Effect of Vanillin on Emotional Stress and Pain-Related Behaviours Induced by Experimental Tooth Movement in Rats

Abstract Background Pain is a common symptom of orthodontic treatment. Therefore, this study aimed to determine the effect of vanillin on emotional stress and pain-related behaviours induced during tooth movement by observing the behaviours of orthodontic rats and to provide a therapeutic basis for the discomfort caused by orthodontic treatment. Methods A 75 g orthodontic force was applied via an orthodontic appliance to the left maxillary incisors and first molars of 200–250 g male Sprague-Dawley rats. The rats were then administered vanillin in three different ways on days 1, 2, 3, 5, and 7 (via gavage, sniffing, or coating around the gingiva of the orthodontic teeth). Behaviour was evaluated at each time point in an open field based on the number of lines crossed in the first 30 s and 5 min, the number of lines crossed to the centre, the rearing time, the facial grooming time, and the Resistance-to-Capture scores. Results In the experimental orthodontic stimulation, the rats showed anxious, pain-related behaviours such as nervousness, rearing, decreased interest in exploring their surroundings, and reduced mobility. Conversely, in orthodontic rats administered vanillin, anxiety and pain-related behaviours were alleviated, and their mobility was restored. Furthermore, each administration method has the advantages of reducing pain and increasing activity. Conclusion This study revealed that three vanillin administration methods have advantages in alleviating anxiety and pain during experimental tooth movement, which can serve as a reference for clinicians to treat patients with orthodontic pain.