Pre-operative planning for mandibular reconstruction - a full digital planning workflow resulting in a patient specific reconstruction.

Abstract

Reconstruction of large mandiblular defects following ablative oncologic surgery could be done by using vascularized bone transfer or, more often, primarily with simultaneous or delayed bone grafting, using load bearing reconstruction plates. Bending of these reconstruction plates is typically directed along the outer contour of the original mandible. Simultaneously or in a second operation vascularized or non-vascularized bone is fixed to the reconstruction plate. However, the prosthodontic-driven backward planning to ease bony reconstruction of the mandible in terms of dental rehabilitation using implant-retained overdentures might be an eligible solution. The purpose of this work was to develop, establish and clinically evaluate a novel 3D planning procedure for mandibular reconstruction.
Three patients with tumors involving the mandible, which included squamous cell carcinoma in the floor of the mouth and keratocystic odontogenic tumor, were treated surgically by hemimandibulectomy.
In primary alloplastic mandible reconstruction, shape and size of the reconstruction plate could be predefined and prebent prior to surgery.
This study provides modern treatment strategies for mandibular reconstruction.

Full text

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RESEARCHOpen Access
Pre-operative planning for mandibular
reconstruction - A full digital planning workflow
resulting in a patient specific reconstruction
Harald Essig†, Majeed Rana*†, Horst Kokemueller, Constantin von See, Martin Ruecker, Frank Tavassol and
Nils-Claudius Gellrich
Abstract
Objectives: Reconstruction of large mandiblular defects following ablative oncologic surgery could be done by
using vascularized bone transfer or, more often, primarily with simultaneous or delayed bone grafting, using load
bearing reconstruction plates. Bending of these reconstruction plates is typically directed along the outer contour
of the original mandible. Simultaneously or in a second operation vascularized or non-vascularized bone is fixed to
the reconstruction plate. However, the prosthodontic-driven backward planning to ease bony reconstruction of the
mandible in terms of dental rehabilitation using implant-retained overdentures might be an eligible solution. The
purpose of this work was to develop, establish and clinically evaluate a novel 3D planning procedure for
mandibular reconstruction.
Materials and methods: Three patients with tumors involving the mandible, which included squamous cell
carcinoma in the floor of the mouth and keratocystic odontogenic tumor, were treated surgically by
hemimandibulectomy.
Results: In primary alloplastic mandible reconstruction, shape and size of the reconstruction plate could be
predefined and prebent prior to surgery.
Clinical relevance: This study provides modern treatment strategies for mandibular reconstruction.
Keywords: Mandibular reconstruction, backward planning, patient specific implant, computer-assisted surgery
Introduction
Indications for partial and total mandibulectomy include
malignancies especially squamous cell carcinomas
(SCC), benign tumors such as ameloblastomas and
sequelae of radiotherapy such as osteoradionecrosis.
Defect size in ablative surgery mainly depends on dig-
nity and dimensions of the pathology. Following mandi-
bulectomy, reconstruction of the mandible is mainly
done with vascularized bone grafts or alloplastic materi-
als (reconstruction plates). However, irrespective of the
type of primary hard tissue reconstruction is simulta-
neous adequacy of the soft tissue reconstruction equally
important: only a well vascularized soft tissue envelope
allows for a successful hard tissue reconstruction. Even
large series of mandibular reconstruction after ablative
surgery or major trauma in literature show that oral
rehabilitation of patients with large segmental defects is
still a challenge [1-4]. Besides soft tissue inadequacies
due to ablative procedures and scarring, the method of
bony reconstruction plays an important role on the
functional and aesthetic result [2,5-8]. Preferred donor
sites for vascularized bone with good survival rates are
the fibula, iliac bone and scapula [9-11]. Limitations in
terms of either primary or secondary dental implant-
based rehabilitations are especially the lack of recreating
the alveolar height and following adverse crown-implant
ratio. But also the lateral and sagittal extension of the
bone volume determines the success rate of dental
implants and therefore is crucial for oral rehabilitation
in cancer patients [12]. Some authors prefer secondary
* Correspondence: rana.majeed@mh-hannover.de
† Contributed equally
Department of Oral and Maxillofacial Surgery, Hannover Medical School,
Hannover, Germany
Essig et al. Head & Neck Oncology 2011, 3:45
http://www.headandneckoncology.org/content/3/1/45
© 2011 Essig et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

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mandibular reconstructions with free bone grafts which
provide adequate volume to insert implants [12-14]. A
prerequisite to apply this method is a secure vascular-
ized soft tissue bed.
Pre-operative planning is highly-developed [15-17] and
image-guided surgery well-established. An ongoing issue
in planning procedures is that virtual reconstruction is
based on a true-to-original outer contour reconstruction
[18]. However, dimension limitations of bone grafts,
especially in height and width, do not match with
prosthodontic needs and often result in unavoidable mal-
positioned dental implants with sequentially lateral cross-
bite situation. Furthermore, dysbalance in soft-tissue-to-
bone-to-implant relationship result in later periimplanta-
tis with consecutive early to late implant loss. Aim of this
study is to implicate the ideal, i.e. prosthodontic driven
planning and positioning of bone grafts in the planning
procedure respecting the desired implant position: back-
ward planning independent of the reconstructive techni-
que. This requires patient specific pre-bending of the
reconstruction plate to guide the bone graft into the
desired position. So the outer contour of the mandible is
not anymore the basis for bending the plate.
Materials and methods
Three patients with tumors involving the mandible,
which included squamous cell carcinoma in the floor of
the mouth and keratocystic odontogenic tumor, were
treated surgically by hemimandibulectomy. Written
informed consent was obtained from the patient. The
patient’s preoperative demographic data are summarized
in Table 1.
Virtual Planning Technique
The imaging and planning platform used in this study
was iPlan 3.0 (Brainlab®, Feldkirchen, Germany). This
platform allows for alignment of the DICOM data set,
viewing and analysis and provides 3D tools for the plan-
ning procedure such as mirroring tools, autosegmenta-
tion with atlas-function and a three-dimensional
modification tool named SmartShaper. iPlan enables
import of different imaging modalities and allows to
automatically image-fuse these data. That facilitates not
only the pre-operative analysis of the data but also the
post-operative quality control. Furthermore this platform
allows for intra-operative navigation of the virtual plan
which is important for midface and skullbase procedures,
however, this was not used in the presented cases.
The basic data used for the virtual planning included the
pre-operative computed tomography (CT) imaging data
with a maximum slice thickness of 1 mm. The data were
transferred on the computer and reconstructed into 3D
images. Different planning modalities include mirroring
tools (case 1), autosegmentation tools (case 2) and the
backward planning tool (case 3). The backward planning
is mainly based on size-variable ideal dental arch models
with adjustable and truly designable virtual hollow cylin-
ders. These hollow cylinders define not only the implant
position but also the needed peri-implant bone volume.
Thus desired bone position as a required subvolume
within the later bone grafts for later insertion of dental
implants could be visualized and already considered dur-
ing the primary alloplastic reconstruction of the mandible.
Outcome of the virtual planning is in each case a vir-
tual template of the mandible (STL-file format) for pro-
duction of a corporeal stereolithographic model. After
prototyping of the model (Phacon GmbH, Leipzig, Ger-
many) a conventional 2.4 Compact UniLOCK recon-
struction plate (Synthes®, Umkirch, Germany) was bent
to bridge the prospective mandible defect.
After ablative surgery was performed, the preformed
reconstruction plate was used for the osteosynthesis. At
the time of secondary reconstruction with free iliac bone
graft the individual reconstruction plate gives the surgeon
a clear direction where the bone should be ideally placed.
The following case studies demonstrate the planning
possibilities, firstly starting with an unilateral defect
using mirroring tools and patient specific reconstruction
plate (case 1), secondly using the autosegmentation to
virtual reconstruct the mandible (case 2) and finally pre-
senting the prosthodontic driven “backward planning”
for optimized bone graft position (case 3).
Case Studies
Case 1
The patient was a 53-year-old man with a large kerato-
cystic odontogenic tumor confirmed by previous biopsy.
Due to the huge extent of the lesion, there was an indi-
cation for hemimandibulectomy of the right side. After
importing the data into the imaging and planning plat-
form (iPlan 3.0) a virtual model was built by using mir-
roring tools (Figure 1). The unaffected left side was
Table 1 Patient’s preoperative demographic data
CaseIDAgeSexPathologyPlanning modality
1
2
3
LF
NK
MB
53
52
66
M
M
F
Keratocystic odontogenic tumor
SCC (T4)
SCC (T4)
Mirroring of the unaffected site, STL-modell, prebending
Autosegmentation, STL-modell, prebending
Backward-Planning using Autosegmentation, SmartShaper, virtual Implant positioning
SCC: Squamous cell carcinoma
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manually segmented and, after alignment of the data set,
mirrored to the affected site. Using logical operations
“union” in the advanced manipulation mode, mirrored
and unaffected left side were grouped and exported as
an STL-file. Stereolithographic model was fabricated and
reconstruction plate bent.
After ten months patient underwent secondary recon-
struction with bone graft from the iliac crest. The
operation was straightforward and quick, with no intra-
operative complications. In the 2D-analysis of the
panorex X-ray (Figure 2) augmentation seems adequate.
Case 2
A 52-year-old male presented with a squamous cell car-
cinoma of the anterior floor of the mouth (pT4 N2 -
Stage 4 UICC). The extent of the primary tumor and
the nodal involvement was evaluated clinically and radi-
ologically (CT scan). The expected size of mandible
resection was defined virtually. Because of arrosion of
the mandible and the large extent of the resection (com-
plete corpus mandibulae), mirroring is no option for vir-
tual planning. Brainlab iPlan 3.0 comes with an
autosegmentation mode. Starting the procedure of auto-
segmentation, the so generated neomandible combines
the existing bony structures with averaged segments of
the autosegmentation. Following 3D analysis of the neo-
mandible, a stereolithographic model was built and, as
above mentioned, prebending performed (Figure 3).
Patient underwent en bloc tumor resection with par-
tial mandibulectomy and bilateral neck dissection. The
individual prebent reconstruction plate was inserted.
Figure 1 CT scan showing an extended mandibular lesion (keratocystic odontogenic tumor). Swelling of the mandible makes
conventionally bending prior to resection difficult (A, B). By Computer assisted pre-operative planning by mirroring of the unaffected left side
(template C, D; mirrored template E, F) a stereolithographic model (G) could be printed and a reconstruction plate could be bended prior to
surgery.
Figure 2 Panorex X-ray Case 1 - after secondary reconstruction
of the mandible.
Figure 3 Even in edentulous patients with severe atrophy of
the mandible (A), Computer assisted planning is possible due
to the autosegmentation (B) provided by the iPlan 3.0
software (BrainLAB®).
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The operation went without complications and second-
ary reconstruction is planned. Plate profile created good
visual appearance of the lower third of the face. Besides
of possible intraoral soft tissue deficiencies, large bone
grafts which offer especially large dimension in width
and height would be needed to enable adequate oral
implantation and to prevent ending up in a cross-bite
situation.
Case 3
The patient was a 66-year-old female who complained
of dysphagia and pain caused by a tumor located on the
alveolar ridge with infiltration of the anterior floor of
the mouth and tongue. Diagnosis of squamous cell car-
cinoma was confirmed by preoperative biopsy (pT4 -
Stage 4 UICC).
Similar to case 2, virtual mirroring as a planning tool
was not feasible due to mandible destruction and atro-
phy. For the autosegmentation mode, atrophy and
destruction has only minor effects on template building.
After autosegmentation of the mandible with iPlan,
backward planning by using virtual ideal upper and
lower dental arches and virtual hollow cylinder as place-
holders was performed (Figure 4). The hollow cylinder
illustrate a total of six dental implants and their
expected requirement of bone: in this planning 3 to 4
mm bone volume was radially disposed around the
cylinder (Figure 5). The diameters of implants were set
at 4 mm respectively 5 mm in the posterior region. The
length of the cylinders is arbitrary and was in this case
between 13 and 15 mm.
The result of placing these hollow cylinders illustrated
the target (neomandible) which should be addressed
with the bone graft in secondary reconstruction. Using
the SmartShaper the virtual mandible is adjusted to the
desired outline of the planned neomandible and
exported as STL-file (Figure 6).
Results
In primary alloplastic mandible reconstruction, shape
and size of the reconstruction plate could be predefined
and prebent prior to surgery. This could improve accu-
racy of the contour of the plate. In limited mandible
defects, good results could be achieved with this simple
planning method (case 1). In larger defects (case 2) sim-
ple mirroring tools are not feasible. The recent iPlan-
Software allows by using the autosegmentation mode a
virtual reconstruction of the mandible and following
prebending of plates.
The base of planning is up to now mostly the outer
contour of the mandible. But in large reconstructions,
this leads to an inappropriate positioning of bone grafts
in secondary reconstruction due to the limited dimen-
sions of bone grafts. In case 3 we could demonstrate the
significant discrepancy between original mandible con-
tour and desired neomandible contour regarding later
oral rehabilitation.
Figure 4 Patient with squamous cell carcinoma facing subtotale mandibulectomy (A). Conventional bending of the reconstruction plate
could be simulated (B). Virtual planning of the mandible by autosegmentation (similar to Figure 3) shows the conventional relation and position
between plate and favored mandible reconstruction (C, D). Conventional bending of the plate follows the outer contour of the original
mandible.
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Discussion
Adequate reconstruction should offer replacement of
dentition and provide improved deglutition, mastication,
and speech [19] and therefore significantly contributes
to oral rehabilitation. These clinically relevant para-
meters depend mainly on soft tissue lining, on the
mobility of the tongue and on the amount of bone avail-
able for dental implantation.
Soft tissue lining has to be addressed at least twice: in
mandibular reconstruction to allow a sufficient blood
supply for the transplanted bone with its bradytrophic
character and before or after implant insertion to allow
a non-irritant interface between mucosa and implant. It
is reported that in accompanying soft tissue deficiencies
mandibular reconstruction is preferably treated with
vascularized bone grafts. Buchbinder et al. demonstrate
that osseocutaneous flaps offer the most rapid rehabili-
tation [19]. In contrast, there is evidence for a better
outcome in oral rehabilitation of non-vascularized iliac
crest grafts compared to osseocutaneous flaps [12].
Problems of bony reconstruction include undercorrec-
tion of the lower facial contour, unsatisfying midline
match and unfavourable sagittal maxillary-mandibular
relationship [12] due to limited bone graft volume. In
literature, however, bony deficiency in width and height
as an important factor for oral rehabilitation is rarely
mentioned [2] and even publications which focus on vir-
tual planning in large mandible reconstruction do not
provide post-operative three-dimensional imaging [17]
to make advantage of virtual planning comprehensible.
Figure 6 Modified neomandible (green, A) respects the future implant position (B) and guides the new position of the reconstruction
plate (green plate, C). The new position is mostly lingual bound (D, E).
Figure 5 Pre-operative planning allows prior to surgery a prosthetic-driven “backward planning”. Even in iliac crest bone transplants
reconstruction size is limited. The position of future implants with their requirements of adequate bony lining is considered (A) and simulated
with different hollow cylinders. Distance between conventional position of reconstruction plates (visualized by the red plate) aligned by the
original outer contour is demonstrated in two different planes (B, C).
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