Macaca mulattais a good model for human mandibular fixation research

Abstract

Biomechanical and clinical studies have yet to converge on the optimal fixation technique for angle fractures, one of the most common and controversial fractures in terms of fixation approach. Prior pre-clinical studies have used a variety of animal models and shown abnormal strain environments exacerbated by less rigid (single-plate) Champy fixation and chewing on the side opposite the fracture (contralateral chewing). However, morphological differences between species warrant further investigation to ensure that these findings are translational. Here we present the first study to use realistically loaded finite-element models to compare the biomechanical behaviour of human and macaque mandibles pre- and post-fracture and fixation. Our results reveal only small differences in deformation and strain regimes between human and macaque mandibles. In the human model, more rigid biplanar fixation better approximated physiologically healthy global bone strains and moments around the mandible, and also resulted in less interfragmentary strain than less rigid Champy fixation. Contralateral chewing exacerbated deviations in strain, moments and interfragmentary strain, especially under Champy fixation. Our pre- and post-fracture fixation findings are congruent with those from macaques, confirming that rhesus macaques are excellent animal models for biomedical research into mandibular fixation. Furthermore, these findings strengthen the case for rigid biplanar fixation over less rigid one-plate fixation in the treatment of isolated mandibular angle fractures.

Dynamic finite element modelling of the macaque mandible during a complete mastication gape cycle

“…While our study was conducted on a rhesus macaque, similarities in feeding mechanics and bone strains between macaques [5,6,38,46], chimpanzees [8] and humans [9,34,47] make our findings and methods relevant to broader anthropological and oral and maxillofacial research. Most previous comparative, anthropological studies of the relationship between diet and mandible morphology have focused on the cross-sectional morphology of the symphysis and corpus, or on the shape of the mandibular condyle [46,[48][49][50][51][52].…”

“…Finite element models (FEMs) combined with rigid-body analysis have been used to study the function of the temporomandibular joint (TMJ) in humans [32,33], but to the best of our knowledge they have not been used to study mandibular strain, loading and deformation regimes during feeding. Instead, early research on the human and non-human primate mandible used three-dimensional static FEMs to study the mechanical behaviour of the feeding system and to test hypotheses on the role of food in species diversification and on adaptive specializations to environmental resources [5][6][7][8][9][10][34][35][36][37]. To determine how mastication on foods with different material properties affects deformation and strain regimes in the macaque mandible, we previously applied muscle force loading regimes recorded while the animal was chewing on three different food types (fresh grapes with skin, shelled nuts, dried fruits) to a series of subject specific, validated and static FEMs [5,6].…”

“…The medial prominence, torus triangularis and endocondylar ridge constitute the load path from the bite point to the balancing-side ramus and are probably important mandible features with which to infer function (diet) from form (shape) in macaques [ 5 ]. Similarities in feeding mechanics between chimpanzees, macaques and humans suggest that this may also be the case in living and fossil hominids [ 5 , 8 , 9 ].…”