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4 Customized Instruments forFacial Bone Contouring Surgery
25
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Part II
Lower Face
The Comprehensive Aesthetic
Analysis forLower Face
SanghoonPark
5
5.1 Pearls
1. The width of the face’s lower third is signicantly inuenced by the mandible’s width,
which is itself encased by muscles and subcutaneous fat tissues. Beyond the mandibular
width, the chin also plays a crucial role in
delineating the facial shape, underscoring the
importance of a comprehensive understanding
of lower facial types for an exhaustive
analysis.
2. Clinical assessments typically offer explicit
cues for diagnosis, including central symmetry and the contour of the lateral face, in conjunction with the chin’s shape and height.
3. The posteroanterior (PA) cephalogram facilitates the evaluation of mandibular angle protrusion or aring, along with symmetry, chin
deviation, and shape. While the PA cephalogram is instrumental in analyzing skeletal
transverse discrepancies and asymmetry, it is
less effective in assessing vertical
dimensions.
4. The lateral cephalogram is employed to examine facial vertical proportions, the anteriorposterior positioning of the chin, the
mandibular plane, and the gonial angle.
S. Park (*)
Center for Facial Bone Surgery, Department of
Plastic Surgery, ID Hospital, Seoul, South Korea
e-mail: spark@idhospital.com
5. Screening for abnormal skeletal relationships
between the maxilla and mandible, alongside
dental occlusion, is essential to identify the
limitation of facial bone contouring surgery.
6. Ideal facial shapes vary signicantly based on
individual preferences, as well as ethnic and
cultural backgrounds. During consultations
with patients from diverse national or ethnic
origins, it’s crucial to attentively consider
their ideal or preferred facial shapes.
5.2 Introduction
Facial impression is largely shaped by the outer
contour of face and convexity of its constituting
parts. Anthropological studies reveal signicant
anthropometric differences among various ethnic
groups in terms of facial contour. For instance,
Koreans tend to have a more developed lower
face compared to Caucasians. This difference is
quantiable: the average bigonial distance of
Caucasian women is between 105 and 109mm,
while in Korean women, it’s typically between
118 and 125mm [1, 2].
The lower third of the face’s width is determined by the mandible’s width, surrounded by
muscles and subcutaneous fat tissues. Notably, in
Asians, a prominent mandibular angle is often
due to the lateral protrusion of the mandibular
angle, rather than soft tissue factors like a hypertrophied masseter muscle [3–5].
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
S. Park (ed.), Facial Bone Contouring Surgery, https://doi.org/10.1007/978-981-97-4992-8_5
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30
abc
S. Park
Fig. 5.1 Evolution of mandible reduction surgery.
Mandible reduction surgery has evolved from (a) simple
resection of the angular portion to (b) contouring of the
total mandible shape as the desire for a slim and small
face has increased. Recently, (c) V-line surgery not only
In addition to mandibular width, chin plays
an important role in dening facial shape, necessitating a thorough understanding of lower
facial types for comprehensive analysis. We
classify the shape of the lower face based on the
chin’s shape.
A thorough understanding of facial shape is
narrows the width of the mandible and contours the jawline but also reduces the size and controls the position of
the chin was introduced to achieve a slim and oval-shaped
jaw
Assessing bony age is pre-requisite, especially
if there’s uncertainty about the bone’s growth
stage. Preoperative assessments include blood
tests, urine analysis, heart exams, chest X-rays,
and a consultation with an anesthesiologist.
Current medications taken by the patient should
also be reviewed and documented.
critical in formulating treatment plans in practice,
which is crucial for achieving aesthetically pleasing results. Mandible reduction has been evolved
5.3.2 Clinical Evaluation
from simple angle redcution to V-line surgery
and choice of proper technique is critical for satisfactory outcome [6–14] (Fig.5.1).
Clinical ndings often provide clear indications
for diagnosis. This comprehensive consultation
and assessment process ensures a tailored
approach to each patient, considering both physi-
5.3 Patient Consultation
cal features and personal expectations.
andAssessment
1. Central Symmetry: The rst step in evalua-
5.3.1 Patient Selection
andConsultation
Patient’s decision to undergo surgery requires a
careful assessment by the surgeon, who must
fully understand the reasons behind the patient’s
choice. It’s crucial to manage and temper unrealistic expectations. For instance, patients with
thick and abundant facial soft tissue may not
achieve the expected results despite successful
bony reduction. Understanding ethnic differences
in expectations is particularly important in
regions where certain ethnic groups are in the
minority. Decisions made in haste or on impulse
should be reconsidered, as bone resection leads
to permanent changes.
tion is assessing central symmetry. A virtual
midline connecting the intercanthal midpoint,
nose, mid-lips, and chin point is drawn and
analyzed.
2. Lateral Face Contour: The lateral contour of
the face is examined next. This includes evaluating the degree of mandibular protrusion,
asymmetry, hypertrophy of the masseter muscle, and the amount of subcutaneous fat. The
shape and width of the lower face in the frontal view are categorized as shown in Fig.5.2
[15, 16]. The extent of the masseter muscle’s
hypertrophy can be assessed by palpating the
tightened and relaxed states of the jaw.
Hyperostosis, predominantly around the mandible angle, is identied in radiologic studies.
5 The Comprehensive Aesthetic Analysis forLower Face
31
Fig. 5.2 Classication of mandibular shape and the
patient’s preference of mandibular shape. The chin should
be designed based on individual needs and demands. For
this, the patient can freely compare the shapes of the mandible, especially chin and consult with the surgeon in
detail
Fig. 5.3 Analyzing skeletal asymmetry and facial proportions in frontal plane analysis. With the use of reliable
vertical baseline (a vertical line that is connected to the
chin, which starts from crista galli (Cg) and crossing
ANS) and horizontal reference lines (Z plane, ZA plane, J
plane, a line connecting the left and right antegonial
notch, a parallel line to Z plane at the level of menton),
degree of parallel of each of the horizon and symmetry of
the facial structure can be assessed. The face is divided
into thirds by horizontal lines drawn adjacent to the menton (Me), the nasal base, the brows (glabella, supraorbital
notch level), and the hairline (Tr). The lower third is further divided into an upper third and lower two-thirds by a
line drawn through oral commissures
32
S. Park
The bigonial width typically accounts for
about 70% of the bizygomatic width (Fig.5.3),
and the bizygomatic width is approximately
75% of the facial height.
3. Chin Shape and Central Vertical Height:
The evaluation of the chin involves assessing
its shape and central vertical height.
• Total Facial Height: Facial height, from
trichion to menton, is divided into upper
facial height (trichion–glabella), midfacial
height (glabella–subnasale), and lower
facial height (subnasale–menton). The
ideal ratio for Asian women is 1:1:0.8 to
1.0, although there’s a trend toward a lower
facial height of 1:1:0.8.
• Lower Facial Height Analysis: Normally,
the ratio between the upper lip length (from
subnasale to stomion) and chin length
(from stomion to menton) is 1:2.
5.3.3 Radiologic Evaluation
Radiologic evaluation is an essential part of preoperative planning in facial bone surgery. The
author routinely acquires a comprehensive set of
radiologic images for each patient, which
includes panoramic views, skull lateral views, PA
cephalograms, and 3D CT images. In addition to
these radiographic examinations, photographs
from frontal, lateral, oblique, and basal views are
taken using standardized techniques. These
images and radiographs are crucial for detailed
aesthetic analysis and form the basis of accurate
preoperative planning.
5.3.3.1 Frontal Plane Analysis
In the PA cephalogram, the extent of protrusion or
aring of the mandible angle and the symmetry,
the deviation, and shape of the chin are assessed.
Although the PA cephalogram is valuable for analyzing skeletal transverse discrepancy and asymmetry, it has limitations in vertical assessments.
a. Chin Shape and Position: Evaluation
includes determining the amount of narrow-
ing, vertical adjustment and midline shift/
correction of the chin if necessary.
b. Angle Shape: It is found that in two-thirds of
cases, there is a mild to moderate increase in
bigonial distance due to lateral aring of the
mandible angle. The remaining one-third
often shows total mandibular hypertrophy,
leading to an accentuated square contour of
the entire lower face.
c. Mandible Body Line: The panoramic view
is particularly useful in assessing the convexity of the mandible’s body and the path of the
inferior alveolar nerve, aiding in determining
the amount and line of the mandibular ostectomy (Fig.5.4).
5.3.3.2 Sagittal Plane Analysis
The lateral cephalogram is used to evaluate the
facial vertical proportion, anterior-posterior position of the chin, the mandibular plane, and the
gonial angle.
a. The chin’s length should be less than twice
the upper maxillary length and less than twothirds of the midface’s length.
b. The anterior-posterior position of the pogo-
nion (Po) is established using Ricketts line
(Fig.5.5).
c. The ideal MP–SN angle ranges between 25°
and 35°.
d. The gonial angle should ideally be within
115° and 125°
After evaluating the balance between the
upper and midface, decisions are made regarding
the necessary advancement or retrusion (setback)
of the mandible in the anterior-posterior
direction.
5.3.3.3 Transverse Plane Analysis
A 3D CT scan and the cervical vertex view is
helpful in identifying the transverse shape of the
mandible.
a. The angle of divergence and the convexity of
the mandible are observed. In cases where
the angle is inwardly curled with a convex
5 The Comprehensive Aesthetic Analysis forLower Face
33
Fig. 5.4 Determination of the amount of mandibular border osteotomy. Based on panoramic view, the amount of
mandibular border osteotomy can be determined considering the inferior alveolar nerve course. In case of asymmetry, a disproportionate osteotomy is mandatory. For
Fig. 5.5 Analyzing vertical facial proportion and determination of the chin position in sagittal plane analysis.
The lateral view is drawn aesthetic proportions showing
the face divided into horizontal thirds on prole. The posi-
example, in this case, the midline of the chin is shifted
2.8mm toward right side. About 3.5mm of mandible border is resected on the right side, and 6.0 mm mandible
border is resected on the left side. However, angular resection is done on a similar amount
tion of chin (Pg) in vertical and horizontal direction is
determined from this view considering facial proportions
and Ricketts line
34
S. Park
Fig. 5.6 Analysis of transverse plane: basal and overhead
views. The exact region and amount of sagittal resection
can be determined by thorough evaluation of the angle of
transverse shape, sagittal resection of the
mandibular body may be needed to effectively reduce its width (Fig.5.6).
b. The position of the chin’s centerline is deter-
mined, which informs the necessity and
extent of midline correction.
This radiologic evaluation process plays a
critical role in the diagnosis and surgical planning for facial bone contouring procedures, offering detailed insights into the structural aspects of
the lower face and mandible.
5.4 Consideration inSurgical
Planning
5.4.1 Chin
The term “chin” encompasses both the bony
structure and the surrounding soft tissues, playing a pivotal role in the morphology of the lower
face. For certain patients, merely resecting the
mandibular angle and the inferior border may not
sufce to create a slender facial appearance.
Often, this inadequacy is due to the presence of a
wide, at chin coupled with a U-shaped lower
divergence and convexity of the mandible from this view.
In addition, the position of the midline of the chin regarding asymmetry is easily identied from this view
facial morphology. However, its signicance in
lower facial contouring surgery is overlooked by
surgeon as well as patients. It is often difcult to
persuade the patient to include the chin in the
procedures.
Width, length, and pointedness are contributing factors. The author generally recommends
that the ideal width of the chin should be similar
to or slightly narrower than the width of the alar
(nostril) in female patients. For male patients, the
recommended chin width falls between the width
of the alar (nostril) and the width of the upper lip.
The amount of central resection of the chin must
be customized based on the individual’s chin
width, preferences for chin shape and overall
facial contour.
To achieve a slenderer and aesthetically pleasing facial contour, it becomes necessary to consider modifying not just the width of the chin but
also its shape and position. The pointedness or
broadness of the chin is evaluated. In individuals
with a square face shape, a pointed chin can contribute to a slimmer appearance. However, for
those with a long face shape, a pointed chin may
give more elongated impression.
Small chin (microgenia) is different from setback chin (retrognathia) even though their frontal
5 The Comprehensive Aesthetic Analysis forLower Face
35
shape is similar because they might need different treatment. A decision about the chin’s position should be made while directly facing the
patient. This face-to-face evaluation allows the
surgeon to consider different perspectives, both
in repose and during expressions such as a broad
smile.
5.4.2 Evaluating Abnormal Skeletal
Relationships Between
theMaxilla andMandible
When considering lower facial contouring surgery, it’s imperative to understand the relationship between the mandible and the maxilla, as
not all patients exhibit a normal intermaxillary
skeletal relationship. In certain cases, individuals
may present with a protruding mandible indicative of a Class III occlusion or a relative underdevelopment of the lower jaw, suggesting a Class II
occlusion. For these patients, orthognathic surgery might be necessary to rectify this skeletal
misalignment. However, in situation where mandibular contouring surgery is considered without
addressing underlying Class II or Class III skeletal issues, it’s vital to approach the procedure
with caution to avoid exacerbating these intermaxillary problems.
For instance, in patients with a prominent
mandible showing a skeletal Class III relationship, an overly aggressive resection of the mandibular angle during reduction surgery can make
a long jawline appear even more pronounced. To
mitigate the risk of accentuating a prognathic
appearance, the angle should be resected conservatively, and sagittal shaving should be executed
judiciously.
In this case, the focus should shift toward the
vertical reduction of the anterior mandible.
Particularly for patients with a steep mandibular
plane, opting for a mini V-line surgery that
doesn’t include resecting the entire mandibular
inferior border and angle can be more benecial
than a full V-line surgery.
Conversely, in patients with a retruded mandible characteristic of a Class II prole, excessive
resection of the mandibular angle can lead to an
obscure cervicofacial line. In such instances, a
conservative approach to mandible resection,
coupled with maximal sagittal shaving of the
mandible’s body and advancement genioplasty, is
recommended. This approach helps in achieving
a more balanced and aesthetically pleasing facial
contour.
5.4.3 Asymmetry
Dental occlusion and overall facial conformation
should be considered to analyze asymmetry of
the face. Special care should be taken if a mismatch is observed between the actual photographs and the radiographs.
The character of asymmetry is rst dened as
central asymmetry versus contour asymmetry.
For this, the position of a nose tip and a midline
of upper and lower incisor teeth and midsymphysis of chin should also be evaluated. If these are
crooked, it is central asymmetry. In these cases,
the patients should fully understand the limitation of mandibular contouring surgery. While
central symmetry is preserved and asymmetry is
mainly due to facial contour, it is good candidate
for facial contouring surgery.
Then, extent of facial asymmetry whether
conned in mandible or extended to maxilla is
examined. Mandibular asymmetry of mild to
moderate degree can be improved by disproportionate resection of mandible border and elaborate three-dimensional shaving.
Asymmetries conned to the chin relative to
the face are most frequently encountered. For
individuals whose chin shifts to one side, mandible reduction makes chin asymmetry more obvious, and concomitant horizontal osteotomy of the
chin and transverse movement may be required.
5.4.4 Soft Tissue Contribution
Hypertrophied masseter muscle, which is a critical factor for determining the width of the lower
face, should be corrected. Generally, detachment
36
S. Park
of the masseter from its insertion to the mandible
alone can reduce the volume of the muscle and
additional resection of the muscle is not recommended. In cases with severe hypertrophy of
masseter muscle, botulinum toxin injection or a
partial resection of the medial aspect of masseter
muscle can be done. However, keep in mind that
this increases swelling and the risk of nerve
injury or inammation by necrotic muscle
debris.
Regarding overlying skin and subcutaneous
fat tissues, if the patient has tight skin with minimal subcutaneous fat, the changes after bone surgery are obvious, and the chance of soft tissue
drooping is minimal. This patient is a good
candidate for mandible contouring surgery. If the
patient has abundant soft tissue or loose skin,
there is a high risk of soft tissue sagging. The
patient should be informed about the possibility
of aggravation of jowl (irregular jawline) and
appropriate adjunctive measures, including liposuction or lifting procedures (Fig.5.7).
A lifting procedure is required for skin and
soft tissue sagging, upon checking the patients’
age and skin elasticity. The high-risk factors for
skin and soft tissue sagging are (1) age over 40,
(2) abundant cheek fat, (3) thin skin and skin laxity, and (4) Class II occlusion or ill-dened
mandible- neck line.
5.4.5 Ethnic Variation andCultural
Background
The ideal facial shapes may be different upon
personal preference, as well as ethnic or cultural
background. Especially when consulting patients
with different national or ethnic backgrounds,
Fig. 5.7 Soft tissue contribution. (Left) The patient has
thin fair skin with minimal subcutaneous fat. The changes
after bone surgery are obvious, and the chance of soft tissue drooping is minimal. (Right) The patient has abundant
soft tissues and thick skin. There is a high risk of soft tis-
sue sagging. The patient should be informed about the
possibility of aggravation of jowl (irregular jawline) and
appropriate adjunctive measures, including liposuction or
lifting procedures