Diagnosis of the state of health of the dental pulpal tissues is a topic of considerable concern to general practitioners, and to dental specialists such as endodontists, oral surgeons, pedodontists, and prosthodontists. Recent work by Burnside (1972) 39 confirming much earlier studies, indicated a very definite tendency for groups of orthodontically treated tee th to have a raised threshold. of sensi ti vi ty to electronic stimulus, almost as if anaesthetized, and it was for the purpose of examining just how long this level of sensitivity lasted and how severe the effect is, that the present investig;ation was begun.