Saturday, October 18, 2008

Facial Implants - cheeks, chin, jaw

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Breast implants at least in the US come in only 2 forms, a silicone (plastic like shell) containing either salt water or silicone gel (a mollases or jello thick substance). Facial implants for bone augmentation come in greater variety of materials - silicone, goretex and porex medpor. The first 2 do not develop tissue ingrowth by surrounding tissue, thus they are easier to remove at a future date should the need arise. However they can also shift in position at any future date since there is little or no ingrown tissue to keep them in place. Porex Medpor does develop tissue ingrowth or incorporation thus the potential for shifting or infection are much less at a future date. In the absence of infection porex implants are fixed in position within a few weeks after placement by this ingrowth. Those patients with silicone or goretex need to take antibiotics prior to any dental procedure while porex patients do not. This is because the body does not treat incorporated ingrown implants as foreign bodies.

In animal studies it has been shown that if a silicone implant is exposed by trauma it must be removed. If a porex implant is exposed by trauma the surrounding skin will grow over the defect and cover the exposed implant because it is incorporated by tissue ingrowth.

Coral has also been used and is called hydroxyappetite. In the absence of movement or infection adjacent bone will grow into hydroxyappetite. Thus, it too gets incorporated eventually becoming completely replaced by adjacent bone ingrowth. The problem with coral is it is much harder to work with in solid form because it is so brittle. A paste form has been described but its use is hampered by its inability to maintain a desired shape before ingrowth is completed.

The advantages of silicone are ease of removal and ease of placement through a smaller incision. The disadvantages of porex medpor are they can be technically hard to remove, until incorporation is completed they are as much a foreign body as non-porous silicone, the material is much less pliable than silicone so if not softened at the time of placement to achieve a custom fit they can rock even after incorporation is complete. The porex medpor implants therefore have a smaller margin for error in terms of an exact fit compared to more pliable silicone implants. Even though the silicone and goretex are easier to remove defects after removal can be as bad or worse than those after porex medpor implant removal. The chin muscle may never reattach to it's original position after chin implant removal and the capsule around a silicone chin implant can collapse after implant removal resulting in a variety of chin deformities.

Goretex Chin Implant

Silicone Chin Implant

Porex Medpor Chin Implant (note the multiple small holes over the entire implant that allow tissue ingrowth and that the implant comes in 2 pieces to allow placement of the stiff implant via a smaller incision)

PEEK(polyetheretherketone) is a recent addition to the surgical implant world. It is used mostly by orthopedic surgeons to replace metallic implants because it has comparable strength for weight bearing bones but unlike metal implants x-rays can go through them and patients with them can get MRIs. It is non-porous and has to be custom made as it cannot be bent or shaped in the operating room. I prefer medpor because it is porous polyethylene so you get vascular ingrowth and it can be temporarily heat softened so you can shape it to the bone surface contour at the time of surgery. It comes in a variety of shapes and sizes to accommodate facial structures and I am not sure you currently have that kind of choice with PEEK implants.

Addendum August 29, 2012:
A retrospective review 662 rhinoplasty procedures performed by 3 faculty surgeons at the University of Colorado from 1999 to 2008 was published this week. The incidence of infection after surgery was 2.8% (19 of 662 patients). In each case of infection, alloplastic material (an implant) had been used. Infections occurred in 20% of rhinoplasty procedures in which medpor implants were used. In patients in whom a goretex implant was used alone, the infection rate was 5.3%. Exposure of the implant developed in 12% of patients in whom an implant was used during surgery. Factors notably not associated with infection on bivariate analysis included sex, surgeon, purpose of procedure (functional vs cosmetic), current tobacco use, or history of cocaine use. These findings did not agree with previous studies regarding the use of medpor in rhinoplasty but did agree with those regarding the use of goretex.

Addendum April 18, 2013:
I just removed an infected silicone nasal bridge implant used to augment an Asian nose. The implant was placed 10 years ago and probably became infected after an injection near the implant less than a year ago. Now I know why I am biased against using silicone implants in the nose.

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