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Chapter 11 Chin
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Fig. 11.22 An 18-year-old woman desired
more strength and denition to her
lower face. A two-piece 5-mm projection
porous polyethylene implant was placed.
A submental lipectomy and a buccal
lipectomy were also performed. The nasal
spine was rongeured. (A) Preoperative
frontal view. (B) Preoperative lateral view. (C)
Postoperative frontal view. (D) Postoperative
lateral view. From Yaremchuk 2003,4 with
permission.
A
C
B
D
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Skeletal asymmetries
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A
C
Fig. 11.23 A 31-year-old man underwent chin augmentation with a 7-mm projection two-piece porous polyethylene implant. A submental
lipectomy was performed. (A) Preoperative frontal view. (B) Preoperative lateral view. (C) Postoperative frontal view. (D) Postoperative lateral
view. (E) Postoperative oblique view. From Yaremchuk 2003,4 with permission.
B
D
E
SKELETAL ASYMMETRIES
Congenital asymmetries of the facial skeleton are usually more complex than
localized areas of volume excess or deficiency. Rather they resemble a warping or twisting of the facial skeleton. This is difficult to discern on physical
examination or plain X-rays but becomes obvious with three-dimensional
CT imaging. CT data also allows fabrication of hard or virtual models for
planning. Computer-aided design and manufacture (CAD/CAM) of implants
provides added sophistication when addressing significant asymmetries (see
Chapters 14 and 15).
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Chapter 11 Chin
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Fig. 11.24 A 43-year-old man underwent
chin augmentation with a 5-mm
projection porous polyethylene implant. A
submental lipectomy was performed. (A)
Preoperative frontal view. (B) Preoperative
oblique view. (C) Preoperative lateral
view. (D) Postoperative frontal view.
(E) Postoperative oblique view. (F)
Postoperative lateral view.
A
B
D
E
SECONDARY SURGERY
Mentalis muscle damage
In the author’s experience, which is similar to Zide’s,24 most patients presenting for additional surgery have had implants placed through an intraoral approach. Some of these patients have problems related to mentalis
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dysfunction, which includes lower lip descent with increased lower incisor
show, a deep sulcus, and often, chin pad ptosis.
C
F
Correction of these deformities requires resuspension of the mentalis. Using
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both intraoral and submental incisions, the chin soft tissues are freed in a subperiosteal plane. A Mitek (Mitek Worldwide, Norwood, MA) anchor is then
placed between the tooth roots and is used as a post to attach the remnant of
the mentalis muscle. The chin pad is also secured to the menton. The chin must
have enough projection to support the elevated chin pad (Fig. 11.25). If projec-
tion is inadequate, chin augmentation is required. Fig. 11.26 shows a sagittal
view of mentalis disruption after horizontal osteotomy of the chin with plateand-screw fixation of the advanced segment. Scarring of the muscle to the fixation material at the step-off complicates the repair. In this situation, an implant
is placed to eliminate the step-off during the mentalis muscle repair.
Secondary surgery
A
D
Fig. 11.25 A patient exhibiting deformity due to mentalis muscle damage including chin ptosis, lip descent and a deepened intraoral sulcus.
(A) Chin pad ptosis. (B) Lower lip descent. (C) Deep sulcus due to loss of mentalis continuity or detachment. (D) Corrected chin ptosis. (E)
Restored lip posture. (F) Restored sulcus.
B C
E
Fig. 11.26 Diagram illustrating mentalis muscle injury further
complicated by descent of muscle to skeletal concavity and
hardware xation. Repair requires freeing of muscle contraction
and irregularities, as well as lling of skeletal contour depression
before muscle reattachment. (A) Muscle scarring to xation
hardware is not uncommon after sliding genioplasty. (B) Repair
includes eliminating step-o at osteotomy site with hand-carved
implants.
F
A B
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Chapter 11 Chin
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Implant-related deformity
Dissatisfaction with previous chin implant surgery most often includes implant
asymmetry (particularly with extended implants), implant malposition, and
poor implant-to-native mandible transition (Figs. 11.14 and 11.16).
Revision surgery requires implant removal and replacement with an
appropriately sized, shaped, and positioned implant (Fig. 11.27). Removal
A
C
Fig. 11.27 A 36-year-old woman presented 17 years after previous smooth silicone chin implant placement. She was displeased with the
asymmetry and unnatural appearance of her chin. Through a submental approach, the silicone implant was removed. It was replaced
154
with a two-piece porous polyethylene implant xed with screws. A submental lipectomy was performed. (A) Preoperative frontal view.
(B) Preoperative lateral view. (C) Postoperative frontal view. (D) Postoperative lateral view. (E) Postoperative oblique view. Despite the
replacement with a symmetrically positioned and immobilized implant, asymmetry, although less, persists. This is due to the soft tissue
distortion caused by the contraction process encapsulating the malpostioned original implant.
B
D
E
of a smooth-surfaced implant often reveals a distorted soft tissue enve-
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lope. The distortion will worsen with time due to ongoing soft tissue
contraction forces if the soft tissues are not supported with an adequate
infrastructure. This distortion can be lessened if the soft tissue envelope
is redraped over another implant or an advanced skeleton after horizontal
osteotomy.
The bone erosion that is inevitable beneath smooth implants and visible on X-rays often raises concern, but is not clinically apparent. However, it may complicate secondary surgery by creating an irregular skeletal
surface.
Bone erosion resulting from an implant positioned over a tooth root may
cause symptoms necessitating root canal surgery. Fig. 11.28 shows a CT scan of
a patient who presented with dental pain resulting from implant-induced bone
erosion damaging a tooth root.
Fig. 11.28 CT scan showing implant over tooth root. Bone erosion
resulted in root exposure and symptoms necessitating implant
removal and root canal surgery.
Sliding genioplasty
SLIDING GENIOPLASTY
Sliding genioplasty involves a horizontal osteotomy of the mandible just
beneath the mental foramen. A freed chin point is positioned as desired, usually anteriorly, to increase chin projection, but theoretically, it can be moved in
any direction. It is usually performed through an intraoral incision, although
the author prefers the submental approach. Strap muscles are left attached to
the distal bone segment to preserve the vascularity of the free segment. Most
often, the distal segment is immobilized in its new position with rigid fixation.
The main advantage of this technique over implant augmentation of the chin
is its ability to increase the vertical height of the chin. The space between the
mandible and the repositioned segment is maintained by filling it with a bone
graft or an alloplastic implant. Another advantage of horizontal osteotomy is
that when the chin point is advanced, the suprahyoid muscles are put on a
stretch, therefore decreasing submental fullness and improving submental contour (Fig. 11.29).
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Chapter 11 Chin
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156
A
Fig. 11.29 Advancement osteotomy of chin results in tightening of the suprahyoid muscles and may decrease submental fullness. (A) Before
osteotomy. (B) After osteotomy and advancement. Note indentation at osteotomy site.
B
Disadvantages of sliding genioplasty include the risk of mentalis muscle
damage, when performed through an intraoral incision, and possible trauma
and even division of the mental nerve during osteotomy. Sliding genioplasty
requires considerable facility in bone carpentry. Free segment malposition or
improper fixation can lead to obvious asymmetries. When the osteotomy is
made oblique, the distal segment can be 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. The notching or indentation is especially detrimental to
those who have a preexisting prejowl sulcus. The shortened distal segment also
creates a poor chin–anterior mandible transition, resulting in a “stuck-on” chin
appearance (Fig. 11.30). These problems are avoidable with proper technique.
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.
Fig. 11.30 Oblique view of acrylic model made from CT data
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of patient who had undergone sliding genioplasty and sagittal split osteotomy. This model demonstrates a poor transition between the advanced chin segment and mandible as
well as indentation along the mandible border at osteotomy
sites.
Despite its continued vascularization after osteotomy and advancement, the
advanced segment of the osseous genioplasty is susceptible to resorption, most
likely due to the altered bone–soft tissue relationship. This bone resorption not
uncommonly allows fixation hardware to become prominent, causing distortion of the overlying soft tissue envelope (Fig. 11.31).
Sliding genioplasty
Fig. 11.31 Intraoperative view of a lag screw that has become
prominent due to resorption of advanced osteotomy segment as
part of sliding genioplasty.
After sliding genioplasty
The mandibular border step-off deformity (notch) and to some extent the lack of
transition with the repositioned chin can be corrected with implants. Implants
are available that bridge the gap between the advanced segment and the intact
mandible (Fig. 11.32). A patient who had revision surgery for this notch deformity is shown in Fig. 11.33.
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Chapter 11 Chin
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A
B
Fig. 11.32 Implants are available that span the gap in inferior border contour after horizontal or sagittal osteotomy (Matrix Surgical, Atlanta,
GA). These implants may be placed at the time of osteotomy surgery or during secondary surgery. (A) Model with osteotomy gap. (B) Implant
spans osteotomy gap resulting in regular mandible border.
Fig. 11.33 A 32-year-old woman was
displeased with the notch deformities after
sliding genioplasty. The indentation was
lled with a porous polyethylene implant
(see Fig. 11.32). (A) Preoperative frontal
view. (B) Postoperative frontal view. (C)
Preoperative lateral view. (D) Postoperative
lateral view.
A
C
B
D
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