Osteoclasts as Key Player in Sutural Adaptation to Mechanical Stimulation

Objectives: To evaluate the tissue, cellular and molecular responses in the sutures during maxillary expansion.
Methods: Sprague-Dawley rats where divided into 4 groups: 1) Control group that did not receive any appliance, 2) Expansion group that received transverse maxillary force with custom-designed spring attached to first and second molars (100cN), 3) Sham group that received similar treatment as the experimental group without activating the spring, 4) Expansion + NSAID group that received low dose anti-inflammatory medication daily in addition to the identical transverse force. Maxillae were collected 0,1,3,7,14 and 28 days post-expansion for micro-computed tomography (μCT), fluorescence and light microscopy, gene expression, protein, and immunohistochemistry analysis.
Results: The expansion group showed early expression of inflammatory cytokines in the mid-palatal suture that was followed by osteoclast activation, bone resorption and a transient decrease in bone density. While there was an early widening of the maxilla, significant widening occurred only after osteoclast activation and bone resorption. Bone formation was a delayed response that occurred after the initial catabolic phase. NSAIDs significantly decreased the magnitude of maxillary sutural widening and bone formation in response to transverse forces. During the transition from the catabolic to the anabolic response, expression of factors known as communicator molecules between osteoclasts and osteoblasts increased significantly.
Conclusions: We demonstrated that maxillary transverse forces stimulate three distinct phases in the mid-palatal suture: 1)The catabolic phase starts with inflammatory markers and osteoclast recruitment and activity, 2) The transition phase where osteoclasts activate osteoblast activity, 3) The anabolic phase, during which osteoblasts restore the integrity of the skeleton.