Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 6 3 2020 02 08 122 128 Mahdie Chavoshzadeh Natanzi School of Dentistry, Shahed University, Tehran, Iran. Maryam Azimi Zavaree Department of Prosthodontics, School of Dentistry, Shahed University, Tehran, Iran. Mehran Torabi Center of Excellence for Railway Engineering, Sciences and Technology University, Tehran, Iran. Farnaz Taghavi Damghani Department of Prosthodontics, School of Dentistry, Shahed University, Tehran, Iran. Seyed Mohammad Reza Hakimaneh Department of Prosthodontics, School of Dentistry, Shahed University, Tehran, Iran. Sayed Shojaedin Shayegh Department of Prosthodontics, School of Dentistry, Shahed University, Tehran, Iran. Farnoosh Taghavi Damghani Department of Prosthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2019 12 27 2020 01 10 Purpose: One of the required information in rehabilitating the occlusal plane in dentistry is the radius of Monson’s sphere, which like other anatomical indices varies in different races. The purpose of this study was to determine the radius of the Monson’s sphere in a group of Iranian. Materials and Methods: 45 Iranian subjects (19 males & 26 females) aged from 18 to 25 were selected for this study. The x,y,z coordinates of cusp tips of all mandibular teeth except for the third molars obtained with a 3-dimensional digitizer, were used to derive a spherical model of the occlusal surfaces’ curvature. From the best interpolating sphere, the radii of the Monson’s sphere was computed. Results: Although all of the computed variables were greater in men, the occlusal curvature of mandibular arch was not influenced by gender. The mean radius of the Monson’s sphere was 111.5mm (121mm in men and 104mm in women which was closer to the classic value of 4 inch, confirming Monson’s observations). Conclusion: The average radius of the Monson’s sphere in this study was greater than the classic 4 inch value proposed by Monson and this result may suggest racial differences in the normal dental arch form that is important in occlusal rehabilitation. Although more researches are necessary in future to improve treatment results. Keywords: Occlusal plane; Monson’s sphere; Curve of spee; Curve of wilson; 3-dimensional digitizer; Iranian adults. https://jcr.tums.ac.ir/index.php/jcr/article/view/304 https://jcr.tums.ac.ir/index.php/jcr/article/download/304/272