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Biomedical subjects

M D Martin

Publications and source records attributed to M D Martin.

At least 19 recordsLinked to original sources
PubMed2004

The inhibition of mercury absorption by dietary ethanol in humans: cross-sectional and case-control studies.

BACKGROUND: Since the inhibition of mercury absorption by ethanol was serendipitously discovered in 1965,(1) a limited number of small number studies with both animal and human subjects have reported results consistent with this finding. AIMS: To investigate this phenomenon in a large scale human study with low level Hg exposed dentists. METHODS: Data were collected for a sample of 1171 dentists, and both cross sectional and case-control methods were utilised to examine the data. RESULTS: Abstainers (n = 345) had significantly higher urinary mercury concentrations (HgU) than drinkers (n = 826): 5.4 microg/l v 4.8 microg/l. Multiple linear regression showed a significant effect of ethanol dose on HgU after adjusting for potential confounders. A case-control analysis in which cases were defined as those individuals with urinary Hg concentrations of > or =15 microg/l (approximately top 5%), and controls as those with concentrations of <1.0 microg/l ( approximately bottom 5%), showed a clear protective dose-response relation; there was a decreasing risk of being a "case" (having an HgU > or =15 microg/l) with increasing ethanol consumption. The significance of the adjusted model is p<0.001, and the chi2 test for trend across ethanol consumption categories in the adjusted model is p<0.05, confirming the dose-response relation. CONCLUSION: We believe that this straightforward investigation provides the first specific confirmation in a large scale human study of the inhibitory effect of ethanol on urinary mercury concentration, and by inference, on mercury absorption.

Adult↗
PubMed2003

Electron-polariton scattering in semiconductor microcavities.

In semiconductor microcavities, electron-polariton scattering has been proposed as an efficient process that can drive polaritons from the bottleneck region to the ground state, achieving Bose amplification of the optical emission. We present clear experimental observation of this process in a structure that allows control of the electron density and we report substantial enhancement of photoluminescence. We show that this enhancement is more effective at higher temperatures due to the different way that electron scattering processes either broaden or relax polaritons.

Journal Article↗
PubMed2002

Risk factors for diagnostic subgroups of painful temporomandibular disorders (TMD).

Temporomandibular Disorders (TMD) encompass several entities, which may have differing etiologies. To test this hypothesis, we investigated risk factors for three diagnostic subgroups of painful TMD. Ninety-seven subjects with myofascial pain only, 20 with arthralgia only, 157 with both myofascial pain and arthralgia, and 195 controls without TMD pain met criteria for study eligibility. Investigated risk factors included both physical and psychological variables. Adjusted odds ratios were calculated by multiple logistic regression analyses. Myofascial pain occurring alone was significantly associated with trauma (Odds Ratio [OR] = 2.0), clenching (OR = 4.8), third molar removal (OR = 3.2), somatization (OR = 3.7), and female gender (OR = 4.2). Myofascial pain with arthralgia was significantly associated with trauma (OR = 2.1), clenching (OR = 3.3), third molar removal (OR = 4.0), somatization (OR = 5.1), and female gender (OR = 4.7). No significant associations were found for the small-arthralgia-only group.

Adolescent↗
PubMed2001

Examination of dietary methylmercury exposure in the Casa Pia Study of the health effects of dental amalgams in children.

This study examined methylmercury concentrations in blood of children participating in the Casa Pia Study of the Health Effects of Dental Amalgams in Children over a 1-yr period and related them to their diets in terms of fish and other seafood consumption. One hundred and fifty children between the ages of 8 and 10 yr who were residents of the Casa Pia School System of Lisbon, Portugal, participated. Parents or caregivers completed a food frequency questionnaire designed specifically for this study at baseline. Children provided urinary and blood samples for mercury determinations at baseline and at 1 yr following placement of dental tooth fillings. Mercury levels in fish samples from children's diets were also obtained. Mercury determinations in urine, blood, and fish were performed using cold vapor atomic fluorescence spectroscopy. The mean value of baseline methylmercury concentrations in blood increased as the report of seafood consumption increased, although not statistically significantly. However, blood methylmercury and total mercury concentrations were significantly lower at 1-yr follow-up than at baseline. Sixty-one percent of parents/caregivers reported that their children consumed fish on a weekly basis. The fish offered at a sample of the schools contained low levels of methylmercury (range 13.9-23.6 ng/g). Thus, children participating in the Casa Pia dental amalgam study are exposed to low dietary levels of methylmercury by way of fish consumption, and this finding was reflected in the low mean blood methylmercury concentrations observed. The present findings indicate that dietary methylmercury is not a significant source of mercury exposure and is not likely to confound the association of dental amalgam mercury with potential health effects in the present study.

Child↗
PubMed2001

Loss of heterozygosity events impeding breast cancer metastasis contain the MTA1 gene.

Breast cancer mortality is seldom attributable to the primary tumor, but rather to the presence of systemic (metastatic) disease. Axillary lymph node dissection can identify the presence of metastatic breast cancer cells and serves as a marker for systemic disease. Previous work in our laboratory determined that rates of loss of heterozygosity (LOH) of a 1.6-Mb region of chromosome 14q 31.2 is much higher in axillary lymph node-negative primary breast tumors than in axillary lymph node-positive primary breast tumors (P. O'Connell et al., J. NATL: Cancer INST:, 91: 1391-1397, 1999.). This unusual observation suggests that, whereas the LOH of this region promotes primary breast cancer formation, some gene(s) mapping to this 1.6-Mb region is rate-limiting for breast cancer metastasis. Thus, if primary breast cancers delete this region, their ability to metastasize decreases. To identify this gene(s), we have physically mapped this area of chromosome 14q, confirmed the position of two known genes and 13 other expressed sequence tags into this 1.6-Mb region. One of these, the metastasis-associated 1 (MTA1) gene, previously identified as a metastasis-promoting gene (Y. Toh et al., J. BIOL: CHEM:, 269: 22958-22963, 1994.), mapped to the center of our 1.6-Mb target region. Thus, MTA1 represents a strong candidate for this breast cancer metastasis-promoting gene.

Breast Neoplasms↗
PubMed2001

Analysis of a growth-promoting factor for Babesia caballi cultivation.

Serum-free media were examined to culture Babesia caballi. Daigo's T (DT) basal medium supplemented with Daigo's GF21 (GF21) or GIT medium, which already contains GF21, supported the parasite propagation at 37 C in a humidified atmosphere under 5% CO2 in air. Growth of B. caballi was dependent of the suitable concentration (10-20%) of GF21. Therefore, GF21 was suggested as the growth-promoting factor for B. caballi. However, GIT medium did not support the growth of parasites from cryopreserved stabilates, and serum supplementation was essential for the retrieval of parasites.

Animals↗
PubMed1998

Validity of spot urine samples as a surrogate measure of 24-hour porphyrin excretion rates. Evaluation of diurnal variations in porphyrin, mercury, and creatinine concentrations among subjects with very low occupational mercury exposure.

Porphyrin, mercury, and creatinine levels in single-void urine specimens ("spot samples") were compared with calculated 24-hour urine concentrations among 146 (77 male and 69 female) practicing dentists who are participating in an ongoing study of urinary porphyrin changes as a biomarker of mercury body burden. All subjects had urinary mercury concentrations < or = 5 micrograms/L, a level comparable to that of the general US population and which is below that determined to be associated with mercury-induced changes in urinary porphyrin excretion rates. The results confirmed previous findings of no significant diurnal variation in any of the porphyrin levels normally found in urine or in total porphyrin levels combined among males but describe significant diurnal variations in most porphyrin levels as well as concentrations of total porphyrins combined among females. Similarly, no evidence of large diurnal variation in mercury excretion among males was apparent, whereas significant diurnal variation in the mercury excretion rate among females was found. Creatinine adjustment of porphyrin or mercury concentrations had no significant effect on these findings. Moreover, no evidence of diurnal variation in urinary creatinine excretion among either male or female subjects was obtained, despite substantial between-subject variability in this parameter. These results support the view that spot urine samples may be utilized to derive reasonably accurate estimates of 24-hour porphyrin and mercury excretion rates in male subjects. In contrast, time of day appears to be of considerably greater importance when spot samples are utilized as 24-hour estimates of either porphyrin or mercury excretion rates among females. Additionally, time of day may be an important consideration in studies involving serial (repeated) porphyrin or mercury measurements using spot urine samples, irrespective of gender distribution of study subjects.

Adult↗
PubMed1997

Functional effects on the acetylcholine receptor of multiple mutations of gamma Asp174 and delta Asp180.

Residues gamma Asp174 and delta Asp180, previously implicated in the binding of acetylcholine (ACh) by the mouse muscle ACh receptor, were each mutated to nine other residues, Asn, Glu, Thr, Ala, Cys, His, Val, Tyr, and Lys. The effects of the mutations on ACh-induced current was determined on surface receptors containing wild-type alpha and beta subunits and mutant gamma and delta subunits. The mutations increased the concentration of ACh eliciting half-maximal current (EC50) by factors from 22 for the Glu mutant to 660 for the Lys mutant. Analysis of the effects in terms of the difference in the accessible surface areas of the mutant and wild-type side chains and the difference in side-chain charges indicated that, per binding site, Delta DeltaG0 for activation was a sum of 10 cal mol-1 A-2 of change in side-chain accessible surface area and of 0.95 kcal mol-1 positive step-1 in side-chain charge, equivalent to 1 mol of charge falling through 42 mV. The effects on the concentration of ACh (IC50, ACh) and of d-tubocurarine (IC50,dTC) causing half-maximal retardation of alpha-bungarotoxin binding were determined on complexes containing wild-type alpha and beta subunits and either mutant gamma or mutant delta subunit. The effects on IC50,ACh correlated well with the effects on EC50, with a similar magnitude for the influence of side-chain charge on the free energy of binding (in this case to the desensitized state) and on the electrostatic potential at the binding site. The effects on IC50,dTC were in all cases less than the effects on IC50,ACh, and the two sets of effects were poorly correlated. In line with the higher ACh affinity and lower d-tubocurarine affinity of the alpha-delta binding site compared to the alpha-gamma binding site, mutations of delta Asp180 had a greater effect on IC50,ACh than did the same mutations of gamma Asp174, and vice versa for effects on IC50,dTC. Consequently, all mutations decreased the asymmetry in the binding properties of the two types of sites.

Affinity Labels↗
PubMed1997

Spontaneous exfoliation of teeth following severe elemental mercury poisoning: case report and histological investigation for mechanism.

BACKGROUND: Although the spontaneous exfoliation of teeth and breakdown of oral tissues from severe mercury intoxication have been noted for over a century, there are no published reports investigating the mechanisms of these phenomena. Severe mercury poisoning is rare in modern times, but it does occur. We present a case report and a histopathologic investigation into the mechanism of the associated tooth loss. METHODS: An exfoliated tooth and periodontal and gingival tissues were obtained from a 15-month-old patient who had been severely intoxicated with elemental mercury over a period of months and hospitalized for severe neurologic and renal effects. The tissues were examined both by routine hematoxylin and eosin stain and by autometallography specific for mercury. For comparison, control tissue from an age-matched subject was examined with the autometallography technique. RESULTS: Under light microscopy, the gingival tissue showed evidence of moderate to severe acute and chronic inflammation. The tooth pulp tissue showed evidence of moderate vascular dilatation and congestion, and it was infiltrated by many neutrophils. The autometallographic sections showed intense accumulations of mercury in the soft tissues of the mercury-exposed subject, but not in the tissues of the control subject. The deposits were primarily found in fibroblasts, which are essential to maintaining the integrity of the oral tissues. CONCLUSIONS: Histopathologic and autometallographic examination of the affected tissue indicates that the primary mechanism of the spontaneous sloughing of tissue and loss of teeth may be the cytotoxic effects of the accumulation of mercury in fibroblasts. Studies of additional cases would be valuable to confirm this hypothesis.

Case-Control Studies↗
PubMed1997

Epidemiologic assessment of measures used to indicate low-level exposure to mercury vapor (Hg).

Mercury (Hg) concentrations in individual spot urine samples collected over consecutive 1-d periods were compared with Hg concentrations measured in combined 24-h urine samples from 69 practicing dental professionals with low exposure to Hg vapor (Hg) in order to validate the use of spot urine samples as an indicator of Hg exposure. The level of Hg in air as an exposure measure was also evaluated by comparing air concentrations of Hg in dental offices with both spot and 24-h urine Hg levels. The results showed: (1) There was little diurnal variation (approximately 9%) in urinary Hg values; (2) a strong correlation (R2 = .85) exists between the Hg concentration in the first morning void and that in a complete 24-h urine sample; (3) adjustment of urinary Hg levels for creatinine concentrations did not improve this correlation; (4) there was no added value in the speciation of total urinary Hg into the inorganic Hg fraction; and (5) concentrations of Hg in air did not significantly correlate with measures of Hg in urine at this low Hg exposure level. We conclude from this study that first morning void urine samples may be used to derive reasonably valid estimates of Hg concentrations found in the total amount of urine collected over a 24-h period. Thus, due to its comparability, ease of collection, and lower cost, the first morning urine void may be used in place of a sample collected over a full 24 h to facilitate Hg exposure assessments in epidemiologic studies that use urinary Hg levels as a measure of low-level Hg exposure.

Air Pollutants, Occupational↗
PubMed1996

The validity of spot urine samples for low-level occupational mercury exposure assessment and relationship to porphyrin and creatinine excretion rates.

Hg and porphyrin levels in single void urine specimens (spot samples) were compared with calculated 24-hr urine levels in 35 (20 [correction of 25] male and 15 female) practicing dentists who had been occupationally exposed to low levels of elemental Hg. The study aimed to: 1) determine the individual variability for Hg and porphyrin concentrations in spot samples over a 24-hr period; 2) test for the presence of diurnal variation in urinary Hg and porphyrin concentrations; and 3) determine the time of day at which a spot sample would give a Hg concentration closest to the 24-hr average concentration. Results confirmed previous reports of a first-order diurnal pattern with a mid-morning peak for Hg concentration (P < .001). A second-order model best described creatinine excretion (P = .0089), with peaks at about 5:00 and 19:00. The use of creatinine adjustment for Hg concentration significantly reduced the intraindividual variation around the diurnal curve. No diurnal patterns were found for any of the porphyrins examined. We recommend that, for small clinical studies using urinary Hg concentration, 24-hr sampling would be ideal, but that for mass screenings and cross-sectional studies, spot samples may be useful because they correlate fairly well with 24-hr averages (creatinine adjusted, r = 0.61; unadjusted, r = 0.74). Because of the existence of diurnal variation, for all cases using serial sampling attention should be paid to time of day.

Adult↗
PubMed1995

Circadian variation in urinary excretion of bone collagen cross-links.

Bone resorption can be evaluated by measuring the urinary excretion of collagen type I cross-linked N telopeptides (NTx). Since it is difficult to obtain (and verify) 24 h urine collections from patients, untimed spot urines are more practical. Such measurements, however, need correction for urine dilution and potentially may vary with collection time since a circadian rhythm in bone metabolism has been reported. This study examined cross-link excretion in urine voids serially collected during a 24 h period from subjects living their normal daily routine (as opposed to a controlled hospital setting). This mimics the situation for walk-in patients visiting a clinician and providing a spot urine. A total of 35 dentists (20 males, 15 females) collected all urine voids separately over a 24 h period. Urines were analyzed for creatinine and NTx. The effects of time of day on the excretion rates of these metabolites (in nmol/h) and on the cross-link:creatinine ratio were assessed. A circadian rhythm was evident in the excretion rate of creatinine with a peak in the late afternoon (18% higher than the 24 h mean, p = 0.0004). The NTx excretion rate peaked in the morning (9% higher than the 24 h mean) but this latter rhythm was not statistically significant (p = 0.31). The NTx:creatinine ratio fell during the day from a high (122% of the 24 h mean) in the early morning to a low in the early evening. This rhythm in the NTx:creatinine ratio in untimed spot urines was statistically significant (p < 0.0001). In conclusion, the NTx:creatinine ratio in spot urines from adult outpatient subjects showed a significant circadian rhythm. Variations in creatinine excretion were the primary cause. Time of day should, therefore, be taken into account when comparing test results of spot urines with normal ranges or with other samples from the same subject.

Adult↗
PubMed1995

Factors contributing to mercury exposure in dentists.

Although mercury exposure levels among dentists have been steadily decreasing, occupational mercury exposure among dental professionals continues to be a matter of interest. This study examined personal professional and office characteristics of dentists to determine which factors contribute most to exposure. The resulting information will help dental professionals change their practices to minimize unnecessary exposure to elemental mercury.

Accidents, Occupational↗
PubMed1995

Distribution of the HLA-DQA1 polymorphism in the population of the Basque Country (Spain).

Allele and genotype frequencies at the HLA-DQA1 locus were determined in Basque Country populations using PCR methodology and a dot-blot assay with ASO probes. The results showed no deviation from the Hardy-Weinberg equilibrium. No differences were found between the three Basque Provinces, but gene frequencies were significantly different from those of some other Spanish and world populations.

Alleles↗
PubMed1994

Topical anesthesia: differentiating the pharmacological and psychological contributions to efficacy.

Pain can be influenced by both pharmacologic and psychologic factors. The purpose of this study was to investigate the pharmacologic and psychologic factors. The purpose of this study was to investigate the pharmacologic and psychologic processes that may play a role when topical anesthesia is used to reduce the pain of dental injections. Subjects were assigned to one of two belief manipulation conditions: one-half of the subjects were led to believe they would receive a placebo, while the remaining subjects were told they would receive the active agent. In reality, all subjects received two separate injections at contralateral sites, one preceded by a placebo and the other by a 20% benzocaine gel. The order in which injections were given was associated with differences in pain report. Second injections were more painful than first injections. Whether injections were preceded by an active or placebo agent did not alter subjects' experienced pain. Likewise, the belief manipulation did not affect the pain report. However, subjects who believed they would receive the active agent anticipated significantly less pain than subjects who thought they would receive placebo. The widespread belief that topical anesthetics are effective at reducing injection pain may serve to reduce the anticipatory anxiety associated with an impending dental injection, thus making the injection experience less aversive.

Administration, Topical↗
PubMed1987

WHO dollar crisis.

Explore the source record for details and available documents.

United States↗
PubMed1986

Skills in cardiopulmonary resuscitation: a survey of dental practitioners.

Emergency preparedness questionnaires were mailed to 4,905 dentists in Florida and 1,600 dentists in Kentucky. A total of 1,605 questionnaires were returned. Of the respondents, 52% reported being certified currently as providers of cardiopulmonary resuscitation. Dentists reported that they used their skills in cardiopulmonary resuscitation more than 900 times during a 10-year period. More than a third of the life-threatening situations occurred in dental offices.

Certification↗