Root resorption in orthodontic treatment with clear aligners: A systematic review and meta‐analysis

Root resorption in clear aligner treatment detected by CBCT: a Systematic review and Meta-analysis

OBJECTIVE

The aim of this study was to evaluate the amount of external apical root resorption in patients who had undergone orthodontic treatment with clear aligners evaluated using cone beam computed tomography.

METHODS

Studies that evaluated external apical root resorption before and after comprehensive orthodontic treatment with clear aligners were assessed by performing an electronic search from 5 databases comprising PubMed, SCOPUS, EBSCO, Cochrane Library, and LILACS and manual searches in the relevant journals and the reference lists of the included studies. Database search, elimination of duplicate studies, and data extraction were performed independently by 2 authors. The quality of the included studies was assessed using the Risk of Bias in Non-randomised Studies-of Interventions and the Cochrane Collaboration's Risk of Bias Tool. Studies that reported the tooth length or volume were used for quantitative analyses.

RESULTS

Nine studies were included in the meta-analysis. The overall root length after clear aligner treatment was significantly decreased compared with the pre-treatment length using cone beam computed tomography (mean differences = -0.56 mm, 95% confidence interval [-0.73, -0.38], P < .00001). However, only the maxillary central incisors, maxillary lateral incisors, and mandibular central incisors had significant reduction in root length. The meta-analysis from 3 studies also indicated that the root volume of the upper incisors also significantly decreased (mean differences = -13.34 mm3, 95% confidence interval [-16.57, -10.10], P < .00001).

CONCLUSIONS

Current evidence suggests that clear aligners can cause minimal root resorption. The highest amount of root resorption was observed in the maxillary central incisors.

Evaluation of External Apical Root Resorption in Cases with Extraction and Non-Extraction Fixed Orthodontic Treatment

OBJECTIVE

The objective of this study was to evaluate external apical root resorption (EARR) in cases with extraction and non-extraction fixed orthodontic treatment.

METHODS

Ninety subjects were included in this study. The patients were divided into two groups: 43 with extraction treatment and 47 with non-extraction orthodontic treatment. EARR was measured using the crown-to-root ratio of the maxillary and mandibular incisors and canines on panoramic radiographs taken at the beginning (T0) and end of the treatment (T1). The Bonferroni corrected Z test was used for multiple comparisons.

RESULTS

There were 24 (55.8%) individuals in the extraction group and 12 (25.5%) in the non-extraction group, with a minimum of one tooth with severe resorption. There was no resorption in 0% of individuals in the extraction group and five (10.6%) individuals in the non-extraction group. There was a statistically significant correlation between the groups and the degree of resorption (p = 0.008). When the maxillary and mandibular teeth in the extraction group were compared, a significant difference was found in all degrees of resorption except for mild resorption.

CONCLUSIONS

There was a significant difference in EARR between the extraction and non-extraction treatment groups, with maxillary incisors showing more resorption in the extraction treatment.

Panoramic evaluation of external root resorption in mandibular molars during orthodontic treatment: a comparison between root-filled and vital teeth treated with fixed appliances or clear aligners

BACKGROUND

This investigation compared the extent of external apical root resorption (EARR) in root-filled teeth (RFT) and their contralateral vital pulp teeth (VPT) counterparts during orthodontic treatment (OT) with clear aligner (CA) treatment or fixed appliance (FA) treatment.

METHODS

Sixty-six patients with similar baseline American Board of Orthodontics (ABO) discrepancy index scores were divided into two groups: 37 patients (21 females, 16 males; mean age 17.45 ± 2.67 years) in the FA group, and 29 patients (18 females, 11 males; mean age 18.33 ± 1.96 years) in the CA group. Digital panoramic radiographs captured pre- and post-OT were used to measure tooth lengths and root surface measurements in mandibular molars. EARR in both RFT and contralateral VPT was evaluated pre- and post-OT. Statistical analysis employed paired t-tests, independent t-tests, and analysis of covariance (ANCOVA) (p < .05).

RESULTS

All teeth exhibited varying degrees of EARR following OT. FA treatment resulted in significantly longer treatment duration (p < .05) and greater EARR compared to CA treatment (p < .05). Moreover, statistically significant differences in EARR were observed within both groups between RFT and VPT (p < .05).

CONCLUSIONS

Comparison of pre- and post-OT radiographs revealed different degrees of EARR in all teeth. CA treatment resulted in less frequent and less severe EARR compared to FA treatment. RFT demonstrated greater resistance to EARR than VPT in both treatment groups.

The orthodontic-endodontic interface: trauma and pulpal considerations

The interpretation of the clinical signs and symptoms arising from the interdisciplinary relationship between orthodontics and endodontics becomes more complicated when superimposed by dental trauma. A history of dental trauma before or during orthodontic tooth movement may have implications for pulpal health and clinical outcomes. An understanding of the biology is essential for appropriate treatment planning. This review and treatment recommendations will assist dental practitioners in managing orthodontic-endodontic interactions.

Does Invisalign Outperform Fixed Appliance in Treating Vertical Discrepancies?

Aligners became popular among adult patients for their superior aesthetics and comfort in comparison to conventional fixed appliances. It has undergone numerous enhancements over time, allowing it to address more complex malocclusions. Many researchers argued that managing vertical discrepancies is more challenging than addressing anteroposterior issues. This complexity arose from the mechanical requirements for treatment and the required mechanics to prevent relapse. Studies assessing the treatment outcome of anterior open bite closure using clear aligners have yielded conflicting results regarding the mechanisms of bite closure. Proposed mechanisms included extrusion of upper or lower incisors, lingual tipping of upper or lower incisors, intrusion of upper or lower molars, counterclockwise rotation of the mandible, or various combinations of these mechanisms. The research highlighted the biomechanical challenges associated with using aligners for the treatment of deep bites as mandibular incisor intrusion and leveling the curve of Spee remain among the least predictable movements. Given the widespread use of aligners, it is imperative to rigorously assess the effectiveness of clear aligners in achieving overbite correction to ensure they deliver the desired outcome. This review aimed to assess the performance of Invisalign in the management of vertical discrepancies. It sought to identify the dentoskeletal effects of clear aligners in addressing deep bite and anterior open bite cases, understand the mechanisms behind overbite correction, and provide a comprehensive overview of the existing research on this topic.

Effect of varying auxiliaries on maxillary incisor torque control with clear aligners: A finite element analysis

INTRODUCTION

This study aimed to evaluate the effects of varying auxiliaries on tooth movement and stress distribution when maxillary central incisors were torqued 1° with a clear aligner through finite element analysis.

METHODS

Three-dimensional finite element models, including maxillary alveolar bone, periodontal ligament, dentition, and clear aligner, were constructed. According to the auxiliaries designed on the maxillary central incisor, 5 models were created: (1) without auxiliaries (control model), (2) with the power ridge, (3) with the semi-ellipsoid attachment, (4) with the horizontal rectangular attachment, and (5) with the horizontal cylinder attachment. The tooth movement and periodontal ligament stress distribution after a palatal root torque of 1° were analyzed for each of the 5 models.

RESULTS

With 1° torque predicted, the maxillary central incisor without auxiliaries showed a tendency of labial tipping, mesial tipping, and intrusion. The rotation center moved occlusally in the power ridge model. The labiolingual inclination variation increased in the semi-ellipsoid attachment model but decreased in the power ridge model. The maxillary central incisor is twisted in the distal direction in the power ridge model. The maxillary central incisor of the horizontal rectangular attachment and the horizontal cylinder attachment model behaved similarly to the control model. Periodontal stresses were concentrated in the cervical and apical areas. The maximum von Mises stresses were 11.6, 12.4, 3.81, 1.14, and 11.0 kPa in the 5 models. The semi-ellipsoid attachment model exhibited a more uniform stress distribution than the other models.

CONCLUSIONS

Semi-ellipsoid attachment performed better efficacy on labiolingual inclination, and power ridge performed better efficacy on root control. However, a distal twist of maxillary incisors could be generated by the power ridge.

Comparative assessment of external apical root resorption between subjects treated with clear aligners and fixed orthodontic appliances: A systematic review and meta-analysis

This review aims to collate and analyze the existing evidence on the comparison of external apical root resorption (EARR) in subjects treated with clear aligners (CAs) and fixed appliances (FA). An electronic search was conducted in six databases for articles published in all languages until July 2023. Studies that evaluated EARR in subjects treated with CAs and FAs were included. The RoB 2 tool for RCTs and the ROBINS-I tool for non-randomized studies were used to analyze the risk of bias (ROB). A random effects meta-analysis was performed to assess EARR extent in maxillary and mandibular anterior teeth for subjects treated with CAs and FAs. Ten studies (eight retrospective, one RCT, and one CCT) were included in this review, out of which six studies reported a moderate ROB, one reported a serious ROB, and three reported a low ROB on qualitative analysis. The quantitative analysis of six studies revealed a significant intergroup difference (P<0.05) in the mean EARR for maxillary central (SMD=-0.62, P<0.00001) and lateral incisors (SMD=-0.47, P=0.01) with a moderate heterogeneity (I2=56%), as well as the mandibular central incisors (SMD=-0.27, P=0.04) with high heterogeneity (I2=79%). EARR was lower in subjects treated with CAs than FAs. A moderate quality of the available evidence suggests that EARR was less evident in subjects treated with CAs when compared with FAs.

Effect of attachment flash on clear aligner force delivery: an in vitro study

BACKGROUND

The introduction of auxiliaries such as composite attachment has improved the force delivery of clear aligner (CA) therapy. However, the placement of the attachment may give rise to a flash, defined as excess resin around the attachment which may affect CA force delivery. This in vitro study aims to determine the differences in the force generated by the attachment in the presence or absence of flash in CA.

MATERIALS AND METHODS

Tristar Trubalance aligner sheets were used to fabricate the CAs. Thirty-four resin models were 3D printed and 17 each, were bonded with ellipsoidal or rectangular attachments on maxillary right central incisors. Fuji Prescale pressure film was used to measure the force generated by the attachment of CA. The images of colour density produced on the films were processed using a calibrated pressure mapping system utilising image processing techniques and topographical force mapping to quantify the force. The force measurement process was repeated after the flash was removed from the attachment using tungsten-carbide bur on a slow-speed handpiece.

RESULTS

The intraclass correlation coefficient showed excellent reliability (ICC = 0.96, 95% CI = 0.92-0.98). The average mean force exerted by ellipsoidal attachments with flash was 8.05 ± 0.16 N, while 8.11 ± 0.18 N was without flash. As for rectangular attachments, the average mean force with flash was 8.48 ± 0.27 N, while 8.53 ± 0.13 N was without flash. Paired t-test revealed no statistically significant difference in the mean force exerted by CA in the presence or absence of flash for both ellipsoidal (p = 0.07) and rectangular attachments (p = 0.41). Rectangular attachments generated statistically significantly (p < 0.001) higher mean force than ellipsoidal attachments for flash and without flash.

CONCLUSION

Although rectangular attachment generated a significantly higher force than ellipsoidal attachment, the force generated by both attachments in the presence or absence of flash is similar (p > 0.05).

Orthodontic treatment of a patient with dentinogenesis imperfecta using a clear aligner system

BACKGROUND

Orthodontic treatment for patients with dentinogenesis imperfecta (DGI) can be risky because of the fragility of their dental hard tissue. Although the Invisalign (Align Technology) clear aligner system should be a suitable orthodontic appliance for patients with DGI, to the authors' knowledge, there has been no related research.

CASE DESCRIPTION

A 28-year-old woman with DGI sought treatment with a 1 mm open bite, edge-to-edge occlusion of the central incisors, and a bilateral Class III cusp-to-cusp molar relationship. Invisalign was applied for her treatment, and after 3 and one-half years of orthodontic therapy, a normal overjet and overbite were achieved, accompanied by retraction of the lower lip as well as a bilateral Class I molar relationship. In addition, there was no iatrogenic injury to the patient's teeth.

PRACTICAL IMPLICATIONS

The Invisalign system may be a suitable orthodontic appliance for patients with DGI because clear aligners lessen the tensile stress to the teeth, decrease the number and area of bonds to the teeth, and offer protective effects through a full wrap of plastic that covers the crowns of the teeth.

Evaluation of Aligners and Root Resorption: An Overview of Systematic Reviews

Background: To evaluate the current evidence on clear aligners and root resorption using 3D and/or combined 2D and 3D methods from available systematic reviews and meta-analyses and to determine the relationship between root resorption and clear aligners using the AMSTAR 2 tool. Methods: A comprehensive literature search of systematic reviews investigating aligners and root resorption, published up until 31 December 2022, was conducted. The following electronic databases were searched: MEDLINE via PubMed, EMBASE, Google Scholar, Science Direct, Web of Science, Scopus, LIVIVO, and LILACS. There were no language restrictions. The inclusion criteria were restricted to studies focusing on root resorption utilizing either 3D methods exclusively or a combination of 2D and 3D techniques. Data were screened and analyzed for quality using the "A Measurement Tool to Assess Systematic Reviews (AMSTAR 2)" tool. Data extraction was conducted independently by two authors. The gathered information was categorized and synthesized narratively based on the primary findings elucidated within the reviews. Results: Out of a total of 1221 potentially eligible studies initially identified, 4 systematic reviews met the inclusion criteria following the exclusion of irrelevant studies. Among these, two systematic reviews (50%) were classified as low-quality, while the remaining two (50%) were deemed to be of critically low quality. Conclusions: Based on the findings of four systematic reviews, the root resorption rate was lower with the use of clear aligners than with fixed aligners. It is advisable to approach the interpretation of this conclusion with caution, as the quality of the available evidence is assessed to be very low. Higher quality systematic reviews are needed to substantiate this conclusion.

Introducing a new auto edge detection technique capable of revealing cervical root resorption in CBCT scans with pronounced metallic artifacts

Cervical resorption is a serious threat to the longevity of the teeth. In this study, the Canny edge-detection algorithm was applied on CBCT images to compare the accuracy of original and Canny views for diagnosing cervical resorption in endodontically treated teeth. Intracanal metallic posts were inserted in 60 extracted teeth being randomly divided into three groups: control, 0.5 mm, and 1 mm cervical resorption. CBCT scans of the teeth were presented to three observers in both original and Canny formats with the accuracy being determined by receiver operating characteristic (ROC) analysis. The DeLong test was used for paired comparisons with the significance level set at 0.05. The highest accuracy belonged to Canny images in 1 mm resorption, followed by Canny images in 0.5 mm resorption, original images in 1 mm resorption, and original images in 0.5 mm resorption, respectively. The Canny images were significantly more accurate in the diagnosis of 0.5 mm (p < 0.001) and 1 mm (p = 0.009) resorption. Application of the Canny edge-detection algorithm could be suggested as a new technique for facilitating the diagnosis of cervical resorption in teeth that are negatively affected by metallic artifacts.

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.

Root resorption during maxillary molar intrusion with clear aligners: a randomized controlled trial

OBJECTIVES

To compare changes in maxillary molar root resorption, intrusion amount, dentoskeletal measures, and maximum bite force (MBF) between clear aligners (CA) and fixed appliances with miniscrew (FM) during molar intrusion.

MATERIALS AND METHODS

Forty adults with anterior open bite were randomized into either CA or FM groups. Lateral cephalograms, cone-beam computed tomography (CBCT), and MBF were collected at pretreatment (T0) and 6 months of treatment (T1). Maxillary molar intrusion in FM were intruded by nickel-titanium (NiTi) closed-coil spring delivered force (150 grams/side) while clear aligners combined with squeezing exercise were performed in CA. Parametric tests were used for statistical analysis.

RESULTS

After 6 months of treatment, significant root resorption of 0.21-0.24 mm in CA and 0.38-0.47 mm in FM were found while maxillary molars were intruded 0.68 and 1.49 mm in CA and FM, respectively. CA showed significant less root resorption and intrusion than FM. Overbite, bite closing, and MBF increased significantly. CA showed significantly less overbite and SN-MP changes but more MBF increase than FM. MBF in CA was correlated with the amount of maxillary molar intrusion (r = 0.736, P < .05).

CONCLUSIONS

Maxillary molar intrusion and root resorption in CA were half the amount in FM in 6 months. The amount of maxillary molar root resorption was one-third of the intrusion distance. CA displayed less overbite increase and bite closing but more MBF increase than FM. MBF in CA was positively correlated with the molar intrusion amount.

Effective contribution ratio of the molar during sequential distalization using clear aligners and micro-implant anchorage: a finite element study

INTRODUCTION

This study aims to investigate the biomechanical effects of anchorage reinforcement using clear aligners (CAs) with microimplants during molar distalization. And also explores potential clinical strategies for enhancing anchorage in the sequential distalization process.

METHODS

Finite element models were established to simulate the CAs, microimplants, upper dentition, periodontal ligament (PDL), and alveolar bone. In group set I, the 2nd molars underwent a distal movement of 0.25 mm in group set II, the 1st molars were distalized by 0.25 mm after the 2nd molars had been placed to a target position. Each group set consisted of three models: Model A served as the control model, Model B simulated the use of microimplants attached to the aligner through precision cuts, and Model C simulated the use of microimplants attached by buttons. Models B and C were subjected to a series of traction forces. We analyzed the effective contribution ratios of molar distalization, PDL hydrostatic stress, and von Mises stress of alveolar bone.

RESULTS

The distalization of the 2nd molars accounted for a mere 52.86% of the 0.25-mm step distance without any reinforcement of anchorage. The remaining percentage was attributed to the mesial movement of anchorage teeth and other undesired movements. Models B and C exhibited an increased effective contribution ratio of molar distalization and a decreased loss of anchorage. However, there was a slight increase in the undesired movement of molar tipping and rotation. In group set II, the 2nd molar displayed a phenomenon of mesial relapse due to the reciprocal force produced by the 1st molar distalization. Moreover, the efficacy of molar distalization in terms of contribution ratio was found to be positively correlated with the magnitude of force applied. In cases where stronger anchorage reinforcement is required, precision cuts is the superior method.

CONCLUSIONS

The utilization of microimplants in conjunction with CAs can facilitate the effective contribution ratio of molar distalization. However, it is important to note that complete elimination of anchorage loss is not achievable. To mitigate undesired movement, careful planning of anchorage preparation and overcorrection is recommended.

Force decay of polyethylene terephthalate glycol aligner materials during simulation of typical clinical loading/unloading scenarios

BACKGROUND

This in vitro study investigated the effect of three distinct daily loading/unloading cycles on force delivery during orthodontic aligner therapy. The cycles were applied for 7 days and were designed to reflect typical clinical aligner application scenarios.

MATERIALS AND METHODS

Flat polyethylene terephthalate glycol (PET-G) specimens (Duran®, Scheu Dental, Iserlohn, Germany) with thicknesses ranging between 0.4 and 0.75 mm were tested in a three-point-bending testing machine. Measurements comprised loading/unloading intervals of 12 h/12 h, 18 h/6 h, and 23 h/1 h, and specimens were exposed to bidistilled water during loading to simulate intraoral conditions.

RESULTS

A very large decay in force for the PET‑G specimens could already be observed after the first loading period, with significantly different residual force values of 24, 20, and 21% recorded for the 12 h/12 h, 18 h/6 h, and 23 h/1 h loading/unloading modes, respectively (Mann-Whitney U test, p < 0.01). In addition, further decays in force from the first to the last loading period at day 7 of 13.5% (12 h/12 h), 9.7% (18 h/6 h), and 8.4% (23 h/1 h) differed significantly among the three distinct loading modes (Mann-Whitney U test, p < 0.01).

CONCLUSION

Although the initial material stiffness of PET‑G is relatively high, the transmission of excessive forces is attenuated by the high material-related force decay already within a few hours after intraoral insertion.

Orthodontically induced external apical root resorption considerations of root-filled teeth vs vital pulp teeth: a systematic review and meta-analysis

INTRODUCTION

The purpose of this systematic review was to research the difference between root-filled teeth (RFT) and vital pulp teeth (VPT) in orthodontically induced external apical root resorption (EARR) and to offer suggestions for clinicians on therapeutic sequence and timing when considering combined treatment of endodontic and orthodontic.

MATERIALS AND METHODS

An electronic search of published studies was conducted before November 2022 in PubMed, Web of Science and other databases. Eligibility criteria were based on the Population, Intervention, Comparison, Outcome, and Study design (PICOS) framework. RevMan 5.3 software was used for statistical analysis. Single-factor meta-regression analysis was used to explore the sources of literature heterogeneity, and a random effects model was used for analysis.

RESULTS

This meta-analysis comprised 8 studies with 10 sets of data. As there was significant heterogeneity among the studies, we employed a random effects model. The funnel plot of the random effects model exhibited a symmetrical distribution, indicating no publication bias among the included studies. The EARR rate of RFT was significantly lower than that of VPT.

CONCLUSIONS

In the context of concurrent endodontic and orthodontic treatment, priority should be given to endodontic therapy, as it serves as the foundation for subsequent orthodontic procedures. The optimal timing for orthodontic tooth movement post-root canal therapy is contingent upon factors such as the extent of periapical lesion resolution and the degree of dental trauma sustained. A comprehensive clinical assessment is essential in guiding the selection of the most suitable approach for achieving optimal treatment outcomes.

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.

The effects of aligner anchorage preparation on mandibular first molars during premolar-extraction space closure with clear aligners: A finite element study

INTRODUCTION

This study aimed to determine the effectiveness of different aligner anchorage preparations on mandibular first molars during premolar-extraction space closure with clear aligners and to assess the effects of different modes of Class II elastics on mandibular first molars.

METHODS

Finite element models were constructed on the basis of cone-beam computed tomography data from an orthodontic patient. The models comprised maxilla, mandible, maxillary and mandibular teeth without first premolars, periodontal ligaments, attachments and aligners. Tooth displacement tendencies were calculated using different aligner anchorage preparations and Class II elastics on the models from the same patient. Three group sets were designed on the basis of the positions of aligner cutouts and buttons (mesiobuccal, distobuccal and lingual). Four groups were established in each of the 3 group sets. Four groups were created: (1) no elastic traction + no anchorage preparation, (2) anchorage preparation only, (3) elastic traction only, and (4) elastic traction + anchorage preparation. Different aligner anchorage preparations (0°, 1°, 2°, 3°) were applied on mandibular second premolars and molars. The Class II traction force was set to 100 g.

RESULTS

With clear aligners, mandibular first molars were subject to mesial tipping, lingual tipping and intrusion. In the condition of no elastic traction, aligner anchorage preparation resulted in distal tipping, buccal tipping, and extrusion effect on mandibular first molars. Aligner anchorage preparation was more effective in the distal and lingual cutout groups than in the mesial cutout group. In the condition of Class II elastic traction, the bodily movement of mandibular first molars was achieved with a 3° anchorage preparation for the mesial cutout group and a 1.7° anchorage preparation for distal and lingual cutout groups. Absolute maximal anchorage was achieved with a 2° anchorage preparation for distal and lingual cutout groups.

CONCLUSIONS

Clear aligner therapy caused mesial tipping, lingual tipping and intrusion of mandibular first molars during premolar-extraction space closure. Aligner anchorage preparation effectively prevented mesial and lingual tipping of mandibular molars. Distal and lingual cutout modes were more effective than mesial cutout modes in aligner anchorage preparation. For each aligner stage (0.25 mm), 1.7° aligner anchorage preparation and Class II elastics with distal or lingual cutouts led to the bodily movement of mandibular first molars, whereas 2° anchorage preparation reached absolute maximal anchorage.

Ribosomal Stress Couples with the Hypoxia Response in Dec1-Dependent Orthodontic Tooth Movement

This study characterized the effects of a deficiency of the hypoxia-responsive gene, differentiated embryonic chondrocyte gene 1 (Dec1), in attenuating the biological function of orthodontic tooth movement (OTM) and examined the roles of ribosomal proteins in the hypoxic environment during OTM. HIF-1α transgenic mice and control mice were used for hypoxic regulation of periodontal ligament (PDL) fibroblasts. Dec1 knockout (Dec1KO) and wild-type (WT) littermate C57BL/6 mice were used as in vivo models of OTM. The unstimulated contralateral side served as a control. In vitro, human PDL fibroblasts were exposed to compression forces for 2, 4, 6, 24, and 48 h. HIF-1α transgenic mice had high expression levels of Dec1, HSP105, and ribosomal proteins compared to control mice. The WT OTM mice displayed increased Dec1 expression in the PDL fibroblasts. Micro-CT analysis showed slower OTM in Dec1KO mice compared to WT mice. Increased immunostaining of ribosomal proteins was observed in WT OTM mice compared to Dec1KO OTM mice. Under hypoxia, Dec1 knockdown caused a significant suppression of ribosomal protein expression in PDL fibroblasts. These results reveal that the hypoxic environment in OTM could have implications for the functions of Dec1 and ribosomal proteins to rejuvenate periodontal tissue homeostasis.

Effects of upper-molar distalization using clear aligners in combination with Class II elastics: a three-dimensional finite element analysis

INTRODUCTION

The effects of upper-molar distalization using clear aligners in combination with Class II elastics for anchorage reinforcement have not been fully investigated yet. The objective of this study is to analyze the movement and stress of the whole dentition and further explore guidelines for the selection of traction methods.

METHODS

Three-dimensional (3D) finite element models are established to simulate the sequential molar distalization process, including the initial distalization of the 2^nd molar (Set I) and the initial distalization of the 1^st molar (Set II). Each group set features three models: a control model without Class II elastics (model A), Class II elastics attached to the tooth by buttons (model B), and Class II elastics attached to the aligner by precision cutting (model C). The 3D displacements, proclination angles, periodontal ligament (PDL) hydrostatic stress and alveolar bone von Mises stress in the anterior area are recorded.

RESULTS

In all of the models, the maxillary anterior teeth are labial and mesial proclined, whereas the distal moving molars exhibit distal buccal inclination with an extrusion tendency. With the combination of Class II elastics, the anchorage was effectively reinforced; model C demonstrates superior anchorage reinforcement with lower stress distribution in comparison with model B. The upper canines in model B present an extrusion tendency. Meanwhile, the mandibular dentition in models B and C experience undesired movement tendencies with little discrepancy from each other.

CONCLUSIONS

Class II elastics are generally effective for anchorage reinforcement as the upper-molar distalization is performed with clear aligners. Class II elastics attached to an aligner by precision cutting is a superior alternative for maxillary anchorage control in cases that the proclination of upper incisors and extrusion of upper canines are unwanted.

Present status and future directions: Root resorption

Root resorption is the loss of dental hard tissue because of odontoclastic action. In permanent teeth, it is undesirable and pathological in nature. Root resorption may occur on the inner aspect of the root canal (internal root resorption) or on the outer aspect of the root (external root resorption). Regardless of its location, root resorption is irreversible, and may result in discomfort for the patient, requires management and/or, in some cases, results in the premature loss of the affected tooth. Root resorption is often challenging to accurately diagnose and manage. The aim of this narrative review is to present the relevant literature on the aetiology, pathogenesis, diagnosis and management, as well as discuss the future directions of diagnosis and management of root resorption.

Root resorption followed by orthodontic treatment in individuals with anterior open bite. A complete vision focused on different treatment alternatives: A review

The aim of this review was to determine the incidence of different types of treatment and the prevalence of root resorption in incisors induced by orthodontic treatment in patients with open bite. Libraries and electronic databases were searched, with 322 articles being selected and 55 articles considered regarding PRISMA checklist. It has been shown that apical root resorption of the incisors is more frequent in patients with premolar extractions than in those treated without extractions, due to greater apical displacement during retraction of the anterior teeth in the space closure phase. On the other hand, it has been described that intrusion of posterior teeth is four times more likely to cause root resorption than extrusion movement, thereby increasing the risk of root resorption in posterior teeth compared to conventional orthodontic treatment not requiring molar intrusions. Finally, aligners, such as orthodontic treatments with fixed appliances, have not been shown to induce clinically significant root resorption in open bite individuals. Literature on root resorption in open bite treatments is scarce making difficult conclusions difficult. However, the amount of root loss in cases of open bite seems to be similar to that of individuals without open bite.

Visualization of orthodontic forces generated by aligner-type appliances

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

Evaluation of Tooth Movement Accuracy with Aligners: A Prospective Study

Background. Clear aligners treatment (CAT) is a common solution in orthodontics to treat both simple and complex malocclusions. This study aimed to evaluate the predictability of CAT, comparing the virtually planned and the achieved tooth movement at the end of stage 15, which is often the time of first refinement. Methods. Seventeen patients (mean age: 28.3 years) were enrolled in the study. Torque, tip and rotation were analyzed in 238 maxillary teeth on digital models at Pre-treatment (T0), at the end of stage 15 (T15) and at virtually planned stage 15 (T15i). Prescription, Achieved movement and performance values were calculated to compare the virtually planned and the clinical tooth position. Data were analyzed by means of Student’s t test with a level of significance set at p < 0.05. Results. The largest iper-performance was the torque correction of the second molars (+2.3° ± 3.1°), the greatest under-performance was the tip correction of the first molars (−2.3° ± 3.3°), while rotation corrections of all the teeth showed more accurate performance. No significant differences were found between mean Prescription and mean Achieved movement for all the assessed movements (p < 0.05). Conclusions. An accurate evaluation of CAT after the 15th aligner is fundamental in order to individuate the movements that are not matching the digital set-up.

Clinical effectiveness of clear aligner treatment compared to fixed appliance treatment: an overview of systematic reviews

OBJECTIVE

To evaluate the available evidence regarding clinical effectiveness of clear aligner treatment (CAT).

MATERIALS AND METHODS

A comprehensive literature search was conducted for systematic reviews investigating effectiveness of CAT published up to July 15, 2021. This was accomplished using different electronic databases. No language restriction was applied. Screening, quality assessment, and data extraction were performed by two authors independently. Information was categorized and narratively synthesized for the key findings from moderate and high-quality reviews.

RESULTS

A total of 361 potentially eligible reviews were identified. After excluding the non-relevant/low-quality reviews, 18 systematic reviews were included. CAT was found to be effective for mild to moderate malocclusions, and was associated with inferior outcomes when treating severe cases or with achieving specific tooth movements. There were conflicting results regarding treatment duration; however, CAT may be associated with shorter treatment in mild to moderate cases. Relapse was greater with CAT, while periodontal health was better. The risk of root resorption tended to be lower with CAT. Regarding pain, the results were unclear, although CAT was found to be more comfortable and associated with a reduced impact on eating and chewing.

CONCLUSIONS

The level of evidence regarding CAT is moderate; hence, further high-quality randomized clinical trials are required. Evidence supports use of aligners as an alternate to fixed appliances in patients with mild-to-moderate malocclusion but not in severe cases. Advancement in technology could enhance the accuracy of CAT in delivering planned outcomes.

CLINICAL RELEVANCE

CAT can be used effectively for selected cases with mild to moderate malocclusion.

REGISTRATION

PROSPERO registration number: CRD42021246855.

Orthodontic root resorption

External apical root resorption (EARR) is one of the most frequently reported iatrogenic side effects of orthodontic movement. Nevertheless, no robust and unequivocal scientific evidence is yet available in the literature regarding the clinical and biological factors that trigger EARR. The purpose of the present position paper is to provide clinicians, residents, and investigators a summary of our current understanding about root resorption caused by orthodontic tooth movement, based on up-to-date available scientific evidence. Morphological, structural, biomechanical, and biological differences account for predisposing the apical third to EARR compared to other root surfaces during orthodontic treatment. In addition, a relevant number of patient and treatment-related factors increase risk of EARR. The main patient-related factors are reviewed and discussed: genetic factors, tooth anatomy, demographic factors, malocclusion factors, previous endodontic treatment, medical history, short root anomaly. Similarly, the influence of treatment-related factors are analyzed with regard to the effect of: biomechanical factors, type of orthodontic appliance, adjunctive therapies to accelerate tooth movement, early treatment, maxillary expansion, teeth extractions, the duration of treatment and the amount of apical displacement. Clinical management of EARR from pre-treatment records to the monitoring strategy as well as recommendations for the post orthodontic-treatment period are presented as a guide for the clinician. Despite years of studies, we still do not fully understand EARR, but the future is promising. True three-dimensional imaging with higher resolution and low radiation, and predictive tools towards an earlier detection without radiographs, will mark future developments in the field of EARR in orthodontics.

Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners

OBJECTIVES

To analyze the biomechanical system of anterior retraction with clear aligner therapy (CAT) with and without an anterior mini-screw and elastics.

MATERIALS AND METHODS

Models including a maxillary dentition (without first premolars), maxilla, periodontal ligaments (PDLs), attachments, and aligners were constructed and imported to finite element software. Three model groups were created: (1) control (CAT alone), (2) labial elastics (CAT with elastics between the anterior mini-screw and buttons on central incisors), and (3) linguoincisal elastics (CAT with elastics between the anterior mini-screw and precision cuts on the lingual sides of the aligner). Elastic forces (0-300 g, in 50 g increments) were applied.

RESULTS

CAT alone caused lingual tipping and extrusion of the incisors. Labial elastics caused palatal root torquing and intrusion and mesial tipping of the central incisors, while linguoincisal elastics produced palatal root torquing and intrusion of both central and lateral incisors. Second premolars were intruded in all three groups, with less intrusion in the linguoincisal elastics group. For the control group, stress was concentrated on both labial and lingual root surfaces, alveolar ridge, and cervical and apical PDLs. Stress was more concentrated in the labial elastics group and less concentrated in the linguoincisal elastics group.

CONCLUSIONS

CAT produced lingual tipping and extrusion of incisors during anterior retraction. Anterior mini-screws and elastics can achieve incisor intrusion and palatal root torquing. Linguoincisal elastics are superior to labial elastics with a lower likelihood of buccal open bite. Root resorption and alveolar defects may occur in CAT, more likely for labial elastics and less likely for linguoincisal elastics.

Impact of Dental Model Height on Thermoformed PET-G Aligner Thickness—An In Vitro Micro-CT Study

The aim of the present study was to investigate whether base height of 3D-printed dental models has an impact on local thickness values from polyethylene terephthalate glycol (PET-G) aligners. A total of 20 aligners were thermoformed on dental models from the upper jaw exhibiting either a 5 mm high (H) or narrow (N), i.e., 0 mm, base height. The aligners were digitized using micro-CT, segmented, and local thickness values were computed utilizing a 3D-distance transform. The mean thickness values and standard deviations were assessed for both groups, and local thickness values at pre-defined reference points were also recorded. The statistical analysis was performed using R. Aligners in group H were significantly thinner and more homogenous compared to group N (p < 0.001). Significant differences in thickness values were observed among tooth types between both groups. Whereas thickness values were comparable at cusp tips and occlusal/incisal/cervical measurement locations, facial and palatal surfaces were significantly thicker in group N compared to group H (p < 0.01). Within the limits of the study, the base height of 3D-printed models impacts on local thickness values of thermoformed aligners. The clinician should consider potential implication on exerted forces at the different tooth types, and at facial as well as palatal surfaces.

Treatment of mild Class II malocclusion in growing patients with clear aligners versus fixed multibracket therapy: A retrospective study

Objective

To compare the dental and skeletal effects of intermaxillary elastics on the correction of mild Angle's Class II division 1 malocclusion with clear aligner treatment (CA) versus fixed multibracket (FMB) in growing patients.

Settings and sample population

The study sample consisted of 49 consecutively patients (mean age ± SD 12.9 ± 1.7 years), 32 females and 17 males referred from the School of Orthodontics of the University of Bratislava Comenius (Slovakia). All patients were treated with a non‐extraction orthodontic treatment, 25 with FMB and 24 with CA.

Methods

The cephalometric analysis was performed at the beginning (T0) and the end of the treatment (T1). The t test for unpaired data was carried out to compare cephalometric values at T0 and changes at T1‐T0 between the two groups. The level of significance was set as P < .0035.

Results

The two groups showed no statistically significant differences (ANPg = −0.1°; P = .762) in the correction of the sagittal intermaxillary relation. The analysis of vertical skeletal changes showed no statistically significant effects on mandibular inclination (SN/MP = 0.1°; P = .840). The two treatments had a statistically significant and clinically relevant difference in controlling the inclination of the lower incisors (L1/GoGn = 4.8°, CAG = −0.5°± 3.9°; FMB = 4.3°± 5.8°; P < .001).

Conclusions

Class II elastics combined with CA and FMB produce a similar correction on sagittal discrepancies in growing patients. CA presented a better control in the proclination of the lower incisors. CA and elastics might be a good alternative in the correction of mild Class II malocclusion in cases where a proclination of lower incisors is unwanted.

Clear aligner orthodontic treatment: Angle Society of Europe consensus viewpoint

Orthodontics has witnessed not only an exponential rise in demand from adult patients but accompanying this, the emergence of alternate aesthetic treatment options to the more traditional fixed labial appliance. The concept of using clear aligners as a means of achieving tooth movement has increased in popularity among both patients and clinicians alike. However, the question over best research evidence as to their clinical effectiveness to treat a range of malocclusion traits remains elusive and controversial among the profession.In an attempt to offer the profession some clear guidance, The Angle Society of Europe reviewed and discussed the current published evidence (2005-2018) on their clinical use, during the annual meeting in January 2020, to help formulate a consensus viewpoint on the clinical applications.

Reasons influencing the preferences of prospective patients and orthodontists for different orthodontic appliances

Objective

To evaluate the reasons influencing the preferences for a certain type of orthodontic appliance over another among prospective patients (PP) and orthodontists.

Methods

A total of 49 PP and 51 orthodontists were asked about their preferences for the following appliances clear aligners (CA), lingual metallic brackets (LMB), polycrystalline and monocrystalline ceramic brackets, and buccal metallic brackets (BMB). The participants rated the importance of 17 potential reasons that would explain their choices. The reasons that contributed most to these preferences were identified. Non-parametric tests (Fisher’s exact, χ² and Mann–Whitney tests) and multivariate analyses (regression and discriminant analysis) were used to assess the data (α = 0.05).

Results

CA and BMB were the most chosen appliances by PP and orthodontists, respectively. LMB was the most rejected option among both groups of participants (p < 0.001). Rates of the importance of pain/discomfort, smile esthetics, finishing details, and feeding/speech impairment showed the highest differences between PP and orthodontists (p < 0.0005). Discriminant analyses showed that individuals who considered treatment time and smile esthetics as more important were more likely to prefer CA, while those who prioritized finishing details and cost were more likely to choose BMB (p < 0.05).

Conclusions

Reasons related to comfort and quality of life during use were considered as more important by PP, while those related to the results and clinical performance of the appliances were considered as more relevant by orthodontists.

Direct to consumer orthodontics: Exploring patient demographic trends and preferences

INTRODUCTION

This study aimed to evaluate market trends on the demographics most likely to select direct to consumer orthodontics and the reasoning behind their decisions.

METHODS

An internet-based cross-sectional survey was conducted. Data analysis was carried out using logistic regression models.

RESULTS

Total of 1573 surveys were completed. While 32.2% of those surveyed selected direct to consumer orthodontics over conventional orthodontics, 10.8% would select direct to consumer orthodontics for their children. Among parents who would seek direct to consumer orthodontics, only 27.8% would consider the same treatment for their children. The odds of seeking direct to consumer orthodontic treatment for divorced participants was 2.52 times higher than that for single participants, for participants with 4 children or more was 2 times higher than that for participant with no children, and in age group 46-59 years was 2.23 times higher than that for age group 18-26 years. Seventy three percent of consumers who selected direct to consumer orthodontics selected cost as an influencing factor. Convenience was also a major determining factor at 69.6%.

CONCLUSIONS

Cost, convenience, and perceived simplicity all appear to factor into a consumer's consideration of direct to consumer orthodontics. As annual household income, age, and education increases consumers are more likely to consider direct to consumer orthodontic treatment.

Frequency of awake bruxism behaviour in orthodontic patients: Randomised clinical trial: Awake bruxism behaviour in orthodontic patients

INTRODUCTION

The influence of aligners on the activity of the masticatory muscles is still controversial, especially regarding the behaviour associated with awake bruxism (AB).

OBJECTIVE

To compare the frequency of AB behaviours between patients treated with aligners and fixed appliances.

METHODS

The sample comprised 38 Class I patients (mean age 22.08 years), divided by simple randomisation into two groups: OA group; orthodontic aligners (n 19) and FA group; fixed appliance (n 19). The frequency of AB was investigated by the ecological momentary assessment using an online device (mentimeter), during 7 following days at different timepoints, before and after appliance placement and in the 2nd, 3rd, 4th and 6th months of orthodontic treatment. These variables were also evaluated: level of anxiety by the State-Trait Anxiety Inventory, stress by the Perceived Stress Scale, catastrophising related to pain and degree of hypervigilance by the Pain Vigilance and Awareness Questionnaire, and the presence of facial pain evaluated by the DC/TMD.

RESULTS

There was no difference between groups in the frequency of AB behaviours, with mean of 53.5% for group OA and 51.3% for FA. The most frequent behaviour was slightly touching the teeth, and in FA group, there was a significant reduction in this behaviour soon after appliance placement. The groups did not differ concerning the degree of anxiety, stress, catastrophising, hypervigilance and facial pain.

CONCLUSION

The orthodontic treatment performed with aligners or fixed appliances did not influence the frequency of AB during the 6 months of treatment. REGISTRY OF CLINICAL TRIALS: (REBEC): RBR-9zytwf.

Orthodontic treatment and root resorption: an overview of systematic reviews

BACKGROUND

Root resorption can be considered the most unfortunate complication of orthodontic treatment.

OBJECTIVE

To evaluate the available evidence regarding orthodontically induced inflammatory root resorption (OIIRR).

SEARCH METHODS

A comprehensive literature search was conducted for the systematic reviews investigating OIIRR published up to 24 May 2020. This was accomplished using electronic databases: MEDLINE via OVID, EMBASE, AMED (Allied and Complementary Medicine Database), PubMed, and Web of Science. Any ongoing systematic reviews were searched using Prospero and a grey literature search was undertaken using Google Scholar and OpenGrey (www.opengrey.eu/). No language restriction was applied.

SELECTION CRITERIA

Only studies investigating OIIRR were included.

DATA COLLECTION AND ANALYSIS

Screening, quality assessment [using the AMSTAR 2 tool (A Measurement Tool to Assess Systematic Reviews)], and data extraction were performed by two authors independently. Information was categorized and narratively synthesized for the key findings from moderate and high-quality reviews.

RESULTS

A total of 2033 potentially eligible studies were identified. After excluding the non-relevant studies, 28 systematic reviews were included. Of which, 20 systematic reviews (71.5%) were of moderate and high-quality level of evidence. The incidence and severity of OIIRR increase with the fixed appliance, especially with heavy force, intrusion, torqueing movements, increased treatment duration, and treatment with extractions or with long apical displacement (particularly for maxillary incisors). There was insufficient evidence regarding most other treatment- and patient-related factors on OIIRR. Following all precautionary measures, pausing treatment and regular monitoring benefits patients with OIIRR.

CONCLUSIONS AND IMPLICATIONS

There is a limited number of high-quality studies in terms of OIIRR. The influence of fixed appliance on root resorption was noted; however, the cause and effect relationship between OIIRR and orthodontic biomechanics has not been confirmed. Avoiding heavy, continuous forces and a greater amount of apical displacement over a long duration of treatment is recommended. Precautionary measures should be carefully considered when treating patients with a high risk of OIIRR.

REGISTRATION

CRD42020166629.