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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_980_Библиотеки_им_академика_М_И_Перельмана
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Bone Contouring inOral
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andMaxillofacial Surgery: Definition,
Indications, andManufacturing
Considerations
ZeinabBakhtiari andArashKhojasteh
1 Introduction
After the advent of additive manufacturing technology in the mid-1980s, patient
computed tomography scan data could be used to provide accurate anatomical models and accurate implants for cranial and facial skeletons [1]. Patient-specic
implant (PSI) is a personalized approach to reconstructive and cosmetic surgery.
Maxillofacial defects are challenging to restore due to a complex 3D contour.
Computer-designed PSI has enhanced stability, more predictable outcomes, higher
accuracy and defect adaption, and better facial contour renement. Premade
implants usually need intraoperative adjustments for complex defects. In the literature, the usual complications associated with other materials, such as infection, foreign body reaction, and displacement, are seldom reported in relation to custom-made
PSI.Maxillofacial PSIs can now be designed using preoperative imaging data as
input to CAD software. The designed implant is then made using a CAM technique,
such as 3D printing. The application of CAD/CAM technique also can simulate the
surgery procedures accurately, which contributes to shorten the actual operative
time [2–4].
An ideal implant should be patient-specic, as well as safe for the patient, inert,
nontoxic, noncarcinogenic, cost-effective, and resistant to infection. It should adapt
easily and blend naturally with adjacent areas. If the implant material can be folded
and compressed, it can be inserted through a small incision, but at the same time, it
Z. Bakhtiari
Department of Oral and Maxillofacial Surgery, School of Dentistry, Tehran University of
Medical Sciences, Tehran, Iran
A. Khojasteh (
Department of Oral and Maxillofacial Surgery, School of Dentistry, Shahid Beheshti
University of Medical Sciences, Tehran, Iran
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023
A. Khojasteh et al. (eds.), Emerging Technologies in Oral and Maxillofacial
Surgery, https://doi.org/10.1007/978-981-19-8602-4_6
*)
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must be resistant to stress and maintain its shape permanently. An ideal implant can
be placed and xed, which reduces mobility. It should also be easily replaceable if
necessary [5].
Bone performs important functions, such as movement, support, and protection
of soft tissues, storage of calcium and phosphate, and storage of bone marrow.
Despite its inert appearance, bone is a highly dynamic organ that is continuously
resorbed by osteoclasts and remodeled by osteoblasts [6]. Patient-specic prostheses implanted for bone replacement can be classied into three general categories.
The criterion of this classication is the extent to which these prostheses can assume
the different roles of the bone or simply act like bone tissue.
Bone contouring PSIs only restore the standard form of the bone. Indeed, the
fabricated products are implanted in the area without any specic role in the mastication, jaw movement, and other functions of the craniofacial organs. On the other
hand, functional bone replacing PSIs, such as TMJ prosthesis, can restore specic
functions (e.g., movement here), But they still cannot act like bone and be dynamic.
Only the prostheses of the last category, functional bone regenerating PSIs, can act
like bone tissue to some extent by guiding the regeneration of bones. Here in this
chapter, we will discuss the rst group, bone contouring PSIs.
Z. Bakhtiari and A. Khojasteh
2 Indication ofFacial Bone Contouring
2.1 Calvaria
Cranioplasty is a surgical intervention to repair calvarial defects for both cosmetic and
functional purposes to ensure adequate protection and function of cerebral structures
[7]. Cranioplasty is often performed after traumatic head injuries. Tumor resection or
decompressive craniectomy is the main cause of skull defects. Congenital defects,
infections, or complications of previous surgery can also cause these defects [8].
The possible benets of cranioplasty mentioned in the studies include improved
appearance, increased cerebral blood ow, changes in cerebrospinal uid hydrodynamics, and reduced epileptic seizures [9–11].
Throughout the history of cranioplasty, several types of materials have been
used. In 1668, the rst bone graft was recorded by Meekeren, who used canine bone
to repair a skull defect. The use of autografts for cranioplasty surgery became common in the early twentieth century [12].
Various bones have been used to repair skull defects. The use of residual skull
bone, or split-thickness skull cranioplasty, is biocompatible, is easy to remove, and
has a lower risk of infection and reaction. For this reason, it is a good option for
cases with a substantial risk of infection and also in pediatric patients, because it is
compatible with the growth and remodeling of the skull [13, 14]. The use of the
tibia, ribs, sternum, and scapula is rarely used today to reconstruct calvaria due to
the severity of transplantation complications, technical difculties, and difculty in
obtaining proper contour. Although ilium has a more suitable contour and is preferred for use, it is unpopular today due to the complications of surgery at the donor
site as well as being more porous, which led to its faster resorption [7].
Bone Contouring in Oral and Maxillofacial Surgery: Denition, Indications…
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The destructive nature of twentieth-century wars motivated the search for alternative metals and plastics to cover large skull defects [12].
The use of alloplastic bone grafts was initiated due to the reduced risk of infection, resorption, and reoperation compared to bone autograft grafts. In addition, the
use of alloplastic bone grafts has reduced operating time due to advances in computer customization and 3D printing, resulting in better aesthetic results. With such
a reduction in the duration of surgery, the risk of postoperative complications, such
as severe pain, infection, and wound dehiscence, is signicantly reduced [15, 16].
In 2021, Mohammadi etal. reported a case of cranioplasty with a custom-made
titanium prosthesis. The patient was a 13-year-old girl with congenital occipital and
bilateral parietal defects. At the age of four, the defect was bridged with a titanium
mesh plate, after which the patient developed relentless petit mal seizure, and 3
months later titanium mesh was exposed, and subsequent infection occurred.
Several debridement was performed and titanium mesh was removed at the age of
ve due to complications. At the age of thirteen, she underwent surgery to place a
patient-specic prosthesis. At 4.5years follow-up, the patient had no side effects,
and healthy skin covers the skull [15].
In a 2018 randomized clinical trial study by Hannibal etal., they compared the
long-term outcomes of patients who received primary titanium cranioplasty or autologous bone graft following decompressive craniectomy. In each group, 32 patients
were studied and one patient from each group died. Over the rst year of post-operative follow-up, 16% of bone graft patients required further reconstruction to address
resorption. After the rst year, this incident dropped to 10%. In addition, 7% of bone
graft patients had seizures. In both groups, 9% of patients experienced headaches
[17]. When the follow-up period was extended to at least 24months, the use of tita-
nium instead of autologous bone for primary cranioplasty resulted in a signicant
reduction in the number of patients requiring cranial rescue surgery (0 vs. 25%,
p=0.001). The costs of hospital health care were also lower. It should be noted that
the factors affecting bone resorption are effective in choosing the type of reconstruction. This study suggests that titanium was a better choice for younger people. The
cost-benet calculation may vary based on location and environmental conditions [17].
In a 2020 study by Hamböck etal., 156 patients who received secondary cranioplasty following decompressive craniectomy have been retrospectively analyzed.
Result showed a lower revision rate in patients with polymethylmethacrylate
(PMMA) implants than in patients with autologous calvarial bone implants. Pediatric
(< 18years) and geriatric (> 65years) patients had an increased risk to suffer complications requiring surgical intervention. Revision rates were not inuenced by the
gender, timing of the secondary cranioplasty, and the severity of the trauma [18].
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2.2 Orbit
The management of orbital fractures is challenging, because the functional and aesthetic clinical consequences may not always be immediately apparent. Deformity
and visual impairment can occur from these injuries, and surgery can prevent and
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eliminate them or can even be a cause for them. Therefore, an observation period
may be reasonable in acute conditions. However, improper management may lead to
decreased visual acuity, persistent enophthalmos, impaired ocular motility, diplopia,
and sensory impairment. Operative management to repair the defect may be immediately necessary, such as for trapdoor fractures with entrapment in pediatric patients
or in the case of a profound oculocardiac reex with the possibility of hemodynamic
instability. Indications for delayed operative management, ideally within 2weeks
after trauma, include enophthalmos (> 2mm), ocular dysmotility, persistent diplopia,
computed tomography (CT) ndings of extraocular muscle entrapment, progressive
infraorbital nerve (ION) hypoesthesia, and abnormal forced duction testing [19, 20].
A systematic review and meta-analysis in 2022 by Kotecha etal. comprised a
total of 628 patients across 11 studies in order to elucidate whether there are any
differences with regard to patient-specic versus conventional implants in outcomes
in patients undergoing post-traumatic orbital reconstruction. No statistically signicant results have been shown in the meta-analysis in favor of patient-specic
implants. However, some individual studies have reported the potential benets of
patient-specic implants in reducing surgical time, improving orbital volume, and
providing better results with respect to postoperative enophthalmos. Inevitably, due
to the retrospective nature of the studies, there will be differences in fracture complexity, operator experience, and technique, as well as patient-based demographics
between groups, which may limit the extent of discernible outcome differences
attributable to treatment effects [19].
The main advantages of custom 3D printing implants are shortening the surgical
time and consequently shortening the anesthesia and reducing its risks. Also, the
accuracy of matching the implant with the bone defect improves the reconstruction
of the orbital volume and in practice leads to better results for ocular motility as well
as binocular vision [21, 22].
Orbital defect reconstruction with a patient-specic implant is shown in
Figs.1 and 2.
Z. Bakhtiari and A. Khojasteh
2.3 Malar
The zygomatic bone, located in the middle third of the face, greatly affects the harmony of the face with its volume and prominence; also its complex three- dimensional
anatomy and unique geometric shape increases the difculty of reconstruction
[23, 24].
There are various approaches to zygomatic reconstruction, including autologous
bone grafts, free tissue aps, prefabricated titanium plates and meshes, patientspecic implants (PSIs), or a combination of the above [25–27].
Reconstruction of the malar region was rst described by Tessier in 1971 [28].
Since the 1980s, the standard option has been bone grafting with free vascular tissue
transplantation [27, 29]. In this approach, original structure of zygomaticomaxillary
complex is less considered and reconstructed only with bar-shape grafts for maxillary
buttress stabilization [30]. However, the reconstruction of the original three- dimensional
shape of the zygomatic complex and orbital walls remains a challenging issue.
ab
Bone Contouring in Oral and Maxillofacial Surgery: Denition, Indications…
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89
c
d
Fig. 1 Shows the process of designing and manufacturing a patient-specic prosthesis in the
orbital region. (a) Processing patient data from CT scan, (b) designing patient-specic prosthesis,
(c) printed model of the patient’s skull structure, (d) a piece of prosthetic model manufactured to
match the patient defect precisely
Further modications to this strategy were aimed at replacing the convexity of
the zygomatic body with the convex surface of the iliac crest or cranial bone graft,
which was inaccurate and time-consuming because of the need to adapt the graft
shape to a complex defect conguration [31, 32].
In a case report by Ahn etal. in 2018, they represented three-dimensional reconstruction with autologous calvarial bone graft to reconstruct a zygomatic defect
after the radical removal of brous dysplasia. The authors used a rapid prototype
model for simulation surgery to remove the radical, and the donor site was selected
from the parietal bone based on the shape, contour, and size of the defect. After
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Z. Bakhtiari and A. Khojasteh
Fig. 2 Shows the patient-specic prosthesis to reconstruct the contour of the orbital area. (a) The
upper part of the prosthesis reconstructs the contour of the upper and medial rim of the orbit. (b)
The lower part of the prosthesis, which restores the contour of the lower part of the orbital rim. (c)
Immediately after the prosthesis placement, note the symmetry. The frost suture is placed on maintaining the position of the lower eyelid. (d) Postoperative radiograph of the patient. (Figure courtesy of Dr. Nemati)
12months of follow-up, adequate bone thickness and symmetrical soft tissue contour were well maintained [31].
The use of CAD-CAM reduces the difculty of properly shaping the donor bone
and reduces the surgical time. It also reproduces orbit zygomatic landmarks and
orbital volume. Manual reconstruction requires multiple settings that are timeconsuming, while with CAD-CAM, these assemblies take only a few minutes [33].
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In a study by Chepurnyi etal. in 2021, 11 patients with zygomatic defects underwent reconstruction with PSI.In this study, determination of the desirable anatomical shape for the PSI for minor zygoma defects was done during the segmentation
and mask editing procedures in accordance with the contour of the mirrored intact
side. Major or complex defects were eliminated using “virtual donors” (a part of
virtual model of the mirrored intact opposite side zygoma, which can be incorporated to the virtual model of the damaged zygoma with minor modication). In all
cases, retention points and additional elements with holes for screw xation were
modeled and created. No major complications occurred during the postoperative
period. PSIs show high performance from the esthetic point of view. The mean
deviation between the reconstructed zygoma and the mirrored intact side was
1.45±0.7mm. Also long-term follow-up revealed no cases of limited mouth opening, exposure of the implant, maxillary sinusitis, or other inammatory complications related to the PSI [27].
The advantage of using PSIs in zygomatic reconstruction is that it retains its
precise 3D contour without the need for any bone grafting. As a result, less surgery
time, easier procedure, and fewer complications at the donor site.
a
def
Fig. 3 Shows the prosthesis to replace the contour of the calvaria, orbit, and zygoma. (a) Prosthesis
design. (b) Placement and xation of the PSI. (c) Postoperative CT scan in the axial cut shows the
zygomatic part of the prosthesis. (d) Three-dimensional reconstruction of the postoperative CT
scan. (e) Preoperative photography of the patient, the defect is evident on the right side of the face.
(f) Postoperative photography of the patient. (Figure courtesy of Dr. Nemati)
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Patient-specic prostheses can be designed to reconstruct all or part of the
patient’s facial contour in one or more surgeries. An example of these prostheses,
which are designed to reconstruct the contour of several bones, is shown in Fig.3.
Z. Bakhtiari and A. Khojasteh
3 Different Material andTheir Properties
3.1 Peek
Polymers with easy processing, good chemical resistance, and light weight are
attractive materials for use in bone replacements. Biodegradable polymers, such as
polylactic acid, polyglycolic acid, and their copolymers, are commonly used to
make scaffolds for tissue engineering applications and have poor mechanical
strength. Nondegradable polymers, such as polyethylene and polyetheretherketone
(PEEK), nd applications that require long-term stability. High-density polyethylene (HDPE) is commonly used to repair tendons and catheter tubes, while ultrahighmolecular- weight polyethylene (UHMWPE) is used as a carrier in joint prostheses
[34–36].
Polyetheretherketone (PEEK) is a semicrystalline polyaromatic linear polymer.
PEEK is biocompatible, mechanically strong, nonallergenic, and nonmagnetic and
also is considered as a high-performance polymer due to its excellent chemical
resistance, high melting temperature (340°C), superior radiation and sterilization
resistance, high modulus of elasticity (3.7–4.0GPa), and tensile strength (103MPa).
PEEK is comparable to cortical bone regarding its elasticity. PEEK has radiographic
translucency and produces no artifacts on radiographic imaging. On the other hand,
titanium is not translucent and may cause diagnostic difculties. PEEK does not
undergo exothermic reactions like methyl methacrylate does. It has been used as an
alloplastic biomaterial in craniofacial reconstructions. PEEK implants provide permanent long-term results and are easily trimmed intraoperatively if needed [37–40].
Despite these advantages, however, bio-inert PEEK is unfavorable for osteoblastic cell adhesion and has no bioactive potential [37, 41].
3.2 Titanium
Titanium is one of the most common metallic materials used in the additive manufacturing, due to its good chemical properties, such as high corrosion resistance, a
key feature for the manufacture of implants and surgical prostheses Titanium has a
modulus of elasticity similar to human bone is known as a bone reconstruction
material due to its high clinical value. Titanium showed low infection rate, high
biocompatibility, biological inertness, signicant corrosion resistance, and benecial handling characteristics. However, it does not have good thermal or electrical
conductivity and is expensive [42–44].
Titanium is lighter and stronger than the human skull bone. In addition, when
made of PSI and mesh, it ts perfectly with the edges of the skull defect and
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shortens the duration of operation. On the other hand, titanium implants trimmed
during surgery sometimes erode the skin due to the increased tensile stress of the
mesh shape, which results in an inappropriate contour [45].
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3.3 PMMA
PMMA, the most used biomaterial, was rst used in human by Zander 1940. The
tensile strength of PMMA is 47–79MPa. To withstand forces, the base structure
should have similar tensile strength. Tensile strength of human skull bone is reported
to be 53 ± 4.9 MPa. Therefore, PMMA has an impact resistance comparable to
human skull bones in any normal stress or impact [46].
Polymethylmethacrylate is a exible acrylic resin that has the similar strength
and protection as native bone tissue. Acrylic resins are stable, chemically inactive,
unaffected by temperature, nonconductive, cheap, well tolerated by tissue, and easily applied and modied. However, lack of porosity, inhibits ingrowth of newly
formed bone tissue into PMMA PSIs. PMMA interferes with osteoconduction and
vascularization, does not interact with the surrounding tissue, and may be more
susceptible to infections than other alternatives [47, 48].
4 Clinical Workflow
PSIs can be fabricated through a manufacturing process and can also be produced
by directly shaping a 3D printed skull model. The design methods for the reconstruction of the cranio-maxillofacial defects are as follows.
Mirrored imaging technique involves mirroring the intact side of the skull on the
opposite side and subsequently applying a logical difference to the implant design.
This method is suitable for skulls with low asymmetry and unilateral lesions and for
signicant defects that do not cross the midline [49, 50]. In the following, the design
of a patient-specic prosthesis performed with this method will be described
in detail.
Template-based technique use a reference skull, which can be an average skull,
or a patient-like skull. Then, the spatial matching between the injured area on the
patient’s skull and the corresponding fragment in reference model is performed to
design the implant geometry. This approach is suitable for very asymmetrical skulls
and large and complex defects, even in the midline [50].
Anatomical reconstruction or free form modeling is a way to design implants
using supportive geometry, for example, the residual geometry of the patient’s bone,
and free form modeling tools such as lines, plates, and curves provided by CAD
software. An example of this method is the “curvature-based lling” function. This
function uses the surface tangent along with the defect to reconstruct the surface.
The results are similar to the original curvature [26, 51].
The thin plate spline (TPS) or interpolation properties of the radial basis func-
tion includes interpolation functions that can approximate the surface of the skull in
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Z. Bakhtiari and A. Khojasteh
a defect by warping and deforming a target based on two sets of homologous points
dened on a reference model and a target. This approach using an average skull can
be suitable for defects of the midface. Because TPS is a supercial interpolation, it
is not suitable when dealing with extensive defect areas [50, 52].
There are also other methods based on statistical analysis and various software.
Also, we can combine the above method to get a better result. In a study by
Mandolini etal. in 2020, they used template-based methods combined with freeform modeling methods for the patient affected by Apert syndrome with a frontal
bone deciency. For managing high skull asymmetry and large defect size for this
patient, adoption of reference geometries was required. Adding free-form tools
ensures a smooth transition at the implant-bone interface [50].
Here is a step-by-step description of a case. This patient was a 49-year-old man
who had lost part of his frontal bone and left orbital oor and roof due to trauma.
After inserting DICOM images and segmentation, the original condition of the
patient’s bones was restored (Fig.4).
In the next step, the extra parts of the model that were not needed were removed
with the cut command, and the remaining structure of the model is shown in Fig.5a.
Then, the sound side was mirrored on the defective side to make the initial design
for the prosthesis (Fig.5b). Using the cut command, parts of the mirrored model
that were placed on the defect were selected, and the rest of the parts were deleted
(Fig.5c).
Finally, the prosthesis was designed to be porous. Hence, a cylinder with a surgi-
Fig. 4 Shows CT scan of the patient before surgery. (Figure courtesy of Dr. Hekmat Farajpour and
Dr. Shahabaldin Azizi)
cal screw diameter (2.7 or 2.1mm) was designed and placed in the desired locations
(with the Reposition command). The cylinders were removed from the prosthesis
(with the Boolean command), and the nal prosthesis was designed, which is shown
in Fig.6. And it was manufactured with 3D printing as shown in Fig.7.
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