Assessment of compression and strength of divergent screws mounted on miniplates for fixation of mandibular fractures: an in vitro experimental study

Macaca mulatta is a good model for human mandibular fixation research

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.

Effect of compression on mandibular fracture haematoma-derived cells

Mechanical stress induces a variety of biochemical and morphological reactions in bone cell biology. This study aimed to investigate appropriate pressures of osteogenesis on the biological responses of 3-dimensional cultured human mandibular fracture haematoma-derived cells by compressive loading. Six patients with mandibular fractures who underwent open reduction and internal fixation were included in the study. During the operation, fracture haematomas that formed fibrin clots were manually removed before irrigation. First, pressures were applied to human mandibular fracture haematoma-derived cell-seeded collagen sponges. The sponges were subjected to mechanical compression using loading equipment applied at no compression, 0.5, or 1 mm. Compressive loading was applied to the samples prior to compression for 0, 6, 12, or 24 hours. Collagen sponge samples were collected for quantification of mRNA using several parameters including alkaline phosphatase (ALP), osteopontin (OPN), osterix (OSX), runt-related gene 2 (RUNX2), protein level, and immunocytochemistry (anti-sclerostin). Among these the 0.5 mm compression group compared with the control and 1.0 mm compression groups upregulated mRNA expression of OPN and OSX after 24 hours. Additionally, compared with the control group, a significantly higher OSX gene expression was observed in both the 0.5 mm and 1.0 mm groups after 6, 12, and 24 hours of compression (p < 0.05). However, no significant differences were observed regarding ALP and RUNX2 expression. These results indicated increased stimulation of osteogenesis of the mandibular fracture-line gap in the 0.5 mm compression group compared with the control and 1.0 mm compression groups.

Assessment of compression and strength of divergent screws mounted on miniplates and dynamic compression plate in fixation of mandibular body fractures: an in vitro study

Achieving compression in the fracture line gap by open reduction and internal fixation leads to more primary bone healing and therefore hastens the healing process and patient's rehabilitation. We aimed to evaluate the application of compression by a modification in screw insertion in miniplates to improve the efficiency of the previous relevant methods. In this in vitro experimental study 20 sheep hemimandibles were prepared. Following intentional fracturing of the hemimandibular bodies, the specimens were divided into two: the control and study groups (n=10 each). The control group was fixed with straight four-hole dynamic compression plate (DCP) without a bar and with parallel screws. The study group was fixed with a straight four-hole miniplate without a bar. Screws were divergently inserted into the bone with an angle of 45°. The differences in the fracture line gap were measured before and after fixation considering the indicators of compression. The strength of the fixation was also assessed with a universal testing machine. The control group provided more compression than the study group (p=0.4). There was no difference in the strength of fixation between the two groups. It is concluded that the application of the miniplates with divergent screws instead of DCP could encompass the advantages of both perspectives such as intraoral incisions and compressive force and prevent the disadvantages of compression plates such as hard adaptation.