Although patients who seek advice about facial cosmetic surgery often focus on structures such as the nose, the eyes, and the laxity of their skin, the facial plastic surgeon's assessment frequently identifies the lower third of the face as an area that could be surgically modified to improve overall facial appearance and harmony. The profile of a patient can be significantly altered with either a chin augmentation or reduction procedure. This, in turn, has a significant effect on overall facial symmetry.
Several surgical options exist for the treatment of chin deformities. Alloplastic chin implants and sliding genioplasty represent the 2 currently accepted methods of chin augmentation. However, to debate whether alloplastic augmentation or osseous genioplasty is the superior choice is beyond the scope of this article. Techniques for chin reduction include genioplasty and direct chin reduction. Skeletal surgery has been through the test of time, and still remains a valued procedure for the facial surgeon. Recent articles from variety of publications confirm the utility of the sliding genioplasty. Wolfe published a 28-year period series in 2006,  and Hoenig published a 10-year experience in 2007. 
History of the Procedure
Surgeons in the mid 1940s started using bony osteotomy techniques to address the retruded mentum. Currently, the sliding genioplasty is performed by physicians from several surgical subspecialties. For the protruding chin, options include a sliding genioplasty or an open reduction with a rotary burr.
Historically, various materials have been used to augment the chin, including paraffin, ivory, and methylmethacrylate, to name a few. Alloplastic implants such as silicone, polytetrafluoroethylene, and polyester mesh have gained a great deal of popularity through the years as a result of patient and surgeon satisfaction, as depicted in the image below. In the 1980s, Beekhuis and Johnson popularized Mersilene mesh (Ethicon, Somerville, NJ). A recent 14-year study showed Mersilene mesh to be safe and well tolerated for chin augmentation. Alloplasts, in general, are easy to place and are less time consuming than a sliding genioplasty, but their application is limited to the mild to moderately retruded chin.
Autografts such as iliac crest and rib cartilage have been used more frequently for chin augmentation in the past. Nasal bone and cartilage have been used as well. Unfortunately, their use appears to be associated with an increased rate of infection, even after as many as 40 years.
When facial analysis identifies a patient's profile with facial dysharmony, determine whether an underlying occlusal and skeletal deformity or merely a poorly or overprojected mentum is present. When the poor projection is skeletal in nature, the situation is considered an Angle class II skeletal deformity. The Angle skeletal classification is based on the position of the first molar. In retrognathia, the mesiobuccal cusp of the maxillary first molar is mesial (or anterior to) the buccal groove of the mandibular first molar. If only a hypoplasia of the mandible exists, the term micrognathia is more accurate and should be used.
When no skeletal malformation is present, the terms for a recessed chin include retrogenia, microgenia, retruded chin, hypoplastic mentum, and horizontal mandibular hypoplasia. The same holds true for the overprojected chin, eg, prognathia, protruded chin. In the literature, all these terms have been used interchangeably. In general, genioplasty implies an osseous movement, whereas mentoplasty suggests the use of an alloplastic implant. However, the two terms are currently used in a synonymous fashion.
Correction of poor projection of the mentum is desirable in approximately 20% of patients undergoing rhinoplasty and about 25% of patients having a rhytidectomy. However, the patient must often be educated that this deficiency exists and that, with surgery, an overall balanced cosmetic result may be achieved.
The preoperative consultation includes a complete history and physical examination, including dental history with occlusal evaluation along with standard facial photographs. In the analysis of the profile, the face is divided into thirds. Dividing the face from the hairline to the glabella, the midface from the glabella to the subnasale, and the lower third from subnasale to the menton is standard. Then the chin can be assessed to determine if it is in harmony with the remainder of the face.
In addition to the facial analysis, study dental occlusion and skeletal structures with the aid of preoperative photography as well as cephalometric and panoramic radiography. Functional and cosmetic goals should be discussed with the patient. When chin abnormalities are present, obtain additional studies. Perform a lateral soft tissue study, lateral cephalometric study, anteroposterior (AP) skull radiography, and occlusal panoramic radiography.
If skeletal or dental deformities are present, order dental models to be fashioned. Use this information to advise the patient on the choices available for obtaining the best result. If a skeletal abnormality exists, suggest orthodontic realignment and orthognathic surgery. When the patient desires a purely cosmetic correction, discuss options of alloplastic implant augmentation versus a sliding genioplasty. If the deformity is amenable to either of these treatment options, recommendations are based on the severity of the deformity and concomitant facial procedures being considered.
It is important to consider the mentolabial fold in planning for a chin augmentation. A large implant may worsen the depth and cause an imbalance in profile harmony. Several authors suggest considering methods to prevent a deep sulcus when performing a sliding genioplasty. Bertossi et al describe using fresh-frozen human bone allograft as an interpositional grafting material, which can also be used to efface the sulcus or fold.  Triaca et al describe a novel shield osteotomy to prevent the labiomental crease from deepening.  The buccal cortex is cut high, creating a shield effect and softening the crease.
Surgical goals include creating an aesthetically pleasing facial contour and establishing proportionate facial height. This may entail reduction of a prominent chin or augmentation of a poorly projected chin.
Ideally, the augmentation procedure should be performed with minimal morbidity. Generally, alloplastic implants are not technically demanding and have a low complication rate. Furthermore, these implants may be easily placed under local anesthesia. This is a well-accepted technique used in the correction of chins that have only mild-to-moderate microgenia and a shallow labiomental fold.
The sliding genioplasty has been reported to have similar rates of success. Additionally, this technique can address abnormalities in 3 dimensions of asymmetry, including vertical microgenia with and without retrogenia, vertical macrogenia with retrogenia, and prognathia. Alloplastic implant augmentation is excellent for minor abnormalities; however, surgical facility with osseous genioplasty permits treatment of more complex deformities. The proponents of the sliding genioplasty stress the fact that abnormalities in 3 dimensions can be addressed, making it a more versatile procedure. This technique has also been utilized when multiple problems with alloplastic chin implants was faced. The osseous genioplasty has been reported to provide the solution to difficulties encountered with the alloplastic techniques. 
Reduction can also be achieved via a direct approach. Through an intraoral labial approach or an external submental incision, the inferior cortex of the mandible may be burred down.
For an augmentation, the depth of the labiomental fold may dictate which technique is used. Alloplastic implants tend to deepen the sulcus, which may be particularly unattractive in female patients. With osseous genioplasty, the fold generally increases with advancements and/or vertical shortening and becomes more effaced with vertical lengthening.
The surgeon should always be cognizant of the location of the mental foramen. The mental foramen lies on the same vertical line defined by the pupil, infraorbital foramen and the second bicuspid tooth.
The mentalis muscle elevates and protrudes the chin. It attaches the chin to an area just beneath the tooth roots. An intraoral incision transects this muscle. Reestablishing this muscle is important; otherwise, chin ptosis may ensue.
When considering a mandibular reduction or a sliding osteotomy, carefully evaluate the teeth and the height of the mandible prior to surgery. Having long teeth with a short mandibular height is a relative contraindication for an osseous genioplasty or an aggressive bony reduction.
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