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

Abstract

Animals with elodont dentition and unfused mandible symphyses are hypothesized to have symmetric incisor morphology. Since these animals maintain their teeth by gnawing, they may provide physiologic feedback on mechanical function when unilateral mandible defects are created that manifest as ipsilateral changes in tooth structure. This defect model would potentially generate important information on the functional/mechanical properties of implants. Rats’ and rabbits’ mandibles and teeth are analyzed with µCT at baseline and post-intervention (n = 8 for each). Baseline incisors were compared. In a unilateral mandible pilot study, defects—ranging from critical size defect to complete ramus osteotomies—were created to assess effect on dentition (rats, n = 7; rabbits, n = 6). Within 90% confidence intervals, animals showed no baseline left/right differences in their incisors. There are apparent dental changes associated with unilateral defect type and location. Thus, at baseline, animals exhibit statistically significant incisor symmetry and there is an apparent relationship between mandible defect and incisor growth. The baseline symmetry proven here sets the stage to study the degree to which hemi-mandible destabilizing procedures result in measurable & reproducible disruption of dental asymmetry. In a validated model, an implant designed to function under load that prevents incisor asymmetry would provide supporting evidence that the implant has clinically useful load-bearing function.

Determination of critical-sized defect of mandible in a rabbit model: Micro-computed tomography, and histological evaluation

“…The advantages of rat models are lower cost and convenience, which includes ease of housing and care. However, the limitations in body size and bone mass make them unsuitable for studying the osteogenic ability of materials, and the differences in relative osteogenic speed make them unsuitable for direct extrapolation in the patient populations [ 31 ]. As for large animals such as dogs, goats, and pigs, their use is limited by their high prices and farming conditions, and their special status as human companions raises more ethical questions.…”

“…Meanwhile, rabbits rank first among all animals used for musculoskeletal research [ 3 ]. The rabbit mandible is physically larger than the rat mandible, making surgical procedures less technically demanding [ 31 ]. Thus, a suitable mandibular defect with enough volume to support a potential synthetic scaffold can be created in rabbits.…”

“…Importantly, rabbits appear to exhibit basic multicellular unit remodelling that is naturally occurring (similar to that in humans). Moreover, rabbits have a cortical bone modulus and strength that are more similar than other animals to humans [ 31 ]. All these factors make rabbits more suitable for bone regeneration research studies.…”

“…On the other hand, avoiding interference with ischemia stemming from the bone defect areas is important in establishing mandibular bone defect models. The presence of the periosteum and neurovascular bundle has been proven to play an important role in the repair of CSDs [ 29 , 31 ]. In the present study, the periosteum and the mental nerve were carefully preserved during defect creation, which prevented the loss of local blood circulation from affecting the process of osteogenesis in the CSD region.…”

Bilateral double site (calvarial and mandibular) critical-size bone defect model in rabbits for evaluation of a craniofacial tissue engineering constructs

“…Alternatively, rabbits are a more suitable option with a short breeding cycle, being easy to handle, similar structure and composition to that of human mandibles and a high tolerance for mandible defects [ 4 , 17 ]. In practical terms, the sufficient volume of alveolar bone in the premolar and/or molar areas in rabbits, which allows for developing a suitable mandibular defect [ 18 , 19 ], gives it another advantage as a jawbone CSD model.…”