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Chapter 14 Designer faces: CAD/CAM facial implants
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ACKNOWLEDGMENT
Presented by Dr. Yaremchuk at the 22nd Annual Hans R. Wilhelmsen MD, DDS
Lectureship in the Craniofacial Sciences, May 17, 2018, at the Johns Hopkins
Hospital in Baltimore, MD.
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Chapter 15
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Implant renement of
postorthognathic surgery
facial contour
Le Fort I maxillary and sagittal split mandibular osteotomies are performed
to correct dental malocclusion and improve facial harmony. Skeletal movements of large magnitude, particularly those for correction of preexisting facial
asymmetries, may create new contour irregularities and disharmony. Both the
midface and lower face can manifest characteristic postorthognathic contour
irregularities that are amenable to alloplastic implant improvement.
MIDFACE CONTOUR IRREGULARITY
Because the Le Fort I maxillary osteotomy and advancement is performed
beneath the infraorbital foramen, the midface skeleton above the foramen
remains deficient in its sagittal projection. The midface skeleton is now more
prominent in its lower half after Le Fort I advancement surgery and, as a result,
the cheeks appear low (Fig. 15.1). This imbalance is in proportion to the magnitude of sagittal skeletal advancement.
A B
Fig. 15.1 Typical facial contour sequelae after orthognathic surgery. (A) Lateral appearance of patient after Le
Fort I advancement osteotomy, sagittal split, and horizontal chin osteotomies. (B) Artist’s rendition showing
skeletal movements responsible for facial contour disharmonies and irregularities.
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Chapter 15 Implant renement of postorthognathic surgery facial contour
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To improve midface contour some surgeons have combined zygomatic osteotomies with the Le Fort I osteotomy.
alloplastic implants
3,4
is performed at the time of the maxillary advancement
1,2
More often, malar augmentation with
procedure. Malar augmentation alone widens the midface, which tends to exaggerate an upper midface parasagittal deficiency potentially creating another
imbalance. Hence, increasing the projection of the infraorbital rim is considered
the critical element in creating midface balance after Le Fort I advancement,
with malar augmentation often an appropriate adjunct.5
LOWER FACE CONTOUR IRREGULARITY
Sagittal split osteotomy of the deficient mandible with advancement in the sagittal plane may result in ramus asymmetry and border irregularities (Figs. 15.1
and 15.2). Ramus asymmetry immediately after surgery occurs when the sur-
geon fails to create similar osteotomies and maintain similar osteotomy gaps
(with rigid fixation) on both sides. The surgeon loses control over the relation
of the proximal and distal fragments because the condyle must be positioned in
its fossa and the body must be positioned to correct the occlusion. The positioning of these two areas dictates ramus and angle position. In the orthognathic
literature, the concern for the improper positioning of the proximal segments
and condyle relates to its potential for condylar resorption and postoperative
relapse.
clockwise rotation of the ramus of the mandible because wire osteosynthesis
did not provide enough stability. Rigid fixation has virtually eliminated these
problems related to inadequate fixation.
with resultant counterclockwise rotation or after very large movements. Clinical experience has revealed that this is due to not only the positional restraints
of condylar positioning and osteotomy variability as described above, but also
6,7
In the pre-rigid fixation era this was almost always due to counter-
8,9
However, contour abnormalities may still occur due to incorrect positioning
A
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Fig. 15.2 Acrylic model of mandible resulting after sagittal split and horizontal chin osteotomies. (A) Frontal view. Note dierences in
posterior mandible width and height. (B) Lateral view. Note border irregularities.
B
Fig. 15.3 Operative ndings after a previous bilateral sagittal split
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osteotomy (BSSO). Note bone loss beneath head of lag screw used
for BSSO xation. Skeletal devascularization or mechanotransduction
are the most likely causes of bone loss.
ramus shape changes resulting from bone atrophy (Fig. 15.3). Depending on the
circumstance, this atrophy may result from devascularization and/or remodeling from altered mechanotransduction forces in accordance with Wolff’s Law.
Gaps at the osteotomy sites after sagittal osteotomy of the mandible or horizontal osteotomies of the chin with advancement can result in border irregularities.
Correction of contour irregularities after skeletal rearrangement have focused on
border defects at the sliding genioplasty osteotomy site, prompting some surgeons to fill the defect with hydroxyapatite.10 Surgical technique and the native
mandible anatomy determine the presence and severity of these irregularities.
Patients with “high-angle” mandibular deficiency, which is seen in association with antegonial notching and vertically deficient rami, are predisposed to
visible notching after bilateral sagittal split osteotomy (BSSO). In patients with
“low-angle” mandibular deficiency, where the ramus height is adequate and
there is no antegonial notching, post-BSSO border irregularities reflect technical
deficiencies in creating and maintaining (assuming rigid fixation) the correct
osteotomy gap geometry of the buccal cortical plates. This geometry should be
the same on both sides.
The extent of parasymphyseal notching after horizontal osteotomy of the
chin with advancement is also influenced by surgical technique. By making the
osteotomy oblique, as the artist has depicted in Fig. 15.1, the distal segment is
shortened as it is advanced, which not only accentuates border irregularities
but also causes the bone cut to exit the inferior mandibular border where the
soft tissue coverage is more tenuous and exposes the notching. By lowering
the bone cut anteriorly, one can eliminate or minimize the obliquity of the osteotomy and, therefore, any shortening with a more proximal inferior border exit.
Implant renement
IMPLANT REFINEMENT
Contour irregularities can be addressed at the time of orthognathic surgery or,
most often, at a later, secondary surgery.
The result obtained with readily available “off-the-shelf” implants can be
limi ted due to the challenge of hand carving three-dimensional implant contours
to correct iatrogenic as well as intrinsic facial asymmetries. Computer-aided
design and manufacture (CAD/CAM) implants provide added sophistication
to the procedure and are preferred by these authors.
When implants are placed at the time of orthognathic surgery, they are usually off-the-shelf implants modified at that time to address the observed skeletal
3,4,11
12
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Chapter 15 Implant renement of postorthognathic surgery facial contour
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deficiency. Orthognathic procedures are now routinely planned with computer
technology and the surgery facilitated with computer-designed cutting guides
and fixation devices. Obligatory skeletal imbalances and contour irregularities
can be predicted. This can provide implants that are computer designed to correct these imbalances and irregularities at the time of the orthognathic procedure.
CAD/CAM IMPLANTS
To computer design and computer manufacture alloplastic implants, computed
tomography (CT) scans with high resolution (<2 mm) are acquired using a recommended protocol. Slice thickness and slice spacing of 0.75–1.25 mm is used
to construct three-dimensional images of both the skeleton and soft tissue envelope from the top of the skull to the hyoid bone.
Implant design
Two options are available for the design process: From the CT data, a threedimensional model is manufactured of the patient’s facial skeleton. The surgeon
augments the deficient areas on the model with clay. The implant company uses
the clay prototypes to manufacture implants. The alternative technique, which
is preferred, involves a Web-based meeting between the surgeon and the manufacturer’s engineer, at which time implants are designed virtually. This method
allows millimeter precision in design and measurable relations between the
upper and lower face (Fig. 15.4). Yu Wang et al.13 use CT data of the postorthognathic image to create a template that is used during the contour-modifying
procedure to modify an off-the-shelf implant.
PEARL
Minor skeletal irregularities can be
camouaged with soft tissue llers or
fat injections.
Upper face
The midface disharmony after Le Fort I osteotomy and advancement is a deficiency in the maxilla above the level of the osteotomy. Its custom implant correction
always includes the infraorbital rim and the medial aspect of the malar prominence.
The amount of its sagittal projection is an aesthetic judgment determined by the
amount of lower midface advancement and by the amount of globe prominence.
A
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Fig. 15.4 CAD and CAM to correct postorthognathic mandible contour irregularities and facial imbalance. (A)
CAD plan document. (B) CAD/CAM porous polyethylene implants.
B
Lower face
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The lower face disharmonies after BSSO include possible asymmetry
in lower face height and width as well as border irregularities. If a sliding genioplasty has been performed, border irregularity at the osteotomy
sites and chin asymmetry may be present. A grid pattern placed over the
image is used to design the implant addressing the central and lateral portions of the mandible separately. Centrally, that is from the midline to the
mental foramen, the implant is designed to be symmetric to the midline
as determined by the position of the columella and the central incisors.
Laterally, gonial angle position is determined by its relation to its respective upper face skeleton rather than the midline. The central and lateral
designs are then coordinated to provide a regular inferior mandible border
(Fig. 15.4).
SURGICAL TECHNIQUE
Since intraoral approaches are intrinsic to these surgeries, it is important for
patients to optimize intraoral hygiene before surgery. Chlorhexidine mouthwashes are prescribed for 3 days prior to surgery. Intravenous antibiotics (a
cephalosporin or ciprofloxicin) are administered intraoperatively and for 5 to 7
days postoperatively.
Surgery is done under general anesthesia. Marcaine with epinephrine is injected
into the operative site soft tissues for pain control and intraoperative vasoconstriction. The operative site is irrigated with an antibiotic solution prior to closure.
Surgical technique
Upper face
The upper face is accessed through an intraoral sulcus incision and a
transconjunctival retroseptal incision with lateral canthotomy. Skin–muscle lower lid flaps are an alternative approach. The midface is elevated
in a subperiosteal plane. The infraorbital nerve is identified and preserved. Large, rigid implants are often segmented to allow their placement through limited exposure. The custom design dictates appropriate
placement, which is secured with screw fixation. The midface soft tissue
envelope is resuspended with sutures tied to the implant or drill holes in
the bone.
Lower face
The posterior mandible is accessed through intraoral sulcus incisions and a
submental incision is used to access the chin. The entire anterior face of the
mandible is elevated in the subperiosteal plane. The mental nerves are identified and preserved. Care is taken to minimize disruption of the masseteric sling
during implant placement. Implants are immobilized with titanium screws.
The wounds are closed in layers after a suction drain is placed, which exits in
the postauricular area. The drain is usually removed the morning after surgery.
Video 15.1 demonstrates the surgical placement of CAD/CAM porous polyethylene implants designed to correct irregularities and imbalances resulting
after sagittal split osteotomy.
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Chapter 15 Implant renement of postorthognathic surgery facial contour
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PATIENT EXAMPLES
Clinical examples of the use of implants to correct postorthognathic surgery
contour irregularities are presented in Figs. 15.5–15.7.
A B
DC
Fig. 15.5 A 35-year-old male had undergone Le Fort I impaction, sagittal split mandibular osteotomy, and horizontal chin osteotomy
with lengthening. The surgery had been redone on two occasions. Surgical renement included CAD/CAM chin and mandible
implants to provide angle denition, correction of contour irregularities, and increase chin projection. The native chin was shortened
to allow lip resuspension. (A) Preoperative appearance. (B) CT image. (C) Postoperative frontal appearance at 18 months. (D) Frontal
implant design.
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Patient examples
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A
C D
Fig. 15.6 A 26-year-old woman had undergone Le Fort I advancement, sagittal split
osteotomy, and horizontal osteotomy with advancement at age 20. Midface and mandible
implant surgery, chin lengthening, and rhinoplasty were performed 6 years later. (A)
Preoperative frontal view. (B) Postoperative frontal view. (C) Preoperative lateral view. (D)
Postoperative lateral view.
B
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Chapter 15 Implant renement of postorthognathic surgery facial contour
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A
D
B
C
E
Fig. 15.7 Clinical example of CAD/CAM implants to rene midface and skeletal contours previously performed to address congenital facial
skeletal asymmetry. (A) Preoperative frontal and worm’s eye views of 15-year-old female. (B) Views after midface and mandibular osteotomies
with residual lower face asymmetry 6 years postoperatively. (C) One year later after CAD/CAM porous polyethylene implant to augment
208
decient left mandible. An osseous genioplasty was also performed. (D) Intraoperative view of genioplasty and left-sided implant. (E) Model
shows postorthognathic mandible with CAD/CAM implant. From Lee etal. 2018,12 with permission.
REFERENCES
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management of midface and maxillary deficiency. J Oral Maxillofac Surg 1994;52(3):327–31.
2. Abubaker AO, Sotereanos GC. Modified Le Fort I (maxillary-zygomatic) osteotomy: rationale,
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3. Nocini PF, Boccieri A, Bertossi D. Gridplan midfacial analysis for alloplastic implants at the
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polyethylene implants and orthognathic surgery for correction of malar deficiency. J Oral
Maxillofac Surg 1998;56(6):734–41; discussion 742.
5. Yaremchuk MJ. Infraorbital rim augmentation. Plast Reconstr Surg 2001;107(6):1585–92;
discussion 1593–1595.
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cases. J Oral Surg 1980;38(4):265–82.
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the condyle in orthognathic surgery: a review. Oral Surg Oral Med Oral Pathol Oral Radiol
2012;114(5):567–76.
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Eur J Orthod 2017;39(3):294–309.
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12. Lee JH, Kaban LB, Yaremchuk MJ. Refining post-orthognathic surgery facial contour with
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