Alloplastic Chin Augmentation

Anatomy and Physiology

Structures Encountered During Alloplastic Chin Implantation

During alloplastic chin implantation, surgeons encounter various structures, including the skin and subcutaneous tissue, the mentalis muscle, mandibular periosteum, gingivolabial mucosa (if using the intraoral approach), and the mental nerve.[3][4][5]

Anatomical Structures at Risk

• The mental nerve is a branch of the inferior alveolar nerve from the mandibular division of the trigeminal nerve, exiting the mandible via the mental foramen inferior to the first premolar. Damage can be mitigated by maintaining dissection along the inferior-most aspect of the mandible. An intraoral approach can provide direct visualization and preserve nerves, aiding precise placement of rigid implants such as Medpor, which may be unnecessary with smaller or more flexible chin implants.

• Improper re-approximation of the mentalis muscle after the implant is placed may lead to a ptotic chin.

Indications

Chin implants are typically considered for patients aiming to address their convex facial profile or transverse microgenia, commonly associated with the following:

• Horizontal (anterior-posterior) microgenia, also known as retrogenia
• Soft tissue deficiency, such as muscular atrophy
• Pre-jowl volume loss [3][6]

Chin implantation is frequently combined with rhinoplasty to achieve a balanced nose-chin relationship and enhance the overall profile aesthetically, with indications in up to 25% of cosmetic rhinoplasty cases. Additionally, alloplastic chin augmentation can significantly improve facelift outcomes by elongating the jawline and providing a more stable framework for repositioning the soft tissues of the face.

Contraindications

Contraindications to chin augmentation with alloplastic implants include suboptimal vertical chin height (shortened mandibular height), retrognathia linked to dental malocclusion, and a history of prior rejection of the implanted material. A relative contraindication may include transverse chin asymmetry, which may be addressed with a carefully shaped and customized implant, and deep mento-labial crease, as alloplastic chin augmentation may accentuate this sulcus.[3][6]

Equipment

The ideal alloplastic implant for augmentation should be easily shaped and secured, biologically inert, noncarcinogenic, noninflammatory, nonallergenic, easily available, maintain its desired form and consistency in situ, resistant to mechanical strain, and integrate into the surrounding tissue.[1]

The most common alloplastic implant materials used for alloplastic chin augmentation are listed below.

• Silastic (solid silicone): Silastic or solid silicone is known for being nonallergenic, minimally reactive, nonporous (preventing fibrovascular ingrowth), and easily manipulated. These implants induce a local inflammatory response, leading to the formation of a surrounding fibrous capsule. Silastic implants come in various shapes, sizes (small, medium, and large), and styles (narrow button style and extended with tapering lateral wings), with available sizers aiding in assessing the 3-dimensional contouring change.

• High-density porous polyethylene: This is a nonallergenic and nonabsorbable implant characterized by large pores (150 μm), enabling fibrovascular ingrowth of surrounding tissues. However, it poses challenges in contouring and removal.

• Meshed materials: Meshed materials, such as polyamide, are flexible and easily shaped, facilitating manipulation during alloplastic chin augmentation. Although these materials may elicit a moderate foreign body reaction, they allow for the ingrowth of fibrous tissue.

• Expanded polytetrafluoroethylene (ePTFE): ePTFE is a commonly used biomaterial. Currently, ePTFE implants are still used in some regions, although they are less common than silicone or porous polyethylene. Availability depends on the manufacturer and country rather than legal prohibition.[7]

Proper equipment and meticulous preparation are essential for ensuring the success and safety of facial alloplastic chin augmentation procedures. This comprehensive list outlines the preoperative, intraoperative, and postoperative equipment and supplies required to conduct the surgery effectively and help the patient recover appropriately.

Preoperatively

• Standard photography capturing straight, oblique, and lateral/profile views
• Preoperative antibiotics, such as weight-based cefazolin
• Alcohol solution or pad for skin cleansing and marking landmarks and proposed incisions
• Surgical marker for marking planned incision sites
• Local anesthesia, such as lidocaine 1% with epinephrine 1:100,000; maximal dosage of lidocaine with epinephrine is 7 mg/kg
• Topical antiseptic, such as povidone-iodine

Intraoperatively  

• Various curved dissectors and periosteal elevators
• Scalpel, such as #15 blade
• Forceps, with teeth for atraumatic soft tissue handling
• Electrocoagulation/electrocautery device
• Skin hooks and/or small retractors
• Sutures, such as 4-0 absorbable for deep layers and 5-0 nonabsorbable for skin closure
• Antibiotic-impregnated solution for soaking the implant and irrigating the wound

Postoperatively

• Antibiotic ointment for wound care
• Chin dressing materials, including non-stick dressing and adhesive tapes, to support healing and protect the surgical site

Personnel

Depending on various factors such as the patient's pain threshold, anxiety level, overall health, complexity of the procedure, and the surgeon's comfort and skill level, chin augmentation with an alloplastic implant may be performed under local anesthesia (with or without oral anxiolysis and analgesia) or under deeper sedation or general anesthesia.

When performing procedures with local anesthesia, it is necessary to have a nurse assistant present as part of the required personnel. When performing procedures under deep sedation or general anesthesia, the necessary personnel are an anesthesiologist, operating room nurse, scrub technician or nurse, and surgical assistant.

Preparation

A thorough assessment of the chin should encompass evaluation in 3 dimensions—vertical (superior-inferior), horizontal (anterior-posterior), and transverse dimensions. In addition, the chin's position relative to the soft tissues of the lips, teeth, maxilla, nose, and neck should be considered. While photographic analysis suffices for minor deformities necessitating an alloplastic implant, more significant deformities, such as vertical height excess or transverse asymmetry, may require radiographic evaluation.

Several techniques exist to help evaluate patients who may benefit from an alloplastic chin augmentation:

• In Goode's method, a line perpendicular to the Frankfort horizontal line passes through the alar groove. According to this approach, the pogonion (the most prominent or anterior point of chin projection) should align with this line or be situated immediately posterior to it.

• Gonzalez-Ulloa proposed a line that runs perpendicular to the Frankfort horizontal line and passes through the nasion (the deepest portion of the radix). According to this method, the pogonion should either intersect with this line or be situated immediately posterior to it. Furthermore, he classified the degree of insufficiency into 3 grades—grade I if within 1 cm posterior to this line, grade II between 1 and 2 cm posterior, and grade III if greater than 2 cm posterior.

• Silver proposed a line perpendicular to the Frankfort horizontal line, crossing through the mucocutaneous junction of the lower lip. According to his suggestion, the pogonion should align with this line or, ideally for women, be within 2 mm posterior to it.

• Merrifield adopted a similar yet slightly different method for chin analysis by introducing the Z-angle. The Frankfort horizontal line forms this angle, along with a line extending from the pogonion to the most anterior projection point of the lips. Ideally, the Z-angle should fall within the range of 75° to 85°.

• Legan introduced an angle-based approach for chin analysis, consisting of a line from the glabella to the subnasal point and another from the subnasal point to the pogonion. The ideal value for this angle is 12°, with an acceptable range between 8° and 16.[8][9][10][11][12]

Finally, for comprehensive chin analysis, the cervicomental angle (CMA) and the mentocervical angle (MCA) are crucial facial angles to consider.

• The CMA is formed by a tangential line from the submental point and another tangential line to the neck at the subcervical intersection or the lowest point between the submental area and the neck. Ideally, the CMA measures 121º for men and 126º for women.

• The MCA is commonly defined as the angle between a line passing through the nasal tip and pogonion and a tangential line through the submental point, with an ideal angle ranging from 110º to 120º.[13]

Although these methods provide valuable insight into achieving an ideal chin position in relation to the lips, face, and neck, only a few account for the crucial relationship between the nose and chin. This relationship is vital to acknowledge, as they directly influence each other's relative appearance in space. As a general rule, a more projected nose tends to make the chin appear less projected, and vice versa. An essential and ideal harmonious balance exists between the projection of the chin and the nose. Notably, all the mentioned analysis methods rely on standardized photography techniques, with four of them utilizing the Frankfort horizontal line—a well-established anatomical reference extending from the superior border of the external auditory canal to the inferior orbital rim.[9] Furthermore, radiographic evaluation, including panoramic radiographs and/or lateral and anterior-posterior (AP) radiographs, may be beneficial for addressing more complex deformities such as vertical height excess, orthognathic abnormalities, and transverse asymmetry, commonly observed in conditions such as hemifacial/craniofacial microsomia, oculoauricular vertebral (OAV) syndrome, or isolated anatomical components.

Technique or Treatment

Once the patient qualifies for an alloplastic implant and the appropriate type and size are determined, the decision to perform the procedure via an intraoral or submental approach is considered.[14] The transoral approach avoids external scarring but involves greater technical complexity and carries a higher risk of infection due to communication with the oral cavity. Conversely, the submental approach may be preferred for its improved exposure during placement and access to the neck for additional procedures such as facelift, neck lift, platysmaplasty, or liposuction. Moreover, this approach mitigates the risk of implant contamination by oral secretions.[1][15][16]

Submental Transcutaneous Approach

• An approximately 2 cm midline incision is made posterior to the existing submental crease, avoiding placement directly within the crease to prevent anterior skin movement and scarring anterior to the native crease.

• Sharp dissection is then performed using a scalpel or electrosurgical knife through the skin and underlying soft tissues, including the mentalis muscle, until it reaches the mandibular periosteum.

• In preparation for the subperiosteal dissection, two vertical incisions are made in the periosteum 1 to 2 cm lateral to the midline. This technique preserves the center portion of the implant in a supraperiosteal plane, potentially reducing bony mentum resorption and facilitating the creation of a more distinct subperiosteal tunnel bilaterally. 

• Subperiosteal dissection is conducted using a periosteal elevator, such as a Freer, Joseph, or #9, proceeding laterally along the inferior border of the mandible. The dissection should cover no more than 10% of the implant's size and extend for the length of the implant wings, typically around 5 cm in most implants. Notably, it is crucial to avoid extending the pocket more than 1 cm superiorly to maintain a tight pocket, prevent damage to the mental nerve, and minimize the risk of implant migration to an undesired, superior position. 

• The implant is initially inserted on one side and then folded on itself to facilitate the placement of the other side limb. Upon removal from sterile packaging, it is crucial to handle the implant with minimal manipulation to reduce the risk of infection, fracture, or damage. Additionally, the implant can be irrigated with antibiotic solution according to surgeon preference while awaiting implantation.

• The implant is fastened with sutures to the periosteum in the midline inferiorly.

• The mentalis muscle is then reapproximated.

• The wound is meticulously closed in layers, with absorbable sutures used for the subcutaneous tissue and deep dermis and non-absorbable everting sutures used to approximate the skin. 

• Finally, a splint-like dressing comprising antibiotic ointment, non-adhesive gauze, and adhesive tape is applied. 

Intraoral Approach

• When opting for an intraoral approach, a gingivolabial incision of 2 to 3 cm is made, followed by a similar dissection through the mentalis muscle down to the periosteum. The implant is then placed in a supraperiosteal plane centrally, while the lateral wings are positioned subperiosteally. Maintaining dissection along the inferior aspect of the mandible helps minimize the risk of mental nerve injury. Following this, the wound is thoroughly irrigated with antibiotic solution, and layers of closure are performed using absorbable sutures, ensuring meticulous approximation of the mentalis and creating a water-tight seal.

• Patients with significant skeletal deformity, vertical deficiencies, or occlusal abnormalities may be better treated with sliding osseous genioplasty or orthognathic surgery.[17][18][17]

Complications

Generally, chin augmentation with alloplastic implants, whether performed through a transoral or subcutaneous approach, is considered a relatively straightforward procedure with a low-risk profile and a high satisfaction rate of approximately 97.8%.[19][20]

However, complications associated with alloplastic chin implantation do occur. Complications may include hematoma, infections (<1%), paresthesia or dysesthesia (generally transient but can be prolonged for months, implant malposition (2.5%), implant migration (secondary displacement, 5.0%), implant extrusion (0.4%), implant-induced resorption of the mentum (8.3%), implant rejection, and alopecia of the submental incision.[21][22][23][22]

The following tips can help to avoid complications: 

• Maintaining a small supraperiosteal strip centrally to limit bony resorption.

• Dissecting a narrow subperiosteal plane laterally to accommodate the chosen implant, thereby limiting implant migration snugly.

• Staying along the inferior border of the mandible reduces mental nerve injury and promotes an aesthetically positioned implant.

• Limiting implant manipulation after removal from sterile packaging reduces infection risk.

• Using an antibiotic solution to bathe the implant and irrigate the recipient compartment, thus lowering infection risk.

• Creating a multilayered and watertight wound closure to prevent extrusion and infection.

• Considering the transcutaneous approach over the transoral approach, theoretically reducing infection risk, although conclusive evidence is lacking in the literature.

• Opting for a transoral approach in men to avoid a submental scar and associated alopecia.[1]

Although not commonly practiced, some authors suggest employing screw fixation to mitigate the risk of implant migration (secondary displacement). This approach might be particularly interesting when combining genioplasty with a neck lift or additional rhytidectomy procedures, as the implant pocket could communicate with the surgical field for additional procedures.[24] 

Clinical Significance

An alloplastic chin implant is used to augment chin projection and improve facial aesthetics. The implant can effectively adjust chin projection and/or width to achieve a balanced nose-chin relationship or enhance the pre-jowl area, resulting in a more pleasing facial harmony. However, successful implementation of an alloplastic chin implant relies on a thorough understanding of facial anatomy and precise surgical techniques to achieve optimal outcomes.

Enhancing Healthcare Team Outcomes

Alloplastic chin augmentation is a cosmetic procedure that improves chin projection, contour, and lower facial balance in patients with microgenia, soft tissue deficiency, or prejowl volume loss. Successful outcomes depend on comprehensive facial analysis, careful patient selection, appropriate implant selection, and meticulous surgical technique. The procedure may be performed through intraoral or submental approaches, with implant placement in a subperiosteal pocket to optimize stability and aesthetic results. Thorough preoperative assessment and postoperative surveillance are essential to minimize complications, including infection, hematoma, implant malposition or extrusion, sensory nerve injury, and bone resorption.

Optimal outcomes require coordinated interprofessional care involving surgeons experienced in alloplastic chin augmentation, primary care clinicians, anesthesiologists, certified registered nurse anesthetists when appropriate, surgical assistants, operating room nurses, pharmacists, and perioperative nursing staff. Preoperative evaluation ensures patient suitability for surgery and anesthesia, while nurses coordinate care, provide patient education, monitor recovery, and identify early signs of postoperative complications. Pharmacists support safe perioperative medication management and counsel patients regarding prescribed analgesics and antibiotics. Surgeons should establish realistic expectations through shared decision-making, coordinate postoperative follow-up, and reinforce activity restrictions and wound care instructions. Close communication among team members, dedicated postoperative monitoring, and timely intervention for complications improve patient safety, optimize aesthetic outcomes, and enhance patient satisfaction.