In vitro evaluation of the resistance of three types of fixation to treat fractures of the mandibular angle

Finite element analysis of 3D-printed personalized titanium plates for mandibular angle fracture

This paper discussed the size of 3 D-printed personalized titanium plates that can gain maximum stability of mandibular fracture and minimize stress shielding through finite element analysis. A 3 D virtual model of mandible with mandibular angle fracture was created from the CT data of patient. 3 D-printed personalized titanium plates varying in length and thickness were designed, and finite element analysis was performed under different loading conditions and fracture healing periods. After that, the stress distribution and deformation of the mandible with gonial fracture could be observed, and the stress shielding rate could be obtained. Finally, SPSS21.0 was used for statistical analysis. The results of finite element analysis indicated that as the thickness of titanium plates and the healing time decreased, the maximum displacement increased, under a certain condition in which the pore size, the width, the hole distance and the bridge spacing were 2.0 mm, 4.0 mm, 6.0 mm, 12.0 mm, respectively. What's more, in this condition, the thicker the titanium plate and the shorter the healing time were, the higher the stress shielding was at central occlusion. When the thickness of the personalized 3 D-printed titanium plate was 1.0 mm, the maximum displacement tended to be stable and the stress shielding was minimized. It can not only improve the bone stability after tension band fixation, but also minimize the stress shielding, which is expected to expand the indications of tension band fixation.

Transbuccal vs. Intraoral Approach using an Angulated Screwdriver in Fixation of a Mandibular Angle Fracture

Objectives:

This study aimed to evaluate surgical stability and cosmetic outcomes in patients with mandibular angle fractures (MAFs) using an angled screwdriver (ASD) versus transbuccal trocar (TBT) for single locking plate fixation.

Methods:

A prospective cohort clinical study was done on 44 male patients (88%) and 6 (12% females patients with MAFs, categorized into 2 groups. Group A patients were treated with strictly intraoral vestibular incision using an angulated screwdriver; group B was treated with TBT. Both groups placed a single locking 2.0 mm mini-plates at the inferior border. The main outcome variables were the perioperative complication rate.

Results:

There were no statistical differences between both groups regarding postoperative wound dehiscence, screw or/and plate looseness, infection rate, and inferior dental nerve injury. The study (ASD) approach took 28.10±3.3minutes, while the TBT approach took 37.40±1.75minutes, indicating a highly significant difference in operating time (P=0.001). Post-operative edema had decreased significantly in the ASD group.

Conclusion:

According to the present results, a strictly intraoral approach for ASD enabled stable fixation of MAFs using a single mini-locking plate. This can significantly reduce operation time and postoperative edema and prevent extraoral scarring.

Experimental validation of finite element simulation of a new custom-designed fixation plate to treat mandibular angle fracture

BACKGROUND

The objective of the study was to validate biomechanical characteristics of a 3D-printed, novel-designated fixation plate for treating mandibular angle fracture, and compare it with two commonly used fixation plates by finite element (FE) simulations and experimental testing.

METHODS

A 3D virtual mandible was created from a patient's CT images as the master model. A custom-designed plate and two commonly used fixation plates were reconstructed onto the master model for FE simulations. Modeling of angle fracture, simulation of muscles of mastication, and defining of boundary conditions were integrated into the theoretical model. Strain levels during different loading conditions were analyzed using a finite element method (FEM). For mechanical test design, samples of the virtual mandible with angle fracture and the custom-designed fixation plates were printed using selective laser sintering (SLS) and selective laser melting (SLM) printing methods. Experimental data were collected from a testing platform with attached strain gauges to the mandible and the plates at different 10 locations during mechanical tests. Simulation of muscle forces and temporomandibular joint conditions were built into the physical models to improve the accuracy of clinical conditions. The experimental vs the theoretical data collected at the 10 locations were compared, and the correlation coefficient was calculated.

RESULTS

The results show that use of the novel-designated fixation plate has significant mechanical advantages compared to the two commonly used fixation plates. The results of measured strains at each location show a very high correlation between the physical model and the virtual mandible of their biomechanical behaviors under simulated occlusal loading conditions when treating angle fracture of the mandible.

CONCLUSIONS

Based on the results from our study, we validate the accuracy of our computational model which allows us to use it for future clinical applications under more sophisticated biomechanical simulations and testing.

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.

In Vitro Evaluation of the Effects of Different Fixation Methods on Stabilization of Mandibular Body Fractures

PURPOSE

Mandibular body fractures are considered to be one of the most affected fracture sites in the maxillofacial region. Although the rates of fracture in this region are high, biomechanical evaluations related to this region are rare. The purpose of this investigation was to reveal the effects of different treatment methods onmandibular body fractures.

METHOD

Twenty-five synthetic polyurethane hemi-mandibles were used in this study. The hemi-mandibles, which simulated simple unfavorable mandibular body fractures, were divided into 5 groups (n = 5/group) according to the treatment method. The bone segments were fixed using different osteosynthesis methods and 2.0 mm miniplate/screw systems. The groups consisted of locking or conventional systems, 5 or 11 mm long screws and 4 or 6 holes. The hemi-mandibles were loaded vertically with compressive strength until they reached 120 N.

RESULTS

The results were analyzed using Tamhane's T2 post hoc test, and the significance level was 0.05. Group 1 had the lowest mechanical resistance of all groups and group 5 had the highest. No significant differences were observed in group 2 or 3.

CONCLUSION

The locking system miniplate group showed better fixation stability than the conventional systems for the same screw length, and the number of holes and screw length seemed to be effective for stabilization.

Integrity of a Single Superior Border Plate Repair in Mandibular Angle Fracture: A Novel Cadaveric Human Mandible Model

PURPOSE

The purpose of this study was to compare the integrity of human mandibular angle fracture after fixation with a single titanium plate along the upper lateral border with that of the native human mandible.

MATERIALS AND METHODS

This cross-sectional anatomic study involved the left hemimandibles of 16 human cadavers. They were selected and divided in 2 groups by remaining dental status. Additional predictor variables, such as height of the left mandibular body and gender, were noted. Left hemisected native mandibles were mounted at the condyle and loaded on an Instron 5565 mechanical unit (Instron Corp, Norwood, MA) until fracture. Fractured left hemimandibles were fixated with a titanium miniplate and screws. After plate fixation, each hemimandible was reloaded on an Instron 5565 until fracture. Data pertaining to primary outcomes of load application were recorded in newtons at displacement values of 3.0, 5.0, and 7.0 mm and at displacement at fixation failure. Primary outcomes of maximum load and displacement at maximum load were recorded in newtons and millimeters, respectively. Descriptive statistics were used to summarize sample characteristics. Statistical comparisons were performed using t test, χ² (or Fisher exact) test, and linear regression. Pearson correlation was used to examine relations between select biomechanical measurements.

RESULTS

The study sample was composed of 12 female and 4 male cadaveric hemimandibles. Donors' age at time of death ranged from 54 to 95 years (mean age, 78.94 yr). The mean maximum load in native and plated hemimandibles was 943.56 and 292.57 N, respectively (P < .0001).

CONCLUSION

Key clinical findings of this study include the inability of single plate mandible fixation to restore the mandible to preinjury levels and verification that gender, dental status, and height of the mandible do not alter the stability of a single plate fixated mandible.

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.