Chin Implants

The chin has a prominent role in establishing facial symmetry and aesthetics. With the nose, it can determine facial balance, especially through its relationship to the face in profile. Surgeons have recognized this for many years, and combination procedures involving rhinoplasty and genioplasty are common.[1] The chin defines the character of the face and, perhaps, the person; a long chin has been associated with strength and power, whereas a short chin portrays weakness.

See the images below.

Before and after.

Before and after.

Osteoplastic genioplasty has been the criterion standard in chin surgery. However, in comparison to alloplastic implants, the procedure is longer, technically challenging, and puts the mental and inferior alveolar nerves at risk. Chin augmentation is often performed in combination with other procedures, including rhinoplasty and rhytidectomy, to address the prejowl sulcus or a ptotic chin pad.[2] Implants, which have been used intermittently over the last century, have regained popularity, especially with the development of alternative alloplastic materials.[3]

Historically, various materials have been used for soft tissue and bony augmentation, including autogenous materials such as iliac and rib bone grafts and nasal cartilage. Aufricht described the successful use of the osteocartilaginous nasal hump for chin augmentation during combined plastic surgery of the nose and chin.[4] He developed this technique in 1928 and reported that in one patient, the autograft remained intact for at least 27 years. He advocated this technique not only because of the convenience of using an autograft but also because of the aesthetic benefit achieved by performing simultaneous rhinoplasty and genioplasty.

Alloplastic materials such as ivory, acrylic, and precious metals are now primarily of historic interest. Other materials such as polytetrafluoroethylene (PTFE) and silicone have also been popular. Newer materials have been developed, including soft materials (eg, nylon mesh, expanded PTFE) and harder materials (eg, high-density polyethylene, hydroxyapatite compounds).

Several general qualities contribute to the biocompatibility of an implant. Most importantly, those materials that do not elicit a chronic inflammatory response or foreign body reaction can be highly biocompatible. Lack of immunogenicity and carcinogenicity are also favorable implant characteristics. Implant material must be nondegradable, yet malleable, such that the shape and position are maintained over time.

For more than 40 years, silicone has been used in the human body. When elemental silicon (number 14 on the periodic table) is interlinked with oxygen, it can polymerize into silicone, which can exist as a liquid form (silicone gel) and a more solid form that is appropriate for facial augmentation. The solid form can be customized by intraoperative carving or by custom molding. A dense fibrous capsule forms around the implant that helps maintain the implant in its proper position, but no tissue ingrowth occurs after implantation. Silicone is easily sterilized, easily carved to the necessary shape, and easily removed in the event of revision or complication. Silicone implants are popular because they are not expensive and are comfortable.

PTFE, a material with a spongy consistency, is an ethylene monomer with 4 fluorine moieties attached. It is manufactured as implants under the trade names Teflon, Gore-Tex, and Proplast. Only Proplast and Gore-Tex have been used for facial plastic surgery. Similar to silicone, PTFE has been in use for more than 40 years and is nonimmunologic and noncarcinogenic.

The original Proplast (Proplast I) was black and consisted of Teflon (PTFE) and graphite. It was replaced by Proplast II, which, unlike the black Proplast I, is a white material composed of Teflon and alumina. It is a porous material with pores ranging from 50-400 µm in diameter, which allow fibrovascular ingrowth of the host's tissues. Proplast was discontinued after it was shown to delaminate under shear stress, form particles, and induce an inflammatory reaction. Gore-Tex is an expanded PFTE sheeting composed of fine expanded PFTE fibrils held together by solid expanded PTFE nodes. Proplast II is easily cut and trimmed for contouring and is porous, with pores ranging from 10-30 µm, which allow for limited fibrovascular ingrowth.

High-density polyethylene, or Medpor, is another alloplastic material, which, unlike PTFE, is not fluorinated or spongy in consistency. It is flexible, contouring with ease when heated in a warm-water bath. It is porous, with pores ranging from 125-250 µm, which allow for soft tissue and some bony ingrowth. It does not induce a foreign body response and is not degraded in the body. As demonstrated in a study contrasting the histologic response of Gore-Tex and Medpor implantation to experimental infection, the faster fibrovascular growth into high-density polyethylene seemed to protect against infection. This may be attributed to the larger pores and increased stability from host tissue ingrowth of the implant. However, fibrous ingrowth into porous materials does not guarantee implant stability.

Hydroxyapatite, another firm porous compound, is available as porous block hydroxyapatite. It is derived from marine coral and has been used in facial augmentation. Its pores allow for fibrous and bony ingrowth. It is applied with rigid fixation to the underlying bone and is associated with minimal bone erosion.

Mersilene mesh is a softer material composed of nonabsorbable polyester fiber sheeting that can be folded and constructed into an appropriate implant. It has been in use for 50 years and was first introduced for hernia repair. Unlike Supramid, the polyamide nylon mesh Mersilene does not degrade. It is cut easily without fraying or shrinking.

Silicone, expanded PTFE, and high-density polyethylene are available as prefabricated implants of variable sizes and shapes. These materials can be cut and carved to individualize them to the patient.[5] Each alloplast has its own benefits and problems, and different surgeons report various experiences with these products.

Surgeons have looked to art to establish an ideal model for the perfect chin. Indeed, analysis has proven that the chin has a central role in facial balance and beauty in a global sense. Chin projection is perceived as it relates to the rest of the face. Various methods of analysis and chin classifications have been described.

Chin augmentation is used to correct microgenia (ie, retrusion of the chin). This is distinct from micrognathia, which is a problem of the mandible, not the chin. When considering chin augmentation, the surgeon contemplates the chin not just as a bony protuberance, but rather, as a 3-dimensional prominence consisting of soft tissue components and bone. Additionally, the chin is considered in relation to the nose. This relationship is critical to facial balance. In a patient with a large nose and small chin, rhinoplasty may not be sufficient unless the chin is addressed.

Frequency

Chin deformities are the most common abnormality of the facial bones. Microgenia is the most common chin abnormality. However, because of a lack of associated functional deficit, microgenia is often left untreated. Most procedures are performed in combination with rhinoplasty.

A patient may present with microgenia or, more commonly, may become aware of microgenia during the process of rhinoplasty evaluation. Again, microgenia, or small chin, is distinctly different from micrognathia, which is mandibular hypoplasia. Microgenia is often a component of micrognathia, but microgenia takes into account all components of the chin.

The chin is located below the labiomental sulcus and consists of skin and subcutaneous tissues, the mentalis muscle, and the underlying bony structures from the mandible. Microgenia occurs and is addressed when there is acceptable occlusion. In situations of severely altered dentoalveolar relationships, orthognathic surgery is more appropriate than chin augmentation. However, chin augmentation by implant is appropriate for mild forms of microgenia.

Gonzalez-Ulloa wrote extensively on profile plasty.[6, 7] With the basic tenet that the skeletal structure and proportions of the skull define beauty, he developed methods of analysis to understand facial relationships. By understanding that the bony skeleton supports the soft tissue and truly is the mechanism for achieving optimal aesthetics, the surgeon can plan the operation in a manner that will most likely result in a successful outcome.

The indication for a chin implant is mild microgenia. Gonzalez-Ulloa based his facial evaluations on the Frankfort plane and the 0° meridian. The Frankfort plane is the horizontal line from the upper external auditory canal to the infraorbital rim. The 0° meridian is drawn in the vertical plane perpendicular to the Frankfort horizontal plane and tangential to the nasion and the pogonion. If the chin is behind the 0° meridian, it is considered retruded. The intervention is determined by the degree of retrusion.

Many methods of analysis have been described and reviewed by several surgeons. Burstone's vertical line is tangential to the subnasale and the pogonion. The upper lip is 3.5 mm anterior, and the lower lip is 2.2 mm anterior.

Gibson uses soft tissue landmarks in the lower facial triangle to determine the ideal chin position with reference to lower facial height.[8] The 3 defining points are the tragion, subnasale, and chin. Goode drops a line perpendicular to the Frankfort horizontal plane at the alar crease to mark the ideal chin position. Legan's angle of facial convexity is 12° between a line to the glabella and subnasale and a second line tangential to the subnasale and pogonion.

Merrifield's Z angle is 80° (± 5°) at the transection of the Frankfort horizontal plane and a vertical tangent from the upper lip to the pogonion. Ricketts drew a vertical line tangential to the nasal tip and pogonion.[9] Posterior to this plane, the upper lip is at 4 mm, and the lower lip is at 2 mm. Steiner's nasal philtral S defines the anterior extent of the lips. A vertical line is dropped tangential to the pogonion, and an inverted S is formed by the lower nasal and upper labial profile.

Just as the Greek Parthenon was based on "the golden rectangle," the chin, in relationship to specific facial features, also follows the golden proportion, or phi. In the golden rectangle, the altitude is the proportion 1 and the base is 1.618 multiplied by the altitude. This relationship is phi.

The golden proportion is found in several of the height relationships of the face. The entire face fits the proportion, with the measurement from forehead to eye as 1 and from eye to menton as phi. The golden proportion is in reverse, with the measurement from menton to nasal ala as 1 and from nasal ala to forehead as phi. Again, the proportion is maintained from the eye to the chin, with the measurement from eye to nasal ala as 1 and from nasal ala to menton as phi. The proportion in reverse is measured from menton to stomion, with the measurement from stomion to eye as phi. Finally, the nose and chin are related in the golden proportion. With the measurement from nasal ala to stomion as 1, phi is measured from stomion to menton and from nasal ala to eye.

The chin derives from the fusion of the 2 mandibular processes at the midline. The muscular portion of the soft tissues stems from the accompanying overlying mesoderm. Muscular fusion occurs at the midline but is often incomplete and separated into 2 halves by a fibrous median raphe. Soft tissue and bony skeleton make up the chin.

Located below the labiomental angle, the soft tissues include the skin and subcutaneous tissues and the muscle below. This chin pad is of variable thickness, especially when the mentalis muscle is hypertrophied. Typically, the mentalis muscle is small, has its origin on the mandible below the incisors, and inserts into the skin of the chin. Its innervation is via the seventh cranial nerve.

The mandible contributes the skeletal portion of the chin, specifically, the symphysis menti, which joins the 2 halves; the mental protuberance, which is an elevation above this junction; and the mental tubercles, which lie at the inferior margin. Projection of the chin is dependent on the mental protuberance and tubercles.

The chin is separate from the lip at the labiomental angle. However, the chin and lip have an intimate relationship. The depressor muscles insert on the mental tubercles and interdigitate with the orbicularis oris muscle. Any intervention on the chin can affect the lips.

Severe microgenia is a contraindication to augmentation mentoplasty. Other contraindications include labial incompetence, lip protrusion, shortened mandibular height, severe malocclusion, and periodontal disease.

See the list below:

• Photodocumentation

  • This is a basic need for all facial plastic surgery procedures.

  • In chin analysis, photography can be helpful to evaluate the patient for chin retrusion. The chin should be considered in its relation to the face shape and length and in reference to the nose. The basic views, full face, oblique, profile, and base, are adequate for this evaluation.

  • From the lateral view, the 0° meridian and other types of analysis can be used to determine the grade of retrusion and the desired augmentation. The lateral view is emphasized, but the full-face view is mandatory to evaluate chin width.

  • Photographs should be taken with the patient smiling and in repose. This provides additional information and documentation of labial competence.

• Cephalometric study

  • This is an excellent method to document skeletal configurations.

  • Population-based comparison data are available.

  • This analysis may be more applicable to the osteoplastic technique.

See the list below:

• Gonzalez-Ulloa bases his staging system on the 0° meridian.[6]

  • First-degree retraction describes the pogonion at less than 10 mm behind the 0° meridian.

  • Second-degree retraction is in the range of 10-20 mm.

  • Third-degree retraction is more than 20 mm.

Chin implantation is popular because of the relative simplicity and low morbidity. In the properly selected patient, an alloplastic implant may be more appropriate than an osteoplastic technique. Alloplastic augmentation and osteoplastic genioplasty have yielded high patient satisfaction.

As with all procedures in facial plastic surgery, adequate preoperative analysis is mandatory. This analysis entails examination of the face as a whole, with specific attention directed at the chin, lips, and nose. The patient is examined from all angles, and this is accompanied by precise photodocumentation in the standard views. Face shape and length and the relationship of the chin and nose to the face are examined. The chin is analyzed for its soft tissue components and its bony structure. The chin pad is assessed, as is the size of the chin in general. Chin projection and width are noted. The position and depth of the labiomental fold are also noted. Lack of fullness in the prejowl region, which is especially pertinent in the rhytidectomy patient, is also assessed. Labial competence is evaluated. The lower lip should be posterior to the upper lip. The lower lip should also be in alignment with the most anterior projection of the soft tissue of the chin.

When a patient is considered a candidate for chin augmentation with an alloplastic implant, the proper implant shape and size is chosen. In general, avoid overaugmentation of the female patient. Women are best treated with undercorrection to circumvent removal of an implant that is perceived as too large. This is rarely the case in male patients. The choice of alloplast is usually left to the surgeon’s discretion.

Pitanguy advised 2 principles for chin augmentation.[10] First, the implant should be positioned at the lowest portion of the mandible; next, it must be immobilized. One approach is intraoral, in which a transverse incision is created above the gingivolabial sulcus. This incision is approximately 2.5 cm long and at least 1 cm above the gingivolabial sulcus. The dissection is performed caudally through the muscular layer, and a pocket is created to place the implant. The midline raphe of the muscle can be used to anchor the implant into place. This is achieved by creating a flap and suturing it to the orbicularis muscle.

The use of a supraperiosteal versus a subperiosteal dissection is controversial. Most surgeons probably agree and studies have indicated that supraperiosteal placement leads to decreased bony absorption under the implant. If subperiosteal implantation is performed, the dissection is performed in the midline to the symphysis and continued with a Freer elevator lateral and inferior to the mental foramina. With the subperiosteal technique, a pocket is created to secure the implant. The periosteum is then closed, and the muscles and mucosa are closed in separate layers.

An alternative approach is the submental approach, in which a 2-cm external incision is made submentally, posterior to the first submental crease. The dissection is continued to the periosteum, and a pocket is created in the midline, inferior to the mental nerves. A tacking suture secures the implant under the periosteum, and the wound is closed in layers.

A chin implant can be performed under general or local anesthesia. The procedure can be combined with other aesthetic procedures, including rhinoplasty and rhytidectomy.

A compressive dressing can be applied overnight or longer. Ice packs may be applied to prevent excess edema. The patient is monitored for the development of excessive edema, hematoma, and infection. With the intraoral approach, hydrogen peroxide oral rinses are advised. Patients are given a short course of an oral antibiotic.

The patient is seen first 7-10 days postoperatively for removal of any external sutures. Thereafter, the patient is monitored at 1 month, 3 months, 6 months, 1 year, and yearly thereafter. Postoperative photodocumentation is performed once edema has subsided.

Minor complications include postoperative edema, hematoma, and temporary lip paresthesia. These usually resolve with minimal intervention. Other risks include infection, skin changes, bony changes, and displacement.[11]

The intraoral and submental approaches are associated with a small risk of infection. Soaking the implant in an antibiotic solution prior to implantation may reduce this risk. In the event of infection, salvage may be attempted with the use of antibiotics. The implant can be removed to avoid unnecessary scarring in the region. Of note, infection has been reported both in the immediate postoperative period and in a delayed fashion.[12]

Abnormalities in chin configuration resulting from the position of the mentalis muscle after postioning of an implant have been described. This may be secondary to a deficit in muscular bulk, displacement of the origin of the muscle, elongation, or improper draping of the muscle over the implant. These problems may lead to ptosis of the chin. Alternatively, muscle contraction may occur and lead to a bunching or dimpling appearance at the chin. Displacement of the depressor muscles may contribute to these abnormalities. Any alteration in the mentalis muscle may lead to labial ectropion, in which the patient complains of loss of oral competence. This dreaded complication may reflect implant displacement or even erosion of the mandible.

Because the chin implant is placed in a dynamic region, it is subjected to micromotion due to oral and labial movements for speaking, expression, and deglutition. This may lead to bony changes under the implant. Erosion is classified as type I if it is up to 3 mm, type II if it is 3-5 mm, or type III if it is more than 5 mm. Bony absorption under the implant is perhaps the most dreaded complication following alloplastic chin augmentation and is a common complication. This has been described with silicone implants and the harder alloplasts (eg, Medpor). By avoiding the subperiosteal plane, some bony absorption can be prevented. Good positioning may also prevent this complication. Larger implants have also been associated with erosion. Erosion has been reported as early as a few months after augmentation.

Displacement is a complication of chin augmentation by implant. Implant displacement manifests as a loss of chin projection. If the displacement is lateral, the mandibular contour is altered. If the displacement is inferior, the mentocervical angle is altered with a perceived double chin. If the displacement is superior, the labiomental angle is altered, and subsequent functional changes involving the lips may occur. This includes speaking and oral competence. Additionally, superior displacement may cause erosion of the alveolar bone and dental roots. Once displaced, the implant is at risk for extrusion, especially if infected.

A literature review by Oranges et al found good results and high patient satisfaction with six different chin augmentation techniques. The investigators looked at augmentation with the following[13] :

• Implants - Silicone, Gore-Tex, Mersilene, Prolene, Medpor, Proplast, hard tissue replacement, porous block hydroxyapatite, and acrylic
• Osteotomy
• Autologous grafts
• Fillers - Hyaluronic acid, hydroxyapatite, and biphasic polymer
• Local tissue rearrangements
• Implants combined with osteotomy

Cosmetic outcomes for all of these options proved satisfactory. The techniques with the highest number of procedures in the chosen studies, implants (n = 3344) and osteotomy (n = 885), had complication rates of 15.7% and 19.7%, respectively. These included 2.4% of implants and 16.4% of osteotomies that were associated with transient mental nerve–related injuries.[13]

Chin augmentation is seemingly simple, and indeed, many patients have been treated successfully. However, analysis of the chin is more complicated than a simple visual estimate of the defect. A chin implant can be considered a failure. This may be secondary to infection or extrusion, displacement, or patient dissatisfaction.[14] Disfigurement is a risk following a failed implant. This can occur with the formation of a capsule, contracture and scarring, or an abnormally draped mentalis muscle.

In the event of a failed implant, treatment is removal. This requires removal of the capsule or debridement of wound in the face of infection. Implant replacement is not recommended. Rather, the patient can be reevaluated and recommended for osteoplastic genioplasty.

Placement of the implant and, specifically, which available material is most suitable for chin augmentation, is controversial. The perfect alloplastic material has yet to be developed, but currently available alloplastic implants have provided excellent results when used for chin augmentation.