Análise mecânica da resistência da fixação na osteotomia sagital do ramo após diferentes movimentos de avanço mandibular: estudo in vitro

Abstract

The objective of this study was to evaluate by means of mechanical testing the fixation strength in sagittal split ramus osteotomy (SSRO) for three different movements of mandibular advancement, as well as the influence of movement associated with clockwise rotation of the mandibular plane, using miniplates (4 and 6 holes) and 6-mm screws of the 2.0 mm system (Engimplan®). Two types of advancement were employed (6 and 12 mm) using polyurethane hemimandibles with factory-standardized SSO, divided into five groups: G1 (test 1) – linear advancement of 6 mm/1 plate and 4 screws; G2 (test 2) – linear advancement of 12 mm/1 plate and 4 screws; G3 (test 3) – linear advancement of 12 mm/2 plates and 8 screws; G4 (test 4) – advancement of 12 mm associated with clockwise rotation of the mandibular plane (15°)/1 plate and 4 screws; G5 (test 5) – advancement of 12 mm associated with clockwise rotation of the mandibular plane (15°)/2 plates and 8 screws. The hemimandibles were submitted to a vertical compressive load in the region of the first molar and the force applied (in Newton) was recorded for displacements of 1, 5 and 10 mm, as was the maximum force applied between 1 and 10 mm. Using a 95% confidence interval, the mean force values were obtained and compared between groups. The Kruskal-Wallis* test was used for analysis of all groups and the Mann-Whitney** test for the comparison of two groups. The results showed higher mean force values for G3 (p < 0.001*), which was therefore the treatment that provided the greatest strength. When only 1 plate was used for fixation of the hemimandible, in the advancement of 12 mm, clockwise rotation resulted in a greater fixation strength than the linear movement for displacements of 1, 5 and 10 mm (p < 0.05**), with no significant difference being observed only for the maximum displacement (p = 0.112**). Important loss of strength in fixation was observed for the large advancement (12 mm) and it was necessary to compensate this situation with the use of more fixation. Clockwise rotation added strength to the SSO only in cases in which a single plate was used.