1 Tissue Engineering Critical-Sized Bone Defects in Mandible of Canine Model (doi: 10.1089/ten.TEA.2016.0241) This paper has been peer-reviewed and accepted for publication, but has yet to undergo copyediting and proof correction. The final published version may differ from this proof . Critical-Sized Bone Defects in Mandible of Canine Model Sepanta Hosseinpour 1 , Farshid Bastami 2 1. Dental and MPH Student, Students’ Research Office, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2. School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Abstract One of the major challengeable issues in bone tissue engineering is regeneration of critical-sized bone defects (CSBD). According to bone formation results of the article conducted by Liu et al "Mesenchymal stem cells systemically injected into femoral marrow of dogs home to mandibular defects to enhance new bone formation. Tissue Engineering Part A. 2014;20(3-4):883-92", we can conclude that creating the correct defect form and interrupting the natural bone healing cascade can be essential as well as creating the accurate defect size to have a true CSBD in animal model of the research. Keywords: critical-sized bone defects, canine model, mandibular bone defect, bone tissue engineering Regeneration of critical-sized bone defects (CSBD) is one of the major challengeable issues in bone tissue engineering. The minimal size of CSBD is different with regard to various bones of different animal species. It is acceptable that the rate of newly bone formed in a CSBD could not be more than 10% during the life time of the animal (1). According to the literature, segmental mandibular CSBD in canine model greater than 15mm demonstrated minimal amount of newly bone formed from the defects edge even after 6 months (2). However, we read with great interest the article conducted by Liu et al "Mesenchymal stem cells systemically injected into femoral marrow of dogs home to mandibular defects to enhance new bone formation. Tissue Engineering Part A. 2014;20(3-4):883-92". According to this study, although mandibular bone defects had similar size with defined CSBD , the results of new bone formation in empty defects could be arguable (3). For instance, the rate of new bone formation, calculated regarding the below equation from figure4 of this study, in empty defects was approximately about 14% in the defects only after 6 weeks; New bone formation(%): 100 0 1   A A In which A 1 is the area of under the curve of figure4 and A 0 is the defect width multiplied by the defect depth. In fact, the defect form created by Liu et al was Tissue Engineering © Mary Ann Liebert, Inc . DOI: 10.1089/ten.TEA.2016.0241 Page 1 of 2 Tissue Engineering Part A Critical-Sized Bone Defects in Mandible of Canine Model (doi: 10.1089/ten.TEA.2016.0241) This article has been peer-reviewed and accepted for publication, but has yet to undergo copyediting and proof correction. The final published version may differ from this proof.