusal Features

Abstract: A multiple logistic regression analysis was used to compute the odds ratios for 11 common occlusal features for asymptomatic controls (n = 147) us five temporomandibular disorder groups: Disc Displacement with Reduction (n = 81), Disc Displacement without Reduction (n = 48), Osteoarthrosis with Disc Displacement History (n = 75), Primary Osteoarthrosis (n = 85), and Myalgia Only (n = 124) Features that did not contribute included: retruded contact position (RCP) to intercuspal position (ICP) occlusal slides 6-7 mm (p < 005 to p < 001), ≥5-6

An in vivo Study of the Influence of the Surface Roughness of Implants on the Microbiology of Supra- and Subgingival Plaque

Abstract: In nine patients with fixed prostheses supported by endosseous titanium implants, 2 titanium abutments (transmucosal part of the implant) were replaced by either an unused standard abutment or a roughened titanium abutment. After 3 months of habitual oral hygiene, plaque samples were taken for differential phase-contrast microscopy, DNA probe analysis, and culturing. Supragingivally, rough abutments harbored significantly fewer coccoid micro-organisms (64 vs. 81%), which is indicative of a more mature plaque. Subgingivally, the observations depended on the sampling procedure. For plaque collected with paper points, only minor qualitative and quantitative differences between both substrata could be registered. However, when the microbiota adhering to the abutment were considered, rough surfaces harbored 25 times more bacteria, with a slightly lower density of coccoid organisms. The presence and density of periodontal pathogens subgingivally were, however, more related to the patient's dental status than to the surface characteristics of the abutments. These results justify the search for optimal surface smoothness for all intra-oral and intra-sulcular hard surfaces for reduction of bacterial colonization and of periodontal pathogens.

Comparative SEM and TEM Examination of the Ultrastructure of the Resin-Dentin Interdiffusion Zone

Abstract: The resin-dentin interdiffusion zone produced by a dentin-adhesive system that removes the smear layer and concurrently decalcifies superficial dentin was morphologically examined by both scanning and transmission electron microscopy. Cross-sectioned resin-bonded dentin discs were etched with an argon-ion beam to make the resin-dentin interface observable by SEM. For the TEM examination, the sections were partly decalcified by an aqueous EDTA solution to facilitate ultramicrotomy and to disclose the ultrastructure of the interdiffusion zone. Both SEM and TEM confirmed the presence of the resin-dentin interdiffusion zone as the junction between the deep unaltered dentin structure and the restorative resin. Within the interdiffusion zone, three sublayers with characteristic ultrastructure and staining were identified by TEM. An upper diffuse black layer contained few structural features. Underneath, partially-altered collagen fibrils were closely packed, mostly running parallel with the interface and perpendicular to the dentinal tubules. Their outline was electron-dense, forming tunnel-like structures. At the base of the upper layer, several stained projections were found to bulge out into the underlying collagen network and appeared to be confined by obstructive, parallel-running collagen fibrils. Finally, the third dense layer, containing hydroxyapatite crystals, demarcated the superficially demineralized dentin layer from the deeper unaltered dentin. Resin diffusion into the decalcified dentin surface layer was evident, but diminished with depth, presumably reducing deeper resin impregnation into the interfibrillar spaces. The citric acid dentin-pretreatment probably caused denaturation of the superficial collagen fibrils. Its decalcifying effect gradually weakened with depth, leaving behind hydroxyapatite crystals at the base of the interdiffusion zone. These crystals appeared to have been resistant to the EDTA TEM-sample decalcification procedure, which suggests that they were protected by resin encapsulation.

Prevalence in the Dutch Adult Population and a Meta-analysis of Signs and Symptoms of Temporomandibular Disorder:

Abstract: A nationwide survey of oral conditions, treatment needs, and attitudes toward dental health care in Dutch adults was carried out in 1986. One of the aims of the study was to assess the prevalence of signs and symptoms of temporomandibular disorder (TMD). A sample of 6577 persons (from 15 to 74 yr of age), stratified for gender, age, region, and socio-economic status, was contacted. Of this sample, 4496 persons participated in the behavioral part of the study, of whom 3526 were examined clinically. The TMD prevalence was based on (1) perceived signs and symptoms of TMD and (2) clinical examination of joint sounds, deviation, and pain on mandibular movements. A total of 21.5% of the Dutch adult population perceived some dysfunction, and 44.4% showed clinically assessed signs and symptoms of TMD. In nearly all age groups, the signs and symptoms of TMD appeared more in women than in men. Agreement between the results of the clinical examination and the anamnestic dysfunction index was significant (p < 0.0001); however, the Pearson's correlation coefficient was low (r = 0.29). The odds-value (risk-ratio) that subjects who perceived signs and symptoms of TMD would present with clinically assessed signs and symptoms of TMD was 2.3. The results of the survey were compared with results of a meta-analysis performed on 51 TMD prevalence studies. The analysis revealed (1) a perceived dysfunction rate of 30% and (2) a clinically assessed dysfunction of 44%, both based on compound samples of, respectively, over 15,000 (23 studies) and over 16,000 (22 studies) randomly selected subjects.

Cytotoxicity and Dentin Permeability of Carbamide Peroxide and Hydrogen Peroxide Vital Bleaching Materials, in vitro

Abstract: There has been recent concern about the inadvertent exposure of dentin with patent tubules as well as gingiva to bleaching systems containing 10-15% carbamide peroxide or 2-10% hydrogen peroxide for more than a few minutes. The aims of the present study were: (1) to determine the cytotoxicity of dilutions of hydrogen peroxide in cell culture; (2) to measure hydrogen peroxide diffusion from bleaching agents through dentin in vitro; and (3) to determine the risk of hydrogen peroxide-induced cytotoxicity from exposure of dentin to these vital bleaching agents. The 50% inhibitory dose (ID50) of hydrogen peroxide to succinyl dehydrogenase activity in cultured cells was found to be 0.58 mmol/L after 1 h. All bleaching materials demonstrated diffusion of hydrogen peroxide through dentin in an "in vitro pulp chamber" device. The one- and six-hour diffusates of all bleaching agents through 0.5-mm dentin exceeded the ID50 in monolayer cultures. Inhibition of succinyl dehydrogenase activity corresponded to the amount of hydrogen peroxide that can rapidly diffuse through dentin in vitro and reach concentrations which are toxic to cultured cells in less than 1 h.

Molecular Orientation of Silane at the Surface of Colloidal Silica

Abstract: The objective of this study was to investigate the silica-silane bond formation present at the filler interface of dental composites Diffuse reflectance infrared Fourier transform spectroscopy was used, and the spectra of pyrogenic silica (Cab-O-Sil) treated with different concentrations of gamma-methacryloxypropyltrimethoxysilane (MPS) were analyzed The outcome of the study suggested that the gamma-methacryloxypropyltrimethoxysilane (MPS) molecules oriented parallel to the colloidal silica surface (Cab-O-Sil) and formed two types of bonds One of these bonds was a siloxane bridge formed by a condensation reaction between the silanol groups of both the silica surface and the hydrolyzed silane Water formed during this reaction and soon became recaptured by the silanol groups of the silica surface These water molecules were not available for additional hydrolyzation reactions of the unhydrolyzed silane under the experimental conditions The intensity of the isolated OH-groups decreased because of this reaction Simultaneous with the condensation reaction, the carbonyl group of the MPS molecule formed hydrogen bonds This hydrogen bond formation resulted in a peak shift of the carbonyl band from 1718-1720 cm-1 to 1700-1702 cm-1 This hydrogen bond formation also occurred with the isolated OH-groups After consumption of the isolated OH-groups, no additional surface reaction occurred because no further OH-groups were available for additional condensation reactions or hydrogen bond formation The findings suggest that the amount of silane needed for filler treatment depends on the number of isolated OH-groups available on the filler surface

Risk Indicators and Risk Markers for Periodontal Disease Experience in Older Adults Living Independently in Ontario, Canada

Abstract: 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. I...

The Association of Mutans Streptococci and Non-Mutans Streptococci Capable of Acidogenesis at a Low pH with Dental Caries on Enamel and Root Surfaces

Abstract: Coronal dental plaque from each of 12 caries-positive subjects (Group I) was pooled from "white spot" tooth surface areas and, separately, from sound surface areas; sound surface areas in each of 18 caries-free subjects (Group II) were sampled similarly. Two samples, one consisting of material from a root-surface lesion and another of plaque from a sound root-surface area, were obtained from each of another 10 subjects (Group III). The samples from Groups I and II were evaluated for: (1) pH-lowering potential in vitro with dispersed plaque suspensions, excess glucose supply, and a 60-minute test; (2) the levels of mutans streptococci (MS) and lactobacilli; and (3) the distribution of the predominant non-mutans streptococci (non-MS) according to their final pH in glucose broth; only microbial analysis was done for the Group III samples. The levels of the MS were generally positively associated with caries. A weaker positive association was found for the levels of those non-MS capable of acidogenesis at low pH (final pH < 4.4). The latter generally far outnumbered the MS in all types of samples. The levels of lactobacilli were nearly always very low. The pH-lowering potential (final pH and pH drop rate) was higher for plaque from "white spot" areas than for plaque from sound surface areas (Group I). The samples from caries-free subjects (Group II), however, exhibited a pH-lowering potential which was not significantly different from that of both types of samples from the caries-active subjects (Group I).(ABSTRACT TRUNCATED AT 250 WORDS)

Release of fluoride and other elements from light-cured glass ionomers in neutral and acidic conditions

Abstract: The purpose of this study was to measure the release of fluoride, sodium, silicon, calcium, strontium, and aluminum from light-cured glass ionomers. The materials tested were: (1) Baseline VLC thick mix; (2) Baseline VLC thin mix; (3) Fuji Lining LC; (4) Vitrebond; and (5) XR-Ionomer. A conventional glass ionomer, Ketac-FilAplicap, and a silver-reinforced glass ionomer, Ketac-Silver, were used as controls. Each test specimen was first stored for 16 days in de-ionized water, followed by a further 16 days in 0.01 mol/L lactic acid (pH 4.0); both solutions were replaced at predetermined intervals. After that, the specimens were immersed for up to 122 days in de-ionized water. During the immersion, light-cured glass ionomers showed considerable variation in the release of fluoride and other elements. In lactic acid, all cements eluted the matrix-forming cations, aluminum and calcium or strontium. This suggests that light-cured materials are as equally susceptible to erosion as are chemically cured glass ionomers. During the immersion, some of the light-cured materials showed a considerable weight gain.

An Assessment of Survival Rates and Within-patient Clustering of Failures for Endosseous Oral Implants

Abstract: This study examined endosseous cylinder implant survival, defined as the unqualified presence of the implant in the mouth at the end of the observation period, in 598 consecutive VA patients, with a total of 2098 implants. Data were taken from the Department of Veterans Affairs (VA) Dental Implant Registry, which has maintained longitudinal data on the survival of individual dental implants in VA patients since 1987. The maximum time of observation in any one patient was 2040 days (5.6 yr). Survival analysis by use of life-table methods was carried out on both an implant- and a patient-specific basis. Implant cases were accrued randomly, and therefore a random censoring model was used. A correlated binomial model was used for assessment of the degree of within-patient clustering of implant removals. Results showed that the implant-specific survival rate during the longest time interval (5.6 yr) was 89.9%; the patient-specific implant survival rate during the same time was 78.2%. Among implants which were removed, the mean time to removal was 292 days. The hazard function, which describes the probability of implant loss as a function of time, decreased steadily throughout the observation period. The correlated binomial model suggested a clustering of removals within patients with multiple implants (rho = 0.11, p = 0.0001). The odds of having a second implant removed were 1.3 times greater if the patient had already had one implant removed. This study suggests that when implants fail, they do so soon after placement, and the likelihood of failure decreases steadily from implantation through the first five years post-surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

New Aspects of the Setting of Glass-ionomer Cements

Abstract: For many years, glass-ionomer cements have been described as setting by the formation of a poly(acrylate) matrix. Recent research has suggested that a second reaction may be involved, namely, the formation of a silica matrix. So that this hypothesis could be tested, non-polymer cements, based on an ionomer glass plus acetic acid, were prepared and stored for up to six months. They were insoluble in water, and their compressive strength was found to increase rapidly over the period of storage. By contrast, the product of the reaction between ZnO and acetic acid was soluble in water. These results support the idea that there is a secondary setting reaction in glass ionomers and suggest that it is responsible for the increase in strength observed.

The Effects of Enamel Anisotropy on the Distribution of Stress in a Tooth

Abstract: Enamel is thought to have highly anisotropic stiffness characteristics, because of its prismatic structure. It is probable that the enamel is stiffer in the prism direction compared with a direction perpendicular to it. The prisms are thought to run approximately perpendicular to the enamel-dentin junction. The curvilinear anisotropy that will result can readily be modeled by TOMECH, a finite element program developed at the University of Sheffield, since curvilinearity of mechanical properties is available as an automated feature of this program. The patterns of stress due to an external load were investigated in two-dimensional abstract models, and in a model of a mandibular second premolar, for both anisotropic and isotropic enamel. Results were compared with the commercial code ANSYS and good agreement obtained. Enamel with anisotropic properties was found to have a profoundly different stress distribution under load when compared with models with isotropic enamel. For isotropic enamel, the load path ...

Comparison of Three Different Methods for Measurement of Plaque-pH in Humans after Consumption of Soft Bread and Potato Chips

Abstract: 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.

Perceptions of Dental Fluorosis

Abstract: Mild dental fluorosis has long been accepted as a side-effect of water fluoridation and, more recently, has been recognized as a consequence of the use of other fluoride-based caries-preventive strategies. Traditionally, dental health professionals have not seen this as being of public health importance, but members of the public have not been asked their opinion. The purpose of the present study was to gather the opinions of lay groups concerning the appearance of the teeth of children with various degrees of fluorosis. Twenty-eight children, born in 1978, who had earlier participated in a study of fluorosis in Perth (Western Australia), allowed 110 observers to look at their upper central incisors under good viewing conditions. Fluorosis in these teeth ranged from TF score 0 (no fluorosis) to TF score 3. The observers were university students, parents, public servants, or dentists. They responded to statement items about the appearance of the teeth. The results, based on just over 3000 responses, showed that lay and dental observers could distinguish between different fluorosis levels. In response to a statement that the teeth appeared pleasing, a large majority agreed when the TF score was 0, but agreement declined as the TF score increased; when the TF score was 3, most people disagreed. Similarly, observers felt that the appearance would increasingly embarrass the child as the TF score increased. Observers, except the dentists, tended to feel that higher TF scores indicated neglect on the part of the child.(ABSTRACT TRUNCATED AT 250 WORDS)

The Effects of Etching, Micro-abrasion, and Bleaching on Surface Enamel

Abstract: Conservative techniques for improving the appearance of discolored teeth have become popular in the past decade. These include: in-office bleaching with 30% hydrogen peroxide, which is applied on etched enamel with a gauze pad and then exposed to a bleaching light; home bleaching with a mild form of peroxide, such as 10% carbamide peroxide, which is applied on the tooth surface with custom-made mouthguards; and enamel micro-abrasion with 18% hydrochloric acid, which is applied in a pumice slurry. In this study, the in-office bleaching and enamel micro-abrasion techniques were performed on extracted teeth for investigation of their microscopic effects on the surface enamel. Specimens treated only with 37% phosphoric acid showed an enamel loss of 5.7 +/- 1.8 microns. The specimens treated with 37% phosphoric acid followed by 30% hydrogen peroxide showed enamel loss of 5.3 +/- 1.6 microns; this loss was probably not caused by the hydrogen peroxide, but rather by the etching with 37% phosphoric acid which preceded the hydrogen peroxide application. A direct application of 18% hydrochloric acid for 100 s resulted in a loss of 100 +/- 47 microns. The extent of enamel loss was much greater when the 18% hydrochloric acid was applied in a pumice slurry for the same period of time (360 +/- 130 microns), and the effect was time-dependent. Thus, the pumice and rotary prophy cup used in conjunction with the 18% hydrochloric acid contributed markedly to the loss of surface enamel, enhancing the non-selective stain-removing action of the hydrochloric acid. Therefore, the hydrochloric acid-pumice technique must be used clinically with caution.

Chemical Characterization of the Resin-Dentin Interface by Micro-Raman Spectroscopy

Abstract: The chemical nature of the interface between dentin and adhesive resin materials was characterized by micro-Raman spectroscopy. The resulting chemical profiles were correlated with photomicrographs obtained by SEM after an argon-ion-beam etching treatment of the sample surface. Two commercially available dentin adhesive systems, of which one was also applied with a different conditioning agent, were investigated. Raman spectra, which were recorded along line scans across the interface with a step increment of 1 micron, revealed that resin effectively penetrated 4 to 6 microns deep into the superficially decalcified dentin zone. Across the interface, a gradual transition from resin to dentin over the interdiffusion zone with a mixed contribution of both substances was noticed. Finally, resin appeared to penetrate to the entire decalcification depth of dentin regardless of the aggressiveness of the conditioning procedure.

Agreement Among Dentists' Recommendations for Restorative Treatment

Abstract: 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 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.

A Microbiological Study of Primary Root-caries Lesions with Different Treatment Needs:

Abstract: Samples of altered or carious dentin for microbiological culture were obtained from 301 primary root-caries lesions in 59 patients by means of a standardized sampling procedure. This involved the cleansing of each root surface of extraneous supragingival plaque by means of a hand-held toothbrush and distilled water and the collection of the sample with a sterile dental excavator passed through the entire vertical dimension of each lesion. The total number of colony-forming units (cfu) in each sample and the numbers of mutans streptococci (primarily Streptococcus mutans), lactobacilli, yeasts, and Gram-positive pleomorphic rods (GPPR) were determined. Individual bacterial counts were expressed as log10 (cfu per sample), as a percentage of the total number of bacteria per sample, and as a frequency of isolation from lesions with different clinical diagnostic criteria. Clinical measurements of each lesion were made for color, texture, position relative to the gingival margin, and treatment need. Lesions clas...

Fracture Toughness of Dentin/Resin-composite Adhesive Interfaces

Abstract: The reliability and validity of tensile and shear bond strength determinations of dentin-bonded interfaces have been questioned. The fracture toughness value (KIC) reflects the ability of a material to resist crack initiation and unstable propagation. When applied to an adhesive interface, it should account for both interfacial bond strength and inherent defects at or near the interface, and should therefore be more appropriate for characterization of interface fracture resistance. This study introduced a fracture toughness test for the assessment of dentin/resin-composite bonded interfaces. The miniature short-rod specimen geometry was used for fracture toughness testing. Each specimen contained a tooth slice, sectioned from a bovine incisor, to form the bonded interface. The fracture toughness of an enamel-bonded interface was assessed in addition to the dentin-bonded interfaces. Tensile bond strength specimens were also prepared from the dentin surfaces of the cut bovine incisors. A minimum of ten specimens was fabricated for each group of materials tested. After the specimens were aged for 24 h in distilled water at 37 degrees C, the specimens were loaded to failure in an Instron universal testing machine. There were significant differences (p < 0.05) between the dental adhesives tested. Generally, both the fracture toughness and tensile bond strength measurements were highest for AllBond 2, intermediate for 3M MultiPurpose, and lowest for Scotchbond 2. Scanning electron microscopy of the fractured specimen halves confirmed that crack propagation occurred along the bond interface during the fracture toughness test. It was therefore concluded that the mini-short-rod fracture toughness test provided a valid method for characterization of the fracture resistance of the dentin-resin composite interface.

Co-activation of Sternocleidomastoid Muscles During Maximum Clenching

Abstract: In an attempt to determine the degree of co-activation present in selected cervical muscles during clenching, we instructed 12 male subjects to produce four brief maximum voluntary contraction (MVC) efforts (clenching) in a position of maximum intercuspation. Surface EMG activity was recorded bilaterally from the masseter and sternocleidomastoid (SCM) muscles. The contraction level for the SCM during clenching was reported as a percentage of the SCM's maximum activity achieved during maximum neck flexion against resistance. All EMG signals for the masseter and SCM were converted to a true RMS voltage signal and digitized at a 100-Hz sampling rate. Mean peak EMG voltage levels were determined for the activity recorded during each brief MVC task. All subjects demonstrated co-activation of the SCM during strong abrupt clenching efforts. The mean levels (± S.D.) of SCM activity were 11.8 ± 9.6% (right) and 14.2 ± 9.4% (left) of the MVC capacity. Fifty percent of masseter activity was required to achieve 5% ac...

Salivary Yeasts, Saliva, and Oral Mucosa in the Elderly:

Abstract: Yeasts are commensals in the oral cavity and may not cause disease unless there are predisposing host factors, such as other disease, or when medication is being taken. The elderly are at increased risk of yeast infection. In this paper, prevalence of salivary yeasts in a group of 368 inhabitants of Helsinki aged 76, 81, and 86 years is reported. Salivary yeasts were counted by the Oricult-N® dip-slide method, salivary secretion rate and buffering capacity were measured, type of dentition was noted, and signs of yeast infection and the occurrence of subjective symptoms were determined.There was no growth of yeasts in 25% of the subjects. From one to 20 colonies/slide were observed in 21%, 21-50 colonies in 21%, and over 50 colonies (a high count) in 33%. Subjects with low salivary flow rates and low buffering capacities had significantly higher yeast counts than did subjects with normal salivary flow rates and buffering capacities. High yeast counts were found in 19% of subjects with natural teeth. The co...

Long-term Effects of Meridol® and Chlorhexidine Mouthrinses on Plaque, Gingivitis, Staining, and Bacterial Vitality

Abstract: The aim of the present study was to compare the effect on plaque growth and gingival response of Meridol, an amine/stannous fluoride solution, during a three-month investigation, with those of a placebo preparation as a negative control and a chlorhexidine solution as a positive control, in a double-blind study. After having their teeth professionally cleaned, 36 volunteers continued their usual oral hygiene for a period of two weeks. Their teeth were then polished again (month 0) after which they rinsed twice daily (morning and evening) with one of the three mouthrinses in addition to their habitual toothcleaning. After three months of rinsing, plaque indices remained lowest in the chlorhexidine group, although the subjects using Meridol had indices significantly lower than those of individuals rinsing with the placebo solution. The gingival index scores in the Meridol group were higher than in the chlorhexidine group and lower than in the placebo group. The plaque vitality scores showed a bactericidal effect in vivo with chlorhexidine and Meridol during the entire experiment. The use of Meridol resulted in more toothstaining than with the placebo, but significantly less than with chlorhexidine. This study demonstrated that Meridol reduced plaque accumulation, retarded gingivitis development, possessed a definite bactericidal action, and produced only slight toothstaining.

Amplitude and Timing of EMG Activity in the Human Masseter Muscle during Selected Motor Tasks

Abstract: Electromyographic (EMG) activity in the human masseter muscle was registered from six different sites, in the anterior, middle, and posterior regions of the superficial and deep layers of the muscle, during static clenching tasks (intercuspal and incisal), selected jaw movements (alternating protrusion/retrusion, right/left latero-deviation, and open/close excursions), and unilateral chewing on right and left sides. Peak-EMG amplitudes and the timing of the peaks were compared. Activity in the regions of the deep masseter was either higher (in mastication and intercuspal open/close excursions) or lower (incisal clenching) than the activities in the superficial masseter. Superficial and deep masseter also differed in their timing of peak EMG: During chewing, peak activity passed from superficial to deep in the balancing-side muscle, and from deep to superficial on the chewing side. During free latero-deviations, peak activity started in the deep masseter, when the jaw moved to the right side (i.e., the side of the muscle), and then passed to the superficial regions, after the jaw movement was reversed to the left side. In addition, within the deep masseter there existed clear anteroposterior differences in activation level (during incisal clenching and open/close excursions) and in timing (during latero-deviation). Such a differentiation of activity was not found in the superficial masseter.

Distribution of substance P and calcitonin gene-related peptide like immunoreactive nerve fibers in the rat temporomandibular joint

Abstract: The density and distribution of substance P-like immunoreactive (SP-LI) and calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerve fibers in rat temporomandibular joint (TMJ) were investigated in whole-mount preparations and frozen sections by immunohistochemistry with the avidin-biotin-peroxidase complex method. Both types of immunoreactive nerves were observed primarily in the joint capsule, the peripheral articular disc, the synovial membrane, and the periosteum. The distribution of CGRP-LI nerves was similar to that of SP-LI nerves. The anterior portion of the joint capsule and disc was most densely innervated, followed by the posterior, lateral, and medial portions. In addition, CGRP-LI nerves were more numerous and more dense in immuno-intensity than SP-LI nerves. In the synovial membrane, many SP- and CGRP-LI nerves terminated in the subsynovial layer, but some branches extended into the superficial synovial lining layer close to the joint cavity. Immunolabeled nerves were prominently located in the disc attachment and peripheral portion of the disc, and occasional nerves were located in the dense collagenous disc band as an actual disc. However, no fibers were detected in the central disc band. Thus, most of the disc was not innervated by any nerves. The present study provides a morphological basis for the possible roles of neuropeptides in endocytosis by synoviocytes, regulation of blood flow in the synovial membrane, nociception mechanisms of the TMJ, and modulation of the inflammatory response in the TMJ.

Effect of Sensory Denervation on the Response of Rat Molar Pulp to Exposure Injury

Abstract: 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.

Caries Risk Assessment in a Longitudinal Discrimination Study

Abstract: Our objective was to develop and perfect a model for the assessment of risk of dental caries onset in children. Even though dental caries prevalence in children is continuing to decline, there is still a significant minority for whom it is a problem. In this study, we sought to ascertain whether a set of variables selected in a previous cross-sectional study could be used to differentiate between caries-free six-year-olds who would or would not subsequently present with clinically-detectable caries. A total of 472 caries-free six-year-olds—286 from a fluoridated community and 186 from a fluoride-deficient community-was selected. Clinical examinations for DMFS, dental fluorosis, and plaque were conducted. Stimulated whole saliva was collected for analysis of mutans streptococci, lactobacilli, total viable flora, and fluoride, calcium, and phosphate concentrations. A questionnaire was used for collection of demographic data as well as information on prior fluoride exposure, dietary habits, and oral hygiene ...

Effect of Jaw Opening on Masticatory Muscle EMG-Force Characteristics

Abstract: This study was designed to evaluate the way in which changes in vertical jaw opening affected the relative contributions of various masticatory muscles to bite force production. EMG activity was recorded simultaneously from the masseter, and anterior, middle, and posterior temporalis muscles, during controlled isometric biting at different force levels and vertical jaw openings. EMG-force characteristics were compared between muscles and bite openings. All but the posterior temporalis muscle displayed significant increases in muscle activity with increased bite force production; the masseter muscle demonstrated the largest activity increments. Statistically significant changes in muscle function due to jaw opening were demonstrated only for the masseter muscle, though similar trends were observed for the anterior and middle temporalis muscles. Minimum increases in muscle activity associated with increases in bite force occurred between 9 and 11 mm of opening, measured at the first molar, for all three muscle groups. The results of this study suggest that changes in masticatory muscle length resulting from vertical jaw opening cause alterations in muscle contractile properties, but the relative contributions of various masticatory muscles toward bite force production may also be affected by biomechanical factors and neural control adaptations.

The Effect of Fluoride Application on Fluoride Release and the Antibacterial Action of Glass lonomers

Abstract: The aim of this study was to investigate whether the release of fluoride and the antimicrobial effect of freshly mixed glass ionomers could be prolonged by application of fluoride on aged material. Test slabs of freshly mixed and aged (14 d in water) conventional and silver glass ionomer (Ketac-Fil and Ketac-Silver, Espe, Seefeld, Germany) and composite (Silux Plus, 3M, St. Paul, MN) were fitted into the bottom of a test tube. A layer ofS. mutans Ingbritt cells was centrifuged onto the test slabs, and the samples were incubated for 20 h in 1.7% sucrose solution. After the incubation, pH, F, and Ca contents of the fluid phase, and F, Mg, P, and K contents of the cells were determined. The aged glass-ionomer samples were then covered with toothpaste (0.1% F) or with fluoride gel (1.25% F), and the composite samples with fluoride gel. After being thoroughly rinsed, S. mutans cells were incubated on the samples as above. The pH fall was significantly inhibited by freshly mixed glass ionomers, and there were c...