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Background:The muscle representations in non-primary motor area (NPMA) are located in the dorsal premotor area (PMd) and in the border region between the premotor area and the supplementary motor area (SMA). Objective:We characterized the plasticity of intracortical inhibitory and excitatory circuits in muscle representations in primary motor cortex (M1) and in NPMA related to acquired fine motor skills. We compared local cortical inhibition and facilitation balance in M1 and in NPMA between control subjects (n = 6) and right-handed string-instrument players (n = 5). Methods:Navigated transcranial magnetic stimulation (TMS) was used to compare motor thresholds (MTs), motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) in non-dominant hand muscle representations in M1 and NPMA. Results:String-instrument players showed reduced SICI in M1 in the actively used left hand abductor digiti minimi (ADM) muscle representation at 3 ms inter-stimulus interval (ISI) with a conditioning stimulus (CS) intensity of 80% of MT and increased SICI in NPMA in ADM representation at 2 ms ISI and CS intensity of 50% of MT in comparison with controls. No differences between string-instrument players and controls were found for the SICI in the left hand opponens pollicis (OP) muscle representation, which is a muscle not intensively trained in string-instrument players. Conclusions:These preliminary results indicate that the stronger inhibition in motor representations outside M1 in string-instrument players may be crucial when accurate movements of single muscles must be performed. In contrast, weaker inhibition in M1 in string-instrument players may benefit the performance of fast finger movements.

We report a successful VLBI observation at 147 GHz (2.1 mm) on the 3 100 km long baseline between the telescopes at Metsähovi (Finland) and Pico Veleta (Spain). The sources 3C 273B and 3C 279 were detected with a SNRof . For these sources we estimate that 25–30% of the total flux is detectable as correlated flux on the 3 100 km baseline, which gives at 147 GHz a lower limit of the brightness temperature of the inner VLBI jet region of ~1$\times$1010K.

Our time series analysis of sixteen BVlight curves of the chromospherically active binary V511 Lyr confirmed the $2\fd7$rotation period uniquely. The seasonal periodicity changes of 3.8% indicated the presence of detectable surface differential rotation. The significant $2\fd67455$periodicity in the light curve minimum epochs suggested that the strongest starspot formation in V511 Lyr was concentrated on one stable active longitude.

Transcranial magnetic stimulation (TMS) can be used for evaluating the function of motor pathways. According to the principles of electromagnetism and electrophysiology, TMS activates those neurons that are suitably oriented with respect to the TMS-induced electric field. We hypothesized that TMS could potentially be able to evaluate the neuronal structure, although until now, this putative application has not been exploited. We have developed a TMS-based method to evaluate the function and structure of the motor cortex concurrently in a quantitative manner. This method produced a measure, the anisotropy index (AI), which is based on the motor-evoked potentials induced at different coil orientations. The AI was demonstrated to exhibit an association with both motor cortex excitability and neuronal structure. In the present study, we evaluated the repeatability (intrasession and intersession) of AI in three consecutive measurements. In addition, we studied the repeatability of the optimal coil angle in inducing motor-evoked potentials. Two of the measurements were conducted on the same stimulation target and the third on a remapped target. The coefficient of repeatability of the AI was 0.022 for intrasession and 0.040 for intersession assessments. For the optimal stimulation angle, the coefficients of repeatability were 3.7° and 5.1°, respectively. Both the AI and the optimal stimulation angle demonstrated good repeatability (Cronbach’s >0.760). In conclusion, the results indicate that the AI can provide a reliable estimation of local functional anisotropy changes under conditions affecting the cortex, such as during stroke or focal dysplasia.

SUMMARYActinomyces israeliihas long been recognized as a causative agent of actinomycosis. During the past 3 decades, a large number of novel Actinomycesspecies have been described. Their detection and identification in clinical microbiology laboratories and recognition as pathogens in clinical settings can be challenging. With the introduction of advanced molecular methods, knowledge about their clinical relevance is gradually increasing, and the spectrum of diseases associated with Actinomycesand Actinomyces-like organisms is widening accordingly; for example, Actinomyces meyeri, Actinomyces neuii, and Actinomyces turicensisas well as Actinotignum(formerly Actinobaculum) schaaliiare emerging as important causes of specific infections at various body sites. In the present review, we have gathered this information to provide a comprehensive and microbiologically consistent overview of the significance of Actinomycesand some closely related taxa in human infections.

Over 13600 continuum observations of extragalactic sources are presented. These observations of 157 sources at 22, 37 and 87 GHz more than doubles the millimeter observations of these sources. The data are between 1990.5 and 1995.5, and combined with our earlier published data they form a 15 year database.

This paper describes a novel risk indicator for extreme weather risks for use in transportation systems. The risk indicator is applied to the European transportation system indicating and ranking the risks for the 27 member states of the European Union (EU-27). The paper starts with definitions of hazards, vulnerability, and risk, based on relevant literature, and then operationalizes the risk, hazard, and vulnerability with the help of EU-27 data. Finally, the paper discusses the extreme weather risk indicator (EWRI) and evaluates its applicability and limitations. The risk indicator is a relative indicator: it should be viewed and treated as a ranking system. The devised indicator is able to assist decision makers at national and state as well as international and federal levels in the prioritization of extreme weather risks within their jurisdiction. The overall approach of EWRI is based on mainstream risk and vulnerability assessment research, following for the most part the existing conceptual models. The novelty of EWRI lies in its application area (transportation) and wide use of both empirical and statistical data. EWRI was used to assess the hazards, vulnerabilities, and risks of extreme weather for the EU-27, but nothing hinders its application, either in this form or a modified form, in other contexts.

Our aim was to study long-term plasticity in the organization of cortical muscle representations due to extensive motor training for different skills. We were especially interested in whether skill-specific demands on independent hand muscle movements and synchronous leg muscle movements are reflected differently in the reorganization of muscle representations. We used navigated transcranial magnetic stimulation to estimate the size of cortical representations of opponens pollicis, abductor digiti minimi, and tibialis anterior muscles in five string instrument players, five figure skaters, and five controls. The extent of the representation area was presented as an amplitude-area curve showing the spatial distribution of motor evoked potentials. The size of representation areas was compared between the dominant and nondominant hemispheres and between the groups. The representation area of the left abductor digiti minimi (critical for reaching right tones) in the right, nondominant hemisphere was smaller in string players and the representation area of the tibialis anterior in the dominant hemisphere (critical for jumps) was larger in figure skaters when compared with controls. Reorganization in the motor cortex may differ depending upon the skill and an individual muscle’s role in the skill. A smaller representation area of the independently used hand muscle in masters of fine motor skills may reflect long-term plasticity toward more focused representation, which may be beneficial in accurate and discrete cortical control of the muscle. Larger cortical representations are related to skill demanding coactivation of proximal and distal lower limb muscles.

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Background:Effects of Fusobacterium nucleatum (F. nucleatum)biofilm on epithelial cell proliferation, apoptotic cell death, and basement membrane constituent collagen IV production were examined in an organotypic dento‐epithelial (OD‐E) model. Methods:The OD‐E model was constructed by seeding keratinocytes on fibroblast‐containing collagen gels and by placing tooth pieces on top. A 3‐day‐old biofilm either a laboratory strain (American Type Culture Collection [ATCC] 25586) or a clinical strain (Anaerobe Helsinki Negative [AHN] 9508) of F. nucleatumwas placed on the top of the model. The coculture was incubated ≤24 hours. The expression and localization of Ki‐67, caspase‐3, and collagen IV were examined by immunohistochemistry. Results:Hematoxylin and eosin staining showed epithelial migration and lateral sprouting into the connective tissue matrix in F. nucleatumOD‐E cocultures. The proliferation pattern of the in vitro dento‐epithelial junction was changed. In controls without bacterial challenge, the Ki‐67 expression was abundant in the cells attached to the tooth, whereas in F. nucleatumbiofilm‐treated cultures, the Ki‐67‐expressing cells were more often in the connective tissue‐facing side of the epithelium. An apoptotic marker caspase‐3 was expressed in controls and in F. nucleatumlaboratory strain ATCC cocultures throughout the epithelium, in contrast to cultures treated with F. nucleatumclinical strain AHN, in which caspase‐3 was absent. Collagen IV stainings were negative in both controls and F. nucleatumcocultures. Conclusion:F. nucleatumbiofilm coculture with OD‐E model causes lateral sprouting of the epithelium with an altered epithelial proliferation pattern, resembling the histologic changes seen in vivo in the early pathogenesis of periodontal disease.

Background:In the present study, the expression and localization of three epithelial peptides (human β‐defensin [hBD]‐2 and ‐3, and cathelicidin [LL‐37]) are studied in an organotypic dento‐epithelial (OD‐E) model exposed to Fusobacterium nucleatum(Fn) biofilm. Methods:Biofilm of FnATCC 25586 or AHN 9508 were produced by culturing each strain on semipermeable membranes. The OD‐E model was constructed by seeding keratinocytes on fibroblast‐containing collagen gels and by placing dentin pieces on the top. A 3‐day‐old biofilm was placed on the top of the OD‐E and the coculture was incubated for 5 hours or 24 hours. Production of epithelial antimicrobial peptides was determined immunohistochemically. Results:After 5 hours of incubation, the biofilm of each Fnstrain stimulated expression of hBD‐2 and ‐3. hBD‐2 was localized on superficial layers and hBD‐3 on basal cell layers of the epithelium and dento‐epithelial junctions, whereas LL‐37 was only weakly expressed. After 24 hours, hBD‐2 expression was extended toward basal cell layers of the epithelium. In contrast, hBD‐3 expression extended toward superficial layers of the epithelium. In the case of FnAHN 9508 biofilm, LL‐37 was localized in the cell layers of the dento‐epithelial junction. Conclusion:In our OD‐E model, epithelial antimicrobial peptide responses to Fnbiofilms have distinct regulation and localization characteristics, resembling those known to occur in the gingival epithelium in vivo.

The frontal cortex undergoes macrostructural and microstructural changes across the lifespan. These changes can be entirely physiological, such as the ones occurring in elderly individuals who are cognitively intact, or pathological, such as the ones occurring in patients with Alzheimer's disease. Here, we use simultaneous electroencephalography (EEG) and transcranial magnetic stimulation (TMS) to study how the excitability of the frontal cortex changes during healthy and pathological aging. Hence, we compared the TMS-evoked EEG potentials collected in healthy elderly individuals with the ones collected in healthy young individuals, and in patients with Alzheimer's disease. We have shown that the EEG response to TMS of the left superior frontal cortex is not affected by physiological aging but is markedly altered by cognitive impairment.

Long term monitoring results from mid 1995 to the end of 2000 of quasar observations at 22, 37 and 87 GHz done at the Metsähovi radio observatory are presented. Approximately 15 700 observations are published here.

Background:The present study evaluates the survival capability of Fusobacterium nucleatumstrains in an aerobic environment and compares the invasive capability of F. nucleatumin biofilm and planktonic forms in an organotypic cell culture (OCC) model. Methods:Biofilms of F. nucleatumAmerican Type Culture Collection (ATCC) 25586 or Anaerobe Helsinki Negative (AHN) 9508 were produced by culturing on semipermeable membranes on brucella agar plates. The oxygen tolerance of the F. nucleatumstrains was examined by incubating 3‐day‐old anaerobically grown biofilms in an aerobic environment (CO2[5% in air] incubator) for an additional 48 hours. The OCC model was constructed by seeding keratinocytes on a fibroblast‐containing collagen gel. In invasion assays, a 3‐day‐old anaerobically grown biofilm (and planktonic bacteria in solution as the control) was placed upside down on the top of OCC and incubated under 5% CO2for 24 hours. Invasion of the bacteria and morphologic changes in OCC were assessed using hematoxylin and eosin, Ki‐67, and periodic acid‐Schiff stainings. Results:In biofilms, both F. nucleatumstrains continuously increased their cell numbers in an aerobic environment for 48 hours. After incubating the bacterial biofilm in contact with the OCC model, F. nucleatumAHN 9508 was able to pass through the epithelial/basement membrane barrier and invade the collagen matrix. The invasiveness of biofilm F. nucleatumATCC 25586 was limited to the epithelium. Cytotoxic effects and invasiveness of F. nucleatumon the OCC were much stronger when the bacteria were in biofilms than in the planktonic form. Conclusion:Biofilm formation regulates the survival and invasiveness of F. nucleatumin an aerobic environment.

Periodontitis is a common chronic multibacterial infection in the tooth-supporting tissues. It has been shown that periodontitis patients carry higher number of disease-associated bacteria than healthy ones. The aim of this study was to generate a novel, single copy gene-based quantitative real-time PCR (qPCR) assay for five major periodontal pathogens — Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Treponema denticola, and Tannerella forsythia. The primer/probe sets were designed for conservative lipopolysaccharide-coding gene regions. They proved to be sensitive and able to detect strains representing different serotypes of the target bacteria. The specificity of designed primers was tested using 49 selected bacterial species and no false positive or negative results were observed. We validated the assay with a case-control population, including 165 saliva samples, and proved the diagnostic accuracy by Receiver Operating Characteristic (ROC) curves. All quantified pathogens alone were able to distinguish significantly between the subjects with and without periodontitis, and provided areas under the ROC curve larger than 0.5. The total pathogen burden comprising all five species associated with periodontitis with an area of 0.821 (95% CI, 0.758—0.885, P50.001). Our prominently sensitive and specific assay may have major importance in the diagnosis, prevention, and treatment of periodontitis.

To assess whether subarachnoid hemorrhage (SAH) and its treatment is followed by volume loss in temporomesial structures.

In this study, the neural mechanisms of novelty detection in children and adults were examined by means of novelty-elicited event-related potentials. The gross morphology of the event-related potentials elicited by complex, novel stimuli was similar in children and adults, suggesting that processing of novel acoustic information is essentially similar across the age groups. The more frontally distributed P3 components and the larger late frontal negativities in children than in adults suggest an age-related change in activity in the frontal part of the brain. This is consistent with the findings showing that the structural maturation of the frontal cortex does not appear to be completed until late adolescence.

An albumin coating on titanium implants will inhibit bacterial adhesion on the implant surface.

Several studies have reported that musculoskeletal disorders of the stomatognathic system, commonly known as temporomandibular disorders (TMD) resemble musculoskeletal disorders and chronic pain disorders in general. There is also general consensus that combined biomedical and biopsychosocial methods best support the assessment and management of the cardinal features of TMD, i.e., pain and dysfunction or physical (peripheral) and psychosocial (central) factors. This overview of the aetiology of TMD will outline conceptualizations of past models and present the current view that patients with TMD should be assessed according to both the physical disorder and the psychosocial illness impact factors. The conceptual theories outlined in this review include biomedical models related to temporomandibular joints, muscles of mastication and occlusal factors, psychological models and the biopsychosocial models. An integrated and multidimensional approach concerning physical and psychosocial factors in temporomandibular pain and dysfunction is presented as an example of how the biopsychosocial model and information processing theory may apply in the conceptualization and management of TMD for various health care professionals.

To examine the longitudinal appearance of hippocampal (HC) damage in a prospective follow-up study of patients with newly diagnosed epilepsy.

ABSTRACTThe purpose of this population-based cohort was to measure maximal bite force (MBF) in the molar and incisal regions and to examine whether MBF was associated with TMD, gender, occlusion (in terms of overjet, overbite, and total number of occluding contacts), and body mass index (BMI). MBF in the molar and incisal regions was measured using a calibrated method in 384 (196 males, 188 females) and 357 (181 males, 176 females) subjects, respectively. Two attempts in each region (right molar, left molar, and incisal) were made in random order. The subjects completed a multiple-choice questionnaire including subjective symptoms of TMD and were subsequently clinically examined. Helkimo's clinical dysfunction index and BMI were calculated. The mean MBF value in the molar region was significantly higher in males (878 N, SD 194) than in females (690 N, SD 175) (p<0.001). The incisal forces were 283 N (SD 95) and 226 N (SD 86) (p<0.001), respectively. According to multiple linear regression, TMJ discomfort was significantly negatively associated with MBF in the molar region (p<0.05) and overjet was significantly negatively associated with maximal incisal bite force (p<0.05). No significant associations between MBFs and body mass were found. The results demonstrate that in a population-based cohort of young adults signs, and symptoms of TMD and studied occlusal factors, unlike body mass, associate independently with MBF.

There is still controversy concerning which patients with asymptomatic carotid stenosis or symptomatic moderate stenosis are likely to benefit from carotid endarterectomy. The surgical candidates for carotid endarterectomy should have a high risk for stroke, but a low risk for operative complications. Therefore, new effective patient selection strategies, including haemodynamic testing, schemes of risk stratification and preoperative cardiac testing, are under investigation. To improve haemodynamic assessment of patients with carotid artery stenosis, we evaluated a novel global cerebral blood flow CBF heterogeneity index at rest and after acetazolamide injection in patients undergoing carotid endarterectomy. CBF heterogeneity index was measured in 15 patients by using basal and acetazolamide enhanced 99mTcHMPAO SPET both before and 1 month after surgery. CBF heterogeneity index was calculated as the coefficient of variation of a total of 44 cerebral regions representing mainly both ipsi and contralateral grey matter. A high linear correlation was observed between CBF heterogeneity index and ipsilateral carotid stenosis degree r0.74, P 0.003. Before surgery, CBF heterogeneity index increased significantly after acetazolamide injection when compared to the basal condition from 7.0 ± 1.5 to 8.3 ±1.7, P0.008. This response disappeared after carotid endarterectomy. When compared to pure asymmetry of CBF ipsicontralateral CBF ratio, the CBF heterogeneity index seemed to reflect, more sensitively, the haemodynamic effects of carotid endarterectomy. The CBF heterogeneity index after acetazolamide injection is a sensitive marker of the haemodynamic consequences of carotid artery stenosis and its operative treatment.

It is well established in nonhuman primates that the medial temporal lobe (MTL) structures, the hippocampus and the entorhinal and perirhinal cortices, are necessary for declarative memory encoding. In humans, the neuropathological and neuropsychological changes in early Alzheimer's disease (AD) further support a role for the rhinal cortex in the consolidation of new events into long‐term memory. Little is known, however, regarding the function of the rhinal cortex in humans in vivo. To examine the participation of the interconnected MTL structures as well as the whole‐brain network of activated brain areas in visual associative long‐term memory, functional magnetic resonance imaging (fMRI) was used to determine the brain regions that are activated during encoding and retrieval of paired pictures in 12 young control subjects. The most striking finding in the MTL activation pattern was the consistent activation of the perirhinal cortex in the encoding‐baseline and encoding‐retrieval comparisons with a strict statistical threshold (P< 0.00001). In contrast, no perirhinal cortex activation was detected in the retrieval‐baseline or retrieval‐encoding comparisons even with a low statistical threshold (P< 0.05). The location of the perirhinal activation area was in the transentorhinal part of the perirhinal cortex, in the medial bank of the collateral sulcus. The hippocampus and the more posterior parahippocampal gyrus were activated in both encoding and retrieval conditions. During the encoding processing, MTL activations were more consistent and the hippocampal activation area located more anteriorly than during retrieval. The frontal, parietal, temporal, and occipital association cortices were also activated in the encoding‐baseline and retrieval‐baseline comparisons. The data suggest that encoding, but not retrieval, of novel picture pairs activates the perirhinal cortex. To our knowledge, this is the first fMRI study reporting encoding activation in this transentorhinal part of the perirhinal cortex, the site of the very earliest neuropathological changes in AD. Hippocampus 2003;13:67–80. © 2003 Wiley‐Liss, Inc.

Penicillin resistance due to beta-lactamase production is surprisingly common among oral bacteria in childhood. Fusobacterium nucleatum, a Gram-negative anaerobic bacillus, is a member of the developing oral commensal flora. As part of the investigation on the emergence of oral bacterial resistance, the aim of the present study was to examine longitudinally the penicillin resistance among salivary F. nucleatum populations as related to age, day care attendance and sibling history, and exposure to antimicrobial agents. Altogether 1492 F. nucleatum isolates from saliva of 44 healthy infants followed at a study clinic at 2, 6, 12, 18 and 24 months of age were tested for beta-lactamase production. Furthermore, the 276 beta-lactamase-positive isolates were examined for their in vitro susceptibility to penicillin G by the NCCLS-approved agar dilution method. Statistical analysis of the associations between penicillin-resistant isolates and infants' age, day care attendance, number of siblings and their ear infections, and exposure to antimicrobial agents was performed by SPSS Windows Version 10. The prevalence of infants harbouring beta-lactamase-producing F. nucleatum strains increased from 2% to 49% during the follow-up time. In nearly all cases beta-lactamase-producing F. nucleatum isolates were found simultaneously with beta-lactamase-negative isolates. Most beta-lactamase-producing isolates (80%) showed an MIC of > or =8 mg/L. In conclusion, the prevalence of infants harbouring penicillin-resistant F. nucleatum due to beta-lactamase production increased with age and usage of antimicrobial agents during the first year of life.

The recently described species, Prevotella pallens, is related to, though distinguishable from, the Prevotellaspecies P. intermediaand P. nigrescens. This study tested the hypothesis that P. pallensis distinct from both P. intermediaand P. nigrescenson the basis of phospholipid analogue distributions. Test strains were cultured and their lipids extracted using chloroform-methanol. Polar lipids were analysed by Fast Atom Bombardment-Mass Spectrometry (FAB MS) in negative ion mode. Both lower mass (carboxylate) and higher mass (phospholipid) peaks were measured for each mass spectrum before being statistically analysed. When Pearson Correlation Coefficients for strain pairs were subjected to average linkage cluster analysis, the resulting dendrogram grouped P. pallensstrains together but separate from P. intermediaand P. nigrescensstrains which clustered together. It is concluded that P. pallensstrains are distinct from those of P. intermediaand P. nigrescenson the basis of phospholipid analogue distributions.

Nineteen patients with acute ischemic stroke (<24 hours) underwent diffusion-weighted and perfusion-weighted (PWI) magnetic resonance imaging at the acute stage and 1 week later. Eleven patients also underwent technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (SPECT) at the acute stage. Relative (ischemic vs. contralateral control) cerebral blood flow (relCBF), relative cerebral blood volume, and relative mean transit time were measured in the ischemic core, in the area of infarct growth, and in the eventually viable ischemic tissue on PWI maps. The relCBF was also measured from SPECT. There was a curvilinear relationship between the relCBF measured from PWI and SPECT (r= 0.854; P< 0.001). The tissue proceeding to infarction during the follow-up had significantly lower initial CBF and cerebral blood volume values on PWI maps (P< 0.001) than the eventually viable ischemic tissue had. The best value for discriminating the area of infarct growth from the eventually viable ischemic tissue was 48% for PWI relCBF and 87% for PWI relative cerebral blood volume. Combined diffusion and perfusion-weighted imaging enables one to detect hemodynamically different subregions inside the initial perfusion abnormality. Tissue survival may be different in these subregions and may be predicted.

Verbal fluency tests (VFTs) are suggested to assess frontal lobe function. This view is supported by functional imaging studies that report left frontal activation during VFTs. VFTs require retrieval of semantically associated words from long-term memory storage. The neural networks that participate in this process, however, are largely unknown. These neural networks are of interest, given that patients with early Alzheimer's disease, typically without frontal pathology, are often impaired in VFTs. In the present study, functional magnetic resonance imaging was performed to determine brain activation areas during VFTs in young subjects. In the activation task, category fluency was contrasted with orderly listing of numbers. As judged from using this comparison, there was activation in the left medial temporal lobe, in the inferior frontal and retrosplenial cortices bilaterally, and in the left superior parietal lobule. Left medial temporal lobe activation was present in 13 of the 14 study subjects either in the hippocampal formation (11 of 14) or in the posterior parahippocampal gyrus (12 of 14). These results suggest that the medial temporal lobe is required for the process of retrieval by category. Functional magnetic resonance imaging combined with a category fluency task may provide a new method to study patients with early Alzheimer's disease. Ann Neurol 2000;47:470–476.

A cohort study with a follow-up period of 11 years.

The intimate relationship with bacteria is a fundamental factor in the health status of an individual. After birth infants are exposed to continuous person-to-person and environmental contacts with microbes, and the development of the indigenous microflora begins on the surfaces of the human body. In a developing ecosystem microbial colonization may easily occur because of the still inadequate host response. Adhesion is the initial event in the colonization of bacteria. In the mouth, only mucosal surfaces are available during the first months of life. After teeth emerge, the number of attachment sites and potential niches increases significantly. Bacteria adhere not only to oral surfaces but also to each other, forming multigeneric communities where specific partner relationships influence their composition and stability. Viridans streptococci and a strictly anaerobic species, Fusobacterium nucleutum, are of interest in this context. The oral colonization pattern differs between individuals already in infancy; variable bacterial load in saliva of attendants and other close contacts and the frequency of this bacterial exposure may partly account for individual differences. In addition, the exposure of an infant to antibiotics affects the quality of colonizing bacteria. This article presents an overview of the age-related acquisition of oral bacteria and the role of the indigenous oral microflora in health and disease.