title: [Histological changes in the circum-maxillary sutures during alternate maxillary expansions and constrictions in a rat model].
abstract: OBJECTIVE
  To investigate changes in the circum-maxillary sutures during alternate maxillary expansions and constrictions in a rat model.
  
  
  METHODS
  Twenty-two male Sprague-Dawley rats (6 weeks old) were used and divided into three groups. In maxillary expansion (ME) group (n=9), an expander was activated for 5 d, and then sacrificed. In alternate maxillary expansions and constrictions (Alt-MEC) group (9 animals), an alternate expansion and constriction protocol (5 d expansion and 5 d constriction for one cycle) was conducted for 2.5 cycles (25 d total), and then sacrificed. The control group comprised 4 animals with no appliances used, each of two sacrificed on day 5 and day 25, respectively. Circum-maxillary sutures (mid-palatal, maxillopalatine, premaxillary, zygomaticotemporal, and frontonasal suture) in each group were characterized histologically.
  
  
  RESULTS
  Histological findings of circum-maxillary sutures: in control group, the normal sutures were divided into 5 zones, the center was polygon mesenchyme zone, the lateral was mature chondrocyte zone, the next lateral was bone tissue. In ME group, the mid-palatal suture was expanded after ME, the fibre and connective tissue were extracted and invaded into cartilage zone. Osteoblast hyperplasia and new bone formation occurred. The orientation of the new bone trabecula was consistent with force. The osteoclast appeared in some area. Findings of other sutures were similar with those of control group, osteogenesis was active in some area without obvious reconstruction in Alt-MEC group, mid-palatal suture and other sutures in some area were widened after Alt-MEC with much more osteoblast hyperplasia and new bone formation. Fibre and connective tissue were extracted, distorted or even broken. Sutures in some areas were narrowed with osteoblast cytopenia and osteoclast hyperplasia. Fibre and connective tissue compressed because of the different force and orientation. Osteoclast count results showed that compared with the control group, the number of the osteoclast was increased only in the palatal suture in ME group (P<0.05). Other sutures did not show obvious changes (P>0.05). In Alt-MEC group, the numbers of the osteoclast in circum-maxillary sutures were the most, and had statistical significances (P<0.05).
  
  
  CONCLUSIONS
  These RESULTS suggested that circum -maxillary sutures were actively reconstructed after Alt-MEC. while only midpalatal suture had active reaction after ME.
authors.affiliation: Department of First Dental Center, Peking University School and Hospital of Stomatology, Beijing 100034, China.
authors.forename: Guang-yao
authors.initials: GY
authors.lastname: Feng
authors.affiliation: Department of Orthodontics, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Bing-shuang
authors.initials: BS
authors.lastname: Zou
authors.affiliation: Department of Orthodontics, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Xue-mei
authors.initials: XM
authors.lastname: Gao
authors.affiliation: Department of Orthodontics, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Xiang-long
authors.initials: XL
authors.lastname: Zeng
mesh_terms: D000818:Animals; D003250:Constriction; D003393:Cranial Sutures; D008297:Male; D008437:Maxilla / Q000254:growth & development*; D010006:Osteoblasts / Q000166:cytology; D010012:Osteogenesis; D010155:Palatal Expansion Technique; D010159:Palate; D051381:Rats; D017207:Rats, Sprague-Dawley