Assessment of local muscular load of dental practitioners.

OBJECTIVE: Hands and forearms are one of the most common localisations of musculoskeletal disorders (MSDs) among dental practitioners. The aim of this study was to objectively assess the local muscular load of hands and forearms of dental practitioners during various treatment procedures using the method of the integrated electromyography (iEMG). This method is used for health risk assessment and categorization of working operation within the official national methodology. METHODS: A total of 24 measurements were performed on 10 dental practitioners during 8 different dental treatments; mostly on those which are most frequent in clinical practice, i.e. endodontic treatment, tooth extraction, tooth restoration with filling and prosthetic treatment. The EMG Holter was used to detect the electromyographic potentials determining the local muscular load. RESULTS: All the muscle groups of the forearm were relatively evenly loaded at work. During the dynamic work activity, the average time-weighted value of maximum voluntary contraction (%MVC) was in the range from 1 to 30 %MVC for all evaluated muscle groups. The mean average time-weighted value of %MVC did not exceed 6% (a critical limit of the mean average time-weighted value of %MVC) in any of the evaluated muscle groups. The results of the frequency analysis showed that large (55-70 %MVC) and rarely the limits exceeding values (above 70 %MVC) were observed for individual muscle groups. These forces are related to performing tasks at inaccessible locations associated with non-physiological working positions. The differences in the mean forearm muscle load between the upper limbs were statistically significant in total (p < 0.001), for flexors (p = 0.017) and for extensors (p = 0.006). CONCLUSION: In view of the results of this study, the work of dentists can be ranked in category 2 in terms of the local muscle load factor according to the currently valid legislation in the Czech Republic.

Exposure to mercury from dental amalgam: actual contribution for risk assessment.

OBJECTIVE: Mercury dental amalgam restorations are an important source of chronic exposure to mercury in the whole population and special attention should be paid not only to occupational exposure to mercury during the preparation and administration of amalgam. The authors' report is an up-to-date contribution to the health risk assessment of mercury use in dentistry, namely occupational exposure to mercury in dentists working with dental amalgam and exposure to mercury in persons treated with amalgam dental restorations. METHODS: Determination of total mercury in samples of biological material (urine, hair) was performed during 2017 and 2018 in 50 persons by the AAS method using the mercury vapour generation technique at 254.6 nm. RESULTS: Current dental exposures based on the most recent findings do not exceed acceptable risk levels and are below the biological limit of mercury in urine valid for occupationally exposed persons (100 µg.g-1 of creatinine), namely median value was 1.48 (min. < limit of detection (LOD), max. 17.14) µg.g-1 of creatinine (40 persons), total mercury content in hair of dental personnel expressed as median value was 0.340 (min. 0.060, max.1.628) µg.g-1. In controls (10 persons) was total mercury content in urine expressed as median value 0.36 (min. < LOD, max. 2.74) µg.g-1 of creatinine, in hair was median value 0.224 (min. 0.059, max. 0.453) µg.g-1. CONCLUSIONS: Authors support opinion that amalgam fillings in the oral cavity are a permanent source of mercury for the body itself.

A New Approach to the Evaluation of Local Muscular Load while Typing on a Keyboard.

OBJECTIVE: The aim of this study was to assess the contribution of using keystroke dynamics (KD) in combination with integrated electromyography (iEMG) for the objective evaluation of local muscular load of hands and forearms while typing on a computer keyboard and to compare it with results of the commonly used method. METHOD: Study was performed on 12 subjects. Data were collected using our own application for capturing KD data and using EMG Holter for detecting electromyographic potentials to determine local muscular load. RESULTS: The results of our study revealed that currently used methods for assessment of the workload while typing on a computer keyboard are not entirely accurate. In particular, the real total number of keystrokes performed during processing of a text is significantly higher than the count of characters the text is consisting of. In addition to this count, also the so-called invisible keys, keyboard shortcuts, and especially corrections in the typed text must be taken into consideration. CONCLUSIONS: The results indicated that all probands in our study exceeded the valid hygienic limits for the total amount of the small repetitive movements of the hands and forearms and the total amount of the keyboard typing movements. Most of the probands in our study also exceeded the valid hygienic limit for the highest average time-weighted value of the percent maximum voluntary contraction (%MVC). This implies that the keystroke dynamics method has a great potential to increase the accuracy of evaluation of local muscular load when using the keyboard and thus to improve the existing methodology for investigation of occupational diseases resulting from overload while working on the computer.

Disk displacement, eccentric condylar position, osteoarthrosis - misnomers for variations of normality? Results and interpretations from an MRI study in two age cohorts.

BACKGROUND: Clinical decision-making and prognostic statements in individuals with manifest or suspected temporomandibular disorders (TMDs) may involve assessment of (a) the position of articular disc relative to the mandibular condyle, (b) the location of the condyle relative to the temporal joint surfaces, and (c) the depth of the glenoid fossa of the temporomandibular joints (TMJs). The aim of this study was twofold: (1) Determination of the prevalence of these variables in two representative population-based birth cohorts. (2) Reinterpretation of the clinical significance of the findings. METHODS: From existing magnetic resonance imaging (MRI) scans of the TMJs that had been taken in 2005 and 2006 from 72 subjects born between 1930 and 1932 and between 1950 and 1952, respectively, the condylar position at closed jaw was calculated as percentage displacement of the condyle from absolute centricity. By using the criteria introduced by Orsini et al. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 86:489-97, 1998), a textbook-like disc position at closed jaw was distinguished from an anterior location. TMJ morphology of the temporal joint surfaces was assessed at open jaw by measuring the depth of the glenoid fossa, using the method proposed by Muto et al. (J Oral Maxillofac Surg 52:1269-72, 1994). Frequency distributions were recorded for the condylar and disc positions at closed jaw. Student's t-test with independent samples was used as test of significance to detect differences of condylar positions between the age cohorts (1930 vs. 1950) and the sexes. The significance levels were set at 5%. First, the results from the measurement of the age cohorts were compared without differentiation of sexes, i.e., age cohort 1930-1932 versus age cohort 1950-1952. Subsequently, the age cohorts were compared by sex, i.e., men in cohort 1930-1932 versus men in cohort 1950-1952, and women in cohort 1930-1932 women men in cohort 1950-1952. RESULTS: In both cohorts, condylar position was characterized by great variability. About 50% of the condyles were located centrically, while the other half was either in an anterior or in a posterior position. In both female cohorts, a posterior position predominated, whereas a centric position prevailed among men. Around 75% of the discs were positioned textbook-like, while the remaining forth was located anteriorly. Age had no statistically significant influence on condylar or on disc position. Conversely, comparison between the age groups revealed a statistically significant decrease of the depth of the glenoid fossa in both older cohorts. This age-dependent changes may be interpreted as flattening of the temporal joint surfaces. CONCLUSIONS: We call for a re-interpretation of imaging findings because they may insinuate pathology which usually is not present. Instead, anterior or posterior positions of the mandibular condyle as well as an anterior location of the articular disc should be construed as a variation of normalcy. Likewise, flattening of articular surfaces of the TMJs may be considered as normal adaptive responses to increased loading, rather than pathological degenerative changes. TRIAL REGISTRATION: Not applicable.

A Robust Supervised Variable Selection for Noisy High-Dimensional Data.

The Minimum Redundancy Maximum Relevance (MRMR) approach to supervised variable selection represents a successful methodology for dimensionality reduction, which is suitable for high-dimensional data observed in two or more different groups. Various available versions of the MRMR approach have been designed to search for variables with the largest relevance for a classification task while controlling for redundancy of the selected set of variables. However, usual relevance and redundancy criteria have the disadvantages of being too sensitive to the presence of outlying measurements and/or being inefficient. We propose a novel approach called Minimum Regularized Redundancy Maximum Robust Relevance (MRRMRR), suitable for noisy high-dimensional data observed in two groups. It combines principles of regularization and robust statistics. Particularly, redundancy is measured by a new regularized version of the coefficient of multiple correlation and relevance is measured by a highly robust correlation coefficient based on the least weighted squares regression with data-adaptive weights. We compare various dimensionality reduction methods on three real data sets. To investigate the influence of noise or outliers on the data, we perform the computations also for data artificially contaminated by severe noise of various forms. The experimental results confirm the robustness of the method with respect to outliers.