Could administering electricity help patients get numb? Invention of local anesthesia has long been considered a crowning achievement in medicine, but even so, administering it can be difficult. After all, the delivery device is still a needle, and many patients are so afraid of needles they will avoid necessary care. Topical anesthetic can be used, but that adds even more time to the procedure. Patients can sometimes spend upwards of half an hour in the chair simply waiting for the two forms of anesthetic to take effect.
Renewed investigation into transcutaneous electrical nerve stimulation (TENS) may suggest a method to address this problem. Electrical applications for pain control date back to ancient Rome, where standing on an electric fish was reported to relieve pain. Throughout history, although most prominently during the Victorian era up to the early 1900s, applying electricity to the body was thought to provide all kinds of beneficial effects, including pain relief. However, very little scientific methodology or knowledge of anatomy has been applied to these devices.
The first modern TENS device was patented in 1974 not as a pain relief method but as a diagnostic tool for testing the tolerance of patients with chronic pain to electrical stimulation. These patients planned to receive surgically-implanted electrodes in the dorsal column of the spinal cord but reported such a relief of symptoms that the implants were often unnecessary. Soon after the effectiveness of this device became known, many companies began releasing TENS devices for a variety of pain regions, both for consumer use and medical procedures.
The method by which TENS attenuates or blocks pain is not well understood. Studies have shown that stimulating peripheral A-beta sensory fibers reliably suppressed A-delta fiber processing of pain signals, while fMRI studies have indicated the effect goes all the way back to the brain, decreasing pain-related cortical activations. Either way, there are other stumbling blocks to this technology. The characteristics of the skin surface vary from person to person, both physically (i.e. presence of hair) and chemically (conductance, water content etc.) which have complicated its effective use for blocking pain during dental procedures. However, a recent study in the Journal of Biointerfaces suggests a system that homogenizes the application of this technology across patients.
The researchers investigated possible methods by which topical anesthetic could be "boosted" and therefore eliminate the need for needles at all. The most common topical anesthetic is a hydrogel suspension composed of prilocaine and lidocaine, which is absorbed by the tissue lining the mouth to provide the numbing effect. The researchers prepared the hydrogel with a polymer to help it adhere to the inside of the mouth, and applied TENS. This small current potentiates a process called iontophoresis, which enhanced the penetration of prilocaine into the mucosa by a factor of 12, resulting in effective pain inhibition.
This technology holds considerable promise in helping dentists to treat high-fear patients. Many patients avoid the dentist due to fear of both needles and oral pain. For short to mid-length procedures, this new anesthetic technique represents a revolutionary non-invasive approach to anesthesia that could dramatically expand the client base dentists can treat.
Cubayachi, C., Couto, R. O., Gaitani, C. M., Pedrazzi, V., Freitas, O. D., & Lopez, R. F. (2015). Needle-free buccal anesthesia using iontophoresis and amino amide salts combined in a mucoadhesive formulation. Colloids and Surfaces B: Biointerfaces, 136, 1193-1201.
Desantana, J. M., Walsh, D. M., Vance, C., Rakel, B. A., & Sluka, K. A. (2008). Effectiveness of transcutaneous electrical nerve stimulation for treatment of hyperalgesia and pain. Curr Rheumatol Rep Current Rheumatology Reports, 10(6), 492-499.
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