Quantification of intrusive/retraction force and moment generated during en-masse retraction of maxillary anterior teeth using mini-implants: A conceptual approach

Friction versus frictionless mechanics during maxillary en-masse retraction in adult patients with Class I bimaxillary dentoalveolar protrusion: a randomized clinical trial

BACKGROUND

Extraction space closure is a challenging phase during orthodontic treatment that affects not only the total treatment duration but also the whole treatment outcome.

OBJECTIVE

To compare the efficiency of friction and frictionless mechanics during en-masse retraction of maxillary anterior teeth in adult patients with bimaxillary dentoalveolar protrusion.

TRIAL DESIGN

Two-arm parallel group, single-center randomized clinical trial.

MATERIALS AND METHODS

Thirty-two adult patients with bimaxillary protrusion were recruited and randomly allocated to two different retraction mechanics. A friction group, using NiTi coil springs and a frictionless group using closing T-loops for en-masse retraction. Randomization in a 1:1 ratio was generated by Microsoft Excel. The randomization numbers were secured in opaque sealed envelopes for allocation concealment. Retraction started in all patients following first premolars extraction using miniscrews as a source of indirect anchorage. Activation was done on a monthly basis until complete retraction of anterior segment. The rate of retraction, amount of anchorage loss, the dental, and soft tissue changes were analyzed on digital models and lateral cephalograms taken before retraction and after space closure.

BLINDING

The outcome assessor was blinded through data concealment during assessment.

RESULTS

Two patients were lost to follow up, so 30 patients completed the trial. The rate of anterior segment retraction was 0.88 ± 0.66 mm/month in the frictionless group compared to 0.72 ± 0.36 mm/month in the friction group which was statistically significant. Anchorage loss of 1.18 ± 0.72 mm in the friction group compared to 1.29 ± 0.55 mm in the frictionless group with no significant difference. Comparable dental and soft tissue changes following en-masse retraction were reported in both groups, with no statistically significant difference.

HARM

one patient complained of soft tissue swelling following miniscrew insertion, but the swelling disappeared after one week of using mouth wash.

LIMITATION

The study focused only on the maxillary arch.

CONCLUSION

Both mechanics have successfully achieved the required treatment objectives in patients with bimaxillary dentoalveolar protrusion. Frictionless group showed a faster rate of retraction than the friction group, which was statistically but not clinically significant.

TRIAL REGISTRATION

Clinicaltrials.gov with the identifier NCT03261024.

Three-dimensional volumetric evaluation of root resorption in maxillary anteriors following en-masse retraction with varying force vectors - a randomized control trial

BACKGROUND

Root resorption in orthodontics is associated with direction and magnitude of force application as primary etiological factors. Well-controlled trials that utilize three-dimensional segmentation to detect volumetric changes in tooth structure are required to assess the quantitative nature of root resorption.

OBJECTIVE

To assess the severity of root resorption (RR) during retraction of maxillary anteriors with three different force vectors (with and without skeletal anchorage) via cone-beam computed tomography (CBCT) superimpositions.

TRIAL DESIGN

Three-arm parallel randomized clinical trial (RCT).

MATERIALS AND METHODS

Forty-two (16 males, 26 females) patients, (17-28 years), in permanent dentition with bimaxillary protrusion were randomly allocated to three groups of 14 patients each using block randomization (1:1:1 ratio) and allocation concealment. En-masse anterior retraction post first premolar extractions was carried out with modified force vectors in the three groups based on anchorage type [Molar, Mini-implant and Infrazygomatic crest (IZC) bone screws]. Volumetric root loss and linear dimensional changes were blindly assessed on initial (T0) and final (T1, end of space closure) CBCT scans. Normality distribution of values was done using Shapiro-Wilk's test. ANOVA and Post-hoc Tukey HSD test were done to compare measurements between groups at significance levels (P < .05).

RESULTS

Forty patients were analysed (14, 14, and 12 in three groups). Significant volumetric loss was noted in all groups. Central incisors demonstrated a significant reduction in IZC group (81.5 ± 21.1 mm3 ) compared to conventional (50.1 ± 26.5 mm3 ) and mini-implant groups (76.1 ± 27.6 mm3 ). Canines demonstrated a significant reduction in mini-implant group (108.9 ± 33.9 mm3 ) compared to conventional (68.8 ± 42.5 mm3 ) and IZC groups (103.1 ± 29.1 mm3 ). Regarding linear parameters, central incisors and canines revealed significant root length reduction in both skeletal anchorage groups. Lateral incisors showed no significant changes between groups.

CONCLUSIONS

Intrusive force vectors generated during skeletally anchored retraction can predispose anteriors to an increased risk of resorption. Greater loss of root volume was noted in the centrals and canines when retracted with skeletal anchorage.

LIMITATIONS

Small sample size and variations during CBCT acquisition.

HARMS

Low-dose CBCT scans were taken at T0 and T1 treatment intervals.

Comparison of two treatment protocols for intrusion and retraction of maxillary anterior teeth using mini-implants : A prospective clinical trial

OBJECTIVE

The primary objective of this study was to compare the magnitude of incisor intrusion and retraction between two different treatment protocols and the secondary objective was to evaluate overall treatment effects.

MATERIALS AND METHODS

Thirty-four patients with proclined upper anterior teeth, increased overbite, and incisal show were randomly assigned to two treatment groups (G1 and G2). Upper first premolar extractions were performed in all cases. In G1, space closure was performed with conventional straight-wire friction mechanics with NiTi (nickel titanium) coil springs placed on 0.019″ × 0.025″ stainless steel wires in a 0.022 slot system with an additional intrusive force via a midline mini-implant. In G2, NiTi coil springs were placed from buccal mini-implants placed onto 0.016″ × 0.022″ SS wires in a 0.022 slot system bilaterally. Lateral cephalograms and study models taken at the beginning and at the end of 6 months of treatment were assessed.

RESULTS

Both groups showed a statistically significant mild maxillary incisor intrusion, reduction in overjet, overbite, incisal show and a reduction in lower anterior facial height. There was a mild intrusion of the maxillary first permanent molar in G2 (not significant). Mesial movement of the maxillary first permanent molar was noted in G1 but distal movement occurred in G2. Constriction of the entire maxillary arch was noted in G1, whereas constriction was seen in the molar region only in G2. Root resorption was noticed in both groups.

CONCLUSION

Both groups produced comparable results. Except for molar control, all the results obtained were comparable between the two mechanics. Application of an intrusive force in the midline may be beneficial in patients treated with conventional straight-wire mechanics to treat increased overbite when anchorage requirement is not high.

Displacement Pattern, Stress Distribution, and Archwire Play Dimensions during En-masse Retraction of Anterior Teeth using Sliding Mechanics: A FEM Study

Aims

This finite element study was undertaken to evaluate the pattern of stress distribution around the implant and anterior teeth during en-masse retraction in the premolar extraction case. Displacement of the teeth and play of wire in the bracket slot were also evaluated to determine the most favorable height of the power arm attached to the arch-wire.

Materials and methods

A three-dimensional (3D) finite element model of the maxilla was constructed using computed tomography (CT) scan. A total of 12 models were fabricated with different heights of power arms placed distal to the canine. A retraction force of 1.5 N was applied from the implant placed between the roots of the second premolar and first molar, and the response was predicted using Analysis of Systems (ANSYS) software.

Results

When power-arm height was near the center of resistance of the anterior segment, stability in the stress distribution around the implant site and anterior teeth was observed. Displacement of the teeth varied along the three planes of space with the change in power-arm height.

Conclusion

For en-masse retraction, power-arm height should be kept at a level of the center of resistance. Play in the bracket slot and the archwire show a negative role in the bodily movement of anterior teeth.

Clinical significance

For efficient en-masse retraction of anterior teeth, it is imperative to study the most effective site of application of force. Therefore, our study recommends certain key points to keep in mind during the attachment of the power arm and engaging wire in the bracket slot, which could benefit the orthodontist immensely.

How to cite this article

Singh H, Khanna M, Walia C, et al. Displacement Pattern, Stress Distribution, and Archwire Play Dimensions during En-masse Retraction of Anterior Teeth using Sliding Mechanics: A FEM Study. Int J Clin Pediatr Dent 2022;15(6):739-744.

Palatal plane inclination on vertical growth pattern among Indians

The skeletal discrepancies in the vertical dimensions can either lead to a long face or a short face. The palatal plane inclination is one such contributing factor. The study sample comprised of 15 lateral cephalograms collected between the time period of June 2019 - March 2020 with 5 cephalograms belonging to skeletal Class I, II and III respectively. The inclination angle and mandibular plane angle were measured using the FACAD software. The obtained results were tabulated and statistically analysed using Pearson's correlation test to determine the correlation between the two variables. There was a statistically significant negative correlation between the skeletal malocclusions with a p value of 0.011. Thus, palatal plane inclination is not a major contributing factor for vertical growth pattern and it is suggestive of a multifactorial influence.

Alveolar bone remodeling during maxillary incisor intrusion and retraction

Background

Maxillary incisor protrusion is a prevalent dental deformity and is often treated by upper incisor intrusion and retraction. The mechanical loading triggers the resorption and apposition of the bone. Alveolar bone remodeling is expected to follow orthodontic tooth movement in a one-to-one relationship. However, in many cases, the outcomes are different. Alveolar bone might still remain thick causing lip protrusion and other aesthetic problems after treatment. Additional corrective procedures such as alveoloplasty. On the other hand, if the labial bone becomes too thin, periodontal problems like gingival recession might occur. The unpredictability of the treatment result and the risk of requiring corrective procedures pose significant challenges to both the providers and patients. The aim of this study is to determine factors that can help to predict the alveolar bone reaction before maxillary incisor intrusion and retraction.

Methods

The cohort included 34 female patients (mean age 25.8 years) who were diagnosed with skeletal class II malocclusion with upper incisor protrusion. These patients underwent extraction and orthodontic treatment with upper incisor intrusion and retraction. Lateral cephalograms at pre-treatment and post-treatment were taken. Linear and angular measurements were analyzed to evaluate the alveolar bone changes based on initial conditions.

Results

The study found that the relative change, calculated as change in alveolar bone thickness after treatment divided by the initial alveolar thickness, was inversely correlated with the initial thickness. There was a significant increase of labial alveolar bone thickness at 9-mm apical from cementoenamel junction (B3) (P < 0.05) but no statistically significant change in the thickness at other levels. In addition, the change in angulation between the incisor and alveolar bone was inversely correlated with several initial angulations: between the initial palatal plane and upper incisor angle, between the initial palatal plane and upper incisor labial surface angle, and between the initial palatal plane and bone labial surface angle. On the other hand, the change in labial bone thickness was neither significantly correlated with the initial thickness nor significantly correlated to the amount of retraction.

Conclusion

The unpredictability of alveolar bone remodeling after upper incisor intrusion and retraction poses significant challenges to treatment planning and patient experience. The study showed that the initial angulation between the incisor and alveolar bone is correlated with the change in angulation after treatment, the initial thickness of the alveolar bone was correlated with the relative change of the alveolar bone thickness (defined as change in thickness after treatment divided by its initial thickness), and the amount of intrusion was correlated with the alveolar bone thickness change at 9-mm apical from the cementoenamel junction after treatment. The results of the present study also revealed that the change in labial alveolar bone thickness was neither significantly correlated with the initial thickness nor significantly correlated to the amount of retraction.

Force direction using miniscrews in sliding mechanics differentially affected maxillary central incisor retraction: Finite element simulation and typodont model

Background/purpose

En masse retraction was still controversy in orthodontics. The aim of this study was to investigate the effect of force directions created by different miniscrew positions and lever arm heights on maxillary central incisor movement using Finite Element (FE) simulation and a Typodont model.

Materials and methods

A typodont model and 3-dimensional FE were used to simulate en masse anterior teeth retraction in sliding mechanics. The lever arm and the miniscrew positions were varied to change the force direction. The maxillary central incisor displacement was recorded and analyzed.

Results

The typodont results revealed that miniscrew vertical position and lever arm height affected the type of tooth movement. The best control in the vertical plane was achieved by a 7 mm lever arm height and miniscrew 9 mm from the archwire. When the lever arm height and miniscrew were 7 mm from the archwire, the tooth extruded. When the lever arm height was 9 mm and the miniscrew was 7 or 9 mm from the archwire, the tooth intruded. The FE stimulation determined that near bodily movement of the maxillary central incisor was achieved when the lever arm height and miniscrew was 9 mm from the archwire. The highest strain distribution in the periodontal ligament was observed at the apical third of the lateral incisor.

Conclusion

In en masse retraction, the appropriate direction of force or the height of the miniscrew and the lever arm may enable orthodontists to maintain better control of the anterior teeth in sliding mechanics.