Remodeling of alveolar aging is expressed in the lower height of the alveolar ridge. Osteoporosis, osteoporotic fractures, and absorption of bone prevail over osteogenesis. Periodontium changes included increasing collagen fiber, thinner periodontal membrane, and declining reactivity of the periodontal ligament reconstruction. Epithelial keratinization and the number of connective tissue cells decreased with age in gingival tissue. The height of the free gingival margin reduced according to the alveolar bone. In addition, osteoporosis accelerated the rate of tooth movement, which prevented the reconstruction and stability of orthodontic tooth in a new position. Orthodontic treatment will be increasingly timeconsuming as patients age because of the decreasing alveolar immature cells, osteoblasts, blood vessels, and marrow cavity. Reduced bone metabolism and tooth movement, prolonged remodeling of perioral muscle, weakened ability of alveolar renewal and rebuilding, slowed periodontal cell activity and collagen formation rate, and pulling side formation and pressing side absorption of alveolar bone also contribute to time-consuming treatment. Under mechanical stimulus, the increase of prostaglandin in gingival crevicular fluid may cause the reduced rate of orthodontic tooth movement in adults.
