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Design Criteria for Patient-Specific Mandibular Implant
and radiotherapy in clinical practice has greatly improved are defined based on the worst mechanical strength
the mandibular reconstruction surgery success rate . mandible filtered from the established database of
[12]
However, current patient-specific mandibular continuity mandible images. The finite element (FE) analysis
defect reconstructed implant designs are demanded and weighted topology optimization methods were
for the following considerations. The structure must be combined to design reconstructed implants for different
optimized for lightweight design to reduce the weight of mandibular continuity defects with corresponding
the large metal implant and withstand the physiological occlusal conditions from the worst mandibular case.
loads from chewing . Micro-interfacial porous structures Further post-operative dental prostheses concerns for
[11]
at the interface between the implant and the residual bone the reconstructed implant can be considered in the
must also be considered to enhance osseointegration for design criteria. Each possible combination reconstructed
bonded strength to improve the overall restored mandible implant was fabricated using the AM technique.
structural stiffness [11,13,14] . Future complex post-operative Biomechanical fatigue testing was performed to carry
dental prostheses that are built based on the long-term out reasonable designs.
surgery success rate are essential to greatly enhance
quality of life [6,9,11,12] . 2. Materials and methods
Mandibular continuity defects may occur in different 2.1. Mandible image database establishment
regions accompanied with complicated occlusal forces and definition of the worst structure case
based on patient-specific consideration . The effective
[18]
structural lightweight optimization analysis should be A total of 105 sets of normal mandibular computed
theoretically targeted at specific reconstructed implant tomography (CT) medical image Digital Imaging
contours and load conditions to generate the most effective and Communications in Medicine (DICOM) files,
structure. However, a huge gap in design and manufacture including facial medical imaged patient skulls aged
induces the lack of clinical efficiency applicability 20–65 years, were collected in this study and approved
because practical patient-specific optimization analysis is by the Ethics Committee (the Institutional Review
a time-consuming and difficult task. Board; IRB) of Taipei Veterans General Hospital,
According to the Food and Drug Administration Taiwan (Measurement and statistical analysis of
(FDA) substantial equivalence (SE) definition, Taiwanese mandibular size; approval number: 2019-
the functional fatigue mechanical performance of 01-050BC). All mandible DICOM images were
reconstructed AM implants must be compared to processed to identify contours and a three-dimensional
traditional reconstruction bone plates based on the same (3D) reconstructed image model of the mandible
indications, implant material, and bone segments . bone. According to the symmetry characteristics, the
[15]
However, it may not be possible to perform fatigue testing mandible can be divided into three segments (A, B, and
immediately before clinical use when considering only C) and their corresponding length, width, and height
one patient’s structural appearance and segment design. measured according to the definitions in Table 1. After
Therefore, it is impossible to comply with the FDA’s measuring the length/height/thickness of each segment
requirements for SE comparison for functional fatigue from 105 CT images, a CT image with the weakest
testing. mandibular structure was selected as the worst case
In addition to performing the pre-clinical testing using V value calculation. This model was used as the
listed in the product regulatory code according to the standard model for patient-specific implant design for
FDA’s inspection and registration requirements for each mandible segment. The V value of each patient
patient-specific implants, it is necessary to define the was calculated using Equation 1:
applicable dimension range of the patient-specific
product and its corresponding functionality testing of the V AB AB Lave BB BB Lave
.
Li
.
Li
structural worst case to ensure safe and effective surgical CB CB Lave AB AB v ve (1)

results . When the mandibular continuity defects can be Li . Hi Ha.
[15]

designed within the classification and effective size range, CB CB Tave
...

Ti
.
building a mandibular continuity defect reconstructed
implant with patient-specific contours and segmental where i=1-105 patients; AB , AB , AB ,
H.ave
L.ave
T.ave
parameterized structure design can be a great benefit to BB L.ave , BB H.ave …… CB T.ave , indicating the average bone
precise personal treatment. length, height, and thickness for A, B, and C segments
This study developed design criterion for obtained from all patients, respectively.
generating patient-specific reconstructed mandibular Taking the A+B bone segment as an example and
implants with contour consideration and structural simplified into a cantilever beam and fixed at the distal
optimization. Different large-scale mandible defects side (Figure 1), the minimum bone stress (σ) occurred
140 International Journal of Bioprinting (2022)–Volume 8, Issue 1