According to Google Health, peripheral neuropathy is most easily defined as "a problem with the nerves that carry information to and from the brain and spinal cord." This can cause pain, loss of all or some sensation, and an inability to control muscles. The three main types of nerves that can be affected by peripheral neuropathy are sensory (those that carry sensations), motor (those that control muscles), and autonomic (those that carry information to organs and glands). Depending on the severity of the peripheral neuropathy a person is experiencing, only one, or in severe cases, all three nerves can be affected. Symptoms include sensation changes, movement difficulties, lack of muscle control, and loss of muscle tissue. While peripheral neuropathy is generally the most serious side effect of denture creams, leukopenia (a drop in white blood cells) and neutropenia (not having enough of a specific type of white blood cells, called neutrophils or granulocytes), can also cause serious health issues and make someone extremely vulnerable to infection.
In a 2008 study published in the American Academy of Neurology journal and conducted by Dr. Sharon P. Nations and other researchers at the University of Texas Southwestern Medical Center, zinc levels in denture cream products like Fixodent and Poligrip can diminish the amount of copper in the body. According to this study, "chronic, excess zinc intake can result in copper deficiency and profound neurologic disease." The study identified patients who wore dentures and used large or excessive amounts of denture cream (two tubes a week) and experienced such symptoms as weakness in the hands, poor balance, cognitive decline, and urinary incontinence. The patients showed "mild neurologic improvement" after stopping their denture cream use.
In a second study published in NeuroToxicology in August of 2009, eleven patients with a progressive myelopolyneuropathy and unexplained hypocupremia with hyperzincinemia were examined. The amount of denture cream they used on a regular basis was compared with the levels of copper and zinc in their blood stream. Denture cream was the source of excessive zinc in 100% of the patients. According to the study, "neurodegeneration of the central and peripheral nervous system associated with hypocupremia (lack of copper) and hyperzincinemia (high amount of zinc) has been widely recognized. Their copper and zinc levels normalized after stopping denture cream use, further confirming that this is the source of high zinc. Inappropriate use of denture cream appears to be the sole source of excessive zinc in these patients."
Unfortunately, the FDA currently classifies denture cream as a Class I medical device and does not require the manufacturers to add ingredients or warnings on the labels of their products. Proctor & Gamble has recently added information to their denture cream website about the potential risk of problems from zinc in Fixodent, advising users to apply as little of the adhesive as possible. However, the company has given no indication that they will issue a Fixodent recall or reformulate their products to remove zinc. On February 18, 2010, GlaxoSmithKline issued a Consumer Advisory Warning regarding the "potential health risks associated with long term, excessive use of zinc-containing denture adhesives" and took a voluntary action to cease production of its zinc-containing denture creams. According to GlaxoSmithKline’s statement, consumers who have been using zinc-containing Super PoliGrip "Original", "Ultra Fresh" or "Extra Care" for several years in greater amounts than directed on the package should stop using the product immediately and see their physician.