Are critical size bone notch defects possible in the rabbit mandible?

Abstract

Objectives Small animal maxillofacial models, such as non-segmental critical size defects (CSDs) in the rabbit mandible, need to be standardized for use as preclinical models of bone regeneration to mimic clinical conditions such as maxillofacial trauma. The objective of this study is the establishment of a mechanically competent CSD model in the rabbit mandible to allow standardized evaluation of bone regeneration therapies. Materials and Methods Three sizes of bony defect were generated in the mandibular body of rabbit hemi-mandibles: 12 mm×5 mm, 12 mm×8 mm, and 15 mm×10 mm. The hemi-mandibles were tested to failure in 3-point flexure. The 12 mm×5 mm defect was then chosen for the defect size created in the mandibles of 26 rabbits with or without cautery of the defect margins and bone regeneration was assessed after 6 and 12 weeks. Regenerated bone density and volume were evaluated using radiography, micro-computed tomography, and histology. Results Flexural strength of the 12 mm×5 mm defect was similar to its contralateral; whereas the 12 mm×8 mm and 15 mm×10 mm groups carried significantly less load than their respective contralaterals ( P <0.05). This demonstrated that the 12 mm×5 mm defect did not significantly compromise mandibular mechanical integrity. Significantly less ( P <0.05) bone was regenerated at 6 weeks in cauterized defect margins compared to controls without cautery. After 12 weeks, the bone volume of the group with cautery increased to that of the control without cautery after 6 weeks. Conclusion An empty defect size of 12 mm×5 mm in the rabbit mandibular model maintains sufficient mechanical stability to not require additional stabilization. However, this defect size allows for bone regeneration across the defect. Cautery of the defect only delays regeneration by 6 weeks suggesting that the performance of bone graft materials in mandibular defects of this size should be considered with caution.

Hydrogel-chitosan and polylactic acid-polycaprolactone bioengineered scaffolds for reconstruction of mandibular defects: a preclinical in vivo study with assessment of translationally relevant aspects

“…However, since bone regeneration is hypothesized to start from the bony edges of the defect, the surface of healing bone (i.e., the drilled bony surface in the surgical bed) should also be considered to genuinely de ne critical size defects. Periosteal removal and cauterization of defect edges should also be considered as factors challenging bone regeneration [52]. Irrespective of the non-critical size of the defects studied herein, it should be noted that non-reconstructed defects did not heal completely over 4 months.…”

Mandible Biomechanics and Continuously Erupting Teeth: A New Defect Model for Studying Load-Bearing Biomaterials

“…This was seen in the rat with more rapid diminution of the defect volume that was exposed to the reserve crown of the incisor (Figure 6) and in the rabbit when the defect was exposed to the reserve crowns of the cheek teeth (Figure 10). Others have reported similar phenomena in rabbit mandible defects in close proximity to reserve crowns [11]. Due to the way elodont dentition is formed, such a defect is problematic if the intent is to test an implant with bone-forming potential.…”

“…For five of the rabbits the defect location was similar to the rat; in the anterior ramus just posterior to the tooth-bearing mandible body (Figure 2C). The other defect was in the tooth-bearing mandible body and conforms to the conventional defect commonly used by investigators studying bone replacement materials in the rabbit mandible [11][12][13][14]. Rabbits were administered buprenorphine for analgesia and anesthetized by acepromazine and midazolam followed by intubation and administration of isoflurane during the procedure.…”

Investigation of Bone Regeneration Efficacy of New Bovine Bone Minerals in a Canine Mandibular Critical Defect Model

“…Unlike long bone fractures, maxillofacial bone fractures occur due to automobile accidents, bicycle accidents, fall injuries, gunshot wounds, or various traumatic injuries. [7,8] Large defects usually occur in the maxillofacial bone following these injuries, whereas the mandible is mostly affected. The prevalence of facial fractures was reportedly 15% in the pediatric population and ≈8% in children aged 12 years.…”