Dental anxiety is a main barrier to access dental care. Besides the negative feelings experienced by the patient, anxiety leads to behaviours that interfere with dental treatment and decrease therapeutic compliance. The aim was to identify the role of irrational beliefs in triggering the negative affect regarding dental treatments. We hypothesized that irrational beliefs are a predictor for activating the negative affect when people are exposed to images and sounds specific to dental treatment. We used a quasi-experimental design. The Irrational Beliefs Scale (ABS2); Self-Assessment Manikin (SAM), and a dental treatment video showing dental bur were used. The study shows that irrational beliefs do not influence dental anxiety. Many other psychological factors may interfere in this process. Although empirical data supports that anxiety contributes to cognitive activation schemes, we do not know if the activation of cognitive schemes leads to increased joint strength implied.