Occurrence Of Rotation Research Articles

Association between Hypodontia of the Permanent Lateral Incisors and other Dental Anomalies in School Children Aged 12-16 Years in Kosovo

Background: Hypodontia of lateral incisors (LI) is frequently associated with other dental anomalies. The objective of this study was to determine the association of LI with other dental anomalies by comparing the two groups: Group 1 with hypodontia of the maxillary LI (MLI1) and Group 2 with hypodontia of the mandibular LI (MLI2), in secondary school education students in Kosovo. Methods and Results: A total of 3306 secondary school students aged 12-16 years, regardless of gender, were included in this prospective study. The abnormalities investigated were recorded by RTG-panoramic and dental charts. The teeth were recorded as a congenital absence when the mineralization of the crown, identified by panoramic tomography, was absent. The prevalence of LI hypodontia was as follows: MLI1 (Group 1) included 36 cases (92.3%) and MLI2 (Group 2) included only 3 cases (7.6%), which indicates a much higher percentage of cases with hypodontia of MLI1. In Group 1, 21(58.3%) cases of LI hypodontia were bilateral and 15(41.7%) unilateral; in Group 2, 2(66.7%) cases were unilateral and 1(33.3%) case – bilateral. Among dental anomalies, the occurrence of rotation was found in 19(48.7%) cases with LI hypodontia: 47.2% cases in Group 1 and 66.7% cases in Group 2. The prevalence of dental inclination anomaly was 30.77% of all cases with hypodontia of LI: 27.8% of cases in Group 1 and 66.7% of cases in Group 2. The prevalence of ectopy was in 17.9% of cases of all hypodontia cases of LI: 16.7% of cases in Group 1 and 33.3% of cases in Group 2. Crown anomalies were evident in 7(17.9%) patients of all hypodontia cases of LI, all of which were in Group 1. Other anomalies such as microdontia were evident in two patients in Group 1. Transposition, bodily movement, and superposition were present in one patient in Group 1; in Group 2, one patient had transposition. At the same time, the frequency of dental transposition was significantly higher in Group 2 than in Group 1 (P=0.02088). Other dental anomalies of crown and root and infraposition were not present in both groups. There were no significant differences in the other dental anomalies between the two groups. Conclusion: The consequences of hypodontia in dental arches are obvious. Knowing the prevalence of hypodontia and its association with other dental anomalies helps classify the need for further treatment for the patients, whether orthodontic, prosthetic, or surgical.

Threshold Behavior of Volume Dust Cluster Untwisting in a Magnetic Field

The action of a magnetic field on the behavior of a bulk dust cluster formed in the strata of a glowing discharge has been studied. The cluster that consists of seven chains of particles and is a hexagonal cell in the horizontal cross-section has been studied. It has been found that the rotation of a dust cluster arises in nonzero magnetic field unlike the dusty structure containing many particles in the horizontal cross-section. Moreover, it has been found that the threshold behavior of the occurrence of rotation in the cluster is affected by the discharge current and plasma-forming gas pressure. The enhancement of the ionization inside a dust cluster is suggested as an interpretation. The radial ion flux that moves in the longitudinal magnetic field from the dusty structure to the discharge tube wall additionally twists the structure with the negative projection of an angular velocity on the magnetic induction vector.

The Influence of Rotation on Horizontal Branch Stars and on RR Lyrae Pulsational Properties

The occurrence of rotation in Globular Cluster stars has been suggested (see e.g. Renzini 1977) as a mechanism producing the observed colour spread in actual Horizontal Branches. If this is the case, canonical results on evolutionary properties of HB stars have to be revisited in order to account for rotation-driven structural variations: faster Main Sequence rotators delay the He flash increasing the mass-size Mc of the He core at the flash and loosing a greater amount of mass during the Red Giant stage.

Molecular Structure and Rubberlike Elasticity. III. Molecular Movements in Rubberlike Polymers

Abstract In Part I of this work, the crystal structures of β-gutta-percha, rubber and polychloroprene (deduced from x-ray diffraction photographs) were described. In pursuance of the idea that rubberlike properties are due to molecular flexibility which result from the swivelling of the chain units around single chain bonds, it is necessary to consider which chain-bond positions are the most stable and what hindrances there are to rotation away from these positions. The question of the most stable bond positions was considered in Part II. I now consider the evidence for the occurrence of rotation in rubberlike substances, the hindrances to rotation in different molecules, their effect on the crystallization or melting temperature, and the explanation of the mechanical properties of these substances in terms of structure and molecular movement, both above and below the crystallization temperature. Rubber is noncrystalline and elastic at room temperature; but on cooling below 0° C it crystallizes, and in that condition has the mechanical properties of gutta-percha; i.e., a frozen specimen no longer has enormous elasticity, but it can be drawn or rolled out irreversibly, whereby the crystals become oriented. Conversely, if gutta-percha is wanned to 70° C, it becomes amorphous (transparent, optically isotropic and noncrystalline), and its mechanical properties are then like those of rubber—it is soft and elastic. The difference between the two substances thus appears to be essentially a difference of crystallization temperature. These crystallization temperatures are remarkably low; e.g., polyethylene, (—CH2—CH2—)n, of comparable molecular length, crystallizes at 115–125° C. In attempting to understand rubberlike elasticity in terms of molecular behavior, the first question is why are the crystallization points of such enormous molecules so low, and why is the crystallization point of the cis-form of polyisoprene (rubber) lower than that of the trans-form (gutta-percha).