Effects of neodymium-doped yttrium aluminium garnet [ND:YAG] laser irradiation on bone metabolism during tooth movement

Introduction: The aim of this study is to evaluate the effects of low-level neodymium-doped yttrium aluminium garnet [Nd:YAG] laser irradiation on orthodontic tooth movement and histological examination

Methods: Eleven male Wistar rats [aged 10 weeks] were included. To produce experimental tooth movement in rats, 10 g force was applied to maxillary first molars with nickel titanium closed coil springs. Right molars were irradiated with Nd:YAG laser on days 0, 1, 2, 3, 7, 10, 14, 17, 21 and 24, while un-irradiated left molars were used as control. Distance between mesial side of second molar and distal side of first molar was measured on uCT image during tooth movement and the rats were sacrificed 4 weeks after the initiation of tooth movement

Results: The amount of tooth movement was significantly greater in the irradiation group [0.20 +/- 0.06] than in the control group [0.14 +/- 0.03] during the first week [P<0.05]. However, no statistically significant difference was found afterwards. There was a tendency of higher tartrate-resistant acid phosphatase [TRAP]-positive nuclei count in the pressure zones of the laser irradiation group, but it was not statistically significant. In immuno-histological examination, expressions of alkaline phosphatase [ALP] and receptor activator of nuclear factor kappa-B ligand [RANKL] were higher at the pressure site of the laser irradiation group than the control group, whereas there was no difference in osteoprotegerin [OPG] expression

Conclusion: The results suggest that low-level Nd:YAG laser may stimulate osteoclast and osteoblast activation and accelerate bone metabolism during tooth movement

COMPARISON OF TRUNK ACCELERATIONS AND KNEE FLEXION ANGLE DURING THREE TYPES OF LANDING BETWEEN BALLET DANCERS AND NON-DANCERS / 体力科学

<b>Purpose:</b> The purpose of this study was to determine whether the impact on the body during landing in dancers is less than in non-dancers by using accelerometers and motion analyzer.<b>Method:</b> Eleven ballet dancers and 11 non-dancers participated in this study. Each subject was instructed to perform 3 types of landing from a height of 30cm: <i>landing, silent landing</i> and <i>raise up landing.</i> Markers were put on the iliac crest, greater trochanter, knee joint, lateral malleolus. The peak vertical and horizontal accelerations of the lumbar, peak vertical acceleration of the greater trochanter and the peak flexion angles of the hip and knee joints were measured after the trials.<b>Result:</b> In the <i>raise up landing,</i> the peak vertical acceleration of the lumbar region in dancers was less than that in non-dancers (p < 0.01), and the peak knee-flexion angle in dancers was greater than that in non-dancers (p < 0.01). There were no differences between the peak hipflexion angles of dancers and non-dancers.<b>Conclusion:</b> The impact on the lumbar during <i>raise up landing</i> was less in dancers. In <i>raise up landing,</i> the trunk tends to be fixed when the dancer stands upright. Moreover, dancers attenuated the shock to the lumbar region by increasing the knee-flexion angle to a greater extent than the non-dancers did. This result may indicate the importance of the knee joint flexion in attenuating the shock during landing and show that dancers excel in using their knees flexibly.