title: Osseointegration of orthodontic micro-screws after immediate and early loading.
abstract: OBJECTIVE
  To investigate the desirable healing time of micro-screws by histomorphologic and histomorphometric evaluations of osseointegration after immediate and early loading.
  
  
  METHODS
  Fifty-four micro-screws were bilaterally placed in the maxillary premolar regions of nine beagles. Then the micro-screws with various healing time of 0 day (0D group), 2 weeks (2W group), and 4 weeks (4W group) were loaded with an orthodontic force (100 g) for 8 weeks. The direction of the orthodontic force was vertical to the long axis of the micro-screws. Hard tissue sections containing micro-screws were prepared for histomorphologic and histomorphometric evaluations.
  
  
  RESULTS
  The survival rate of the micro-screws in this study was 100%. Bone remodeling, close contact bone-implant interface, and endochondral ossification were observed in all osseous specimens. Activated osteoblasts aggregated to the bone-implant interface of the 4W group, and lamellar bone was found in the peri-implant regions. Micro-screws of the 2W group were partially surrounded by collagen fibers; and neonatal lines of bone, woven bone, and osteoclasts were found in the peri-implant regions. Micro-screws of the 0D group were surrounded by more collagen fibers compared with the other two groups. Bone implant contact ratios of the three groups were 43.74% (0D group), 66.26% (2W group), and 73.28% (4W group), respectively and statistical differences were significant (ANOVA, P < .01).
  
  
  CONCLUSIONS
  All micro-screws in the three groups can provide stable orthodontic anchorage. However, to obtain improved stationary anchorage, a 4-week healing time is recommended before orthodontic loading.
authors.affiliation: State Key Laboratory of Oral Diseases, West China Stomatological Hospital, Sichuan University, Sichuan, PR China.
authors.forename: Linkun
authors.initials: L
authors.lastname: Zhang
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhao
authors.forename: Yu
authors.initials: Y
authors.lastname: Li
authors.forename: Jiapei
authors.initials: J
authors.lastname: Wu
authors.forename: Leilei
authors.initials: L
authors.lastname: Zheng
authors.forename: Tian
authors.initials: T
authors.lastname: Tang
mesh_terms: D000539:Alveolar Process / Q000601:surgery; D000704:Analysis of Variance; D000818:Animals; D001863:Bone Screws; D003799:Dental Stress Analysis; D004285:Dogs; D008297:Male; D008437:Maxilla / Q000601:surgery; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D016348:Osseointegration; D018709:Statistics, Nonparametric; D013997:Time Factors; D014945:Wound Healing