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Growth characteristics underlying retrogenia in pigs: A histomorphometric study THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Jeffrey Price, DDS Graduate Program in Dentistry The Ohio State University 2014 Master’s Examination Committee: Dr. Zongyang Sun, Advisor Dr. Katherine Vig Dr. Shiv Shanker Dr. Kelly Kennedy Copyright by Jeffrey Alan Price 2014 ABSTRACT Objectives: To establish an animal model for studying human retrogenia, this project characterized bone modeling activities at the symphyseal surfaces of juvenile pigs which normally lack chin projections. Material and Methods: Ten domestic pigs of two age groups (4- and 6-month-old) were included. Their symphyseal specimens 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; CI: concavity index; OI: osteoclast index) were obtained and tested by a multivariate two-way mixed model analyses of variance (MANOVA) for the differences between different symphyseal regions and ages. Results: Qualitatively, the labial and lingual surfaces were characterized by abundant mineral apposition and bone resorption, respectively. Quantitatively, measurements of the labial surface mineral apposition showed an interaction between the region and age factor (for MAR, p=0.127; for MAZ, p=0.012), indicating increase of mineral apposition with age at the inferior region. Measurements of bone resorption of the lingual surface showed the inferior-lingual region tended to have stronger resorption than the superior-lingual region (region*age interaction for OI, p=0.087; regional difference for CI, p= p=0.025). Conclusion: A ii possible explanation for retrogenia in pigs is that the entire labial surface is appositional and the growth differential between the superior and inferior labial regions is inadequate for developing a chin projection. The pig may be used as a reasonable animal model to study growth modification approaches for human retrogenia. iii Dedication Dedicated to my amazing wife Jessica and my parents Patti and Sid. Thank you for all of your support! iv Acknowledgements I would like to thank the following: My thesis committee, Zongyang Sun, Shiva Shanker, Kelly Kennedy, and Katherine Vig for their feedback and guidance during this project Boon Ching Tee for all her help with specimen preparation, data compilation and analysis The faculty, staff, alumni, and patients of The Ohio State University, College of Dentistry, Section of Orthodontics, who provided me with the best orthodontic education available anywhere My fellow residents, from whom I learned more than anyone My family, for their boundless love and support Delta Dental for the research grant that funded this project v Vita May 12th, 1985…………….Born-Columbus, OH 2007............................B.A., Ohio Wesleyan University, Delaware, OH 2011............................D.D.S., The Ohio State University, Columbus, OH 2011-2014 ..................Resident, Graduate Orthodontics Program, The Ohio State University Fields of Study Major Field: Dentistry Specialty: Orthodontics vi Table of Contents Abstract ..........................................................................................................ii Dedication .....................................................................................................iv Acknowledgements .......................................................................................v Vita ................................................................................................................vi List of Tables ................................................................................................viii List of Figures ...............................................................................................ix Chapter 1: Introduction and Literature Review .............................................1 Chapter 2: Materials and Methods .................................................................28 Chapter 3: Manuscript....................................................................................34 Chapter 4: Results..........................................................................................46 Chapter 5: Discussion ....................................................................................53 Bibliography .................................................................................................58 vii List of Tables Table 1. Measurements of growth rates and growth zones at the labial surface ........................... 48 Table 2. Concavity indexes and osteoclast indexes at the lingual surface ..................................... 50 viii List of Figures Figure 1. Left half of the mandible1 .................................................................................... 2 Figure 2. Internal aspect of Mandible (Right)1 ................................................................... 3 Figure 3. The origin of osteoclasts2 .................................................................................... 6 Figure 4. Lower Jaws of 3 species showing a chin projection in homo sapiens only10 ...... 7 Figure 5. Symphyseal development from birth to old age1 ................................................ 9 Figure 6. Clinical diagnosis of chin prominence23............................................................ 11 Figure 7. Classification of Chin based on Convexity23..................................................... 12 Figure 8. Landmarks and measurements of the symphyseal region24 .............................. 13 Figure 9. Adverse Reaction to Dermal Filler32 ................................................................. 16 Figure 10. Infection Post Chin Implantation33 .................................................................. 17 Figure 11. Capsular Contracture around a Silicone Implant and the Repair33 .................. 18 Figure 12. Failure to reattach mentalis muscle after implant removal33 ........................... 19 Figure 13. Bony Nonunion after Osseous Genioplasty33 .................................................. 20 Figure 14. Bone Resorption after Implant Placement33 .................................................... 21 Figure 15. Malposition of Chin Implant33 ........................................................................ 22 Figure 16. Under augmentation of the chin and the replacement chin implant33 ............. 23 Figure 17. Simulation showing how pig chin was separated from the mandible and divided into superior (S) and inferior (I) regions .............................................................. 29 Figure 18. Methods for histomorphometric analyses.. ..................................................... 31 Figure 19. Representative fluorescent and H&E images of symphyseal surfaces. ........... 47 Figure 20. Mean mineral apposition measurements from the lingual and labial surfaces 49 Figure 21. Mean bone resorption measurements from the lingual surface.. ..................... 51 Figure 22 Comparison between the symphyses of humans and pigs. ............................... 54 ix Chapter 1 INTRODUCTION Anatomy of the Chin The chin, or symphysis, is the most anterior part of the mandibular body. The mandibular body is U-shaped, has internal and external surfaces and is separated by upper and lower borders1. The chin is bordered superiorly by the alveolar bone and roots of the mandibular incisors and laterally by the mandibular body. The upper symphyseal surface sometimes shows a faint median ridge, which indicates fusion of the right and left halves of the fetal bone (symphysis menti)1. The ridge diverges inferiorly to enclose the triangular mental protuberance, which has a central depression at its base and mental tubercles on each side1(Figure 1). 1 Figure 1. Left half of the mandible1 The internal surface of the mandible is split by the mylohyoid line that extends from behind the third molars to the mental symphysis between the digastric fossae1(Figure 2). 2 Figure 2. Internal aspect of Mandible (Right)1 Below the mylohyoid line is the submandibular fossa and the area above it widens anteriorly into the triangular shaped sublingual fossa1. The posterior aspect of the symphysis is slightly elevated and is divided into upper and lower parts that contain the mental spines (genial tubercles)1. Superior to the mental spines, in most human mandibles, is a median pit that opens to a canal whose contents are ambiguous but is a useful radiological landmark1. 3 Histology of the Chin The chin is a bony structure, a specialized form of connective tissue that is made up of cells and extracellular matrix2, which together control bone growth, development, remodeling and repair. The main types of cells present in bone are osteoblasts, osteocytes, bone-lining cells, and osteoclasts. The first three are differentiated from the same ancestor cells--mesenchymal stem cells, but differ from each other in differentiation stages. These cells mainly contribute to osteogenesis, a process of new bone formation, which is pertinent to normal bone function2. Mesenchymal stem cells are abundantly present in bone marrow and they have the potential to differentiate into osteoblasts, fibroblasts, chondrocytes, adipocytes, and muscle cells upon proper inductions from other cells