1.6\ Chin and Jaw Augmentation

1.6.1\ Discussion

Mandible augmentation can be performed with the chin (Figs. 1.39, 1.40, and 1.41), submental (Fig. 1.42), chin/prejowl or prejowl (Fig. 1.42), and lateral/mandibular angle implants (Fig. 1.43), or a combination of these. The implants are typically inserted between the periosteum and cortex of the mandible. Bone graft implants are less commonly used due to the tendency to resorb over time. On the other hand, high-density porous polyethylene and silicone implants molded to the contours of the underlying mandible are popular materials for augmentation. These can be combined with other materials, such as the bone. Screw fixation is occasionally used, particularly for providing stability to combined grafts. Complications include hematoma, infection, seroma, bone erosion, and migration. Seromas may resemble infection on imaging and can alter the intended cosmetic effect, although this may be transient (Fig. 1.44). Mandible implants are sometimes intentionally positioned asymmetrically, but should remain in close approximation to the surface of the mandible. However, pressure-­ induced bone erosion from the implants is abnormal and can undermine the desired cosmetic

effect (Fig. 1.45). Implant migration can also alter cosmetic result and may be associated with underlying infection. Facial CT can readily characterize implant migration (Fig. 1.46). Bone formation along the periosteum overlying the chin implants is not an uncommon occurrence and is usually thin linear or punctate (Fig. 1.47). Occasionally, the new bone can become large enough to alter the desired cosmetic effects. This phenomenon can be characterized via CT. The bone may be more difficult to discern on MRI, since it may appear as low signal, similar to the silicone implants.

a

b

Fig. 1.39  Chin augmentation with “button” bone graft. Axial CT image demonstrates a bone graft anterior to the mandibular symphysis (arrow)

Fig. 1.40  Chin augmentation with silicone implant. Axial CT (a) shows a crescent-shaped slightly hyperattenuating implant anterior to the body of the mandible (arrowheads). The implant (arrow) appears hypointense on the sagittal T1-weighted MRI (b)

Fig. 1.43  Mandibular angle implants. Axial CT image demonstrates bilateral silicone implants deep to the masseter muscles (arrowheads)

Fig. 1.44  Chin implant seroma. Axial CT image shows fluid surrounding the silicone implant resulting in altered cosmetic effect

Fig. 1.45  Chin implant bone erosion. Sagittal CT image shows the silicone implant has receded into a smooth defect in the body of the mandible, resulting in diminished cosmetic effect and impingement upon the roots of the teeth

Fig. 1.46  Prejowl implant migration. Coronal CT image shows inferior displacement of the left side of the implant (arrow)