Mechanical and sensory testing of overfilled breast implants

To obtain an ideal outcome in breast augmentation procedures, breast implants may be overfilled to reduce wrinkles and improve longevity. Determination of the optimal volume for saline-filled breast implants remains problematic for plastic surgeons. We sought to evaluate the effect of overfilling or underfilling implants on sensory response and on implant shell mechanical properties. Fifty-three Mentor Style 1600 smooth saline-filled mammary implants (275-cc base volume) were examined. Saline fill volumes ranged from 230 cc to 1650 cc. Implants were incubated at 37°C and 100% humidity for 6 weeks. Before destructive testing to determine strength, elasticity, and toughness, 22 women ranging in age from 18 to 55 years graded the implants for firmness to palpation. Objective indices of firmness were measured by durometer. Implants filled 50% above manufacturer's recommended volume were considered firm, whereas implants 50% below manufacturer's recommended volume were considered natural or soft. A linear relationship was observed between sensory response and durometer hardness data. Fill volume did not affect shell mechanical properties: shell strength, toughness, and elasticity remained unchanged (P > .05). Saline-filled breast implants can be safely filled far beyond manufacturer's recommendations with regard to the mechanical properties of the Silastic polymer implant shell. Clinical judgment is required to avoid hardness due to overfill. Repeating this study using an in vivo incubation method is required to determine how overfill will affect implant shells over time in the harsh milieu of a biologic environment.