Stress-mediated Apoptosis In The Expansion Of Rat Palatal Seam In The Role Of The Tissue Remodeling Process

Part 1The sequence of histological changes of midpalatal sutureresponse to maxillary expansion in the of the growing ratObjective To study the sequence of histological changes and regularityof midpalatal suture osteogenesis during maxillary expansion.Methods Fifty-five four-week-old male wistar rats were randomlydivided into five experimental groups and six control groups (5 rats ineach group). In the experimental groups, rectangular appliances with twohelical loops were set between the right and left upper molars to expandthe midpalatal suture. The initial force was adjusted to 50 g, measuredwith a strain gauge (Dentaurum, Germany). Two days later, 50 gexpansion force was added on the appliance. Another two days later, thetwo helical loops were fixed with acrylic resin. The rats were sacrificedon 0 d, 1 d, 2 d, 4 d, 7 d and 11 d days after the start of activationrespectively. Sections were cut perpendicular to the midpalatal suture andstained with hematoxylin and eosin for observation of celluar response.Immunostained with anti-osteocalcin for evaluation of bone formation.The changes of collagen were observed through Masson staining.Results One day after the force was applied, the pre-existingcartilaginous cell layers were laterally displaced. Stretched mesenchymalcells were arranged parallel to the expansion force and osteoblasts differentiation were detected. Two days expansion period later, a greatamount of osteoblasts and fibroblasts proliferated. After the helical loopswere fixed for three days, lots of proliferation cells arranged parallel tothe margin of the suture. Another four days retention later, new boneformation was observed as digitation on the inner lateral side of thepre-existing cartilaginous cell layers.Conclusion The bone formation mechanism can be altered fromendochondral ossification in normal palatal suture to intramembranousosteogenesis on the inner lateral side of the pre-existing cartilaginous celllayers by the expansion force.Part 2A series of apoptosis cells expression in response to themaxillary expansion of rat midpalatal sutureObjective To investigate the expression of apoptosis cells in midpalatalsuture in response to the maxillary expansion of the growing rats.Methods Fifty-five four-week-old male wistar rats were randomlydivided into five experimental groups and six control groups (5 rats ineach group). In the experimental groups, rectangular appliances with twohelical loops were set between the right and left upper molars to expand the midpalatal suture. The initial force was adjusted to 50 g, measuredwith a strain gauge (Dentaurum, Germany). Two days later, 50 gexpansion force was added on the appliance. Another two days later, thetwo helical loops were fixed with acrylic resin. The rats were sacrificedon 0 d, 1 d, 2 d, 4 d, 7 d and 11 d days after the start of activationrespectively. Paraffin sections (5μm) were prepared and apoptosis cellswere detected by fluorimetric TUNEL system counterstained withpropidium iodide (PI) according to the assay protocol.Results The expression of apoptosis cells in the experiment groupincreased significantly in 1 day group and reduced slightly in 2 day group,then increased again in 4 day group after 50 g expansion force added. In 7day group and 11day group, the expression and distribution of apoptosiscells was similar. Furthermore, apoptosis cells were observed accompanyto the proliferation cells.Conclusion The results indicated that apoptosis can be induced byexpansion force and it may play a role in the signal pathway of boneremodeling during maxillary expansion.