Do mandibular titanium miniplates affect the biomechanical behaviour of the mandible? A preliminary experimental study

Biomechanical analysis of fixation methods for bone flap repositioning after lateral orbitotomy approach: A finite element analysis

OBJECTIVE

In ophthalmic surgery, different materials and fixation methods are employed for bone flap repositioning after lateral orbitotomy approach (LOA), yet there is no unified standard. This study aims to investigate the impact of different fixation strategies on orbital stability through Finite Element Analysis (FEA) simulations of the biomechanical environment for orbital rim fixation in LOA.

METHODS

A Finite Element Model (FEM) was established and validated to simulate the mechanical responses under various loads in conventional lateral orbitotomy approach (CLOA) and deep lateral orbital decompression (DLOD) using single titanium plate, double titanium plates, and double absorbable plates fixation methods. The simulations were then validated against clinical cases.

RESULTS

Under similar conditions, the maximum equivalent stress (MES) on titanium alloy fixations was greater than that on absorbable plate materials. Both under static and physiological conditions, all FEM groups ensured structural stability of the system, with material stresses remaining within safe ranges. Compared to CLOA, DLOD, which involves the removal of the lateral orbital wall, altered stress conduction, resulting in an increase of MES and maximum total deformation (MTD) by 1.96 and 2.62 times, respectively. Under a horizontal load of 50 N, the MES in FEM/DLOD exceeded the material's own strength, with an increase in MES and MTD by 3.18 and 6.64 times, respectively, compared to FEM/CLOA. Under a vertical force of 50 N, the MES sustained by each FEM was within safe limits. Bone flap rotation angles remained minimally varied across scenarios. During follow-up, the 12 patients validated in this study did not experience complications related to the internal fixation devices.

CONCLUSION

Under static or physiological conditions, various fixation methods can effectively maintain stability at the orbitotomy site, and absorbable materials, with their smoother stress transmission properties, are more suited for application in CLOA. Among titanium plate fixations, single titanium plates can better withstand vertical stress, while double titanium plates are more capable of handling horizontal stress. Given the change in the orbital mechanical behavior due to DLOD, enhanced fixation strength should be considered for bone flap repositioning.

Mandibular Titanium Miniplates Change the Biomechanical Behaviour of the Mandible in the Case of Facial Trauma: A Three-Dimensional Finite Element Analysis

Our study aimed to compare the biomechanical behaviour of mandibles with or without titanium miniplates when subjected to an impact after bone healing using a finite element model (FEM) of the human mandible. We simulated mandibular trauma on an FEM of a human mandible carrying or not two parasymphyseal miniplates and applying a concentrated force of 2000 N to four different areas, including the insertion area, the area straddling the edge of the miniplates and the adjacent bone, at a distance from the miniplates on the symphysis, and on the basilar border of the mandible below the miniplates. Then, we compared the Von Mises stress distributions between the two models. In the case of an impact on the miniplates, the maximum Von Mises stress occurred in two specific areas, on the cortical bone at the posterior border of the two miniplates at a distance from the impact, while in the model without miniplates, the Von Mises stresses were homogenously distributed in the impact area. The presence of titanium miniplates in the case of trauma affects the biomechanical behaviour of the mandible and could cause more complex fractures. We recommend informing patients of this potential risk.

Innsbruck-style Retromandibular Anterior Trans-parotid Approach for Condylar Fractures: A Retrospective Review of 39 Fractures

The retromandibular anterior trans-parotid (RAT) approach and a triangular-positioned double mini-plate osteosynthesis (TDO) technique have been reported from Innsbruck Medical University. This minimally invasive technique involves direct visualization of the condyle and is associated with lower incidence of facial palsy.

Methods

A retrospective review was performed on the RAT approach and TDO technique conducted by a surgeon and team at two hospitals in Tokyo during a period of 3 years and 10 months.

Results

This technique was performed on 35 patients with 39 condylar fractures. Sixty-nine percent of cases were due to accidental fall, 17% to traffic accidents, and 9% to sports. Furthermore, 92% cases were condylar base fractures. Nighty-seven percent of cases achieved good occlusion. The mean maximum mouth opening was 49 ± 1.3 mm. Postoperatively, facial palsy developed in three patients (7.7%), and two of them developed Frey syndrome at approximately 2.5 years postoperatively (5.1%). All patients completely recovered within 3 months postoperatively. One case each of salivary fistula, visible scar, and condylar resorption was found (2.6%). No case of massive bleeding during surgery, hematoma, or TMJ pain after surgery was found.

Conclusion

This technique could achieve good occlusion with low incidence of complications and could contribute to early social reintegration among patients.