Objective Through orthodontic tooth movement in the pregnant and non- pregnant rats, to investigate the osteopontin（OPN）mRNA expression pattern in the periodontal tissues, and to probe its possible roles in or - thodontic periodontal remodeling. Methods Fixed appliances were used to mesially move the rats′maxillary first molars. In situ hybridization method was used to detect the expression changes of OPN mRNA in periodontal tissues. Results Compared to the non- pregnant rats, the expression of OPN mRNA in periodontal cells of the pregnant rats was more intensive. During the gestational period, the expression intensity had significant difference at different pregnant stages. The highest expressions occurred at the mid- pregnant stage, less at the late- stage and lest at the early- stage. Conclusion Under the pregnant state, the expression of OPN mRNA in periodontal tissues may be up- regulated by increased serum progesterone level.
