title: Growth characteristics underlying the lack of a chin in pigs: a histomorphometric study.
abstract: OBJECTIVE
  Despite similar mandibular growth to that of humans, pigs lack a chin projection as shown in most humans. To understand whether this divergence is contributed to differences in local symphyseal growth, this project characterized bone modeling activities at the symphyseal surfaces of juvenile pigs.
  
  
  METHODS
  Symphyseal specimens from two age groups (4- and 6-month-old, n = 10) were processed into histological sections with and without decalcification, which were assessed for surface mineral apposition and bone resorption, respectively. In a blinded fashion, measurements of four parameters (MAR: mineral apposition rate, MAZ: mineral apposition zone, ES/BS: eroded surface and OC.N/BS: osteoclast number) were obtained and tested by a multivariate two-way mixed-model analyses of variance (manova) for the differences between symphyseal regions and ages.
  
  
  RESULTS
  Qualitatively, pig symphyseal labial and lingual surfaces were horizontally oriented and characterized by mineral apposition and bone resorption, respectively. Quantitatively, labial mineral apposition tended to be greater rostrally than caudally at 4 months, which became greater caudally than rostrally at 6 months (region/age interactions: p = 0.127 for MAR, p = 0.012 for MAZ). Lingual bone resorption tended to be greater caudally than rostrally, but only ES/BS measurements were significant (p = 0.039) regardless of age, while OC.N/BS measurements varied with ages and regions (age/region interaction, p = 0.087).
  
  
  CONCLUSIONS
  Insufficient differential in symphyseal surface modeling between the labial-caudal and labial-rostral regions contributes to the lack of chin projection in the pig.
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: J
authors.initials: J
authors.lastname: Price
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: B C
authors.initials: BC
authors.lastname: Tee
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: K
authors.initials: K
authors.lastname: Vig
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shanker
authors.affiliation: Division of Oral and Maxillofacial Surgery, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kennedy
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Sun
mesh_terms: D000367:Age Factors; D000818:Animals; D016723:Bone Remodeling / Q000502:physiology; D001862:Bone Resorption / Q000473:pathology / Q000503:physiopathology; D002113:Calcification, Physiologic / Q000502:physiology; D002452:Cell Count; D002680:Chin / Q000033:anatomy & histology / Q000254:growth & development*; D005260:Female; D005456:Fluorescent Dyes; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008334:Mandible / Q000033:anatomy & histology / Q000254:growth & development*; D023421:Models, Animal; D010010:Osteoclasts / Q000473:pathology; D010012:Osteogenesis / Q000502:physiology; D013552:Swine
chemical_list: D005456:Fluorescent Dyes
keywords: Sus scrofa; bone formation; chin; histology; osteogenesis