Age-related changes on bone regeneration in midpalatal suture during maxillary expansion in the rat

The purpose of the present study was to investigate age-related changes in bone regeneration during expansion of a midpalatal suture in rats. When the midpalatal suture was expanded for 7 days in rats of four different ages (6, 15, 24, and 52 weeks), it was found to have significantly widened in all groups by the analysis of a histomorphometric method. The expansion-induced widening of the suture was similar in 6, 15, and 24-week-old rats but was significantly less in 52-week-old rats. When the newly mineralized bone area and the osteoid area along the suture in all groups were quantified, newly mineralized bone area in all expansion groups significantly increased compared with corresponding controls, but expansion-induced newly mineralized bone area decreased in an age-dependent manner. Osteoid area also significantly increased by expansion, but expansion-induced osteoid area unexpectedly increased with age up to the 24-week-old rats. In the expansion-induced total bone area (expansion-induced newly mineralized bone area plus osteoid area), there was no significant difference among 6, 15, and 24-week-old rats, but it was markedly decreased in 52-week-old rats. Alkaline phosphatase activity in the suture strongly increased in all expansion groups, whereas increase in the rate of alkaline phosphatase activity clearly was less in 24 and 52-week-old rats. These results suggested that the difficulty of rapid-palatal expansion in 52-week-old rats and age-related decrease in bone regeneration after expansion of the suture within 24-week-old rats may be caused by decrease in mineralization of the bone matrix. Therefore, midpalatal suture can expand even in the cases exceeding the pubertal growth period, but more time may be necessary for mineralized bone to regenerate in the suture.