History

Chin malformations can be due to any combination of soft tissue/bony excess, deficiency, or asymmetry. Consequently, treatment of a small chin with an implant is not always correct because all small chins are not the same. Moreover, not all implants are the same. Decisions regarding the surgical approach, implant size, type, and fixation depend on the following: (1) the thickness of the chin pad; (2) the chin pad percentage as a function of the height of labiomental fold; (3) the vertical height of the chin; (4) static ptosis; (5) dynamic pad ptosis with smile; (6) the inclination from the lower lip white roll to the labiomental fold; (7) the shape of the chin; and (8) the chin pad takeoff below the fold. Fortunately, the majority of patients who seek consultation for the treatment of a chin deformity suffer from a mild sagittal deficiency. This two-dimensional chin deficiency naturally lends itself to alloplastic augmentation at the lower border of the symphysis. However, unless the surgeon takes all of the above factors into consideration, a simple alloplastic chin augmentation may not deliver expected results. For example, surgeons continue to identify the sagittally deficient chin, but overlook the inclination of the lower lip and the height of the labiomental fold; this oversight leads to unanticipated outcomes. In sum, when making a treatment plan, your assessment must be right on or the “simple” alloplastic chin augmentation will deliver simply awful results.

The earliest chin implants, described by Gustave Aufricht in 1934, were made of autologous bony-cartilaginous tissue removed from the patient’s nasal dorsum. However, in the latter half of the 20th century, alloplastic chin augmentation became the operation of choice for enhancing a sagittally deficient chin. Alloplastic chin augmentation is deceptively simple because it can be performed on an outpatient basis with minimal equipment. The alloplastic material may at times be an alternative to an osteotomy. In general, alloplastic chin augmentation causes less pain, swelling, and bruising than an osteotomy. Furthermore, like a sliding genioplasty, alloplastic augmentation can fill lateral mandibular deficiencies and even improve the submental skin/soft tissue contour. There are a variety of alloplastic implant materials from which to choose: silicone elastomer, polyethylene, hydroxyapatite, etc. While chin implants primarily improve the sagittal projection of the pogonion, they also can augment the width of the chin immediately lateral to the symphysis. Alloplastic augmentation cannot change the vertical height of the chin, but augmentation often gives the illusion of a vertically longer chin. This chapter is devoted to an overview of alloplastic augmentation of the sagittally deficient chin.

Physical evaluation

The aesthetics of the chin must be evaluated in relation to the appearance and proportion of the face. Emphasis is placed on proper facial balance rather than anthropometric numerical standards. Whether dealing with a complex multidimensional soft and hard tissue chin deformity or a sagittal chin deficiency, we use a systematic assessment from the nose to the chin in order to reliably evaluate the nose, midface, lips, maxillomandibular dental relationship, chin pad thickness, labiomental fold depth and height, static chin pad position, and dynamic chin pad motion with smile. The patient’s aesthetic goals, as well as any previous surgical or orthodontic interventions are noted. The patient’s face is observed and photographed in repose and smiling from the frontal and profile views. Mandibular and/or mentum deficiency, excess, or asymmetry is documented. Below are some of the highlights of the nose-to-chin assessment:

Lower lip analysis

The inclination of the lower lip white roll to labiomental fold affects perception of chin size after augmentation or reduction (Fig. 36.1). If the inclination of the lower lip is vertical and the demarcation between the lip and chin is poor, the patient will appear to have an excessively large chin after augmentation. This is particularly true if a full height implant is incorrectly used. The lower lip analysis is intermingled with the labiomental fold analysis because the lip inclination helps define the labiomental fold. If a patient has a deep overbite and the lip is everted, then the lower lip will have an oblique inclination. The obliquity of the lower lip will contribute to a deeper labiomental fold with a more acute angle. The surgeon should note this because an alloplastic implant that is too tall will deepen the fold and make the labiomental fold angle even more acute. If it is helpful, the lower lip inclination can be classified as follows: Type I is nearly vertical, type II is slightly posterior, type III is significantly posterior, and type IV is most oblique.

Fig. 36.1 The inclination of the lower lip white roll to labiomental fold affects perception of chin size after augmentation or reduction. The classification of lip-to-labiomental fold inclination: type I is nearly vertical, type II is slightly posterior, type III is significantly posterior, and type IV is most oblique.

Labiomental fold analysis

If two chins project exactly the same amount, the chin with the higher and/or shallower labiomental fold will always appear larger from the front (Fig. 36.2). Since the chin is primarily seen as the pad, the labiomental fold defines the apparent vertical height of the chin. Thus, augmenting a patient with a high, shallow labiomental fold tends to increase the appearance of the vertical height of the chin as well as its overall size. To overcome this problem, the surgeon should reduce the vertical height of the implant (see below) to limit augmentation to the lower pogonion. If the chin is long with a high fold, the patient may need both a vertical chin reduction and a sagittal augmentation. In contrast, a patient with a low, distinct labiomental fold will tolerate chin augmentation much better because the implant accentuates only the chin pad.

Fig. 36.2 Line drawings demonstrating that the position of the labiomental fold determines the chin pad percentage of the lower facial height. A, The relationship of the lip height to chin pad height is determined by the labiomental fold. B, High indistinct labiomental fold gives the illusion of a large chin. C, Low distinct labiomental fold gives the illusion of a smaller chin.

Static and dynamic chin pad analysis

The normal chin pad thickness is 8–11 mm. The chin pad thickness can be easily estimated by paramedian palpation. Soft tissue chin projection should be greatest at the lower part of the pogonion. The soft tissue chin pad position and static chin pad ptosis are noted. Chin pad clefting or fasciculations are documented. Since the chin pad is dynamic, soft tissues are also assessed during smiling.

The observer will note that when a chin pad is thick, a smile usually improves the patient’s appearance because the thick pad becomes effaced (Fig. 36.3). In contrast, as a thin chin pad is effaced upon smiling, the chin appears even more prominent (Fig. 36.4). During a normal smile, elevation of the corners of the mouth brings the chin pad superiorly. Some patients have a horizontal non-lifting smile such that the lower lip depressors are unopposed. Unopposed activation of the lower lip depressors produces dynamic chin pad ptosis with smiling as the chin pad drops (Fig. 36.5).

Fig. 36.3 Effect of smiling on a thick chin pad. A, Lateral photograph of patient in repose. B, During a smile, the thick chin pad becomes effaced, usually improving the appearance of the chin.

Fig. 36.4 Effect of smiling on a thin chin pad. A, Lateral photograph of patient in repose. B, Smiling will cause effacement of a thin soft tissue chin pad unmasking the underlying bony chin prominence.

Fig. 36.5 During a normal smile, the zygomaticus and levator muscles elevate the corners of the mouth brings the chin pad superiorly. Some patients have a horizontal non-lifting risorius-dominated smile. In a horizontal smile, the lower lip depressors are unopposed. Unopposed activation of the lower lip depressors produces dynamic chin pad ptosis with smiling. A, Lateral photograph of patient in repose. B, Unopposed activation of the lower lip depressors produces dynamic chin pad ptosis with smiling.

Submental analysis

Subcutaneous adipose and skin laxity are assessed. The surgeon should determine if preplatysmal or subplatysmal adipose is contributing to submental fullness. Skin and pre/subplatysmal adipose may need to be excised in order to improve the chin/neck contour.

During the physical evaluation, the surgeon must keep in mind that chin augmentation in women should be conservative. Female patients are more apt to complain that a chin implant is too large and request removal. It is important to note, that removing an excessively large implant is no simple matter. Removing an implant can result in surface irregularities and fasciculations or the redundant tissue can cause static chin pad ptosis (Fig. 36.6). When evaluating a patient with an excessively large implant, rather than simply removing the implant, we recommend that the existing implant be exchanged with a smaller implant (see below) or an osseous genioplasty should be performed. The new implant or osseous advancement will support the chin pad soft tissues and reduce fasciculations and/or ptosis.

Fig. 36.6 Unsupported redundant chin soft tissue produces surface irregularities, fasciculations and/or static ptosis after removal of an implant without replacement. We recommend that an existing excessively large implant be exchanged with a smaller implant or an osseous genioplasty. The new implant or osseous advancement will support the chin pad soft tissues and reduce surface irregularities, fasciculations and/or ptosis. A, Static chin ptosis (left > right) following chin implant removal without replacement. B, Surface irregularities when pouting.

Anatomy

On the labial surface of the mandible in the midline is the symphyseal spine which is also referred to as the surgical spine. The symphyseal spine divides to enclose a triangular eminence called the mental protuberance. The center of the mental protuberance is depressed, but its raised lateral borders form the mental tubercles. On either side of the upper symphysis, just below the mandibular incisors are the incisive fossae. The incisive fossae are the origins of the mentalis muscle. The mentalis muscles coalesce to form the bulk of the chin pad and they insert into the chin pad dermis to maintain lip position in repose and elevate and protrude the lower lip in animation. The mentalis muscles have horizontal and oblique components (Fig. 36.7). The upper horizontal portion which originates just below the attached gingiva is responsible for the lip level and position in repose. The function of the horizontal portion of the mentalis muscle, in isolation or in conjunction with the orbicularis oris, determines the shape and position of the labiomental fold as well as the lower lip position. The oblique portion of the mentalis muscles may fuse centrally (as in most cases) or remain separate superiorly or inferiorly to form a cleft. Thus, a cleft in the chin is, in essence, a muscle deficient zone. The oblique portion of the mentalis muscles tends to pull the chin pad against the mandible, drawing up the lip and allowing us to pout. Finally, the oblique fibers also elevate the central portion of the lip. Lateral to the mentalis muscle, beneath the second premolar midway between the superior and inferior borders of the body are the mental foramina. In a vertically short mandible the foramina may be higher than expected.

Fig. 36.7 The mentalis muscles have horizontal and oblique components. A, The upper horizontal portion (arrow) of the mentalis muscle originates just below the attached gingival. The horizontal portion sets the lower lip level and position in repose and determines the shape and position of the labiomental fold. B, The oblique portion (arrow) of the mentalis muscle pulls the chin pad superiorly against the mandible, bringing the lip superiorly and allowing us to pout. The oblique fibers also elevate the central portion of the lip.

The lingual surface of the mandible is marked in the midline by a median furrow. Inferior to the median furrow are the bilateral parasymphyseal mental spines. The mental spines are the origin for the genioglossus muscles. Immediately inferior to the mental spines is a median impression that is the origin of the geniohyoid. Also inferior and lateral to the mental spines are oval depressions for the attachment of the anterior bellies of the digastrics. Running distal and superior from either side of the lower part of the symphysis are the mylohyoid lines which give origin to the mylohyoid muscles bilaterally.

Sensory innervation of the chin is provided for the most part by the mental nerves. The mental nerve is a branch of the third division of the trigeminal nerve that exits the skull base through the foramen ovale and gives off nine branches including the inferior alveolar nerve. At the lateral pterygoid, the inferior alveolar neurovascular bundle passes between the sphenomandibular ligament and the ramus and enters the mandibular foramen on the medial surface of the ramus. The mandibular foramen is usually located about 2 cm from the anterior border of the ramus and nearly opposite the antilingula (on the buccal surface of the mandible). The inferior alveolar nerve is a sensory nerve, but a few motor and sensory fibers from the mylohyoid nerve run alongside. The inferior alveolar nerve usually travels in a single canal (2.0–2.4 mm in diameter) to supply the mandibular molars, premolars, and adjacent gingiva (Fig. 36.8). The terminal branch of the inferior alveolar nerve passes as much as 4.5 mm below and 5 mm mesial to the mental foramen before looping up to emerge as the mental nerve. The mental nerve innervates all of the skin of the chin (except for quarter size patches of skin on either side of the chin pad), the lower lip, the lower lip mucosa, the gingiva, the incisors, and the canines. The quarter size patches of skin on either side of the chin pad are supplied by a sensory branch of the mylohyoid nerve.

Fig. 36.8 The inferior alveolar neurovascular bundle enters the mandibular foramen on the medial surface

of the ramus. The inferior alveolar nerve usually travels in a single canal (2.0–2.4 mm in diameter). The terminal branch of the inferior alveolar nerve passes as much as 4.5 mm below and 5 mm mesial to the mental foramen before looping up to emerge as the mental nerve. The mental nerve innervates all of the skin of the chin (except for quarter size patches of skin on either side of the chin pad), the lower lip, the lower lip mucosa, the gingiva, the incisors, and the canines. The quarter size patches of skin on either side of the chin pad are supplied by a sensory branch of the mylohyoid nerve.

Ultimately, the size and shape of the chin is affected by the soft tissues draped over the external surface of the mandible and the chin musculature. A vertical lower lip gives the appearance of a tall chin, while an oblique lower lip gives greater demarcation between the lip and chin resulting in a more defined smaller chin pad. The labiomental sulcus is the dividing line between the lower lip and the superior part of the chin pad. The vertical location and depth of this fold affects the perception of chin size. A high, shallow labiomental fold gives the illusion of a vertically long chin. In contrast a lower, more defined labiomental fold gives the appearance of a smaller chip.

Normal chin pad soft tissue thickness is 8–11 mm. Palpation of the soft tissue thickness of the chin is essential for accurate anatomic assessment of the chin. When the pad is thick, the observer will note that a smile usually improves the patient’s appearance as the thick pad is effaced. In contrast, as a thin chin pad is effaced with a smile, the chin appears more prominent. Chin pad fasciculations are usually a result of mentalis strain to obtain lip competence or seal. During a normal smile, the zygomaticus and levator muscles elevate the corners of the mouth moving the chin pad superiorly. Some patients have a horizontal non-lifting smile (risorius dominated) such that the lower lip depressors are unopposed; this results in dynamic chin pad ptosis with smiling (Fig. 36.5). All muscles of facial expression around the chin are innervated by branches of the facial nerve except for the mylohyoids and anterior bellies of the digastrics which are innervated by the third division of the trigeminal nerve.

Technical steps

Most patients seeking aesthetic chin surgery will present with normal occlusion and a mild sagittal deficiency. However, the surgeon should be alert for angle class II or compensated class I dental occlusions with retrogenia. Dental malocclusions with retrogenia may be better treated with orthognathic operations. Unfortunately, in many cases, the surgeon cannot convince the patient that years of previous orthodontics should be undone and/or a more extensive jaw operation should be performed; instead, in some circumstances, the surgeon may need to camouflage the small chin with an alloplastic bony and soft tissue operation. Camouflaging a dysmorphic chin when orthognathic surgery is indicated can be challenging.

To sagittally augment a small chin, we choose either a silicone or textured implant. We tend to choose textured over silicone when operating on men, performing revision chin surgery, and when treating the tension chin. A silicone implant can be used in the same way as a textured implant, but it is harder to securely fix it to the mandible. Moreover, a capsule tends to form around the silicone elastomer, which may lead to more difficulties if the chin implant is later revised. We would never use a second silicone implant when revising a previously placed implant.

The patient is n.p.o. for 4 hours before the procedure. We administer 20 mg of diazepam and 3 mg of alprazolam by mouth to the patient in the preoperative area 30–45 minutes before the procedure. (Dosages are for the average otherwise healthy young 60–80 kg adult. Dosages are adjusted for older patients since the half-life of these drugs increases with age. We do find that lorazepam works better in men.) Bilateral inferior alveolar nerve blocks are performed with 1% lidocaine with 1 : 200,000 epinephrine. Ten minutes later, the mental plus, jawline, and submental injections are performed with a 50 : 50 mixture of 1% lidocaine/0.5% bupivacaine with 1 : 200,000 epinephrine. The patient is positioned supine on the operating room table with a pillow under the shoulders to allow the head to extend into a gel head rest. A pulse oximeter is used although respiratory depression from oral benzodiazepines is rare. An intravenous line can be placed, but this is optional. Using this preoperative balanced anesthetic regimen, we find that patients are comfortable throughout the operation, but they are awake enough to respond to commands.

The facial midline, from the labiomental fold to the hyoid and the intended incision is marked. During the first 10 minutes, while the last injection of local anesthesia is taking effect, we perform the following steps: (1) the upper 30–50% of the implant is carved down with a burr or knife; (2) the lateral wings of the implant are tapered; (3) the upper edge of the implant is tapered 45° angle with a burr or knife; (4) for textured implants, two pilot holes are drilled in each half of the implant (in some cases when the implant is short, one hole per side is satisfactory). The first pilot hole is drilled about 3–5 mm from the midline and the second pilot hole is drilled halfway between the first and the end of the implant; (5) textured implants can be divided in the midline (Fig. 36.9).

Fig. 36.9 The surgeon should customize the commercially available textured implant to reduce the vertical height and shorten the horizontal length. A, The upper 30 to 50% of the textured implant is removed so that the implant will only provide projection at the pogonion. The lateral projection of the textured implant is trimmed and then tapered. B, The upper portion of the implant, a burr is used to taper the upper edge at a 45-degree angle. C, The implant is divided in the midline and two drill holes are placed in each half of the implant. The first drill hole is approximately 3 mm from the midline and the second drill hole is halfway between the first hole and the end of the implant.

An intraoral or submental incision may be performed. The choice is based on surgeon preference, but we find that it is much easier to precisely position an implant through a submental incision. The intraoral incision is selected when mentalis muscle correction (e.g. resuspension) is necessary. The submental incision provides excellent exposure and enables the operating surgeon to remove skin and/or pre/subplatysmal adipose. Through either access incision, electrocautery dissection is carried down through the subcutaneous tissues to the periosteum. Electrocautery is used to clear the mandibular border from canine to canine and then a periosteal elevator is used to complete the lateral pockets. At the most lateral extent of the dissection, the elevator is levered up to gain additional room in the pockets. (If a silicone implant will be used, we limit the size of the dissection pocket in order to help secure the implant.) Next, the midline of the mandible at the menton is marked with electrocautery, bur or drill. This is a key step that should never be omitted (Fig. 36.10).

Fig. 36.10 Placement of an alloplastic chin implant. A, Through either access incision, electrocautery dissection is carried down through the subcutaneous tissues to the periosteum. Electrocautery is used to clear the mandibular border from canine to canine. B, At the most lateral extent of the dissection, the elevator is levered up to gain additional room in the pockets. (If a silicone implant will be used, we limit the size of the dissection pocket in order to help secure the implant.) C, The midline of the mandible at the menton is marked. D, The textured implant is inserted into the dissection pocket and the central portion of the implant is aligned with the midline menton mark and a screw is placed through the medial pre-drilled pilot hole. This screw is partially tightened. Then the lateral segment of the implant is exposed and held along the inferior border. The second screw (distal) is placed through the pre-drilled implant pilot hole and then both screws are tightened completely, so that the screw heads are below the implant surface. This allows for further reduction of the anterior surface of the implant, if necessary (depicted here with a knife). E, The incision is closed in layers and a small drain is brought out through the skin caudal to the access incision.

When using a textured implant, we commonly divide it in half. The first half is inserted into the dissection pocket and the central portion of the implant is aligned with the midline menton mark and a screw is placed through the medial pre-drilled pilot hole. This screw is partially tightened. Then the lateral segment of the implant is exposed and held along the inferior border (Fig. 36.10). The second screw (distal) is placed through the pre-drilled implant pilot hole and then both screws are tightened completely, so that the screw heads are below the implant surface. This allows for further reduction of the anterior surface of the implant, if necessary. The same procedure is performed on the opposite side of the mandible.

A small drain is passed from the implant to exit the skin caudal to the submental incision. A 4-0 polypropylene is passed through the drain and skin and then tied. The submental incision is then closed in three layers: muscle, subcutaneous tissues, and skin. The procedure usually takes about 40 minutes. Typical results are shown in Figs 36.11 and 36.12.

Fig. 36.11 Typical patient presenting for primary alloplastic chin augmentation. The 43-year-old patient has sagittal chin deficiency and dynamic chin ptosis. Through a submental approach, a textured implant was secured along the lower border of the mandible. A small fleur-de-lys skin excision was performed. A, Preoperative frontal view. B, Preoperative lateral view. C, Postoperative frontal view. D, Postoperative lateral view.

Fig. 36.12 Typical patient presenting for revision alloplastic chin operation. The 41-year-old patient complains of oversized high-riding chin implant. The patient’s oversized malpositioned implant was removed through a submental approach. A smaller textured implant was secured to the lower border of the mandible. A small amount of skin and subcutaneous adipose were removed submentally. A, Preoperative frontal view. B, Preoperative lateral view. C, Postoperative frontal view. D, Postoperative lateral view.

When a patient has a mentalis origin greater than 8 mm below the attached gingival margin and he/she is unhappy with lip volume loss, difficulty maintaining lip closure, or excessive amount of mandibular tooth show, the horizontal portion of the mentalis muscle can be resuspended (i.e. mentalis reefing) (Fig. 36.13). In this case, an intraoral incision is necessary. An incision is made superior to the labiobuccal sulcus on the lip and dissection is carried down to bone. The atrophic/malpositioned mentalis origins are divided and subperiosteal dissection is performed widely from mental nerve to mental nerve and down to the menton. The inferior symphyseal periosteum is scored and subperiosteal dissection is performed along the inferior border of the mandible from bicuspid to bicuspid and 4–5 cm submentally. This dissection is essential to mobilize and resuspend the mentalis superiorly. The proximal cuff of labiobuccal sulcus mucosa is elevated to expose the alveolar bone. An absorbable bone anchor is placed between the tooth roots at the superior edge of the incisive fossa (i.e. true mentalis origin). If a textured implant is placed the inferior border of the mentalis should be sutured to the implant, otherwise a second bone anchor should be placed at the level of the pogonion. (Suturing the inferior mentalis to a textured implant or using a pogonial bone anchor off-loads the weight of the chin allowing the surgeon to reposition the origin of the muscle at the incisive fossae.) Once the inferior portion of the mentalis is supported, the alveolar bone anchored sutures are placed through the mentalis muscle to elevate it superiorly into a more natural anatomic position.

Fig. 36.13 Resuspension of the mentalis muscle origin. If a patient has a mentalis origin greater than 8 mm below the attached gingival margin and is unhappy with excessive mandibular tooth show, the mentalis muscle origins can be resuspended. A, Patient in repose with excess mandibular tooth show. B, Mentalis muscle origin is greater than 8 mm below the attached gingiva. C, Through an intraoral incision and subperiosteal dissection is performed to expose the alveolus and menton from canine to canine. D, An absorbable bone anchor is placed between the tooth roots at the superior edge of the incisive fossa (i.e. true mentalis origin). E, Subperiosteal dissection is performed along the inferior border of the mandible and 4–5 cm submentally. This dissection is essential to mobilize and resuspend the mentalis superiorly. F, A second bone anchor should be placed at the level of the pogonion. G, Tying the pogonial bone anchor supports the chin. H, The alveolar bone anchored sutures are placed through the mentalis muscle to elevate it superiorly into a more natural anatomic position.

Secondary alloplastic chin augmentation can be challenging. If the previous implant is too large or has migrated superiorly, the implant pocket cannot be relied upon to maintain a new silicone chin implant in the correct position. Therefore, when reoperating on a chin implant, we approach the chin through a submental incision (irrespective of the initial access route for implant placement). We always use a textured secured chin implant for revision chin augmentation. Importantly, if the first implant was too large, we always down-size the implant or perform an osseous genioplasty. We never remove an implant without replacement (alloplastic or osseous) because the unsupported soft tissues and capsule would result in ptosis and contour irregularities (Fig. 36.6).

Postoperative care

A light compression dressing is applied across the chin at the labiomental fold and just below the chin pad to ensure soft-tissue contact with the underlying bone. For submental incisions, the chin support strap is worn continuously for 2 days and at night for 2 weeks. Drains, if employed, are removed within 1–2 days. There is no evidence to support routine postoperative antibiotics for alloplastic augmentation.

Complications

Mental nerve injury is one of the most concerning complications associated with alloplastic chin augmentation. The nerve is usually not injured during subperiosteal dissection, but rather by retraction or screw fixation. Remembering that the inferior alveolar nerve travels as much as 4.5 mm inferior and 5 mm mesial to the mental foramina is important for screw placement.

Improperly placed or secured implants can produce step-off deformities which can be palpated and sometimes seen. If the implant pocket is too small the implant can fold resulting in skin contour irregularity and dimpling. Conversely, when using a silicone implant, if the pocket is too large the implant can become displaced or malpositioned. Displacement/malposition of an implant is usually due to poor pocket design, inadequate fixation, or to placement within a soft-tissue pocket rather than a subperiosteal pocket. Movement or pressure from a high-riding implant may result in erosion of the mandible or the implant may impinge on the mental nerve (Fig. 36.14). Displaced/malpositioned implants are treated by removal and replacement with a textured secured implant through a submental incision or by osseous genioplasty. Early postoperative infections (1.4%) and seroma (<0.5%) affect few patients. The incident of alloplastic chin implant removal is relatively low (1.6%). Removing a malpositioned, displaced, infected, or wrong-sized implant without replacement usually causes chin surface irregularities and ptosis. In some cases, implant removal and osseous genioplasty may be the only reliable solution.

Fig. 36.14 Three dimensional CT scan of a displaced/malpositioned implant impinging on the right mental nerve.

Acknowledgment

The authors would like to thank Dr Barry M. Zide for his valuable contributions to this chapter.