Intrusive Force Research Articles

Biomechanical simulation of segmented intrusion of a mandibular canine using Robot Orthodontic Measurement & Simulation System (ROSS)

ObjectiveAim of this study was to investigate the forces and moments during segmented intrusion of a mandibular canine using Cantilever-Intrusion-Springs (CIS). MethodsThree different CIS modifications were investigated using a robotic biomechanical simulation system: unmodified CIS (#1, control), CIS with a lingual directed 6° toe-in bend (#2), and CIS with an additional 20° twist bend (#3). Tooth movement was simulated by the apparative robotic stand, controlled by a force-control algorithm, recording the acting forces and moments with a force-torque sensor. Statistical analysis was performed using Shapiro-Wilk, Kolmogorov-Smirnov, Kruskal-Wallis ANOVA and post hoc tests with Bonferroni correction (α = 0.05). ResultsThe initial intrusive force, which was uniformly generated by a 35° Tip-Back bend, decreased significantly (p < 0.05) from 0.31 N in group (#1) to 0.28 N in group (#3). Vestibular crown tipping reduced significantly (p < 0.05) from 2.11° in group (#1) and 1.72° in group (#2) to 0.05° in group (#3). Matching to that the direction of orovestibular force significantly (p < 0.05) shifted from 0.15 N to vestibular in group (#1) to 0.51 N to oral in group (#3) and the orovestibular tipping moment decreased also significantly (p < 0.05) from 4.63 Nmm to vestibular in group (#1) to 3.56 Nmm in group (#2) and reversed to 1.20 Nmm to oral in group (#3). Apart from that the orovestibular displacement changed significantly (p < 0.05) from 0.66 mm in buccal direction in group (#1) to 0.29 mm orally in group (#2) and 1.49 mm in oral direction as well in group (#3). SignificanceNone of the modifications studied achieved pure mandibular canine intrusion without collateral effects. The significant lingual displacement caused by modification (#3) is, not least from an aesthetic perspective, considered much more severe than a slight tipping of the canine. Consequently, modification (#2) can be recommended for clinical application based on the biomechanical findings.

Are zygomatic implants an alternative to orthognathic surgery in the treatment of a vertical discrepancy ? A case series to describe an open bite treatment protocol

IntroductionThis report aims to present case series to describe a treatment protocol for correction of severe open bite in non-growing patients MethodologyPatients diagnosed with skeletal open bite malocclusion (overbite range: -3 to -6 mm) were treated using a bonded appliance and skeletal anchorage. Intrusive force was applied between buccal bars of appliance and zygomatic multipurpose implants (MPI). Intrusion was continued until positive overbite occurred. Treatment progressed with conventional fixed orthodontic treatment for alignment and settling. MPIs were retained until the end of treatment for retention of intrusion ResultsClinically effective open bite correction was achieved by intrusion of maxillary buccal segment and mandibular counterclockwise autorotation ConclusionThis protocol includes zygomatic anchorage and an appliance that aims triple intrusion effect through combination of orthodontic and physiological forces. Achieving significant maxillary intrusion, controlling mandibular eruption and maximizing mandibular counterclockwise autorotation are the main outcomes of this protocol.

Analysis of the Forces and Moments in Canine Bodily Movement with Different Clear Aligners’ Extraction Space Designs

This study aimed to optimize space closure efficiency by comparing the forces and moments exerted by different designs of clear aligners (CAs) during the movement of maxillary canines into the premolar extraction space. The forces and moments were measured using a multi-axis force/moment transducer on the maxillary right canine. The CAs were fabricated from thermoformed polyethylene terephthalate glycol. The following four edentulous space designs were tested: the edentulous space was left intact (Group 1); the edentulous space was replaced with a premolar pontic (Group 2); the edentulous space was replaced with a half-sized premolar pontic (Group 3); and the edentulous space was replaced with a rectangular column beam (Group 4). The maxillary right canine was moved 0.25 mm distally. All groups experienced buccodistal and intrusive forces; compared with the other groups, Group 1 showed significantly greater intrusive and smaller distal forces, and Group 4 showed significantly greater distal forces. All groups experienced distal tilting, lingual inclination, and mesial rotational moments. These findings suggest that modifying the thickness and extent of the adjacent teeth in the edentulous area of the CA can improve local stiffness, thereby reducing the tipping of the teeth into the edentulous space. This study emphasizes the importance of the CA design in controlling forces and moments for effective orthodontic treatment.

Dentoalveolar effects of open-bite correction with the dual action vertical intra-arch technique: A finite element analysis.

To evaluate tooth displacement and periodontal stress generated by the dual action vertical intra-arch technique (DAVIT) for open-bite correction using three-dimensional finite element analysis. A three-dimensional model of the maxilla was created by modeling the cortical bone, cancellous bone, periodontal ligament, and teeth from the second molar to the central incisor of a hemiarch. All orthodontic devices were designed using specific software to reproduce their morpho-dimensional characteristics, and their physical properties were determined using Young's modulus and Poisson's coefficient of each material. A linear static simulation was performed to analyze the tooth displacements (mm) and maximum stresses (Mpa) induced in the periodontal ligament by the posterior intrusion and anterior extrusion forces generated by the DAVIT. The first and second molars showed the greatest intrusion, whereas the canines and lateral incisors showed the greatest extrusion displacement. A neutral zone of displacement corresponding to the fulcrum of occlusal plane rotation was observed in the premolar region. Buccal tipping of the molars and lingual tipping of the anterior teeth occurred with intrusion and extrusion, respectively. Posterior intrusion generated compressive stress at the apex of the buccal roots and furcation of the molars, while anterior extrusion generated tensile stress at the apex and apical third of the palatal root surface of the incisors and canines. DAVIT mechanics produced a set of beneficial effects for open-bite correction, including molar intrusion, extrusion and palatal tipping of the anterior teeth, and occlusal plane rotation with posterior teeth uprighting.

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

BackgroundThe 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.MethodsCone-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.ResultsFor 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.ConclusionsThe 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.

Correlation between different intrusion force magnitudes and pain intensity in a group of adolescent females (A randomized clinical trial)

Correlation between different intrusion force magnitudes and pain intensity in a group of adolescent females (A randomized clinical trial)

Periodontal considerations during orthodontic intrusion and extrusion in healthy and reduced periodontium.

In patients with advanced periodontal disease, pathological tooth migration may occur, which may require subsequent orthodontic treatment for both aesthetic and functional purposes. When planning orthodontic treatment mechanics, intrusive or extrusive forces are frequently indicated. Understanding tissue reactions during these movements is essential for clinicians when devising a comprehensive orthodontic-periodontal treatment plan. This knowledge enables clinicians to be fully aware of and account for the potential effects on the surrounding tissues. The majority of our understanding regarding the behavior of periodontal tissues in both healthy and compromised periodontal conditions is derived from animal studies. These studies offer the advantage of conducting histological and other assessments that would not be feasible in human research. Human studies are nevertheless invaluable in being able to understand the clinically relevant response elicited by the periodontal tissues following orthodontic tooth movement. Animal and human data show that in dentitions with reduced periodontal support, orthodontic intrusion of the teeth does not induce periodontal damage, provided the periodontal tissues do not have inflammation and plaque control with excellent oral hygiene is maintained. On the contrary, when inflammation is not fully controlled, orthodontic intrusion may accelerate the progression of periodontal destruction, with bacterial plaque remnants being displaced subgingivally, leading to further loss of attachment. Orthodontic extrusion, on the other hand, does not seem to cause further periodontal breakdown in dentitions with reduced periodontal support, even in cases with deficient plaque control. This is attributed to the nature of the tooth movement, which directs any plaque remnants coronally (supragingivally), reducing the risk of adverse effects on the periodontal tissues. This specific type of tooth movement can be leveraged to benefit periodontal conditions by facilitating the regeneration of lost hard and soft periodontal tissues in a coronal direction. As a result, orthodontic extrusion can be employed in implant site development, offering an advantageous alternative to more invasive surgical procedures like bone grafting. Regardless of the tooth movement prescribed, when periodontal involvement is present, it is essential to prioritize periodontal therapy before commencing orthodontic treatment. Adequate plaque control is also imperative for successful outcomes. Additionally, utilizing light orthodontic forces is advisable to achieve efficient tooth movement while minimizing the risk of adverse effects, notably root resorption. By adhering to these principles, a more favorable and effective combined orthodontic-periodontal approach can be ensured. The present article describes indications, mechanisms, side effects, and histological and clinical evidence supporting orthodontic extrusion and intrusion in intact and reduced periodontal conditions.

The effect of orthodontic Force Application and Tooth Movement on Dental Pulp

This systematic review aimed to conclusively investigate the effect of continuous intrusive force application on human pulpal blood flow (PBF). It is a well-established fact that applying a severe orthodontic force for an extended period can cause irreversible pulpitis and necrosis in the pulp by accelerating the inflammation process. In contrast, utilizing moderate and intermittent forces allows for ample tooth movement, limits pulp damage, and facilitates pulp healing. Materials and methods: A comprehensive search of published studies was conducted in several electronic databases such as MEDLINE, PubMed, EMBASE, Scopus, Web of Science, CINAHL, and the Cochrane Database of Systematic Reviews, as well as Google Scholar. The search was conducted without limitations to find published studies. The results showed that orthodontic forces can lead to a decrease in pulpal blood flow, which causes a reduction in tooth sensitivity. This reduction is indicated by an increase in response thresholds and more negative responses to tooth sensitivity tests. Conclusion: applying a severe orthodontic force over a prolonged period of time can lead to irreversible pulpitis and necrosis in the pulp due to an increase in the inflammation process. However, using moderate and intermittent forces can facilitate sufficient tooth movement while minimizing damage to the pulp. This highlights the importance of the endodontic-orthodontic interface and the need to consider dental pulp health during orthodontic treatment to avoid dental trauma.

Clinical application of a lingual retractor with temporary anchorage devices (TADs) for patients with lip protrusion and anterior open bite

Anterior open bite (AOB) is considered one of the most difficult malocclusions to correct and achieve successful and stable results. Various treatment approaches have been proposed for the treatment of AOB in adults. Intrusion of the entire maxillary dentition is necessary for AOB patients with severe incisor exposure. In previous reports, a labial appliance with temporary anchorage devices (TADs) implanted in various positions has been used to achieve total intrusion of the maxillary dentition. This article describes the design and biomechanics of an anteroposterior lingual retractor (APLR) to attempt retraction of anterior teeth and total intrusion of maxillary dentition after premolar extraction in patients with both lip protrusion and AOB and the functions of each component of APLR is considered. When force is applied between the anterior lever arm of the APLR and a TAD in the midpalatal area, the anterior teeth are intruded and retracted with torque control. Because the direction of the APLR force and the guide bar are not parallel, intrusive force is generated in the posterior teeth. Due to this total intrusion of the maxillary dentition, the mandible is rotated counterclockwise, improving AOB with severe incisor exposure. Various cases are presented in which APLR was applied to AOB patients, and the clinical considerations behind the treatment are explained in detail.

Nonsurgical synergistic full-arch vertical intrusion treatment of bimaxillary protruded hyperdivergent skeletal Class II malocclusion using aligners.

A bone-borne full-arch vertical control strategy using miniscrews was deployed with aligners to treat a case of skeletal hyperdivergent Class II malocclusion with bimaxillary protrusion. Miniscrews were inserted in the posterior buccal and palatal regions and the anterior buccal region of the maxilla to distribute vertical intrusive force through the upper arch by anchoring vertical elastics from the miniscrews to the aligners. Synergetic lower anterior intrusion was completed using bilateral posterior miniscrews to counteract the extrusive force generated. Substantial full upper arch and lower anterior vertical intrusion was achieved. In conjunction with en masse anterior-posterior retraction, synergetic posterior and anterior vertical intrusion facilitated counterclockwise rotation of the mandible, creating significant esthetic improvement. Anterior vertical elastics also provided flaring of the anterior teeth, reducing the side effect of lingual tipping from en masse retraction, while successfully controlling overbite and incisor torque during space closure. The bone-borne full-arch vertical intrusion strategy can work well with aligners to address hyperdivergent skeletal Class II malocclusion with bimaxillary protrusion.

Efficacy of maxillary molar intrusion and quantification of related external apical root resorption - A comparison of two approaches.

This retrospective single-centre study aimed to compare the efficacy of maxillary second molar intrusion with two different approaches, miniscrew-assisted molar intrusion and traditional segmental archwire intrusion, and to compare orthodontically induced external apical root resorption (OIERR) during intrusion between two groups via cone beam computed tomography (CBCT). A total of 40 adult patients (33.6 ± 10.3 years old) with supraerupted maxillary second molars due to the loss of antagonistic teeth were recruited, with 20 patients in each group. A segmental archwire with adjacent teeth as an anchorage was used in the control group, and 60-100 g of intrusive force was applied by using miniscrews in the experimental group to intrude the overerupted molars. Full-volume CBCT was performed before and after intrusion, and the amount of intrusion and extent of OIERR of the overerupted molars were compared between the two groups. Supraerupted maxillary second molars could be successfully intruded in an average of 5 months. There was more intrusive movement of the buccal and palatal cusps in the mininscrew group than that in the segmental archwire group (P < .05). The intrusive amount of palatal cusp was 3.67 ± 1.13 mm in the miniscrew group and 2.38 ± 0.74 mm in the segmental archwire group. More palatal OIERR was observed in the miniscrew group (30.3 ± 11.6 mm3) than in the segmental archwire group (21.0 ± 8.66 mm3) (P = .0063). There was no significant difference in OIERR between the two groups for mesial and distal buccal roots (P > .05). Miniscrews help effectively with supraerupted maxillary second molar intrusion, especially for palatal cusps. There was more OIERR in the palatal root when using miniscrews compared to the segmental archwire approach.

Effect of clear aligner type on maxillary full-arch intrusion: 3D analysis using finite element method

BackgroundVertical maxillary excess (VME) is one of the most common reasons for seeking orthodontic treatment. Total intrusion with aligners is a promising alternative to surgery in some cases. Considering the elastic deformation of aligners, this study aimed to evaluate the possible desirable and undesirable teeth displacements during full maxillary arch intrusion using clear aligners and temporary anchorage devices (TADs).MethodsThe maxillary arch and clear aligners were modeled in SolidWorks. Four aligner brands including Leon, Duran, Duran Plus, and Essix Plus were selected based on their material properties. Anterior and posterior intrusion forces of 80 and 300 g were applied from attachments between the canines and first premolars and between the first and second molars, respectively. Vertical and anteroposterior tooth displacements were determined.ResultsThe greatest intrusion was recorded at the buccal of the second molar, followed by the first molar. The lowest value was measured at the palatal of the molars with all aligners except Duran, which indicated minimal intrusion in the central incisor. All teeth were mesially displaced at the incisal/occlusal except incisors that moved distally. All apices showed distal movement.ConclusionsTotal intrusion using clear aligners may be accompanied by other tooth movements, including buccal tipping and mesial-in rotation of the molars, retrusion of incisors, and mesial movement of other teeth.

Anterior open bite correction via molar intrusion: Diagnosis, advantages, and complications

Anterior open bite can be effectively treated nonsurgically via molar intrusion. This technique, involving the intrusion of posterior teeth using temporary skeletal anchorage devices, prompts counterclockwise rotation of the mandible. This rotation not only corrects anterior open bite but also contributes to a decrease in anterior facial height, improvements in lip incompetency, and forward movement of the chin. For successful outcomes, temporary skeletal anchorage devices, installed on both the buccal and palatal sides, must deliver equivalent intrusion force to the maxillary teeth. Treatment planning should consider factors such as skeletal discrepancies, vertical excess, incisor exposure, and configuration of the occlusal plane. Clinicians are advised to closely monitor periodontal changes and consider overcorrection to ensure lasting stability and maintenance of incisal overlap post-treatment.

Evaluation of Rate of Intrusion, Retraction and Amount of Periapical Root Resorption with Jayade’s Intrusion Arch versus Modified Three-piece Intrusion Arch using CBCT: A Research Protocol

Introduction: Deep bite, a common orthodontic malocclusion, necessitates timely intervention to prevent potential side-effects. If left untreated, a deep bite can lead to increased tooth wear, dental injuries, and Temporomandibular Joint (TMJ) disorders. Various treatment modalities, such as anterior teeth intrusion and posterior teeth extrusion, are employed to correct deep bite. However, selecting the optimal approach requires careful consideration of patient-specific factors and treatment objectives. While anterior teeth intrusion is effective for mild to moderate cases, posterior teeth extrusion may be preferred in severe deep bite scenarios. There are various treatment modalities for deep bite correction such as intrusion arches and mini screw implants. Jayade’s intrusion arch, detailed by A.V. Jayade in “Refined Begg for Modern Times” (2001), is an orthodontic appliance designed to correct vertical dental misalignments by intruding over-erupted anterior teeth. The modified three-piece intrusion arch is an advancement of the traditional intrusion arch technique. It incorporates three distinct segments: two lateral segments and a central segment. This design allows for greater precision and control over the intrusion forces applied to specific teeth or groups of teeth. Need of the Study: Simultaneous intrusion and retraction mechanics in orthodontic treatment are very challenging, and there is a paucity of data regarding the best modalities for achieving these with minimal root resorption. Aim: Comparative evaluation of the rate of intrusion, retraction and amount of periapical root resorption with Jayade’s intrusion arch and the modified three-piece intrusion arch using Cone Beam Computed Tomography (CBCT). Materials and Methods: The present prospective, two-arm parallel interventional study will be conducted in the Department of Orthodontics and Dentofacial Orthopaedics Outpatient Department, Sharad Pawar Dental College, Sawangi (Meghe), Wardha, Maharashtra, India, from September 2024 to February 2026. Study will involve the recruitment of 20 patients and all these patients will be divided into two groups for comparative analysis. The intervention will entail the use of the McLaughlin, Bennett and Trevisi (MBT) bracket system equipped with triple tubes on maxillary teeth, characterised by a slot dimension of 0.022 inches by 0.028 inches, as the standardised starting point for all cases. After initial alignment and leveling, and extractions as per the case, the intrusion arch will be applied. Jayade’s intrusion arch will be given in group A, while the modified threepiece intrusion arch will be given in group B. The assessment of intrusion rate, retraction rate and amount of root resorption will be conducted both prior to the initiation of intrusive and retractive forces, as well as, at intervals of two, four and six months following the application of the intrusion arches.

Evaluation of force systems generated by Memory Titanol® springs with different preactivation bends.

This study evaluated the force system generated by the Memory Titanol® spring (MTS) with different preactivation bends using an orthodontic force tester (OFT). Three preactivations were tested using a 0.017 × 0.022-in stainless steel (SS) wire and a 0.018 × 0.025-in NiTi segment, with an activation of 30º in the posterior segment (β), with 0º (Group 1 [G1]), 45º (Group 2 [G2]), and 60º (Group 3 [G3]) in the anterior segment (α). The molars showed extrusion values of -1.33 N for G1 and -0.78 N for G2, and an intrusion value of 0.33 N for G3. The force in the premolars was intrusive with a variation of 1.34 N for G1 and 0.77 N for G2; and extrusive with a variation of -0.31 N for G3. Regarding the upright moment (Ty) of the molar, a distal moment was observed with values of 53.45 N.mm for G1 and 19.87 N.mm for G2, while G3 presented a mesial moment of -6.23 N.mm. G1, G2, and G3 all exhibited distal premolar moments (Ty) of 3.58, 2.45, and 0.68 N.mm, respectively. The tested preactivations exerted an extrusive force in G1 and G2 and an intrusive force in G3 during molar vertical movement. The premolar region in G1 and G2 showed intrusive force and distal moment.

The Communication Context of Live Press Conferences in Social Engagement: The Challenge of Journalists’ Practice and Coping Strategies

&lt;p&gt;數位時代社群平臺直播伴隨網友的即時評論，不但縮短消息來源與閱聽人的距離，也改變記者與消息來源的互動形式。研究以Goffman之戲劇理論和Foucault的圓形監獄全景敞視權力與規訓概念，來檢視2020年疫情指揮中心直播記者會的傳播情境。以深度訪談法研究後發現，直播傳播情境具記者、網友、消息來源三方權力競逐的特質，記者會的前臺以各式道具凸顯政府防疫成果，記者成為被觀看的對象，提出尖銳問題則易被網友攻擊或「出征」，使記者產生被規訓的節制行為，採取消極避禍策略；在後臺則出現外人侵入記者與官員互動的封閉對話群組，兩造的對話被擴散至社群媒體，使記者承受網路騷擾的壓力。處於前臺與後臺雙重壓力的記者，仍在困境中以不同策略實踐媒體問責。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;In this digital age, live streaming on social media platforms, accompanied by real-time comments from netizens, not only shortens the distance between the news source and the audience but also changes the way reporters interact with their sources. This study employs Goffman’s dramaturgical theory and Foucault’s views on the panopticon and disciplinary power to examine the communicative context of the live broadcasts of the 2020 Central Epidemic Command Center press conferences during the COVID-19 pandemic. Using the in-depth interview method, the researcher found that the live broadcast communication creates a three-party power competition situation involving reporters, netizens, and news sources. In the front stage of the press conference, various props are used to highlight the outcomes of epidemic prevention. Reporters become the observed subjects, and those who raise sharp questions risk facing attacks by netizens. This dynamic caused the reporters to exert self-restrain, be &amp;ldquo;disciplined,&amp;rdquo; and adopt passive ways to avoid being embroiled in awkward situations. In the back stage, closed dialogues between reporters and officials are being leaked to social media platforms by external intrusive forces, thus exposing the reporters to the pressure of online harassment. Under dual pressures from both the front stage and the backstage, the reporters continue to navigate the dilemma by implementing various strategies to practice media accountability.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Investigation of Forces and Moments during Orthodontic Tooth Intrusion Using Robot Orthodontic Measurement and Simulation System (ROSS).

The Robot Orthodontic Measurement and Simulation System (ROSS) is a novel biomechanical, dynamic, self-regulating setup for the simulation of tooth movement. The intrusion of the front teeth with forces greater than 0.5 N poses a risk for orthodontic-induced inflammatory root resorption (OIIRR). The aim was to investigate forces and moments during simulated tooth intrusion using ROSS. Five specimens of sixteen unmodified NiTi archwires and seven NiTi archwires with intrusion steps from different manufacturers (Forestadent, Ormco, Dentsply Sirona) with a 0.012″/0.014″/0.016″ wire dimension were tested. Overall, a higher wire dimension correlated with greater intrusive forces Fz (0.012″: 0.561-0.690 N; 0.014″: 0.996-1.321 N; 0.016″: 1.44-2.254 N) and protruding moments Mx (0.012″: -2.65 to -3.922 Nmm; 0.014″: -4.753 to -7.384 Nmm; 0.016″: -5.556 to -11.466 Nmm) during the simulated intrusion of a 1.6 mm-extruded upper incisor. However, the 'intrusion efficiency' parameter was greater for smaller wire dimensions. Modification with intrusion steps led to an overcompensation of the intrusion distance; however, it led to a severe increase in Fz and Mx, e.g., the Sentalloy 0.016″ medium (Dentsply Sirona) exerted 2.891 N and -19.437 Nmm. To reduce the risk for OIIRR, 0.014″ NiTi archwires can be applied for initial aligning (without vertical challenges), and intrusion steps for the vertical levelling of extruded teeth should be bent in the initial archwire, i.e., 0.012″ NiTi.

The displacement of teeth and stress distribution on periodontal ligament under different upper incisors proclination with clear aligner in cases of extraction: a finite element study

ObjectivesTo investigate the displacement of dentition and stress distribution on periodontal ligament (PDL) during retraction and intrusion of anterior teeth under different proclination of incisors using clear aligner (CA) in cases involving extraction of the first premolars.MethodsModels were constructed, consisting of the maxilla, PDLs, CA and maxillary dentition without first premolars. These models were then imported to finite element analysis (FEA) software. The incisor proclination determined the division of the models into three groups: Small torque (ST) with U1-SN = 100°, Middle torque (MT) with U1-SN = 110°, and High torque (HT) with U1-SN = 120°. Following space closure, a 200 g intrusion force was applied at angles of 60°, 70°, 80°, and 90° to the occlusal plane, respectively.ResultsCA therapy caused lingual tipping and extrusion of incisors, mesial tipping and intrusion of canines, and mesial tipping of posterior teeth in each group. As the proclination of incisors increased, the incisors presented more extrusion and minor retraction, and the teeth from the canine to the second molar displayed an increased tendency of intrusion. The peak Von Mises equivalent stress (VMES) value successively decreased from the central incisor to the canine and from the second premolar to the second molar, and the VMES of the second molar was the lowest among the three groups. When the angle between the intrusion force and occlusal plane got larger, the incisors exhibited greater intrusion but minor retraction.ConclusionsThe "roller coaster effect" usually occurred in cases involving premolar extraction with CA, especially in patients with protruded incisors. The force closer to the vertical direction were more effective in achieving incisor intrusion. The stress on PDLs mainly concentrated on the cervix and apex of incisors during the retraction process, indicating a possibility of root resorption.

Uncanny parallels: exile, pandemic, and the Palestinian experience

ABSTRACT Inspired by Said’s concept of exile, Camus’ 1947 novel The Plague, and testimonies from our students, this paper explores the striking similarities between experiences of exile and the COVID-19 pandemic. Both exile and the pandemic are seen as intrusive forces causing rupture and discontinuity in one’s life at the physical, psychological and socio-cultural levels. This paper demonstrates that for many Palestinians – including us and our students – the pandemic manifests what Freud termed ‘repetition compulsion’. That is, many of our students interpret the detrimental and precarious impact of the pandemic as a complex form of exile, a nuanced understanding that blends a historical, communal memory of displacement with a present, universal crisis. This paper further explains that the themes of exile and displacement in Camus’ The Plague provide us and our students with a focal point to examine the striking, albeit anachronistic, similarities between the pandemic caused by Israeli occupation and the COVID-19 virus. This uncanny relationship between the pandemic and exile is further substantiated by the fact that the pandemic has provided cover, or at least distraction, for the escalation of oppressive political actions, thus deepening the entrenchment of a physical and psychological ‘exile’ for Palestinians.

Evaluation of different models of intrusive force application and temporary anchorage device (TAD) placement in total arch intrusion using clear aligners; a finite element analysis

IntroductionPresent study aims to evaluate different models of total arch intrusion using clear aligners in a finite element setup, which might be helpful in gummy smile patients who seek this treatment modality.MethodsFour patterns of intrusive forces were applied on each side of the upper arch aligner model: (1) Distal to the lateral incisors (facial − 80 g) and distal to the first molar (palatal − 150 g). (2) Distal to the lateral incisors (facial − 80 g) and distal to the first molars (facial − 80 g and palatal − 80 g). (3) Distal to the canines (facial − 80 g) and distal to the first molars (facial − 150 g). (4) Distal to the lateral incisors (facial − 80 g) and mesial to the first molars (facial − 150 g). Vertical and horizontal movements of the teeth were measured.ResultsExtrusion movements were solely detected at buccal cusps of the first and second molars in the first model. Palatal movements of posterior teeth were detected in this model. Model II showed a homogeneous intrusion in anterior and posterior teeth and the amount of palatal movements of posterior teeth was reduced compared to model I. In contrast to Model IV, Model III had more intrusion in the posterior compared to anterior teeth. Facial movements of posterior teeth were detected in the third and fourth models. Incisor teeth showed facial movements among all of the models except for the lateral incisor in the third model.ConclusionsEach model of force application, causes different outcomes and side effects which is beneficial in certain clinical situations.