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.

Pain and root resorption due to surgical interventions to accelerate tooth movement in orthodontics: A systematic review and meta-analysis.

BACKGROUND: There are several publications that show the efficacy of surgical interventions in accelerating the rate of tooth movement in orthodontics. Consequently, possible adverse effects must also be evaluated. OBJECTIVES: The aim of the present study was to compare the perception of pain and root resorption between orthodontic treatment with a surgical acceleration intervention vs. conventional orthodontic treatment. MATERIAL AND METHODS: An electronic search was conducted in the MEDLINE, Scopus, Web of Science (WoS), ScienceDirect, Cochrane Library, and Virtual Health Library (VHL) databases up to September 12, 2022. Randomized or non-randomized, controlled, parallel-arm or split-mouth clinical trials were included. Fixed-and random-effects meta-analyses were performed with regard to heterogeneity. The risk of bias (RoB) was assessed using the RoB 2.0 and ROBINS-I tools. RESULTS: A total of 1,395 articles were initially retrieved, 40 studies were finally included in the review and 15 studies were eligible for quantitative analysis. The meta-analysis showed a significant difference in pain perception between acceleration surgery vs. conventional orthodontics at 24 h (p = 0.040); however, this difference was not significant at 7 days (p = 0.080). Overall, the patients who underwent any acceleration procedure presented significantly less resorption as compared to those who were applied conventional treatment (p < 0.001). A similar significant difference was found in retraction movements (p < 0.001) and alignment movements (p = 0.030). CONCLUSIONS: In the first 24 h, surgical interventions for the acceleration of tooth movement produce a greater perception of pain as compared to conventional orthodontic treatment, but the perception is similar after 7 days. Acceleration surgery results in less root resorption - in alignment movements, and especially in retraction movements.

Extracellular Matrix Remodelling of the Periodontium under Orthodontic Force.

As the biological mechanisms of orthodontic tooth movement have been explored further, scholars have gradually focused on the remodelling mechanism of the extracellular matrix (ECM) in the periodontal ligament (PDL). The ECM of the PDL consists of various types of collagens and other glycoproteins. The specific process and mechanism of ECM remodelling during orthodontic tooth movement remains unclear. Collagen I and III, which constitute major components of the PDL, are upregulated under orthodontic force. The changes in the contents of ECM proteins also depend on the expression of ECM-related enzymes, which organise new collagen fibre networks to adapt to changes in tooth position. The matrix metalloproteinase family is the main enzyme that participates in collagen hydrolysis and renewal and changes its expression under orthodontic force. Moreover, ECM adhesion molecules, such as integrins, are also regulated by orthodontic force and participate in the dynamic reaction of cell adhesion and separation with the ECM. This article reviews the changes in ECM components, related enzymes and adhesion molecules in the PDL under orthodontic force to lay the foundation for the exploration of the regulatory mechanism of ECM remodelling during orthodontic tooth movement.

Surface alterations and compound release from aligner attachments in vitro.

AIM: The aim of the present study was to assess the alterations in morphology, roughness, and composition of the surfaces of a conventional and a flowable composite attachment engaged with aligners, and to evaluate the release of resin monomers and their derivatives in an aqueous environment. METHODS: Zirconia tooth-arch frames (n = 20) and corresponding thermoformed PET-G aligners with bonded attachments comprising two composite materials (universal-C and flowable-F) were fabricated. The morphological features (stereomicroscopy), roughness (optical profilometry), and surface composition (ATR-FTIR) of the attachments were examined before and after immersion in water. To simulate intraoral use, the aligners were removed and re-seated to the frames four times per day for a 7-day immersion period. After testing, the eluents were analyzed by LC-MS/MS targeting the compounds Bis-GMA, UDMA, 2-HEMA, TEGDMA and BPA and by LC-HRMS for suspect screening of the leached dental material compounds and their degradation products. RESULTS: After testing, abrasion-induced defects were found on attachment surfaces such as scratches, marginal cracks, loss of surface texturing, and fractures. The morphological changes and debonding rate were greater in F. Comparisons (before-after testing) revealed a significantly lower Sc roughness parameter in F. The surface composition of the aligners after testing showed minor changes from the control, with insignificant differences in the degree of C = C conversion, except for few cases with strong evidence of hydrolytic degradation. Targeted analysis results revealed a significant difference in the compounds released between Days 1 and 7 in both materials. Insignificant differences were found when C was compared with F in both timeframes. Several degradation products were detected on Day 7, with a strong reduction in the concentration of the targeted compounds. CONCLUSIONS: The use of aligners affects the surface characteristics and degradation rate of composite attachments in an aqueous environment, releasing monomers, and monomer hydrolysates within 1-week simulated use.

Effect of bone-marrow-derived mesenchymal stem cells on the rate of orthodontic tooth movements in rabbits.

Mesenchymal stem cells from bone marrow, such as bone marrow aspirate concentrate (BMAC) and cultured and isolated bone marrow mesenchymal stem cells (BM-MSCs), have been used as therapeutic alternatives to enhance remodeling in the bone. OBJECTIVE: This study aimed to evaluate the effects of BMAC and BM-MSCs on orthodontic tooth movements in rabbits. METHODS: A100- gram nickel-titanium closed-coil springs were used to initiate orthodontic tooth movement of the lower first premolars in 35 male New Zealand rabbits for 21 days. Using a split-mouth design, autologous BMAC or BM-MSCs were submucosally injected into the right sides of the lower jaw, while the left sides served as the control. On days 7, 14, and 21, a three-dimensional digital model scan was used to measure the amount of tooth movement. The microfocus computed tomography (Micro-CT) and histological findings were examined on day 0 as the baseline measurement and on days 7, 14, and 21. RESULTS: Compared to the control group, the quadrant receiving BMAC and BM-MSCs had a considerably greater amount of tooth movement. Histomorphometric analysis revealed that both BMAC and BM-MSCs had significantly higher numbers of osteoclasts and active bone-resorptive lacunae. The resorptive changes were greater in the BMAC and BM-MSCs groups than in the control group. CONCLUSION: The submucosal injection of BMAC and BM-MSCs accelerates orthodontic tooth movement (OTM) by decreasing bone density and supplying more osteoclast progenitor cells.

The effect of vitamin E incorporated into injectable platelet-rich fibrin on orthodontic tooth movement in rabbits.

To evaluate the effects of injectable platelet fibrin (iPRF) and combined vitamin E-iPRF on orthodontic tooth movement (OTM) rates in rabbits, 35 male New Zealand white rabbits were involved in this study using splitmouth design. OTM was carried out on the mandibular first premolar using 100g nickel titanium closing coil. Right side served as study group, isolated iPRF in one group and combined vitamin E-iPRF in other group was injected buccally and lingually (iPRF group, Vit E-iPRF group), and left side acted as positive control group (CG) by injecting normal saline (positive CG). The rate of OTM was measured using intra-oral scanner on days 7,14 and 21. Histological and Micro CT scan were examined on days 0, 7, 14 and 21. The iPRF and combined Vitamin E-iPRF demonstrated significant greater rate of OTM on days 7 and 14 in comparison to control group, only significant differences between iPRF and combined vitamin E-iPRF were seen on day 14. In all time intervals as compared to the CG, the number of osteoclasts was significantly higher in the isolated iPRF and combined vitamin E-iPRF groups. Significant reduction in bone volume fraction (BV/TV) was demonstrated in iPRF and combined vitamin E-iPRF groups in all time points, however, non-significant differences were found in trabecular thickness (Tb.Th) and trabecullar separation (Tb.Sp). Local injection of iPRF and combined vitamin E-iPRF showed temporary increase in the rate of OTM.

Orthodontic maxillary molar movement-induced zygomatic pillar remodeling and its consequences on occlusal characteristics and stress distribution.

OBJECTIVE: We aimed to evaluate changes in the zygomatic pillar during orthodontic treatment involving premolar extraction, analyze the effects of maxillary first molar movement on zygomatic pillar remodeling, and examine occlusal characteristics and stress distribution after remodeling. METHODS: Twenty-five patients who underwent premolar extraction were included in the study. The zygomatic pillar measurement range was defined, and cross-sectional areas, surface landmark coordinates, alveolar and cortical bone thicknesses, and density changes were assessed using Mimics software based on the cone-beam computed tomography scans taken before (T0) and after the treatment (T1). Multiple linear regression analysis was performed to determine the correlation between changes in the zygomatic pillar and maxillary first molar three-dimensional (3D) movement and rotation. Additionally, the correlation between pillar remodeling and occlusal characteristics was analyzed by Teetester. Pre- and post-reconstruction 3D finite element models were constructed and loaded with an average occlusal force of two periods. RESULTS: The morphological and structural remodeling of the zygomatic pillar after orthodontic treatment involving premolar extraction showed a decreased cross-sectional area of the lower segment of the zygomatic pillar. The zygomatic process point moved inward and backward, whereas the zygomatico-maxillary suture point moved backward. The thicknesses of the zygomatic pillar alveolar and cortical bones were thinner, and reduced alveolar bone density was observed. Simultaneously, the movement and angle change of the maxillary first molar could predict zygomatic pillar reconstruction to a certain extent. With decreasing the total occlusal force and the occlusal force of the first molar, occlusal force distribution was more uniform. With zygomatic pillar remodeling, occlusal stress distribution in the zygomatic alveolar ridge decreased, and occlusal stress was concentrated at the junction of the vertical and horizontal parts of the zygomatic bone and the posterior part of the zygomatic arch. CONCLUSIONS: Orthodontic treatment involving premolar extraction led to zygomatic pillar remodeling, making it more fragile than before and reducing the occlusal force of the maxillary first molar and the entire dentition with stress concentrated in weak areas. CLINICAL RELEVANCE: No other study has focused on the effects of orthodontics on pillar structures. The present study indicates that the mesial movement of the maxillary first molar weakened the zygomatic pillar and reduced occlusal function, thereby providing insights for inserting anchorage screws and facial esthetics.

Predictability of expansion movements performed by clear aligners in mixed dentition in both arches: a retrospective study on digital casts.

BACKGROUND: to evaluate the predictability of expansion achieved in patients in early mixed dentition treated with Clear Aligners (CA), analyzing the efficiency of the expansion at the end of the first set of aligners and at the end of the therapy in the upper and lower arch. METHODS: 36 patients (20 F, 16 M; mean age 8.3 ± 1.5 years) were selected retrospectively from the Department of Orthodontics of the Hospital of Rome "Tor Vergata". All subjects were treated with CA with no other auxiliaries than attachments. For each patient a standardized sequential expansion protocol was planned for both arches. Digital dental casts were created at three observation periods from an intraoral scanner: prior to treatment (T0), at the end of the first set of aligners (T1), at the end of treatment (T2). The 3D models in planned position determined by the first Clincheck (CC) were obtained for comparison with T1 and T2. Six linear transversal measurements were used to evaluate the dimensional changes and the predictability of expansion movements, comparing T1-CC and T2-CC. RESULTS: a statistically significant increase within the pre-treatment and the final outcomes for all the variables examined was found. In the upper arch, the greatest level of predictability was detected at the level of the first (46.44%) and second deciduous molar width (44.95%) at T1. The analysis of T2-CC changes showed a significant increase in the percentage of predictability of expansion at the level of the first permanent molars, at mesial (54.86%) and distal (58.92%) width. In the lower arch, a higher percentage of predictability than the upper arch was reported at T1-CC and T2-CC, with the greatest values at the level of second (T1-CC: 48.70%; T2-CC: 75.32%) and first deciduous molar width (T1-CC: 45.71%; T2-CC: 72.75%). CONCLUSIONS: CA can induce significant transversal increments. The predictability of expansion is variable, but it did not exceed the 50% during the first set of aligners. It was necessary to apply refinement set to achieve a good predictability for expansion of about 70%. The expansion in the lower arch was observed to be more predictable than in the upper arch.

Finite element analysis of the mechanical behavior of 3D printed orthodontic attachments used in aligner treatment.

The composite attachment loss during orthodontic clear aligner therapy is an adverse event that commonly happens in clinical practice and can affect the overall outcome and length of treatment. The aim of our research is to provide a basis for the further study of an innovative digital protocol and application method for orthodontic aligner attachments. Two 3D models were designed, one based on the proposed protocol and the other on the conventional method for aligner attachment application. Four attachment shapes were used to identify the maximum values for the von Mises equivalent stresses, the maximum displacements values and the areas in which these values were recorded through FEM analysis. The results of the mechanical simulation show lower values of von Mises stress recorded in the 3D printed attachments assemblies, independent of their shape, when simulated under the same boundary and load conditions. The trapezoidal prism shaped 3D printed model has a 3.7 times smaller displacement value (0.088 [mm]) compared to the adhesive resin model (0.326 [mm]). In conclusion, the proposed protocol for aligner attachments and the introduction of innovative materials is a promising method of solving conventional attachment problems in current orthodontic treatments.

Facial soft-tissue shape changes after fixed edgewise treatment with premolar extraction in individual artificial-intelligence-classified facial profile patterns.

OBJECTIVE: To examine the patterns of pretreatment facial soft tissue shape in orthodontic cases with premolar extraction using artificial intelligence (AI) and to investigate the corresponding changes. METHODS: One hundred and fifty-two patients who underwent orthodontic treatment with premolar extraction were enrolled. Lateral cephalograms were obtained before and after the treatment. For each record, the outlines of the nose-lip-chin profile and corresponding 21 cephalometric variables were extracted. The AI method classified pretreatment records into three subject groups based on the feature variables extracted from the outline. Dentoskeletal and soft tissue facial form changes observed after treatment were compared statistically (P < 0.05) between the groups using ANOVA. Multivariate regression models were used for each group. RESULTS: Group 1 (n = 59) was characterized by Class II high-angle retrognathic mandible with an incompetent lip, group 2 (n = 55) by Class I malocclusion with retruded and thin lips, and group 3 (n = 38) by Class I malocclusion with an everted superior lip before treatment. The ratios of anteroposterior soft tissue to hard tissue movements in Group 1 were 56% (r = 0.64) and 83% (r = 0.75) for the superior and inferior lips, respectively, whereas those in Group 2 were 49% (r = 0.78) and 91% (r = 0.80), and 40% (r = 0.54) and 79% (r = 0.70), respectively, in Group 3. CONCLUSIONS: The modes of facial form changes differed depending on the pre-treatment profile patterns classified by the AI. This indicates that the determination of the pre-treatment profile pattern can help in the selection of soft tissue to hard tissue movement ratios, which helps estimate the post-treatment facial profile with a moderate to high correlation.

An Immunohistochemical and Histological Study of the Animal Periodontal Ligament During Orthodontic Force Application with Concomitant Application of Electric Current - An Animal Study.

INTRODUCTION: The application of direct current can have a significant impact on the rate of tooth movement and surrounding periodontal ligament collagen turnover. This study aims to provide insight into the optimal characteristics of applied current to achieve enhanced tissue response. METHOD: Eighteen male Wistar rats were divided into three groups (I, II, and III). Split mouth design was used, and each side was allocated into an experimental group or control group. Experimental sides of groups I, II, and III received 20, 10, and 15 µA of current (15 min, twice daily for 3 days). Both the experimental and control groups receive an orthodontic force via the NiTi closed coil spring. The amount of tooth movement was determined daily. Immunohistochemistry slides were scored using the immunoreactive scoring (IRS) system for collagen types I and III. One-way Analysis of Variance (ANOVA) and Tukey post hoc test were used to analyse the rate of tooth movement, while Mann-Whitney test was used to analyse IRS distribution between control and experimental groups. RESULTS: Compared with the control group, there was a statistically significant difference in tooth movement in all the experimental groups, with group 3 showing the maximum rate on days 2 and 3. This was supported by immunoreactive scores for both collagen types I and III. CONCLUSIONS: After 72 hours, the expression of collagen types 1 and 3 increased significantly for group III. This finding was in harmony with the rate of tooth movement, which was maximum for group 3 (15 µA) as compared to other groups.

Temporary Anchorage Device Misplaced into Infratemporal Space - A Case Report.

INTRODUCTION: During orthodontic treatment, temporary anchoring devices (TADs) are used to restrain tooth movement. They are a relatively recent addition to the dental toolkit. AIM: As TADs have limitations, Dr. Eric Lieu of Taiwan developed Infra Zygomatic Crest (IZC) screws which are placed between the maxillary second premolar at the bony crest. TREATMENT PLANNING: The goal of this case study is to emphasize the value of anatomy, site selection, and IZC retrieval in the event of an accident. Cone beam computed tomography was used as a diagnostic tool for the precise location of the displaced IZC and immediate surgical retrieval was done under local anesthesia from the infratemporal space to prevent further complications. TAKEAWAY LESSONS: Orthodontists knowledge of soft tissue and hard tissue anatomy and precise positioning is crucial for successful TAD implantation.

Salivary levels of eluents during Invisalign™ treatment with attachments: an in vivo investigation.

BACKGROUND: The aim of the present study was to investigate qualitatively and quantitatively the elution of substances from polyester-urethane (Invisalign™) aligners and resin composite attachments (Tetric EvoFlow) in vivo. METHODS: Patients (n = 11) treated with the aligners and attachments (16 per patient, without other composite restorations) for an average of 20 months, who were planned for attachment removed were enrolled in the study. Patients were instructed to rinse with 50 mL of distilled water upon entry and the rinsing solution was collected (before removal). Then, the attachments were removed with low-speed tungsten carbide burs for adhesive residue removal, a thorough water rinsing was performed immediately after the grinding process to discard grinding particle residues, and subsequently, after a second water-rinsing the solution was collected for analysis (after removal). The rinsing solutions were analyzed for targeted (LC-MS/MS: Bis-GMA, DCDMA, UDMA, BPA) and untargeted (LC-HRMS: screening of leached species and their degradation products) compounds. RESULTS: Targeted analysis revealed a significant reduction in BPA after attachment removal (4 times lower). Bis-GMA, DCDMA, UDMA were below the detection limit before removal but were all detectable after removal with Bis-GMA and UDMA at quantifiable levels. Untargeted analysis reviled the presence of mono-methacrylate transformation products of Bis-GMA (Bis-GMA-M1) and UDMA (UDMA-M1), UDMA without methacrylate moieties (UDMA-M2), and 4-(dimethylamino) benzoic acid (DMAB), the degradation product of the photo-initiator ethyl-4-(dimethylamino) benzoate (EDMAB), all after attachment removal. Several amino acids and endogenous metabolites were also found both before and after removal. CONCLUSIONS: Elevated levels of BPA were traced instantaneously in patients treated with Invisalign™ and flowable resin composite attachments for the testing period. BPA was reduced after attachment removal, but residual monomers and resin degradation products were found after removal. Alternative resin formulations and attachment materials may be utilized to reduce eluents.

Three-dimensional finite element analysis of the optimal mechanical design for maximum inward movement of the anterior teeth with clear aligners.

This study aims to refine clinical designs within clear aligner therapy, exploring the appropriate ratio of anterior tooth retraction to intrusion under maximum anchorage. Using a three-dimensional finite element model and evaluating 19 load scenarios with first premolar extraction, the research identifies the optimal force angle for anterior tooth retraction as 45 to 55°. For clinical planning, it is recommended to design a retraction of 0.19 mm combined with an intrusion of 0.16 mm to achieve anterior tooth retraction. This investigation is crucial for enhancing understanding of biomechanical principles in clear aligner orthodontics, offering significant insights for effective treatments.