Biomedical subjects

Mark E Cohen

Publications and source records attributed to Mark E Cohen.

10 recordsLinked to original sources

PubMed2006

Mercury vapor levels in exhaust air from dental vacuum systems.

OBJECTIVE: This study was undertaken to determine mercury (Hg) vapor levels in the air exhausted from dental vacuum systems. METHODOLOGY: Hg vapor concentrations from the dental vacuum system exhaust ports of three dental clinics were measured utilizing the Jerome 431-X mercury vapor analyzer and the United States Occupational Safety and Health Administration's (OSHA) method ID-140 in units of ng Hg/m3. Air velocity measurements and temperatures were determined with a constant temperature thermal anemometer. Hg emissions per unit time were then calculated in ng Hg/min. Ambient Hg concentrations from a location approximately 1000 feet away from the closest clinic sampled in this study were measured with an Ohio Lumex Inc. RA-915+ Hg vapor analyzer. RESULTS: Mean Hg vapor concentrations analyzed with the Jerome 431-X were: 46,526, 72,211, and 36,895 ng/m3 for clinic I (110 chairs), clinic II (30 chairs) and clinic III (2 chairs), respectively. Mean Hg vapor concentrations utilizing OSHA method ID-140 were 45,316, 73,737, and 35,421 ng/m3, respectively. Air flow values were: 11.6, 1.8, and 0.5 standard m3/min, respectively. Hg emission data utilizing air flow measurements were calculated to be 532,684, 131,353, and 18,079 ng/min, respectively, (P<0.001). There was no statistical difference between the two methods used to measure Hg vapor concentrations. The mean Hg concentration in ambient air approximately 1000 feet from the nearest clinic sampled was 13.2 ng/m3. CONCLUSION: The two different methods used to measure Hg vapor concentrations provided similar estimates of Hg concentrations from the exhaust air of three dental vacuum systems. Hg vapor release to the atmosphere from dental vacuums can be substantial and can exceed human exposure limits.

Air Movements↗

PubMed2006

In vitro radiographic determination of distances from working length files to root ends comparing Kodak RVG 6000, Schick CDR, and Kodak insight film.

Previous studies suggest that digital and film-based radiography are similar for endodontic measurements. This study compared the accuracy and acceptability of measured distances from the tips of size #10 and #15 files to molar root apices in cadaver jaw sections using the newly developed Kodak RVG 6000, and the Schick CDR digital systems to digitized Kodak film. Standardized images were taken of files placed 0.5 to 1.5 mm short of true radiographic lengths. Images were imported into Adobe PhotoShop 7.0, thereby blinding observers who measured distances from files to root apices and assessed images for clarity (acceptability). Repeated measures ANOVA and Tukey-Kramer post hoc tests demonstrated that Kodak RVG 6000 images with enhanced contrast produced significantly less measurement error than unenhanced contrast Schick CDR images (p < 0.05) and significantly higher acceptability ratings than all other systems (all p < 0.002). Among these conditions, the newly developed Kodak RVG 6000 system provided the best overall images.

Analysis of Variance↗

PubMed2005

Effect of iodine on mercury concentrations in dental-unit wastewater.

OBJECTIVE: This study was undertaken to determine whether iodine used to control bacteria in dental unit waterlines could increase mercury concentrations in dental wastewater. METHODS: The study was conducted in four parts. Part 1. Solutions containing iodine in concentrations ranging from zero (control) to 20 mg/L were mixed with ground and sieved dental amalgam and then allowed to equilibrate by settling. Cold vapor atomic absorption spectrometry was used to determine mercury levels in the settled supernatants at 24 h and at 7 days. Part 2. Deionized water was pumped through an iodine-releasing water-treatment cartridge, collected, and mixed with ground and sieved dental amalgam. Mercury levels in settled supernatants were measured at 24 h and at 7 days. Part 3. Iodine in water from two commercial iodine-releasing cartridges was measured using Inductively Couple Plasma Mass Spectrometry. Part 4. Baseline mercury levels in settled supernatants from wastewater collected from two dental chairs were compared to samples taken from chairs equipped with iodine-releasing cartridges. RESULTS: Part 1. A linear correlation between iodine and mercury concentration (r2=0.9167 and 0.9459, respectively, both P<0.001) was seen at both 24 h and 7 days. Part 2. Mean mercury levels in 24h samples were 3.0 times higher than the controls (0.2864 mg/L compared with 0.0939mg/L for the 24 h controls). Mean mercury levels in the 7-day samples were 5.9 times higher than the 7-day controls (0.2048 mg/L compared with 0.0348 mg/L for the 7-day controls). Part 3. The effluent from two iodine-releasing cartridges showed iodine concentrations averaging 3.2 mg/L (n=10, SD=0.8, range=2.5-4.6). Part 4. Data from the clinical study showed a statistically significant 2.5-fold increase in mercury levels with iodine-containing samples compared to baseline (0.0853 mg/L, n=18, SD=0.0441 and 0.0345 mg/L, n=18, SD=0.0145, respectively; P<0.001). SIGNIFICANCE: Data suggest that iodine can increase concentrations of dissolved mercury in dental unit wastewater.

Dental Amalgam↗

PubMed2005

Oral surgical handpiece use time parameters.

PURPOSE: To evaluate the clinical usage time parameters of handpieces used in oral surgical procedures. METHOD AND MATERIALS: One hundred randomly selected clinical oral surgery exodontia procedures were timed to record lengths of continuous segments of both handpiece use and non-usage. Providers with experience ranging from general dentists to board certified oral surgeons were timed during surgical exodontia treatment involving 1 to 4 teeth of various complexities. Usage times were compared with manufacturers' recommendations that on times should not exceed 20 seconds in any 50-second interval (20/50 rule). RESULTS: Handpiece run time increased with the number of teeth and surgical case complexity (both P < .001) but was unrelated to operator experience (P = .763), in a 3-predictor model (R2 = 0.20; P < .001). Ninety-four of the 100 cases experienced at least 1 second in violation of the 20/50 rule and 42% of all run seconds were in violation. CONCLUSION: Clinicians should be aware of recommended handpiece duty use cycles. Manufacturers' recommendations about handpiece use time cycles do not reflect actual clinical usage. Under the conditions of this study, actual surgical handpiece use time was not correlated with user experience. Less experienced providers did require longer to complete treatment, but increased treatment times were due to time spent that did not require surgical handpiece use.

Clinical Competence↗

PubMed2004

The effect of a translucent post on resin composite depth of cure.

OBJECTIVE: To evaluate the effect of a light-transmitting post on the depth of cure of a resin composite. METHODS: Acetate resin molds were filled with resin composite in which a light-transmitting post was inserted into the center and photopolymerized to the manufacturer's recommendations. Identical molds without a light-transmitting post were photopolymerized in a similar matter and served as a control. Molds were sectioned on a water-cooled, diamond saw at prescribed distances and the depth of cure was determined using a Knoop Hardness bottom-to-top ratio criterion. Data within each group were analyzed using 2-way (depth-by-distance) repeated measure ANOVA. Between-group contrasts (post versus no post) were accessed by a 3-way (2 within-subjects and 1 between-subjects) ANOVA with critical p = 0.05. RESULTS: The presence of the post did increase (p < 0.001) Knoop Hardness values in simulated apical regions as compared to a control. However, there was no difference in the depth of cure between the groups (3-way analysis p = 0.2) and also when evaluated using an 80% bottom-to-top Knoop Hardness ratio. SIGNIFICANCE: The results suggest that these posts may have a limited utility when judged against a Knoop Hardness ratio criterion.

Analysis of Variance↗

PubMed2004

Statistical estimation of resin composite polymerization sufficiency using microhardness.

With respect to determining sub-surface resin polymerization sufficiency, this study compared a traditional method of applying linear regression to bottom- to top-surface Knoop hardness ratios to an alternative method based on nonlinear regression. Inverse linear regression on ratios was used to estimate the exposure duration required for 80% bottom-surface hardness with respect to the top, in six light-by-material groups. Alternatively, a one-phase, two-parameter, exponential association of the form Y=Y(max)(1-e(-kt)) (where Y(max) is maximum hardness, k is a rate constant, and t is exposure duration), was used to model hardness. Inverse nonlinear regression estimated, for each condition, the exposure duration required for the bottom surface to achieve 80% of corresponding condition (light and material) top-surface Y(max). Mathematically, analysis of ratios was demonstrated to yield potentially less precise and biased estimates. Nonlinear regression yielded better statistical fit and provided easily accessible tests for differences in k across light-system groups. Another recently proposed nonlinear model for polymerization, Y=Y(max)kt(n)/(1+kt(n)), was also considered. While this new model has substantially greater phenomenological and mechanistic justification, we found that the model-fitting process was more sensitive to initial parameter values and sometimes yielded untenable results when applied to our data. However, we believe that these problems would not occur if sample points are well distributed across a wide range of exposure durations, and that the model, Y=Y(max)kt(n)/(1+kt(n)), should be considered for such data sets.

Analysis of Variance↗

PubMed2004

Reference values for pulmonary function in Asian Indians living in the United States.

OBJECTIVE: To establish reference values for pulmonary function in the Asian-Indian population living in the United States. DESIGN: Five-year cross-sectional study of pulmonary function in healthy adult Asian Indians living in the United States, using American Thoracic Society guidelines for measuring pulmonary function. SETTING: Measurement of pulmonary function in healthy nonsmoking Asian Indians in a pulmonary function laboratory or at festivals, picnics, and ceremonies where subjects could be conveniently recruited. PARTICIPANTS: Four hundred sixty subjects from a population of Asian Indians residing in the Chicago metropolitan area. MEASUREMENTS: Spirometry was performed in all subjects with measurements of FEV(1), FVC, and forced expiratory flow between 25% and 75% of vital capacity (FEF(25-75)). Lung volumes were measured in eighty subjects. Prediction equations for FEV(1), FVC, and FEF(25-75) were derived using multiple regression analysis. RESULTS: Three hundred sixty-three subjects (226 men and 137 women) met the inclusion criteria. Spirometric values derived from our prediction equations, when compared to the values for whites from the selected studies in the literature, showed FVC to be 20 to 24% lower in men and 25 to 28% lower in women. FEV(1) was 16 to 23% lower in men and 20 to 26% lower in women. Differences were not quite as large when compared to values from African Americans and other studies on Asians. CONCLUSIONS: We provide reference values for pulmonary function in nonsmoking Asian Indians living in the United States. These reference values should be used for evaluation of pulmonary function in this population.

Adult↗

PubMed2003

Determination of methyl mercury in dental-unit wastewater.

OBJECTIVE: The objective of this investigation was to establish whether monomethyl mercury (MMHg) is present in dental-unit wastewater and if present, to determine the concentration relative to total mercury. METHODS: Wastewater samples were collected over an 18-month period from three locations: at the dental chair; at a 30-chair clinic, and at a 107-chair clinic. Total mercury determinations were completed using United States Environmental Protection Agency's (USEPA) method 1631. MMHg was measured utilizing modified USEPA method 1630. RESULTS: The total mercury levels were found to be: 45182.11 microg/l (n=13, SD=68562.42) for the chair-side samples, 5350.74 microg/l (n=12, SD=2672.94) for samples at the 30-chair clinic, and 13439.13 microg/l (n=13, SD=9898.91) for samples at the107-chair clinic. Monomethyl Hg levels averaged 0.90 microg/l (n=13, SD=0.87) for chair side samples, 8.26 (n=12, SD=7.74) for the 30-chair facility, and 26.77 microg/l (n=13, SD=34.50) for 107-chair facility. By way of comparison, the MMHg levels for the open ocean, lakes and rain are orders of magnitude lower than methyl mercury levels seen in dental wastewater (part per billion levels for dental wastewater samples compared to part per trillion levels for samples from the environment). SIGNIFICANCE: Environmentally important levels of MMHg were found to be present in dental-unit wastewater at concentrations orders of magnitude higher than seen in natural settings.

Dental Waste↗

PubMed2002

Polymerization efficiency of LED curing lights.

PURPOSE: The purpose of this study was to compare the curing efficiency of three commercially available light-emitting diode (LED)-based curing lights with that of a quartz tungsten halogen (QTH) curing light by means of hardness testing. In addition, the power density (intensity) and spectral emission of each LED light was compared with the QTH curing light in both the 380- to 520-nm and the 450- to 500-nm spectral ranges. MATERIALS AND METHODS: A polytetrafluoroethylene mold 2 mm high and 8 mm in diameter was used to prepare five depth-of-cure test specimens for each combination of exposure duration, composite type (Silux Plus [microfill], Z-100 [hybrid]), and curing light (ZAP Dual Curing Light, LumaCure, VersaLux, Optilux 401). After 24 hours, Knoop hardness measurements were made for each side of the specimen, means were calculated, and a bottom/top Knoop hardness (B/T KH) percentage was determined. A value of at least 80% was used to indicate satisfactory polymerization. A linear regression of B/T KH percentage versus exposure duration was performed, and the resulting equation was used to predict the exposure duration required to produce a B/T KH percentage of 80% for the test conditions. The power densities (power/unit area) of the LED curing lights and the QTH curing light (Optilux 401) were measured 1 mm from the target using a laboratory-grade, laser power meter in both the full visible light spectrum range (380-780 nm) and the spectral range (between 450 and 500 nm), using a combination of long- and short-wave edge filters. RESULTS: The emission spectra of the LED lights more closely mirrored the absorption spectrum of the commonly used photoinitiator camphorquinone. Specifically, 95% of the emission spectrum of the VersaLux, 87% of the LumaCure, 84% of the ZAP LED, and 78% of the ZAP combination LED and QTH fell between 450 and 500 nm. In contrast, only 56% of the emission spectrum of the Optilux 401 halogen lamp fell within this range. However, the power density between 450 and 500 nm was at least four times greater for the halogen lamp than for the purely LED lights. As a result, the LED-based curing lights required from 39 to 61 seconds to cure a 2-mm thick hybrid resin composite and between 83 and 131 seconds to adequately cure a microfill resin composite. By comparison, the QTH light required only 21 and 42 seconds to cure the hybrid and microfill resin composites, respectively. CLINICAL SIGNIFICANCE: The first-generation LED-based curing lights in this study required considerably longer exposure durations than the QTH curing light to adequately polymerize a hybrid and a microfill resin composite.

Composite Resins↗

PubMedDate not supplied

Volumetric polymerization shrinkage of resin composites under simulated intraoral temperature and humidity conditions.

This study measured the volumetric shrinkage of resin composites polymerized under temperature and humidity conditions simulating the oral cavity and compared them to those occurring under ambient room conditions. Small, semispherical specimens of a microhybrid (Z100), microfill (Filtek A110) and flowable microhybrid (4 Seasons Flow) resin composite were manually formed and light activated for 40 seconds using a halogen light-curing unit (Spectrum Curing Light). The volumetric polymerization shrinkage of 10 specimens of each brand of resin composite was measured using a drop shape analysis unit (Drop Shape Analysis System, model DSA10 Mk2) under each of two temperature/relative humidity conditions: room conditions (22 +/- 2 degrees C and 60 +/- 5%) and those simulating intraoral conditions (35 degrees C and 92 +/- 5%). Mean volumetric shrinkage values were calculated for each resin composite and the data were analyzed using two-way analysis of variance and t-test (a=0.05) to determine if significant differences existed between the amount of volumetric polymerization shrinkage that occurred under ambient room conditions and that which occurred under simulated intraoral conditions. Mean volumetric shrinkage values measured for the resin composites were: 2.26 +/- 0.04% (ambient) and 2.61 +/- 0.04% (intraoral) for Z100; 1.96 +/- 0.04% (ambient) and 2.28 +/- 0.04% (intraoral) for Filtek A110 and 4.53 +/- 0.06% (ambient) and 5.34 +/- 0.05% (intraoral) for 4 Seasons Flow. For each resin composite, statistical analysis indicated that the amount of volumetric shrinkage measured under simulated intraoral conditions was significantly greater than what was measured under ambient room conditions (p<0.0001).

Body Temperature↗