Actual contribution ratio of maxillary and mandibular molars for total molar relationship correction during maxillary molar sequential distalization using clear aligners with Class II elastics: A finite element analysis

The effects of palatal anchorage device on molar distalization with clear aligner: Three-dimensional finite element analysis

INTRODUCTION

This study aimed to analyze the biomechanical effects of the combined use of clear aligner and palatal anchorage devices (transpalatal arch [TPA], combination of TPA and microimplant [MI]) during maxillary molar distalization.

METHODS

Three-dimensional finite element models were established to simulate molar distalization, incorporating 7 configurations: Without-TPA, TPA-no-MI, TPA-with-MI1, TPA-with-MI2, TPA-with-MI3, TPA-with-MI4, and TPA-with-MI5. The 3-dimensional displacements of upper teeth and von Mises stress distribution in the periodontal ligament were evaluated.

RESULTS

The use of palatal anchorage devices enhanced the anchorage of anterior teeth and improved molar distalization. The efficacy of anchorage enhancement is related to the relative position of MI and the center of resistance of the maxillary dentition.

CONCLUSIONS

TPA placed on the first premolars effectively reinforces anterior anchorage during molar distalization with clear aligner. The combination of TPA and palatal MI can strengthen anterior tooth anchorage further.

Effects of maxillary molar distalization using clear aligners during the mixed dentition and early permanent dentition with 3 types of Class II traction: a three-dimensional finite element analysis

BACKGROUND

Impacts of the developmental stages of maxillary second molars, methods for distalization of the maxillary first molars, Class II traction application, and different traction modes on three-dimensional molar movements, anchorage tooth displacement, and stress distribution remains poorly understood.

METHOD

Patients with maxillary second molars in Nolla 4-6 and 7-8 stages were selected for 3D finite element modeling. We analyzed three-dimensional movements and stress distribution in maxillary and mandibular dentitions after unilateral and bilateral distalization of maxillary first molars using clear aligners, with no traction and three types of Class II traction.

RESULTS

In Nolla 4-6 and 7-8 stages, after bilateral molar distalization, maxillary anterior labial inclination, tooth, periodontal membrane and alveolar bone stress were more significant. Movements of maxillary first molars were greater in Nolla 7-8 stages regardless of unilateral or bilateral molar distalization. Either unilateral or bilateral molar distalization, Angel button group provided better anchorage control for central incisors. Precision incision group provided superior anchorage control for lateral incisors and achieved the largest distal movements of maxillary first molars. Lingual button group provided anchorage control for deciduous or permanent canines. Molar distalization modes had no effect on mandibular dentition. Movements and maximum periodontal membrane stress values of mandibular dentition were the smallest in the Angel button group.

CONCLUSION

When moving molars distally, it's necessary to consider the development of maxillary second molar and evaluate the distalization modes, Class II traction modes and the influence on anchorage teeth, to design personalized treatment plan.

An integrated approach to posterior anchorage preparation and incisor torque compensation in premolar extraction cases using clear aligners

BACKGROUND

In clear aligner treatment (CAT), closure of the premolar space is achieved by reducing aligner length. Posterior anchorage preparation is effective in preserving molar angulation; however, the resulting distal tipping can contribute to anterior anchorage loss. This study aims to identify an approach that balances anterior torque compensation with posterior anchorage preparation in CAT.

METHODS

Two finite element models were developed to simulate en-masse incisor retraction using clear aligners (CAs). Model 1 simulated first premolar extraction cases, while Model 2 simulated second premolar extraction cases. In Step I, only distal tipping was applied to the posterior teeth as an anchorage preparation strategy. In Step II, a positive torque of 0.08 degrees was introduced to the incisors to simulate torque compensation in a single orthodontic step.

RESULTS

In Model 1, the maxillary lateral incisor and mandibular central incisor tipped further lingually compared to cases without posterior anchorage preparation. The posterior terminal teeth showed a tendency to tip mesially in Step I, which was partially reduced with anterior torque compensation in Step II. In Model 2, all incisors had a stronger tendency to tip lingually in Step I. Molar anchorage control improved with incisor torque compensation of 0.08 degrees. Tipping was more pronounced in the maxillary arches compared to the mandibular arches. Posterior anchorage loss was greater in Model 2, while Model 1 showed more pronounced anchorage loss in anterior teeth.

CONCLUSIONS

Posterior anchorage preparation alone increases the risk of anterior anchorage loss. Combining this approach with incisor torque compensation helps distribute the anchorage burden more effectively. As an advanced approach, anterior and posterior anchorage management should be strategically coordinated and adapted to the number of orthodontic steps required in premolar extraction cases treated with CAs.

CLINICAL TRIAL NUMBER

Not applicable.

What is the role of second molars in leveling the curve of Spee? A finite element analysis study

INTRODUCTION

This study aimed to assess the effect of the mandibular second molars on the stress distribution and initial displacements during leveling the curve of Spee using different archwire thicknesses and materials by means of finite element analysis.

METHODS

After construction of all anatomic structures, including the mandibular alveolar bone, periodontal ligament, and dentition, 0.022-in slot brackets and 0.022 × 0.028-in molar tubes were placed on the buccal surfaces of the teeth. Different archwires were modeled, with 2 different thicknesses (0.016-in and 0.017 × 0.025-in) and 3 different materials (nickel-titanium, stainless steel, and titanium molybdenum). Two different models were created: The mandibular dentition (1) with and (2) without second molars. The initial teeth movements and periodontal ligament stress distribution after leveling were analyzed for each of the models and archwires.

RESULTS

The initial stress levels with all archwires were higher when the second molars were also included. The highest von Mises stresses were 16.75 N/mm2 with the 0.017 × 0.025-in stainless steel archwire. Periodontal stresses were mostly concentrated in the apical area of the incisors. The tendency of labial tipping increased with the attachment of second molars. Thicker archwires with all materials were noticed to enhance the anterior tipping of the incisors. In both scenarios, the least movement occurred on the x-axis.

CONCLUSIONS

The inclusion of the second molars enhanced the stress level and the initial anterior tipping of the incisors. However, the bonding of the second molars did not have any effect on the initial displacement in the transverse direction for all the archwires used. As the archwire dimension increased, higher stress values were observed on the whole mandibular dentition.

Impact of Molar Distalization with Clear Aligners on Periodontal Ligament Stress and Root Resorption Risk: A Systematic Review of 3D Finite Element Analysis Studies

Background/Objectives: Molar distalization with clear aligners is increasingly used for Class II malocclusions, yet the associated periodontal ligament (PDL) stress and potential root resorption risk remain unclear. Three-dimensional finite element analysis (3D FEA) provides insight into these factors, but variations in attachments and anchorage strategies merit systematic evaluation. To determine whether molar distalization with clear aligners exceeds the PDL stress thresholds for root resorption and to assess how different attachments and anchorage methods influence stress distribution. Methods: In accordance with the PRISMA 2020 guidelines, four electronic databases were searched without language or date restrictions. Studies were included if they (1) employed 3D FEA, (2) analyzed PDL stress during aligner-based molar distalization, and (3) assessed root resorption risk or stress thresholds. Two reviewers independently screened and extracted data, yielding eight studies. Results: Attachments lowered PDL stress and distributed forces more evenly, reducing root resorption risk compared with no attachment cases. Micro-implants shifted stress to molars and protected anterior teeth; palatal mini-screws achieved greater distalization but higher stress, requiring caution, while buccal mini-screws showed lower stress in first premolar roots. Placing a mini-screw between first and second molars yielded the lowest, most uniform stress. Class II elastics-with precision cuts-demonstrated low compressive stress and improved anchorage, although some resorption risk persisted in maxillary anteriors. Conclusions: Clear aligner-based molar distalization can elevate PDL stress to potentially resorptive levels. Although attachments, micro-implants, and Class II elastics improve stress distribution and lessen root resorption risk, it is not fully eliminated. Careful, individualized treatment planning remains essential, and further clinical validation is needed to establish definitive guidelines.

Biomechanical effects of functional clear aligners on the stomatognathic system in teens with class II malocclusion: a new model through finite element analysis

OBJECTIVES

The Functional Clear Aligner (FCA) is a novel orthodontic appliance designed for the treatment of Class II malocclusion with mandibular retrognathia in adolescents. The aim of this study was to investigate the biomechanical characteristics of the masticatory muscles, jawbone, and temporomandibular joint (TMJ) during mandibular advancement using either FCA or Class II elastics combined with clear aligner (Class II elastics) through finite element analysis.

MATERIALS AND METHODS

A 3D finite element model of the 'muscle-jawbone-TMJ-appliance' system was constructed based on CBCT and MRI images of a boy with skeletal Class II malocclusion. Masticatory muscles included masseter, temporal, medial pterygoid, and lateral pterygoid muscles. The TMJ consists of the temporal bone's glenoid fossa, disc, and mandibular condyle. To observe the biomechanical characteristics of the muscles and TMJ during orthodontic appliance wearing and the retention phase, two different protocols were used: Model 1: The mandibular advancement using FCA; Model 2: The mandibular advancement using Class II elastics.

RESULTS

The FCA group produced greater and more coordinated masticatory muscle forces compared to the Class II elastics group. Temporal and masseter muscles exhibited the most pronounced variation in muscle strength during mandibular advancement. The FCA group exhibited greater TMJ region stress compared to the Class II elastics group. Interestingly, the stress on the articular discs in both models decreased over time. Tensile stresses were observed in both the condyle and the posterior region of the articular fossa.

CONCLUSION

During skeletal Class II malocclusion treatment, masticatory muscle forces and stress on the TMJ were higher in the FCA group compared to the Class II elastics group. In both models, stress cushioning was provided by the articular disc.

Anchorage loss of the posterior teeth under different extraction patterns in maxillary and mandibular arches using clear aligner: a finite element study

BACKGROUND

Extracting the premolars is an effective strategy for patients with bimaxillary dentoalveolar protrusion. Clear aligners (CAs) close the extraction spaces through shortening the length of aligners. The contraction force generated by the terminal of aligners makes the posterior teeth tip mesially, which is known as the roller coaster effect. This phenomenon is even worse in the 2nd premolar extraction cases. Posterior anchorage preparation is commonly used to protect the angulation of molars, taking the form of presetting distal tipping value. However, the distal tipping design aggravates the anchorage loss of anterior teeth simultaneously. This study aimed to explore the different anchorage loss of the posterior teeth when the 1st or 2nd premolars were extracted using CAs, respectively in maxillary and mandibular arches, further providing guidance for anchorage preparation design in clinical practice.

METHODS

Two bimaxillary finite element models with different extraction patterns were established to simulate the anterior en-masse retraction process of the CAs. In Model 1, the maxillary and mandibular 1st premolars were extracted, while in Model 2, the 2nd premolars were extracted. Finite element analysis methods were utilized to analyze the tipping angle of the anterior and posterior teeth.

RESULTS

Compared between two models, the anterior teeth exhibited a greater lingual inclination tendency and the posterior teeth exhibited a slighter mesial tipping tendency in Model 1 regarding individual tooth. The closer to the extraction spaces, the greater the tip, and the distal tipping tendency of the 1st premolars was more evident than the mesial tipping tendency of the 1st molars in Model 2. Compared between the maxillary and mandibular arches, the mesial tipping tendency of individual posterior tooth was more evident in the maxilla. In addition, the highest hydrostatic stress of the periodontal ligaments was concentrated on the cervical and apical parts directly adjacent to the extraction spaces, and it exhibited relatively uniform distribution in Model 1.

CONCLUSIONS

The individual posterior tooth showed the same mesial tipping direction but to different degree when the 1st or the 2nd premolars were extracted during clear aligner treatment. Presetting anchorage preparation design for the posterior teeth is essential to alleviate the roller coaster effect, especially in the 2nd premolar extraction cases. Furthermore, larger anchorage preparation value should be proposed for the maxillary posterior teeth.

Miniscrew anchorage versus Class II elastics for maxillary arch distalization using clear aligners

OBJECTIVES

To identify whether intramaxillary miniscrew anchorage could achieve a better maxillary arch distalization effect in clear aligner treatment compared to Class II elastics.

MATERIALS AND METHODS

Thirty adult patients with Class II dentition who were treated with whole maxillary arch distalization using clear aligners were collected. Either intramaxillary miniscrew anchorage (miniscrew group, n = 17) or intermaxillary Class II elastics (Class II elastic group, n = 13) were used to support maxillary arch distalization. Three-dimensional predicted and achieved displacements, and angular changes of maxillary posterior teeth and anterior teeth, were measured and compared.

RESULTS

The achieved distalization efficiency was 36.2%-43.9% in the posterior teeth and the retraction efficiency was 36.9%-49.4% in the anterior teeth. No statistically significant differences were found in maxillary arch distalization efficiency between the groups. The miniscrew group achieved less incisor extrusion and posterior tooth distal tipping than the Class II elastic group. Both groups achieved comparable arch expansion, posterior tooth buccal inclination, and anterior tooth lingual inclination.

CONCLUSIONS

Intramaxillary miniscrew anchorage and intermaxillary Class II elastics achieved comparable efficiency in maxillary arch distalization. However, the miniscrew anchorage showed better vertical control in anterior teeth and mesiodistal tipping control in posterior teeth.

Effects of different intrusion patterns during anterior teeth retraction using clear aligners in extraction cases: an iterative finite element analysis

Background

Overtreatment design of clear aligner treatment (CAT) in extraction cases is currently primarily based on the clinical experience of orthodontists and is not supported by robust evidence on the underlying biomechanics. This study aimed to investigate the biomechanical effects of overtreatment strategies involving different maxillary anterior teeth intrusion patterns during anterior teeth retraction by CAT in extraction cases.

Materials and methods

A finite element model of the maxillary dentition with the first premolar extracted was constructed. A loading method of clear aligners (CAs) based on the initial state field was proposed. The iterative method was used to simulate the long-term orthodontic tooth movement under the mechanical load exerted by the CAs. Three groups of CAs were utilized for anterior teeth retraction (G0: control group; G1: incisors intrusion group; G2: anterior teeth intrusion group). Tooth displacement and occlusal plane rotation tendency were analyzed.

Results

In G0, CAT caused lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, mesial tipping, and intrusion of the posterior teeth. In G1, the incisors showed minimal extrusion, whereas the canines showed increased extrusion and distal tipping tendency. G2 showed the smallest degree of posterior occlusal plane angle rotation, while the inclination tendency of the canines and second premolars decreased.

Conclusion

1. In CAT, tooth displacement tendency may change with increased wear time. 2. During anterior teeth retraction, the incisor intrusion pattern can provide effective vertical control for the lateral incisors but has little effect on the central incisors. Anterior teeth intrusion patterns can alleviate the inclination of canines and second premolars, resulting in partial relief of the roller-coaster effect.

Molar distalization in orthodontics: a bibliometric analysis

OBJECTIVES

The study endeavors to undertake a bibliometric analysis on molar distalization, with the objective of illuminating its evolutionary trajectory, current status, and prognosticating future research hotspots and trends.

MATERIAL AND METHODS

A comprehensive exploration of the literature on molar distalization was carried out by conducting a search in the Web of Science (WOS) core database of the University of Hong Kong Electronic Library. The search for topic terms employed included "molar distalization," "molar distalisation," "move molar distally," "molar distal movement," and "molar backwards." The search results were subsequently subjected to meticulous analysis using CiteSpace software. This analysis encompassed various facets such as the citation count; the geographical distribution of the countries, institutions, and journals responsible for publishing the articles; the distribution of the authors; the utilization of keywords within the articles; and the analysis of references.

RESULTS

A total of 516 articles were included in the analysis. The top 5 countries in terms of the number of published papers were the United States (USA), South Korea, Turkey, Italy, and Germany, and the top 5 institutions in terms of the number of published papers were Kyung Hee University, A.T. Still University of Health Sciences, Catholic University of Korea, Seoul St. Mary's Hospital, and Universidade de Sao Paulo. The top 5 authors in terms of the number of published papers were Park, Kook, Bayome, Janson, and Lee. There was little cooperation overall. The top 3 journals in terms of the most published related articles were all orthodontic-related journals. After molar distalization and anchorage, the most frequently used keywords were distalization, movement, and pendulum appliance. Kinzinger GSM is the most frequently cited author in references, and one of his articles also has the highest centrality score in references.

CONCLUSIONS

As the tides of time shift and scholars display an ever-growing dedication to unraveling the intricacies of this therapeutic modality, the realm of molar distalization has undergone notable advancements in technology. Initially, the traditional appliance suffered from aesthetic drawbacks and discomfort. However, contemporary iterations of the appliance have transcended these limitations, boasting enhanced elegance and convenience while concurrently elevating their efficacy. Nevertheless, limitations of current appliances, including their durability and propensity for recurrence post-treatment, continue to necessitate further advancement. Hence, the ongoing scientific inquiry aims to delve deeper into refining treatment modalities and fabricating cutting-edge appliances within this realm.

CLINICAL RELEVANCE

This study holds the potential to significantly enhance the ability of orthodontists to devise treatment protocols and offer state-of-the-art clinical recommendations, thereby empowering them to deliver advanced and refined orthodontic interventions.