Comparative evaluation of different fixation techniques of the sagittal split ramus osteotomy in 10 mm advancements: Mechanical testing and screw insertion torque.

PURPOSE: To compare the mechanical characteristics of five techniques for the functionally stable fixation of simulated sagittal split ramus osteotomy with 10 mm of advancement and to evaluate the screw insertion torque. MATERIALS AND METHODS: Fifty polyurethane hemimandibles with sagittal split ramus osteotomy and containing an advancement of 10 mm fixed and distributed as follows: Customized 3D Plate Group: 1 customized 3D miniplate; 4-Hole Plate Group: 2 miniplates with 4 holes; 6-Hole Plate Group: 2 miniplates with 6 holes; Hybrid Group: 1 flat miniplate with 4 holes and 1 bicortical screw; and Bicortical Screw Group: 3 bicortical screws. We conducted a mechanical test using vertical linear loading with a displacement velocity of 1 mm/min on a universal testing machine and assessed the screw insertion torque using a digital torque wrench. RESULTS: The means of strength for the 1-, 3- and 5-mm displacements were determined by a one-way analysis of variance (ANOVA) followed by the post hoc Tukey test. Statistically significant differences were observed only for the 5-mm displacement (F = 3.36; p = 0.01). There was a difference between the 4-H2P and HG groups (p = 0.04). CONCLUSION: The customized miniplate, the fixation methods with three bicortical screws, or with two straight miniplates with either 4 or 6 holes, all offer a similar mechanical resistance suitable for fixation.

Evaluation of cyclic and linear mechanical resistance of prebent and manually-bent plates used for maxillary advancement in orthognathic surgery.

The aim of the present study was to compare prebent and manually-bent plates used in maxillary advancement. The prebent plates were fixed in polyurethane blocks for the linear test and aluminium blocks for the cyclic test, and the manually-bent plates were fixed in polyurethane and aluminium blocks. The linear load tests were done using an Instron® 4411 mechanical testing machine and the cyclic test with an Instron® E3000 testing machine. The linear mechanical test showed that there was no significant difference between the plates. In the cyclic test the prebent plates reached the limit of 500000 cycles without fracturing whereas the manually-bent plate group fractured before reaching the limit of cycles (p=0.008). The decision to use prebent or manually-bent plates during operations should be influenced by the production of the bends and their consequent brittleness.

In Vitro Mechanical Analysis of Different Techniques of Internal Fixation of Combined Mandibular Angle and Body Fractures.

PURPOSE: To evaluate in vitro resistance of 5 techniques of internal fixation of bilateral fractures involving the mandibular angle and body. MATERIALS AND METHODS: Twenty-five polyurethane mandibles were used as substrates, fixed with a 2-mm fixation system, and divided into 5 groups: I, 1 4-hole plate, without intermediate space, in the neutral zone of the mandibular body and another similar plate in the external oblique ridge of the contralateral mandibular angle; II, 1 6-hole plate, with intermediate space, in the neutral zone of the mandibular body and a similar plate in the external oblique ridge of the left mandibular angle; III, 1 4-hole locking plate, with intermediate space, in the right neutral zone and another similar plate in the left external oblique ridge; IV, 2 4-hole plates, with intermediate space, one in the tension zone and the other in the compression zone of the mandibular body, and 1 4-hole plate, with intermediate space, in the external oblique ridge of the contralateral mandibular angle; V, 2 4-hole plates with intermediate space, one in the tension zone and the other in the compression zone of the mandibular body and similarly in the buccal side of the left mandibular angle. Mandibles were subjected to vertical linear load tests by a mechanical testing machine (Instron 4411, Instron Corp, Norwood, MA) to record peak load and load for displacements of 3, 5, and 7 mm. RESULTS: Group I had the least mechanical resistance of all groups, regardless of displacement, and group IV had the greatest mechanical resistance. Among groups II, III, and V, there was no statistically meaningful difference. CONCLUSION: Fixation of bilateral mandibular fractures involving the mandibular angle and body using 2 plates in the region of the body and 1 plate in the tension zone in the region of the mandibular angle was the technique that presented the best mechanical resistance.

Comparative in vitro mechanical evaluation of techniques using a 2.0 mm locking fixation system for simulated fractures of the mandibular body.

PURPOSE: To perform a comparative evaluation of the mechanical resistance of simulated fractures of the mandibular body which were repaired using different fixation techniques with two different brands of 2.0 mm locking fixation systems. MATERIALS AND METHODS: Four aluminum hemimandibles with linear sectioning simulating a mandibular body fracture were used as the substrates and were fixed using the two techniques and two different brands of fixation plate. These were divided into four groups: groups I and II were fixed with one four-hole plate, with four 6 mm screws in the tension zone and one four-hole plate, with four 10 mm screws in the compression zone; and groups III and IV were fixed with one four-hole plate with four 6 mm screws in the neutral zone. Fixation plates manufactured by Tóride were used for groups I and III, and by Traumec for groups II and IV. The hemimandibles were submitted to vertical, linear load testing in an Instron 4411 servohydraulic mechanical testing unit, and the load/displacement (3 mm, 5 mm and 7 mm) and the peak loads were measured. Means and standard deviations were evaluated applying variance analysis with a significance level of 5%. RESULTS: The only significant difference between the brands was seen at displacements of 7 mm. Comparing the techniques, groups I and II showed higher mechanical strength than groups III and IV, as expected. CONCLUSION: For the treatment of mandibular linear body fracture, two locking plates, one in the tension zone and another in the compression zone, have a greater mechanical strength than a single locking plate in the neutral zone.

Perception of oral and maxillofacial surgeons, orthodontists and laypersons in relation to the harmony of the smile.

OBJECTIVE: Harmony is one of the main objectives in surgical and orthodontic treatment and this harmony must be present in the smile, as well as in the face. The aim of the present study was to assess the perceptions of professionals and laypersons in relation to the harmony of the smile of patients with or without vertical maxillary alterations. MATERIALS AND METHODS: Sixty observers (oral and maxillofacial surgeons, orthodontists and laypersons) reported the degree of harmony of six smiles using an objective questionnaire and the participants indicated if there was a need for corrective surgery or not. The classification of observers was recorded on a Likert scale from 1 to 5. Mixed regression was used to determine differences between the three groups. RESULTS: Statistically significant differences were found only for the harmony of the smile between the oral and maxillofacial surgeons and laypersons, with laypersons being more critical when assessing the smile. There was no statistical difference between the other groups for the harmony of the smile or the indication of corrective surgery. The patterns of greater or lesser harmony determined by observers during the smile were similar to those found in the literature as the ideal standard in relation to vertical maxillary positioning. CONCLUSIONS: Laypersons had a tendency to be more critical in relation to facial harmony than surgeons, although no statistical differences were found in the other groups in relation to the harmony of the smile or indication for the corrective surgery. In addition, the patterns of greater or lesser harmony of the smile determined by the participants were similar to those found in the literature as the ideal standard in relation to vertical maxillary positioning. Overall, the present study demonstrates that adequate interaction between surgeons, orthodontists and laypersons is essential in order to achieve facial harmony with orthodontic and/or surgical treatment. CLINICAL RELEVANCE: Opinion of specialists and laypersons about the smile in relation to the vertical positioning of the maxilla.

Fractographic analysis of 2.0-mm plates with a screw locking system in simulated fractures of the mandibular body.

PURPOSE: The purpose of the present study was to analyze the fractured plates from 2 brands of 2.0-mm locking fixation systems submitted to axial linear load testing. MATERIALS AND METHODS: Four aluminum hemimandibles with linear sectioning to simulate a mandibular body fracture were used as a substrate and fixed with 2 fixation techniques from 2 national brands: Tóride and Traumec. The techniques were as follows: one 4-hole plate, with four 6-mm screws in the tension zone, and one 4-hole plate, with four 10-mm screws in the compression zone; and one 4-hole plate, with four 6-mm holes in the neutral zone. The hemimandibles were submitted to vertical linear load tests using an Instron 4411 mechanical test machine. The system was submitted to the test until complete failure had occurred. Next, a topographic analysis of the surface of the plates was performed using a stereomicroscope and an electronic scanning microscope. The samples were evaluated using different magnifications, and images were obtained. RESULTS: The surface of the fracture analyzed in scanning electron microscopy demonstrated a ductile-type fracture, usually found in the traction test bodies of ductile materials, such as titanium. No evidence of failure was observed in any fracture surface from a change in the structure or composition of the material. CONCLUSIONS: The plates were fractured by a ductile rupture mechanism, as expected, suggesting that the manufacturing of the national brand name plates used in the present study has been under adequate quality control, with no structural changes produced by the manufacturing process that could compromise their function.