Effectiveness of different intrusion modes of maxillary anterior teeth with mini-implants in clear aligner treatment: a three-dimensional finite element analysis.

BACKGROUND: The intrusion of maxillary anterior teeth is often required and there are various intrusion modes with mini-implants in clear aligner treatment. The objective of this study was to evaluate the effectiveness of maxillary anterior teeth intrusion with different intrusion modes, aiming to provide references for precise and safe intrusion movements in clinical practice. METHODS: Cone-beam computed tomography and intraoral optical scanning data of a patient were collected. Finite element models of the maxilla, maxillary dentition, periodontal ligaments (PDLs), clear aligner (CA), attachments, and mini-implants were established. Different intrusion modes of the maxillary anterior teeth were simulated by changing the mini-implant site (between central incisors, between central and lateral incisor, between lateral incisor and canine), loading site (between central incisors, on central incisor, between central and lateral incisor, between lateral incisor and canine), and loading mode (labial loading and labiolingual loading). Ten conditions were generated and intrusive forces of 100 g were applied totally. Then displacement tendency of the maxillary anterior teeth and CA, and stress of the PDLs were analyzed. RESULTS: For the central incisor under condition L14 and for the canine under conditions L11, L13, L23, and L33, the intrusion amount was negative. Under other conditions, the intrusion amount was positive. The labiolingual angulation of maxillary anterior teeth exhibited positive changes under all conditions, with greater changes under linguoincisal loading. The mesiodistal angulation of canine exhibited positive changes under labial loading, while negative changes under linguoincisal loading except for condition L14. CONCLUSIONS: The intrusion amount, labiolingual and mesiodistal angulations of the maxillary anterior teeth were affected by the mini-implant site, loading site, and loading mode. Labial and linguoincisal loading may have opposite effects on the intrusion amount of maxillary anterior teeth and the mesiodistal angulation of canine. The labiolingual angulation of the maxillary incisors would increase under all intrusion modes, with greater increases under linguoincisal loading.

Evaluation of palate-related factors of the effectiveness of microimplant-assisted rapid palatal expansion in late adolescents and adults.

INTRODUCTION: This study investigated the factors of the effectiveness of microimplant-assisted rapid palatal expansion (MARPE) in late adolescents and adults, such as age, midpalatal suture maturation (MPSM) stage, palate length (PL), palatal index (PI), and midpalatal bone thickness (MBT), and at each microimplant position, the palate bone thickness (PBT), the nasal cortical bone thickness (CoTN), the cancellous bone thickness (CaT), and the palate cortical bone thickness (CoTP) were evaluated. METHODS: Cone-beam computed tomography (CBCT) images of 50 patients (mean, 23.30 ± 7.03 years; range, 16-51 years) treated with MARPE were evaluated. Maxillary expansion ratio (MER) was used to assess the MARPE effectiveness and grouped patients into low and high MER groups according to the mean of MER. MER was the ratio of maxillary expansion width to MARPE screw expansion measured in CBCT images. The t-test was used to analyze the differences between the low and high MER groups. The Pearson correlation test was performed to investigate the correlation between MER and age, MPSM stage, PL, PI, MBT, PBT, CoTN, CaT, and CoTP. RESULTS: Age, MPSM stage, and MBT in regions 18 mm and 21 mm behind the incisor foramen correlated negatively with MER ([Formula: see text], - 0.390, - 0.386, and - 0.335, respectively, all [Formula: see text]), whereas PBT and CoTN of anterior microimplant positions correlated positively with MER ([Formula: see text] and 0.418, respectively, all [Formula: see text]). No correlation was observed between other variables and MER. CONCLUSIONS: MARPE effectiveness decreased as age and midpalatal suture maturation stage increased, respectively. Thinner midpalatal suture bone in regions 18 mm and 21 mm behind the incisor foramen, thicker palate bone, and nasal cortical bone of anterior microimplant positions were related to more effective MARPE. CLINICAL RELEVANCE: In patients with older chronological age and later MPSM stages, MARPE effectiveness might be unsatisfactory. Clinicians should carefully evaluate the palate bone thickness before MARPE treatment.