Evaluation of Optimal Insertion Sites and Angles for Orthodontic Mini-Implants at the Anterior Nasal Spine Region Based on Cone-Beam Computed Tomography

Background: To infer the optimal angulation and height level of mini-implant insertion in the anterior nasal spine (ANS) region from alveolar bone depth (BD) and labial cortical bone thickness (CBT) through cone-beam computed tomography (CBCT), the influences of sex, age, and growth pattern on BD, CBT, and the starting point of the ANS were examined. Material and methods: BD and CBT were measured on CBCT median sagittal images at specific angles (0, 15, 30, 45, and 60 degrees) to simulate the angulation of insertion. The height level of the first axial image with obvious bone ridge was recorded as the start of ANS. Results: The average height of ANS start was 9.42 mm from the alveolar bone crest between the central incisors. The variations in height level and insertion angle combined, or either of them individually, significantly influenced BD and CBT, demonstrating overall decreasing trends (p < 0.001). BD was not influenced by sex, age, or growth pattern (p > 0.05). However, CBT was found to be correlated with sex and growth pattern, while the height level of ANS start was associated only with growth pattern, particularly in hypodivergent patients (p < 0.05). Conclusion: The recommended insertion height level is 14-16 mm from the alveolar bone crest and the recommended angulation is 30-45(degrees). An innovative inequity in the relationship between a certain height level and the insertion angulation is proposed.