Chin Alloplastic Implants

Coburn et al state, "The chin, the nose, and the forehead are the three balancing masses of the face."[1] An aesthetically and visually pleasing chin provides balance, harmony, and symmetry to the rest of the face. As a prominent structure of the face, it affects the general appearance of other facial structures. The shape and size of the chin may create visual prejudices in others' eyes. A small chin, for example, may convey a sign of weakness, whereas a pointed and ptotic chin (witch's chin) may create negative connotations beyond those of unattractiveness. A prominent chin, as long as it is proportional, conveys the sense of a strong, determined, and decisive personality. One undesirable feature in a field of otherwise handsome structures may create disharmony. Conversely, a proportional and pleasing chin may improve the overall aesthetics of the face.

The aesthetic surgeon, in considering and evaluating the structures of the face, normally considers the face (particularly in profile view) as divided into thirds. The upper third consists of the forehead, brows, and upper eyelids; the middle third consists of the lower lids, cheeks, and nose; and the lower third consists of the mouth and chin. When deficiencies, significant disproportion, and disharmony are present among these 3 zones, correction by augmenting, reducing, or otherwise surgically modifying one or more of the zones is considered.

In the chin, minor deviations often can be corrected by the simple insertion of an implant.[2, 3] Cohen states, "In evaluating the chin from an aesthetic viewpoint, the absolute measurements of facial structures are not as important as the relative size and proportion of each structure in comparison with the others."[4] More significant malrelationships may require major surgical intervention that includes orthognathic or craniofacial surgery.[5] In addition, occlusal relationships of the teeth need to be evaluated before augmentation mentoplasty is considered. However, consider augmentation of the chin in patients with a small or weak chin who have a normal or near-normal occlusion or when orthognathic surgery is not warranted.

Rubin et al mentioned the first alloplastic prosthetic materials for chin augmentation in 1948: "The important role the chin plays in facial appearance has been recognized since antiquity. Ivory, bovine bone, and a variety of alloplasts are but a few of the materials that have been used clinically with variable success to augment the contour of the chin."[6] Millard wrote a significant article about chin implants in 1953. Eppley noted:

The use of implantable biomaterials and devices plays a potential role in most forms of reconstructive surgery. … The significant advances in materials science and engineering during the latter half of this century have made the internal use of synthetic implants an integral part of many surgical procedures. Their frequency of modern surgical use can also be traced to the simultaneous development of broad-spectrum antibiotics and the continuing refinement of sterile operative techniques.

Prior to the introduction of alloplastic implants, autogenous materials were used. This was particularly true where reduction rhinoplasties yielded autogenous graft materials in the form of the dorsal nasal hump bone and associated cartilage. Such materials placed as onlay grafts were generally unsuccessful and unsightly, since they were absorbed readily but unevenly. Their placement and positioning also were not part of a thorough understanding of the elements of "profileplasty."

Terino writes, "During the 1950s several varieties of chin implants composed of different materials were developed." Since their initial use, alloplastic chin implants have been made of a variety of materials (eg, silicone, Proplast I & II [synthetic porous composite of Teflon polymer and alumina], Mersilene, Teflon, Dacron, Gore-Tex, acrylic, polyethylene, methylmethacrylate, hydroxyapatite) and in numerous shapes. Some of the earliest implants were short and shaped like an extended oval. They were designed for placement on the central chin, a concept that was flawed. Except in a limited number of circumstances, these implants produced an oddly pointed chin shape.

In more recent times, they have been replaced by anatomic implants, which were created and developed by Ed Terino before their introduction by a commercial company. These more closely resemble the shape and dimensions of the chin and extend from just beyond the mental nerve on each side.[7] Initial placement of the implant extraperiosteally evolved to the more satisfactory subperiosteal placement. Eppley states, "Alloplastic materials offer the potential for ‘off-the-shelf' solutions to reconstructive tissue needs which avoid donor scars and morbidity and typically simplify the procedure in terms of time and complexity of technique."

As more and improved injectable implant materials, including permanent injectable implants, are developed, they should be considered in the armamentarium of the aesthetic plastic surgeon.

The presence of a small or retrusive chin contour, whether alone or in the setting of large, disproportionate nasal contours, indicates consideration of augmentation mentoplasty with alloplastic material.[8]

Frequency

The incidence of relative or absolute microgenia is not defined. However, the American Society of Plastic Surgeons reported in its 2004 statistical survey of Board Certified Plastic Surgeons that its members performed more than 15,000 augmentation mentoplasties in the United States. However, this number represents just a fraction of the chin augmentations performed as reported by the American Society of Aesthetic Plastic Surgeons, which reported more than 32,039 chin augmentation procedures for 2004 in the United States. Clearly, although not the most common cosmetic surgery, chin augmentations, most of which are by alloplastic implant, are quite common.

For information, including news and CME activities, on aesthetic procedures, see Medscape’s Aesthetic Medicine Resource Center.

The workup can be divided into 2 distinct segments: (1) the initial evaluation of the need for mentoplasty and/or genioplasty and the magnitude of the problem and (2) the presurgical medical examination.

Initial evaluation

In the initial evaluation, the extent of the workup depends in part on whether the surgeon is a purely aesthetic (cosmetic) plastic surgeon or whether he or she also performs reconstructive procedures, including maxillofacial work.

The aesthetic plastic surgeon may reserve alloplastic mentoplasty for those patients with mild-to-moderate microgenia and/or retrogenia or retrusion, preferring to send patients with more severe retrusion and/or significant occlusive disorders to a colleague who concentrates on the reconstructive aspects of maxillofacial surgery. On occasion, even more severe retrusion with Class II or Class III malocclusion can be managed with an alloplastic mentoplasty alone.

For the aesthetic plastic surgeon performing routine alloplastic mentoplasty, workup of the problem can be limited to physical examination of the face, head, and neck region, including an evaluation of the patient's dental occlusion and accurate clinical photographs. In more severe situations, in which alloplastic mentoplasty still is considered, an oral surgical and orthodontic evaluation that includes dental models, panoramic radiographs, and cephalometrigrams is appropriate, as are accurate clinical photographs.

Generally, a decision to correct a small or retrusive chin contour usually is made on the basis of physical examination, photographic evaluation, and the plastic surgeon's "artistic impression." If, in profile, a "plumb line" dropped from the nasal spine to the chin projection does not graze the edge of the chin, sufficient indication exists to consider alloplastic mentoplasty.

Presurgical medical evaluation

Once the decision is made to proceed, the patient requires the same preoperative medical history and physical examination as for any individual undergoing surgery. This is the second stage of the workup.

Include a complete medical history; thorough physical examination; laboratory studies appropriate for the patient's age, magnitude of surgery, and associated medical conditions; and type of anesthetic planned. Such guidelines fall within the purview of the department of anesthesia and are individual to each hospital institution or approved/licensed outpatient center.

Under circumstances in which occlusion is reasonably normal (overbite and underbite are acceptable but not malocclusion) and the chin is retrusive or hypoplastic to either a minor or moderate degree, correction and/or improvement by placement of an alloplastic implant is indicated. The decision between a sliding genioplasty or alloplastic implant correction is an individual one made by the plastic surgeon and patient. Cohen writes, "A variety of authors have proposed aesthetic and cephalometric systems to evaluate the relative size and shape of the chin. None of these systems is absolute, and surgical decisions should be based on aesthetic relations and not cephalometric values."[4]

Cohen states:

The bony portion of the chin is the mandibular symphysis. Embryologically, two hemimandibular segments form independently from the first branchial arch system, with an ossification center appearing at about the sixth week of gestation. Intramembranous ossification continues to envelop and invade much of Meckel's cartilage, and the two mandibular bodies meet at the mandibular symphysis generally between the fourth and twelfth months after birth, as ossification converts the syndesmosis into a synostosis.[4]

Anatomically, the chin is defined as the region inferior to the labiomental fold, the groove that separates the lower lip from the chin. Several muscles cover the bony mandibular symphysis or chin. These include the mentalis, quadratus labii inferioris, triangularis, orbicularis oris, and some platysma fibers. Branches of the facial nerve innervate these muscles. The geniohyoid, genioglossus, and anterior bellies of the digastric muscle attach along the posterior and inferior surfaces of the mandibular symphysis (chin).

The sensory innervation of the chin area is from the mental nerve on either side, which is a branch of the inferior alveolar nerve, itself a branch of the mandibular nerve. All of these originate from the trigeminal (fifth cranial) nerve. The motor innervation is from the marginal mandibular branch of the facial (seventh cranial) nerve.

Contraindications include significant malocclusion, associated craniofacial abnormalities, magnitude of microgenia too great for implant correction, and the standard physical and psychiatric contraindications to surgery, particularly elective cosmetic surgery. These contraindications include a health condition that precludes any surgical procedure, uncontrolled hypertension, uncontrolled diabetes, tenuous cardiovascular or pulmonary condition, and terminal malignancy. Common sense dictates that most, if not all, of these situations take precedence over a cosmetic operation. In the psychological realm, contraindications range from gross and overt psychosis to the more subtle personality disorders manifested by unrealistic expectations, unrealistic motivation, and apparent inability to be pleased with any change or improvement in appearance.

While the surgical procedure may appear to be, and is, quite straightforward and technically simple, the criteria for patient selection, as for any surgery, must be applied.

See the list below:

• Perform studies appropriate to the level of surgery and type of anesthetic planned based on patient age, general state of health, and present medical conditions. Include complete blood count and urinalysis. If bleeding history is of concern, include prothrombin time, activated partial thromboplastin time, and bleeding and clotting times.

See the list below:

• Obtain a chest radiograph if the patient has a history of smoking or is a woman older than 50 years or a man older than 45 years. Most of the time this is performed only if indicated by history and physical examination.

• For a straightforward alloplastic mentoplasty, facial radiographs, panoramic radiographs of the mouth, and cephalometrigrams are not indicated.

• In more severe situations, in which alloplastic mentoplasty still is considered, an oral surgical and orthodontic evaluation that includes dental models, panoramic radiographs, and cephalometrigrams is appropriate, as are accurate clinical photographs.

See the list below:

• Obtain an ECG if relevant history indicates the need or for a woman older than 50 years or a man older than 45 years.

No appropriate medical therapy is available.

The surgical treatment of microgenia includes procedures beyond the purview of this article and can be found elsewhere in Medscape Drugs & Diseases (see Orthognathic Surgery). These techniques include orthognathic advancements of the mandible and/or chin, including the simplest technique, sliding genioplasty; nonalloplastic and/or autogenous implantation; and alloplastic chin implantation. The last of these, discussed in this article, corrects microgenia with the use and insertion of alloplastic implant materials.

Conceptually, a space is created over the surface of chin (mentum), and an implant is placed in this space. The list of types of alloplastic materials available and those that have been used is quite extensive and includes silicone, Proplast, Teflon, Dacron, Gore-Tex, Mersilene mesh, acrylic, porous polyethylene (Medpor), Proplast I and II, methylmethacrylate, and hydroxyapatite.[9] The most commonly used alloplastic implant material is silicone. Technically, the procedure for implantation is basically the same regardless of implant material type.

The preoperative regimen varies with physician preference. The author reviews the surgical plan with the patient during the week prior to the scheduled surgical date. At this time, the course of surgery, postoperative instructions, and surgical risks are discussed. The patient has the opportunity to have questions answered, and the surgical consent is signed.

For 2 weeks before and after surgery, patients are asked to eliminate all medications, vitamins, and food supplements that have not been authorized specifically by the surgeon and/or his or her staff. Alcohol, aspirin, aspirin-containing medications, nonsteroidal anti-inflammatory drugs (NSAIDs), and the complete list of drugs that may inhibit platelet aggregation and clotting must be eliminated.

For 2 days prior to surgery, patients are requested to use an antibacterial facial cleanser for face washing when an external incision is planned and mouthwash 3 times daily when an intraoral incision is planned.

Whether a local or general anesthetic is planned, patients must have nothing by mouth for at least 8 hours prior to surgery.

Technically, essentially 2 surgical approaches are available, the intraoral and the external (submental). The author prefers the external or submental approach for a number of reasons. It reduces the incidence of postoperative infection, and the patient's healing process is simpler, shorter, and easier.[10] The disadvantage, of course, is the presence of a visible, albeit small, scar in the submental region.

As mentioned earlier, many types of implants and implant materials are available. However, probably the most commonly used alloplastic chin implant is made of pliable solid silicone. These implants are available in a variety of shapes and sizes. In general, the most natural and appropriate of these for routine chin enhancement is in the anatomic shape.

The surgery routinely is performed on an outpatient basis. Either local or general anesthesia is suitable, although the author prefers a general anesthetic because it provides a more controlled and predictable situation.

Following induction of anesthesia, infiltrate the planned incision site and surrounding area of dissection with a local anesthetic agent with epinephrine (usually 0.5% lidocaine with epinephrine 1:200,000). This provides hemostasis, but it also reduces the magnitude and/or depth of general anesthesia necessary. Next, wash the facial region with a mild soap (eg, Castile soap, baby shampoo) and paint the chin region with topical antiseptic solution.

Submental approach

See the list below:

• Place the incision just inferior to the natural submental crease. Placement in the crease leads to a depression and ultimately may produce a witch's chin deformity.

• Placing some traction superiorly, proceed with the dissection through the soft tissue to the inferior surface of the chin (mentum) and at the insertion of the mentalis muscle.

• Incise the periosteum and, using a periosteal elevator, develop a subperiosteal pocket. The pocket's position, whether directly over the leading edge of the chin (as is most often the appropriate location) or slightly above toward the labiomental sulcus on the flat surface, is determined by the desired or needed improvement. Approximating the size and preferred position of the implant by employing sterile implant sizers is useful. Laying a sizer over the chin and outlining it on the skin allows the surgeon initially to dissect a pocket that is not excessively large. Anatomically shaped sizers are meant to be resterilized for repeated use. With the pocket developed, the sizer then can be inserted into this space to obtain a general idea of the best implant size.

• Once a determination is made and an implant is selected, any additional necessary dissection can be performed.

• When performing the dissection, keep the elevator against the surface of the bone at all times. The pocket should extend just to the inferior edge of the mandible.

• Take care to avoid slipping below this edge or into the soft tissue inferiorly or lateral for fear of injury to the marginal mandibular nerve. This nerve, a branch of the facial (seventh cranial) nerve, travels inferior to the edge of the mandible until it crosses the mandible just anterior to the mid point of the horizontal ramus of the mandible. Technically, while dissecting with the periosteal elevator, keeping the index finger of the opposite hand on the inferior border to guide and ensure the elevator's position at all times is helpful.

• The mental nerve emanates from the bone approximately 1 cm above the edge of the mandible and approximately 2.5-3.5 cm from the mid line. It should be visible, with retraction, through the submental incision. Keeping this in mind, avoiding injury to either nerve in the dissection should be possible.

• Position the implant inferior to the mental nerve. Once the pocket is developed and bleeding is controlled, irrigate the space with topical antiseptic solution and insert the sterile implant into the space. Handle the implant minimally.

• Once the implant is in place, any adjustments to pocket dimensions or implant position can be made. The blue marker that delineates the middle on most implants facilitates positioning of the implant in the mid line. Align this point with the central mental tubercle. Close the wound.

• The author prefers to place a central suture that begins the closure of the periosteum through the implant to stabilize it in position. The wound usually is closed in multiple layers with a final intradermal pullout suture for the skin.

• Dress the wound with Steri-Strips; other Steri-Strips or tape can be used to support the area. No other dressing is necessary.

Intraoral approach

Coburn states, "Since Converse (1950) demonstrated the safety and feasibility of introducing autogenous bone grafts through intraoral incisions, this approach has been widely used."[1]

• Prepare the mouth with mouthwash for several days.

• Following induction of anesthesia, instill local lidocaine with adrenaline into oral mucosa in the buccal-gingival sulcus and for approximately 1.5 cm above the sulcus on the labial side and into the adjacent gumline. Then, reprep the mouth with topical antiseptic solution.

• Make an incision on the labial side of the sulcus, leaving a cuff of labial mucosa to create a secure closure. The mucosal incision should be transverse.

• While many surgeons perform the rest of the dissection via a transverse incision through muscle to bone, consider making the muscular incision and/or dissection vertically and then dividing the midline raphe of the mentalis muscles vertically.

• Rapidly proceed with the dissection to the bone and create a subperiosteal pocket. The dissection is similar to the external approach. Be careful to dissect inferiorly enough to make the pocket extend along the inferior edge of the mandible.

• It must be clear that the soft tissue and musculature are released sufficiently so that the implant is seated properly in the desired position along the inferior border of the chin.

• With bleeding meticulously controlled, irrigate the space with topical antiseptic solution and insert the selected implant.

• Close the space in a multilayer fashion including periosteum. For the mucosal closure, select a suture that is soft, pliable (eg, silk, Vicryl), and nonirritating to the gums.

Postoperative instructions include the following:

• Eat a soft diet.

• Elevate the head of the bed or use 2-3 pillows.

• Limit touching or manipulating the chin area.

• Practice good oral hygiene (for patients with intraoral approach).

  • Gentle irrigation with antiseptic mouthwash and lukewarm water 2-3 times daily

  • No use of toothbrush around lower central incisors

  • Keep tongue away from incision

• Take prescribed antibiotics for 1 week.

• Tale pain medication as needed.

• Continue normal (but not strenuous) exercise for 2 weeks.

Remove sutures 5-7 days postsurgery for external sutures and 7-10 days postsurgery for intraoral sutures.

Provide follow-up care as appropriate for any aesthetic surgical patient. Generally, barring any unforeseen circumstances or complications, see the patient weekly for the first month, then at 3 months, 6 months, and 1 year postsurgery. Subsequent follow-up care or recall is on an as-needed basis.

Complications of this surgery can be divided into those that are immediate and those that occur weeks or years later.

Immediate complications

See the list below:

• Bleeding: Bleeding can occur within hours to several days postoperatively with the formation of a tense or expanding hematoma that threatens the integrity of the skin overlying the implant. This necessitates surgical exploration with evacuation of hematoma and control of bleeding.

• Nerve injury with either paralysis or loss of sensation: Injury to one or both mental nerves causes alteration or loss of sensation of the chin and lower lip on the injured side(s). Realistically, no other action can be taken but to wait and observe whether sensation returns. This may take days to several months. However, one cause of anesthesia is malposition of the implant with pressure on the mental nerve. If the end of the implant on the anesthetic side is not palpable in the correct position, surgical exploration may be indicated after several weeks of persistent anesthesia.

• Paralysis: Injury to one or both marginal mandibular branches of the facial nerve results in paralysis. To cause such an injury, dissection would have had to be inferior to the lower mandibular border and off the surface of the bone. Even then, the injury is likely to cause only transient neurapraxia. Obviously, if a nerve transsection may have occurred, initiate immediate microsurgical nerve repair.

• Malposition of implant: This problem should be infrequent as an immediate complication, since the implant has sufficient landmarks and markers so that with direct vision placement of the implant, the exact placement of the implant should be clear.

Delayed complications

See the list below:

• Infection: Infection following mentoplasty, especially using the external incision, is quite unusual (< 1%). As expected, infection is more common when the intraoral route is used. Incidence also is higher with certain implant materials than with others; it is lowest with commercially produced solid silicone implants. Solid silicone implants that have been carved by the surgeon from a block of silicone have a higher incidence of infection, as do porous implants such as those made of Teflon, Dacron, Mersilene, Gore-Tex, and similar materials. Infection around implants is not eliminated by antibiotic therapy; thus, remove the implant. Reimplantation can be performed at a later date once all evidence of infection is gone. This may be several weeks to 3 months later.

• Postinfection deformity: Chin deformity following implant removal has been reported. Therefore, planning reimplantation following resolution of infection or subsequent osseous genioplasty (sliding genioplasty) may be important.[11]

• Malposition: Besides malposition immediately following surgery caused by technical error, the forces of scar capsule formation around the implant can cause movement leading to malposition.

• Implant extrusion: This is an unusual complication of inadequate soft-tissue coverage; it is more likely to occur with an intraoral incision, especially if inadequate dissection of the pocket along the lower border of the chin occurred.

• Implant mobility: Together with the natural formation of a periprosthetic capsule, subperiosteal dissection should keep the implant immobile.

• Bone resorption: This phenomenon probably occurs with all types of chin implants. However, according to Terino, "… studies have failed to reveal pathologic, functional, or even aesthetic consequences."

The aesthetic results of mentoplasty with alloplastic implants are almost universally good. This includes objective improvements in appearance and patient satisfaction.

A retrospective study by Lutz et al reported that among 24 high-density, porous polyethylene facial implants (including three chin implants) placed for augmentation in 14 patients, no hematomas, infections, migrations, or hypoesthesia was observed. Although two implants were removed because the aesthetic results were not satisfactory, of 11 patients surveyed, 82% were strongly satisfied with their overall outcome. Mean follow-up was 41 months.[12]