Linear viscoelastic and dielectric measurements were conducted for a blend of polyisoprene (PI, M ) 19. 9 × 10 3 ) and poly(4-tert-butyl styrene) (PtBS, M ) 69. 5 × 10 3 ) with a PI/PtBS composition of 8/2 (w/w). In general, PI and PtBS exhibit the lower-critical-solution-temperature (LCST) type phase behavior. At temperatures examined, T e 70 °C, our PI/PtBS blend was in a statically homogeneous state. The PI chain has the so-called type-A dipoles parallel along the backbone, and its large-scale (global) motion activates prominent dielectric relaxation, while the PtBS chain has no type-A dipoles and its global motion is dielectrically inert. In fact, at angular frequencies ω between 10 1 s -1 and 10 5 s -1 and at T e 70 °C, the dielectric signal of the blend was exclusively attributed to the PI chains therein. The time-temperature superposition failed for the dielectric loss ′′ of the PI chains, despite the fact that the blend was statically homogeneous. This result suggested that the frictional environment for the global motion was not the same for all PI chains. Namely, the PtBS chains relaxed more slowly than PI (as revealed from comparison of G* and ′′ data) and their dynamic concentration fluctuation was frozen in the time scale of PI relaxation to give a spatially nonuniform frictional environment for the PI chains. The magnitude of this frictional nonuniformity changed with T thereby leading to the failure of the timetemperature superposition for PI. In contrast, the superposition worked excellently for the viscoelastic modulus ∆G* of the PtBS chains (obtained by subtracting the PI contribution from the blend modulus). This result suggested that the PI chains relaxing faster than PtBS erased the heterogeneity in the time scale of the PtBS relaxation to provide all PtBS chains with the same frictional environment thereby allowing this relaxation to obey the superposition.

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BackgroundThe purpose of this cross-sectional study was to investigate the effects of congenitally missing teeth on craniofacial morphology and to characterize the features of maxillofacial morphology of oligodontia patients associated with individual skeletal maturity by assessment with the cervical vertebrae maturation (CVM) method.MethodsA total of 106 non-syndromic Japanese patients with congenitally missing teeth (except for third molars) were selected and categorized into two groups according to the severity of congenitally missing teeth (hypodontia group, 1–5 missing teeth [n = 56]; oligodontia group, ≥ 6 missing teeth [n = 50]). A control group included orthodontic patients without either skeletal disharmony or congenitally missing teeth (n = 63). Subjects in oligodontia and control groups were further categorized into two subgroups on the basis of cervical stage (CS): stage I (CS2 or 3; n = 27 and n = 31, respectively) and stage II (CS4 or above; n = 23 and n = 32, respectively). Lateral cephalograms were analyzed by using eight angular and eight linear measurements. Z-scores were formulated on the basis of age and sex and were matched to the Japanese norm. Tukey tests and t tests were performed.ResultsCompared with the control group, the hypodontia group had significantly smaller U1 to FH plane angle and A-B plane angle; U1-L1 was significantly larger. The oligodontia group had significantly smaller ANS-Me, L1 to mandibular plane angle, and Ptm-A; U1-L1 was significantly larger. At stage I, the oligodontia group had significantly smaller ANS-Me, gonial angle, and ANS-U1. At stage II, the oligodontia group had significantly smaller U1 to FH plane angle, L1 to mandibular plane angle, Ptm-A, and Go-Pog; it also had significantly larger U1-L1.ConclusionsThe present study suggested that skeletal patterns differ along with the number of congenitally missing teeth and that, in oligodontia patients, skeletal patterns differ before and after growth peak. It is important to consider the skeletal characteristics of tooth agenesis patients when designing a treatment plan.

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The present paper deals with an analysis of the kinematics and geometry of the tooth engagement of the harmonic drive, and presents a new method for determining tooth profiles of the harmonic drive. First, two assumptions are set up: (1) Though there is relative motion among the respective teeth of the flexspline during flexing, the individual teeth themselves can be considered to be rigid. (2) The pitch between the respective teeth of the flexspline is constant on the neutral line. Experiments confirm the existence of a neutral line along the flexspline rim which maintain the same length as that prior to bending. Then, tooth profiles of the circular spline and the flexspline are determined according to the theory of gear mechanism that the common tooth normal at the meshing point passes through the pitch point. The analysis is carried out in a plane mechanism.