The changes of threshold for loading force and electric pain perception thresholds in the dental pulp and the periodontal tissue in response to orthodontic tooth movement

This study was carried out to investigate the nature of pain associated with orthodontic tooth movement. The longitudinal change of the thresholds of pain were examined in three infringement stimulations : loading force, electric current to dental pulp and electric current to periodontal tissue in orthodontic patients. The thresholds for loading force were measured by compression of tension guage on tooth surface. The electric pain perception thresholds of dentalpulp were measured with a dental pulp tester. The electric pain perception threshold in periodontal tissue were measured using a electric stimulator. A modified #25 silver needle was used as an electrode, which was inserted into the marginal periodontal pocket. In preliminary examination, the difference of threshold of pain were examined 31 non-orthodontic patients, and 21 orthodontic patients for three infringement stimulations. The orthodontic patients had lower pain thresholds compared with non-orthodontic patients. Next, changes in the pain thresholds were examined over time in three infringement stimulation between 22 patients with an applied lingual arch with spring approximately 100 gram, 31 patients with an applied initial arch wire by multi-bracket system. Results : The decreases in the thresholds for three infringement stimulations were almost identical in the lingual arch and multi-bracket system. 1) The threshold of loading force began to decrease significantly after 3-6 hrs. 2) The maximum decrease of pain thresholds for the loading force, electric current to dental pulp, and electric current to periodontal tissue was observed in 1day, 2days or 6hrs, respectively. 3) In all stimulations, the original threshold was not regaind after one month. These results suggest that teeth undergoing orthodontic treatment aresen-sitive to infringement stimulation such as occlusion stress.