Silicone breast implants are thicker than water.

Abstract

Sir: Silicone gel breast implants have conventionally been categorized by volume in cubic centimeters (cm3/ml). This tradition has persisted until McGhan started manufacturing their anatomical cohesive gel implants. Since 2001, all McGhan implants, round or anatomical, are categorized in mass (g), whereas the Mentor implants remained unchanged with the volume (cm3/ml) categorization. The McGhan representatives, however, maintain that their silicone gel breast implants measured in grams can be virtually taken as the same as cm3/ml. They believe that the mass:volume ratio of these implants is close to 1:1, much like water. Nonetheless, the final breast sizes of augmentation, mammaplasty, or reconstruction seem to be smaller than expected when assuming mass equals to volume. We therefore acquired the most commonly used breast implants and measured their actual mass, volume, and density. The implants evaluated included McGhan (Styles 410, CML, MLP, SLD) and Mentor (Styles CPG, Siltex, SR). Investigations or any such activities pertinent to producing this study were carried out to a high ethical standard. Implants were measured on digital scales for their actual mass (g). With controlled temperature at 20°C, each implant was dipped into a full beaker containing pure ethanol (density = 0.7891). As the density of any implants is higher than pure ethanol, all implants sink. Based on the Archimedes principle of displacement, volume of the displaced ethanol captured would equal to volume of the sink implant. Density of each implant was subsequently calculated from the actual mass and the displaced ethanol volume (g/ml). Both McGhan’s (Table 1) and Mentor’s (Table 2) textured anatomical, textured round, and smooth round implants were examined. Table 1 demonstrates McGhan implants’ stated mass, actual mass, volume, density, and discrepancy. The discrepancy, varies from 7 to 15 ml, is to highlight the difference between the measured volume and the stated mass.Table 1: Four Models of McGhan Breast Implants with Their Stated Mass, Actual Mass, Volume, Density, and DiscrepancyTable 2: Three Models of Mentor Breast Implants with Their Mass, Stated Volume, Actual Volume, and DensityIn 2009, Allergan sold 287 million US dollar worth of breast aesthetic products.2 Allergan and Mentor dominated the global medical aesthetic devices market with a combined share of 40%.3 The categorization method McGhan adopted has significant impact on global breast surgery. Our observation of the final breast size disparity caused by this policy was confirmed by the experiment. All silicone breast implants tested are denser than water. Moreover, the density of silicone implants is not always uniform. Even within the same model of implants (McGhan Style 410), their densities vary from 1.02 to >1.07 g/ml depending on the mass of the implants (Table 1). Furthermore, textured implants seem to be slightly denser than the smooth implants with similar mass. This, however, needs to be proven with a bigger scale of study. Interestingly, different models of silicone gel do not show much difference with their densities. McGhan Styles 410 and CML contain cohesive gel, known to have a tighter molecular bonding resulting in a more solid material, and have similar densities as MLP and SLD containing responsive gel. This finding perhaps is not conclusive as the volumes of the samples were merely around 300 ml. We have demonstrated that silicone breast implants are denser than water, and the variation of densities is inversely proportional to the implant sizes. This is observed both in McGhan and Mentor implants. This should be kept in mind by all breast surgeons. ACKNOWLEDGMENT We thank Device Technologies, NSW, Australia. DISCLOSURE The authors have no financial interest to declare in relation to the content of this article. The Article Processing Charge was paid for by the authors.