Abstract: PURPOSE: To investigate the role of visual analogue scale (VAS) and pain-related factors, like tumor necrosis factor-alpha (TNF-α), interleukin-8 (IL- 8), interleukin-6 (IL-6) and interleukin-1 beta (IL-1β) in evaluation of the impact of different orthodontic forces on human dental pulp in patients who underwent fixed dental treatment. METHODS: From January 2014 to April 2015, 156 patients with maxillary bilateral premolar treated with tooth fixed were randomly divided into 4 groups, 42 patients in control group, 40 patients in 100 g-force group, 40 patients in 150 g-force group, and 39 in 200 g-force group. VAS was used to evaluate before and after removed. TNF-α, IL-8, IL-6 and IL-1β in pulp tissues were measured by ELISA and pathological changes of pulp were observed on HE staining sections. The data were analyzed with SPSS 13.0 software package. RESULTS: Except for the control group, all patients in other groups had pain after 1-7 days, and the pain peaked at 3~5 days. The pain reaction disappeared on 10th day, and VAS increased in a force dependent manner (P<0.05). TNF-α, IL-8, IL-6 and IL-1β were higher in different force groups than in control group after 1~2 weeks of treatment, and in a force dependent manner (P<0.05). After 3~4 weeks, the expression of IL-8, IL-6 and IL-1β returned to normal (P> 0.05). Except for the control group, blood vessels on the pulp tissue increased and thickened at 1 week after application of force. Occasionally, odontoblast nucleus was enlarged and the nuclear chromatin and cytoplasmic basophilic staining were enhanced, some odontoblasts displayed vacuolar degeneration, connective tissue in the central pulp presented edema; with the increase of applied force, the changes above mentioned became more obvious, in a force dependent way. CONCLUSIONS: The larger the sustained force, the pain, pain-related factors and pathological changes became more obvious, but restored to normal within 3 weeks.

Key words: Visual analog scale, TNF-α, IL-8, IL-6, IL-1β, Orthodontic force, Dental pulp