No abstract

Playing wind instruments may have adverse effects on musculoskeletal functions among junior high school students playing in music clubs as compared with playing NW instruments. The prevalence of TMD among the students playing wind instruments was higher than in those playing other instruments. Long duration of playing those instruments affects musculoskeletal function, and this effect is more marked in girls than in boys, irrespective of height or weight.

The aim of this study was to investigate effects of interocclusal distance (IOD) on bite force and masseter electromyographic (EMG) activity during different isometric contraction tasks. Thirty-one healthy participants (14 women and 17 men, 21·2 ± 1·8 years) were recruited. Maximal Voluntary Occlusal Bite Force (MVOBF) between the first molars and masseter EMG activity during all the isometric-biting tasks were measured. The participants were asked to bite at submaximal levels of 20%, 40%, 60% and 80% MVOBF with the use of visual feedback. The thickness of the force transducer was set at 8, 12, 16 and 20 mm (= IOD), and sides were tested in random sequence. MVOBF was significantly higher at 8 mm compared with all other IODs (P < 0·001). Only in women, IOD always had significant influence on the corresponding root-mean-square (RMS) value of EMG (P < 0·011). When biting was performed on the ipsilateral side to the dominant hand, the working side consistently showed higher masseter EMG activity compared with the balancing side (P < 0·020). On the contralateral side, there was no difference between the masseter EMG at any IODs. The results replicated the finding that higher occlusal forces can be generated between the first molars at shorter IODs. The new finding in this study was that an effect of hand dominance could be found on masseter muscle activity during isometric biting. This may suggest that there can be a general dominant side effect on human jaw muscles possibly reflecting differences in motor unit recruitment strategies.

The solidification structure of a hot-dip Zn-11%Al-3%Mg-0.2%Si coated steel sheet with a slight Ti addition was investigated by EBSD. In every center of the primary Al phase of the alloy-coating layer, TiAl 3 was observed by a scanning electron microscope, which suggests that TiAl 3 acts as a heterogeneous nucleation site of the primary Al phase. The latter was revealed to have perfect lattice coherency with the nucleus TiAl 3 phase. The crystal orientation relationships between TiAl 3 and the primary Al are ð001Þ TiAl3 == ð001Þ Al and ½100 TiAl3 == ½100 Al , ð100Þ TiAl3 == ð001Þ Al and ½001 TiAl3 == ½100 Al , ð102Þ TiAl3 == ð110Þ Al and ½ 2 201 TiAl3 == ½ 1 110 Al , ð110Þ TiAl3 == ð110Þ Al and ½ 1 110 TiAl3 == ½ 1 110 Al , indicating that the primary Al phase grows in an epitaxial manner from the nucleus TiAl 3 phase. The planar disregistry between the two phases was calculated to be less than 5%, owing to this good lattice coherency. The TiAl 3 phase is considered to decrease the degree of undercooling necessary for the nucleation of the primary Al phase.

The articular disc motion to the condyle in the PBC group was smaller than in the ABC group irrespective of the configuration of the disc, even though there were no significant differences between the two types of bony changes in the disc position during jaw closing. The joint vibration analysis of the TMJ showed that joint sounds with a higher frequency were observed in the PBC group than in the ABC group. High energy levels needed to produce the higher frequencies (over 300 Hz) were observed only in the PBC group.