It is estimated that over 10 million people in the United States suffer from jaw joint and muscle disorders. Artificial temporomandibular joint (TMJ) implants have been used to replace the jaw joint in some patients in an effort to decrease pain and increase jaw function. The safety and effectiveness of these implants, like other medical devices, is overseen by the Food and Drug Administration (FDA), an agency within the Department of Health and Human Services (HHS). Two implants used in the 1970s and 1980s that were later removed from the market caused severe side effects for some patients. In 1998, FDA began to require certain TMJ implant manufacturers sponsoring these devices to demonstrate the implants' safety and effectiveness before receiving approval. Since 1998, four TMJ implants from three sponsors were approved. In response to your request, GAO described (1) the types of concerns raised by FDA and how it addressed these concerns for the implants approved since 1998 and (2) how FDA has monitored sponsors' compliance with conditions of approval. GAO examined documentation related to the four TMJ implants approved by FDA since 1998 and sponsors' annual reports, which FDA uses to monitor compliance with conditions of approval. GAO also interviewed FDA officials, TMJ implant sponsors, and patient advocacy groups.