Expression of the type I collagen gene in rat periodontal ligament during tooth movement as revealed by in situ hybridization

The in situ hybridization technique used digoxigenin-labelled oligodeoxynucleotide. In untreated molars, cells expressing a positive signal for type I collagen mRNA were distributed uniformly in the periodontal ligament space. After experimental tooth movement, the density of cells expressing a positive signal appeared to be much greater in the tension side than the pressure side. In both sides the distribution of the positively hybridizing cells was uniform along the principal fibres of the ligament. This characteristic distribution appeared at 12 h after the initiation of tooth movement, reached a maximum at 1-3 days, and persisted for about 14 days during the treatment. These results indicate that the remodelling of collagen fibres in periodontal ligament occurs in an orderly manner throughout the principal fibres, mainly on the tension side, and that the recovery of gene expression for type I collagen occurs within the first 14 days in response to experimental tooth movement.