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Background/Objectives: This numerical analysis of stress distribution in the dental pulp and neuro-vascular bundle (NVB) of lower premolars assessed the ischemic and degenerative–resorptive risks generated by 2 and 4 N during orthodontic movements (rotation, translation, tipping, intrusion and extrusion) in intact periodontium. Methods: The numerical analysis was performed on nine intact periodontium 3D models of the second lower premolar of nine patients totaling 90 simulations. Results: In intact periodontium, both forces displayed a similar stress distribution for all five orthodontic movements but different amounts of stress (a doubling for 4 N when compared with 2 N), with the highest values displayed in NVB. In intact periodontium, 2 N and 4 N induced stresses lower than the maximum hydrostatic pressure (MHP) with no ischemic risks for healthy intact teeth. The rotation was seen as the most stressful movement, closely followed by intrusion and extrusion. Translation was quantitatively seen as the least stressful when compared with other movements. Conclusions: Larger orthodontic forces of 2 N and 4 N are safe (with any expected ischemic or resorptive risks) for the dental pulp and NVB of healthy intact teeth and in intact periodontium. Nevertheless, rotation and translation movements can induce localized circulatory disturbances in coronal pulp (i.e., vestibular and proximal sides) generating ischemic and resorptive risks on previously treated teeth (i.e., direct and indirect dental pulp capping). The intrusion and extrusion movements, due to the higher NVB-induced deformation when compared with the other three movements, could trigger circulatory disturbances followed by ischemia on previously traumatized teeth (i.e., occlusal trauma). [ABSTRACT FROM AUTHOR]

Objectives: The objective of this study is to analyse the gene expression profile of the dental pulp (DP) of human premolars subjected to 7 and 28 days of orthodontic force (OF) in vivo by using RNA sequencing. The maxillary and mandibular DP were additionally compared. Methods: Healthy patients requiring orthodontic premolar extractions were randomly assigned to one of the three groups: control (CG) where no OF was applied, 7 and 28 days, where premolars were extracted either 7 or 28 days after the application of a 50–100 g OF. Total RNA was extracted from the DP and analysed via RNA‐seq. Differentially expressed genes (DEGs) were identified using a false discovery rate and fold change threshold of <0.05 and ≥1.5, respectively. Functional analysis was performed. Results: After 7 days of OF, pulp reaction indicates immune response, hypoxia, DNA damage and epigenetic regulation. After 28 days, cell adhesion, migration, organization and tissue repair are evident. The maxillary and mandibular pulp tissues react differently to OF. The maxilla exhibits minimal alterations, mostly related to immune response at 7 days and tissue repair at 28 days, whereas the mandible shows mostly DNA damage and epigenetic regulation at 7 days and return to the original state at 28 days. Conclusions: This study demonstrates that the early reaction of the DP to OF is marked by immune response, hypoxia and DNA damage. In contrast, after 28 days, cell adhesion, migration, organization, tissue repair and dentine formation are observed. Maxillary and mandibular premolars react differently to OF: although the maxilla exhibits minimal alterations at both time points, the mandible mostly shows DNA damage, epigenetic regulation, and immune response at 7 days. These disparities could stem from different blood supplies or the lower maxillary bone density, potentially triggering faster biological changes. Our findings provide insights into the gene regulatory networks modulating DP response to OF. [ABSTRACT FROM AUTHOR]

This study aimed to report forces and moments delivered by 3D-printed aligners. Tera Harz TC-85 resin and Zendura FLX (ZF) thermoformed sheets (0.76 mm) were used. Rectangular strip specimens (50 × 10 × 0.6 mm) were produced for a three-point bending test (3PB) at different temperatures. Full anatomical aligners were produced for 3D force measurements on different teeth and directions at 37 °C, using a custom-made device. ZF exhibited flexural forces between 1.7 and 2.3 N, while TC-85 from 0.3 N to 2.7 N, with temperature affecting TC-85 more significantly. At lower temperatures, TC-85 was stiffer than ZF, but at higher temperatures, it became less rigid. The 3D-force measurements indicated comparable values for both materials. Force ranged from 0.3–1.7 N and moment from 4.8–9.4 Nmm. The study concluded that TC-85 3D-printed aligners deliver biologically compatible forces for orthodontic movement and offer better control over thickness.HighlightsThe 3D-printed Tera Harz TC-85 resin revolutionises aligner production.Tera Harz TC-85 aligners generate forces within the orthodontic accepted range.Shape recovery of TC-85 can enable adaptability and larger incremental step size.The 3D printing offers greater control over aligner design and thickness.

Objectives: To investigate the effects of material type and thickness on force generation and distribution by aligners. Materials and methods: Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89 mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75 mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50 mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films. Results: The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1 N, 50.5 N), Zendura FLX (88.9 N, 60.7 N), and Zendura Viva (92.5 N, 68.5 N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9 N, 71.8 N) and Zendura (149.7 N, 89.8 N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (FI-FC) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (FI-FM) was higher with single-layered materials. Both overall force and net force (FI-FM) were significantly higher with 0.75 mm compared to those with a thickness of 0.50 mm. Conclusions: Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred. Clinical relevance: This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement. [ABSTRACT FROM AUTHOR]

• The finite element method is a valuable method for understanding the biomechanics of aligners. • Trimming line design of orthodontic aligners has a key role in force transmission. • Extended straight aligner trimming line improves control of tooth movement. • Properly designed thin aligners offer enhanced efficiency and comfort. • Aligners present a higher likelihood of uncontrolled tipping than bodily movement. A finite element model was used to investigate the effect of different designs and thicknesses of orthodontic aligner margins on their biomechanical behavior. A three-dimensional data set of an upper jaw was imported into the 3-matic software. The upper right central incisor tooth (Tooth 11) was separated from the remaining model, and its periodontal ligament and surrounding bone were designed. Aligners were designed with four different trimming lines (scalloped, straight, scalloped extended, straight extended), each with four different thicknesses (0.3, 0.4, 0.5, and 0.6 mm). The models were imported into a finite element package (Marc/Mentat). A linear elastic constitutive material model was applied. A facial 0.2 mm bodily malalignment of tooth 11 was simulated. The maximum resultant force was in the range of 1.0 N to 2.2 N. The straight trimming designs deliver higher resultant forces compared with scalloped trimming designs. Increasing the aligner thickness and/or extending the aligner edge beyond the gingival line leads to an increase in the resultant force. All designs showed an uneven distribution of the normal contact forces over the tooth surface with a predominant concentration toward the cervical third and distal third, particularly with the extended trimming designs. All designs showed uncontrolled tipping of the tooth. Based on the current model outcomes, the use of a straight extended trimming line design for aligners is favored because of its positive impact on force distribution and, consequently, the control of tooth movement. These findings provide aligner companies and orthodontists a valuable biomechanical evidence and guidance to enhance control over tooth movement and therefore optimize treatment outcomes. This can be achieved by trimming the edges of aligners with a straight extended design and selecting the appropriate aligner thickness. [ABSTRACT FROM AUTHOR]

Background/Objectives: This numerical analysis of stress distribution in the dental pulp and neuro-vascular bundle (NVB) of lower premolars assessed the ischemic and degenerative–resorptive risks generated by 2 and 4 N during orthodontic movements (rotation, translation, tipping, intrusion and extrusion) in intact periodontium. Methods: The numerical analysis was performed on nine intact periodontium 3D models of the second lower premolar of nine patients totaling 90 simulations. Results: In intact periodontium, both forces displayed a similar stress distribution for all five orthodontic movements but different amounts of stress (a doubling for 4 N when compared with 2 N), with the highest values displayed in NVB. In intact periodontium, 2 N and 4 N induced stresses lower than the maximum hydrostatic pressure (MHP) with no ischemic risks for healthy intact teeth. The rotation was seen as the most stressful movement, closely followed by intrusion and extrusion. Translation was quantitatively seen as the least stressful when compared with other movements. Conclusions: Larger orthodontic forces of 2 N and 4 N are safe (with any expected ischemic or resorptive risks) for the dental pulp and NVB of healthy intact teeth and in intact periodontium. Nevertheless, rotation and translation movements can induce localized circulatory disturbances in coronal pulp (i.e., vestibular and proximal sides) generating ischemic and resorptive risks on previously treated teeth (i.e., direct and indirect dental pulp capping). The intrusion and extrusion movements, due to the higher NVB-induced deformation when compared with the other three movements, could trigger circulatory disturbances followed by ischemia on previously traumatized teeth (i.e., occlusal trauma).

Using finite-element analysis, we aimed to determine the center of resistance (CRes) of the maxillary canine for setting orthodontic forces. The inclination of the canine was measured by first loading from the mesial to the distal side of the mesial root surface, then the position and direction of the load that minimized the inclination were investigated. The CRes was defined as the set of midpoints of the minimum distances between two inclination lines. Twenty-one CRes values were calculated from a set of seven lines. These CRes data were then aggregated as a 95% confidence ellipsoid of width 0.170x0.016x0.009 mm with center points 4.269, 0.224, and 4.315 mm in the apical, mesial, and lingual directions from the origin, respectively. Further studies are required to effectively apply the CRes identified in this study to clinical applications. [ABSTRACT FROM AUTHOR]

To develop a new orthodontic force simulation system with a simulated periodontal ligament (PDL) that enables measurement of the delivered force at the root apex and to clarify the relationship between the applied orthodontic force and the delivered force at the root apex. In vitro study. Orthodontics department of a university, Tokyo, Japan. A new orthodontic force simulation system that enables measurement of the force at the root apex of the maxillary central incisor, was developed. Lingual and intrusion movements were simulated with applied orthodontic force at three levels: 50, 100 and 200 gf. The delivered forces at the root apex were compared between the two movements. Furthermore, the ratio of delivered force at the root apex to the applied orthodontic force (the apex force ratio) was calculated. The magnitudes of delivered forces at the root apex were significantly greater in intrusion movement than in lingual movement (P < 0.01). The apex force ratios were in the range of 47.3%–56.2% for lingual movement and 85.6%–86.2% for intrusion movement. The present study, of a newly developed orthodontic force simulation system, showed that the characteristics of the delivered force at the root apex differed according to the direction of tooth movement. [ABSTRACT FROM AUTHOR]

Background/purpose: The present study aimed to compare the force decay of invisible aligners for maxillary anterior teeth with 0.1 mm (D1), 0.2 mm (D2), and 0.3 mm (D3) labial movement within a simulated oral environment over 7 days. Materials and methods: The prepared invisible aligners were immersed in saliva (S) and subjected to applied force (F) for 7 days. The aligners were set and placed on the maxillary right central incisor with 0.1 mm (D1), 0.2 mm (D2), and 0.3 mm (D3) labial movement. Thin-film pressure sensors were used to measure the aligner force changes. The data were collected and analyzed by statistical methods. Results: Significant differences were observed in the initial and first-day force between the D2 and D3 groups under simulated oral environment force (SF) (P

Background and Objectives: Herein we used numerical analysis to study different biomechanical behaviors of mandibular bone subjected to 0.6 N, 1.2 N, and 2.4 N orthodontic loads during 0–8 mm periodontal breakdown using the Tresca failure criterion. Additionally, correlations with earlier FEA reports found potential ischemic and resorptive risks. Materials and Methods: Eighty-one models (nine patients) and 243 simulations (intrusion, extrusion, rotation, tipping, and translation) were analyzed. Results: Intrusion and extrusion displayed after 4 mm bone loss showed extended stress display in the apical and middle third alveolar sockets, showing higher ischemic and resorptive risks for 0.6 N. Rotation, translation, and tipping displayed the highest stress amounts, and cervical-third stress with higher ischemic and resorptive risks after 4 mm loss for 0.6 N. Conclusions: Quantitatively, rotation, translation, and tipping are the most stressful movements. All three applied forces produced similar stress-display areas for all movements and bone levels. The stress doubled for 1.2 N and quadrupled for 2.4 N when compared with 0.6 N. The differences between the three loads consisted of the stress amounts displayed in color-coded areas, while their location and extension remained constant. Since the MHP was exceeded, a reduction in the applied force to under 0.6 N (after 4 mm of bone loss) is recommended for reducing ischemic and resorptive risks. The stress-display pattern correlated with horizontal periodontal-breakdown simulations. [ABSTRACT FROM AUTHOR]

Transient apical breakdown (TAB) appears to be a repair process taking place in the pulp and periapical area of traumatised teeth which may display crown discoloration and have no responses to pulp sensitivity tests. Few TAB cases induced by orthodontic forces have been reported so far. Presented is a case report in which TAB occurred on the maxillary right central incisor during orthodontic treatment. The affected tooth suddenly displayed crown discoloration and had no response to pulp testing at 6 weeks after the placement Invisalign Clear Aligner appliances. Condition of the discoloured tooth was monitored by periodic recall examinations without any active treatment. Six months after the occurrence of discoloration, the affected tooth recovered to its original shade and responded normally to pulp sensitivity tests. [ABSTRACT FROM AUTHOR]

Background and Objectives: This numerical analysis investigated the biomechanical behavior of the mandibular bone as a structure subjected to 0.5 N of orthodontic force during periodontal breakdown. Additionally, the suitability of the five most used failure criteria (Von Mises (VM), Tresca (T), maximum principal (S1), minimum principal (S3), and hydrostatic pressure (HP)) for the study of bone was assessed, and a single criterion was identified for the study of teeth and the surrounding periodontium (by performing correlations with other FEA studies). Materials and Methods: The finite element analysis (FEA) employed 405 simulations over eighty-one mandibular models with variable levels of bone loss (0–8 mm) and five orthodontic movements (intrusion, extrusion, tipping, rotation, and translation). For the numerical analysis of bone, the ductile failure criteria are suitable (T and VM are adequate for the study of bone), with Tresca being more suited. S1, S3, and HP criteria, due to their distinctive design dedicated to brittle materials and liquids/gas, only occasionally correctly described the bone stress distribution. Results: Only T and VM displayed a coherent and correlated gradual stress increase pattern for all five movements and levels of the periodontal breakdown. The quantitative values provided by T and VM were the highest (for each movement and level of bone loss) among all five criteria. The MHP (maximum physiological hydrostatic pressure) was exceeded in all simulations since the mandibular bone is anatomically less vascularized, and the ischemic risks are reduced. Only T and VM displayed a correlated (both qualitative and quantitative) stress increase for all five movements. Both T and VM displayed rotation and translation, closely followed by tipping, as stressful movements, while intrusion and extrusion were less stressful for the mandibular bone. Conclusions: Based on correlations with earlier numerical studies on the same models and boundary conditions, T seems better suited as a single unitary failure criterion for the study of teeth and the surrounding periodontium. [ABSTRACT FROM AUTHOR]

The present study aimed to compare the force decay of invisible aligners for maxillary anterior teeth with 0.1 mm (D 1), 0.2 mm (D 2), and 0.3 mm (D 3) labial movement within a simulated oral environment over 7 days. The prepared invisible aligners were immersed in saliva (S) and subjected to applied force (F) for 7 days. The aligners were set and placed on the maxillary right central incisor with 0.1 mm (D 1), 0.2 mm (D 2), and 0.3 mm (D 3) labial movement. Thin-film pressure sensors were used to measure the aligner force changes. The data were collected and analyzed by statistical methods. Significant differences were observed in the initial and first-day force between the D 2 and D 3 groups under simulated oral environment force (SF) (P < 0.05). There was a significant difference in force decay between Day 1 and Day 7 for all groups (P < 0.05). The SFD 1 group showed a significant decrease in force on Day 5 (P < 0.05), while the SFD 2 and SFD 3 groups showed significant force decay on Day 4 (P < 0.05). The force decay ratio on Day 7 was higher in the SFD 3 group than in the SFD 1 and SFD 2 groups, but no significant difference was observed. Larger labial movement of the aligners resulted in higher force decay under artificial saliva environments, and the force decay of invisible aligners was increased by immersion time in artificial saliva. [ABSTRACT FROM AUTHOR]

Aim: To analyze the pulpal stress in varied orthodontic tooth movements at ideal force levels and different bone levels, and compare any differences in pulpal stress values between anterior and posterior teeth. Materials and Methods: Four Finite Element Method models of incisor and molar teeth were simulated with normal bone height and 50% bone height. Each of these models was loaded with five different types of orthodontic tooth movements—Tipping, Translation, Intrusion, Extrusion, and Rotation. The ideal force levels simulated for each type of tooth movement were: Intrusion-20 g, Extrusion-60 g, Tipping-60 g, Translation-120 g, Rotation-60 g. The pulpal stress was evaluated at three levels—pulp chamber, pulp canal, and below root apex, so that we get three values of pulpal stress for anterior and posterior teeth, for each type of tooth movement and its corresponding force level. Results: The results showed that in both incisor and molar models with normal bone height as well as 50% bone height, rotation gave the highest pulpal stress while translation gave the least. In both incisor and molar models with normal bone height as well as 50% bone height, pulpal stress was found out to be highest in the root apex region of the tooth. The stress values for incisor and molar models with 50% bone height were found to be almost double that of the models with normal bone height. The pulpal stress for incisor teeth was found to be greater than the molar teeth for all types of tooth movement. Conclusion: The present findings indicate that the stress manifested below the root apex is highest. Rotational movements induce the highest stress and translational forces develop the lowest stress related to the physiologic capillary blood pressure. Furthermore, in situations with reduced periodontium, lower forces are needed to reach the maximum tolerable stress compared with teeth with intact periodontium. [ABSTRACT FROM AUTHOR]

The aim of this study is to study the effect of aging in different media (deionized water and artificial saliva) on the force/torque generation by thermoplastic orthodontic aligners. Ten thermoformed aligners, made of Essix ACE® thermoplastic sheets, were aged in deionized water and in artificial saliva over two weeks at 37 °C, five in each medium. The force/torque generated on upper second premolar (Tooth 25) of a resin model was measured at day 0 (before aging), 2, 4, 6, 10, and 14, using a biomechanical test set-up. The results showed that aging of aligners by storage in aging agent has no significant impact on their force/torque decay. No significant differences were also found in force/torque between the aligners stored in deionized water nor artificial saliva. The vertical extrusion-intrusion forces were measured in the range of 1.4 to 4.6 N, the horizontal oro-vestibular forces were 1.3 to 2.5 N, while the torques on mesio-distal rotation were 5.4 to 41.7 Nmm. It could be concluded that the influence of saliva only on the mechanical properties can be classified as insignificant, and no significant difference between artificial aging in deionized water or artificial saliva was observed.

Objectives: To determine and compare the effects of high-frequency mechanical vibration (HFV) with light force and optimal force on the tooth movement and root resorption in rat model. Materials and methods: Seventy-two sites in 36 male Wistar rats were randomly assigned using a split-mouth design to control (no force/no vibration) or experimental groups: HFV (125 Hz), light force (5 g), optimal force (10 g), light force with HFV, and optimal force with HFV for 14 and 21 days. The amount of tooth movement, 3D root volume, and root resorption area were assessed by micro-computed tomography and histomorphometric analysis. Results: Adjunction of HFV with light force significantly increased the amount of tooth movement by 1.8-fold (p = 0.01) and 2.0-fold (p = 0.01) at days 14 and 21 respectively. The HFV combined with optimal force significantly increased the amount of tooth movement by 2.1-fold (p = 0.01) and 2.2-fold (p = 0.01) at days 14 and 21 respectively. The root volume in control (distobuccal root (DB): 0.60 ± 0.19 mm3, distopalatal root (DPa): 0.60 ± 0.07 mm3) and HFV (DB: 0.60 ± 0.08 mm3, DPa: 0.59 ± 0.11 mm3) were not different from the other experimental group (range from 0.44 ± 0.05 to 0.60 ± 0.1 mm3) with the lowest volume in optimal force group. Conclusions: Adjunction of HFV with orthodontic force significantly increased tooth movement without causing root resorption. Clinical relevance: Using light force with HFV could help to identify alternative treatment option to reduce the risk of root resorption. [ABSTRACT FROM AUTHOR]

This case report describes a 21‐year‐old orthodontic patient experienced the external apical root resorption of maxillary central incisors with pulpitis during the orthodontic movement. The active cooperation of orthodontists and endodontists demonstrated the satisfactory treatment outcome and prevented further apical root resorption. The etiology of external apical root resorption is comprehensive, orthodontists should be armed with an adequate training and scientific knowledge, and keep the treatment mechanism simple and precise to guard against it. Besides, we should know the right timing of endodontic treatment and applying orthodontic force when external apical root resorption occurs. [ABSTRACT FROM AUTHOR]

Highlights: Aging effect of saliva on mechanical properties of aligners is insignificant. In artificial aging, artificial saliva or deionized water have similar effect. The experimental studies of aligners have limitations. Force generation by aligner is direction dependent. The aim of this study is to study the effect of aging in different media (deionized water and artificial saliva) on the force/torque generation by thermoplastic orthodontic aligners. Ten thermoformed aligners, made of Essix ACE® thermoplastic sheets, were aged in deionized water and in artificial saliva over two weeks at 37 °C, five in each medium. The force/torque generated on upper second premolar (Tooth 25) of a resin model was measured at day 0 (before aging), 2, 4, 6, 10, and 14, using a biomechanical test set-up. The results showed that aging of aligners by storage in aging agent has no significant impact on their force/torque decay. No significant differences were also found in force/torque between the aligners stored in deionized water nor artificial saliva. The vertical extrusion-intrusion forces were measured in the range of 1.4 to 4.6 N, the horizontal oro-vestibular forces were 1.3 to 2.5 N, while the torques on mesio-distal rotation were 5.4 to 41.7 Nmm. It could be concluded that the influence of saliva only on the mechanical properties can be classified as insignificant, and no significant difference between artificial aging in deionized water or artificial saliva was observed. [ABSTRACT FROM AUTHOR]

Abstract Background External root resorption is one of common complications of orthodontic treatment, while internal root resorption is rarely observed, and the difference between pulp and periodontal tissues during orthodontic treatment is still unknown. The purpose of this study was to evaluate the effects of orthodontic forces on histological and cellular changes of the dental pulp and periodontal tissues. Methods Orthodontic tooth movement model was established in Forty-eight adult male Wistar rats. The distance of orthodontic tooth movement was quantitatively analyzed. The histological changes of pulp and periodontal tissues were performed by hematoxylin–eosin staining, tartrate-resistant acid phosphate staining was used to analyze the changes of osteoclast number, immunohistochemistry analysis and reverse transcription polymerase chain reaction were used to examine the receptor of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) expression. The width of tertiary dentine was quantitatively analyzed. Tartrate-resistant acid phosphate staining and the erosion area of osteo assay surface plate was used to evaluate osteoclast activity. Results The orthodontic tooth movement distance increased in a force dependent manner, and reached the peak value when orthodontic force is 60 g. Heavy orthodontic force increased the RANKL expression of periodontal ligament srem cells (PDLSCs) which further activated osteoclasts and resulted in external root resorption, while the RANKL expression of dental pulp stem cells (DPSCs) was relatively low to activate osteoclasts and result in internal root resorption, and the dental pulp tend to form tertiary dentine under orthodontic force stimulation. Conclusions Heavy orthodontic forces activated osteoclasts and triggered external root resorption by upregulating RANKL expression in rat periodontal tissues, while there was no significant change of RANKL expression in dental pulp tissue under heavy orthodontic forces, which prevented osteoclast activation and internal root resorption.

Abstract Background Fluoride has a major role in strengthening the structure of enamel against acids. Despite differences between caries and root resorption processes, both events inherently involve acidic dissolution of dental tissues. The aim of the present study was to investigate the effects of water fluoridation levels on the surface roughness of root cementum and resorption craters. The findings provided more insight into the influence of fluoride on the surfaces of intact cementum surface and resorption craters. Methods Twenty-eight orthodontic patients were recruited from two cities in Turkey, with high (≥ 2 ppm) and low (≤ 0.05 ppm) water fluoridation. These patients needed bilateral maxillary first premolar extraction as part of their orthodontic treatment and were allocated into two study groups (n = 14 in each group) based on water fluoridation exposure level: the high-fluoride group (HF) and low-fluoride group (LF). 150 g of buccal tipping forces was applied to all maxillary first premolar teeth for 12 weeks with a beta-titanium spring which was reactivated every 4 weeks. All maxillary premolars were removed at the end of the experiment for surface roughness assessment using three-dimensional confocal microscopy and the associated software. The buccal root surface and the largest buccal resorption crater were investigated. Results Resorption craters were significantly rougher in LF group compared to HF group (p = 0.002). Craters were rougher than the intact root surfaces (p = 0.000). Cervical and apical regions were significantly rougher than the middle region (p = 0.000 and p = 0.024, respectively). Conclusions Higher water fluoridation level of ≥ 2 ppm resulted in significantly smoother root resorption craters than low water fluoridation level of ≤ 0.05 ppm when the teeth were subjected to 150 g of buccal tipping force. Fluoride seems to have a protective role at the interface of root resorption, and further mineral or histological studies may shed light on the exact protective process against root resorption.

Abstract This case report describes a 21‐year‐old orthodontic patient experienced the external apical root resorption of maxillary central incisors with pulpitis during the orthodontic movement. The active cooperation of orthodontists and endodontists demonstrated the satisfactory treatment outcome and prevented further apical root resorption. The etiology of external apical root resorption is comprehensive, orthodontists should be armed with an adequate training and scientific knowledge, and keep the treatment mechanism simple and precise to guard against it. Besides, we should know the right timing of endodontic treatment and applying orthodontic force when external apical root resorption occurs.

Objectives: To design a finite element (FE) model that might facilitate understanding of the complex mechanical behavior of orthodontic aligners. The designed model was validated by comparing the generated forces — during 0.2-mm facio-lingual translation of upper left central incisor (Tooth 21) — with the values reported by experimental studies in literature. Materials and methods: A 3D digital model, obtained from scanning of a typodont of upper jaw, was imported into 3-matic software for designing of aligners with different thicknesses: 0.4, 0.5, 0.6, 0.7 mm. The model was exported to Marc/Mentat FE software. Suitable parameters for FE simulation were selected after a series of sensitivity analyses. Different element classes of the model and different rigidity values of the aligner were also investigated. Results: The resultant maximum forces generated on facio-lingual translation of Tooth 21 were within the range of 1.3–18.3 N. The force was direction-dependent, where lingual translation transmitted higher forces than facial translation. The force increases with increasing the thickness of the aligner, but not linearly. We found that the generated forces were almost directly proportional to the rigidity of the aligner. The contact normal stress map showed an uneven but almost repeatable distribution of stresses all over the facial surface and concentration of stresses at specific points. Conclusions: A validated FE model could reveal a lot about mechanical behavior of orthodontic aligners. Clinical relevance: Understanding the force systems of clear aligner by means of FE will facilitate better treatment planning and getting optimal outcomes. [ABSTRACT FROM AUTHOR]

Background and Objectives: Herein we used numerical analysis to study different biomechanical behaviors of mandibular bone subjected to 0.6 N, 1.2 N, and 2.4 N orthodontic loads during 0–8 mm periodontal breakdown using the Tresca failure criterion. Additionally, correlations with earlier FEA reports found potential ischemic and resorptive risks. Materials and Methods: Eighty-one models (nine patients) and 243 simulations (intrusion, extrusion, rotation, tipping, and translation) were analyzed. Results: Intrusion and extrusion displayed after 4 mm bone loss showed extended stress display in the apical and middle third alveolar sockets, showing higher ischemic and resorptive risks for 0.6 N. Rotation, translation, and tipping displayed the highest stress amounts, and cervical-third stress with higher ischemic and resorptive risks after 4 mm loss for 0.6 N. Conclusions: Quantitatively, rotation, translation, and tipping are the most stressful movements. All three applied forces produced similar stress-display areas for all movements and bone levels. The stress doubled for 1.2 N and quadrupled for 2.4 N when compared with 0.6 N. The differences between the three loads consisted of the stress amounts displayed in color-coded areas, while their location and extension remained constant. Since the MHP was exceeded, a reduction in the applied force to under 0.6 N (after 4 mm of bone loss) is recommended for reducing ischemic and resorptive risks. The stress-display pattern correlated with horizontal periodontal-breakdown simulations.

Bone remodeling and orthodontic tooth movement (OTM) are controlled by certain essential molecules, one of which is vitamin D. Increased levels of vitamin D have been associated with increased rates of OTM. The purpose of this study was to determine the effect of vitamin D deficiency on the rate of OTM, and to determine their association after applying orthodontic forces. Materials and Methods: Wistar rats were divided into two groups: control group with average vitamin D levels and experimental group with induced vitamin D deficiency. Orthodontic appliances were fixed to initiate tooth movement. Distance between the reference teeth were measured in millimeters on day zero, and repeated every 7 days, till day 21. Results: A significant difference within the experimental group was found; as well as within the control group, there was also no significant interaction between time and the type of group. Conclusion: The rate of Orthodontic tooth movement was not affected by induced vitamin D deficiency in rats.

Context: The proliferation and differentiation of human periodontal ligament stem cells (hPDLSC) into other cell types are also mediated by mechanical stresses; they might offer therapeutic benefits in tissue regeneration and angiogenesis. Objectives: The study was planned to assess the proliferation, clonogenic potential, and osteogenic differentiation of human periodontal ligament stem cells (PDLSC) following the application of light and heavy orthodontic forces. Materials and Methods: A couple forces of 50 gm (light force) were applied on the 1st premolar on the one side and 250 gm (heavy force) on the contralateral side in the upper arch of patients requiring orthodontic treatment with extraction of all 1st premolars. After 30 days, periodontal tissues were scrapped from extracted teeth for the establishment of PDLSC in vitro. PDLC from the lower premolar teeth where no orthodontic force was applied acted as the control group. Morphology, viability, proliferating rate and population doubling time, clonogenicity, and alkaline phosphatase activity were analysed. Result: The osteogenic potential was confirmed by Alizarin red staining and the expression of the osteogenic markers by qRT-PCR. The morphology, growth kinetics, potency, and osteogenic lineage characteristics inferred the application of high force reduced the proliferative ability and osteogenesis of PDLSC, though the difference was not significant. Conclusion: The established PDLSCs demonstrated their MSC-like properties based on morphology, growth kinetics, colony forming ability, and AP activity. The culture-expanded PDLSCs showed their differentiation potential into osteocytes. The application of high force reduced the proliferative ability and osteogenesis of PDLSCs, variations were not significant.

Several studies indicate the influence of olanzapine on bone metabolism; however, the results are contradictory. We evaluated the effects of olanzapine on the Wnt/β-catenin signaling pathway, physiological alveolar bone turnover, and alveolar bone modeling due to an applied orthodontic force. Adult male rats (n=48) were treated with either olanzapine or a vehicle for 21 days; then 8 rats from each group were sacrificed and the rest were divided into 4 groups: control, appliance-only, olanzapine-only, and olanzapine-appliance. The rats in the appliance groups were mounted with a superelastic closed coil spring that maintained constant orthodontic force between molars and incisors. We studied the effects of olanzapine on physiological alveolar bone turnover on day 21 of the experiment, and on alveolar bone modeling due to orthodontic force on day 56. We determined tooth movement, alveolar bone volume, activity of bone-specific cells, serum alkaline phosphatase (ALP) activity, and gene expression levels of Wnt/β-catenin signaling target genes. During forced bone modeling, olanzapine increased osteoblast volume (P

Abstract Background Although preformed archwires with a variety of arch forms are currently commercially available, the effects of variation in the shape of these archwires on the orthodontic force at each tooth are not well understood. Therefore, we evaluated the forces delivered by various types of commercially available preformed nickel–titanium alloy (NiTi) archwires in a simulated mandibular dental arch. Methods Sixty-three types of 0.019 × 0.025-inch preformed NiTi archwires from 15 manufactures were selected for analysis. The intercanine width (ICW) and intermolar width (IMW) of each archwire were measured at the mean canine and first molar depths of 30 untreated subjects with normal occlusions. Each archwire was placed in a multi-sensor measurement system simulating the mandibular dental arch of subjects with normal occlusions, and orthodontic forces in the facial-lingual direction at the central incisors, canines, and first molars were measured. Correlations between the ICW, IMW, and ICW/IMW ratio of archwires and the delivered forces were analyzed. The archwires were classified into the following four groups according to the ICW and IMW: Control group, ICW and IMW are within the means ± standard deviations of the normal ranges; Ovoid group, narrow ICW and IMW; Tapered group, narrow ICW; and Square group, narrow IMW. The forces were compared among these groups for each tooth. Results Significant correlations between the measured archwire width and force to each tooth were found, except between IMW and forces at the central incisors and canines. Significant differences in the forces were found among all groups, except between the Ovoid and Tapered groups at all teeth and between the Ovoid/Tapered and Control groups at the first molar. Significantly greater orthodontic forces in the facial direction were delivered at the central incisors by the archwires in the Ovoid and Tapered groups when compared with the archwires in the other groups. Conclusion These findings suggest that there is a possible risk of a clinically significant level of unfavorable orthodontic force being delivered to the mandibular incisors in labial inclination when using a preformed archwire with an ICW that is narrower than the dental arch.

Orthodontically induced inflammatory root resorption (OIIRR) is considered an undesired and inevitable complication induced by orthodontic forces. This inflammatory mechanism is regulated by immune cells that precede orthodontic tooth movement (OTM) and can influence the severity of OIIRR. The process of OIIRR is based on an immune response. On some occasions, the immune system attacks the dentition by inflammatory processes during orthodontic treatment. Studies on the involvement of the PD-1/PD-L1 immune checkpoint have demonstrated its role in evading immune responses, aiming to identify possible novel therapeutic approaches for periodontitis. In the field of orthodontics, the important question arises of whether PD-L1 has a role in the development of OIIRR to amplify the amount of resorption. We hypothesize that blocking of the PD-L1 immune checkpoint could be a suitable procedure to reduce the process of OIIRR during orthodontic tooth movement. This review attempts to shed light on the regulation of immune mechanisms and inflammatory responses that could influence the pathogenesis of OIIRR and to acquire knowledge about the role of PD-L1 in the immunomodulation involved in OIIRR. Possible clinical outcomes will be discussed in relation to PD-L1 expression and immunologic changes throughout the resorption process. [ABSTRACT FROM AUTHOR]

Context: The proliferation and differentiation of human periodontal ligament stem cells (hPDLSC) into other cell types are also mediated by mechanical stresses; they might offer therapeutic benefits in tissue regeneration and angiogenesis. Objectives: The study was planned to assess the proliferation, clonogenic potential, and osteogenic differentiation of human periodontal ligament stem cells (PDLSC) following the application of light and heavy orthodontic forces. Materials and Methods: A couple forces of 50 gm (light force) were applied on the 1st premolar on the one side and 250 gm (heavy force) on the contralateral side in the upper arch of patients requiring orthodontic treatment with extraction of all 1st premolars. After 30 days, periodontal tissues were scrapped from extracted teeth for the establishment of PDLSC in vitro. PDLC from the lower premolar teeth where no orthodontic force was applied acted as the control group. Morphology, viability, proliferating rate and population doubling time, clonogenicity, and alkaline phosphatase activity were analysed. Result: The osteogenic potential was confirmed by Alizarin red staining and the expression of the osteogenic markers by qRT-PCR. The morphology, growth kinetics, potency, and osteogenic lineage characteristics inferred the application of high force reduced the proliferative ability and osteogenesis of PDLSC, though the difference was not significant. Conclusion: The established PDLSCs demonstrated their MSC-like properties based on morphology, growth kinetics, colony forming ability, and AP activity. The culture-expanded PDLSCs showed their differentiation potential into osteocytes. The application of high force reduced the proliferative ability and osteogenesis of PDLSCs, variations were not significant. [ABSTRACT FROM AUTHOR]

BACKGROUND: Root resorption is the most common complication in orthodontic treatment, and is also a hot topic in current orthodontic research. Currently, the remodeling process of collagen fibers in the inferior periodontal tissue and its relationship with matrix metalloproteinase-9 remain unclear at different time points during root resorption. OBJECTIVE: To investigate the remodeling of collagen fibers and the expression of matrix metalloproteinase-9 in the inferior periodontal tissue at different time points on the pressure side during orthodontic root resorption. METHODS: Thirty eight-week-old male Wistar rats were selected, and the orthodontic tooth movement model was established by pulling the left maxillary first molars towards the near middle in the experimental group, and the right side was not treated as the control group. The changes of collagen fibers and expression of matrix metalloproteinase-9 in alveolar bone, root surface and periodontal tissue at 1, 3, 5, 7, 14, and 21 days were observed and analyzed by histomorphology after force application. RESULTS AND CONCLUSION: (1) Hematoxylin-eosin staining and Masson's trichrome staining results confirmed that compared with the control group, the alveolar bone and tooth root surface of the experimental group had different degrees of resorption. The periodontal tissue collagen fibers underwent structural remodeling. The remodeling was most significant at 7 and 21 days. The expression of collagen fibers per unit area decreased first and then increased with the extension of the force. (2) Immunohistochemical staining confirmed that compared with the control group, the expression of matrix metalloproteinase-9 in the experimental group increased. The expression level showed a trend of first increasing and then decreasing with the extension of the application time. Pearson correlation analysis confirmed that the matrix metalloproteinase-9 expression was negatively correlated with the expression of collagen fibers in periodontal tissues (r=-0.933, P < 0.01). (3) The above results indicate that during orthodontic tooth root resorption in rats, the collagen in periodontal tissues is prolonged with time of stress. The expression level of matrix metalloproteinase-9 is related to the dynamic changes of collagen fibers and the changing trend of tooth root resorption. [ABSTRACT FROM AUTHOR]

An orthodontic traction technique with a miniscrew-anchored cantilever spring was used for the traction of a deeply impacted maxillary third molar to substitute its adjacent second molar with severe root resorption. A 30-year-old woman sought multidisciplinary treatment planning for a second molar with severe root resorption caused by a deeply impacted third molar. Panoramic radiographs and cone-beam computed tomographic images showed that the third molar was located on the apical and palatal side of the second molar and that the second molar had severe root resorption. The second molar was removed, and the impacted third molar was orthodontically tractioned occlusally with the aid of a miniscrew-anchored cantilever spring. After 12 months of orthodontic treatment, the maxillary left third molar was successfully tractioned occlusally and well aligned with adjacent teeth for the substitution of the second molar. The patient was satisfied with the treatment outcome. A palatal miniscrew-anchored cantilever spring is an effective and viable technique for the orthodontic traction of deeply impacted third molars to substitute second molars with severe root resorption. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effect of compressive force combined with vibration on expression of CC-chemokine ligand 2 (CCL2) and 5 (CCL5) in human periodontal ligament (hPDL) cells., Methods: Human PDL cells were cultured and assigned into four groups: control (Con), compressive force 2.0 g/cm 2 for 24 h and 48 h (C), vibration 0.3 g 30 Hz for 20 min every 24 h (V), and compressive force combined with vibration (VC). At 24 h and 48 h, mRNA and protein levels of CCL2 and CCL5 were examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively., Results: At 24 h and 48 h, CCL2 mRNA and protein levels in C and VC were significantly higher than Con. At 24 h, VC showed significantly higher CCL2 mRNA expression than C. However, there was no significant difference between CCL2 protein in C and VC at both time points. At 24 h and 48 h, CCL5 mRNA expression was significantly down-regulated in V and VC, whereas CCL5 protein was undetectable in all groups., Conclusions: Application of compressive force combined with vibration resulted in the upregulation of CCL2 mRNA and protein levels, whereas CCL5 mRNA expression was down-regulated., Competing Interests: The authors have no conflicts of interest to declare., (© 2024 The Authors. Published by Elsevier B.V. on behalf of Craniofacial Research Foundation.)

Background and Objectives: This numerical analysis investigated the biomechanical behavior of the mandibular bone as a structure subjected to 0.5 N of orthodontic force during periodontal breakdown. Additionally, the suitability of the five most used failure criteria (Von Mises (VM), Tresca (T), maximum principal (S1), minimum principal (S3), and hydrostatic pressure (HP)) for the study of bone was assessed, and a single criterion was identified for the study of teeth and the surrounding periodontium (by performing correlations with other FEA studies). Materials and Methods: The finite element analysis (FEA) employed 405 simulations over eighty-one mandibular models with variable levels of bone loss (0–8 mm) and five orthodontic movements (intrusion, extrusion, tipping, rotation, and translation). For the numerical analysis of bone, the ductile failure criteria are suitable (T and VM are adequate for the study of bone), with Tresca being more suited. S1, S3, and HP criteria, due to their distinctive design dedicated to brittle materials and liquids/gas, only occasionally correctly described the bone stress distribution. Results: Only T and VM displayed a coherent and correlated gradual stress increase pattern for all five movements and levels of the periodontal breakdown. The quantitative values provided by T and VM were the highest (for each movement and level of bone loss) among all five criteria. The MHP (maximum physiological hydrostatic pressure) was exceeded in all simulations since the mandibular bone is anatomically less vascularized, and the ischemic risks are reduced. Only T and VM displayed a correlated (both qualitative and quantitative) stress increase for all five movements. Both T and VM displayed rotation and translation, closely followed by tipping, as stressful movements, while intrusion and extrusion were less stressful for the mandibular bone. Conclusions: Based on correlations with earlier numerical studies on the same models and boundary conditions, T seems better suited as a single unitary failure criterion for the study of teeth and the surrounding periodontium.

Background: External root resorption is one of common complications of orthodontic treatment, while internal root resorption is rarely observed, and the difference between pulp and periodontal tissues during orthodontic treatment is still unknown. The purpose of this study was to evaluate the effects of orthodontic forces on histological and cellular changes of the dental pulp and periodontal tissues. Methods: Orthodontic tooth movement model was established in Forty-eight adult male Wistar rats. The distance of orthodontic tooth movement was quantitatively analyzed. The histological changes of pulp and periodontal tissues were performed by hematoxylin–eosin staining, tartrate-resistant acid phosphate staining was used to analyze the changes of osteoclast number, immunohistochemistry analysis and reverse transcription polymerase chain reaction were used to examine the receptor of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) expression. The width of tertiary dentine was quantitatively analyzed. Tartrate-resistant acid phosphate staining and the erosion area of osteo assay surface plate was used to evaluate osteoclast activity. Results: The orthodontic tooth movement distance increased in a force dependent manner, and reached the peak value when orthodontic force is 60 g. Heavy orthodontic force increased the RANKL expression of periodontal ligament srem cells (PDLSCs) which further activated osteoclasts and resulted in external root resorption, while the RANKL expression of dental pulp stem cells (DPSCs) was relatively low to activate osteoclasts and result in internal root resorption, and the dental pulp tend to form tertiary dentine under orthodontic force stimulation. Conclusions: Heavy orthodontic forces activated osteoclasts and triggered external root resorption by upregulating RANKL expression in rat periodontal tissues, while there was no significant change of RANKL expression in dental pulp tissue under heavy orthodontic forces, which prevented osteoclast activation and internal root resorption. [ABSTRACT FROM AUTHOR]

Tooth root resorption is multifactorial, leading to progressive destruction and eventual loss of tooth root dentin and cement. There are internal and external types of root resorption, each having its variety. The etiology and pathogenesis of tooth root resorption are poorly understood, and the most significant etiological factors are trauma, pulpal infection, tooth bleaching, and orthodontic treatment. Tooth root resorption is primarily asymptomatic; thus, it is revealed accidentally by radiographic examination. Progressive clinical manifestations are pain, tooth discoloration, tooth mobility, and other conditions. Awareness of the causes and risk factors allowing tooth root resorption, and regular radiographic examination, in case of necessity, make it possible to reveal resorption at an early stage and to prevent its further development. Thus, the aim of this study is to present etiopathogenesis, a clinical course, and diagnostic peculiarities of internal and external types of tooth root resorption, enabling practicing dentists to timely diagnose root resorption and take appropriate measures to avoid further complications. Within the limitation of this review, even though the etiopathogenesis of tooth root resorption is yet not fully understood, it is suggested that the etiological factors fall into two groups (endogenic and exogenic) to enhance further understanding of the possible causes and mechanisms of root resorption and allow practitioners to monitor high-risk patients and make timely diagnoses. Moreover, radiographic examination and CBCT are indispensable for the diagnosis of root resorption. [ABSTRACT FROM AUTHOR]

Recently, the number of patients who request esthetically pleasing aligner-type orthodontic appliances (referred to as aligners) has been increasing. However, the orthodontic forces generated by these aligners are still unknown. This study aimed to verify whether the orthodontic force in aligners can be estimated by measuring near infrared 2D birefringence, and to visualize the orthodontic force. We measured the mechanical and photoelastic properties of transparent orthodontic thermoplastic specimens to correlate the optical retardation with the applied load. The results confirmed equivalence between the mechanical properties and the photoelasticity. In addition, the 2D retardation distribution that occurred when stress was applied to the sample was mapped and visualized. This indicates that it is possible to estimate and visualize the orthodontic force using the retardation obtained by near infrared 2D birefringence measurement. [ABSTRACT FROM AUTHOR]

Background: Fluoride has a major role in strengthening the structure of enamel against acids. Despite differences between caries and root resorption processes, both events inherently involve acidic dissolution of dental tissues. The aim of the present study was to investigate the effects of water fluoridation levels on the surface roughness of root cementum and resorption craters. The findings provided more insight into the influence of fluoride on the surfaces of intact cementum surface and resorption craters. Methods: Twenty-eight orthodontic patients were recruited from two cities in Turkey, with high (≥ 2 ppm) and low (≤ 0.05 ppm) water fluoridation. These patients needed bilateral maxillary first premolar extraction as part of their orthodontic treatment and were allocated into two study groups (n = 14 in each group) based on water fluoridation exposure level: the high-fluoride group (HF) and low-fluoride group (LF). 150 g of buccal tipping forces was applied to all maxillary first premolar teeth for 12 weeks with a beta-titanium spring which was reactivated every 4 weeks. All maxillary premolars were removed at the end of the experiment for surface roughness assessment using three-dimensional confocal microscopy and the associated software. The buccal root surface and the largest buccal resorption crater were investigated. Results: Resorption craters were significantly rougher in LF group compared to HF group (p = 0.002). Craters were rougher than the intact root surfaces (p = 0.000). Cervical and apical regions were significantly rougher than the middle region (p = 0.000 and p = 0.024, respectively). Conclusions: Higher water fluoridation level of ≥ 2 ppm resulted in significantly smoother root resorption craters than low water fluoridation level of ≤ 0.05 ppm when the teeth were subjected to 150 g of buccal tipping force. Fluoride seems to have a protective role at the interface of root resorption, and further mineral or histological studies may shed light on the exact protective process against root resorption. [ABSTRACT FROM AUTHOR]

Orthodontic forces can cause stress and strain concentration and microcracks on tooth root surfaces. This study aimed to analyze whether a lingual orthodontic appliance was more likely to cause root stress concentration and root resorption than the traditional buccal appliance. A finite element model of the root of the maxillary central incisor with straight, buccal, and lingual curvatures was established. A load perpendicular to the tooth surface on the buccal and lingual surfaces of the central incisor was applied, and the stress and strain concentration at the root apex was compared. The stress and strain at the root apex of the lingual cingulum group were lesser than those of the buccal group; little difference was observed between the lingual and buccal clinical crown central augmentation groups. The stress and strain at the root apex of the lingual direction movement group were greater than those of the buccal direction movement group. The direction of the root curvature also influenced the amount of stress and strain at the root apex. The difference in the risk of root resorption between lingual and buccal orthodontics is dependent on the height of the bracket placement. The loading direction of the orthodontic force and direction of the root curvature also affect the stress and strain at the root apex.

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Correction of Class III malocclusions with maxillary deficiency and posterior cross bites in adults can be challenging. Depending upon the severity of the malocclusion treatment options include comprehensive orthodontic treatment with or without surgical aid. With advent of clear aligners systems as Invisalign many patients are seeking orthodontic treatment as an alternative to comprehensive orthodontic treatment with traditional fixed braces. Two cases with posterior cross-bites are presented here. The first case of a 17-year-old female illustrates the difficulty in correcting posterior cross-bites and the second case of a 35-year-old female demonstrates the treatment of posterior cross-bite and maxillary midline diastema using clear aligners (Invisalign®). The exploration of using Invisalign® combined with palatal expanders in conjunction with removable elastics to gain desired results was shown to be a useful device for orthodontic correction. It is described to aid the clinician in the management of maxillary transverse deficiency in skeletally mature patients who desire non-traditional methods. [ABSTRACT FROM AUTHOR]

[Display omitted] Bone remodeling and orthodontic tooth movement (OTM) are controlled by certain essential molecules, one of which is vitamin D. Increased levels of vitamin D have been associated with increased rates of OTM. The purpose of this study was to determine the effect of vitamin D deficiency on the rate of OTM, and to determine their association after applying orthodontic forces. Wistar rats were divided into two groups: control group with average vitamin D levels and experimental group with induced vitamin D deficiency. Orthodontic appliances were fixed to initiate tooth movement. Distance between the reference teeth were measured in millimeters on day zero, and repeated every 7 days, till day 21. A significant difference within the experimental group was found; as well as within the control group, there was also no significant interaction between time and the type of group. The rate of Orthodontic tooth movement was not affected by induced vitamin D deficiency in rats. [ABSTRACT FROM AUTHOR]

Objectives: Orthodontic treatment in adult patients predisposed to mild or severe periodontal disease is challenging for orthodontists. Orthodontic malpractice or hyper-occlusal forces may aggravate periodontitis-induced destruction of periodontal tissues, but the specific mechanism remains unknown. In the present study, the combined effect of mechanical stress and tumor necrosis factor (TNF)-α on the inflammatory response in human periodontal ligament stromal cells (hPDLSCs) was investigated. Materials and methods: hPDLSCs from 5 healthy donors were treated with TNF-α and/or subjected to cyclic tensile strain (CTS) of 6% or 12% elongation with 0.1 Hz for 6- and 24 h. The gene expression of interleukin (IL)-6, IL-8 and cell adhesion molecules VCAM and ICAM was analyzed by qPCR. The protein levels of IL-6 and IL-8 in conditioned media was measured by ELISA. The surface expression of VCAM-1 and ICAM-1 was quantified by immunostaining followed by flow cytometry analysis. Results: TNF-α-induced IL-6 gene and protein expression was inhibited by CTS, whereas TNF-α-induced IL-8 expression was decreased at mRNA expression level but enhanced at the protein level in a magnitude-dependent manner. CTS downregulated the gene expression of VCAM-1 and ICAM-1 under TNF-α stimulation, but the downregulation of the surface expression analyzed by flow cytometry was observed chiefly for VCAM-1. Conclusions: Our findings show that mechanical force differentially regulates TNF-α-induced expression of inflammatory mediators and adhesion molecules at the early stage of force application. The effect of cyclic tensile strain is complex and could be either anti-inflammatory or pro-inflammatory depending on the type of pro-inflammatory mediators and force magnitude. Clinical relevance: Orthodontic forces regulate the inflammatory mediators of periodontitis. The underlying mechanism may have significant implications for future strategies of combined periodontal and orthodontic treatment. [ABSTRACT FROM AUTHOR]

Background: Although preformed archwires with a variety of arch forms are currently commercially available, the effects of variation in the shape of these archwires on the orthodontic force at each tooth are not well understood. Therefore, we evaluated the forces delivered by various types of commercially available preformed nickel–titanium alloy (NiTi) archwires in a simulated mandibular dental arch. Methods: Sixty-three types of 0.019 × 0.025-inch preformed NiTi archwires from 15 manufactures were selected for analysis. The intercanine width (ICW) and intermolar width (IMW) of each archwire were measured at the mean canine and first molar depths of 30 untreated subjects with normal occlusions. Each archwire was placed in a multi-sensor measurement system simulating the mandibular dental arch of subjects with normal occlusions, and orthodontic forces in the facial-lingual direction at the central incisors, canines, and first molars were measured. Correlations between the ICW, IMW, and ICW/IMW ratio of archwires and the delivered forces were analyzed. The archwires were classified into the following four groups according to the ICW and IMW: Control group, ICW and IMW are within the means ± standard deviations of the normal ranges; Ovoid group, narrow ICW and IMW; Tapered group, narrow ICW; and Square group, narrow IMW. The forces were compared among these groups for each tooth. Results: Significant correlations between the measured archwire width and force to each tooth were found, except between IMW and forces at the central incisors and canines. Significant differences in the forces were found among all groups, except between the Ovoid and Tapered groups at all teeth and between the Ovoid/Tapered and Control groups at the first molar. Significantly greater orthodontic forces in the facial direction were delivered at the central incisors by the archwires in the Ovoid and Tapered groups when compared with the archwires in the other groups. Conclusion: These findings suggest that there is a possible risk of a clinically significant level of unfavorable orthodontic force being delivered to the mandibular incisors in labial inclination when using a preformed archwire with an ICW that is narrower than the dental arch. [ABSTRACT FROM AUTHOR]

Abstract Background Osseointegrated implants are considered as clinically non-movable. Parathyroid hormone (PTH) is known to play a significant role in the regulation of bone remodeling and in intermittent, low doses, result in osteoanabolic effects. This study aimed to investigate the effects of PTH and corticotomy, both under traction force, on osseointegrated implants. Methods Four implants—two in each hemimandible—were placed in each of the three study mongrels. Each mongrels were designated as control, normal dose PTH (PTH-1), and high dose PTH (PTH-2) groups, with each groups further subdivided into non-surgery implant and surgery implant. After osseointegration, mechanical force with NiTi closed coil springs (500 g) was applied around each implants. Corticotomy was performed around one of four implants in each mongrels. Parathyroid hormone was administered locally on a weekly basis for 20 weeks. Clinical movement of the implants were evaluated with the superimposed 3D- scanned data, bone- microarchitectural and histologic examinations. Results Superimposition analysis showed continuous movement of the non-surgery implant of PTH-1 group. Movement was further justified with lowest bone implant contact (adjusted BIC; 44.77%) in histomorphometric analysis. Upregulation of bone remodeling around the implant was observed in the normal dose PTH group. In the surgery implants, the remarkably higher adjusted BIC compared to the non-surgery implants indicated increased bone formation around the implant surface. Conclusion The results indicate that the catabolic and anabolic balance of osseointegrated implants in terms of bone remodeling can be shifted via various interventions including pharmacological, surgical and mechanical force. Clinical relevance Upregulated bone remodeling by PTH and corticotomy under continuous mechanical force showed the possible implications for the movement of osseointegrated dental implant.

Objectives: Investigating the impact of thermal and mechanical loading on the force generation of orthodontic aligners made from various thermoplastic materials and different compositions., Materials and Methods: Five distinct materials were utilized including, three multi-layer (Zendura FLX, Zendura VIVA, CA Pro) and two single-layer (Zendura A and Duran). A total of 50 thermoformed aligners (n = 10) underwent a 48-hour ageing protocol, which involved mechanical loading resulting from a 0.2 mm facial malalignment of the upper right central incisor (Tooth 11) and thermal ageing through storage in warm distilled water at 37°C. The force exerted on Tooth 11 of a resin model was measured both before and after ageing using pressure-sensitive films and a biomechanical setup., Results: Before ageing, pressure-sensitive films recorded normal contact forces ranging from 83.1 to 149.7 N, while the biomechanical setup measured resultant forces ranging from 0.1 to 0.5 N, with lingual forces exceeding facial forces. Multi-layer materials exhibited lower force magnitudes compared to single-layer materials. After ageing, a significant reduction in force was observed, with some materials experiencing up to a 50% decrease. Notably, multi-layer materials, especially Zendura VIVA, exhibited lower force decay., Conclusions: The force generated by aligners is influenced by both the aligner material and the direction of movement. Multi-layer materials exhibit superior performance compared to single-layer materials, primarily because of their lower initial force, which enhances patient comfort, and their capability to maintain consistent force application even after undergoing ageing., (© 2024 The Author(s). Orthodontics & Craniofacial Research published by John Wiley & Sons Ltd.)

Numerous experimental studies have examined how much orthodontic force is needed to move teeth more smoothly; however, no reports have examined this clinically in individual, living subjects. We aimed to develop a method for quantifying the force exerted on individual teeth by an orthodontic wire to measure how loads placed on crowded teeth change dynamically over time. Accordingly, we fabricated a series of dental casts of patients undergoing orthodontic treatment (using optical impressions and a three-dimensional printer), fitted these models with nickel-titanium wire, and subjected them to bending load tests. During leveling, nickel-titanium wire is generally considered to exert a weak force due to its low elastic modulus, with a weak orthodontic force applied over a long period of time due to its superelasticity; however, we found that the actual energy exerted by nickel-titanium wire is also largely affected by other factors (e.g., amount of crowding). [ABSTRACT FROM AUTHOR]

Root resorption is a common complication during orthodontic treatment. Microcracks occur on the root surface after an orthodontic force is applied and may be related to the root resorption caused by the orthodontic process. However, the mechanisms underlying root resorption induced by microcracks remain unclear. In this study, a rat orthodontic model was used to investigate the biological mechanisms of root resorption caused by microcracks. First, the first molar was loaded with 0.5-N orthodontic force for 7 days, and microcracks were observed on the root apex surface using a scanning electron microscope. Second, to describe the mechanical principle resulting in microcracks, a finite element model of rat orthodontics was established, which showed that a maximum stress on the root apex can cause microcrack extension. Third, after 7 days of loading in vivo, histological observation revealed that root resorption occurred in the stress concentration area and cementoclasts appeared in the resorption cavity. Finally, proteomics analysis of the root apex area, excluding the periodontal ligament, revealed that the NOX2, Aifm1, and MAPK signaling pathways were involved in the root resorption process. Microcrack extension on the root surface increases calcium ion concentrations, alters the proteins related to root resorption, and promotes cementoclast formation. [ABSTRACT FROM AUTHOR]

ABSTRACT Objective: To assess the effect of orthodontic forces on changes in root length of immature mandibular second premolars. Methods: Sixty-four mandibular second premolars (MSP) with immature apices (left and right sides) of 32 patients aged between 10 and 13 years were evaluated. Orthodontic treatment was started after obtaining periapical radiographs (T1) from the MSPs of each patient. Brackets were bonded, except the ones of MSPs (left or right by random as control MSP, and the other side as test MSP). After 9-12 months, a second periapical radiograph (T2) was obtained from the MSPs of each patient. Then, brackets were bonded to the control MSPs, which were not bonded before. After 18 ± 3 months, a third periapical radiograph (T3) was obtained. Changes in root length were evaluated by using a new formula. The test and control MSPs at T1, T2 and T3 were compared using repeated measures ANOVA and parametric tests. P-value smaller than 0.05 was statistically significant. Results: There was no significant difference between the test and control groups in the mean root length of MSP at T1 (p= 0.48) and T3 (p= 0.078). The root length at T2 (p= 0.001) was significantly different between test and control MSPs, and the test group showed longer root length than the control group. Conclusions: Orthodontic force applied for leveling and alignment of immature MSPs may not have destructive effects on the roots, and may accelerates root formation in short-term. Normal root length was achieved at the end of root development.

This report describes the surgical and orthodontic management of a patient with a buccally impacted permanent mandibular canine. Following surgical exposure, orthodontic traction was applied to reposition the canine with resultant proper functioning, excellent esthetics, and good periodontal health. [ABSTRACT FROM AUTHOR]