Investigate the Change in Facial Pain Threshold During Auricular Acupuncture in Healthy Volunteers: A Pilot Study

The effects and biological mechanisms of auricular acupuncture on the human body have been increasingly observed in clinical and experimental studies, particularly the analgesic effects. When the downward neurotransmitter pathway is activated, endogenous opioids (beta endorphins) are released, which inhibit pain perception. Furthermore, according to the gate control theory (spinal segmentation mechanism), auricular acupuncture aids in the activation of pain-suppressive stimuli by myelinated afferent fibers (Aβ), as opposed to stimuli with damage from poorly myelinated (Aδ) or unmyelinated (C) fibers. Besides, according to human physiology, the trigeminal nerve is involved in sensory control of the face, has a branching distribution to the skin of the pinna, and has afferent conduction of mechanical stimuli acting on it. Auricular acupuncture in the Shenmen, Nervous Subcortex, Jaw and Tooth groups has been shown in the Acupuncture 2 textbook of the Faculty of Traditional Medicine - University of Medicine and Pharmacy, Ho Chi Minh City and clinical studies to be effective in reducing facial pain.

This was the first study in Vietnam to investigate the effect of auricular acupuncture on the change in facial pain threshold during auricular acupuncture on acupoints such as Shenmen, Nervous Subcortex, Jaw and Tooth. The findings of the study can be used to supplement scientific evidence regarding the effects of auricular acupuncture in the treatment of clinical facial pain.

The investigators performed a randomized, controlled crossover experiments. A crossover study has two advantages over both a parallel study and a non-crossover longitudinal study. First, the influence of confounding covariates is reduced because each crossover patient serves as their own control. In a randomized non-crossover study it is often the case that different treatment-groups are found to be unbalanced on some covariates. In a controlled, randomized crossover designs, such imbalances are implausible (unless covariates were to change systematically during the study). Second, optimal crossover designs are statistically efficient, and so require fewer subjects than do non-crossover designs (even other repeated measures designs). In our study, the subjects are randomly assigned to two arms of the study which receive different treatments. A crossover trial has a repeated measures design in which each patient is assigned to a sequence of two treatments, one of which is auricular acupuncture, and a placebo test is performed on that volunteer a week later. Wilcoxon sign-rank test, paired T test and Pearson's chi-squared test were used for comparison of means.