Mandibular Contouring of Square Face with Low Gonial Angle in Orientals: Categorization, Design and Technique

Abstract

Introduction:In East Asian population, square face is considered unappealing as it imparts a coarse and masculine look. So, oriental women prefer to have an ovoid and slender facial contour, which is thought to be more feminine and attractive. Nowadays, mandibular contouring surgery has become a commonly performed procedure. Clinical data shows majority of patients who have severe form are characterised by a definite square shaped face with low gonial angle. Square face is usually visualised in frontal view but lateral view provides additional information regarding gonial angle, mandibular plane steepness, chin deficiency and more importantly length of the ramus. These factors are the key points for a precise categorization, design, selection of surgical methods and choosing the ostectomy line for contouring on square face with low angle.

Patients and Methods: From 2005 to 2009, 94 women were diagnosed as square face with low angle. 3 types of surgical design based on procedures such as mandibular “V-Line” ostectomy, mandibular outer cortex split ostectomy, sliding genioplasty and inlay bone graft in various combinations were constructed depending upon the presenting facial features.

Results: Precise categorization, designs and techniques resulted in higher satisfaction as these procedures provided an overall narrowing and harmonizing effect on the lower facial contour postoperatively.

Conclusion: Patients with square face and low gonial angle come with multitude of features so that design and technique applied should be tailored to each individual to achieve perfection.

Keywords: square face; low gonial angle; mandibular “V-Line” ostectomy; mandibular outer cortex split ostectomy; sliding genioplasty

In East Asians a prominent mandible angle that gives a squared face is a commonly encountered facial feature, however such feature esp. in a woman is considered unattractive or unfriendly as it confers a muscular appearance, quadrangle, coarse look, and thus diminishes the attributes of femininity. So, many East Asian women pursue an ovoid facial contour. However, with increasing influence of media, even women who have ovoid faces are demanding to have slender oval faces or so called "melon seed face" in East Asian terms. This typical face makes one look even more feminine, beautiful and attractive, and nowadays, many women who have a square face pursue such contour by various facial contouring surgeries^1-4.

The conventional procedure used to fix a square contour into an oval one was either resection of the mandibular angle, or reduction of the mandible itself^1-4. These procedures no doubt brought about changes in square contour, however, in some patients it failed to make the lower face appear slender, smooth and natural. While reviewing these unsatisfactory cases, we discovered that the majority of them were related to square face with low gonial angle deformity, which means the gonial angle (Ar-Go-Me) is below 110° and the mandible plane angle (MP-HP) is less than 20° (Fig.1).

Patients, who have severe square shaped face in frontal view, usually have associated low gonial angle deformity in lateral view, and wide, flat and retracted chin resulting in too flat and/or flagging mandibular outline. Likewise the ramus may also appear short or long as measured by the distance between the lower end of the ear lobule and the gonial angle. However, while correcting square face, the conventional procedure that only reduces the mandibular width or resects the posterior mandible might not result in good clinical outcome. This is true particularly when patient presents with a short ramus. Moreover in patients with short ramus where resection of the posterior mandible is not indicated, genioplasty alone can bring about favourable changes in the mandible in lateral view. Thus, in our current concept of mandibular contouring, the entire mandibular shape should be considered as a whole, and planning for mandibular contouring surgery should be based on observation of mandible from all three planes. Square face is usually visualised in frontal view but lateral view provides more valuable information regarding gonial angle, mandibular plane steepness, chin deficiency and more importantly length of the ramus. These factors are the key points for a precise categorisation, design and selection of surgical methods, and choosing the appropriate osteotomy/ostectomy line for mandibular contouring.

PATIENTS AND METHODS

Patients

From January of 2005 to October of 2009, 176 women underwent mandible contouring surgery at Centre of Orthognathic Surgery, Sichuan University. Of these patients, 94 belonged to square face with low gonial angle. Their age ranged from 20 to 31 years, with an average age of 26 years.They had following facial appearance characteristics: wide lower face with/without wide chin in frontal view, Ar-Go-Me angle less than 110°, approximately 90° and MP-HP less than 20°, approximately 0°, ramus length either short or long, with/without deficient chin in lateral view, and the mandibular inferior border too flat, or flagging mandibular outline. Photographs and the panoramic radiographs, PA and lateral cephalometric radiographs were obtained for all the patients before surgery and 10 to 39 months after surgery. The pre and postoperative radiographs were taken to analyse the mandibular form and symmetry, and to calculate Ar-Go-Me and MP-HP.

Categorization and Surgical Design

Categorisation of square jaw with low gonial angle would be helpful to delineate the various options available for contouring. Basic categorisation and surgical design for square face with low gonial angle was thus based on the combination of features the patients presented with. Gonial angle, mandibular plane angle, length of the ramus and nature of chin (normal or deficient) was looked for when categorising and was divided into 3 types. The surgical designs were constructed based on the type of facial features the patient presented with Fig. 2：

Type 1:

Features:low gonial angle;decreased mandibularinferior plane steepness;long ramus; normal chin.

Type 2:

Features: low angle;decreased mandibularinferior plane steepness;short ramus;deficient chin.

Type 3:

Features: low angle;decreased mandibularinferior plane steepness;long ramus;deficient chin.

Thus in our study, out of 94 cases, 47 cases matched Type 1 and were subsequently treated with mandibular ‘V’ line ostectomy (MVO) combined with Mandibular outer cortex split ostectomy (MOCSO). Likewise, 33 cases presented with Type 2 features and were treated with sliding genioplasty (SG) combined with MOCSO and inlay bone graft (IBG) obtained from MOSCO. 14 cases with Type 3 mentioned features were treated with MVO and SG combined with MOCSO. Posterior segment of the resected bone obtained from MVO was used as grafting bone to avoid step off and attain one plane inferior mandibular border. Likewise in patients with associated wide chin on frontal view, narrowing genioplasty was performed either independently or in combination with sliding genioplasty.

Operative Technique

All patients were performed under general anaesthesia using naso-tracheal intubation. The surgical procedures were performed intraorally. The incision was made over the anterior edge of the ascending ramus and extended to the central incisor on the buccal side along the external oblique line of the mandible. It was deepened to the periosteum and then was dissected along the subperiosteal plane, exposing the lateral cortex of the ramus, the mandibular body region, and the mental region, with care taken to expose and protect the mental nerve. The other side was also similarly prepared so the surgery area was completely exposed.

Mandibular “V-Line” ostectomy (MVO)

The “V- line” ostectomy was designed according to the appearance of the patient, and this surgical technique has been described in detail by our group previously ⁵. The key point in this procedure is to determine the line of ostectomy. The forward slanting nature of the ostectomy lines is determined by the location of mandibular canal, shape of mental region, and the adjustment of lower mandibular plane angle. Thus new gonial angle is formed by the posterior edge of the ascending ramus and ostectomy line. The point of ostectomy line on the posterior edge of the ascending ramus determines the distance from lower edge of auricular lobule to gonial angle postoperatively.Generally speaking, distance between the lower edge of the auricular lobule and the newly formed gonial angle should be around 2cm on a body-surface projection.

The mandibular outer cortex split ostectomy (MOCSO)

A MOCSO, using methods similar to those described by Kun Hwang, Han and Kim^6,7, was performed with a reciprocating saw, bur, and osteotome. The resected mandibular inferior margin and mandibular outer cortex were harvested for future inlay grafting.

Sliding genioplasty（SG）and inlay bone graft（IBG）

The sliding and narrowing genioplasty was similar to those described by Han and Kim^6,7 .For sliding genioplasty, after completion of osteotomy, the ostectomised segment was advanced forward and fixed with miniplate and screws to correct the deficient chin. For narrowing genioplasty, the muscular attachment was stripped off after resecting the central segment. Two segments were then approximated medially and fixed with microplate and screws. Vertical height was also increased where deemed necessary by placing the graft obtained from MVO or MOSCO. Finally, to obtain a more natural curvature of the lower border of the mandible and to avoid hour glass effect, bony edges at the lateral border were trimmed using an oscillating saw and burs.

For patients with strong masseter, masseter myectomy was performed, and for those with buccal fat pad hypertrophy “buccal fat pad resection” was performed. The negative pressure drainage was applied and was removed 2 days postoperatively, and antibiotics were used for 3 to 5 days postoperatively in all cases.

RESULTS

The preoperative and the postoperative photographs and radiographs of each patient were compared to evaluate the effectiveness of the corrective procedures. Postoperatively, the Ar-Go-Me improved to 120~130º, the MP-HP improved to 25~35º and the mandibular width decreased remarkably. A wide, flat or retracted chin was reduced in width, and/or advanced in horizontal direction and/or lengthened in vertical height. Therefore, the contours of the lower face were efficiently changed both in frontal ,oblique and lateral view.

Postoperative recovery was uneventful, and all wounds healed by primary intention without local infections. No facial paralysis or trismus was observed in any of the patients. Transient sensory disturbance of the skin around the mental nerve area was observed in 94 cases but all recovered without sequelae within 6 months. No major complications such as facial nerve injury or unexpected fractures of the mandible body, ramus, or condyle were observed during surgery and post-surgery. All of the patients reported great satisfaction with the postoperative results(Table 1) .

Clinical Cases

Case 1

A 22-year-old woman who had a constant complaint about the shape of her wide lower face sought treatment for a square jaw.

Facial appearance characteristics: In anterior view, the lower face was wide and symmetrical, the gonial angle was 105º, and lower mandibular plane angle was 15º in lateral view, with square but not too weak chin and buccal fat pad hypertrophy. In March 2006, the mandibular “V-Line” ostectomy combined with mandibular outer cortex ostectomy and buccal fat pad resection were performed (Fig.3). In subsequent visit 14 months after the operation, the postoperative contour improved expectedly, the mandibular plane angle improved to 35º, and the gonial angle improved to 130º. The appearance showed that the facial proportion was suitable; the lower face was narrow and symmetrical in anterior view with slick mental region. The contour of lower mandible margin was smooth and steep from mental region to mandibular angle region with satisfying final outcome (Fig.4).

Case 2

A 24-year-old woman complained about her broad, short lower face. Facial appearance characteristics: In anterior view, the lower face was square and short, chin was wide and stunted. The gonial angle was 110º, lower mandibular plane angle was 20º, and chin was deficient that was not consistent with the standard Ricketts's E-line in lateral view. The lower 3^rd of the face compared to the middle 3^rd was shorter by 4mm. The mandibular inferior border was too flat, the mandibular ramus was too short, and the distance from auricular lobule to gonial angle was 2.2cm. In March 2007, the sliding genioplasty combined with mandibular outer cortex ostectomy were performed on this patient. Sliding genioplasty was performed by downward sliding 4 mm and forward sliding 8 mm. Finally, bone graft inlay was placed in the space produced by downward sliding of the fragments, using the trimmed mandibular outer cortex segment and fixed with miniplate and screws(Fig.5).In subsequent visit 13 months after the operation, the postoperative contour improved expectedly. The gonial angle improved to 125º and the mandibular plane angle improved to 30º. The contour of lower mandible was steep and smooth from mental region to mandibular angle region. The appearance showed that the lower face was tapering，soft and slender oval with slick mental region, and the facial proportion was balanced and harmonious (Fig.6).

Case 3

A 20-year-old woman presented with a trapezoid lower face, weak chin and masculine features. She desired alteration of the lower face to a more feminine appearance with a pointed chin.

Facial appearance characteristics: In anterior view, the lower face was square and short, chin was short and stunted. The gonial angle was 95º, lower mandibular plane angle was 5º, and chin was severely retrusive that failed to meet the requirement of Ricketts's E-line in lateral view. The lower 3^rd of face compared to the middle 3^rd was shorter by 8mm. After mandibular “V-Line” ostectomy combined with mandibular outer cortex ostectomy, sliding genioplasty was accomplished with downward movement of 8 mm and forward movement of 6 mm, and bone graft was placed within the space produced by downward sliding, using the trimmed mandibular “V-Line” ostectomy segment (Fig.7). One-year postoperative, the appearance showed that the lower face was tapering, the mental region was slick, and the facial proportion was suitable. The patient was very satisfied with her new facial contour (Fig.8).

DISSCUSSION

Ethnic and racial traits impart unique attributes to facial form and features. East Asians are usually mesocephalic with short, wide face due to increased bimalar and bigonial width, and this is accentuated by the increased prominence of zygoma, mandibular angle and chin¹. Whereas these features are favoured in the western population, East Asians and females in particular, find these features very much unpleasing. A prominent mandibular angle results in a square face and symbolises masculine toughness likewise prominent and broad chin suggests mandibular prognathism because Orientals usually have flat, rather bulky eyelids, and a low nose ².

Patients with square face come with multitude of features and one commonly seen is low angle deformity which means the Ar-Go-Me is below 120° and the MP-HP is less than 20°. When reviewing the unsatisfactory cases of mandibular reduction, we found out that majority of failed cases were pertaining to square face with low angle deformity. This critical factor is easily missed when one focuses too much on frontal appearance and neglects the lateral view, which is governed by the direction and extent of protrusion of the mandibular angle and the relative position of the angle³. One other factor which is usually overlooked in lateral view is the length of the ramus on body surface projection. Length of the ramus as defined anatomically is the distance from mandibular notch to the lower border of the mandible and usually measures 47.9±4.8mm in East Asian population⁴. But more significant is the amount of exposure of ramus and is determined by the distance between the lower end of earlobe and the gonial angle, which as we have analysed is usually around 2cm for an aesthetically pleasing lateral appearance ⁵.

While reviewing past articles, much attention has been paid to reducing bigonial width, increasing gonial angle and raising the slope of the mandibular plane. However, there is dearth of information pertaining to preoperative ramus length and various mandible contouring procedures. Especially when a patient presents with a square face with short ramus, there is a certain dilemma regarding whether to proceed with the conventional mandible reduction procedures such as mandibular angle ostectomy, “V” line ostectomy, etc or not. Nevertheless these procedures result in an increase in gonial angle and steepness of the mandibular plane, but this also results in upward shift of the gonial angle making the lateral appearance very much unnatural and unpleasing aesthetically⁵.

Here we have divided the patients presenting with square face with low angle deformity into 3 types based on the height of ramus and the quality of the chin. Likewise the design of the treatment and the technique applied also varied as per the subtype. Patients with long ramus and normal chin underwent MVO combined with MOCSO whereas patients with long ramus and deficient chin underwent MVO and MOCSO combined with SG and IBG. Patients with short ramus and deficient chin underwent SG combined with MOCSO and IBG obtained from MOSCO.

In patients with long ramus MOCSO combined with MVO were performed and SG with inlay bone graft was added if there was a deficient chin. MOCSO can reduce the width between mandibular angles in frontal view however it cannot steepen the flat mandibular inferior margin nor can it raise the low angle. Furthermore, the flagging mandibular angle cannot be lifted upward through MOCSO thus additional surgery in the form of MVO is required^6,7. MVO procedure can eliminate the mandibular inferior margin, and effectively increase the gonial angle and mandibular plane angle⁵. Likewise there is an upward shift in the gonial angle and the inferior mandible border, thus not only shortening the long ramus but also increasing the exposure of the neck making it look long and elegant⁸.SG is a versatile procedure and can efficiently reposition the chin, however Ricketts's E-line should be considered when bodily repositioning the chin⁹. A distance of almost 0mm from both lips to Ricketts's E-line is considered ideal for Orientals¹. SG can thus be applied for narrowing, widening, lengthening, shortening and deviation correction of the chin. Likewise when grafting is required, the combined procedure has the added advantage in that the resected bone from the MOCSO or MVO can be used thus obviating the need for secondary site exploration.

However, in patients with low angle and short ramus, the conventional procedures such as MVO are not indicated. As the ramus is already short and the gonial angle is already close to the ear lobule, further shortening can result in gonial angle too close or hidden in the shadow of the ear lobule; leading to unnatural appearance in lateral view. Thus the critical point in these cases is to avoid the upward shift of gonial angle. In such patients, we advocate MOSCO along with SG for reduction of gonial thickness and increase of mandibular plane. Downward and forward sliding of the mobile cut segment with placement of graft in-between the upper and the lower segments tends to mildly increase the steepness of the inferior mandible border in lateral view. Postoperatively, however, transient numbness of the lower lip was observed in most of the cases but none resulted in permanent numbness.

In our current concept regarding mandibular contouring procedures, the mandible should be considered as a single unit, and inspection of the disproportional shape should be carried out in all the planes¹⁰. On frontal view not only the width of the lower face at angle region and wide chin anteriorly should be noted but the height of the face should be evaluated to obtain a balanced harmony. An ideal face is vertically divided into equal 3^rds by horizontal lines adjacent to trichion, glabella, subnasale and menton. In the ideal lower 3^rd of the face, upper lip is usually half the height of lower lip and chin. On lateral view, not only the gonial angle, mandibular steepness, chin deficiency but the length of the ramus should also be assessed. Likewise the projection of skeletal tissues on its soft tissue counterparts should also be taken into account. Thus overall observation helps to achieve a good clinical outcome and avoid complications.

Acknowledgements

Disclosure: None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this article.

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Figure Legends

Fig.1. Lateral cephalometric landmarks and reference lines. 1. The gonial angle (Ar-Go-Me) 2. The mandibular plane angle (MP-FH)

Fig.2. Lateral illustrations of mandibular contouring of square face with low gonial angle. Type 1: low gonial angle;decreased mandibularinferior plane steepness;long ramus; normal chin. Procedure: MVO + MOCSO. Type2: low angle; decreased mandibular inferior plane steepness;short ramus;deficient chin. Procedure: MOCSO+ SG+IBG. Type 3: low angle;decreased mandibularinferior plane steepness;long ramus;deficient chin. Procedure: MVO+MOCSO + SG+IBG.

Fig.3. Photograph of the designed ostectomy lines for MVO + MOCSO (a).The excised mandibular angle, inferior margin and mandibular outer cortex (b).

Fig.4. Preoperative views of a 22-year-old woman in Case 1(a,c). Postoperative views after MVO combined with MOCSO(Type I) and buccal fat pad resection (b,d). 14 months postoperative views showed that the facial proportion was suitable and the lower face was narrow and symmetrical with slick the mental region. The contour of lower mandible margin was smooth and steep from mental region to mandibular angle region.

Fig.5. Photograph of the designed ostectomy/osteotomy lines for MOCSO (a) + SG+IBG (b).

Fig.6. Preoperative views of a 24-year-old woman in Case 2 (a,c). Postoperative views after MOCSO + SG+IBG(Type II) (b,d). Sliding genioplasty was performed by downward sliding 4 mm and forward sliding 8 mm. 13 months postoperative views showed that the contour of lower mandible was steep and smooth from mental region to mandibular angle region. The appearance showed that the lower face was tapering，soft and slender oval, the mental region was slick and more delicate, and the facial proportion was balanced and harmonious (b.d).

Fig.7. Photograph of the designed ostectomy/osteotomy lines for MVO+MOCSO + SG (a) +IBG (b).

Fig.8. Preoperative views of a 20-year-old woman in Case 3 (a,c). Postoperative views after MVO+MOCSO + SG+ IBG (Type III)(b,d). SG was accomplished with downward movement of 8 mm and forward movement of 6 mm, and bone graft was placed within the space produced by downward sliding, using the trimmed MVO segment. 12 months postoperative, the appearance showed that the lower face was tapering, the mental region was slick, and the facial propor