Mechanical and photoelastic analysis of four different fixation methods for mandibular body fractures

Biomechanical Comparison of WE43-Based Magnesium vs. Titanium Miniplates in a Mandible Fracture Model in Sheep

In fractures of the mandible, osteosynthesis with titanium plates is considered the gold standard. Titanium is an established and reliable material, its main disadvantages being metal artefacts and the need for removal in case of osteosynthesis complications. Magnesium, as a resorbable material with an elastic modulus close to cortical bone, offers a resorbable alternative osteosynthesis material, yet mechanical studies in mandible fracture fixation are still missing. The hypothesis of this study was that magnesium miniplates show no significant difference in the mechanical integrity provided for fracture fixation in mandible fractures under load-sharing indications. In a non-inferiority test, a continuous load was applied to a sheep mandible fracture model with osteosynthesis using either titanium miniplates of 1.0 mm thickness (Ti1.0), magnesium plates of 1.75 mm (Mg1.75), or magnesium plates of 1.5 mm thickness (Mg1.5). No significant difference (p > 0.05) was found in the peak force at failure, stiffness, or force at vertical displacement of 1.0 mm between Mg1.75, Mg1.5, and Ti1.0. This study shows the non-inferiority of WE43 magnesium miniplates compared to the clinical gold standard titanium miniplates.

Photoelasticity for Stress Concentration Analysis in Dentistry and Medicine

Complex stresses are created or applied as part of medical and dental treatments, which are linked to the achievement of treatment goals and favorable prognosis. Photoelasticity is an optical technique that can help observe and understand biomechanics, which is essential for planning, evaluation and treatment in health professions. The objective of this project was to review the existing information on the use of photoelasticity in medicine and dentistry and determine their purpose, the areas or treatments for which it was used, models used as well as to identify areas of opportunity for the application of the technique and the generation of new models. A literature review was carried out to identify publications in dentistry and medicine in which photoelasticity was used as an experimental method. The databases used were: Sciencedirect, PubMed, Scopus, Ovid, Springer, EBSCO, Wiley, Lilacs, Medigraphic Artemisa and SciELO. Duplicate and incomplete articles were eliminated, obtaining 84 articles published between 2000 and 2019 for analysis. In dentistry, ten subdisciplines were found in which photoelasticity was used; those related to implants for fixed prostheses were the most abundant. In medicine, orthopedic research predominates; and its application is not limited to hard tissues. No reports were found on the use of photoelastic models as a teaching aid in either medicine or dentistry. Photoelasticity has been widely used in the context of research where it has limitations due to the characteristics of the results provided by the technique, there is no evidence of use in the health area to exploit its application in learning biomechanics; on the other hand there is little development in models that faithfully represent the anatomy and characteristics of the different tissues of the human body, which opens the opportunity to take up the qualitative results offered by the technique to transpolate it to an application and clinical learning.

Photoelastic analysis of conventional and locking system for treatment of mandibular angle fractures with a single plate

Background

This photoelastic analysis evaluated stress distribution in different osteosynthesis systems, conventional and locking, used for treatment of mandibular angle fractures with a single plate.

Material and Methods

Angle fractures were simulated in mandibles made of photoelastic resin. Following Champy’s method, plate osteosynthesis was performed. The samples were divided into five groups: Group 1, non-fractured mandible; Group 2, two screws were installed in each segment using a conventional system; Group 3, two screws were installed in each segment using a locking system; Group 4, three screws were installed in the proximal segment and four screws in the distal segment using a conventional plate; Group 5, three screws were installed in the proximal segment and four screws in the distal segment using a locking plate. In an universal testing machine coupled to a polariscope, a load was applied to the first molar 10 times. The 50 images were randomly numbered and analyzed qualitatively and quantitatively by two raters.

Results

The locking system promoted better stress distribution along the osteosynthesis. The locking system reduced stress magnitude in the distal segment, with a significant between-group difference (P≤ 0.001).

Conclusions

The locking plate/screw system can distribute stress more evenly throughout the osteosynthesis, especially when long seven-hole plates are used.

Key words:Internal fracture fixation, osteosynthesis, mandibular fracture, bone plates.

What is a better modality of maxillomandibular fixation: bone-supported arch bars or Erich arch bars? A systematic review and meta-analysis

Any procedure that aims to manage maxillofacial fracture is incomplete without meticulous maxillomandibular fixation (MMF). For decades, Erich arch bars (EABs) have been used for this purpose, but with the advent of bone-supported arch bars (BSABs), more surgeons now prefer them to conventional EABs. The present study was designed to identify which of the two methods is best. An exhaustive literature search was conducted in June 2020 on various electronic databases to select studies that compared EABs and BSABs. Outcomes such as duration of placement, stability, oral hygiene, and complications such as damage to the roots of teeth and needle-stick injury, were analysed. A total of 716 studies were identified, of which seven were eligible for inclusion. The meta-analysis showed that the use of BSABs is significantly faster with no needle penetration and better oral hygiene. Both arch bars are equally stable, but root damage is an associated complication. The available literature to date shows that BSABs are a better option than EABs. However, further research is recommended, as these studies are associated with various confounding factors.

A PHOTOELASTIC MODEL OF THE PATELLOFEMORAL JOINT TO STUDY PATELLAR HEIGHT

Background: Patellar height has been related to anterior knee pain and Osgood–Schlatter disease. To study the influence of patellar height on knee biomechanics, a bidimensional photoelastic prototype of the patellofemoral joint was developed. Methods: Nine tests were performed at different knee flexion angles and patellar heights. A free body diagram was constructed for each test. The following parameters were calculated: lengths (patella, patella thickness and ligamentum patellae); patellar height index; angles (knee flexion, patellar flexion, quadriceps and ligamentum patellae force and reaction force at the ankle); moment arms (extensor, quadriceps and ligamentum patellae in relation to both the tibiofemoral and patellofemoral contact points), effective moment arm and forces around the extensor mechanism relative to the applied force. Results: Femoropatellar and femorotibial reaction forces were greater with increased knee flexion and a fixed patellar height. With fixed knee flexion and different patellar heights, these forces were greater if the patella was elevated. A decrease in the angle between the tibial axis and ligamentum patellae was observed when patellar height increased. Patellar flexion angle increased when patellar height increased. This was accompanied by an increase in the angle of action of the quadriceps force. Extensor moment arm decreased with increased patellar height when knee flexion and the tibiofemoral contact point were fixed. Conclusion: A new application of photoelasticity is presented. The preliminary findings obtained confirm the influence of patellar height on patellar biomechanics, and specifically on forces around the extensor mechanism of the knee.

Visualization method for stress-field evolution during rapid crack propagation using 3D printing and photoelastic testing techniques

Quantitative visualization and characterization of stress-field evolution during fracture rapid growth is critical for understanding the mechanisms that govern the deformation and failure of solids in various engineering applications. However, the direct capture and accurate characterization of a rapidly-changing stress field during crack propagation remains a challenge. We report an experimental method to quantitatively visualize and characterize rapid evolution of the stress-field during crack propagation in a transparent disc model containing a penetrating fusiform crack. Three-dimensional (3D) printing technology and a stress-sensitive photopolymer resin were adopted to produce the disc model and to alleviate the residual processing stress that usually blurs the dynamic stress field due to overlap. A photoelastic testing system that synchronized a high-speed digital camera and a pulsed laser with a nanosecond full width at half maximum (FWHM) was used to capture the rapid evolution of the stress field in the vicinity of crack tips. The results show that the proposed method is suitable to directly visualize and quantitatively characterize the stress-field evolution during crack rapid propagation. It is proved that the crack propagation velocity is strongly governed by the stress field around the crack tips.

In-vitro comparison of mechanical resistance between two straight plates and a Y-plate for fixation of mandibular condyle fractures

OBJECTIVE

To compare the mechanical resistance of conventional plates with a modified Y-plate in mandibular condyle fracture.

MATERIALS AND METHODS

40 synthetic hemi-mandibular polyurethane replicates were used. Two groups of fixing materials were included: 20 mandibles fixed with 40 straight plates with four roles each (2.0 mm system) and 20 mandibles fixed with 20 Y-shaped plates (2.0 mm system and 1.5 mm thickness). The samples were submitted to linear loading in the following directions: 10 mandibles from each group from lateral to medial and 10 mandibles from each group from anterior to posterior. A universal loading machine, Instron Universal 4411, was used to performed the tests, and the resistance of each fixed mandible was assessed at displacements of 1 mm, 3 mm, and 5 mm. The t-test for independent samples was performed. The p value was set at <0.05.

RESULTS

The worst mechanical resistance was found in the Y-plates loaded from anterior to posterior. The best mechanical resistance was in two straight hole plates loaded from lateral to medial. The Y-plates and two straight hole plates showed similar resistance when a lateral to medial load was applied.

CONCLUSION

There was no difference between the plates when lateral to medial loading was tested.

Biomechanical evaluation of two plating configurations for fixation of a simple transverse caudal mandibular fracture model in cats

OBJECTIVE To evaluate biomechanical properties of intact feline mandibles, compared with those for mandibles with an experimentally created osteotomy that was stabilized with 1 of 2 internal fixation configurations. SAMPLE 20 mandibles from 10 adult feline cadavers. PROCEDURES An incomplete block study design was used to assign the mandibles of each cadaver to 2 of 3 groups (locking plate with locking screws [locking construct], locking plate with nonlocking screws [nonlocking construct], or intact). Within each cadaver, mandibles were randomly assigned to the assigned treatments. For mandibles assigned to the locking and nonlocking constructs, a simple transverse osteotomy was created caudal to the mandibular first molar tooth after plate application. All mandibles were loaded in cantilever bending in a single-load-to-failure test while simultaneously recording load and actuator displacement. Mode of failure (bone or plate failure) was recorded, and radiographic evidence of tooth root and mandibular canal damage was evaluated. Mechanical properties were compared among the 3 groups. RESULTS Stiffness, bending moments, and most post-yield energies for mandibles with the locking and nonlocking constructs were significantly lower than those for intact mandibles. Peak bending moment and stiffness for mandibles with the locking construct were significantly greater than those for mandibles with the nonlocking construct. Mode of failure and frequency of screw damage to tooth roots and the mandibular canal did not differ between the locking and nonlocking constructs. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that both fixation constructs were mechanically inferior to intact mandibles. The locking construct was mechanically stronger than the nonlocking construct.