A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study

Biomechanical assessment of mandibular fracture fixation using finite element analysis validated by polymeric mandible mechanical testing

The clinical finite element analysis (FEA) application in maxillofacial surgery for mandibular fracture is limited due to the lack of a validated FEA model. Therefore, this study aims to develop a validated FEA model for mandibular fracture treatment, by assessing non-comminuted mandibular fracture fixation. FEA models were created for mandibles with single simple symphysis, parasymphysis, and angle fractures; fixated with 2.0 mm 4-hole titanium miniplates located at three different configurations with clinically known differences in stability, namely: superior border, inferior border, and two plate combinations. The FEA models were validated with series of Synbone polymeric mandible mechanical testing (PMMT) using a mechanical test bench with an identical test set-up. The first outcome was that the current understanding of stable simple mandibular fracture fixation was reproducible in both the FEA and PMMT. Optimal fracture stability was achieved with the two plate combination, followed by superior border, and then inferior border plating. Second, the FEA and the PMMT findings were consistent and comparable (a total displacement difference of 1.13 mm). In conclusion, the FEA and the PMMT outcomes were similar, and hence suitable for simple mandibular fracture treatment analyses. The FEA model can possibly be applied for non-routine complex mandibular fracture management.

Management of Lingual Cortex Fracture of Mandible Using Lingual Arch Bar: A Finite Element Analysis of Reduction with a Pilot Clinical Trial

Purpose

Fractures of lingual cortex are frequently left untreated leading to poor resolution of patient's symptoms and function. Positioning an implant on same side of fracture would provide better reduction. The study aims at improving stability offered by Erich arch bar placed on lingual surface, by Finite element analysis (FEA) along with a pilot clinical trial.

Methods

Two FEA models were generated from CT scan of an individual having lingual cortex fracture: control model with labial arch bar and study model with lingual arch bar. Parameters assessed: Stress distribution (Mpa) along lines of osteosynthesis; Separation of fracture fragments (mm) across fracture line. Associated, was a clinical trial of 5 patients, managed by placing lingual arch bar. Feasibility of arch bar, post-operative pain, radiographic inter-fragmentary gap and complications were assessed clinically.

Results

Lingual positioning of arch bar demonstrated less displacement (mm) of fracture fragments compared to labial placement (0.123 vs. 0.677) upon application of masticatory load. Insignificant lingual splay and lesser degree of stress distribution (Mpa) was observed (83.1 vs. 99.3) favoring placement of arch bar on lingual side. Clinical trial correlated with outcomes of FEA, resulting in improvement of patient's symptoms.

Conclusion

FEA and supporting clinical trial provided an effective method of reduction for lingual cortical fracture.

Finite element analysis of low-profile reconstruction plates for atrophic mandibles: a comparison of novel 3D grid and conventional plate designs

OBJECTIVES

This study aimed to compare the reconstruction with type 2.4 and three-dimensional (3D) grid plates relating the areas of weakness to anatomical regions of force incidence in atrophic mandibles with and without segmentation using finite element analysis (FEA).

MATERIALS AND METHODS

Strength and force quality in the mandible were also determined. The atrophic mandible models with and without segmentation were divided into four groups, and the behavior of each plate was analyzed using finite element analysis. In the atrophic mandible without segmentation using the type 2.4 reconstruction plate, the highest stress concentration in the plate was observed in the posterior region of the mandibular body and in the grid type 3D reconstruction plate was observed in the mandibular angle.

RESULTS

In the segmented atrophic mandible with the 2.4 reconstruction plate, higher stress concentration was observed in the mandibular segment defect. Analysis of the 3D grid-like reconstruction plate revealed that the geometry of the plate conferred greater stiffness to the assembly, as the most significant stress concentration was observed at the mandibular angle.

CONCLUSION

The width of the plate design may influence the strength, not the thickness.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Comparison of the mechanical properties of biodegradable and titanium osteosynthesis systems used in oral and maxillofacial surgery

To guide the selection of osteosynthesis systems, this study compared the mechanical properties of biodegradable and titanium osteosynthesis systems. SonicPins Rx and xG were subjected to pull-out tests. Additionally, 15 biodegradable (Inion CPS 2.0 and 2.5 mm; LactoSorb 2.0 mm; Macropore 2.0 mm; Polymax 2.0 mm; BioSorb FX 2.0 mm; ResorbX 2.1 mm; Osteotrans-MX 2.0 mm with plate thicknesses 1.0 and 1.4 mm; SonicWeld Rx_plate/Rx_pins, xG_plate/Rx_pins and xG_plate/xG_pins 2.1 mm without and with tapping the burr hole) and six titanium (CrossDrive (2006), CrossDrive (2018), MaxDrive; all 1.5 and 2.0 mm) straight, four-hole osteosynthesis systems were evaluated. All systems were subjected to tensile, bending and torsion tests. Pull-out loads of the SonicPins were comparable (P = 0.423). Titanium systems’ tensile loads were higher than biodegradable systems (P < 0.001). CrossDrive (2018) and MaxDrive systems’ tensile and torsional stiffness were lower, accompanied with higher ductility, than corresponding CrossDrive (2006) systems (P < 0.001). Bending stiffness of 1.5 mm titanium systems was comparable to, and of the 2.0 mm systems higher than, all biodegradable systems (P < 0.001). Regarding biodegradable systems, Inion CPS 2.5 mm had highest tensile load and torsional stiffness, SonicWeld 2.1 mm highest tensile stiffness, and BioSorbFX 2.0 mm highest bending stiffness (P < 0.001). On the basis of the results of this study, the CrossDrive (2018) and MaxDrive 1.5 mm titanium systems are recommended for midface fractures (e.g., zygomatic or maxillary fractures) and osteotomies (e.g., Le Fort I osteotomy), and the CrossDrive (2018) and MaxDrive 2.0 mm titanium systems for mandibular fractures and osteotomies when a titanium osteosynthesis system is used. When there is an indication for a biodegradable osteosynthesis system, the SonicWeld 2.1 mm or BioSorbFX 2.0 mm are recommended for midface fractures and osteotomies, and the Inion CPS 2.5 mm biodegradable system for mandibular osteotomies and non-load bearing mandibular fractures, especially when high torsional forces are expected (e.g., mandibular symphysis fractures).

The Influence of the Gonial Angle on the Initial Biomechanical Stability of the Plate Osteosynthesis in Polyurethane Mandibles With Angle Fractures

The aim of the present study was to examine the biomechanical stability of the mandibular angle fractures (MAF) fixated with standard titanium miniplates in polyurethane models with different gonial angles (GA). Three custom molds were prepared for 3-dimensional printed mandibles with low, normal and high GA. Twenty polyurethane replicas were cast per group and standard MAFs were created on each sample. Fractures were stabilized with 1 4-hole standard titanium miniplate inserted over the superior alveolar border. Half of the samples were subjected to molar loading and the other half to the incisal loading up until 150 N force magnitude. The load-displacement curves and the horizontal moment arms were recorded and analyzed. The samples with high GA demonstrated greater displacement than those with normal and low GA during molar loading (P < 0.05 for both). After correcting for the effects of the moment arm, the incisal loading also resulted in higher mean displacement in the high GA group than the others (P < 0.05 for both) and the normal GA samples showed higher displacement after 100 N level compared to those in low GA (P < 0.05). Within the limits of this in vitro study, it can be concluded that the MAFs of the polyurethane mandibles with high GA fixated with 1 standard monocortical plate are more likely to demonstrate higher displacement values under the effects of the molar and incisal loadings than do the mandibles with normal and low GA.

Assessment of Lingual Stability in Mandible Fracture: Monocortical Versus Bicortical Fixation Using FEM Analysis

Aim of the study

The present study compares lingual stability of monocortical miniplate fixation with that of bicortical miniplate fixation in parasymphysis fracture using FEM analysis.

Materials and methods

Using multislice CT scanner, 3D FEM of patient's mandible was created. Fracture was simulated at parasymphysis region and fixed with 2-mm titanium miniplates and screws of length 8, 10, 12 mm, respectively. Loading force of 120 N applied at molar region and 62.8 N at incisor region. These three models were imported into ANSYS Workbench FEM software.

Result

There is no significant difference in results between bicortical fixation and monocortical fixation.

Conclusion

It was concluded that use of monocortical fixation provides sufficient lingual stability. This suggests monocortical fixation system is as reliable as bicortical fixation.

Bite Force as a Parameter for Comparison Between Three-Dimensional and Standard Titanium Miniplates for the Management of Anterior Mandibular Fractures: A Prospective Randomized Double-Blinded Clinical Trial

Background and Objectives

To compare the efficacy of three-dimensional (3D) miniplates with standard miniplates in the osteosynthesis of anterior mandibular fractures on the basis of bite force recordings and other clinical parameters.

Methods

A prospective randomized double-blinded clinical trial was carried out for the treatment of anterior mandibular fractures. In total, 20 patients were randomly divided into two groups of 2-mm 3D and standard titanium miniplates. The assessment of patients was done at weekly intervals for 6 weeks using bite force recordings and other clinical parameters.

Results

A statistically significant difference was found in the duration of surgery which was less in group A as compared to group B (p = 0.03). No significant difference was found in other clinical parameters.

Interpretation and Conclusion

The clinical outcome of both the 3D and standard miniplate systems in the present study was similar; however, the following advantages with the use of 3D miniplates can be highlighted:Relatively lesser operating time.Three-dimensional stability of the fracture site and simultaneous stabilization at superior and inferior borders in the fixation of mandibular fractures.

A customized fixation plate with novel structure designed by topological optimization for mandibular angle fracture based on finite element analysis

Background

The purpose of this study was to design a customized fixation plate for mandibular angle fracture using topological optimization based on the biomechanical properties of the two conventional fixation systems, and compare the results of stress, strain and displacement distributions calculated by finite element analysis (FEA).

Methods

A three-dimensional (3D) virtual mandible was reconstructed from CT images with a mimic angle fracture and a 1 mm gap between two bone segments, and then a FEA model, including volume mesh with inhomogeneous bone material properties, three loading conditions and constraints (muscles and condyles), was created to design a customized plate using topological optimization method, then the shape of the plate was referenced from the stress concentrated area on an initial part created from thickened bone surface for optimal calculation, and then the plate was formulated as “V” pattern according to dimensions of standard mini-plate finally. To compare the biomechanical behavior of the “V” plate and other conventional mini-plates for angle fracture fixation, two conventional fixation systems were used: type A, one standard mini-plate, and type B, two standard mini-plates, and the stress, strain and displacement distributions within the three fixation systems were compared and discussed.

Results

The stress, strain and displacement distributions to the angle fractured mandible with three different fixation modalities were collected, respectively, and the maximum stress for each model emerged at the mandibular ramus or screw holes. Under the same loading conditions, the maximum stress on the customized fixation system decreased 74.3, 75.6 and 70.6% compared to type A, and 34.9, 34.1, and 39.6% compared to type B. All maximum von Mises stresses of mandible were well below the allowable stress of human bone, as well as maximum principal strain. And the displacement diagram of bony segments indicated the effect of treatment with different fixation systems.

Conclusions

The customized fixation system with topological optimized structure has good biomechanical behavior for mandibular angle fracture because the stress, strain and displacement within the plate could be reduced significantly comparing to conventional “one mini-plate” or “two mini-plates” systems. The design methodology for customized fixation system could be used for other fractures in mandible or other bones to acquire better mechanical behavior of the system and improve stable environment for bone healing. And together with SLM, the customized plate with optimal structure could be designed and fabricated rapidly to satisfy the urgent time requirements for treatment.

Osteosynthesis using cannulated headless Herbert screws in mandibular angle fracture treatment: A new approach?

INTRODUCTION

Fractures of the mandibular angle are a common type of facial skull fracture. Although operative treatment includes a wide range of fixation techniques, a definite gold standard method has yet to be established. Headless, cannulated Herbert screws, often used in many forms of minimally invasive trauma surgery, provide functional and stable fracture fixation.

MATERIALS AND METHODS

In a prospective, double-randomised, controlled, parallel-group - designed, in vitro trial, the biomechanical behaviour of the Herbert bone screw system was compared to that of a conventional locking plate system in 40 mandibular angle fractures of human mandible cadaver phantoms.

RESULTS

The mean stress values were 250 (±68.0) N in the plate subgroup and 200 (±61.0) N in the screw subgroup. The respective mean strain values were 7.90 (±2.7) mm and 6.90 (±2.2) mm, and the respective mean stiffness were values 1.10 (±0.61) N/m and 0.78 (±0.40) N/m. The differences in the results obtained using the two treatments were not significant (p = 0.55).

CONCLUSIONS

The biomechanical behaviour of the two fixation systems within the tested loads did not significantly differ with respect to postoperative parameters clinically relevant in osteosynthesis. Both systems met the mandibular angle assessment criterion, which is considered to be sufficient for clinical use. The results indicate the potential clinical utility of these two systems, and recommend further testing.

Single Miniplate Fixation for Mandibular Symphysis and Parasymphysis Fracture as a Viable Alternative to Conventional Plating Based on Champy's Principles: A Prospective Comparative Clinical Study

To compare long term and short term outcomes of fixing mandibular symphysis and parasymphysis fractures with single mini plate and conventional fixation using two mini plates.

STUDY DESIGN

in this prospective clinical comparative study, 30 patients with fracture in study region were randomly divided into two groups. Group A patients received single 2.5 mm titanium miniplate and Group B patients received two 2 mm titanium miniplates as per Champy's lines of osteosynthesis. Patients were followed up at intervals of 1, 12 and 24 weeks. Parameters assessed were: duration of surgery, fracture stabilization, paresthesia, occlusion and wound dehiscence. Statistically significant difference was observed in mean duration of surgery and wound dehiscence (P < 0.05). No significant difference was observed with respect to other parameters. Single 2.5 mm miniplate for mandibular symphysis and parasymphysis fractures is a time saving and cost effective technique with post-operative outcomes similar to conventional 2 plate fixation.

Comparison of postoperative changes in the distal and proximal segments between conventional and sliding mini-plate fixation following mandibular setback

Objective

The purpose of the present study was to evaluate the postoperative three-dimensional (3D) changes in the proximal segments after mandibular setback sagittal split ramus osteotomy and to compare the changes between the conventional mini-plate fixation and semi-rigid sliding plate fixation.

Methods

Cone-beam computed tomography (CBCT) images were used to evaluate the postoperative 3D changes in the proximal segments during the healing process. CBCT images were superimposed using the symphysis and the lower anterior mandible as references.

Results

There were no statistically significant differences between the conventional mini-plate and semi-rigid sliding plate groups (p > 0.05). With respect to the distribution of changes greater than 2 mm in the landmarks, the right condylion, right coronoid process, and left condylion showed ratios of 55.6%, 50.0%, and 44.4%, respectively, in the semi-rigid sliding plate group; however, none of the landmarks showed ratios greater than 30% in the conventional mini-plate group.

Conclusions

There were no statistically significant differences in postoperative changes in the segments between the conventional mini-plate and semi-rigid sliding plate groups. Nevertheless, while selecting the type of fixation technique, clinicians should consider that landmarks with greater than 2 mm changes were higher in the semi-rigid sliding plate group than in the conventional mini-plate group.

Effect of interfragmentary gap on the mechanical behavior of mandibular angle fracture with three fixation designs: A finite element analysis

BACKGROUND

The aim of this study was to simulate stress and strain distribution numerically on a normal mandible under physiological occlusal loadings. The results were compared with those of mandibles that had an angle fracture stabilized with different fixation designs under the same loadings. The amount of displacement at two interfragmentary gaps was also studied.

MATERIALS AND METHODS

A three-dimensional (3D) virtual mandible was reconstructed with an angle fracture that had a fracture gap of either 0.1 or 1 mm. Three types of plate fixation designs were used: Type I, a miniplate was placed across the fracture line following the Champy technique; Type II, two miniplates were used; and Type III, a reconstruction plate was used on the inferior border of the mandible. Loads of 100 and 500 N were applied to the models. The maximum von Mises stress, strain, and displacement were computed using finite element analysis. The results from the control and experimental groups were analyzed and compared.

RESULTS

The results demonstrated that high stresses and strains were distributed to the condylar and angular areas regardless of the loading position. The ratio of the plate/bone average stress ranged from 215% (Type II design) to 848% (Type I design) irrespective of the interfragmentary gap size. With a 1-mm fracture gap, the ratio of the plate/bone stress ranged from 204% (Type II design) to 1130% (Type I design). All strains were well below critical bone strain thresholds. Displacement on the cross-sectional mapping at fracture interface indicated that uneven movement occurred in x, y, and z directions.

CONCLUSIONS

Interfragmentary gaps between 0.1 and 1 mm did not have a substantial effect on the average stress distribution to the fractured bony segments; however, they had a greater effect on the stress distribution to the plates and screws. Type II fixation was the best mechanical design under bite loads. Type I design was the least stable system and had the highest stress distribution and the largest displacement at the fracture site.

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 evaluation of bite forces in patients after treatment of mandibular fractures with miniplate osteosynthesis and internal locking miniplate osteosynthesis

Aims and Objectives:

The aim of present study was to compare the stability of fractured mandibular fragments under functional load, when fixed with conventional miniplate and internal locking miniplate.

Materials and Methods:

Bite force (in kg) recorded in twenty mandible fractured patients and fifty normal healthy individuals. Bite force was measured at incisor and molar regions. Comparative evaluation of bite force generated was performed between 10 cases treated with conventional miniplates and 10 cases treated with internal locking miniplates. Bite force generated by patients in mandibular fracture between symphysis and the angle of mandible was recorded in incisor and molar regions preoperatively. The fracture fragments were fixed using the above fixation techniques. Then same recording was undertaken on the 7^th, 14^th, 21^st, 28^th, and 90^th days postoperatively.

Results:

Bite force generated by patients treated with locking plates at the 7^th, 14^th, 21^st, 28^th, and 90^th postoperative days was significantly higher as compared to those in patients treated with miniplates.

Conclusion:

It was observed in our study that the locking plate/screw system offers significant advantages over the conventional plating system. There are no intraoperative difficulties associated with placement of the plate.

Comparison of Stability of Fracture Segments in Mandible Fracture Treated with Different Designs of Mini-Plates Using FEM Analysis

AIM

To compare the displacement gap of mandible fracture segments treated with different designs of mini-plates under various loading conditions.

MATERIALS AND METHODS

Fracture in the body of mandible was bridged with 15 different designs and configuration of titanium mini-plates. Bite forces were applied at 3 locations, ipsilateral fractured side, contra lateral side and incisor site. 3D finite element methods (FEM) model of mandible was generated using 10 nodal tetrahedral elements. A commercial FE solver was used to solve bone inter fragmentary displacement during loading.

RESULTS

Superior position of mini-plates produced better stability than inferior position. Positive bending moments can be reduced by larger plate in lower border in 2 plate system. Results of X mini-plate are comparable to 2 plate configuration. If length of middle portion of plate increased, stability decreased. Number of screws did not affect fracture stability.

CONCLUSION

Finite element methods analysis is used to determine the gap between mandible fragments which is otherwise impossible to measure clinically. The results obtained from this study offered us a choice of mini-plate design and configuration for clinical application.

Assessment of the fixation of mandibular symphysis fractures using conical cannulated screws: mechanical and photoelastic tests

OBJECTIVE

The aim of this study was to use mechanical and photoelastic tests to compare the performance of cannulated screws with other fixation methods in mandibular symphysis fractures.

STUDY DESIGN

Ten polyurethane mandibles were allocated to each group and fixed as follows: group PRP, 2 perpendicular miniplates; group PLL, 1 miniplate and 1 plate, parallel; and group CS, 2 cannulated screws. Vertical linear loading tests were performed. The differences between mean values were analyzed with the Tukey test. The photoelastic test was carried out using a polariscope.

RESULTS

The results revealed differences between the CS and PRP groups at 1, 3, 5, and 10 millimeters of displacement. The photoelastic test confirmed higher stress concentration in all groups close to the mandibular base, whereas the CS group showed it throughout the region assessed.

CONCLUSIONS

Conical cannulated screws performed well in mechanical and photoelastic tests.

Use of miniplates in parasymphysis fractures : a survey conducted among oral and maxillofacial surgeons of India

Aim of the study was to find out the number of miniplates used by Indian Oral and Maxillofacial Surgeons for parasymphysis fractures. A survey was done among Oral and Maxillofacial Surgeons of India at the 34th annual meeting of Association of Oral and Maxillofacial Surgeons of India. Four questions were given to each individual to find out their opinion regarding use of miniplates in parasymphysis fractures. Eighty-eight per cent of Indian surgeons were in favour of using intra-operative or post-operative intermaxillary fixation. Thirty-eight per cent responded in favour of using single miniplate for parasymphysis fracture instead of using two miniplates. Fifty-four per cent maxillofacial surgeons use various modifications depending on different conditions. Forty-two per cent of maxillofacial surgeons accepted that lower arch bar can be used as a tension band. Use of miniplates for the treatment of parasymphysis fracture varies from centre to centre and from surgeon to surgeon. Though miniplates are best used following Champy's principle, still many surgeons use single miniplate. Arch bars placed for intermaxillary fixation can be used as a tension band, again eliminating the need for upper plate.

In vitro mechanical assessment of 2.0-mm system three-dimensional miniplates in anterior mandibular fractures

This study constituted a comparative assessment of the mechanical resistance of square and rectangular 2.0-mm system three-dimensional miniplates as compared to the standard configuration using two straight miniplates. 90 polyurethane replica mandibles were used for the mechanical trials. Groups 1, 2, and 3 simulated complete symphyseal fractures characterized by linear separation of the central incisors; groups 4, 5, and 6 simulated parasymphyseal fractures with an oblique configuration. Groups 1 and 4 represented the standard method with two straight miniplates set parallel to one another. Square miniplates were used in groups 2 and 5, and rectangular miniplates in groups 3 and 6. A universal testing machine set to a velocity of 10mm/min and delivering a vertical linear load to the first left molar was used to test each group. Maximum load values and load values with pre-established dislocation of 5mm were obtained and submitted to statistical analysis using a calculated reliability interval of 95%. The mechanical performances of the devices were similar, except in the case of rectangular plates used in the parasymphyseal fractures. The innovative fixation methods used showed significantly better results in the case of symphyseal fractures.

A Prospective Study of Strut versus Miniplate for Fractures of Mandibular Angle

This prospective randomized clinical trial compared the treatment outcomes of strut plate and Champy miniplate in fixation of mandibular angle fractures. Patients with mandibular angle fracture were consented and enrolled into this study. Exclusion criteria include patients with severely comminuted fractures. The patients were randomly assigned to receive the strut plate or Champy miniplate for angle fracture fixation. Patient demographics, fracture characteristics, operative and postoperative outcomes were collected prospectively. Statistical analysis was performed to evaluate the significance of the outcome. A total of 18 patients were included in this study and randomly assigned to receive either the strut plate or Champy miniplate. Out of which five patients were excluded postoperatively due to complex fracture resulting in postoperative maxillomandibular fixation. The final enrollment was 13 patients, N = 6 (strut) and N = 7 (Champy). There was no statistically significant difference in the pretreatment variables. Nine of these patients had other associated facial fractures, including parasymphyseal and subcondylar fractures. Most of the (11) patients had sufficient follow-up after surgery. Both groups exhibited successful clinical unions of the mandibular angle fractures. The complications associated with the mandibular angle were 20% in the strut plate group and 16.7% in the Champy group. One patient in the strut plate group had a parasymphyseal infection, requiring hardware removal. The strut plate demonstrated comparable surgical outcome as the Champy miniplate. It is a safe and effective alternative for management of mandibular angle fracture.

Transoral Miniplate Fixation of Mandibular Angle Fracture with and without 2 Weeks of Maxillomandibular Fixation: A Clinical Trial Study

Background and Objectives The ideal line of osteosynthesis in mandibular angle fractures indicates that a plate might be placed either along or just below the external oblique ridge. Some authors believe that using one miniplate at this line at the mandibular angle region provides sufficient strength to stabilize the fracture but others imply a second plate is required. Such controversies exist in the use of maxillomandibular fixation (MMF). The intention of the present study was to compare efficiency and complications of using one miniplate with and without MMF in mandibular angle fractures. Methods and Materials Forty patients with facial trauma with mandibular angle fractures including displaced and unfavorable fractures were categorized into two groups of 20 persons. In all patients, one miniplate was placed on the external oblique ridge. In the first group, patients had light maxillomandibular elastic bands just after surgery but no rigid MMF. In the second group, patients had rigid MMF for 2 weeks after surgery. Patients were followed to evaluate complications and treatment efficiency. Conclusions Our study showed that use of a single miniplate in the external oblique ridge is a functionally stable treatment for all types of angle fractures (including displaced and unfavorable fractures) except comminuted and long oblique fractures, which were not included in our study. Use of postoperative MMF did not improve the results.

Evaluation of different miniplates in fixation of fractured human mandible with the finite element method

The objective of this study was to develop a 3-dimensional finite element model (FEM) to formulate biomechanical justification of the positioning of different plates to achieve stable fixation of a fractured mandible. Miniplate systems that give acceptable levels of rigidity were investigated, and recommendations about miniplate location, orientation, and type selection are made. A fracture near the body region was bridged with a variety of commonly used plate configurations. Number, positioning and type of the plate system parameters. The results of this fracture model support the advantage of 2-plate systems. Using a longer plate in the superior position and a shorter one in the inferior position produced a more stable condition. Number of screws or length of the miniplate had no significant effect on the stability of fractured segments. The results obtained from this study offer the choice of a particular plate size, thickness, design, or configuration for application and thus provide information for clinical use.

Fixation of mandibular osteotomies: Comparison of locking and nonlocking hardware

BACKGROUND

: The outcome of patients undergoing rigid plate fixation of symphyseal mandibular osteotomies for exposure, resection, and reconstruction of tumors in the oral cavity or oropharynx was analyzed to determine the impact of hardware selection on complications.

METHODS

: Forty-five patients underwent titanium plate rigid internal fixation of mandibular osteotomies during cancer resection and free flap reconstruction at an academic medical center. The incidence of hardware-related complications and mandibular nonunion was compared in patients receiving either locking hardware or nonlocking hardware.

RESULTS

: The incidence of osteotomy-related complications in patients with an inferior border nonlocking mandibular fracture plate was 21%. In the patients with locking hardware or an inferior border nonlocking mandibular fracture plate combined with a tension band, there were no hardware-related complications and no mandibular nonunions. This difference was statistically significant (chi(2) = 6.01, p < .05).

CONCLUSIONS

: Locking mandibular reconstruction plates are associated with fewer complications than inferior border nonlocking mandibular fracture plates for rigid fixation of mandibular osteotomies in patients undergoing resection of head and neck cancer.

Evaluation of osteotomy fixation changing the number, the extension and the location of the plates

We used a two-dimensional model that simulated a fractured human mandible to study the extent of load resistance of different plates. We studied 49 bovine ribs in seven groups using varying number (1 or 2), lengths of plates (4 or 6-holes), and location (near the lower or upper border). The number and location of plates had a greater effect on resistance to load than length of plates. The best mean resistance values were achieved by a combination of two parallel plates secured near the lower and upper borders, followed by single plates secured near the upper border. The lowest values were with single plates secured close to the lower border.

Fracture Patterns and Bone Healing in Recurrent Mandibular Fractures: A Clinical Study of 13 Patients

BACKGROUND

Recurrent fractures of the previously treated fractured mandible are rare.

METHODS

In this retrospective study, 13 cases of repeated mandibular fractures were evaluated according to age, sex, cause, fracture localizations and patterns, treatment modalities, and complications.

RESULTS

All of the patients were men, with a mean age of 27.5 years and 32 years for the first and the subsequent fractures, respectively. The mean time interval between fractures was 4.3 years. In 10 cases, the cause for the second fracture was an assault, with 90 percent related to alcohol intake. Angle, body, and parasymphysis region of the mandible were the most common sites to be involved in the first occasion. In 10 cases, an internal rigid fixation procedure was performed for the treatment. In the recurrent injuries, none of the fractures occurred at exactly the same anatomical site. Fractures were either in the neighboring side or the contralateral side of the previously healed area of mandible. On the second occasion, angle fractures were common and body and subcondylar fracture rates increased. At second presentation, the complication rate increased from 23.1 percent to 53.8 percent and most commonly involving malocclusion.

CONCLUSIONS

This study showed that assault is the major etiologic factor for recurrent mandible fractures and that these fractures occur in different locations from the original injury. They necessitate a cautious approach for the prevention of unfavorable outcomes. Further retrospective clinical and experimental studies are necessary to elucidate the fracture patterns and bone-healing quality of these recurrent mandible fractures.

Treatment of mandibular angle fractures with a matrix miniplate: a preliminary report

Mandibular angle fractures are technically challenging, and a spectrum of techniques for treatment of these fractures has been proposed in the literature. Currently, fixation with one or two miniplates has become a widely accepted method of providing internal fixation and eliminating the need for postoperative maxillomandibular fixation. In this study, the utility of a single 2.0-mm matrix miniplate for mandibular angle fracture management was examined. In a laboratory biomechanical analysis, the overall stability of the single 2.0-mm matrix miniplate compared favorably with two 2.0-mm miniplates in a simulated fracture setting. The matrix miniplate demonstrated an overall better intrinsic stability, more resistance to out-of-plane fracture movement, and a higher load tolerance when motion out-of-plane was challenged. Clinically, the matrix miniplate performed well. In a series of 22 consecutive patients, there were no cases of nonunion, malunion, or plate failure. Two patients developed infection that was managed in both cases by drainage with maintenance of the miniplate. Both went on to full union. These results compare very favorably to previously published series using one or two miniplates.

Treatment modalities for mandibular angle fractures

PURPOSE

Management of mandibular angle fractures is often challenging and results in the highest complication rate among fractures of the mandible. Optimal treatment for angle fractures remains controversial. Historically, treatment of mandible fractures included intraoperative maxillomandibular fixation (MMF) along with rigid internal fixation. More recently, noncompression plates miniplates, which produce only relative stability, have gained popularity. The absolute necessity of intraoperative MMF as an adjunct to internal fixation has also become controversial. The current trends in the management of simple, noncomminuted mandibular angle fractures are examined.

MATERIALS AND METHODS

A survey was submitted to North American and European AO ASIF (Arbeits-gemeinschaft fur Osteosynthesefragen Association for the Study of Internal Fixation) faculty in July 2001. Statistical analysis of results included both Fisher's exact and chi-square tests. Results were considered significant if P <.05.

RESULTS

One hundred ten of 127 potential responses were received (87%). Among 104 surgeons who treat mandible fractures, 86 (83%) treat more than 10 mandibular fractures per year. Preferred techniques for simple, noncomminuted mandibular angle fractures in this group were: single miniplate on the superior border (Champy technique) with or without arch bars (44 surgeons, 51%); tension band plate on the superior border and nonlocking, bicortical screw plate on the inferior border (11 surgeons, 13%); dual miniplates (9 surgeons, 10%); a locking screw plate on the inferior border only (6 surgeons, 7%), and 3-dimensional plates (5 surgeons, 6%). Eleven surgeons (13%) gave multiple answers. Although only 13% of surgeons surveyed primarily use the combination of tension band and nonlocking, bicortical screw plates, many surgeons (73%) continue to use this technique in certain circumstances. Within this group, 32 (51%) place screws in a neutral position, while 31 (49%) place screws in an eccentric position, resulting in compression. For simple noncomminuted angle fractures, the number of surgeons performing internal fixation without MMF were: 14 often (16%); 20 occasionally (23%); 17 seldom (20%); and 35 never (41%). Surgeons treating more than 10 versus those who treat less than 10 fractures per year, International versus North American faculty, and Oral and Maxillofacial surgeons (OMS) versus non-OMS surgeons were compared. Surgeons who treat more than 10 fractures per year favor the Champy technique over the tension band and bicortical plate combination (44 [51%] vs 11 [13%]), while those surgeons who treat less than 10 per year favor the tension band and bicortical plate combination over the Champy technique (9 [50%] vs 3 [17%]; P < .01, Fisher exact test). International faculty are less likely to use intraoperative MMF than North American faculty (29 [81%] vs 31 [43%]; P < .01, Fisher exact test). OMS surgeons are less likely to use the tension band and bicortical plate combination than non-OMS surgeons (22 [56%] vs 42 [90%]; P < .017, Fisher exact test).

CONCLUSION

This survey suggests an evolution in the management of mandibular angle fractures. A single miniplate plate on the superior border of the mandible has become the preferred method of treatment among AO faculty. When using large, inferiorly based plates more surgeons are now favoring neutral rather than eccentric screw placement. Intraoperative MMF is not considered mandatory by some surgeons in certain circumstances.

Photoelastic analysis of bone deformation in the region of the mandibular condyle during mastication

INTRODUCTION

The purpose of this experimental study was to demonstrate the stress patterns arising in the region of the mandibular condyle during mastication.

MATERIAL AND METHOD

Stress analysis was performed using reflection photoelasticity to demonstrate deformation occurring on the surface of the mandible. The rami of three fresh dentate human mandibles were coated with a shell of photoelastic resin. Using a novel loading device, these mandibles were then subjected to external forces (muscular traction, resultant mandibular forces and intra-articular reaction force) reproducing a unilateral biting task between the first right molars. Deformations were measured from the working side.

RESULTS

The trace of isostatic lines from the isoclinic fringes revealed major differences in stress distributions between the three mandibles. These differences were attributed to differences in shape between the three mandibles. Conversely, we consistently found compressive stress patterns along the posterior border of the ramus and tensile stress patterns along the anterior border of the ramus and in the zone situated below the siqmoid notch.

CONCLUSION

These findings suggest that during this particular task, the mandible is subjected to sagittal forces which tend to straighten the mandibular angle. This implies that new concepts are needed for the positioning of osteosynthesis plates in the condylar region, close to the tensile strain lines, as has been recommended also for other parts of the mandible when applying semi-rigid internal fixation.

A computer study of biodegradable plates for internal fixation of mandibular angle fractures

PURPOSE

This computer-based study was performed to determine the suitability of small biodegradable plate systems for mandibular angle fractures.

MATERIALS AND METHODS

In a 3-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. The angle fracture was fixed with 2 polylactide (PLA) midiplates or with 2 PLA maxiplates. The first plate was positioned buccally on the external oblique ridge. Two positions of the second plate were studied: halfway up the height of the mandible or on the lower border. Maximum fracture mobility was set at a limit of 150 microm to enable undisturbed fracture healing. Maximum plate strain was set at the yield strain of PLA.

RESULTS

Fixation with the PLA maxiplates, with the second plate positioned halfway up the height of the mandible, resulted in fracture mobility below the set limit for all bite points. For the other PLA fixation strategies, fracture mobility exceeded the set limit. Fixation with the second plate positioned halfway up the height of the mandible generally resulted in less fracture mobility than with the plate positioned on the lower border. The yield strain of PLA was not exceeded in any of the fixation strategies.

CONCLUSIONS

Based on the computer model, 2 PLA maxiplates are suitable for fixation of mandibular angle fractures. One plate should be positioned buccally on the external oblique ridge, and the other should be positioned halfway up the height of the mandible.

Development of a static simulator of the mandible

Our aim was to build and assess a static mandibular simulator capable of reproducing various masticatory exercises as closely as possible to physiological situations. Unlike existing devices that reproduce a small number of exercises and of muscular bundles, our simulator is able to reproduce all types of effort in the sagittal plane and integrates eleven muscular groups considered by the majority of authors as being the most important in mastication. The value of our simulator arises from its ability to replicate the external forces (including muscular traction, intra-articular reaction and resultant forces applied to the mandible) as determined in vivo during previous studies. The importance of such a versatile simulator, in addition to enabling study of the mechanical behaviour of the mandible, is that it greatly enhances evaluation of a possible mathematical model by means of finite element analysis. Stages of the development and evaluation of this device are described.

A computer study of fracture mobility and strain on biodegradable plates used for fixation of mandibular fractures

PURPOSE

This computer-based study was done to determine whether a small biodegradable plate system was suitable for internal fixation of mandibular fractures.

MATERIALS AND METHODS

In a three-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. Simulated solitary angle, body, and symphysis fractures were fixed with one titanium miniplate, one polylactide (PLA) midiplate, one PLA maxiplate, or two PLA midiplates. Fractures with and without interfragmentary bone contact were studied. In the case of fractures with bone contact, the loads were transmitted through the fracture surfaces and the plate; when there was no contact, the loads were transmitted only through the plate. Maximum fracture mobility was set at 150 microm. Maximum plate strain was set at the yield strain of PLA and titanium.

RESULTS

For fractures without interfragmentary bone contact, all plate fixations resulted in a fracture mobility and plate strain higher than the limits set, except for the symphysis fracture fixed with two PLA midiplates. Interfragmentary bone contact significantly reduced fracture mobility and plate strain. For the angle fracture with bone contact, all PLA plate fixations resulted in a fracture mobility above the limit, whereas the titanium miniplate fixation had a fracture mobility below the limit. For the body and symphysis fracture with bone contact, only double PLA midiplate fixation resulted in a fracture mobility below the limit.

CONCLUSIONS

From a mechanical point of view, based on the computer model, small PLA plates are only suitable for symphysis fractures with and without interfragmentary bone contact and for body fractures with interfragmentary contact. However, fixation with two PLA plates is always necessary to provide sufficient reduction of fracture mobility and plate strain.