Is there an optimal initial amount of activation for midpalatal suture expansion?

Abstract

Accelerated bone-borne expansion protocols on sutural separation and sutural bone formation were evaluated via histomorphometry and immunohistochemistry to determine the optimal initial activation without disruption of bone formation. Sixteen New Zealand white rabbits were randomly divided into fourgroups. Modified Hyrax expanders were placed across the midsagittal sutures and secured with miniscrew implants with the following activations: group1 (control), 0.5 mm expansion/day for 12days; group2, 1 mm instant expansion followed by 0.5 mm expansion/day for 10days; group3, 2.5 mm instant expansion followed by 0.5 mm expansion/day for 7days; and group4, 4 mm instant expansion followed by 0.5 mm expansion/day for 4days. After 6weeks, sutural expansion and new bone formation were evaluated histomorphometrically. Statistical analysis was performed using Kruskal-Wallis/Mann-WhitneyU tests and Spearman's rho correlation (p < 0.05). The smallest median sutural separation was observed in group1 (3.05 mm) and the greatest in group4 (4.57 mm). The lowest and highest amount of bone formation were observed in group4 (55.82%) and in group3 (66.93%), respectively. Immunohistochemical analysis revealed significant differences in median levels of alkaline phosphatase and osteopontin expression between all experimental groups. The highest level of these proteins was attained in group3, followed by groups2, 1, and 4, respectively. Sutural appositional bone formation corresponded with the amount of initial expansion to apoint. 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 7days.