2022, Vol. 26 ›› Issue (29): 4687-4692

Displacement and rate changes of orthodontic tooth movement in Sprague-Dawley rats with chronic fluorosis

Ding Xue1, Jia Ying1, Liu Chun1, Yang Shirong1, Lai Lingyan1, Yang Hua1, Ding Qi2   

Abstract: BACKGROUND: The orthodontic course is clinically reported to be longer in patients with dental fluorosis than in non-fluorosis patients. However, it is unclear in which parts of the tooth movement cycle the slowing down of the tooth movement rate is mainly reflected.
OBJECTIVE: To study the displacement and rate changes of orthodontic tooth movement in Sprague-Dawley rats with chronic fluorosis during a tooth movement cycle, thereby providing an experimental basis for future related mechanistic studies and orthodontic treatment of patients with dental fluorosis.
METHODS: Twelve 3-week-old Sprague-Dawley rats of both sexes were randomly divided into fluoride group and control group, with six rats per group. Rats in the fluoride group were fed with 150 mg/L sodium fluoride solution daily to replicate the fluorosis model. Two groups of rats were then fitted with a nickel-titanium tension spring orthodontic loading device. The bilateral maxillary first molars were moved mesially under a force of 70 g. The the distance from the midpoint of the proximal surface of maxillary first molars to the distal-lingual-gingival angle of the Ipsilateral maxillary central incisors was measured with a digital vernier caliper and the proximal displacement and movement rate of first molars was observed on days 0, 3, 7, 14, 21, and 28.
RESULTS AND CONCLUSION: In the fluoride group, Grade II-III dental fluorosis appeared, and the urine fluoride level was higher than normal (P < 0.05), indicating the successful replication of chronic fluorosis model. There was no significant sex difference in the total displacement and total rate of tooth movement between the two groups. There was a tendency for the total displacement and total rate of tooth movement to be lower in the fluoride group than in the control group, but no statistical difference was observed during the observation period. The segmental displacement and segmental rate of tooth movement of rats in both groups showed a trend of increasing, then decreasing and increasing again with time, and the second increase was more obvious in the fluoride group. All these findings indicate that tooth movement in rats with chronic fluorosis is inhibited to some extent in a full tooth movement cycle. The total displacement and total rate of rats with chronic fluorosis are reduced, and there is no significant sex difference. Orthodontic tooth movement in rats with chronic fluorosis conforms to the typical tooth movement cycle involving three phases of “rapid–retarded–rebound.” The shortened retarded phase in rats with chronic fluorosis suggests possible destructive alterations.
Key words: chronic fluorosis, orthodontic tooth movement, Sprague-Dawley rat, displacement, movement rate, tooth movement cycle