Jayanthi Parthasarathy
B.D.S.
e-mail: jayanthi@ou.edu
Binil Starly
Assistant Professor
e-mail: starlyb@ou.edu
Shivakumar Raman
David Ross Boyd Professor
e-mail: raman@ou.edu
Center for Shape Engineering and Advanced
Manufacturing,
School of Industrial Engineering,
University of Oklahoma,
202 W. Boyd Street, Room 124,
Norman, OK 73019-0631
Computer Aided Biomodeling and
Analysis of Patient Specific
Porous Titanium Mandibular
Implants
Custom implants for the reconstruction of mandibular defects have recently gained im-
portance due to their better performance over their generic counterparts. This is attrib-
uted to their precise adaptation to the region of implantation, reduced surgical times, and
better cosmesis. Recent introduction of direct digital manufacturing technologies, which
enable the fabrication of implants from patient specific data, has opened up a new
horizon for the next generation of customized maxillofacial implants. In this article, we
discuss a representative volume element based technique in which precisely defined po-
rous implants with customized stiffness values are designed to match the stiffness and
weight characteristics of surrounding healthy bone tissue. Dental abutment structures
have been incorporated into the mandibular implant. Finite element analysis is used to
assess the performance of the implant under masticatory loads. This design strategy
lends itself very well to rapid manufacturing technologies based on metal sintering
processes. DOI: 10.1115/1.3192104
Keywords: CT reconstruction, mandibular implants, porous titanium, layered
manufacturing
1 Introduction
Mandibular reconstruction after tumor resection presents a sig-
nificant challenge to maxillofacial surgeons today 1. Mandibular
defects occur due to trauma, orofacial tumors, infection, and other
space occupying lesions like cysts. Defects in continuity of the
mandible lead to severe facial deformities, major difficulties in
verbalization, deglutition, and mastication. The extent of the af-
fliction increases with the size and location of the defect. Other
than somatic effects, the patient’s quality of life is significantly
affected due to the loss of mandibular continuity.
Several methods of defect reconstruction, such as autogenous
bone grafts, generic alloplastic bone plates, and custom mandibu-
lar reconstruction trays are being used presently. Autografts are
the “gold standard” from an immune response point of view.
However, the use of autografts are limited due to issues such as
donor site morbidity, lack of sufficient graft quantity, chances of
infection, and patient discomfort 2–5. Generically available
mandibular reconstruction plates do not confirm to the exact mor-
phology of the resected part of the mandible, making it difficult
for post operative dental reconstruction Figs. 1a and 1b. Mar-
tola et al. 6 suggested plates that match closely the three-
dimensional shape of the mandible to avoid requirements of intra-
operative bending.
Custom designed and fabricated implants have been found to
have advantages of better fit, reduced operating time, and lesser
chances for infection, faster recovery, and better cosmesis in cran-
iofacial surgery 7–9. Custom mandibular trays have been used
for mandibular reconstruction by Samman et al. 10. A mandibu-
lar replica was reconstructed from clinical measurements made
from the patient’s mandible. The titanium implant is built through
a casting or swaging process or CNC milling Fig. 2. Yaxiong et
al. 11 and Singare et al. 12,13 fabricated custom mandibular
titanium implants using computer aided design CAD software
and rapid prototyping RP technologies. Patient specific CT scan
data of the defect site was used to produce a virtual reconstruction
of the mandibular implant. Data from the contralateral side were
mirrored and processed in a virtual CAD environment to arrive at
the final shape of the mandibular implant. A stereolithographic
SLA physical prototype model of the skull and the final design
of the implant were fabricated. The SLA negative mold of the
implant was used as a sacrificial part to cast titanium into the
mold. Holes were then drilled into the body of the implant to
reduce its weight. This process is now extensively used in a clini-
cal setting and has greatly improved treatment modalities, but still
have inherent deficiencies, enumerated below, making it necessary
to explore newer methods for improved treatment outcome. The
deficiencies of the above process are as follows.
a Titanium implants built using this process are often
heavy and can cause discomfort to the patients. The
Young’s modulus of titanium is almost five times that of
cortical bone resulting in stress shielding effects 14,15.
b Secondary processing increases cost and time, resulting
in subsequent delay in treatment and increased cost of
health care to the patient/insurance provider.
c RP models are used only as sacrificial models and sec-
ondary manufacturing methodologies, such as casting
and swaging, are required to be used for fabrication of
the final implants.
While virtual reconstruction of the mandible implant has re-
sulted in significant design improvements, newer technologies to
custom design the implant to match the mechanical properties of
the surrounding tissue need to be adopted. New generation of
implants would be porous, enabling the in-growth of healthy bone
tissue for additional implant fixation and stabilization. Newer im-
plants would conform to the external shape of the defect site that
is intended to be replaced. More importantly, the effective elastic
modulus of the implant should match that of surrounding tissue.
Ideally the weight of the implant should also be equal to the
weight of the tissue that is being replaced, resulting in increased
Manuscript received February 24, 2009; final manuscript received: April 29,
2009; published online September 1, 2009. Review conducted by Vijay Goel.
Journal of Medical Devices SEPTEMBER 2009, Vol. 3 / 031007-1 Copyright © 2009 by ASME
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