A 3-Dimensional Finite Element Analysis of Resected Mandibular Bone to Determine the Most Stable Implant Positions for a Fixed Prosthesis
This study was conducted to determine the most secure implant positioning on the marginally resected mandible to support a fixed complete denture through finite element analysis. Three or 4 implants were placed at near, middle, or far positions from the resected margin in a simulation model with a symmetrical marginal defect in the mandibular symphysis. The height of the residual bone was 5, 10, or 15 mm. The 4 possible implant patterns for 3 or 4 implants were defined as (1) asymmetrically isolated position 1 to position 2, (2) asymmetrically isolated position 1 to position 3, (3) asymmetrically isolated with greater-length position 1 to position 2, and (4) 2 implants symmetrically positioned on each side of the defect. The von Mises stress in the resected and peri-implant bone with respect to the occlusal force was calculated. Initially, because the peri-implant bone stress around the isolated implant at the near position was greater than at the middle and far positions regardless of the residual bone height, the near position was excluded. Second, the von Mises stress in the resected bone region was >10 MPa when the isolated implant was at the far position, and it increased inversely depending on the bone height. However, the stress was <10 MPa when the isolated implant was placed at the middle position regardless of the bone height, and it was significantly lower compared with the far position and equivalent to the symmetrically positioned implants. Furthermore, the use of a greater-length implant reduced peri-implant bone stress, which was even lower than that of the symmetrically positioned implants. These results suggest that the asymmetrically positioned 3-implant–supported fixed denture, using a greater-length isolated implant, placed neither too close to nor too far from the resected margin, can be an effective alternative to the symmetrically positioned 4-implant–supported fixed denture.
(a) A schema of the models used in the present study. Three types of the defects were created according to the residual bone height (5, 10, and 15 mm). Distances between the defect margin and each implant were 5 mm (near position), 15 mm (middle position), and 25 mm (far position), respectively. All implants were connected to a superstructure. (b–d) The mandibular ramus was constrained from the X, Y, and Z directions. Points on the superstructure, corresponded to the bilateral molars and the midline, were loaded. The loading forces on all 3 points were equal.
An isolated 10-mm implant was positioned on one side of the mandible at the near (a–c), middle (d–f), and far (g–i) positions and two 10-mm implants were positioned on the opposite side at the near-middle, middle-far, and near-far positions. N, near; M, middle; F, far.
An isolated 10-mm implant was positioned on one side of the mandible at the near (a), middle (b), and far (c) positions, and three 10-mm implants were positioned on the opposite side, one each at near, middle, and far positions. N, near; M, middle; F, far.
An isolated 15-mm implant was positioned on one side of the mandible at the near (a–c), middle (d–f), and far (g–i) positions and two 10-mm implants were positioned on opposite side at the near-middle, middle-far, and near-far positions in the opposite side. N, near; M, middle; F, far.
Two 10-mm implants were symmetrically positioned on each side of the mandible. N, near; M, middle; F, far.
The von Mises stress in the peri-implant and resected bone region in the pattern “asymmetrically isolated position 1 to position 2” (1 implant vs 2 implants). (a) The von Mises stress in the peri-implant bone region. (b) The von Mises stress in the resected bone region. (c) The mean stress in the resected bone region according to the isolated implant position. **P < .01.
The comparison of von Mises stress in the pattern “asymmetrically isolated position 1 to position 2” (1 implant vs 2 implants; pattern 1) and “asymmetrically isolated position 1 to position 3” (1 implant vs 3 implants; pattern 2). (a) The von Mises stress in the resected bone region. (b) The von Mises stress in the peri-implant bone region. The mean stresses in the resected bone region and peri-implant bone region in asymmetric pattern 1 were mostly equal to those in pattern 2.
Comparison of von Mises stress in the peri-implant resected bone regions in the pattern “asymmetrically isolated with greater-length position 1 to position 2” (1 greater length implant vs 2 implants; pattern 3), “asymmetrically isolated position 1 to position 2” (1 implant vs 2 implants; pattern 1) and “symmetrically positioned paired implants (pattern 4).” (a) The von Mises stress in the resected bone region. (b) The von Mises stress in the peri-implant bone region. The von Mises stress in the resected bone region was reduced when an isolated implant with greater length was placed at the near or far position. The von Mises stress in the peri-implant bone region was reduced when an isolated implant with greater length was placed at the near, middle, and far positions.
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