Dynamic biomechanical changes of clear aligners during extraction space closure: Finite element analysis.

INTRODUCTION: Clear aligners (CAs) have recently become popular and widely used orthodontic appliances. Research on CA biomechanics has become a focal point in orthodontics to improve the efficiency of CA treatment and address challenging issues, such as extraction. The biomechanical characteristics of CAs in space closure have been reported. However, previous studies have mainly focused on static biomechanical analysis that cannot demonstrate the dynamic biomechanical changes in CAs during space-closing. Given that these biomechanical changes can be significant and have considerable clinical value, this study aimed to investigate these characteristics. METHODS: Sequential extraction space-closing models were derived from included patient data and refined using modeling and CA design software. A finite element analysis was performed to obtain biomechanical raw data. This study introduced a dual coordinate system and space geometry analysis to demonstrate the biomechanical properties accurately. RESULTS: As space closure progressed, the instantaneous tooth displacements increased, indicating an enhanced space closure force because of the increased strain in the CA extraction area. Meanwhile, the central axis of rotation of the anterior teeth continuously moved toward the labial-apical direction, showing a gradually enhanced vertical and torque control effect. CONCLUSIONS: During space closure, CAs undergo specific biomechanical changes, including increased contraction and control forces on both sides of the gap. These biomechanical effects are beneficial to alleviate the roller coaster effect gradually. Meanwhile, more reasonable staging design strategies can be proposed on the basis of this biomechanical mechanism.

Different biomechanical effects of clear aligners in closing maxillary and mandibular extraction spaces: Finite element analysis.

INTRODUCTION: Compared with fixed treatments, clear aligners (CAs) have the advantages of comfort, esthetics, and hygiene, and are popular among patients and orthodontists. However, CAs exhibit control deficiencies in extraction patients because of insufficient root control and retention effects. These deficiencies can magnify biomechanical differences in bimaxillary dentition, further causing different orthodontic requirements between maxillary and mandibular dentition. This study aimed to elaborate on the biomechanical characteristics of bimaxillary dentition in extraction space closure and provided feasible biomechanical compensation strategies for use in clinical practice. METHODS: We constructed a 3-dimensional (3D) bimaxillary model based on patient data. Several 3D modeling-related software was used to generate a standard first premolar extraction model, CAs, and attachments. Subsequently, finite element analysis was performed to demonstrate the biomechanical effects. RESULTS: The maxillary and mandibular dentition showed a roller coaster effect during space closure. Compared with the maxillary dentition, the mandibular posterior teeth exhibited stronger relative anchorage causing greater anterior teeth retraction. The tipping and vertical movements of the anterior teeth were related to tooth length. The longer the anterior tooth, the less tipping and greater vertical displacement occurred. Generally, when having the same retraction distance, the mandibular dentition exhibited greater retroclination and fewer extrusions. Both mechanical and retention compensations should be considered to prevent these unwanted tipping movements. Adding specific attachments to bimaxillary dentitions compensated for the retention and root control deficiencies of CAs. CONCLUSIONS: When applying CAs to extraction patients, different biomechanical effects can present in the bimaxillary dentition because of specific dentition morphologies. To effectively treat these patients, mechanical compensation through overcorrection of the target position should be designed on the basis of bimaxillary control deficiencies, and retention compensation by adding specific attachments should also be considered according to the overcorrections.

Finite element analysis of the biomechanical effect of clear aligners in extraction space closure under different anchorage controls.

INTRODUCTION: Clear aligners (CAs) have attracted increasing attention from patients and orthodontists because of their excellent esthetics and comfort. However, treating tooth extraction patients with CAs is difficult because their biomechanical effects are more complicated than those of traditional appliances. This study aimed to analyze the biomechanical effect of CAs in extraction space closure under different anchorage controls, including moderate, direct strong, and indirect strong anchorage. It could provide several new cognitions for anchorage control with CAs through finite element analysis, further directing clinical practice. METHODS: A 3-dimensional maxillary model was generated by combining cone-beam computed tomography and intraoral scan data. Three-dimensional modeling software was used to construct a standard first premolar extraction model, temporary anchorage devices, and CAs. Subsequently, finite element analysis was performed to simulate space closure under different anchorage controls. RESULTS: Direct strong anchorage was beneficial for reducing the clockwise occlusal plane rotation, whereas indirect anchorage was conducive for anterior teeth inclination control. In the direct strong anchorage group, an increase in the retraction force would require more specific anterior teeth overcorrection to resist the tipping movement, mainly including lingual root control of the central incisor, followed by distal root control of the canine, lingual root control of the lateral incisor, distal root control of the lateral incisor, and distal root control of the central incisor. However, the retraction force could not eliminate the mesial movement of the posterior teeth, possibly causing a reciprocating motion during treatment. In indirect strong groups, when the button was close to the center of the crown, the second premolar presented less mesial and buccal tipping but more intrusion. CONCLUSIONS: The 3 anchorage groups showed significantly different biomechanical effects in both the anterior and posterior teeth. Specific overcorrection or compensation forces should be considered when using different anchorage types. The moderate and indirect strong anchorages have a more stable and single-force system and could be reliable models in investigating the precise control of future tooth extraction patients.

Different biomechanical effects of clear aligners in bimaxillary space closure under two strong anchorages: finite element analysis.

BACKGROUND: Clear aligner (CA) treatment has been gaining popularity, but the biomechanical effects of CAs in bimaxillary dentition have not been thoroughly investigated. Direct and indirect strong anchorages are two common anchorage control methods, but the underlying biomechanical mechanism has not yet been elucidated. This study aimed to investigate the different biomechanical effects of CAs in closing the bimaxillary space under different anchorage controls, further instructing the compensation strategies design and strong anchorage choice in clinical practice. METHODS: Three-dimensional (3D) bimaxillary models of different anchorage controls were created based on cone-beam computed tomography and intraoral scan data. Four first premolars were extracted using 3D modeling software. Finite element analysis was conducted to simulate the space closure process of the CAs. RESULTS: In the two strong anchorage groups, the bimaxillary dentition presented different movement patterns during the space closure process, and the lower dentition was more vulnerable to elastic force. From the vertical view, direct strong anchorage with elastic force had the advantage of flattening the longitudinal occlusal curve and resisting the roller-coaster effects, whereas indirect strong anchorage could lead to a deep longitudinal occlusal curve. From the sagittal view, indirect strong anchorage with metallic ligaments had a greater instantaneous anchorage protection effect, particularly in the lower dentition, which reduced the mesial movement of the posterior teeth by nearly four times that of the direct anchorage group. In addition, indirect strong anchorage presented better anterior teeth torque/tipping control, while direct strong anchorage could aggravate lingual tipping of the upper central incisors. Due to the differences in anterior-posterior anchorage and arch shape, compared with the upper dentition, anchorage preservation and vertical control effects were amplified in the lower dentition. CONCLUSIONS: The biomechanical effects of CAs differed between the two strong anchorage groups. Due to the differences in dentition morphology, anterior-posterior anchorage, and dental arch shape, CAs present different biomechanical effects in bimaxillary space closure. Orthodontists should consider the corresponding mechanical compensation according to specific anchorage control methods and dentitions.

Topographic Cues Guiding Cell Polarization via Distinct Cellular Mechanosensing Pathways.

Cell polarization exists in a variety of tissues to regulate cell behaviors and functions. Space constraint (spatially limiting cell extension) and adhesion induction (guiding adhesome growth) are two main ways to induce cell polarization according to the microenvironment topographies. However, the mechanism of cell polarization induced by these two ways and the downstream effects on cell functions are yet to be understood. Here, space constraint and adhesion induction guiding cell polarization are achieved by substrate groove arrays in micro and nano size, respectively. Although the morphology of polarized cells is similar on both structures, the signaling pathways to induce the cell polarization and the downstream functions are distinctly different. The adhesion induction (nano-groove) leads to the formation of focal adhesions and activates the RhoA/ROCK pathway to enhance the myosin-based intracellular force, while the space constraint (micro-groove) only activates the formation of pseudopodia. The enhanced intracellular force caused by adhesion induction inhibits the chromatin condensation, which promotes the osteogenic differentiation of stem cells. This study presents an overview of cell polarization and mechanosensing at biointerface to aid in the design of novel biomaterials.

Surface Epitaxial Nano-Topography Facilitates Biomineralization to Promote Osteogenic Differentiation and Osteogenesis.

Biomimetic modification of hydroxyapatite on a polymer surface is a potent strategy for activating biological functions in bone tissue engineering applications. However, the polymer surface is bioinert, and it is difficult to introduce a uniform calcium phosphate (CaP) layer. To overcome this limitation, we constructed a specific nano-topographical structure onto a poly(ε-caprolactone) substrate via surface-directed epitaxial crystallization. Formation of the CaP layer on the nano-topological surface was enhanced by 2.34-fold compared to that on a smooth surface. This effect was attributed to the abundant crystallization sites for CaP deposition because of the increased surface area and roughness. Bone marrow mesenchymal stromal cells (BMSCs) were used to examine the biological effect of biomineralized surfaces. We clearly demonstrated that BMSCs responded to surface biomineralization. Osteogenic differentiation and proliferation of BMSCs were significantly promoted on the biomineralized nano-topological surface. The expression of alkaline phosphatase and osteogenic-related genes as well as extracellular matrix mineralization was significantly enhanced. The proposed strategy shows potential for designing bone repair scaffolds.

The UV absorption of graphene oxide is size-dependent: possible calibration pitfalls.

Graphene oxide (GO) is often quantified via its UV absorption, typically at around 230 nm. This is convenient but the effect of the size of GO on the accuracy of this method has been ignored so far. The authors report that the molar absorbance of GO is size-dependent. Data are presented on the absorbance of small (hydrodynamic diameter 1 µm), medium sized (1.5 µm), and large (2.2 µm) GO particles at wavelengths of 210, 230 and 250 nm. In general, linear relationship and good regression fits are obtained, but with different slope depending on size even at the same wavelength. This implies that using the UV absorption-based calibration may cause significant errors in GO quantification. Ultimately, this leads to incorrect dosages and faulty conclusions. This may also explain a variety of inconsistent results obtained in previous biological applications of GO. Graphical abstract The size of graphene oxide (GO) determines its UV absorption and the UV absorption-based calibration (GO-s, GO-m and GO-l represent the GO with small, medium and large size).

Antibiofilm effect of drug-free and cationic poly(D,L-lactide-co-glycolide) nanoparticles via nano-bacteria interactions.

AIM: Recently, nano-bio interactions and their biomedical impacts have drawn much attention, but nano-bacteria interaction and its function are unknown. Herein, we aim to synthesize drug-free and cationic nanoparticles (CNPs) and investigate CNP-bacteria interaction and its antibiofilm effect. MATERIALS & METHODS: The bioactivity of CNPs against Streptococcus mutans was examined by colony-forming units counting and scanning electron microscopy. CNP-bacteria interaction force was measured by atomic force microscopy. RESULTS: CNPs (217.7 nm, 14.7 mv) showed a concentration-dependent activity against bacteria. Particularly, CNPs at 200 µg/ml completely inhibited planktonic bacterial growth and biofilm formation, and disrupted ∼70% mature biofilm. CNP-bacteria interaction force was up to 184 nN. CONCLUSION: CNPs have great potentials for convenient local use for prevention and treatment of bacteria-related oral diseases.

Concentration-dependent protein adsorption at the nano-bio interfaces of polymeric nanoparticles and serum proteins.

AIM: A comprehensive understanding of nanoparticle (NP)-protein interaction (protein corona formation) is required. So far, many factors influencing this interaction have been investigated, like size and ζ potential. However, NPs exposure concentration has always been ignored. Herein, we aim to disclose the correlation of NPs exposure concentration with protein adsorption. MATERIALS & METHODS: Four polymeric NPs systems possessing similar sizes (230 ± 20 nm) but varied ζ potentials (-30 ∼ +40 mv) were prepared. Physicochemical properties and protein adsorption upon NP-protein interaction were characterized. RESULTS: Protein adsorption capacity and adsorbed protein types were NPs concentration-dependent. CONCLUSION: Considering the critical impacts of protein adsorption on NPs delivery, our work could be an urgent warning about the possible risks of dosage adjustment of nanoformulations.