Abstract: Objective: To evaluate the feasibility of third palatal ruga as a reliable reference for clinical mini-screw implant anchorage (MIA) implantation by measuring bone thickness, cortical bone thickness, and mucosa thickness in the third palatal ruga region. Methods: Thirty patients with malocclusion, mean age (18.7±6.5) years, who attended the Department of Orthodontics at Stomatology Hospital of Jilin University between January 2019 and January 2023 were selected. All patients completed the collection of CBCT (cone beam computed tomography) volume and maxillary digital models. The data were analyzed using BLUE SKY PLAN software. Mucosa thickness, were measured on the integrated model at third palatal ruga (TR),and 2 mm anterior and 2 mm posterior to the third palatal ruga (TRA and TRP) at different sagittal planes (mid-palatal suture plane, 3 mm lateral, and 6 mm lateral). Results: In the same coronal plane, bone thickness varied from distal to proximal mid-palate, with a significant reduction at the mid-palatal suture (P<0.05). Cortical bone thickness at the mid-palatal suture was significantly less than that adjacent to the mid-palatal suture (P<0.017). The difference in the mucosa thickness between the mid-palatal suture and the 6 mm lateral to the mid-palatal suture was also statistically significant (P<0.017). In the same sagittal plane, bone thickness increased from anterior to posterior in the region of the mid-palatal suture (P<0.017). The difference in anterior-posterior bone thickness in the area adjacent to the mid-palatal suture was not significant (P>0.05), bone cortical thickness did not change significantly from anterior to posterior (P>0.05), and mucosal thickness did not change significantly from anterior to posterior (P>0.017). Conclusion: For MIA implantation, 8-mm-length MIAs were available in the third palatal ruga region except for the mid-palatal suture, in which neck-length 1.5 mm MIAs were available 3 mm lateral to the mid-palatal suture, and neck-length 2 mm MIAs were available 6 mm lateral to the mid-palatal suture. CBCT examinations were necessary for MIA implantation at the mid-palatal suture to avoid damaging the nasopalatal canal. When MIA implantation is performed next to the mid-palatal suture in the region of the third palatal ruga, this area can be considered a safe area, thus reducing the need of CBCT examinations. The third palatal ruga is a reliable marker for MIA implantation, being closer to the safety zone and easier to locate than the tooth-adjacent points.

Key words: mini-screw implant anchorage, third palatal ruga, bone thickness, cortical bone thickness