Biomechanical evaluation of unilateral subcondylar fracture of the mandible on the varying materials: A finite element analysis

Biomechanical analysis of an absorbable material for treating fractures of the inferior orbital wall

AIM

To investigate the biomechanical properties and practical application of absorbable materials in orbital fracture repair.

METHODS

The three-dimensional (3D) model of orbital blowout fractures was reconstructed using Mimics21.0 software. The repair guide plate model for inferior orbital wall fracture was designed using 3-matic13.0 and Geomagic wrap 21.0 software. The finite element model of orbital blowout fracture and absorbable repair plate was established using 3-matic13.0 and ANSYS Workbench 21.0 software. The mechanical response of absorbable plates, with thicknesses of 0.6 and 1.2 mm, was modeled after their placement in the orbit. Two patients with inferior orbital wall fractures volunteered to receive single-layer and double-layer absorbable plates combined with 3D printing technology to facilitate surgical treatment of orbital wall fractures.

RESULTS

The finite element models of orbital blowout fracture and absorbable plate were successfully established. Finite element analysis (FEA) showed that when the Young's modulus of the absorbable plate decreases to 3.15 MPa, the repair material with a thickness of 0.6 mm was influenced by the gravitational forces of the orbital contents, resulting in a maximum total deformation of approximately 3.3 mm. Conversely, when the absorbable plate was 1.2 mm thick, the overall maximum total deformation was around 0.4 mm. The half-year follow-up results of the clinical cases confirmed that the absorbable plate with a thickness of 1.2 mm had smaller maximum total deformation and better clinical efficacy.

CONCLUSION

The biomechanical analysis observations in this study are largely consistent with the clinical situation. The use of double-layer absorbable plates in conjunction with 3D printing technology is recommended to support surgical treatment of infraorbital wall blowout fractures.

The Use of Hydroxyapatite Polymer with Curdlan in the Treatment of Bone Defects Associated with Ectopic Tooth Extraction in Dogs-A Case Series

Ectopic teeth are an eruption disorder in which teeth are located in anatomical structures where, physiologically, they should not occur. An ectopic tooth is a very rare phenomenon, affecting approximately 0.5% of the canine population, and few descriptions of the treatment of such teeth in dogs can be found in the available literature. This article describes the diagnostic and therapeutic handling of cavities following extraction of ectopic teeth in nine dogs. The cases are subdivided into uncomplicated (when the ectopic tooth was encapsulated in the surrounding connective tissue, without lysis of the bone around the tooth) and complicated (in which, in addition to the presence of the ectopic tooth, a dentigerous cyst had formed). Four cases of complicated ectopic teeth are described in more detail. In this study, special attention was paid not only to the technique of tooth extraction itself but also to the method of securing and healing large bone defects after the extraction using hydroxyapatite curdlan polymer. Owing to the plastic properties of the bone substitute preparation, it was possible to implant the material without enlarging the bone defect created during the tooth extraction. Control radiographs showed features of bone regeneration, and clinical examination at both the early and late stages revealed no postoperative complications.

Biomechanical Comparison of Titanium and Poly- L -Lactic Acid Trapezoidal Plates Applied in a Subcondylar Fracture Model

BACKGROUND/AIM

Different types of plates are used in clinical practice for the management of subcondylar fractures. This study aimed to compare the performance of poly- L -lactic acid (PLLA) and titanium trapezoidal plates in the fixation of subcondylar mandibular fractures using finite element analysis.

METHODS

Titanium and PLLA trapezoidal plates and screws were placed on the virtual model obtained from computed tomography images of a patient with a subcondylar fracture to perform finite element analysis. The analysis included maximum tension distribution, maximum principal strain, displacement, and deformation of the bone, plates, and screws.

RESULTS

The maximum tension distribution and maximum principal stress were found to be significantly higher on the titanium plate than on the PLLA plate and screws. Almost no difference was found between the trapezoidal and PLLA plates regarding the displacement of the fracture fragments at the fracture line. No difference was recorded regarding the displacement of the PLLA and titanium screws. The values of maximal principal strain between the PLLA and titanium materials showed no significant difference.

CONCLUSIONS

The trapezoidal PLLA plates can be an alternative to trapezoidal titanium plates due to their functional stability and rigidity.

Magnesium-Based Compression Screws in Acute Scaphoid Fractures and Nonunions

BACKGROUND

Magnesium-based bioabsorbable osteosynthesis material continues to receive increasing attention. The following study documents our experience with bioabsorbable magnesium screws in scaphoid fracture treatment in hopes to capture further evidence and successful application.

METHODS

Eight acute scaphoid fractures and four nonunions were treated with the magnesium-based bioabsorbable compression screw MAGNEZIX^®. Objective outcome was assessed by X-ray imaging and/or CT scan for bone healing. Clinical assessment was achieved using the modified Mayo Wrist Score. Patient-reported outcome measure was performed threefold via QuickDASH, PRWE, and EQ-5D-5L questionnaires in all patients. Follow-up was 32.5 months (SD 18.7) in the acute fracture group and 31 months (SD 7.4) in the nonunion group.

RESULTS

Bone healing was achieved in all eight patients with acute scaphoid fractures and in three of four patients with scaphoid nonunion. The modified Mayo Wrist Score was 95 (SD 7.1) in fractures and 80 (SD 7.1) in nonunion patients during follow-up. QuickDASH score was 3.9 (SD 5.8) in fracture and 19.3 (SD 10.6) in nonunion patients. All but one patient (87,5%) with scaphoid fractures presented with a full health state during follow-up (EQ-5D-5L). Nonunion patients had problems in 10 out of 19 dimensions in EQ-5D-5L. Acute fractures presented with a score of 3.9 (SD 7.9) and nonunions with a score of 19.7 (SD 32.4) in PRWE total scoring during follow-up.

CONCLUSIONS

Magnesium-based implants have excellent clinical outcomes when used for scaphoid fractures in eight presented cases and good to moderate clinical outcomes when used for nonunions in three of four presented cases. Additional studies are required to further analyze the differentiated applicability in scaphoid nonunion as well as overall performance when compared to non-absorbable screws in larger cohorts.

The Use of Lactide Polymers in Bone Tissue Regeneration in Dentistry-A Systematic Review

(1) Background: Different compositions of biodegradable materials are being investigated to successfully replace non-resorbable ones in bone tissue regeneration in dental surgery. The systematic review tried to address the question, "Can biodegradable polymers act as a replacement for conventional materials in dental surgery procedures?" (2) Methods: An electronic search of the PubMed and Scopus databases was conducted in October 2022. The following keywords were used: (lactide polymers) and (hydroxyapatite or fluorapatite) and (dentistry) and (regeneration). Initially, 59 studies were found. Forty-one studies met the inclusion criteria and were included in the review. (3) Results: These usually improved the properties and induced osteogenesis, tissue mineralisation and bone regeneration by inducing osteoblast proliferation. Five studies showed higher induction of osteogenesis in the case of biomaterials, UV-HAp/PLLA, ALBO-OS, bioresorbable raw particulate hydroxyapatite/poly-L-lactide and PLGA/Hap, compared to conventional materials such as titanium. Four studies confirmed improvement in tissue mineralisation with the usage of biomaterials: hydroxyapatite/polylactic acid (HA/PLA) loaded with dog's dental pulp stem cells (DPSCs), Coll/HAp/PLCL, PDLLA/VACNT-O:nHAp, incorporation of hydroxyapatite and simvastatin. Three studies showed an acceleration in proliferation of osteoblasts for the use of biomaterials with additional factors such as collagen and UV light. (4) Conclusions: Lactide polymers present higher osteointegration and cell proliferation rate than the materials compared. They are superior to non-biodegradable materials in terms of the biocompability, bone remodelling and healing time tests. Moreover, because there is no need of reoperation, as the material automatically degrades, the chance of scars and skin sclerosis is lower. However, more studies involving greater numbers of biomaterial types and mixes need to be performed in order to find a perfect biodegradable material.

In Silico Biomechanical Evaluation of WE43 Magnesium Plates for Mandibular Fracture Fixation

Titanium fixation devices are the gold standard for the treatment of mandibular fractures; however, they present serious limitations, such as non-degradability and generation of imaging artifacts. As an alternative, biodegradable magnesium alloys have lately drawn attention due to their biodegradability and biocompatibility. In addition, magnesium alloys offer a relatively high modulus of elasticity in comparison to biodegradable polymers, being a potential option to substitute titanium in highly loaded anatomical areas, such as the mandible. This study aimed to evaluate the biomechanical competence of magnesium alloy WE43 plates for mandibular fracture fixation in comparison to the clinical standard or even softer polymer solutions. A 3D finite element model of the human mandible was developed, and four different fracture scenarios were simulated, together with physiological post-operative loading and boundary conditions. In a systematic comparison, the material properties of titanium alloy Ti-6Al-4V, magnesium alloy WE43, and polylactic acid (PLA) were assigned to the fixation devices, and two different plate thicknesses were tested. No failure was predicted in the fixation devices for any of the tested materials. Moreover, the magnesium and titanium fixation devices induced a similar amount of strain within the healing regions. On the other hand, the PLA devices led to higher mechanical strains within the healing region. Plate thickness only slightly influenced the primary fixation stability. Therefore, magnesium alloy WE43 fixation devices seem to provide a suitable biomechanical environment to support mandibular fracture healing in the early stages of bone healing. Magnesium WE43 showed a biomechanical performance similar to clinically used titanium devices with the added advantages of biodegradability and radiopacity, and at the same time it showed a remarkably higher primary stability compared to PLA fixation devices, which appear to be too unstable, especially in the posterior and more loaded mandibular fracture cases.

Change in Pull-Out Force during Resorption of Magnesium Compression Screws for Osteosynthesis of Mandibular Condylar Fractures

BACKGROUND

Magnesium has been used as degradable fixation material for osteosynthesis, but it seems that mechanical strength is still a current issue in these fixations. The aim of this study was to evaluate the axial pull-out force of compression headless screws made of magnesium alloy during their resorption.

METHODS

The tests included screws made for osteosynthesis of the mandible head: 2.2 mm diameter magnesium alloy MgYREZr (42 screws) and 2.5 mm diameter polylactic-co-glycolic acid (PLGA) (42 pieces, control). The screws were resorbed in Sørensen's buffer for 2, 4, 8, 12, and 16 weeks, and force was measured as the screw was pulled out from the polyurethane block.

RESULTS

The force needed to pull the screw out was significantly higher for MgYREZr screws than for PLGA ones (p < 0.01). Within eight weeks, the pull-out force for MgYREZr significantly decreased to one third of its initial value (p < 0.01). The dynamics of this decrease were greater than those of the pull-out force for PLGA screws (p < 0.05). After these eight weeks, the values for metal and polymer screws equalized. It seems that the described reduction of force requires taking into account when using magnesium screws. This will provide more stable resorbable metallic osteosynthesis.