Abstract: BACKGROUND: The free peroneal muscle flap is currently an important method for repairing unilateral maxillary defects. In clinical practice, both single-layer free peroneal muscle flaps and double-layer folded free peroneal muscle flaps are commonly used to address these defects. However, there is still a lack of relevant biomechanical studies on the restoration of the bony struts of the maxilla following the reconstruction with either technique.
OBJECTIVE: To analyze the biomechanical characteristics of unilateral maxillary defects repaired with a single-layer free fibular flap and a double-layer folded free fibular flap, and to simulate the biomechanical properties of each structure after implant restoration using the three-dimensional finite element method.
METHODS: CT data of the maxilla and fibula from a 52-year-old male patient scheduled for "subtotal maxillectomy with simultaneous vascularized fibular osteomyocutaneous flap reconstruction" were collected. The data were imported into Mimics 21.0 software to digitally simulate subtotal maxillectomy and to establish 3D models of single-layer and double-layer folded fibular flap reconstructions. The models were then imported into Geomagic Studio 2014, SolidWorks 2019, and Ansys 18.0 to construct three-dimensional finite element models: a normal maxillary complex (Model A), a unilateral maxillary defect reconstructed with a single-layer free fibular flap and simulated implant restoration (Model B), and a unilateral maxillary defect reconstructed with a double-layer folded free fibular flap and simulated implant restoration (Model C). The stress distribution and biomechanical stability of the maxilla, miniplates, and implant prostheses under bilateral posterior vertical loading were compared among the models.
RESULTS AND CONCLUSION: (1) In Models A, B, and C, maxillary stress was primarily distributed in the healthy maxilla near the zygomatic region, the reconstructed fibular region, and the bilateral lateral orbit, medial orbit, and nasal root areas. Model B exhibited significantly higher stress at the left piriform aperture margin compared with Model C, with a prominent red stress concentration zone in this area. (2) Under various loads, the displacement at the junction between the fibula and the alveolar process in Model B was greater than that in Model C. The maximum displacement occurred under a 250 N load on the affected side: 30 μm for Model B and 23 μm for Model C. (3) In both Models B and C, the maximum stress on the miniplates was located at the bending points connecting the fibular segments. The peak stress values were similar between the two models. The maximum displacement of the miniplates occurred at the first screw hole of the miniplate connecting the fibula and the alveolar process, with the highest displacement (27 μm) observed in Model B under a 250 N load on the affected side. (4) Under three loading conditions, stress in the implants of Models B and C was concentrated at the neck regions, with the highest stress occurring in the distal implants. Model C exhibited significantly greater stress (160.6 MPa) than Model B (58.5 MPa). Meanwhile, the maximum displacement occurred in the anterior implants of both models, increasing with load magnitude, and Model C showed slightly lower displacement than Model B. (5) The results confirmed that both single-layer and double-layer folded free fibular flaps effectively restored the biomechanical support of the maxilla after unilateral defect reconstruction. However, the single-layer reconstruction led to stress concentration near the nasal region, increasing the risk of fracture under high external forces. Therefore, the double-layer folded fibular reconstruction is more favorable for restoring nasomaxillary support. Between the two methods, the double-layer folded fibular flap provided better stability, though it resulted in higher localized stress on the implant prostheses.

Key words: maxillary defect, double fold fibula, implant denture, finite element analysis, stress, digital design, miniplates, biomechanical pillar