Search

We present a measurement system for the viscosity and density of a fluid featuring a permanent magnet as measurement body, which is levitated in an actively controlled magnetic field. The behavior of the system is illustrated using different measurement body shapes. The basic concepts and the modeling of the electromechanical system are discussed. Utilizing special measurement modes, the sensor system allows for measuring viscosity and density independently. When put into operation, the magnet is controlled to stay at a constant levitation position. Due to a special actuation scheme, the magnet also rotates around its vertical axis. Using this setup and immersing the magnet in a fluid, it is possible to analyze viscosity and density of all kinds of fluids, except ferrofluids (which would distort the magnetic fields). The magnetic levitation system avoids any electrical or mechanical connections penetrating the walls of the measurement chamber; only the levitated permanent magnetic measurement body is in contact with the sample fluid.

We present a measurement system where a spherical permanent magnet is levitated in an actively controlled magnetic field. The sensor system measuring viscosity and density independently. In operation mode, the magnet is held in a constant levitation position. Due to a special actuation scheme, the magnet rotates around its vertical axis. Using this setup and immersing the magnet in a fluid, it is possible to analyze viscosity and density of all kinds of fluids, except ferrofluids. The magnetic levitation system avoids any connection penetrating the walls of the measurement chamber; only the spherical permanent magnet measurement body is in contact with the sample fluid. Due to this, the measurement procedure is reproducible, repeatable and resource saving.

Introduction The purpose of this retrospective study was to assess the prevalence of taurodont and pyramidal molars among a German dental school patient population. Methods A total of 800 patients’ full-mouth periapical radiographs were screened. The radiographs were evaluated under optimal conditions using double magnifying glasses. A total of 4,885 molars (including third molars) were evaluated. The relative incidence and the correlations regarding the location of taurodont and pyramidal teeth (right versus left side and maxillary versus mandibular) were analyzed using the chi-square test. Results Eighteen patients were found to have a taurodont molar (13 women and 5 men [ p = 0.097]). Fifteen patients were found to have a pyramidal molar (11 women and 4 men [ p = 0.124]). The overall incidence of patients with taurodont molars was 2.25% and with pyramidal molars 1.88%, respectively. The prevalence of taurodont molars from all teeth examined was 0.61%, and the prevalence of pyramidal molars was 0.50%. No significant differences were obtained regarding the location of the affected teeth ( p > 0.05). Conclusions The occurrence of taurodont or pyramidal molars among this German population was rare.

The purpose of this retrospective study was to assess the prevalence of three-rooted mandibular first molars among a German dental school patient population. A total of 800 patients' full-mouth periapical radiographs were screened, and, out of these, 524 patients possessing at least one mandibular first molar were selected. The radiographs of these cases were evaluated under optimal conditions using double magnifying glasses. The incidence of three-rooted mandibular first molars and the correlation between left- and right-side occurrences and between males and females were recorded and analyzed using the chi-square test. A total of 1,024 mandibular first molars were evaluated. Left molars comprised 500 teeth and right molars 524 teeth. Seven patients were found to have a three-rooted mandibular first molar, three females and four males (p = 0.981). The overall incidence of patients with three-rooted mandibular first molars was 1.35%. All three-rooted molars occurred unilaterally. The prevalence of teeth showing an extra root from all teeth examined was 0.68%. The right first molar had an incidence of 0.57% and the left molar of 0.80%, respectively (p = 0.953). In conclusion, the occurrence of three-rooted mandibular first molars among this German population was rare.