Rapid palatal expansion: Part 1. Mineralization pattern of the midpalatal suture in cats

The mineralization pattern of the midpalatal suture after rapid palatal expansion was investigated in 10 treated and 2 control cats, in light of the tendency of RPE to relapse. The rapid palatal expansion treatment consisted of active (25 days), retention (60 days), and relapse (60 days) phases. Standardized occlusal radiographs were taken periodically and analyzed for suture width, suture optical density in anterior vs. posterior regions, and suture area measurements of radiopaque vs. radiolucent zones. Nine cats exhibited suture splitting. During the active phase, the radiolucent zone (nonmineralized tissue) increased 12-fold and the increase in optical density was 50% greater in the anterior over the posterior suture region, demonstrating increased formation of loose connective tissue at the anterior region. During the retention period, the suture's radiopaque zone (mineralized tissue) increased by 62%, the radiolucent zone declined (64%) and the suture width decreased (65%) indicating reorganization of mineralized tissue. The decrease in optical density (increased mineralization) was 2.5 times greater in the posterior over the anterior suture region, indicating that the remineralization (closure) pattern of the expanded suture is analogous to a zipper closed in a posteroanterior direction. During the relapse phase, the reduction in total suture area (41%) and in the radiopaque zone (32%) indicates medial convergence of the maxillary horizontal processes. From our findings we extrapolated that the retention of the suture anterior region should be longer than the posterior region to catch up the lag in rebuilding and maturation of the newly deposited hard tissue.