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.