title: An in vitro evaluation of rigid internal fixation techniques for sagittal split ramus osteotomies: setback surgery.
abstract: OBJECTIVE
  The aim of this study was to evaluate the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomy for mandibular setback in vitro.
  
  
  METHODS
  Sixty polyurethane replicas of human hemimandibles were used as substrates, simulating a 5-mm setback surgery by sagittal split ramus osteotomy. These replicas served to reproduce 3 different techniques of fixation, including 1) a 4-hole plate and 4 monocortical screws (miniplate group), 2) a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3) 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). After fixation, hemimandibles were adapted to a test support and subjected to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge with an Instron 4411 mechanical testing unit. Peak loadings at 1, 3, 5, and 10 mm of displacement were recorded. Means and standard deviation were analyzed using analysis of variance and Tukey test with a 5% level of significance, and failures during tests were recorded.
  
  
  RESULTS
  Regardless of the amount of displacement and direction of force, the miniplate group always showed the lowest load peak scores (P < .01) compared with the other fixation techniques. The hybrid group demonstrated behavior similar to the inverted-L group in lateral and vertical forces at any loading displacement (P > .05). Molar load tests required more force than incisal load tests to promote the same displacement in the mandibular setback model (P < .05).
  
  
  CONCLUSIONS
  For mandibular setback surgery of 5 mm, this study concluded that the fixation technique based on the miniplate group was significantly less rigid than the fixation observed in the hybrid and inverted-L groups. Mechanically, adding 1 bicortical positional screw in the retromolar region in the miniplate technique may achieve the same stabilization offered by inverted-L fixation for mandibular sagittal split ramus osteotomy setback surgery in vitro.
authors.affiliation: College of Dentistry, Federal University of Sergipe, Aracaju, Sergipe, Brazil. bernardobrasileiro@ufs.br
authors.forename: Bernardo Ferreira
authors.initials: BF
authors.lastname: Brasileiro
authors.forename: Rafael
authors.initials: R
authors.lastname: Grotta-Grempel
authors.forename: Glaucia Maria Bovi
authors.initials: GM
authors.lastname: Ambrosano
authors.forename: Luis Augusto
authors.initials: LA
authors.lastname: Passeri
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry; D001696:Biomechanical Phenomena; D001732:Bite Force; D001860:Bone Plates; D001863:Bone Screws; D003799:Dental Stress Analysis / Q000295:instrumentation; D004867:Equipment Design; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D008334:Mandible / Q000033:anatomy & histology; D008422:Materials Testing; D008953:Models, Anatomic; D008963:Molar / Q000033:anatomy & histology; D059229:Osteotomy, Sagittal Split Ramus / Q000295:instrumentation* / Q000379:methods; D018583:Pliability; D011140:Polyurethanes / Q000737:chemistry; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry; D054159:Torsion, Mechanical
chemical_list: D001672:Biocompatible Materials; D011140:Polyurethanes; D014025:Titanium