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Surgery and Cosmetics

Silicone: A History of Uncertainty, a Future of Possibility

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Tuesday, August 02, 2005

Chemical Properties of Silicone

Silicones are a large family of inert and inorganic compounds that possess a repetitive backbone structure of oxygen and silicon, the second-most abundant element in the world.

The term "siloxane" is an acronym for "silicon," "oxygen," and "methane," and when put into long chains with additional organic radicals, these polymers are referred to as "polyorganosiloxanes." This latter group, and more specifically dimethyl polysiloxane (DMPS), is one of the few "medical-grade" silicones that are typically used by dermatologists for injection. Also known as liquid injectable silicone (LIS), this material is injected into facial soft tissue contour deformities by a specific microdroplet technique that causes an immunologic and fibroblastic reaction that leads to collagen deposition and capsule formation around each droplet several weeks after implantation. Silicone, as opposed to other currently popular soft tissue "fillers," is advantageous because its collagen-producing effects are permanent.

The length of the silicon-oxygen backbone determines the viscosity of the synthetic polymer, and thus an increase in the polymer chain will increase the viscosity of the material. In addition, the heat stability of the substance depends on the number of attached carbon atoms, with a greater number of silicon-methyl bonds making the material more heat stable. It is well known that silicone can exist in solid, liquid, and gel forms, allowing for its widespread functionality. The viscosity of silicone is expressed in centistokes (cS), which is a unit of measure representing kinematic viscosity. "Medical-grade" LIS used today is typically 350cS of pure dimethylpolysiloxane fluid, in comparison to the viscosity of water, which is equivalent to 1cS.

The electronic structure of the bonds in the silicon-oxygen backbone allows for an increased bond angle length and thus the formed material can move very freely - more so than if there was a carbon-carbon backbone.1 This property, along with DMPS being inexpensive, easily made, inert, inorganic, and easily stored, makes its potential use very attractive to physicians. Furthermore, when pure, this material is resistant to bacterial growth on its surface. Other beneficial properties of silicone include its mechanical resiliency, biocompatibility, and lack of carcinogenicity.2

Risks of Silicone

However, silicone, and LIS more specifically, are not free of risks. Both have experienced much scrutiny in the scientific and lay communities due to a history riddled with unethical use, improper technique, and anecdotal reports of horrific complications.

Moreover, a sheer lack of scientific data regarding its efficacy and adverse-effect profile has stifled this product's potential therapeutic uses. It is true that there can be complications from LIS, although most of these are inherent to the procedure or related to the technique of the physician. Allergies, granulomas, infections, and migration can occur, yet the most common side effects of liquid silicone injections are minor and mostly attributable to the ineptness of the physician performing the procedure. These include transient erythema, pain, under- or overcorrection, and asymmetry.

Nevertheless, in order to appreciate the possible future of silicone, one must understand its controversial past.

History of Silicone

The grandfather of silicon, Frederic Stanley Kipping, was born in Manchester, England, in 1863. At the turn of the century, he became Chair of Chemistry at University College of Nottingham where he pioneered the study of silicon and coined the term "silicone" to describe a chemical reaction between a ketone and silicon.

Although his many papers on the subject were the cardinal experiments addressing the newly discovered substance, he could not appreciate an application for the material at that time. But it was soon realized during the rubber shortage of World War II that these silicones could be used as greases, water repellents, synthetic rubbers, and hydraulic fluids. Researchers at Corning Glass Works and Dow Chemicals eventually joined forces to form the Dow Corning Corporation (Midland, MI) - the major supplier of silicone products to the U.S. government during World War II as well as the major researcher and manufacturer of silicones throughout the remainder of the 20th century.

Unfortunately, Kipping died in 1949, and was not able to appreciate the profound effect that silicone would eventually have on the future of society.

When the war came to an end, a scientist for Dow Corning - R.R. McGregor - began to investigate other uses for the silicones. These included paints, polishes, and insulation, to name a few.3 One of the first medical applications of silicone at this time took advantage of its ability to prevent liquid from adhering to glass by being used to coat blood-handling glassware and penicillin bottles.4 With more investigation into this material, scientists and physicians alike began to appreciate the vast potential uses. In 1950, De Nicola performed the first documented human silicone implant where a silicone urethra was placed into a patient whose genitals were ravaged from venereal disease.5

Subsequently, other authors began noting their own experiences with silicone. Holter, in 1955, developed a silicone implant for use as a shunt to drain excess fluid in children with hydrocephalus. Around this time, Dow Corning also set a precedent by compounding the first silicone rubber made specifically for medical use that eventually served as an artificial bile duct. Throughout the latter half of the 20th century and beginning of the 21st century, silicone continued to play a pivotal role in many fields of medicine. Its biggest impact has come in the fields of surgery, dermatology, ophthalmology, gynecology, and urology. (See Tables 1-4.)

Many know of Cronin and Gerow and their development, in 1961, of a bag-like prosthesis filled with silicone for the purpose of breast augmentation.6 However, many may not be aware that silicone breast augmentation was first experimented 2 decades earlier by American soldiers in Japan. Dr. M. Sharon Webb documents correspondence with American army officers who were in Japan during World War II, and these men stated that officers administered "cooling fluid" that contained silicone into the breasts of Asian sex workers who desired a more Western appearance.7 It seems that American physicians became aware of this unsanctioned procedure as Asian patients arrived in the United States after the war ended. Initially, the use of silicone for breast augmentation remained a "black market" type of procedure, carried out by non-scientific personnel to cater to the demands of women in the entertainment industry.

As the years progressed, more women took to the practice of having silicone injected into their breasts, and likewise, more side effects of the practice were noted by the medical community. Cystic lesions, mastitis, lumpy or rock-hard breasts, and severe pain were among the many noted adverse reactions.8 It has been argued that much of these sequelae were attributable to the use of non-medical grade silicone in the breasts, the adulterants within, and excessive amounts being injected.9 However, the unsanctioned behavior of injecting patients with "dirty" silicone and the subsequent side effects precipitated an epidemic of fear and distrust regarding silicone and its use in medicine. The state of Nevada ultimately criminalized its use in 1964.

Silicone use for soft-tissue augmentation has never received approval from the U.S. Food and Drug Administration (FDA). When Dow Corning finally developed its first medical-grade silicone, MDX 4-4011, in the early 1970s, it opted not to gain FDA approval because it "could not effectively prevent misuse of the product."10

Clinical investigations of LIS, under FDA-approved and monitored protocol, did take place from 1978 to 1988. Patients selected to be studied had severe facial deformities and were also refractory to other forms of treatment. The results were promising; however, there was one report of massive facial necrosis in a patient who had concomitant immunologic and infectious chronic inflammatory diseases.11 Reports such as this, combined with the knowledge that three New York physicians and one California physician were injecting liquid silicone for facial wrinkles and furrows, prompted the FDA to ban LIS in 1992.

The Microdroplet Technique and the Future of Silicone

It must be noted that the injections of massive amounts of "dirty," adulterated silicone from over 40 years ago were much different than the currently available pure forms of liquid silicone. Furthermore, there are now guidelines for suggested sites of injection, and when performed by responsible physicians this allows for much safer use of the product. For example, lips and breasts should not be injected with silicone.12

Areas that respond well to LIS include the nasolabial and glabellar furrows as well as perioral lines.12 HIV-associated facial lipoatrophy has been another realm of success for LIS where microdroplets are injected into the cheeks and temples to restore the faces of patients damaged by the sequelae of this infectious disease.13 Serial punctures injecting small droplets of LIS into these depressed skin areas over the course of multiple visits can lead to dramatic results. Not only does the use of purified silicone in such small needles decrease the pain associated with injection, but this microdroplet protocol also prevents drifting or shifting of the injected liquid and granuloma formation.14

Drs. Benedetto and Lewis have described a specific protocol that allows for easy and precise injection of LIS while minimizing the common unwanted adverse effects.14 They have found that the Becton Dickinson (Franklin Lakes, NJ) 3/10cc insulin U-100 syringe with a swaged 28-gauge 0.5-inch long Micro-Fine IV needle is better than any other standard syringe for injecting controlled microdroplets of LIS intradermally. Not only does the syringe allow for better control, the swaged needle helps reduce inaccurate dosing because there is no dead space between the hub and barrel. Also, the shorter needle length reduces resistance to the flow of the viscous fluid.

There are many variations of actual technique; however, most dermatologists abide by a protocol similar to the following:

  • After thoroughly cleansing and marking the areas to be injected and positioning the lights to properly illuminate the facial anatomy, needle punctures should be 2-4mm apart.
  • No more than 0.01cc should be injected at each needle insertion.
  • Finger pressure should also be applied immediately after injection to reduce patient bruising.
  • Topical anesthetic 45 minutes prior to injection can also be added to this microdroplet technique for patient comfort.
  • Visits for follow-up injections should be spaced at approximately one-month intervals.

Medical-grade silicone used properly by the microdroplet technique for filling defects such as facial furrows and wrinkles is considered a very effective cosmetic procedure. Drs. Duffy,9 Orentreich,15 and Aronsohn16 adamantly state that they treated well over 100,000 patients safely and effectively with silicone over the course of multiple decades. Dr. David Duffy defends the merits of silicone and contends that "almost no good news regarding the benefits of its use ever appears in the lay or scientific publications."9

Seeing that the potentially therapeutic uses of silicone could be marred by its unsightly past, the American Society of Dermatologic Surgery defended the product by saying, "there was a wealth of clinical experience in dermatology with the use of liquid injectable silicone by the microdroplet technique, which showed its efficacy and safety in many individuals over many years."17

In 1994, the FDA approved silicone oil for certain complicated cases of retinal detachment to prevent blindness. There are currently two FDA-approved LIS available for this indication - Adatosil 5000 (Escalon Medical Corp, Chicago, IL) and Silikon 1000 (Alcon Laboratories, Fort Worth, TX). This approval has allowed dermatologists to use silicone in an off-label manner - specifically for soft-tissue augmentation.

Hexsel et al.12 address the aformentioned history and controversial issues regarding silicone and contend that LIS is a highly useful filler substance for a number of indications. Unfortunately, because the literature is riddled with anecdotal reports of horrific adverse effects of silicone, many physicians remain hesitant to use the product in their practices. However, it must be understood that in almost all of these reports there is a lack of uniformity with respect to the exact nature and quality of material injected, and thus, the true number of adverse cases treated with LIS cannot be known.18

In an attempt to rid silicone of its historical stigma and understand its actual side-effect profile, there are two current trials to obtain FDA-approval for silicone as a soft-tissue augmenting product. Maybe only after success in these trials will much of the medical and lay community see the unadulterated side of silicone.

Table 1. Surgical Uses of Silicone

IV/TPN tubing19
Artificial embolization20
Eustachian tube insufficiency21
Craniofacial defects22
Breast augmentation23
Ear impressions24
Hydrocephalus shunts26
Kienbock's disease28
Biliary stenting29
Tracheobronchial stenosis31
Voice restoration32

Table 2. Dermatologic Uses of Silicone

Soft tissue augmentation33
Painful digit and sole scars35
Hypertrophic scars/keloids36
Tissue expansion37
Bilamellar artificial skin38
Diabetic foot ulcers39
Skin surface impressions40
Prevention of post-graft cobblestoning41
Prevention of onchyocryptosis42

Table 3. Ophthalmic Uses of Silicone

Reconstruction of conjuctival fornices43
Retinal tear/detachment44
Torn cannaliculi45
Symblepharon repair46
Lacrimal system obstructions47
Cataract surgery48
Proliferative retinopathy49
Corneal refractive surgery50

Table 4. Genitourinary Uses of Silicone

Penile prosthesis51
Intrauterine device52
Urinary incontinence53
Laparoscopic sterilization54
Fecal incontinence55


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