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Dual Plane Augmentation Genioplasty Using Gore-Tex Chin Implants

Background The chin shape and position is important in determining the general shape of the face, and augmentation genioplasty is performed alone or in combination with other aesthetic procedures. However, augmentation genioplasty using osteotomy is an invasive and complex procedure with the potential to damage mentalis muscle and mental nerve, to affect chin growth, and prolonged recovery. Our aim was to present our experience with a modified augmentation genioplasty procedure for hypoplastic chins using a Gore-Tex implant. Methods Two vertical slit incisions were made at the canine level to create a supraperiosteal pocket between the incisions, preserving the periosteum and mentalis muscle. Minimal sub-periosteal dissection was performed lateral to the incisions along the mandibular border. The both wings of implant were inserted under the periosteum to achieve a stable dual plane implantation. Results In total, 47 patients underwent dual plane chin augmentation using a Gore-Tex implant between January 2008 and May 2013. The mean age at operation was 25.77 years (range, 15-55 years). There were 3 cases of infection; one patient was treated with antibiotics, the others underwent implant removal. Additionally, two patients complained of postoperative parasthesia that spontaneously improved without any additional treatment. Most patients were satisfied with the postoperative outcomes, and no chin growth problems were observed among the younger patients. Conclusion Dual plane Gore-Tex chin augmentation is a minimally-invasive operation that is simple and safe. All implants yielded satisfactory results with no significant complications such as mental nerve injury, lower lip incompetence, or chin growth limitation.


INTRODUCTION
The chin is located in the central portion of lower face and is a critical feature that contributes to the frontal profile and symmetry of the face. Microgenia is defined as an abnormally small chin.
Unlike micrognathia, which designates hypoplastic mandibles with type II dental malocclusion, individuals with microgenia have normal dental occlusion. Microgenia is a cosmetic concern and contributes to the appearance of a disproportionately short face. A proportional nose can appear larger in comparison, and the neck soft tissue can sag due to the shortened fulcrum.
There have been many discussions on aesthetically pleasing profiles of the chin. Gonzalez-Ulloa and Stevens [1] described the ideal chin projection as a tangential line from the soft tissue nasion that is perpendicular to the Frankfort horizontal line. Farkas et al. [2] analyzed the inclination of the facial profile as an angle between the perpendicular line at the glabella and the line connecting the glabella and pogonion, which has been estimated to be around -3° in men and -4° in women. A few millimeters be-     of Gore-Tex enables supra-periosteal implantation, and capsule formation is less than that around silicone; therefore discomfort from mental nerve traction can be reduced. Furthermore, Gore-Tex is inert, non-carcinogenic, seldom allergenic, and causes minimal tissue reaction. In addition, Gore-Tex is pliable and could be easily trimmed and conformed to deep tissue bed.
Implantation of alloplastic materials has been contraindicated in children because of the possibility of bone growth retardation.
It is generally accepted that facial osteotomies are not advised until growth completion (14-16 years old in females and 16-18 years old in males) [5]. Silicone implants inhibit bone growth when inserted under the periosteum, whereas bone growth is not interfered when implants are placed over the periosteum [6,7]. Two However, Gore-Tex has some disadvantages, including a relatively high risk of local inflammatory reaction causing erythema and edema at the skin site, infection, and displacement. It also is These findings suggest that no significant changes in shape occur with Gore-Tex over time.
This technique does not damage the normal structure. Supraperiosteal plane dissection does not violate the mentalis muscle.
The mentalis muscles are a pair of fan-shaped structures joined in the midline. They originate from the alveolar process of the mandible below incisors roots and have their insertion in the skin. The function of the mentalis muscles, which is to elevate the lower lip and chin, can be disrupted by a horizontal intraoral incision.
Compared with the conventional horizontal incision, 2 vertical incisions minimize pain, bleeding, scar formation, tethering effects, and food becoming trapped between wound margins. In addition, every effort was made to keep the mental nerve undamaged. The position of mental foramen is below the second mandibular premolar root or in the interdental space between the first and second premolar teeth, approximately 1.5 cm above the mandible lower border. A region of at least 5 mm between the mental foramen and upper margin of the implant was preserved to decrease the risk of injury. An extraoral sub-mental approach can be a good alternative that prevents damage to the mentalis muscle and minimize infection from intraoral flora [3]. However, a noticeable scar is of great concern to cosmetic patients, especially among East Asian patients.
Dual plane Gore-Tex chin augmentation is a very simple method that takes less operative time. The average operation time was 43 minutes from incision to closure. Furthermore, local anesthesia with mental nerve block was sufficient for most cases of isolated augmentation genioplasty. However, it is difficult to correct asymmetric chin, vertical shortness, or complex deformity of the chin. Genioplasty with osteotomy could be an alternative in these cases, and ancillary correction could be performed using a Gore-Tex implant. The learning curve of this procedure lies in the creation of an adequate pocket size and preparing a Gore-Tex implant that conforms well to the underlying bone contour, which is important to prevent implant migration and exposure.
This study is limited by its retrospective design and small sample size. Furthermore, objective assessment tools should be performed to assess postoperative outcomes. The effect of the Gore-Tex chin implants on bone growth when placed over the periosteum should be investigated in future studies.
In conclusion, dual plane augmentation genioplasty using the Gore-Tex implant is an easy and effective surgical procedure that can produce aesthetically acceptable outcomes with minimal morbidity. Moreover, limited subperiosteal dissection preserves normal bone growth potential; therefore, it can also be used in younger patients who are still in their growth phase.