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RESEARCH REPORTS
Biomaterials & Bioengineering
ABSTRACT
Orthodontic procedures seem to be more time-- consuming in adults than in juveniles. This might be related to delay in the initial tissue response or to a slower turnover of the bone and periodontal ligament in adults. To study this problem, we studied orthodontic tooth movement in two groups of 30 rats, aged 6 wks and 9-12 mos, respectively. At one side of the maxilla, 3 molars together were moved mesially with a standardized orthodontic appliance delivering a force of 10 cN. The other side served as a control. The results showed a faster initial tooth movement in juvenile than in adult animals. However, once tooth movement had reached the linear phase, the rate of tooth movement was the same in both groups. The results indicate that, besides a delay in the onset of tooth movement in adult animals, tooth movement could be equally efficient in adults once it had started.
KEY WORDS: orthodontics, tooth movement, velocity, age-effect, rats.
INTRODUCTION
Although a tremendous increase in the demand for adult orthodontic therapy was seen in the past decades, our knowledge on the efficiency of adult tooth movement is still rather incomplete. Clinical experience has shown that tooth movement through the alveolar bone in adults is indeed possible by means of treatment modalities based on experiences in adolescents. However, certain treatments seem to be more time-consuming in adult than in juvenile patients. This led Goz (1990) to the conclusion that, in adults, the biological possibilities for tooth movement are decreased to about one-third of those found in children.
This might be due to the biological limitations of the adult bone, since it is well-known that, during aging, the bone composition changes, its cells become less reactive, and its metabolism slows (Klingsberg and Butcher, 1960; Baumhammers et al., 1965). Another possible cause might be the use of inappropriate stimuli, because the biological requirements for inducing optimal tissue responses in young and adult individuals may be different (Melsen, 1991).
In contrast, Bond (1972) and Melsen (1991) suggested that, in the clinical situation, adults and juveniles are equally responsive to mechanical stimuli once tooth movement has started, and that the longer treatment duration in adults might be caused by a...