The role of biology in the orthodontic practice (Page 3)

The age factor on the tissue response to orthodontic force has occupied the minds of orthodontists since Hunter, in the 18th century, and probably earlier. Hunter observed that orthodontic treatment takes longer in adults than in children. Studying histological sections of human teeth and their surrounding tissues, Reitan concluded that the periodontal ligament (PDL) is less cellular in adults than in children. Therefore, he recommended, when treating adults, to initially subject their teeth to light forces, in order to stimulate cellular proliferation, then to increase the force magnitude, in order to stimulate these cells to remodel the paradental tissues.

This observation implies that, in essence, the nature of the biological response to orthodontic forces is similar in young and adult subjects. This hypothesis was confirmed by Shimpo et al (2003). These investigators moved molars blingually in young (13 week old) and old (60 week old) rats, then studied their compensatory alveolar bone apposition under the lingual periosteum. They reported that in both age groups there had been vigorous compensatory alveolar bone growth. Thus, alveolar bone is successfully maintained, even in aged rats. Age can also refer to the duration of healing of a postoperative regenerate following distraction osteogenesis (Nakamoto et al, 2002). In an experiment on 15 month old beagles, mandibular premolars were moved into a 2-week or a 12-week regeneration period. The former consisted of immature, fibrous, and poorly mineralized bone, while the latter was composed of mature, well-organized and mineralized bone. Tooth movement was significantly faster in the “young”, immature regenerate, but this movement was accompanied by extensive root resorption that extended from the cementoenamel junction to the root apex.

Page 1     Introduction

Page 2     Tissue remodelling and orthodontic tooth movement

Page 3     The age factor

Page 4     The effects of pre-existing medical conditions and the development of complications

Page 5     The etiology of tooth resorption

Page 6     The biological nature of an optimal orthodontic force

Page 7     How to move teeth without resorbing their roots

Page 8     Summary