Principle and stability of locking plates.

A new internal Mini-Locking-System was tested compared with conventional 2.0 mm Miniplates. Standardised osteotomies in the angular region of 16 human cadaver mandibles were fixed with a 6-hole-plate at the oblique line. Osteosynthesis and stability of fixation was proofed in a three-dimensional in-vitro-model in which functional load was simulated. Comparison of the different osteosynthesis techniques showed that in the case of Miniplate fixation torsion and gapping of the bone fragments occurred following plate application and screw tightening when the plates were pressed onto the bone, so last incongruences between bone surface and plate were transferred to the mobile bone fragments resulting in more extended gaps and torsion. This was only observed to a much lesser extent with the Mini-Locking-System due to the fixation principle avoiding pressure to the bone. During functional loading the Mini-Locking-System showed also a significant higher stability in comparison to conventional Miniplates. Due to the fixation method imitating the principles of a fixateur the screws form together with the plate and the cortical bone a frame construction. Loading forces are transmitted without the need of plate friction directly from bone over the screws to the plate resulting in higher stability.