Predictability of orthodontic tooth movement with aligners: effect of treatment design

Efficacy of clear aligner wear protocols in orthodontic tooth movement-a systematic review

BACKGROUND AND OBJECTIVES

Different expedited aligner wear protocols are currently in practice. This review was undertaken to systematically appraise the available evidence on the comparative efficacy of orthodontic tooth movement (OTM) across the different wear protocols.

SEARCH METHODS

Two assessors conducted comprehensive searches of electronic databases, including MEDLINE (via PubMed), Scopus, Embase, Web of Science, Google Scholar, Directory of Open Access Journals, Cochrane Library, OpenGrey, and Clinical Trial Registry, till 18 February 2024. Titles and abstracts were independently screened.

SELECTION CRITERIA

Prospective or retrospective studies comparing expedited wear protocols with the conventional 14-day protocol were included.

DATA COLLECTION AND ANALYSIS

A pre-piloted data extraction form was used. Risk of bias (RoB) assessment employed the Cochrane RoB 2.0 tool for randomized-controlled trials (RCTs) and the Newcastle-Ottawa scale for non-RCTs. The quality of evidence was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluation Pro tool.

RESULTS

Six studies, including 3 RCTs and 3 non-RCTs, were selected from 9076 records. Four studies (two RCTs and two retrospective cohort) found no statistically significant difference (P > 0.05) in the OTM efficacy between expedited and conventional protocols. Two studies (one RCT and one prospective cohort) found greater efficacy (P < 0.05) with the 14-day protocol, with the RCT reporting greater efficacy for certain movements, such as maxillary posterior intrusion, maxillary posterior distal tipping and buccal torquing, and mandibular posterior intrusion and extrusion. One RCT reported statistically insignificant difference (P > 0.05) in pain perception between the 10-day and 14-day protocols. Two studies demonstrated low RoB, two moderate, and two high RoB. The evidence level was very-low for OTM efficacy and high for pain perception. Meta-analysis was precluded due to significant heterogeneity among the studies.

CONCLUSIONS

Within the limitations of the study, the 7-day, 10-day, and 14-day protocols did not show any significant difference in OTM efficacy, except for certain movements that exhibited superior outcomes with the 14-day wear. Hence, a 'hybrid aligner-wear protocol', based on clinical judgement, might serve a better alternative in complex situations.

REGISTRATION

PROSPERO CRD42021288179.

A narrative review of the effects of vitamin D3 on orthodontic tooth movement: Focus on molecular and cellular mechanisms

Orthodontic tooth movement (OTM) is a critical process in dental alignment, driven by the application of calibrated orthodontic forces. This study delves into the intricate molecular and cellular mechanisms by which vitamin D3 influences OTM. Vitamin D3 is identified as a critical regulator in bone metabolism, enhancing osteoblast activity and bone formation while also modulating osteoclast quantity and RANKL expression, essential for the remodeling of the alveolar bone. The precise mechanisms through which vitamin D3 facilitates these processes are explored, highlighting its potential in accelerating bone remodeling and, consequently, tooth alignment. This comprehensive review underscores vitamin D3's anabolic impact on bone metabolism and its pivotal role in the synthesis and mineralization processes governed by osteoblasts. The findings illuminate vitamin D3's promise in augmenting orthodontic therapy, suggesting its utility in improving treatment efficiency and reducing duration. However, the need for further research into the optimal application of vitamin D3 in orthodontics is emphasized, particularly concerning dosage, timing, and delivery methods.

Biomechanics of clear aligner therapy: Assessing the influence of tooth position and flat trimline height in translational movements

OBJECTIVE

The present clear aligner therapy (CAT) research focuses on isolating and reporting the biomechanical performance for three separate teeth, three translational movements and two flat trimlines at different heights. By identifying key patterns, the research seeks to inform the development of improved aligner designs, ultimately enhancing the effectiveness of clinical orthodontic treatments.

MATERIALS AND METHODS

In an in vitro setting using the Orthodontic Force Simulator (OFS), the biomechanical response of 30 aligners was investigated on three different teeth of a straight symmetric maxillary dentition (central incisor, canine and first molar). Each tooth was tested under two flat trimline conditions (trimmed at gingival margin, TL0; extended 2.0 mm below, TL2) and for three types of translational movements (palatal translation, mesial translation and intrusion). Forces and moments were reported at the centre of resistance for each displaced tooth as well as the two neighbouring teeth, evaluating a total of 18 distinct scenarios.

RESULTS

Findings indicate significant variability in the biomechanical responses based on tooth location in the arch, trimline height and movement performed. For palatal translations, the palatal force required to perform the movement was observed highest in molar cases, followed by canine and incisor cases, with a notable difference in the distribution of side effects, indicating a strong influence of tooth anatomy and position in the arch. Similarly, in mesial translations and intrusions molars experienced greater forces and moments than the corresponding movements applied on canines and incisors, but uniquely dispersed for each configuration tested. Regarding the shape of the aligner, TL2 consistently showed improved control over orthodontic movements compared to TL0. Neighbouring teeth frequently displayed compensatory reactions up to about half of the intensity observed on the tooth being moved, with notable variations from case to case.

CONCLUSIONS

This research supports fundamental factors impacting CAT: Characteristic patterns in the direction and intensity of forces and moments are associated with each of the three translational movements tested. Tooth anatomy and arch location significantly influence the biomechanical performance of aligners, with an observed trend for molars to display higher forces and moments over canines and incisors, but distributed differently. The height of a flat trimline, specifically TL2, shows enhanced control over orthodontic movements. Additional findings revealed a compensatory activity of neighbouring teeth, which varies based on tooth region and movement type. It potentially could influence CAT outcomes negatively and merits attention in future investigations. These results support a tailored CAT method that improves aligner design for better force application. This method needs to be used alongside, and confirmed by, clinical knowledge. Future research should extend these findings to a wider range of clinical conditions for greater applicability in the day-to-day orthodontic practice.

Digital intraoperative evaluation of restorative space and nontemplate-guided tooth preparation when replacing failed anterior restorations: A dental technique

Assessing the correlation between the current restorative space and the target restorative space is important in determining whether additional tooth preparation is required when replacing failed prostheses. However, existing techniques are not always accurate or efficient. This article describes a digital workflow for the accurate chairside evaluation of the current restorative space and nontemplate-guided tooth preparation. Reference data was obtained from an initial scan of the existing restoration with an intraoral scanner. After removing the existing restoration, a second scan of the tooth was made and compared with the reference data to evaluate the current restorative space. Subsequently, the abutment tooth was prepared and rescanned, with the restorative space being re-evaluated until it met the requirements. This workflow enables the immediate and accurate evaluation of the restorative space, facilitating accurate chairside tooth preparation without the need for silicone indices or other templates, thereby saving time and cost.

Aligner biomechanics: Where we are now and where we are heading for

Aligner orthodontics has gained significant popularity as an alternative to traditional braces because of its aesthetic appeal and comfort. The biomechanical principles that underlie aligner orthodontics play a crucial role in achieving successful outcomes. The biomechanics of aligner orthodontics revolve around controlled force application, tooth movement, and tissue response. Efficient biomechanics in aligner orthodontics involves consideration of attachment design and optimized force systems. Attachments are tooth-colored shapes bonded to teeth, aiding in torque, rotation, and extrusion movements. Optimized force systems ensure that forces are directed along the desired movement path, reducing unnecessary strain on surrounding tissues. Understanding and manipulating the biomechanics of aligner orthodontics is essential for orthodontists to achieve optimal treatment outcomes. This approach requires careful treatment planning, considering the mechanics required for each patient's specific malocclusion. As aligner orthodontics continues to evolve, advances in material science and treatment planning software contribute to refining biomechanical strategies, enhancing treatment efficiency, and expanding the scope of cases that can be successfully treated with aligners.

Does aligner refinement have the same efficiency in deep bite correction?: A retrospective study

BACKGROUND

Refinements are very common in clear aligner treatments. The aim of this study is to assess whether the predictability of deep overbite correction is similar over several refinements using clear aligners (Invisalign, Align Technology, San Jose, Calif) and examine the accuracy of vertical movement and inclination change of individual teeth.

METHODS

This retrospective study included 20 deep bite patients (7M and 13F; 32.63 ± 11.88 years old; an initial overbite of 5.09 ± 0.98 mm), consecutively treated from September 2016 and March 2023, who completed at least two sets of aligners, including refinements. The initial, predicted, and achieved models were exported from ClinCheck or OrthoCAD (Cadent Inc, Carlstadt, NJ) and superimposed via best-fit surface-based registration using SlicerCMF (version 4.9.0; cmf.slicer.org). We also examined 15 out of 20 patients who completed treatments. The overbite correction and changes in vertical movement and inclination for individual teeth were measured. Descriptive statistics and a paired t-test or Wilcoxon signed-rank test were performed. P < 0.05 was considered statistically significant.

RESULTS

The mean accuracy of overbite correction was 37.63% after 1st set, followed by 11.19%, 6.32%, and 13.80% (2nd-4th sets), respectively. There were statistically significant differences between the predicted and achieved vertical movements and inclination changes for all teeth for the 1st and 2nd sets. For the completed cases, the mean overbite correction was 38.54% compared to the initially planned overbite correction, which is similar to one of the 1st set. Still, the vertical movements and inclination changes of all teeth present statistically significant differences between the initially planned and finally achieved movements except for maxillary lateral incisor torque.

CONCLUSIONS

The most overbite correction occurs during the 1st set of aligners, and refinement treatment does not significantly improve the deep bite correction.

Effects of clear aligners on the vertical position of the molar teeth and the vertical and sagittal relationships of the face: a preliminary retrospective before-after clinical trial

INTRODUCTION

Despite the popularity of clear aligners, their predictability has not been assessed adequately. Moreover, no study has investigated their effects on numerous dentomaxillary variables. Therefore, this study was conducted for the first time, assessing several new or controversial items. The aim of the study was to evaluate the effects of clear aligners on the vertical position of the molar teeth and the vertical and sagittal relationships of the face.

METHODS

This preliminary retrospective before-after non-randomized clinical trial was performed on 168 observations of 84 patients (33.60±9.28 years, 54 females) treated with 0.75mm Invisalign appliances. Pretreatment and posttreatment values were measured for: mandibular plane angle, occlusal plane angle, Y-Axis, ANB, facial angle, lower anterior facial height, overbite, and the distances of the molars from the palate and mandibular plane were measured. The alterations in parameters caused by treatment (delta values) were calculated for each measurement. Effects of treatment and some parameters on delta values were analyzed statistically (α=0.05).

RESULTS

Mean±SD of ΔMP-FH, ΔOP-FH, ΔY-Axis, ΔLAFH, ΔNPog-FH, ΔANB, ΔOverbite, ΔSNB, Δ6-PP, Δ7-PP, Δ6-MP, and Δ7-MP were respectively 0.11±1.61, 0.80±1.56, 0.15±1.18, 0.07±0.91, -0.22±1.25, 0.03±0.62, 0.04±1.15, -0.06±1.14, -0.36±0.94, -0.32±1.14, 0.19±0.96, 0.18±1.10. Only the alterations in OP-FH, 6-PP, and 7-PP were significant (P≤0.011). Age, sex, treatment duration, or pretreatment mandibular plane angle were not correlated with any delta values. However, the pretreatment occlusal plane angle was negatively correlated with ΔOP-FH and ΔY-Axis. Crowding was correlated negatively with ΔOP-FH and ΔY-Axis and positively with ΔNPog-FH. Overjet was negatively correlated with ΔANB and ΔOverbite (P≤0.035).

CONCLUSIONS

Invisalign intruded first/second maxillary molars and increased the occlusal plane angle. Age, sex, and treatment duration were not correlated with post-treatment anatomic alterations.

Orthodontic aligners: between passion and science

INTRODUCTION

The benefits and safety of using orthodontic aligners have been reported more by clinical experience and expert opinion than by scientific evidence. Another important aspect is that aligners are constantly evolving. It is important to obtain evidence that allows for new updates in manufacturing technology, in the development of new movement planning protocols, in the incorporation and design of attachments, and in the aid of skeletal anchorage.

METHODS

Evidence retrieved from six electronic databases (CINAHL, MEDLINE, EMBASE, Psych Info, the Cochrane Library and the Joanna Briggs Library) is presented by means of questions and answers.

CONCLUSIONS

There is evidence that the aligners presented different levels of difficulty in performing each type of movement, with rotational and vertical movements being the most difficult to perform. Regarding perception of pain due to tooth movement, it seems to have less impact at the beginning of treatment; but dealing with more phonoarticulatory changes seems to require more treatment time in more complex cases. Aligners do not prevent the occurrence of root resorption, although the incidence and severity of resorption may be reduced, making oral hygiene easier and accepting the risk of white spots, caries and periodontal disease. Given the conflicting evidence, the release of bisphenol-A from the aligner cannot be denied. Solutions must be found to reduce the environmental impact of aligners disposal. There is an urgent need for well-designed randomized controlled trials.

Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners

BACKGROUND

This study explores how different post-processing methods affect the mechanical properties and degree of conversion of 3d-printed polyurethane aligners made from Tera Harz TC-85 resin.

METHODS

Using Fourier-transform infrared (FTIR) spectroscopy, the degree of conversion of liquid resin and post-processed materials was analyzed. This investigation focused on the effects of various post-curing environments (nitrogen vs. air) and rinsing protocols (centrifuge, ethanol, isopropanol, and isopropanol + water). The assessed mechanical properties were flexural modulus and hardness.

RESULTS

The degree of conversion showed no significant variance across different groups, though the polymerization environment influenced the results, accounting for 24.0% of the variance. The flexural modulus varied considerably, depending on both the rinsing protocol and the polymerization environment. The standard protocol (centrifugation followed by nitrogen polymerization) exhibited the highest flexural modulus of 1881.22 MPa. Hardness testing revealed significant differences, with isopropanol treatments showing increased resistance to wear in comparison to the centrifuge and ethanol rinse treatments.

CONCLUSIONS

This study conclusively demonstrates the adverse effects of oxygen on the polymerization process, underscoring the critical need for an oxygen-free environment to optimize material properties. Notably, the ethanol rinse followed by nitrogen polymerization protocol emerged as a viable alternative to the conventional centrifuge plus nitrogen method.

Predictability of Dental Distalization with Clear Aligners: A Systematic Review

The current review aims to evaluate the scientific evidence relating to the effectiveness of treatment with clear aligners (CAs) in controlling distalization orthodontic tooth movement. "Orthodontics, aligners" and "distalization" were the search terms used on the Scopus, Web of Science and Pubmed databases with the Boolean operator "AND". The results of the last ten years of research were 146 studies; of these, 19 publications were included for this review. The distalization movement is possible with invisible masks alone, but the risk of losing anchorage in the anterior sectors is very probable. The stability of the results and the reduction of unwanted effects can be guaranteed by the use of skeletal anchoring devices and interproximal enamel reduction (IPR), with which compensations are obtained to reduce the initial overjet. Temporary anchorage devices (TADs) can be used to manage posterior anchorage after distalization of maxillary molars with aligners. This hybrid approach has demonstrated the greatest orthodontic success. TADs are useful aids to provide direct and indirect skeletal anchorage. The opposite effect must be considered when planning dental distalization, especially of the molars, in patients with large overjet, and corrective measures or the use of auxiliaries may be necessary to prevent midcourse corrections. This systematic review provides a critical evidence-based assessment of the predictability of dental distalization with CAs, an ever-evolving orthodontic technique.

Impact of Invisalign G-series Updates on Improving Predicted Outcomes: A Retrospective Study

BACKGROUND

Understanding the real-world implications of periodic changes to orthodontic appliances can provide valuable insights for future treatment strategies and patient outcomes. This study aimed to investigate the impact of the latest updates added to the G7 and G8 Invisalign series on actual versus predicted outcomes and the percentage accuracy of the treatment.

METHOD

This retrospective study was conducted in private orthodontic practices in Riyadh, Saudi Arabia. Orthodontists carried out Invisalign® treatment using the latest updates added to the G7 and G8 Invisalign series. The study group comprised patients with different malocclusion types who received non-extraction Invisalign treatment. The Invisalign treatment plan was provided by the ClinChecks program (Invisalign, San Jose, United States) for patients treated throughout the years (2016-2022). Different dimensions were assessed to record predicted and actual treatment outcomes with the aid of iTero® (Align Technology, San Jose, United States) and ClinCheck® (Invisalign, San Jose, United States). The percentage accuracy was determined using the formula (100%-((Predicted-Actual)/Predicted) *100%).

RESULTS

A total of 108 patients (male = 34 (31.5%) and female = 74 (68.5%)) treated with Invisalign G7 and G8 series were considered in this study. The overall mean and standard deviation values of vertical distance (2.91±1.42), intermolar distance in the lower arch (52.68±3.15), overjet (2.71±1.06), and inter-incisal angle (138.24±12.18) were higher than the predicted model. However, the predicted model showed higher mean and standard deviation values for intercanine distances in the upper (36.94±1.57) and lower arches (28.48±1.40) and upper intermolar distances (57.21±2.91). The G7 versus G8 intercanine distance in lower (61.28±47.67 vs. 80.51±38.32), intermolar distance in upper (61.72±47.67 vs. 69.95±44.11), and intermolar distance in lower (100.68±3.80 vs. 100.89±2.52) were relatively higher in the G8 series than the G7. The accuracy percentage was higher with the G8 series than with the G7 regarding the intercanine distance in the upper arch. In contrast, the G7 series showed a higher mean percentage accuracy of vertical distance (91.11±84.83 vs. 76.76±65.45), overjet (58.44±35.17 vs. 53.71±45.87), and inter-incisal angle (34.47±44.06 vs. 27.53±37.98) than the G8 series.

CONCLUSION

The percentage accuracy of aligner therapy administered using the Invisalign G7 and G8 series demonstrated no significant variation.

Efficiency and Predictability of Coronal Maxillary Expansion Repercussion with the Aligners System: A Retrospective Study

The Invisalign® system (SmartForce® G8) aims to guarantee aesthetics and provide good orthodontic treatment results. Dentoalveolar expansion is possible with clear aligners and can be used to correct dentoalveolar crossbite, resolve crowding or modify the arch shape. Despite the treatment's effectiveness, there is still disagreement among professionals concerning its true clinical potential. This study aimed to analyze the effectiveness and predictability of coronal tooth expansion movement in permanent dentition in patients who had completed the first phase of treatment with Invisalign® orthodontic aligners.

MATERIALS AND METHODS

The tooth movement tables of 75 previously selected cases were analyzed in terms of dental-arch width and expansion efficiency, through the Invisalign® platform, considering the pre-treatment (T0), planned treatment (TP) and post-treatment models (T1) using ClinCheck Pro® 6.0 software. All patients were treated by an orthodontic specialist and Invisalign® Diamond Provider in a private practice (T.P.).

RESULTS

Difference between T1 and T0: for each maxillary and mandibular measurement, there was a statistically significant difference between pre- and post-aligner treatment values. The greatest amount of expansion occurred in both the upper and the lower premolars. Difference between TP and T1: for each maxillary measurement, statistically significant differences were verified for the molar and canine. At the mandibular level, statistically significant differences were only verified in the first molar.

CONCLUSIONS

The Invisalign® clear aligners are effective for simultaneous intra-arch expansion in both jaws.

The Power of Customized Clear Aligners in Closing Molar Edentulous Spaces: Clinical and Medico-Legal Considerations in a Scoping Review and Case Report

Successful closure of edentulous spaces with clear aligners (CAs) is influenced by many factors. CAs are tailored orthodontic devices whose predictability may have relevant medico-legal implications. This study presents a scoping review about missing molar space closure (MMSC) with CAs and a clinical case. This study aims to highlight the feasibility of molar space closure by mesialization with CAs without hybrid supports. Following PRISMA Sc-review guidelines, English-written randomized/non-randomized/observational clinical studies on PubMed, Scopus, Cochrane and Lilacs were searched. An 18-year-old patient, with upper and lower edentulous spaces due to the loss of two first molars, was rehabilitated with CAs (Sorridi®, Sorridi srl, Latina, Italy) without hybrid supports and attachments. The therapy was carried out over 10 months. Currently, there are no studies documenting MMSC by mesialization with only CAs. Existing articles document the closure of premolar or incisor spaces. The upper and lower left second molars replaced the missing first molars, and erupting third molars replaced adjacent teeth. The biomechanical effects in space closure with CAs related to extraction cases appear as priorities of clinical/medico-legal interest. Our case turns attention to this movement of CAs without attachments/hybrid supports, indicating that even such a complex treatment can be comfortable for patients and safely predictable for specialists.

Research and orthodontics: About scientific progress in biomechanics

This article describes the importance of biomechanics in orthodontics through the development of the segmented arch technique and the research performed in this field. Clinicians are encouraged to develop specific goals of treatment based on a precise diagnosis and to design appliances that will deliver the desired force system. In this article we emphasize the importance of a thorough analysis of the force system needed to achieve the desired orthodontic tooth movement and avoid any of the undesired side effects of treatment mechanics. We show that a well-thought out and planned treatment will lead to better clinical outcomes that will benefit our patients.

Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study

OBJECTIVE

To assess the possibility of extrusion of a maxillary central incisor with the use of buccal and lingual pressure columns in the absence of attachments, and to evaluate the forces and moments experienced by the teeth using both thermoformed and 3D-printed clear aligners.

MATERIALS AND METHODS

A three-axis force and moment sensor (Aidin Robotics, Anyang, South Korea) was used to measure the forces and moments during extrusion of an upper left central incisor (UL1) and any forces experienced by the upper right central incisor (UR1) using thermoformed aligners and 3D-printed aligners. For the thermoformed aligners, the materials used were ATMOS® (American Orthodontics, Sheboygan, WI) and Zendura FLX® (Bay Materials LLC, Fremont, CA). 3D-printed aligners were fabricated using TC-85 clear photocurable resin (Graphy Inc., Seoul, South Korea). For each material type, three conditions were tested: Group 1: No attachment or pressure columns (control); Group 2: Attachment only; and Group 3: Pressure columns only. Each group was planned for 0.5 mm of extrusion on the UL1.

RESULTS

All force readings collected demonstrated statistically significant differences when compared by materials and when compared by groups, with a P value of < 0.001. In the absence of attachment or pressure columns (Group 1), ATMOS® and TC-85 groups exerted extrusive force on the UL1. However, significantly lower forces and moments were exerted by the TC-85 group in comparison to the ATMOS® and Zendura FLX® groups. In the presence of attachment (Group 2), all three ATMOS®, Zendura FLX® and TC-85 groups exerted extrusive force on the UL1, with the TA group showing different directions of faciolingual force, mesiodistal force and faciolingual inclination on the UR1 when compared to the other two thermoformed groups. Whereas in the presence of pressure columns (Group 3), only the TC-85 3D-printed aligner group exerted extrusive force. Thermoformed aligners generated significantly higher mean forces and moments than 3D-printed aligners. Significant levels of unintended forces and moments were present in all groups.

CONCLUSIONS

Force levels generated during extrusion with clear aligners are significantly lower with those 3D-printed using TC-85 than with those thermoformed using ATMOS® or Zendura FLX®. Attachments consistently generated extrusive forces, and may be an effective adjunct in achieving extrusion of incisors. Extrusion may be achieved without the use of attachments by utilizing pressure columns in 3D-printed aligners using TC-85. While different strategies can generate extrusive forces, there are significant unintended forces and moments.

Is maxillary arch expansion with Invisalign® efficient and predictable? A systematic review

BACKGROUND

The main objective of this review is to assess the effectiveness and predictability of the transverse expansion movement performed by Invisalign®. The secondary objectives are to determine whether the expansion is of a dentoalveolar or skeletal nature, and to locate the areas of expansion on the dental arch.

METHODS

Two investigators used the PubMed database to search for articles related to the subject. After using a research equation, specific inclusion and exclusion criteria were applied and the final selection of articles was done after being read in full. The ROBINS-I tool for non-randomized studies was applied to assess risk of bias in the results of each included study.

RESULTS

After reading the articles in full, 12 articles were included. Regarding effectiveness, most studies showed an increase in all measured interdental distances, with a maximum expansion at the premolar level. As for predictability, significant differences were found between post-treatment models and Clincheck® models, making it generally weak. Concerning the nature and areas of expansion, increase of arch width was due to buccal tipping of the crowns following a decreasing gradient from anterior to posterior.

CONCLUSIONS

Invisalign® treatment is effective in achieving a maxillary transverse expansion. However, this expansion is mainly dentoalveolar, with a facial crown tipping of the posterior teeth. Clincheck® software tends to overestimate the expansion movement when compared to the clinical outcome, therefore the predictability of movement is low.

Effectiveness and predictability of treatment with clear orthodontic aligners: A scoping review

INTRODUCTION

In an ideal clinical setting, orthodontic therapy with clear aligners (CA) should improve the patients' initial malocclusion and must guarantee equivalence between the results predicted and those obtained clinically to be considered an effective treatment. Therefore, this scoping review aimed to identify the orthodontic literature concerning the effectiveness and predictability of CA treatments.

METHODS

A systematic computerized search was performed in 3 databases: PubMed, Scopus, and Embase. Inclusion criteria selected observational and clinical studies performed in at least 10 adult orthodontic patients, whose results of CA treatment's effectiveness and/or predictability were assessed.

RESULTS

The 3 database computerized searches resulted in 1,553 articles, and 169 full texts were considered potentially relevant. After applying the eligibility criteria, 33 studies were included. Most studies (76%) were designed as cohort studies and have been published in the last 5 years (79%). The majority included only non-extraction treatments (73%), and 79% reported results achieved with the Invisalign® system. The most predictable movement was the buccolingual tipping, while the least predictable movements were rotation, intrusion, and extrusion. Aligner treatment was effective for mild to moderate crowding resolution, and the success of overbite correction still seems to be limited.

CONCLUSIONS

The studies have demonstrated improvement of initial malocclusion through CA treatments. Still, predictability degree is overestimated and does not accurately reflect the occlusion immediately at the end of treatment. In future studies, there should be an effort to broaden the utilization of alternative aligner systems beyond Invisalign® and broadly disseminate their outcomes to strengthen clear aligners evidence base.

A new method assessing predicted and achieved mandibular tooth movement in adults treated with clear aligners using CBCT and individual crown superimposition

The purpose of this study was to demonstrate a new method for quantifying the difference between predicted and achieved tooth movement with Invisalign using stable three-dimensional (3D) mandibular landmarks and dental superimposition. Cone-beam computed tomography (CBCT) scans before (T1) and after (T2) the first series of aligners, their corresponding digital models (ClinCheck initial of the first series as T1 and ClinCheck initial of the refinement series as T2), and the ClinCheck final model of the first series as the predicted were obtained from 5 patients treated with non-extraction Invisalign therapy. After segmentation of the mandible and its dentition, T1 and T2 CBCTs were superimposed on stable anatomic structures (Pogonion and bilateral mental foramen) along with the pre-registered ClinCheck models. The 3D prediction differences between the predicted and achieved tooth position for 70 teeth with four types (incisor, canine, premolar and molar) were measured using a combination of software. The method employed in this study was tested to be reliable and repeatable with a very high intraclass correlation coefficient (ICC) for both intra- and inter-examiner reliability. Premolar Phi (rotation), Incisor Psi (mesiodistal angulation), and Molar Y (mesiodistal translation) showed a significant prediction difference (P < 0.05), which is also clinically relevant. The method involving CBCT and individual crown superimposition to measure the 3D positional changes in the mandibular dentition is a robust and novel one. While, our finding in terms of the predictability of Invisalign treatment in the mandibular dentition mainly served as a crude, cursory examination, which warrants further and more rigorous investigations. With this novel methodology, it is possible to measure any amount of 3D tooth position difference in the mandibular dentition either between the simulated and the actual or with treatment and/or growth. Deliberate use of overcorrection of which specific type of tooth movement with clear aligner treatment and to what extent, might be possible with future studies.