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Monocortical Mini- and Microplate Osteosynthesis
M. Champy
Biomechanical Principles
The biomechanical principles of monocortical miniplate osteosynthesis are based on mathematical and experimental studies performed in Strasbourg, France, by the Group d‘Etudes en Biomécanique Osseuse et Articulaire de Strasbourg (GEBOAS). This research work, which concerned the mandible only, resulted in the development of a tension bending osteosynthesis system, able to guarantee fracture healing with neither maxillomandibular fixation nor interfragmental compression. This was achieved as a result of the following considerations and experiments.
Goals
The ideal method of treatment of mandibular fractures is one that establishes a functional therapy by movement. Therefore, it should aim for:
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perfect anatomical reduction
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complete and stable fixation, allowing painless mobilization of the injured region
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maintenance of the blood supply of the fragments, of the fracture surfaces and of the surrounding tissues
The biomechanical requirements for optimal osteosynthesis are
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the plates and screws must withstand the various stresses due to those tensile and torsional forces to which the mandibular bone is typically subject
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the plates have to be malleable for easy adaptation to the bone surface, especially in the curved symphysis and molar region, to secure anatomical reduction and to restore perfect dental occlusion
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the dimensions of the plates should ensure minimal periosteal elevation and fracture site exposure; furthermore, the oral mucosa must be able to cover the plate without any difficulty; and finally
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the size of the screws has to be appropriate for the thickness of the cortex.
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Fig. 1 Forces exerted on the mandible
Throughout the body of the mandible, biting forces produces tension (dashed line)
forces at the upper border and compressive (solid line) forces at the lower border. Torsion forces are produced anterior to the canines (dotted line).
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Fig. 2 The ideal osteosynthesis position and ideal osteosynthesis line on the mandibular body |
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Fig. 3 Osteosynthesis position on the mandibular body with a comminuted fracture and a displaced basal triangle segment
The small fragment may be replaced in anatomic position between larger mandibular segments so that the compressive forces at the lower border can reestablish the physiological strains when the miniplate neutralizes the distraction forces at the upper border. The fracture on the mandibular angle is fixed on the inner surface of the external oblique line.
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Fig. 4 Elective zones of miniplate osteosynthesis
Favorable regions are colored blue. The red zone is a region where microplates can be used. The green zone is a region where micro- or miniplates can be used. |
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