Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 10 2 2023 10 16 58 68 Azamsadat Madani Oral and Maxillofacial Diseases Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. Amirtaher Mirmortazavi Oral and Maxillofacial Diseases Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. Mohammad Bagheri Iraj Department of Prosthodontics, School of Dentistry, North Khorasan University of Medical Sciences, Bojnord, Iran. 2023 07 22 2023 09 30 Introduction: The effectiveness of two soft and hard splint thicknesses in reducing temporomandibular  joint (TMJ) pain and dysfunction was compared.  Materials and Methods: Sixty patients with TMJ pain and dysfunction were randomly  assigned to four groups (n=15); the patients treated with hard occlusal splints of 1 and 3mm thicknesses  were assigned to Groups A and B, respectively, and those treated with soft occlusal splints of  1 and 3mm thicknesses were assigned to Groups C and D, respectively. Maximum mouth opening  (MMO) and the severity of pain based on the visual analog scale (VAS) were assessed before treatment  and after 7, 30 and 90 days.  Results: After both 7 and 30 days, no significant differences were found between the groups for  any variable (P>0.05). However, Group C had a significantly lower MMO compared to Groups A  and B after 90 days (P=0.001). Additionally, and in relation to masticatory muscle pain, Group C  had a significantly higher VAS score than other groups (P<0.05). The VAS score for TMJ pain at  rest was also significantly higher in Group C compared to Groups A and B (P<0.05).  Conclusion: A 3-mm hard occlusal splint seems to be the best treatment to reduce pain and  dysfunction of the TMJ.  Keywords: Temporomandibular disorders; Soft and hard occlusal splints; Pain; Dysfunction. https://jcr.tums.ac.ir/index.php/jcr/article/view/447 https://jcr.tums.ac.ir/index.php/jcr/article/download/447/378