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Design Criteria for Patient-Specific Mandibular Implant
implant structure optimization [8,9] . These studies also
advocated the importance of “custom-made” personalized
implants that can be fabricated using the AM technique.
In addition to reducing the reconstruction implant weight,
performing implant structure optimization analysis
also reduces the stress shielding that might cause bone
resorption and eventual failure . The current analysis
[23]
results showed that the reconstructed implant weights in
different segments can be reduced by at least 50% through
the lightweight optimization structural design. This result Figure 5. Finite element displacement comparison between B
was consistent with the study by Cheng et al. who produced segmental mandible defect restored with reconstructed implants
a titanium canine mandibular implant that possessed a and bone plate.
personalized external shape for appearance recovery and
structural optimization and a weight reduction of 37.2% . trials. The number of mandible CT images in the database
[8]
However, the maximum stress values of the reconstructed can be gradually expanded to include patients outside of
implant and the remaining bone were not obviously Taiwan after the clinical application of our reconstructed
reduced in this study. The stress values were, however, far implant is successful. Following up with the developed
lower due to the materials’ ultimate strength. This is still technique in this study, remote design, and manufacture
within the acceptable range. The stress concentrations of of the reconstructed implant can be performed through the
the reconstructed implants were also noted the same as on medical network for clinical treatment.
the connected fixation wing and fixation screws with other
studies. This inferred that implant failure can occur due to 5. Conclusions
high stress concentration on the screws in the fixation unit This study developed a design criterion for patient-
and implied that the fixation wing can be improved for specific reconstructed implants with lightweight
further design . structural optimization for various mandibular
[8]
The biomechanical fatigue test results indicated that continuity defects. The sizes and positions of the internal
all mandibular continuity defects using AM reconstructed support beams for the reconstructed implant are defined
implants based on our design criteria can pass the 250,000 parametrically through corresponding segmental bone
cyclic load test, that is, survival in actual occlusal length, width, and height. Biomechanical fatigue testing
situations for about 6 months after clinical surgery. validated that all mandibular continuity defects using
However, failure tests with mandibular condyle head the AM reconstructed implant can pass cyclic dynamic
fracture, bone plate fracture, or bone screw loosening loads. Condyle head, bone plate fractures, and bone
were found corresponding with mandibular continuity screw loosening can be found in restored mandibular
defects using traditional bone plate. This phenomenon defects using bone plates.
was because the traditional bone plate cannot provide
enough stiffness to maintain stability for the restored Acknowledgments
mandible, causing it to become strongly distorted when
receiving repeated occlusal force. Taking the B segment as Authors would like to appreciate Anji Technology Co.,
an example for FE analysis, the simulated result found that Ltd., for assistant in metal 3DP manufacture.
the twist displacement of the mandibular defect used with Funding
traditional bone plate was much larger than that used in
the AM reconstructed implant (Figure 5). In addition, an This study is supported in part by MOST project
axial force state induced the bending moment effect on the 108-2622-E-010-001-CC2 and 108-2622-B-010-005,
reconstructed implant only when applied on the mandible Taiwan.
of the current biomechanical test. Standard 4-point
bending fatigue tests based on ASTM F382 testing method Conflict of interest
need to be performed in the future to compare the implant
mechanical strength between different AM reconstructed The authors declare no conflicts of interest.
implants and traditional bone plate to comply with the Authors contributions
FDA’s SE functional test comparison for marketing .
[23]
The mandibular bone CT image database was All authors have made substantial contributions to
constructed using images of only 105 patients in this study. conception and design of the study. Y.T. Wang, C.M.
The current most important task is to apply our reconstructed Chang, and W.H. Tsai have been involved in data
implant for restored severe mandibular defect in clinical collection and data analysis. C.L. Lin, Y.T. Wang, and

150 International Journal of Bioprinting (2022)–Volume 8, Issue 1