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Bone Contouring in Oral and Maxillofacial Surgery: Denition, Indications…
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Fig. 5 Remaining structure of the model after removal of the defect area (a). The brown areas
indicate the areas of the mirrored image (b). Model image after deleting unwanted parts (c).
(Figure courtesy of Dr. Hekmat Farajpour and Dr. Shahabaldin Azizi)
Fig. 6 Shows the patient-specic implant made with computer-assisted design with mirroring
technique. (a) Left side view. (b) Full face view. (c) Right side view. (d) Top view. (e) Bottom view.
(Figure courtesy of Dr. Hekmat Farajpour and Dr. Shahabaldin Azizi)
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Fig. 7 Shows three-dimensional model of the skull. (a) Reconstructed 3D model from the patient’s
CT scan. (b) The patient-specic prosthesis designed to reconstruct the frontal bone, orbital rim,
and orbital walls. (Figure courtesy of Dr. Hekmat Farajpour and Dr. Shahabaldin Azizi)
Z. Bakhtiari and A. Khojasteh
5 Complications
5.1 Infection
In a systematic review and meta-analysis by Gerstl etal. in 2022, there was no difference in terms of infection rate between autologous bone and combined alloplasts
[53]. In a systematic review by Vijfeijken et al. in 2018, comparing autologous
cranioplasty versus alloplastic cranioplasty, depending on the materials used in cranioplasty, the risk of infection varies as follows: PMMA (7.8%), autologous cranioplasty (6.9%), PEEK (5.9%), titanium and (5.4%) hydroxyapatite cranioplasty
(3.3%). Staphylococci were the most common infectious agents identied, causing
infection in 90.7% of cases that examined the type of bacteria. More specically,
71.1% were positive for Staphylococcus aureus (methicillin-resistant Staphylococcus
aureus (MRSA; 28.9%) and methicillin-sensitive Staphylococcus aureus (MSSA;
4.1%)), 4.1% for Propionibacterium acnes, 2.1% S. epidermidis, and 24.7% for different bacterial strains [54]. The size of the skull defect, the type of cranioplasty,
and the blood glucose level have been reported to affect the incidence of infection
after surgery [55]. A study by Rosenthal etal. recommends to receive preoperative
culture swabs in selected patients planned for the cranioplasty, such as patients who
have a long hospitalization stay or previous serious infections treated with
Bone Contouring in Oral and Maxillofacial Surgery: Denition, Indications…
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antibiotics. In patients who have been colonized with MRSA or other resistant
organisms, delaying cranioplasty or prescribing an appropriate antibiotic for resistant organisms (such as vancomycin for MRSA) may be considered for preoperative
prevention [56].
In a study by Jarvinen etal., they used PEEK PSIs for maxillofacial deformities. They concluded that the use of intraoperative antibiotics in combination with
PSIs had no clear effect on the rate of infection. Intraoperative implant modication also has no apparent effect on the rate of infection. They suggest that simultaneous intraoral and extraoral approaches, if they can be avoided, may be safer
for patients [38].
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5.2 Wound Dehiscence
Despite all attempts to enhance bone and soft tissue healing around PSI restorations,
soft tissue dehiscence and recurrent infection remained a concern. The problem
with these complications is the difculty in management and recurrence that may
necessitate, in some cases, the removal of the whole assembly [57]. The implant
volume and shape in different anatomical locations should always be evaluated precisely, not only to achieve good esthetic and functional results but also to ensure that
the surrounding soft tissue can adapt to it. In case of wound dehiscence, if infection
exist, it can be treated with re-suturation and antibiotics. However, if the volume and
shape of the implant are greater than the soft tissue can withstand, reshaping are
required [38].
5.3 Other Complications
In a systematic review by Vijfeijken etal., the most common complications of cranioplasty are infection (5.6%), bone resorption (5.2%), hematoma (1.9%), cerebrospinal uid leakage (1.4%), and wound opening (1.1%) [54].
Rosenthal etal. reported CSF rhinorrhea 3months after PEEK cranioplasty in a
patient. Endoscopy with uorescein was performed, but the site of leak could not be
identied. Final treatment approach was 1week of lumbar drainage. Patient had no
recurrence of CSF leak during 2years of follow-up [56].
Jarvinen etal. reported in one case with PSIs on zygomatic bones and lateral
orbital rims transient facial paralysis of the zygomatic branch of the facial nerve
occurred 2weeks after surgery. They suggested postoperative swelling as probable
cause [38].
Temporary diplopia has been reported in the rst month after surgery in patients
with zygomatic PSI.On the other hand, a PSI can be designed to t the shape of the
orbit perfectly to recover lost orbital volume and allow the orbital oor to be normalized. This “lock and key”-type t has been reported to improve enophthalmos
and diplopia [27, 58].
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Z. Bakhtiari and A. Khojasteh
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Z. Bakhtiari and A. Khojasteh
Functional Bone Replacement inOral
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andMaxillofacial Surgery: Definition,
Indications, andManufacturing
Considerations
FarshidBastami andArashKhojasteh
1 Introduction
Reconstruction of critical-sized mandibular bone defects has been remained as a
challenging issue among oral and maxillofacial surgeons. Comprehensively, four
approaches have been described to reconstruct large bone defects of mandible
including (1) free vascularized or non-vascularized bone grafting procedures [1, 2],
(2) functional bone replacement techniques using patient-specic prostheses fabricated by computer-aided design and manufacturing (CAD/CAM); (3) functional
bone regeneration approaches [3]; and (4) in situ bone regeneration techniques [4].
The last two approaches mentioned are fully discussed in the next chapters. In the
current chapter, we explain functional bone replacement techniques in detail.
Microvascular bone grafting showed favorable functional and esthetic results
due to the probability of dental implant insertion and adequate prosthetic rehabilitation. Although it has been most widely used in recent decades, it has some limitations including complicated surgical technique, limited availability, and donor site
morbidities, which led to using novel approaches [5].
Optimal functional and anatomical results can be achieved using virtual surgical
planning and patient-specic implants, such as plates, prosthesis, etc. [6]. Patientspecic prosthesis for the reconstruction of mandibular bone defect demonstrated
signicant advantages, including the highest precision to restoring the anatomical
shape and size of mandible, a signicant decrease in surgery time, and no additional
F. Bastami · 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_7
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trauma to the donor site with a considerable reduction in postoperative comorbidities [7]. CAD/CAM technology has prepared several advantages, including accurate
preoperative planning, making virtual resections or osteotomies, and design of
patient-specic implants. Furthermore, it has allowed fabrication of patient-specic
prosthesis from virtual models and designs [8].
The surgeon should have a good conception about biomaterials and 3D fabrication techniques to be able to lead the bioengineering team for selection of favorable
ones for different purposes of oral and maxillofacial reconstruction. In the current
chapter, we discuss about desirable biomaterials and technologies to functionally
replace mandibular defects and two challenging defects, including the ramus/condyle unit (RCU) and total mandible. In addition, delayed functional mandibular
bone replacement after pathologic tumor resection is explained. Finally, we present
reconstruction of a bilateral RCU defect with a novel design customized prosthesis,
in which bilateral condyles were preserved.
F. Bastami and A. Khojasteh
2 Patient-Specific Prosthesis
In patients with pathologic lesions, especially malignancies and aggravating comorbidities, a desirable restoration after tumor resection can be obtained using customized mandibular prosthesis [9]. The use of patient-specic prosthesis can functionally
replace the mandibular bone defect, without any disadvantages of other reconstructive techniques such as autogenous bone grafting procedures. For functional mandibular bone replacement, clinicians require a prosthesis, which can replace the
load-bearing bone deciency with normal function. In mandibular defects, the prosthesis can normally function under chewing forces; in addition, it should reconstruct
facial contours and esthetic. Macro plates have been conventionally used to x the
remaining parts of the mandibular bone after segmental resection and preserve the
continuity of the mandibular bone. However, this technique has some disadvantages, such as lack of proper reconstruction of the mandibular bone contour and
esthetic. Moreover, the remaining bone defect needs a second reconstructive surgery a year later using autogenous bone harvested from iliac or rib donor sites, in
this method. Nonetheless, patient-specic prosthesis fabricated by CAD/CAM can
reconstruct normal maxillofacial esthetic by adaptation to normal contours of
the bone.
The characteristics of biomaterials used for prosthesis fabrication should have
followed the biomechanics of the mandibular bone. Also, high bio-integration and
biocompatibility potential can be expected from porous implants [10]. They can
provide both stability in strength and load-bearing specications as well as the
native bone, when creating great integration into the surrounding host bone [11].
Metallic biomaterials for additive manufacturing (AM), which have been conrmed to be the choices for clinical applications, are titanium and its alloys, stainless steel and cobalt-chromium [12, 13]. In addition, magnesium (Mg), iron (Fe),
and zinc (Zn) as biodegradable metals have been still under investigations for
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AM.Element loss and porosity due to evaporation during melting process under a
high-energy beam is a common processing problem of biodegradable metals for
AM [14]. Furthermore, stainless steel is no longer used due to its disadvantages,
such as corrosion, screw loosening, and macrophage-related inammatory reaction.
Titanium and its alloys are commonly used for bone implantation due to their
advantages, including biocompatibility, light weight, corrosion resistance, favorable
integration into surrounding tissues, high strength to weight ratio, and osteoconductive properties. The three main groups of titanium alloys are α, β, and α+β alloys.
The standard combinations are α and β titanium alloys, which demonstrate biocompatibility, favorable mechanical properties, and resistance to corrosion. β titanium
alloys showed desirable properties, like corrosion resistance, low stress-shielding,
and low elastic modulus [12, 15].
Patient-specic titanium implants can fabricate by CAD/CAM or 3D printing
technologies. Application of these implants have been conrmed for clinical applications in the oral and maxillofacial areas [16–18]. The patient-specic titanium
prosthesis successfully xes bone grafts and bony fragments, which lead to favorable reconstruction of maxillofacial bone defects [19–21]. Therefore, porous titanium implants, which have biomechanical similarity to the native bone and high
osseointegration capabilities, are the biomaterial of choice for implants used in
functional bone replacement.
Virtual surgical planning (VSP) can help clinician to specically design the prosthesis according to the patient’s condition and the areas which should be removed
with respect to the safe margin around the tumor. In addition, surgical guide prototypes can be designed to determine the exact location of tumor resection. These
prototypes can fabricate from a polymer using a fused deposition modeling (FDM)
process [22]. In fact, surgical guides help surgeons to position the osteotomy perfectly on the area where the prosthesis is to be placed and to avoid size mismatch.
In addition, this procedure decreases the time of surgery and tumor resection.
Biomechanics is one of the most important factors which should be evaluated to
determine durability of the patient-specic prosthesis. For certainty from the biomechanics of the prosthesis, nite element analysis can be performed before manufacturing. This analysis can assess tolerance of the prosthesis under mandibular
function and chewing forces, and possible errors can be corrected before a large cost
is imposed on the patient [13].
The current advancements in technological manufacturing, including selective
laser melting (SLM) and 3D printing, have increased the interest of using titanium
implants in functional bone replacement. To illustrate, the best physicochemical
characteristics for customized titanium implants are provided by annealing and
SLM.Annealing temperatures ranging from 625 to 725°C increase plasticity up to
16% after SLM. The titanium implant can achieve the desired physicochemical
characteristics under annealing procedure at 675°C for 1h, associated to wrought
titanium (GOST R ISO 5832-2, grade 4). The porous structures, which only underwent SLM without annealing procedure, can change from the original cubical form
due to low mechanical strength and local thermal stresses [23].
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F. Bastami and A. Khojasteh
3 Mandibular Ramus/Condyle Unit (RCU) Reconstruction
Reconstruction of RCU has been still a challenging issue among oral and maxillofacial surgeons. Appropriate form and length of mandible, normal jaw movements,
and occlusal consistency should be considered through RCU reconstruction to
achieve successful outcomes [24]. A traditional method to reconstruct RCU defects
is costochondral graft (CCG) with or without iliac bone graft [24, 25]. Nonetheless,
in addition to autogenous bone grafting pitfalls including donor site morbidity, need
to second surgery, and increasing operation times, CCG demonstrated unpredictable
growth and may possibly fail in sites that underwent multiple surgeries or anatomical structures discrepancies because of end-stage pathology [26, 27]. Moreover,
needing intermaxillary xation for 7–10days is the major disadvantage of CCG,
while the practice of immediate mouth opening is required to prevent TMJ ankylosis [26].
Using alloplastic prostheses is another choice of RCU defect reconstruction but
has a main concern about the relation among the condyle and glenoid fossa, which
is resolved by temporal glenoid fossa prosthesis for prevention of trauma to the
middle cranial fossa or bone resorption in glenoid fossa [28]. As for alloplastic
mandibular ramus and temporal glenoid fossa prostheses, the Biomet Microxation
TMJ Replacement System (Biomet Microxation, Jacksonville, FL, USA) has been
introduced either as custom or stock [29]. Custom prosthesis can overcome the limitations of CCG or stock prosthesis, such as difcult adaptation and stable xation to
the glenoid fossa and ramus [27, 29–31]. Using TMJ prosthesis has several benets
like biocompatibility and availability, but these prostheses are expensive and technique sensitive, especially in customized one [32], and require to be replaced with a
life span of 10–20years [33].
CAD/CAM technology and patient-specic titanium implants have been introduced in several approaches for RCU defect reconstruction. Ow etal. demonstrated
reconstruction of a unilateral RCU defect immediately after resection of a pathologic lesion in a fully edentulous patient by only a custom-made condyle implant
without glenoid fossa prosthesis [34]. To reduce the risk of damage to or perforation of the glenoid fossa, the condylar segment of prosthesis was under mirror
polishing, and vertical dimension of prosthesis was slightly reduced. Although
they radiographically observed some degree of condylar sag, it had no clinical
effects, and function of the jaw was well 2 years, postoperatively. In another
approach, U etal. reconstructed both the RCU and glenoid fossa, employing titanium and high- molecular- weight polyethylene, respectively, and reported desirable outcomes after 6 months passed from surgery [35]. Touré etal. preserved the
ipsilateral condyle to reconstruct the unilateral RCU defect and observed well
functional results with no complications 18 months after the surgery [36].
Consequently, these case reports observed favorable outcomes of unilateral RCU
reconstruction in three approaches, with or without glenoid fossa prosthesis and
with preserving ipsilateral autogenous condyle structure. To illustrate, some modications, such as preserving autogenous condyle, or some techniques, like mirror
polishing the condylar segment of the prosthesis, can reduce the concerns about
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