The biophysics of mandibular fractures: an evolution toward understanding

Simplified Fabrication of a Lingual Splint for Management of Mandibular Fractures

Lingual splints have been used to treat mandibular fractures, particularly in cases of complicated mandibular fractures, and serve as a noninvasive adjunctive procedure for reduction and fixation. Furthermore, when used in conjunction with open reduction and internal fixation, the lingual splint provides feasible external fixation against displacing forces exerted by the robust musculature of the mandible. However, the conventional method for lingual splint fabrication is performed preoperatively, and the procedure is time-consuming. This technical note describes a simplified and efficient technique for the intraoperative manufacture of a lingual splint for mandibular fractures using a thermoplastic material, polycaprolactone. Our results demonstrated satisfactory fixation outcomes, reduced lingual splint fabrication time, and superior cost-effectiveness, offering an alternative option for adjunctive external fixation of mandibular fractures.

The biomechanical stability of miniplate osteosynthesis configurations in bilateral mandibular angle fractures

PURPOSE

The present study investigated the biomechanical stability of three miniplate osteosynthesis configurations used for internal fixation of bilateral mandibular angle fracture (BMAF).

METHODS

Standard fracture lines were created in 72 polyurethane mandibles and stabilized with 2.0-mm, 4-hole standard titanium miniplates and monocortical screws. The group descriptions and miniplate configurations were: 2Plates (1-1), 3Plates (1-2) and 4Plates (2-2). The mandibles were subjected to either incisal or molar loads (from both sides in the 3Plates group) up to a force of 120 N. The displacements of the constructs were recorded at each force increment of 10 N. ANOVA and Tukey's post-hoc tests were used for statistical analysis.

RESULTS

The 2Plates group showed higher displacement under both loading conditions (P < 0.05 for each). The same group reached displacement levels of 1 mm and 3 mm during molar loading and 1 mm, 3 mm, and 5 mm during incisal loading at lower force magnitudes relative to others (P < 0.05 for each).

CONCLUSION

Bone-plate constructs for BMAFs stabilized with three or four standard miniplates are more likely to provide similar resistance when subjected to incisal or molar loads, in contrast to the two-miniplate configuration, which is relatively more prone to displacement.

An In vitro study of biomechanical comparison between titanium 4-hole 3D plates and titanium conventional 4-hole miniplates for internal fixation of mandibular angle fractures

Background

Fracture fixation, in the present times, is classically done using mini plates. The position and number of plates to fixate a mandibular angle fracture have been and are still extensively researched and reported in the literature. A more recent addition is 3D mini plates.

Aim

To compare and evaluate the biomechanical behavior of one 2.0 mm titanium 3D miniplate fixation plate (4- hole) and one 2.0 mm titanium 4-hole miniplate in internal fixation of mandibular angle fractures.

Objective

To measure load at break, maximum load, and displacement at maximal load for internal fixation done with 3D mini plates and conventional mini plates respectively.

Methods

Five dry cadaveric mandibles were sectioned into 10 hemi-mandibles. Each cadaveric mandible was sectioned at the angle of mandible to simulate unfavorable mandibular angle fracture. The obtained hemimandible were divided into experimental groups (GROUP 1 and GROUP 2) with 5 samples in each group, plated with a linear miniplate and 3D miniplate respectively. Maximal load, Load at break, and displacement at maximum load were the only obtained parameters for comparison.

Results

Conventional miniplate showed greater mean maximum load values of 174.93 N±54.45 compared to 3D mini plates which recorded a mean maximum load value of 106.96 N ± 23.86. Load at break and displacement at maximum load were found to be both insignificant.

Conclusion

The results in this study showed statistically no significant difference with any of the above parameters except maximal load, between the two groups evaluated. Conventional linear miniplate according to Champy's lines of osteosynthesis can be used successfully for providing satisfactory osteosynthesis with the definitive advantage of cost-effectiveness.

Fracture Fixation Technique and Chewing Side Impact Jaw Mechanics in Mandible Fracture Repair

Lower jaw (mandible) fractures significantly impact patient health and well‐being due to pain and difficulty eating, but the best technique for repairing the most common subtype—angle fractures—and rehabilitating mastication is unknown. Our study is the first to use realistic in silico simulation of chewing to quantify the effects of Champy and biplanar techniques of angle fracture fixation. We show that more rigid, biplanar fixation results in lower strain magnitudes in the miniplates, the bone around the screws, and in the fracture zone, and that the mandibular strain regime approximates the unfractured condition. Importantly, the strain regime in the fracture zone is affected by chewing laterality, suggesting that both fixation type and the patient's post‐fixation masticatory pattern—ipsi‐ or contralateral to the fracture— impact the bone healing environment. Our study calls for further investigation of the impact of fixation technique on chewing behavior. Research that combines in vivo and in silico approaches can link jaw mechanics to bone healing and yield more definitive recommendations for fixation, hardware, and postoperative rehabilitation to improve outcomes. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The Effects of Frontal Trauma on 4 Interforaminal Dental Implants: A 3-Dimensional Finite Element Analysis Comparing Splinted and Unsplinted Implant Configurations

PURPOSE

With increased implant-prosthodontic rehabilitation for mandibular edentulism together with the increased life expectancy and activity of the elderly population, a greater number of implant patients may be at risk of facial trauma. The aim of this 3-dimensional (3D) finite element analysis (FEA) was to evaluate the biomechanical effects of the edentulous mandible (EM) with and without implants exposed to frontal facial trauma including assessment of the fracture risk of different mandibular areas.

MATERIALS AND METHODS

By use of a 3D FEA, our experimental study design comprised 3 different models (model A, EM; model B, EM with 4 unsplinted interforaminal implants; and model C, EM with 4 splinted interforaminal implants) exposed to application of symphyseal frontal trauma of 2 MPa. In 3 defined regions of interest (ROIs) (ROI 1, symphyseal area; ROI 2, mental foraminal area; and ROI 3, condylar neck), the effective stress was measured at predefined sites in the superficial cortical mandibular area. The stress values of all ROIs evaluated were compared within each model (intramodel) as well as between the 3 models (intermodel).

RESULTS

For all models evaluated, a frontal traumatic load generated the highest stress levels in the condylar neck. However, for both models with implants (models B and C), the stress values were reduced significantly (P < .01) in the condylar neck region (ROI 3) but increased significantly (P < .001) in the mental foraminal area (ROI 2) compared with the EM model without implants. For the symphyseal area (ROI 1) evaluated, the unsplinted 4-implant model (model B) presented significantly (P < .001) higher stress values than the splinted implant model (model C) when frontal forces were applied.

CONCLUSIONS

Regardless of splinting or lack of splinting of 4 interforaminal implants, force absorption or transmission may shift the predominant risk factor from the condylar neck to the corpus or foramen mandibulae. However, splinting of 4 interforaminal implants may be beneficial in reducing the risk of bone fracture by providing protection for anterior risk situations.

Treatment of mandibular angle fracture: Revision of the basic principles

Biodynamics of mandibular angle fractures has been extensively discussed in the literature in search for the best way to fixate and expedite recovery of trauma patients. Pioneers like Michelet and Champy had the greatest impact on evolving of osteosynthesis in maxillofacial traumatology; they introduced their basic principles frequently used to describe the biomechanics of mandibular fixation. Their concept states when a physiologic load is applied on mandibular teeth a negative tension will be created at superior border and a positive pressure will appear at inferior border. These simple definitions are the basis for the advent of fixation modalities in mandibular angle fracture. This article sought to reassess these principals based on load location via finite elements method.

Titanium Lag Screw Versus Miniplate Fixation in the Treatment of Anterior Mandibular Fractures

PURPOSE

The use of plates for open reduction and internal fixation of mandibular fractures has become a widely accepted method in the past 3 decades. However, the anterior mandible is well suited to lag screw fixation owing to the thickness of its bony cortices. Hence, the purpose of the present study was to comparatively evaluate clinical outcomes of fixation using lag screws and miniplates in anterior mandibular fractures.

PATIENTS AND METHODS

Fifty patients reporting to the department of oral and maxillofacial surgery with noncomminuted anterior mandibular fractures were randomly divided into 2 groups of 25 patients each. Patients in group A were treated with 2.5-mm lag screws 22 to 26 mm in length and those in group B were treated with 2.0-mm 4-hole miniplates with a gap using monocortical screws. Subsequent follow-up was performed at 3, 6, 12, and 24 weeks postoperatively. The primary determinants included radiographic analysis of the fracture gap and biting efficiency of the patients in groups A and B. The secondary determinants included evaluation of duration of surgery, occlusion before and after injury, and postoperative complications. Results were evaluated using χ² and unpaired t tests.

RESULTS

The mean age of the patients in this study was 29.1 ± 8.32 years (range, 18 to 67 yr). The mean postoperative fracture gap was considerably larger in group B. The mean duration of surgery (minutes) was 37.60 ± 9.30 for group A and 47 ± 6.55 for group B. The difference was statistically significant (P = .001). The lag screw group showed faster improvement in biting efficiency compared with the miniplate group.

CONCLUSIONS

Lag screw fixation was found to have good stability and rigidity, was inexpensive, and was less time consuming in treating anterior mandibular fractures compared with miniplates.

Biomechanical assessment of fixation methods for segmental mandible reconstruction with fibula in the polyurethane model

BACKGROUND

A variety of plating techniques are employed by microsurgeons to provide rigid fixation for vascularized bone constructs of the mandible. The aim of this study was to biomechanically compare three commonly utilized plating techniques for rigid fixation of fibula bone flaps in reconstructing lateral segmental mandibular defects.

MATERIALS AND METHODS

Polyurethane mandibles with 3-cm segmental defects were reconstructed using polyurethane fibula models. Three fixation techniques were compared (n = 5 models per group): Group 1 used two 2.0-mm miniplates at each osteotomy site, Group 2 used a single 2.3-mm plate, and Group 3 used a single 2.7-mm plate. Biomechanical testing of maximum force and displacement at failure for each plating technique was assessed and statistical comparison performed.

RESULTS

The average displacement for Group 1 was 14.08 ± 1.42 mm, Group 2 was 5.79 ± 0.89 mm, and Group 3 was 6.03 ± 1.59 mm. Group 1 had significantly greater (P < 0.05) displacement when compared with Group 2 and 3. Analysis of variance demonstrated the three groups varied significantly in mean displacement (0 < 0.01). The average force before failure for Group 1 was 616.4 ± 33.83N, Group 2 was 737.8 ± 72.57N, and Group 3 was 681.0 ± 67.98N. Group 2 withstood significantly greater force than Group 1 (P < 0.05), and withstood greater force than Group 3, although the difference was not significant. Analysis of variance showed the three groups varied significantly in mean force at failure (P < 0.05).

CONCLUSION

Reconstruction using a single 2.3-mm plate provided the best rigid fixation for lateral segmental defects of the mandible. © 2016 Wiley Periodicals, Inc. Microsurgery 36:330-333, 2016.

Preoperative Planning of Virtual Osteotomies Followed by Fabrication of Patient Specific Reconstruction Plate for Secondary Correction and Fixation of Displaced Bilateral Mandibular Body Fracture

This paper describes the course of treatment of a severely diplaced bilateral mandibular body fracture, where the first osteosynthesis failed. The subject developed an open bite due to a posterior rotation of the distal part of the mandible and anterior rotation of the proximal parts of the mandible. This situation was evaluated with CBCT and the facial skeleton was segmented using computer software. Correct occlusion was virtually established by bilateral virtual osteotomies in the fracture areas of the mandible. After segmentation, the mandible was virtually rotated back into position and the open bite was closed. A patient specific mandibular reconstruction plate was outlined and fabricated from the new virtual situation and the plate was thereafter installed utilizing the preoperative plan. Osteotomy- and drill-guides was used and thus simplified the surgery resulting in uneventful healing. Virtual planning and patient specific implants and guides were valuable in this case of secondary reconstructive trauma surgery.

Finite-element analysis of 3 situations of trauma in the human edentulous mandible

PURPOSE

Maxillofacial trauma resulting from falls in elderly patients is a major social and health care concern. Most of these traumatic events involve mandibular fractures. The aim of this study was to analyze stress distributions from traumatic loads applied on the symphyseal, parasymphyseal, and mandibular body regions in the elderly edentulous mandible using finite-element analysis (FEA).

MATERIALS AND METHODS

Computerized tomographic analysis of an edentulous macerated human mandible of a patient approximately 65 years old was performed. The bone structure was converted into a 3-dimensional stereolithographic model, which was used to construct the computer-aided design (CAD) geometry for FEA. The mechanical properties of cortical and cancellous bone were characterized as isotropic and elastic structures, respectively, in the CAD model. The condyles were constrained to prevent free movement in the x-, y-, and z-axes during simulation. This enabled the simulation to include the presence of masticatory muscles during trauma. Three different simulations were performed. Loads of 700 N were applied perpendicular to the surface of the cortical bone in the symphyseal, parasymphyseal, and mandibular body regions. The simulation results were evaluated according to equivalent von Mises stress distributions.

RESULTS

Traumatic load at the symphyseal region generated low stress levels in the mental region and high stress levels in the mandibular neck. Traumatic load at the parasymphyseal region concentrated the resulting stress close to the mental foramen. Traumatic load in the mandibular body generated extensive stress in the mandibular body, angle, and ramus.

CONCLUSIONS

FEA enabled precise mapping of the stress distribution in a human elderly edentulous mandible (neck and mandibular angle) in response to 3 different traumatic load conditions. This knowledge can help guide emergency responders as they evaluate patients after a traumatic event.

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.

Finite Element Analysis: A Maxillofacial Surgeon's Perspective

The science of finite element analysis (FEA) is purely a mathematical way of solving complex problems in the universe. In medical field, this is an innovation in biomedical research and development, as it gives easier mathematical solution to biological problems. This article deals with the understanding of various basic material properties of bone like Young's modulus, yield strength, Bulk modulus, shear modulus, Poisson's ratio and density from a maxillofacial surgeon's perspective. Basic concepts in FEA, its application, advantages, disadvantages, and limitations in the field of maxillofacial surgery have been discussed. The importance of surgical fraternity to be in coordination with evolving technologies has been emphasized for the future of evidence based practice of oral and maxillofacial surgery.

A new biomechanical model for evaluation of fixation systems of maxillofacial fractures

The aim of this study was to develop a new type of biomechanical model for biomechanical researches of maxillofacial fractures and then evaluate it. Twenty synthetic polyurethane maxillary and mandibular models were used to simulate the mandible and maxilla. Springs were used to represent the forces of masseter, medial pterygoid, temporalis, and lateral pterygoid muscles acting on the models. Four masticatory conditions, namely clenching in the intercuspal position (ICP), incisal clenching (INC), left unilateral molar clenching (L-MOL, contralateral side of fracture) and right unilateral molar clenching (R-MOL, fracture side) were simulated. The strain on a miniplates placed across a simulated fracture was measured using strain gauges attached to the plate surface. During INC and L-MOL, the strain on the miniplates confirmed the findings of Champy. The upper miniplate was subjected to tension force and the lower miniplate to compression. When the bite point moved to the fracture, the tension-compression zone reversed, with the upper miniplate relatively compressed and the lower miniplate tension. During ICP, the tension-compression zone changed again, with both miniplates tension. In conclusion, we have successfully developed a model which is much closer to physiological conditions than models used previously. It is reliable and useful for biomechanical tests of mandibular fractures. Models including soft tissue need developing to further understand fracture healing biomechanics.