Labial incompetence: a marker for progressive bone resorption in silastic chin augmentation

Bone erosion below silicone rubber implants is a wellknown sequela, occurring in a majority of patients undergoing augmentation genioplasty. It is generally considered to be self-limiting and with minimal adverse consequences. However, if bone erosion progresses to the extent to which teeth are jeopardized or alterations in sensibility of the mental nerve occur, removal of the implant is indicated. Osteoplastic genioplasty may be required to restore aesthetic contour to the chin and to avoid functional anomalies that may occur from explantation. A number of factors have been identified that contribute to this phenomenon; however, speculation regarding its etiology has not acknowledged the functional aberration of a tensed mentalis muscle. A study of six patients with aesthetically positioned and appropriately sized Silastic implants revealed a correlation between preoperative baseline labial incompetence and mentalis muscle hyperactivity and progressive bony erosion. One patient had grade II erosion and four patients had grade III erosion, one with the exposure of dental roots. The sixth patient with mentalis muscle strain, subsequent to attempts to contain her lower denture, also had severe resorption. Such findings suggest that attention should be paid to an alternative approach in microgenic patients presenting with lip strain, since labial incompetence appears to be a reliable marker for ongoing mandibular resorption following Silastic augmentation. Furthermore, since most patients are asymptomatic until significant erosion occurs or are satisfied and do not return, in those individuals with labial incompetence who have already had Silastic chin implants, consideration should be given to routine follow-up examination and radiographs.