The effects of lingual buttons, precision cuts, and patient-specific attachments during maxillary molar distalization with clear aligners: Comparison of finite element analysis.

INTRODUCTION: This study aimed to analyze the biomechanical effects of the combined use of clear aligners (CA) and auxiliaries (precision cuts, lingual buttons, and patient-specific attachments) on mesial tipping and extrusion of the premolars during maxillary molars distalization. METHODS: Three-dimensional finite element method was employed to simulate clinical scenarios of CA with different auxiliaries for molar distalization. As such, 200 g of distal force was applied to the microimplants from the notches, lingual buttons, and hooks. Orthodontic tooth movement and the hydrostatic pressure in the periodontal ligament were compared. RESULTS: Adding auxiliaries can provide the maxillary arch anchorage and promote the distal tipping of premolars and retroclination of maxillary incisors. In contrast, this effect was more pronounced in patient-specific attachment applications than in other types of auxiliaries. The independent application of the CA caused mesial tipping and extrusion of the premolar and also caused the incisor proclination. CONCLUSIONS: The anchorage loss caused by the CA alone could be alleviated with the assistance of auxiliaries. Notably, patient-specific attachments further reinforce the anchorage of the anterior arch by incorporating anchor teeth as 1 anchorage unit.

Temporal and spatial effects on C-reactive protein's regulation of inducible nitric oxide synthase production in periodontal disease.

BACKGROUND: Inducible nitric oxide synthase (iNOS) is associated with inflammation and osteoclastic differentiation in periodontal disease. This study was conducted to compare the time-dependent variation in iNOS production between the gingiva and other periodontal tissues and to explore the potential association with C-reactive protein (CRP) in early periodontal disease. METHODS: Ligature-induced periodontal disease models (0-14 days) were established in wild-type and CRP knockout rats. Changes in CRP, iNOS, and autophagy levels were examined in the gingiva and other periodontal tissues. Macrophages were treated with lipopolysaccharide and chloroquine to explore the role of autophagy in iNOS production. iNOS, CRP, and autophagy-related proteins were analyzed using Western blotting, immunostaining, and enzyme-linked immunosorbent assays. mRNA expression was detected by quantitative real-time polymerase chain reaction. Hematoxylin and eosin staining was used for histological analysis. Cathepsin K immunostaining and microcomputed tomography of the maxillae were performed to compare alveolar bone resorption. RESULTS: iNOS and CRP levels increased rapidly in periodontal tissues, as observed on Day 2 of ligature, then decreased more rapidly in the gingiva than in other periodontal tissues. CRP deficiency did not prevent iNOS generation, but effectively accelerated iNOS reduction and delayed alveolar bone loss. The CRP effect on iNOS was accompanied by a change in autophagy, which was reduced by CRP knockout. CONCLUSIONS: The regulation of iNOS by CRP shows temporospatial variation in early periodontal disease and is potentially associated with autophagy. These findings may contribute to the early detection and targeted treatment of periodontal disease.

Efficacy of various multi-layers of orthodontic clear aligners: a simulated study.

BACKGROUND: In the invisible orthodontic treatment, composite thermoforming film materials have become the focus of orthodontic clear aligners. The orthodontic efficacy of clear aligners which consisted of multi-layers materials remains unclear. This study aims to evaluate the biomechanical effects of various multi-layers of clear aligners on en-mass retraction of maxillary anterior teeth. METHODS: A patient-specific 3D non-linear finite element model numerical analysis was constructed to simulate the en-mass retraction of maxillary anterior teeth with clear aligner after extraction of the first premolars. Four kinds of multi-layers clear aligners with different proportion of film materials were simulated. The biomechanical responses of four different clear aligners on invisible orthodontics were calculated. The tooth displacement in all directions, the hydrostatic pressure of periodontal ligament, the orthodontic deformation of clear aligner, and the stress distribution of alveolar bone were compared and investigated. RESULTS: In all experimental models, the maximum equivalent deformation of alveolar bone, the vector displacement of tooth and the compressive/tensile stress of periodontal ligament decreased with the increase of soft layer thickness. The elastic strain of clear aligners also decreased with the increase of the ratio of soft/hard layers. CONCLUSIONS: The multi-layers clear aligner is better than the single-layer clear aligner in tooth movement, stress distribution of periodontal ligament and mechanical loading of alveolar bone, especially when the ratio of soft layer to hard layer is more than 50%. Moreover, the side effects of the multi-layers clear aligner are significantly less than those of the single-layer one.

Assessment of labially impacted canines traction mode with clear aligners vs. fixed appliance: A comparative study based on 3D finite element analysis.

Purpose: The objective of this study was to evaluate and compare the biomechanical differences between clear aligner and fixed appliance in the traction of labially impacted canines based on 3D finite element analysis. Methods: A series of patient-oriented finite element models were constructed, including a maxillary dentition with a right labially canine, maxilla, periodontal ligaments, traction attachments, and clear aligners. The two most common clinical scenarios were investigated: Scenario A: impacted canine (distal) and Scenario B: impacted canine (mesial). For each clinical scenario, three traction models with clear aligners and one fixed appliance model were established. Results: In all four models, the impacted canines exhibited similar initial displacement tendencies of mesially rotated in Scenario A and distally rotated in Scenario B, and with small differences in periodontal ligament stress magnitude. However, the sum of the periodontal ligament stresses of the anchorage teeth in the clear aligner mode was in the range of 56.28-76.21 kPa and in the fixed appliance mode was in the range of 6.61-7.22 kPa. The maximum value of initial displacement of the anchorage teeth in the clear aligner mode was in the range of 13.71-19.72 µm, while in the fixed appliance mode was 3.10-3.92 µm. Conclusion: For impacted canines, clear aligner mode and fixed appliance mode have little difference in biomechanical effect. However, the anchorage teeth in the clear aligner mode endure higher stress and show a more pronounced displacement tendency. In addition, the biomechanical effects of different clear aligner traction models are various but not obvious.

Biomechanical Effects of 3D-Printed Bioceramic Scaffolds With Porous Gradient Structures on the Regeneration of Alveolar Bone Defect: A Comprehensive Study.

In the repair of alveolar bone defect, the microstructure of bone graft scaffolds is pivotal for their biological and biomechanical properties. However, it is currently controversial whether gradient structures perform better in biology and biomechanics than homogeneous structures when considering microstructural design. In this research, bioactive ceramic scaffolds with different porous gradient structures were designed and fabricated by 3D printing technology. Compression test, finite element analysis (FEA) revealed statistically significant differences in the biomechanical properties of three types of scaffolds. The mechanical properties of scaffolds approached the natural cancellous bone, and scaffolds with pore size decreased from the center to the perimeter (GII) had superior mechanical properties among the three groups. While in the simulation of Computational Fluid Dynamics (CFD), scaffolds with pore size increased from the center to the perimeter (GI) possessed the best permeability and largest flow velocity. Scaffolds were cultured in vitro with rBMSC or implanted in vivo for 4 or 8 weeks. Porous ceramics showed excellent biocompatibility. Results of in vivo were analysed by using micro-CT, concentric rings and VG staining. The GI was superior to the other groups with respect to osteogenicity. The Un (uniformed pore size) was slightly inferior to the GII. The concentric rings analysis demonstrated that the new bone in the GI was distributed in the periphery of defect area, whereas the GII was distributed in the center region. This study offers basic strategies and concepts for future design and development of scaffolds for the clinical restoration of alveolar bone defect.