Mechanical stability of 2-plate versus 4-plate osteosynthesis in advancement Le Fort I osteotomy. An in vitro study.

INTRODUCTION: Stability in orthognathic surgery is nowadays considered as efficient and adequate. The objective of this study was to determine and to compare the mechanical resistance to vertical load of a Le Fort I advancement osteotomy stabilized by mean of two different osteosynthesis techniques, one using two 10-hole pre-bent T-shaped plates, the other using four manually bent 4-hole L- and J-shaped plates. MATERIEL AND METHODS: Standardized Le Fort I advancement osteotomies have been made on polyurethane models. The maxillary advancement was 5mm. Two groups of five models each were created. Group 1 was stabilized by mean of two 10-hole pre-bent T-shaped plates fixed by monocortical screws in the paranasal region. Group 2 was stabilized by mean of manually bent four 4-hole L-shaped plates fixed monocortical screws in the zygomatic and paranasal regions. A testing machine was used to load vertically the models at the range of 1mm/min linear displacement until peak load and system failure. Statistical analysis was realized using ANOVA and t-test, considering P as significant if <0.005. RESULTS: The maximal tolerated load was 15N in group 1and 42.71N in group 2 (P=0.003). DISCUSSION: The use of two T-shaped 10-holes pre-bent plates allows for less resistance in vertical loading than the use of four 4-holes manually bent L-shaped plates.