Abstract: Objective To investigate the biomechanical effects of varying retention pin numbers and positions on 3D printed individualized titanium mesh used for restoring extensive bone defects through finite element analysis. Methods A digital model of extensive bone defects in the mandible was constructed. Virtual bone augmentation was performed using 3-Matic 15 and Geomagic Wrap 2021 software, followed by the design of individualized titanium meshes. Five models with different retention pin numbers and positions were analyzed: (A) four retention pins (buccal mesial, buccal median, mandibular ramus, and lingual side); (B) three retention pins (buccal mesial, buccal median, mandibular ramus); (C) two retention pins (buccal mesial, buccal median); (D) two retention pins (buccal mesial, mandibular ramus); (E) two retention pins (buccal median, mandibular ramus). Finite element analysis models were constructed to evaluate the displacement and stress distribution of the titanium meshes in each group. Results Titanium mesh with four retention pins exhibited the smallest overall displacement (maximum: 0.088 mm), effectively protecting the internal bone graft material. The mesh with three retention pins showed relatively uniform displacement on the buccal side and alveolar ridge crest; however, the absence of lingual-side retention pins resulted in larger displacements, concentrated in the distal lingual area (maximum: 0.263 mm). In the three models with two retention pins, when the pins were located at the buccal mesial and median, the absence of retention pins in the distal regions led to increasing displacement as the distance from the pins increased, with a maximum displacement of 3.255 mm. In the model with retention pins at the buccal mesial and mandibular ramus, the long span of the titanium mesh caused downward deformation in the central section under load, with the deformation gradually decreasing toward both ends, while the free mesial end experienced upward buckling forces, resulting in a maximum displacement of 0.728 mm. In the model where the pins were located at the buccal median and mandibular ramus, the longer mesial cantilever beam led to significant deformation closer to the mesial end, with the maximum deformation reaching 3.823 mm. Titanium meshes with four retention pins and those with pins at the buccal mesial and median exhibited uniform stress distribution without notable stress concentrations. Meshes with three retention pins showed stress concentrations on the buccal side and around the retention pins. For meshes with pins located at the buccal mesial and mandibular ramus, or at the buccal median and mandibular ramus, stress was concentrated around the two pins. Maximum stresses for models A, B, C, D and E were 183.29, 451.30, 722.22, 904.84 and 1462.40 MPa, respectively. Conclusion Increasing the number of retention pins reduces the displacement of individualized titanium mesh under load. For the same number of retention pins, their positions significantly influence mesh displacement.

Key words: Individualized titanium mesh, Guided bone regeneration, 3D finite element analysis, Bone augmentation