الفهرس 
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Abstract
The present in vivo study was designed to investigate the thrastructural changes of the human pulpal nerve tissues in response to Iifferent magnitude of orthodontic forces.
3 Eighteen young adult orthodontic patients of both sexes, requiring the removal of non carious and non restored upper first premolars as a part of orthodontic therapy, were selected to participate in this study.
The sample was divided into two groups according to the amount of force (light and moderate) applied to the experimental teeth. Consequently each group was subdivided into three subgroups as a result of duration of force application prior extraction ( 2 hours, 24 hours and 4 weeks)
The orthodontic force was applied to the experimental teeth by means of a fixed sectional arch. Thirty five specimen were obtained from the upper first premolars, five of them were control