Correlation between pain and hyalinization during tooth movement induced by different types of force

Objectives: To evaluate the correlation between pain and tissue reactions during induced tooth movement (ITM). Materials and Methods: Forty-two male Wistar rats (Rattus norvegicus; similar to 90 days of age, 300 g) were used. The animals were divided into seven groups of six rats each: one control group and six experimental groups subjected to ITM by continuous force (CF) or interrupted continuous force (ICF) for 1, 3, and 5 days. Hyalinization of the periodontal ligament (PL) and occurrence of pain were observed. Animal behavior (walking, climbing, immobile posture, resting/sleeping, and directed face grooming) and the presence of chemical mediators associated with nociception, cyclooxygenase-2 (COX-2), and interleukin-1 beta (IL-1 beta) in the PL were analyzed. Results: There was a moderate positive correlation between hyalinization and the presence of COX-2 (r(s) = 0.404; P < .05) and IL-1 beta (r(s) = 0.429; P < .05). There was a moderate negative correlation between hyalinization and exploratory behaviors (walking, r = -0.586, P < .01; climbing, r = -0.573, P < .01), and a moderate positive correlation between hyalinization and resting/sleeping (r = 0.467; P < .01). Conclusions: The results suggest a correlation between pain and undesirable tissue reactions in ITM.