Finite Element Evaluation of Stable Fixation in Combined Mandibular Fractures.

PURPOSE: The fixation of combined mandibular fractures, especially symphyseal-condylar fractures, although occurring commonly and having a higher complication rate in the clinic, is rarely investigated regarding predictable therapeutic approaches. Thus this study's aim was to assess different forms of condylar fixation when combined with symphyseal fracture fixation. MATERIALS AND METHODS: Using finite element models, we analyzed the stress distribution that occurs when a condylar fracture is fixed with 1 miniplate, 2 miniplates, or a trapezoidal condylar miniplate and when a symphyseal fracture is fixed with 2 parallel plates, 2 perpendicular plates, or 2 lag screws. The null hypothesis was that there would be no differences among the different fixation techniques. RESULTS: The results showed a stress concentration in the anterior region of the condyle, close to the sigmoid notch. Moreover, adequate fixation in the symphysis could result in less tension at the condylar region. Therefore, when the symphysis was fixed with a lag-screw technique, condylar fixation was less required, showing a more adequate stress distribution when the condyle was fixed with 1 or 2 plates. Conversely, when the symphyseal fixation was less effective, by use of perpendicular plates, there was a change in the stress distribution at the condylar region, altering fixation behavior and resulting in more tension and displacement in the condyle, especially when a trapezoidal plate was used. CONCLUSIONS: A lag screw and parallel double plates appear to be suitable for symphyseal fixation, whereas 2 straightly positioned plates and a trapezoidal plate are suitable for condylar fixation. However, the combination of perpendicular plates in symphyseal fixation and a trapezoidal plate in condylar fixation showed an altered stress distribution.

Mechanical evaluation of different techniques for symphysis fracture fixation--an in vitro polyurethane mandible study.

PURPOSE: The aim of this study was to make a comparative evaluation of the mechanical behavior of 4 different internal fixation systems for mandibular symphysis fractures. MATERIALS AND METHODS: Forty polyurethane mandible replicas (Nacional, Jaú, SP, Brazil) were used. These were divided into 4 groups of different fixation methods: group 1P, 1 2.0-mm miniplate; group 2PLL, 2 2.0-mm parallel miniplates; group 2PERP, 2 2.0-mm perpendicular miniplates; and group LST, 2 2.0-mm lag screws. Each group was subjected to linear vertical loading in the molar region in an Instron 4411 servohydraulic mechanical testing unit (Instron Corporation, Norwood, MA). The load resistance values were measured at load application displacements of 1, 3, 5, and 10 mm. Means and standard deviations were compared with respect to statistical significance using analysis of variance (P < .05) and compared by the Tukey test. RESULTS: Group 1P showed the lowest peak load scores compared with other fixation methods. Group LST showed a statistically significant higher resistance than group 2PLL for all displacements. Group 2PERP showed lower resistance than group LST when displacements were 1 and 3 mm and statically significant similarity at displacements of 5 and 10 mm. However, group 2PERP showed no statistically significant differences compared with group 2PLL. CONCLUSIONS: The LST showed better mechanical behavior for symphysis fracture fixation than the other systems when the fixation methods were subjected to linear vertical loading in the molar region.