[Experimental studies of the biomechanical stability of different miniplate configurations for the mandibular angle]

Miniplate fixation of mandibular fractures has become the treatment of choice in most cases. In fractures of the mandibular angle one 4- or 6-hole miniplate is applied ventral to the oblique line of the buccal cortex of the mandible. Not in every case adequate stabilization is being accomplished by one plate. In order to find out if stability might be increased by a two miniplate fixation technique in which a second plate is applied at the inferior border of the mandibular angle 16 polyurethane and 16 humane mandibles were used and standardized osteotomies were performed at the right mandibular angle. These two groups were divided in 4 sub-groups of four mandibles each and plate fixation of the sub-groups was performed as follows: 6-hole plate on the buccal side of the oblique line, 6-hole plate as before and an additional 2-hole plate at the inferior margin of the mandible, 2-hole plate at the oblique line and 6-hole at the inferior margin and finally two 4-hole plates at the same position. The stability of fixation was measured according to Kroon's method (Kroon et al. 1988), based on a three-dimensional in-vitro model in which muscle forces during mastication acting on the mandible were simulated. Axial loading forces close to the fracture site produced significantly inferior splaying and lingual compression in single miniplated angle fractures. Application of a second miniplate at the inferior border provided significantly higher resistance to loading forces close to the fracture line where two 4-hole miniplates showed superior results. We conclude that two miniplates are an effective method of treating mandibular angle fractures with minor fracture surfaces by establishing a second line of osteosynthesis to neutralize rotational forces.