Determination of the tooth mobility change during the orthodontic tooth movement studied by means of Periotest and MIMD (the mechanical impedance measuring device for the periodontal tissue).

Two mechanical devices were selected to attempt to assess any changes in tooth mobility when orthodontic force was applied. A Periotest (PT) for assessing mobility and a mechanical impedance measuring device (MIMD) were the instruments chosen to diagnose the changes in the periodontal condition. The relative mobility of four canines after orthodontic tooth movement manipulation was assessed over a 4-week period. Both devices were able to detect very small changes in tooth mobility and could follow the changes during tooth movement. According to the Periotest unit, the tooth mobility changes were not within the clinically abnormal range, despite the initial retraction load from a sectional arch, applied in a horizontal direction with about 150 gm for each tooth. In all instances, the contiguous maxillary first premolar had been removed 1 to 2 months before force application. The tooth mobility observed in this investigation could be different from that caused by periodontal disease or traumatic injury. Just after orthodontic tooth movement manipulation, the Periotest values (PTV), as measured on the Periotest, of tooth mobility decreased and the resistance as measured by the mechanical impedance measuring device (MIMDM) was increased. Thus, initially, there is a greater resistance to movement with decreased mobility. After the experimental period of 4 weeks, there was an increase in the mobility, as measured by the Periotest and the mechanical resistance decrements were observed. However, the Periotest units showed some different changes occasionally that did not seem to reflect the state of tooth movement. This needs to be investigated further over a longer period of time. On the basis of the results obtained, it does appear that it is feasible to use these devices to determine mobility changes in patients at various stages of orthodontic treatment.