Development of viscoelastic measurement system and histological examination of periodontal ligament and alveolar bone.

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It is imperative to clarify the changes in periodontal tissues during orthodontic treatment in terms of not only tooth movement but retention. Orthodontic treatment involves various kinds of changes in which, particullary, tooth mobility is said to reflect viscoelastic property of periodontal ligament and alveolar bone as correctly as they are.In this study, a new system for an assessment on a dog's tooth mobility was developed in order to compare histological findings with tooth mobility.Minimization of the loading mass to a tooth is essential for the measurement of the tooth mobility accurately. Furthermore a sensor should be conditioned as a lighter or possibly a non-touched type. In the preliminary experiment we examined the possibility and accuracy of the measurement of tooth mobility on the simulation models using Laser Displacement Meter (LDM).Then, in the experimental dogs, the quantity and phase of displacement were measured with loading forces at the lingual surface of 3rd incisors. At the same time vibration was given by an impulse hammer and the frequency was analyzed by FFT real time analyzer.The results on the simulation models showed high accuracy of this measuring system, which were 2.7% at 200g and 1.3% at 500g. The frequency peaks were shown with the same spectrum.On the dog's teeth the quantities of displacement were 18 mum at 50g, 38mum at 100g, 47 mum at 200g, 65mum at 500g, respectively, with a frequency peak of 375 -600Hz.In conclusion it was suggested that this system is suitable enough to investigate the temporal changes in tooth mobility in orthodontic tooth movement in dogs.