Title of Thesis:
Effect of masticatory hypofunction on orthodontic tooth movement in adult rats.
Author: Yeh Chin-Chia
Thesis directed by: Chi-Yang Tsai, DDS, PhD (Graduate Institute of Oral Science, College of Oral Medicine, Taipei Medical University)
:
During orthodontic treatment, orthodontic tooth movement (OTM) is affected by bite force generated from masticatory system. In rats, alteration of masticatory function can be achieved by injecting botulinum toxin (BTX). Amount of BTX procedures is steadily increasing since introducing into the markets. Its role as a versatile clinical tool is expanding. BTX also can be used as an adjunct to orthodontic treatment, but not a research has been conducted to test whether it can affect orthodontic tooth movement.
The aim of this study is to investigate the impact of BTX-induced masticatory hypofunction in weight, orthodontic tooth movement, condyle and alveolar bone density.
:
In this study, 30 male adult Sprague-Dawley rats were enrolled at 56 days of age. After acclimatization for 7 days, half of the rats (n=15) were randomly assigned to be injected with 5U BTX into masseter muscles bilaterally and the other half (n=15) were to be injected with the same amount of 0.9% normal saline.
14 days later, maxillary left first molars were pulled forward by orthodontic appliance from maxillary incisors with a force of 25g.
The experimental duration was 28 days. Distance of tooth movement was recorded every 3 to 4 days since D14. Weight was measured every 3 to 4 days. All the rats in two groups were sacrificed on day 28 (D28). Bone density of alveolar bone and condyle heads was evaluated using micro-computed tomography.
:
Significant differences in weight were found between two groups after day 4 (D4). During the experimental period of orthodontic tooth movement, the experiment group remained larger amount and higher velocity of tooth movement than that in the control group, significantly larger and higher in the first 7 days, but getting closed to that in the control group as a trend. Significant lower bone mineral density (BMD), bone volume fraction (BV/TV), trabecular thickness (Tb. Th.), and higher trabecular separation (Tb. Sp.) in the alveolar bone under maxillary left first molars of the experiment group were showed in comparison with that of the control group.
:
• Masticatory hypofunction induced by BTX was accompanied with a smaller weight increase in adult rats.
• Orthodontic tooth movement was significantly faster in the first 7 days in adult rats with masticatory hypofunction.
• Orthodontic tooth movement under the masticatory hypofunctional condition resulted in less trabecular bone density and quality in the underlying alveolar bone.
