Miniature pigs as an animal model for implant research: bone regeneration in critical-size defects Baerbel Ruehe, DVM, a Stefan Niehues, DMD, b Susanne Heberer, DDS, a and Katja Nelson, DDS, PhD, a Berlin, Germany CHARITÉ-CAMPUS VIRCHOW CLINIC Objective. Standardized experimental investigations determining the critical-size defect (CSD) in the mandible of miniature pigs are still lacking. The aim of the present study was to obtain information about the new bone formation in created defects of varying sizes. Study design. Marginal resection of the alveolar crest of the lower jaw was performed in 3 female miniature pigs. The animals used in the study were 3 years of age and weighed 55 kg. For histologic evaluation the dental implants were harvested with the surrounding bone tissue 10 weeks after implant placement. For this, bone segments including the implants were removed from each side of the mandible. The sizes of the resected bone blocks varied, showing the following volumes: 10.1 cm 3 , 4.2 cm 3 , and 1.9 cm 3 . Periosteal coverage of the defects was performed. Computerized tomography (CT) of the skull of the miniature pig was performed immediately after the surgical procedure as well as 6 weeks later using a 64-channel mult-slice scanner. Results. The CT showed that 6 weeks after obtaining the biopsies, the filling of the defects with new bone varied. The percentage of newly formed bone in relation to the size of the original defect was 57.4% for the small- and 87.2% for the middle-sized defect. The large-sized defect showed 75.5% newly formed bone compared with baseline. Conclusion. Considering the amount of new bone formation found within this study, it is questionable if the critical defect size of 5 cm 3 stated in the literature is valid. Further research concerning the mandibular model in minipigs is required and more refinement needed to assure a standardized CSD, allowing qualitative and quantitative evaluation of bone grafts and bone graft substitutes. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:699-706) The development and modification of dental implants and heterologous materials has been performed for many years with the effort to create an optimal inter- action between the bone and the implanted material. To determine whether a newly designed dental implant or material conforms to the requirement of biocompatibil- ity, mechanical stability, and safety, it must undergo rigorous testing both in vitro and in vivo. For this reason the use of animal models is often essential in testing dental implants and materials before clinical application in humans. 1 Although animal models may closely represent the mechanical and physiologic hu- man clinical situation, it should be remembered that they reflect only approximations, with each animal model having unique advantages and disadvantages. After all, the ultimate goal of the use of an animal model is to transfer the obtained results to clinical practice. The pig demonstrates similarities to human bone regarding anatomy, morphology, healing, and re- modeling and is considered to be closely representative to human bone and therefore a suitable species of choice. 2 The microstructure of the bone in pigs is described as having a lamellar bone structure which is similar to that of humans. 3 Porcine bone also shows similarities in bone mineral density and bone mineral concentration to human bone. 4 Commercial breeds of pigs are generally considered to be undesirable for research owing to their large growth rates and excessive final body weight. Besides, pigs are often difficult to handle, noisy, and aggressive. However, the develop- ment of miniature pigs has overcome these problems regarding weight and handling to some extent, so that the use of these animals is a common model in the domain of dental implant research, as several studies have shown. 5-8 Some investigators also chose miniature pigs as an appropriate animal model for maxillofacial bone re- search. 9-11 The development and eventual clinical ap- plication of new bone repair materials (BRMs) requires strict adherence to scientific methodology. 12 A prereq- a Department of Oral and Maxillofacial Surgery. b Department of Radiology. Received for publication Nov 10, 2008; returned for revision May 12, 2009; accepted for publication Jun 29, 2009. 1079-2104/$ - see front matter © 2009 Published by Mosby, Inc. doi:10.1016/j.tripleo.2009.06.037 699 Vol. 108 No. 5 November 2009 ORAL AND MAXILLOFACIAL IMPLANTS