MATERIALS AND METHODS: Sixteen New Zealand white rabbits were randomly divided into four groups. Modified Hyrax expanders were placed across the midsagittal sutures and secured with miniscrew implants with the following activations: group 1 (control), 0.5 mm expansion/day for 12 days; group 2, 1 mm instant expansion followed by 0.5 mm expansion/day for 10 days; group 3, 2.5 mm instant expansion followed by 0.5 mm expansion/day for 7 days; and group 4, 4 mm instant expansion followed by 0.5 mm expansion/day for 4 days. After 6 weeks, sutural expansion and new bone formation were evaluated histomorphometrically. Statistical analysis was performed using Kruskal-Wallis/Mann-Whitney U tests and Spearman's rho correlation (p osteopontin expression between all experimental groups. The highest level of these proteins was attained in group 3, followed by groups 2, 1, and 4, respectively.
CONCLUSIONS: Sutural appositional bone formation corresponded with the amount of initial expansion to a point. When initial expansion was increased to 4 mm, sutural bone remodeling was disturbed and new bone formation was decreased. The most effective sutural expansion was achieved with 2.5 mm initial activation followed by 0.5 mm expansion/day for 7 days.