A 3-dimensional finite-element analysis investigating the biomechanical behavior of the mandible and plate osteosynthesis in cases of fractures of the condylar process. 2002

Arne Wagner, and Wolfgang Krach, and Kurt Schicho, and Gerhard Undt, and Oliver Ploder, and Rolf Ewers
University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna, Austria. arne.wagner@univie.ac.at

OBJECTIVE The condylar region is one of the most frequent sites for mandibular fractures, with direct application of miniplates being the most commonly used open-fixation technique today. Yet, anatomic and biomechanical limitations continue to make this application technically challenging with a considerable complication rate. We sought to analyze such incongruencies with respect to the complex biomechanical behavior of the mandible. METHODS Individual human mandible geometry, the specific bone density distribution, and the position and orientation of the masticatory muscles were evaluated by performing computed tomography scans and a sequential dissection of the cadaver mandible. Three-dimensional finite-element analysis was performed for different fracture sites, osteosynthesis plates, and loading conditions. RESULTS Osteosynthesis of fractures of the condylar neck with 1 or 2 miniplates of a diameter of 2.35 x 1.00 mm was found to be an insufficient fixation method. This also applies for plates (3.60 x 1.54 mm), according to Pape et al,(8) when used in singular fashion (high condylar neck fractures excepted). In cases of singular occlusal contacts in the molar region (particularly at the contralateral side of the fracture), the highest stress values inside the mandible and osteosynthetic devices could be observed. With even the static yield limit of titanium being exceeded in such cases, consecutive rapid failure of the miniplates becomes most likely when loading of the condylar region caused by bite forces cannot be prevented. CONCLUSIONS We strongly recommend the use, whenever possible, of 2 plates in the manner described by Pape et al(8) for osteosynthesis of fractures of the condylar neck in combination with bicortically placed screws. The stiffness of a singular osteosynthesis plate made of titanium in a diametrical dimension of approximately 5.0 x 1.75 mm was found to be equivalent to the physiological bone stiffness in the investigated fracture sites. The actual stiffness of such a fixation plate is approximately 3 times higher than the stiffness of devices commonly in use.

UI MeSH Term Description Entries
D008335 Mandibular Condyle The posterior process on the ramus of the mandible composed of two parts: a superior part, the articular portion, and an inferior part, the condylar neck. Condyle, Mandibular,Condyles, Mandibular,Mandibular Condyles
D008337 Mandibular Fractures Fractures of the lower jaw. Fracture, Mandibular,Fractures, Mandibular,Mandibular Fracture
D008410 Masticatory Muscles Muscles arising in the zygomatic arch that close the jaw. Their nerve supply is masseteric from the mandibular division of the trigeminal nerve. (From Stedman, 25th ed) Masticatory Muscle,Muscle, Masticatory,Muscles, Masticatory
D001732 Bite Force The force applied by the masticatory muscles in dental occlusion. Masticatory Force,Occlusal Force,Bite Forces,Force, Bite,Force, Masticatory,Force, Occlusal,Forces, Bite,Forces, Masticatory,Forces, Occlusal,Masticatory Forces,Occlusal Forces
D001860 Bone Plates Implantable fracture fixation devices attached to bone fragments with screws to bridge the fracture gap and shield the fracture site from stress as bone heals. (UMDNS, 1999) Bone Plate,Plate, Bone,Plates, Bone
D003799 Dental Stress Analysis The description and measurement of the various factors that produce physical stress upon dental restorations, prostheses, or appliances, materials associated with them, or the natural oral structures. Analyses, Dental Stress,Analysis, Dental Stress,Stress Analyses, Dental,Stress Analysis, Dental,Dental Stress Analyses
D005593 Fracture Fixation, Internal The use of internal devices (metal plates, nails, rods, etc.) to hold the position of a fracture in proper alignment. Osteosynthesis, Fracture,Fixation, Internal Fracture,Fixations, Internal Fracture,Fracture Fixations, Internal,Fracture Osteosyntheses,Fracture Osteosynthesis,Internal Fracture Fixation,Internal Fracture Fixations,Osteosyntheses, Fracture
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D013314 Stress, Mechanical A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area. Mechanical Stress,Mechanical Stresses,Stresses, Mechanical
D014025 Titanium A dark-gray, metallic element of widespread distribution but occurring in small amounts with atomic number, 22, atomic weight, 47.867 and symbol, Ti; specific gravity, 4.5; used for fixation of fractures.

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