Comparative characterization of maxillary expansion and alternate maxillary expansions and constrictions in rats.

The purpose of this study was to evaluate whether the cranial and circumaxillary sutures react differently to maxillary expansion (ME) and alternate maxillary expansions and constrictions (Alt-MEC) in a rat model. Twenty-two male Sprague-Dawley rats (6 weeks old) were used and divided into three groups. In ME group (n=9), an expander was activated for 5 days. In Alt-MEC group (9 animals), an alternate expansion and constriction protocol (5-day expansion and 5-day constriction for one cycle) was conducted for 2.5 cycles (25 days total). The control group comprised 4 animals with no appliances used, each of two sacrificed on day 5 and day 25 respectively. Midpalatal suture expansion or constriction levels were assessed qualitatively and quantitatively by bite-wing X-rays and cast models. Distances between two central incisors and two maxillary first molars were measured on cast models after each activation. Circumaxillary sutures (midpalatal, maxillopalatine, premaxillary, zygomaticotemporal and frontonasal suture) in each group were characterized histologically. Results showed that midpalatal suture was widened and restored after each expansion and constriction. At the end of activation, the widths between both central incisors and first molars in Alt-MEC group were significantly larger than those in ME group (P<0.05). Histologically, all five circumaxillary sutures studied were widened in multiple zones in Alt-MEC group. However, only midpalatal suture was expanded with cellular fibrous tissue filling in ME group. Significant osteoclast hyperplasia was observed in all circumaxillary sutures after alternate expansions and constrictions, but osteoclast count increase was only observed in midpalatal suture in ME group. These results suggested that cranial and circumaxillary sutures were actively reconstructed after Alt-MEC, while only midpalatal suture had active reaction after ME.