In vitro comparison of biomechanical characteristics of sagittal split osteotomy fixation techniques

Influence of the mandibular plane and magnitude of the movement in sagittal split ramus osteotomy: an in vitro study

PURPOSE

The aim of this study was to evaluate fixation resistance in mandibular sagittal split ramus osteotomy in standardized polyurethane hemimandibles with two types of advancement (6 and 12 mm), with or without mandibular plane rotation, using a 2.0-mm plate/screw system.

METHODS

Seven groups were evaluated using a vertical compressive load in the first molar region, and the applied force in Newtons was recorded in 1 mm, 5 mm, and 10 mm displacements, as well as the maximum force.

RESULTS

There was a statistical intergroup difference and it was observed that increasing the advancement decreased fixation resistance with a single plate, and inserting an additional plate significantly increased osteosynthesis resistance.

CONCLUSION

In the 12 mm advancements, clockwise rotation proved to be more resistant when fixed with only one plate. By contrast, counterclockwise rotation was significantly more resistant in stabilizing the mandibular sagittal ramus osteotomy when two plates were used.

Biomechanical evaluation of magnesium plates for management of mandibular angle fracture

The aim of this study was to evaluate the efficacy of magnesium plates for the management of fractures of the mandibular angle. Fresh sheep hemimandibles were divided into 7 groups and a biomechanical cantilever bending test was used for the groups: Group 1 included fractured hemimandibles fixed at the angle with a single 1mm magnesium miniplate; Group 2 had fixation with a 1mm double magnesium miniplate; Group 3 used a 2mm thick single magnesium miniplate; Group 4 used double 2mm magnesium plates; Group 5 each had a single 1mm thick titanium plate; Group 6 used 1mm thick double titanium plates; and Group 7 comprised intact hemimandibles. Each group was tested using universal testing machine yield loads; yield displacements and stiffness were compared using one way analysis of variance (ANOVA) Group 1 (1mm single magnesium plate) and Group 2 (1mm double magnesium plates) showed lower stability than other groups, while the 2mm magnesium plate showed stability similar to the corresponding 1mm titanium plate. Pure magnesium has good mechanical properties and when it is designed properly it can be used for the management of mandibular fracture.

Investigation of a Modified Novel Technique in Bilateral Sagittal Splitting Osteotomy Fixation: Finite Element Analysis and In Vitro Biomechanical Test

Purpose

To evaluate the biomechanical properties of the modified novel 2-hole monocortical plate fixation (2HMCPf) and traditional 4-hole monocortical plate fixation (4HMCPf) techniques in bilateral sagittal splitting osteotomy (BSSO) synthesis using a finite element analysis (FEA) and an in vitro biomechanical test with the application of a shearing loading force on a sawbone mandible model.

Materials and Methods

A three-dimensional mandible models were generated using the geometry obtained from the computerized tomography image of a sawbone mandible. Plates and screws were generated and combined with the mandible in a CAD environment. The 2HMCPf and traditional 4HMCPf techniques for BSSO osteosynthesis were then analyzed under the occlusal load using the FEA. An in vitro biomechanical test was executed to verify the result of FEA. The force on fixation failure and pattern of failure were recorded.

Results

The results revealed that the von Mises Stress on the mandible cortical bone (75.98 MPa) and the screw/plate (457.19 MPa) of the 2HMCPf group was lower than that of the 4HMCPf group (987.68 MPa, 1781.59 MPa). The stress concentrated on the central region of the 4HMCPf group and the distal set of the 2HMCPf group. In vitro study using the sawbone mandible model showed mechanical failure at the region of the proximal segment near the osteotomy site with the 4HMCPf group (average 32.198 N) but no failure on the fixation sites with the 2HMCPf group. Instead, the mandible sawbone fractured on the condyle neck region (average 44.953 N).

Conclusion

From the biomechanical perspective, we proved that the 2HMCPf method was able to withstand a higher shearing loading force than the 4HMCPf fixation method in BSSO osteosynthesis.

Biomechanical evaluation of hybrid fixation method of sagittal split ramus osteotomy in mandibular advancement

PURPOSE

In this study, eight different fixation methods applied after sagittal split ramus osteotomy (SSRO) were compared experimentally.

MATERIALS AND METHODS

SSRO was performed to 48 sheep hemimandibles in eight groups of 6 each. Group A- a four hole standard miniplate; Group B- a four hole standard miniplate and one bicortical screw; Group C-a four hole locking plate; Group D-a four hole locking plate and one bicortical screw; Group E-a six hole straight miniplate; Group F-a six hole straight miniplate and one bicortical screw; Group G- a sliding plate, which was specifically designed for SSRO; Group H- sliding plate and one bicortical screw.

RESULTS

In terms of measured values of displacement, the highest degrees of displacement were observed in decreasing order in Groups G, C, A, and E. The least displacement values were detected in Groups H, F, D and B with values being very close to each other. For linear force applied up to 70N, 3 mm or higher displacement values were not seen in any fixation system.

CONCLUSION

According to the results of study, all systems are suitable for clinic usage. However, intermaxillary fixation or functional elastics may be needed for sliding plate systems during the healing period of hard tissue.

Fixation methods in sagittal split ramus osteotomy: a systematic review on in vitro biomechanical assessments

The aim of this systematic review was to assess the stability of rigid internal fixation (RIF) techniques in sagittal split ramus osteotomy (SSRO) based on in vitro biomechanical assessments, with particular interest in large mandibular advancements. In general, RIF methods can be divided into three groups: bicortical screws, miniplates, and a combination of the two. An electronic search of the PubMed, CINAHL, and Embase databases was performed, and studies published between January 2003 and March 2018 were screened for inclusion. Comparative studies with an in vitro experimental design, using biomechanical assessments to measure the stability of RIF methods in SSRO, were included. Of 104 unique studies identified in the initial search, 24 were included. Twenty-two of these 24 studies analyzed an advancement of the mandible of 7mm or less. The use of a single four-hole or six-hole miniplate was less stable than the use of bicortical screws, hybrid techniques, double miniplates, or grid plates. Two studies analyzed advancements of 10mm, for which two miniplates placed in parallel and a grid plate showed most stability. Although there was agreement between studies with regard to results, more biomechanical studies are required to quantify the stability of fixation methods in larger mandibular advancements.

Comparison of the Stability of Mandibular Sagittal Osteotomy Fixation between Two Types of Titanium Miniplates: A Biomechanical Study in Sheep Mandibles

This study aimed to compare the biomechanical stability of the fixation of mandibular sagittal split osteotomy of the ramus by two types of titanium miniplates in sheep mandibles. Seven preserved sheep mandibles with similar weight and size were selected, dissected with complete removal of soft-tissue structures, and sectioned in their midline. After performing sagittal split osteotomy, 5 mm of advancement was standardized and samples were divided into two groups according to the type of titanium miniplate (GI = seven hemimandibles were fixed with straight titanium miniplate, GII = seven hemimandibles were fixed with L-shaped titanium miniplates), and then subjected to compressive load. The means (standard deviation) of the compressive load and extension values were 70.68 N (22.26) and 63.36 mm (15.60) to straight miniplates, and 78.80 N (32.54) and 70.55 mm (5.42) to L-shaped miniplates. After comparison and statistical analysis, the results showed no significant difference between the two types of titanium miniplates.

In vitro study of a modified sagittal split osteotomy fixation technique of the mandible: a mechanical test

This study was performed to evaluate the compressive mechanical strength of rigid internal fixation (RIF) using 1.5-mm L-shaped plates fixed with monocortical screws in sagittal split osteotomy (SSO). Thirty synthetic hemimandibles, which had all undergone a 5-mm advancement, were divided into three groups: three 12-mm bicortical titanium screws were placed in an inverted L pattern in group A; one straight 2.0-mm system spaced titanium plate fixed with four 5-mm monocortical screws was used in group B; two 1.5-mm system L-shaped titanium plates, each fixed with four 5-mm monocortical screws, were used in group C. The models were subjected to compressive and progressive mechanical tests with forces applied in the area between the second premolar and first molar to verify resistance in Newtons (N). A displacement speed of 1mm/min was applied, with a maximum 10mm displacement of the distal segment or until disruption of the fixation. The deformity and/or eventual rupture of the plates were evaluated, and consequently their technical stability was determined. The results showed that the modified fixation technique tested in this study on synthetic mandibles resulted in adequate stability and superior mechanical behaviour compared to simulated osteosynthesis with the use of a straight 2.0-mm titanium plate.

Evaluation of Intersegmental Displacement After Mandibular Setback Split Ramus Osteotomy Using Modified L-Shaped Monocortical Plate: Cone-Beam Computed Tomography Superimposition

PURPOSE

The purpose of the current study is to compare intersegmental displacements after mandibular setback sagittal split ramus osteotomy (SSRO) using 4 types of osteosynthesis methods.

PATIENTS AND METHODS

This is a retrospective study of 53 subjects who presented underwent bilateral setback SSRO at Pusan National University Hospital from January 2009 to December 2013. The subjects were divided into 4 groups according to the osteosynthesis method applied: group A-modified L-type monocortical plate; B-conventional miniplate; group C-bicortical screws; group D-metal and absorbable screws. To obtain the intersegmental displacement, the mean of the differences of the 3-dimensional from T0 (2 days after surgery) to T1 (6 months after surgery) was calculated for the right and left condylar heads (condylion, Cd) and the right and left coronoid processes (Cps) using 3-dimensional imaging software (Ondemand 3D; Cybermed Co, Seoul, Korea).

RESULTS

For the condylion in the x, y, z coordinate system, in group A, there were significant differences in the y-axis for the right and left Cd; in group B, significant differences in the y-axis for the right Cd and in the y- and z-axes for the left Cd; in group C, no significant differences in the axis for the Cd; and in group D, there were significant differences in the y- and z-axes for the right Cd and in the x- and y-axes for the left Cd. For the Cps, the results are not much different from the condylion movement in all group.

CONCLUSION

In the current study, group C manifested the greatest displacement for the healing period. Group A did not show the significant difference to group B. In view of these results, modified L-shaped monocortical plate can be applied for osteosynthesis effectively.

Biomechanical Loading Evaluation of Unsintered Hydroxyapatite/poly-l-lactide Plate System in Bilateral Sagittal Split Ramus Osteotomy

OSTEOTRANS MX^® (Takiron Co., Ltd., Osaka, Japan) is a bioactive resorbable maxillofacial osteosynthetic material composed of an unsintered hydroxyapatite/poly-l-lactide composite, and its effective osteoconductive capacity has been previously documented. However, the mechanical strength of this plate system is unclear. Thus, the aim of this in vitro study was to assess its tensile and shear strength and evaluate the biomechanical intensity of different osteosynthesis plate designs after sagittal split ramus osteotomy by simulating masticatory forces in a clinical setting. For tensile and shear strength analyses, three mechanical strength measurement samples were prepared by fixing unsintered hydroxyapatite/poly-l-lactide composed plates to polycarbonate skeletal models. Regarding biomechanical loading evaluation, 12 mandibular replicas were used and divided into four groups for sagittal split ramus osteotomy fixation. Each sample was secured in a jig and subjected to vertical load on the first molar teeth. Regarding shear strength, the novel-shaped unsintered hydroxyapatite/poly-l-lactide plate had significantly high intensity. Upon biomechanical loading evaluation, this plate system also displayed significantly high stability in addition to bioactivity, with no observed plate fracture. Thus, we have clearly demonstrated the efficacy of this plate system using an in vitro model of bilateral sagittal split ramus osteotomy of the mandible.

Resistance and Stress Finite Element Analysis of Different Types of Fixation for Mandibular Orthognathic Surgery

Abstract The aim of this study was to evaluate the stress and dislodgement resistance by finite element analysis of different types of fixation in mandibular orthognathic surgery. A 3D solid finite element model of a hemi-mandible was obtained. A bilateral sagittal split osteotomy was simulated and the distal segment was advanced 5 mm forward. After the adjustment and superimposing of segments, 9 different types of osteosynthesis with 2.0 miniplates and screws were simulated: A, one 4-hole conventional straight miniplate; B, one 4-hole locking straight miniplate; C, one 4-hole conventional miniplate and one bicortical screw; D, one 4-hole locking miniplate and 1 bicortical screws; E, one 6-hole conventional straight miniplate; F, one 6-hole locking miniplate; G, two 4-hole conventional straight miniplates; H, two 4-hole locking straight miniplates; and I, 3 bicortical screws in an inverted-L pattern. In each model, forces simulating the masticatory muscles were applied. The values of stress in the plates and screws were checked. The dislodgement resistance was checked at the proximal segment since the distal segment was stable because of the screen at the occlusal tooth. The regions with the lowest and highest displacement were measured. The offset between the osteotomized segments was verified by millimeter intervals. Inverted-L with bicortical screws was the model that had the lowest dislodgment and the model with the lowest tension was the one with two conventional plates. The results suggest that the tension was better distributed in the locking miniplates, but the locking screws presented higher concentration of tension.

Mechanical evaluation of six techniques for stable fixation of the sagittal split osteotomy after counterclockwise mandibular advancement

We have evaluated the resistance to displacement of six stable methods of fixation of a sagittal split ramus osteotomy (SSRO) in the mandibular advancement with counterclockwise rotation. We tested 60 synthetic hemimandibles in six groups of 10 each: Group I - fixation with a straight four-hole 2.0mm miniplate; Group II - a straight six-hole 2.0mm miniplate; Group III - two straight 2.0mm four-hole miniplates; Group IV - an eight-hole 2.0mm (grid plate); Group V - a 2.0mm four-hole straight miniplate and 2.0×12mm bicortical screw; and Group VI - a straight four-hole 2.0mm locking miniplate. We applied a linear force in the region between the canine and the first premolar using a universal testing machine (EMIC- DL2000) with a loading cell of 10 KN. The loads at 1, 3, and 5mm displacement were recorded (N) and the data transmitted from the load cell to a computer. Results were analysed using analysis of variance (ANOVA) (p<0.001) and the Tukey post-test for comparison of the significance of the differences between the groups. For the three degrees of displacement, fixation with two straight 2.0mm plates and with the grid plate gave higher load values.

In vitro biomechanical comparison of six different fixation methods following 5-mm sagittal split advancement osteotomies

The sagittal split ramus osteotomy (SSRO) is a surgical technique used widely to treat many congenital and acquired mandibular discrepancies. Stabilization of the osteotomy site and the potential for skeletal relapse after the procedure are still major problems. The aim of this study was to compare the mechanical stability of six methods of rigid fixation in SSRO using a biomechanical test model. Sixty polyurethane replicas of human hemimandibles were divided into six groups. In group I, the osteotomies were fixed with two four-hole titanium miniplates; in group II, with one four-hole miniplate; in group III, with one four-hole miniplate+a bicortical screw; in group IV, with a grid miniplate; in group V, with a four-hole locking miniplate; and in group VI, with a six-hole miniplate. A linear load in the premolar region was applied to the hemimandibles. The resistance forces (N) needed to displace the distal segment by 1, 3, and 5mm were recorded and the data transmitted from the load cell to a computer. One-way analysis of variance with Tukey's post hoc test was performed to compare the means between groups. For the three displacement conditions, there was a strong tendency for the 2.0-mm plate+screw and the grid plate to have higher values.

TMJ response to mandibular advancement surgery: an overview of risk factors

Objective

In order to understand the conflicting information on temporomandibular joint (TMJ) pathophysiologic responses after mandibular advancement surgery, an overview of the literature was proposed with a focus on certain risk factors.

Methods

A literature search was carried out in the Cochrane, PubMed, Scopus and Web of Science databases in the period from January 1980 through March 2013. Various combinations of keywords related to TMJ changes [disc displacement, arthralgia, condylar resorption (CR)] and aspects of surgical intervention (fixation technique, amount of advancement) were used. A hand search of these papers was also carried out to identify additional articles.

Results

A total of 148 articles were considered for this overview and, although methodological troubles were common, this review identified relevant findings which the practitioner can take into consideration during treatment planning: 1- Surgery was unable to influence TMJ with preexisting displaced disc and crepitus; 2- Clicking and arthralgia were not predictable after surgery, although there was greater likelihood of improvement rather than deterioration; 3- The amount of mandibular advancement and counterclockwise rotation, and the rigidity of the fixation technique seemed to influence TMJ position and health; 4- The risk of CR increased, especially in identified high-risk cases.

Conclusions

Young adult females with mandibular retrognathism and increased mandibular plane angle are susceptible to painful TMJ, and are subject to less improvement after surgery and prone to CR. Furthermore, thorough evidenced-based studies are required to understand the response of the TMJ after mandibular advancement surgery.

Comparison and validation of finite element analysis with a servo-hydraulic testing unit for a biodegradable fixation system in a rabbit model

The aim of this study was the biomechanical validation of three-dimensional finite element analysis (FEA) with a servo-hydraulic testing unit (STU) for a resorbable fixation system (RFS) in a rabbit model. Bilateral mandibular vertical body osteotomies (BMVBO) were performed in 15 female New Zealand rabbits. The animals were divided into three groups. The STU and FEA tests were done immediately after surgery in group 1 (1 day), at the first postoperative month in group 2, and at the third postoperative month in group 3. Both stress tests were carried out by applying vertical forces at the lower incisal edge, loading from 0 N force and increasing this until breakage occurred at the bone. The maximum forces that the hemimandibles could stand and the amount of deformation were recorded and analysed with the FEA and STU tests. We found the STU and FEA test results to be similar and that they could be used interchangeably for groups 1 and 3. However, the FEA results differed most from the real STU values in group 2 because of callus formation that had not ossified at the osteotomy line.

Biomechanical in vitro evaluation of three stable internal fixation techniques used in sagittal osteotomy of the mandibular ramus: a study in sheep mandibles

Among the osteotomies performed in orthognathic surgery, the sagittal osteotomy of the mandibular ramus (SOMR) is the most common, allowing a great range of movements and stable internal fixation (SIF), therefore eliminating the need of maxillomandibular block in the postoperative period.

OBJECTIVES

The purpose of this study was to evaluate the biomechanical resistance of three national systems used for SIF in SOMR in sheep mandibles.

MATERIAL AND METHODS

The study was performed in 30 sheep hemi-mandibles randomly divided into 3 experimental groups, each containing 10 hemi-mandibles. The samples were measured to avoid discrepancies and then subjected to SOMR with 5-mm advancement. In group I, 2.0x12 mm screws were used for fixation, inserted in an inverted "L" pattern (inverted "L" group). In group II, fixation was performed with two 2.0x12 mm screws, positioned in a linear pattern and a 4-hole straight miniplate and four 2.0x6.0 mm monocortical screws (hybrid group). In group III, fixation was performed with two 4-hole straight miniplates and eight 2.0x6.0 mm monocortical screws (mini plate group). All materials used for SIF were supplied by Osteosin - SIN. The hemimandibles were subjected to vertical linear load test by Kratos K2000MP mechanical testing unit for loading registration and displacement.

RESULTS

All groups showed similar resistance during mechanical test for loading and displacement, with no statistically significant differences between groups according to analysis of variance.

CONCLUSION

These results indicate that the three techniques of fixation are equally effective for clinical fixation of SOMR.

Evaluation of intersegmental displacement according to osteosynthesis method for mandibular setback sagittal split ramus osteotomy using cone-beam computed tomographic superimposition

PURPOSE

To compare intersegmental displacements after mandibular setback sagittal split ramus osteotomy with reference to the fixation system applied: miniplate with monocortical screw, 3 bicortical screws, and 1 bicortical screw and 2 resorbable screws.

MATERIALS AND METHODS

The 42 subjects were divided into 3 groups according to the osteosynthesis method applied. To evaluate the intersegmental displacements from immediately after surgery (T0) to 6 months after surgery (T1), 2 cone-beam computed tomographic data sets were superimposed on the symphyseal area and the lower part of the mandible below the root apex. On the superimposed 3-dimensional images, the mean and standard deviation of the differences of the coordinates (x, y, z) between T0 and T1 were calculated.

RESULTS

From T0 to T1, group B (bicortical screws) manifested the greatest condylion (Cd) and coronoid process (Cp) displacements (P < .05). In group A, the right Cd moved anteriorly and the left Cd moved anteriorly and inferiorly, whereas the right and left Cps moved anteriorly. In group B, the right and left Cps moved laterally and inferiorly. In group C, the right Cd moved anteriorly and inferiorly, the left Cd changed laterally and anteriorly, the right Cp moved anteriorly, and the left Cp moved anteriorly and inferiorly.

CONCLUSIONS

In the present study, group B (bicortical screws) showed the greatest displacement after the healing period. In view of these findings, surgeons should consider carefully their choice of osteosynthesis method to effectively decrease intersegmental displacement.

An in vitro evaluation of rigid internal fixation techniques for sagittal split ramus osteotomies: setback surgery

PURPOSE

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.

MATERIALS AND 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).

CONCLUSION

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.

In vitro evaluation of conventional and locking miniplate/screw systems for the treatment of mandibular angle fractures

This in vitro study evaluated the influence of the type of miniplate and the number of screws installed in the proximal and distal segments on the stability and resistance of Champy's osteosynthesis in mandibular angle fractures. Sixty polyurethane hemimandibles with bone-like consistency were randomly assigned to four groups (n=15) and sectioned in the mandibular angle region to simulate fracture. The bone segments were fixed by different osteosynthesis methods using 2.0 mm miniplates and 2.0 mm × 6 mm monocortical screws. In groups 1 and 2, two conventional (G1) or locking (G2) screws were installed in each bone segment using a conventional (G1) or a locking (G2) straight miniplate; in groups 3 and 4, three conventional (G3) or locking (G4) screws were installed in the proximal segment and four conventional (G3) or locking (G4) screws were installed in the distal segment using a conventional (G3) or a locking (G4) seven-hole straight miniplate. The hemimandibles were loaded in compressive strength until a 4mm displacement occurred between the segments, vertically or horizontally. Locking plate/screw systems provided significantly greater resistance to displacement than conventional ones (p<.01). Locking miniplates offered more resistance than conventional miniplates. Long locking miniplates provided greater stability than short ones.

Biomechanical evaluation of a T-shaped miniplate fixation of a modified sagittal split ramus osteotomy with buccal step, a new technique for mandibular orthognathic surgery

OBJECTIVE

The purpose of this study was to biomechanically evaluate the stability of a T-shaped miniplate fixation of a modified sagittal split ramus osteotomy (MSSRO) with buccal step and to compare it with single or double-parallel straight miniplates fixing a standard sagittal split ramus osteotomy (SSRO).

STUDY DESIGN

Eighteen Synbone mandibular replicas were used in the study and divided into 3 groups. Standard SSRO was applied in the first and second groups, and the third group was cut for MSSRO with buccal step. After 7 mm of advancement, fixation modalities for the 3 groups included a single straight miniplate, double-parallel straight miniplates, and a T-shape miniplate, respectively. Each model was secured in a jig and subjected to vertical load on the anterior teeth.

RESULTS

The T miniplate group showed a significantly higher value for stability than the group with a single straight miniplate. There was no significant difference in stability between the T miniplate and the double-parallel straight miniplate groups.

CONCLUSION

For mandibular advancement surgery of 7 mm in a laboratory environment, a T-shaped miniplate used with MSSRO and buccal step as a combination significantly optimize the resistance and stability of the fixation compared with a standard SSRO fixed with a single straight miniplate.

Three lateral osteotomy designs for bilateral sagittal split osteotomy: biomechanical evaluation with three-dimensional finite element analysis

Background

The location of the lateral osteotomy cut during bilateral sagittal split osteotomy (BSSO) varies according to the surgeon's preference, and no consensus has been reached regarding the ideal location from the perspective of biomechanics. The purpose of this study was to evaluate the mechanical behavior of the mandible and screw-miniplate system among three lateral osteotomy designs for BSSO by using three-dimensional (3-D) finite element analysis (FEA).

Methods

The Trauner-Obwegeser (TO), Obwegeser (Ob), and Obwegeser-Dal Pont (OD) methods were used for BSSO. In all the FEA simulations, the distal segments were advanced by 5 mm. Each model was fixed by using miniplates. These were applied at four different locations, including along Champy's lines, to give 12 different FEA miniplate fixation methods. We examined these models under two different loads.

Results

The magnitudes of tooth displacement, the maximum bone stress in the vicinity of the screws, and the maximum stress on the screw-miniplate system were less in the OD method than in the Ob and TO methods at all the miniplate locations. In addition, Champy's lines models were less than those at the other miniplate locations.

Conclusions

The OD method allows greater mechanical stability of the mandible than the other two techniques. Further, miniplates placed along Champy's lines provide greater mechanical advantage than those placed at other locations.

In vitro biomechanical evaluation of the use of conventional and locking miniplate/screw systems for sagittal split ramus osteotomy

PURPOSE

The aim of this in vitro study was to assess the biomechanical stability of 9 different osteosynthesis methods after sagittal split ramus osteotomy by simulating the masticatory forces and using a 3-point biomechanical test method.

MATERIALS AND METHODS

Forty-five polyurethane hemimandibles with bone-like consistency were randomly assigned to 9 groups (n = 5) and subjected to sagittal split ramus osteotomy. After 4-mm advancement of the distal segment, the bone segments were fixed by different osteosynthesis methods using 2.0-mm miniplate/screw systems: group A, one 4-hole conventional straight miniplate; group B, one 4-hole locking straight miniplate; group C, one 4-hole conventional miniplate and one bicortical screw; group D, one 4-hole locking miniplate and 1 bicortical screw; group E, one 6-hole conventional straight miniplate; group F, one 6-hole locking straight miniplate; group G: two 4-hole conventional straight miniplates; group H, two 4-hole locking straight miniplates; and group I, 3 bicortical screws in an inverted-L pattern. All models were mounted on a base especially constructed for this purpose. Using a 3-point biomechanical test model, the hemimandibles were loaded in compressive strength in an Instron machine (Norwood, MA) until a 3-mm displacement occurred between segments vertically or horizontally. Data were analyzed by analysis of variance and Tukey test (alpha = 1%).

RESULTS

The multiparametric comparison of the groups showed a statistically significant difference (P < .01) between groups that used 2 miniplates (groups G and H), 1 miniplate and 1 bicortical screw (groups C and D), and only bicortical screws (group I) compared with groups that used only 1 miniplate with 2 screws per segment (groups A and B) and 3 screws per segment (groups E and F).

CONCLUSION

The placement of 2.0-mm-diameter bicortical screws in the retromolar region, associated or not with conventional and locking miniplates with monocortical screws, promoted a better stabilization of bone segments. Locking miniplates presented a better performance in bone fixation in all groups.

Histologic and tomographic analyses of the temporomandibular joint after mandibular advancement surgery: study in minipigs

OBJECTIVE

The aim was to elucidate the changes occurring in temporomandibular joint (TMJ) after surgical mandibular advancement with different fixation materials: bicortical screws and miniplates.

STUDY DESIGN

Eighteen minipigs were randomly divided into 3 groups: group I (control), nonoperated animals; group II, animals submitted to surgical advancement surgery and osteosynthesis by bicortical screws; and group III, animals submitted to surgical advancement surgery and osteosynthesis by miniplates. Four months after the surgeries, TMJs were collected and histologically prepared after computerized tomography (CT) scanning for the blind detection of erosion, flattening, and osteophyte.

RESULTS

The CT analysis revealed significant alterations in the shape of the condyles (erosion: P = .0010; flattening: P < .0001) for group II compared with groups I and III. Descriptive histologic analysis was compatible with the CT findings.

CONCLUSIONS

The results indicated that bicortical screw fixation resulted in more pronounced condylar alterations in the shape of the condyles than miniplate osteosynthesis. However, further clinical studies are necessary to confirm these data.

Biomechanical comparison of different plating techniques in repair of mandibular angle fractures

OBJECTIVE

The purpose of this study was to evaluate the biomechanical behaviors of different miniplate fixation techniques for treatment of fractures of the mandibular angle.

STUDY DESIGN

Twenty sheep hemimandibles were used to evaluate 4 different plating techniques. The groups were fixated with Champy technique, biplanar plate placement, monoplanar plate placement, and 3-dimensional (3D) curved angle strut plate. A custom-made 3-point biomechanical test model was used for the samples. Each group was tested with compression forces by an Instron Lloyd LRX machine. The biomechanical behavior of the groups for the forces (N) that caused displacement of 1.75 mm were compared using the Instron software program and displacement graphics.

RESULTS

The variance analyses showed that biplanar plate placement had more favorable biomechanical behavior than Champy technique and monoplanar plate placement (P < .05). In addition, the 3D curved angle strut plate technique had more favorable biomechanical behavior than the Champy technique (P < .05) but was not significantly different from biplanar or monoplanar plate placement techniques (P > .05).

CONCLUSION

The study demonstrated that 3D strut plates or dual miniplate techniques had greater resistance to compression loads than the Champy technique. In addition, biplanar plate orientation may provide a more favorable biomechanical behavior than monoplanar plate placement.