Discomfort and bite force in painful masseter muscles after intramuscular injections of local anesthetic and saline solution.

Thirty women with a history of daily pain in the masseter muscles were injected with either lidocaine or saline. The participants were told that they were being given an anesthetic injection to reduce their muscular discomfort. The dentist performing the injections did not know which fluid was used. The discomfort in the masseter muscle was assessed by using Borg's new rating scale before and 10 minutes after injection. The evaluation was followed up on day 1, day 3, and day 7. Bite force was registered between the first molars on the injection side. When scale values were compared individually within groups before and after injection, a significant decrease in discomfort was found in both groups, with the exception of day 1 for the lidocaine group and days 1 and 3 in the saline group. The total lidocaine and saline groups assessed the discomfort similarly except on day 3 when the lidocaine group showed significantly less discomfort. The intraindividual force values increased significantly after injection in the saline group. This effect was not found in the lidocaine group. Despite the minor tendencies for lidocaine to have a better effect, the placebo effect was considered to be high and important.