The Safe Zone for Placement of Chin Implants

Abstract

Alloplastic chin augmentation requires the surgeon to predict the location of the mental foramen and the origin of the mentalis muscle to avoid the postoperative sequelae lower lip parasthesia, lower lip incompetence, or chin ptosis. The authors define a safe zone of dissection along the inferior border of the mandible for placement of alloplastic chin implants. Fourteen fresh cadaveric hemifaces were dissected with the aid of loupe magnification. Previously described anatomic landmarks were used to identify the origin of the mentalis muscle and the location of the mental foramen along the alveolar ridge of the mandible. Vertical distances were then measured from the mandibular border to the inferior aspect of the mentalis muscle origin and the lower edge of the mental foramen to construct the zone of safe dissection. The mentalis was identified as a fan-shaped muscle originating from the alveolar process below the incisors roots and inserting into the chin just below the labiomental sulcus. The mental foramen was located most commonly below the roots of the first and second premolars or in the space between the roots. The mentalis origin and the mental foramen were 1.8 ± 0.3 cm and 1.5 ± 0.2 cm cephalad to the inferior edge of the mandible, respectively. These distances define the borders of a safe zone above the mandibular border. A safe zone of dissection for alloplastic chin augmentation is identified. This study is applicable to implant placement through a submental or an intraoral incision. This safe zone is also useful for reconstructive or orthognathic mandible procedures.