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The precise fit of the CAD/CAM implant to the underlying skeletal con­tour makes for a more predictable result. There is a fundamental techni­cal problem to placing off-the-shelf bilateral implants in similar positions on opposite sides of the face (Fig. 14.3). Remote incisions routinely provide limi ted access and therefore limited exposure of the areas to be augmented. Furthermore, the surgeon never has the ability to see the position of both implants in a single view. CAD/CAM implants are made to augment precisely defined areas of the facial skeleton, making implant positioning less problematic. These implants can also be designed with registration features, for example, a flange on a malar implant that rests on the infraorbital rim or on the superior edge of the zygomatic arch. Cus­tom implants are designed to avoid any gaps between the posterior surface of the implant and the anterior surface of the skeleton (Fig. 14.4). Gaps are unavoidable when using off-the-shelf implants. These gaps add to the effective projection of the implant. A 2-mm gap beneath a 3-mm implant will result in an unanticipated 5-mm projection. An implant designed and manufactured to have its posterior surface mirror that of the underlying skeleton will avoid that unanticipated contour result. 

Because the native facial skeleton is not symmetric, implant augmen­tation will provide a “relative symmetry.” Chin implants should create symmetry relative to the midline structures – nasal radix, nasal septum, central incisors, and central lip elements. This symmetry should extend from mental foramen to mental foramen. Lateral to the mental foramen, mandible implants should relate to the width of the upper face. For exam­ple, the extent of lateral augmentation of the mandible angles should relate to the lateral orbital rims in the same way (Fig. 14.7). Designing an implant for one side of the face and mirroring it to create an implant for the opposite side will create mandible symmetry only if the mandible and midface are symmetric prior to augmentation. When augmenting the midface, the goal is to achieve similar implant-plus-skeleton projection (Fig. 14.8). Because the contours of the midface will vary from one side to the other, mirroring one side to the other is unlikely to result in similar contours.

disappointing to the patient.

Clinical examples are presented in Figs. 14.9–14.12.

Presented by Dr. Yaremchuk at the 22nd Annual Hans R. Wilhelmsen MD, DDS Lectureship in the Craniofacial Sciences, May 17, 2018, at the Johns Hopkins Hospital in Baltimore, MD.