Orthodontic retention: what's on the horizon?

Survival of periodontal ligament myofibroblasts after short-term mechanical strain in rats and in vitro: Could myofibroblasts contribute to orthodontic relapse?

OBJECTIVES

To investigate in vivo whether myofibroblasts formed in the PDL after exposure to short-term high experimental orthodontic forces in rats survive. To study in vitro whether human PDL fibroblasts can differentiate into myofibroblasts and survive when chemical or mechanical stimuli are removed.

DESIGN

Nine 6-week-old male Wistar rats were used in this experiment. Rat molars were exposed to high but rapidly decreasing experimental orthodontic forces by applying a rubber band and analyzed for the presence of myofibroblasts using ASMA staining. In vitro, human periodontal ligament (PDL) fibroblasts were exposed to transforming growth factor β1 (TGFβ1) and/or mechanical stress and monitored for myofibroblast formation and survival after these stimuli were abrogated.

RESULTS

In vivo exposure to orthodontic forces strongly induced myofibroblast formation in the stretched regions of the PDL. Furthermore, many PDL myofibroblasts remained present 6 days after exposure to these short-term high orthodontic forces. Human PDL fibroblasts were shown to differentiate into myofibroblasts after 2 days of TGFβ1 exposure and survive for at least 2 more days after removing chemical stimuli (TGFβ1) or mechanical strain. Under in vitro conditions, both TGFβ1 and mechanical strain for 3 days promoted (myo)fibroblast formation, and these cells persisted for 3 more days after the removal of both stimuli.

CONCLUSIONS

PDL myofibroblasts survive after the removal of mechanical strain in vivo and in vitro. This supports the hypothesis that myofibroblasts, which form in response to mechanical strain and chemical cues in the periodontal ligament (PDL), play a role in relapse following orthodontic tooth movement.

A Novel 3-Dimensional Printed Nanoceramic Hybrid Resin Fixed Lingual Retainer: Characterization and Mechanical Tests

Introduction: An innovative retention protocol was developed to create a new 3D-printed fixed retainer employing SprintRay OnX nanoceramic hybrid resin. The feasibility and usability of the retainer were subsequently evaluated. Methods: Identification and characterization of SprintRay OnX was done using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and flexural strength. Load-deflection and pull-out tests were conducted on the 3D-printed straight wires, with three distinct cross-sectional geometries: round (1 mm), oval (1 mm × 1.5 mm) and semielliptical (1 mm × 1.5 mm). Twisted G&H and coaxial Respond stainless steel multistrand retainers were used for comparison. In the load-deflection test, a three-point bending test (3PBT) was employed. For the pull-out test, the retainer wire was inserted into the composite, which was placed in a centrally located hole of an acrylic block; the retainer wire was subjected to a tensile force along its long axis. Results: Characteristic bands close to those of PMMA were observed in the FTIR spectra. SEM-EDX and XRD revealed a crystalline material with homogeneously distributed Yb element signals (19.4%). On FE-SEM micrographs, small clumps were displayed on smooth surfaces. The flexural strength and the flexural modulus were, respectively, 142.48 MPa and 7.842 GPa. All groups of 3D-printed wires exhibited significantly higher load-deflection levels than the multistrand wires (MSWs). Concerning pull-out forces, they fell in between twisted G&H (96 N) and coaxial Respond (48.09 N) retainer wires. The 3D-printed wires fractured cohesively without detachment from the adhesive, suggesting that the chemical bond was adequate for satisfactory wire integration, yet the wire's strength was compromised. Concerning the cross-sectional geometry, the load-deflection and the pull-out forces of 3D-printed oval and semielliptical wires were significantly higher than that of 3D-printed round wires, which was attributed to the larger cross-sections of the wires. Conclusion: Oval and semielliptical 3D-printed wires offered favorable features as lingual retainers.

The effects of fulvic acids and low-level laser therapy on orthodontic retention in rats

BACKGROUND

Shortening retention time and minimizing relapse rates are ongoing challenges in orthodontics. This study investigated the effects of natural fulvic acids (FAs) and low-level laser therapy (LLLT) on orthodontic retention in rats.

METHODS

Seventy-two male Sprague-Dawley rats underwent mesial movement of the left maxillary first molar using a 50 g force via a nickel-titanium tension spring. After three weeks of movement, the rats entered the retention phase with retainer wires and were divided into four groups: Control (no intervention), FAs (80 mg/kg orally daily), LLLT (808 nm laser twice weekly), and FAs + LLLT (both treatments). Retainers were removed on days 7, 14, and 21 for a 3-day relapse assessment. Maxillary impressions were analyzed for relapse rates using 3Shape software, alongside histological and immunohistochemical evaluations of bone morphogenetic protein-2 (BMP-2) expression in periodontal tissues, with differences among groups analyzed using an ordinary two-way analysis of variance (ANOVA).

RESULTS

The relapse rate decreased over time, particularly at 10, 17, and 24 days (p < 0.001). The FAs group did not significantly affect relapse rates compared to the control group (p = 0.084). In contrast, both the LLLT and FAs + LLLT groups significantly reduced relapse rate (p < 0.001), with no significant difference between these groups (p = 0.555). Histological examination revealed active osteoclasts on day 10, decreasing by days 17 and 24. The LLLT and FAs + LLLT groups showed less local cementum resorption and better periodontal fiber arrangement. All treatment groups significantly increased BMP-2 expression (P < 0.05) compared to controls. with LLLT and FAs + LLLT differing significantly from FAs (P < 0.001), though no difference was observed between LLLT and FAs + LLLT (P = 0.578).

CONCLUSIONS

FAs did not significantly reduce relapse rate with retainers, while LLLT effectively reduced relapse rates, showing no additional benefit from combining FAs with LLLT. Both FAs and LLLT increased BMP-2 expression in PDL fibroblasts but with no synergistic effect.

Keeping the teeth in line: Exploring the necessity of bonded retainers in orthodontics: A narrative review

In most recent studies, long-term retention after orthodontic treatment has been hypothesized that may be necessary to maintain the stability of the dentition and avoid post-treatment changes. The bonded fixed retainer is characterized by its clinical effectiveness, patient acceptance, and lack of patient complaints as compared with a removable retainer. An electronic database (such as PubMed, PubMed Central, Web of Science, Science Direct, Cochrane Library, Scopus, and ResearchGate) has been collected using specific keywords. Of the 152 articles, only randomized clinical trials that investigated different types of fixed retainers or compared fixed with removable retainers were illustrated in tables and included in this review. The present review has gone some way towards enhancing our understanding of the bonded fixed retainer, types, material, bonding methods, and how to improve its the success rate, besides the importance of new technology in fixed orthodontic retention.

Comparison of relapse of orthodontic treatment following aligner versus conventional fixed appliance treatment. A systematic review

Background

Aligners are an alternative that are currently being widely used in orthodontic treatment, however, post-treatment relapse following aligner versus conventional treatment has not been compared. The objective of this study was to compare post-treatment relapse of orthodontic treatment with dental aligners versus conventional fixed orthodontics through a systematic review.

Material and Methods

An exhaustive search was carried out in the MEDLINE (via PubMed), EBSCO, SCOPUS and EMBASE databases up to September 30, 2023. A total of 522 articles were found and after applying the selection criteria, the full texts of 24 articles were chosen for evaluation. At the end of the evaluation, only 3 studies were considered, two observational studies and one randomized clinical trial. The Newcastle Ottawa and Risk of bias (ROB-2) tools were used to assess the risk of bias.

Results

Of the three studies, only one (evaluated three years post-orthodontic treatment) identified significant differences in the frequency of relapse following total, maxillary and mandibular anterior alignment using conventional orthodontics. The other two studies (one evaluated at six months and the other two years post-orthodontic treatment) did not show statistically significant differences (p>0.05). In addition, the two latter studies reported slight relapse related to detachment of the fixed retainer.

Conclusions

The current evidence available indicates a lack of well-designed studies comparing post-treatment orthodontic relapse following the use of dental aligners versus conventional fixed orthodontic treatment, and the studies published to date have a high or moderate risk of bias. However, there are apparently no significant differences in frequency of relapse between the two types of treatment, suggesting similar stability results. Nonetheless, more well-designed studies are required to confirm this observation. Key words:Aligners, brackets, relapse, orthodontic.

Predictors for long-term relapse of orthodontic treatment in patients with cleft lip and palate. A clinical follow-up study

OBJECTIVES

To identify predictors for long-term relapse of orthodontic therapy in patients with cleft lip and palate (CLP).

MATERIALS AND METHODS

Patients with uni- and bilateral non-syndromal CLP were followed up at least two years after completion of their orthodontic therapy. Plaster casts of the start of treatment (T1), after completion of treatment (T2), and at follow-up (T3) were measured using the modified Huddart Bodenham Index. Characteristics of multidisciplinary therapy were taken from the patient files. Potentially influencing factors of relapse were investigated using logistic regression analyses and Spearman correlations.

RESULTS

In total 58.07% of the included 31 patients showed a stable treatment outcome at follow-up after an average of 6.9 years. Even if relapse occurred, 61.54% of these patients still showed improvement regarding their occlusion compared to baseline. Predictors for the occurrence of relapse were the severity of dysgnathia at baseline (p = 0.039) and the extent of therapeutic change (p = 0.041). The extent of therapeutic change was additionally a predictor for the extent of post-therapeutic relapse (ρ = 0.425; p = 0.019).

CONCLUSIONS

Patients with CLP benefit from their orthodontic therapy in the long term despite an increased tendency to relapse.

CLINICAL RELEVANCE

Results of this long-term study could be used to adapt the treatment concept for patients with CLP and reinforce the significance of a patient-centered orthodontic treatment concept for affected patients.

Stability and failure rate during 3 years of fixed retention: A follow-up of an randomized clinical trial on adolescents with four different lingual retainers

OBJECTIVE

To evaluate stability outcomes and failure rates associated with four types of lingual retainers: (1) dead-soft wire, (2) multistrand stainless steel (SS) wire, (3) CAD/CAM nitinol, and (4) connected bonding pads (CBPs) after 3 years of retention.

METHODS

This study enrolled 96 patients (66 females, 30 males) with a median age of 19 years with four types of lingual retainers: (1) 0.016 × 0.022-inch dead-soft wire, (2) 0.0215-inch five-strand SS wire, (3) 0.014 × 0.014-inch CAD/CAM nitinol wire, and (4) CBPs. The irregularity index, intercanine distances, and arch lengths were obtained and used to evaluate mandibular stability. Failure rates were also assessed during this study. Data were statistically analysed.

RESULTS

Irregularity increased, whereas intercanine width and arch length decreased after 3 years of retention. The greatest irregularity was associated with the CBPs and the least with the CAD/CAM retainers. Changes in stability measurements were significantly higher in the dead-soft wire and CBPs than those in the CAD/CAM nitinol and multistrand SS wires. Parallel to these changes, the frequency of failure yielded similar results with the same significance between the groups. The failure rate of CBPs, in contrast to the CAD/CAM nitinol and multistrand SS wires, was significantly higher in the right quadrant (P < .05).

CONCLUSION

After taking the 3-year results into consideration, CAD/CAM nitinol and multistrand SS wires were found to be more successful than the others in maintaining mandibular stability. The most failures were observed with CBPs after 3 years of retention.

Three-dimensional microanalysis of tooth movement during the first 6 months of orthodontic double retention

INTRODUCTION

This study performed a 3-dimensional analysis of tooth movement during orthodontic retention to assess the effectiveness of double retention (fixed and removable) in preventing undesired tooth movement.

METHODS

One hundred randomly selected patients were included at the initiation of double orthodontic retention with fixed retainers and vacuum-formed splints (recommended to be worn 22 h/d) in both arches. Intraoral scans were performed directly (T0), 1 month (n = 88), 3 months (T2) (n = 78), and 6 months (T3) (n = 66) after retainer bonding. Nine reference points were marked on each tooth in every patient. Subsequent scans were superimposed, and point displacement was calculated. Statistical analysis was performed using the R statistical software (version 4.2.2; R Core Team, Vienna, Austria).

RESULTS

Sample size calculation determined at least 55 patients were needed. The total dropout between T0 and T3 was 34 patients (did not show up for appointment). The median absolute displacement value of a single point between T0 and T3 was 0.015 mm. The most stable teeth were mandibular central incisors, whereas the least stable were mandibular molars. Most tooth displacements occurred between T0 and T2, then slowed down significantly.

CONCLUSIONS

Double orthodontic retention prevents major tooth displacements in most patients during the first 6 months of retention; however, larger, unpredictable single-tooth displacement may occur in individual patients.

The role of the general dental practitioner in the management of the hypodontia patient

The general dental practitioner (GDP) is usually the first person to suspect that a young patient is affected by hypodontia. The condition occurs rarely in the primary dentition but is relatively common in the permanent dentition. Between the ages of 7 and 12 years, failure of a permanent tooth to erupt as expected will lead the GDP to initiate and then contribute to the ideal management of the patient's condition. This ranges from reassurance and preventive measures to providing aspects of treatment in a long-term management plan, alongside a multidisciplinary specialist team and thereafter, delivery of life-long dental care.

Preclinical in vitro study of streptococcus mutans accumulation in three fixed retainer designs: Microbiological assay

The use of fixed retainers in the lower arch is frequent; however, its presence increases the accumulation of biofilm and dental calculus. The objective of this research was to evaluate, in vitro, the accumulation of Streptococcus mutans (S. mutans) in 3 designs of fixed retainers. Nine models were reproduced in heat-cured acrylic resin and divided into groups: straight retainer (SR), retainer with vertical strap (RVS), retainer with horizontal strap (RHS). The accumulation of S. mutans was assessed using the MTT assay (3-4,5-dimethyl-thiazol-2-yl-2,5-diphenyltetrazolium bromide) and then measured using an automated reader. The RHS group showed less biofilm accumulation compared to the other groups (p<0.05). The distance between the tooth surface and the retainer showed a strong negative correlation with biofilm accumulation (rs=-0.79, p=0.00037). The RHS showed significantly less accumulation of S. mutans due to the distance between the retainer and the tooth surface. This research provides relevant data for a future randomized clinical trial.

Clear Aligner Therapy: Up to date review article

The advantages of Clear Aligners Therapy (CAT) include the braces being virtually invisible, comfortable to wear, and removable for eating and brushing; that way, CAT can be used to treat a wide range of orthodontic issues. In 1999, the company Align Technology introduced the frst commercial clear aligner system called Invisalign. The Invisalign system was initially only available to orthodontists, but later became available to general dentists as well. The system quickly gained popularity among patients who were looking for a more discreet and comfortable alternative to traditional braces. In 2000, Align Technology received FDA clearance for the Invisalign system, which further increased its popularity. The biomechanics of clear aligners involve the use of custom-made tooth aligners that are specifcally shaped to guide teeth into desired positions. These aligners are typically made from flexible materials such as polyurethane or ethylene vinyl acetate and are adjusted to apply the necessary forces for tooth movement. Attachment devices, such as power ridges or buttons, are often used to enhance or assist in specifc tooth movements and for retention of the aligner. The use of attachments allows for the exertion of desired force on the teeth, which is crucial for the success of Clear Aligner Therapy. CAT should be used if patients are concerned about the esthetic appearances of their teeth-for example, actors and other individuals that rely on their appearances in public in a professional context-and if the misalignment is not severe, so that clear aligners can still work. One should not use CAT in cases of severe crowding or spacing issues that require extractions. If the patient has complex jaw discrepancies or skeletal issues or if teeth need to be moved extensively in multiple directions, CAT is likely not going to be strong enough. In conclusion, Clear Aligner Therapy is a safe, effective, and convenient orthodontic treatment option that offers patients a virtually invisible way to achieve a straighter, more beautiful smile. With continued advancements in technology and a growing body of research supporting its effectiveness, the future of Clear Aligner Therapy looks bright.

Compliance with retainer wear using audiovisual integration and reminder: a randomized clinical trial

Active audiovisual representation of instructions ensures vibrant knowledge acquisition and improves acquaintance needed for self-care with retainer wear. The aim of this trial is to assess the impact of audiovisual instructions with additional weekly electronic reminder messages on improving adherence to instructed wear time of Hawley retainer, periodontal outcomes, and participants' experiences. Fifty-two participants (mean age 26.1 y) planned for removable retention, were randomly assigned to two parallel groups to receive either (1) audiovisual instructions with an additional weekly reminder, or (2) verbal instructions alone. Each participant received a Hawley retainer equipped with a TheraMon microsensor and was instructed to wear it for 22 h daily. Participants were monitored for adherence to the wear time after 3 (T1) and 6 months (T2), and had their periodontal health and experiences assessed at T2. Overall, the mean objectively measured daily wear time at T1 was 14.9 (± 4.9 h), and 14.3 (± 5.4 h) at T2. After 3 months, no significant differences were found between the groups (p = 0.065), however, a significant difference favoring better compliance with wear instructions was observed in the audiovisual group after 6 months (p = 0.033). A non-significant difference was observed between both groups regarding the gingival (p = 0.165) and plaque index scores (p = 0.173). Participants' experiences were similar in both groups, except for satisfaction with the way of delivering instructions, being favorably reported in the audiovisual group. Audiovisual instructions with weekly reminders seem to have a significant effect on patient compliance in the longer term.Trial registration: TCTR20230220002.

Direct 3D-Printed Orthodontic Retainers. A Systematic Review

Three-dimensional (3D) printing technology has shed light on many fields in medicine and dentistry, including orthodontics. Direct 3D-printed prosthetics, implants or surgical devices are well-documented. The fabrication of orthodontic retainers using CAD technology and additive manufacturing is an emerging trend but the available data are scarce. The research approach of the present review included keywords in Medline, Scopus, Cochrane Library and Google Scholar up to December 2022. The searching process concluded with five studies eligible for our project. Three of them investigated directly 3D-printed clear retainers in vitro. The other two studies investigated directly 3D-printed fixed retainers. Among them, one study was in vitro and the second was a prospective clinical trial. Directly 3D-printed retainers can be evolved over time as a good alternative to all the conventional materials for retention. Devices that are 3D-printed are more time and cost efficient, offer more comfortable procedures for both practitioners and patients and the materials used in additive manufacturing can solve aesthetic problems, periodontal issues or problems with the interference of these materials with magnetic resonance imaging (MRI). More well-designed prospective clinical trials are necessary for more evaluable results.

Orthodontic Retainers-A Critical Review

The achievement of aesthetic, functional occlusion should not mark the end of the orthodontic intervention. To prevent relapse, retention needs advance planning, and may vary in duration. This review aims to present and comment on the available means of retention. The ever-popular, passive Hawley-like removable appliances are credible in maintaining the desired occlusion. Modifications are the removable appliance Wrap Around, having the labial archwire extending to the premolars; the translucent retainer, Astics, a unique aesthetic Hawley-type device; and the reinforced removable retainer, which features a metallic grid reinforcing the acrylic base. Vacuum-formed retainers are easy to fabricate and are readily prescribed. By contrast, fixed retainers are made of orthodontic wire and composite resin bonded on the lingual or palatal surfaces of the anterior teeth. Patient-related variables need evaluation to select the appropriate retainer, while patients ought to realize the importance of retention and comply with offered guidance. Overall, the orthodontist is responsible for keeping the patient informed on the properties and the duration of retention, even before starting active orthodontic treatment.

Orthodontic Retainers-A Critical Review

The achievement of aesthetic, functional occlusion should not mark the end of the orthodontic intervention. To prevent relapse, retention needs advance planning, and may vary in duration. This review aims to present and comment on the available means of retention. The ever-popular, passive Hawley-like removable appliances are credible in maintaining the desired occlusion. Modifications are the removable appliance Wrap Around, having the labial archwire extending to the premolars; the translucent retainer, Astics, a unique aesthetic Hawley-type device; and the reinforced removable retainer, which features a metallic grid reinforcing the acrylic base. Vacuum-formed retainers are easy to fabricate and are readily prescribed. By contrast, fixed retainers are made of orthodontic wire and composite resin bonded on the lingual or palatal surfaces of the anterior teeth. Patient-related variables need evaluation to select the appropriate retainer, while patients ought to realize the importance of retention and comply with offered guidance. Overall, the orthodontist is responsible for keeping the patient informed on the properties and the duration of retention, even before starting active orthodontic treatment.

Calcium Phosphate Delivery Systems for Regeneration and Biomineralization of Mineralized Tissues of the Craniofacial Complex

Calcium phosphate (CaP)-based materials have been extensively used for mineralized tissues in the craniofacial complex. Owing to their excellent biocompatibility, biodegradability, and inherent osteoconductive nature, their use as delivery systems for drugs and bioactive factors has several advantages. Of the three mineralized tissues in the craniofacial complex (bone, dentin, and enamel), only bone and dentin have some regenerative properties that can diminish due to disease and severe injuries. Therefore, targeting these regenerative tissues with CaP delivery systems carrying relevant drugs, morphogenic factors, and ions is imperative to improve tissue health in the mineralized tissue engineering field. In this review, the use of CaP-based microparticles, nanoparticles, and polymer-induced liquid precursor (PILPs) amorphous CaP nanodroplets for delivery to craniofacial bone and dentin are discussed. The use of these various form factors to obtain either a high local concentration of cargo at the macroscale and/or to deliver cargos precisely to nanoscale structures is also described. Finally, perspectives on the field using these CaP materials and next steps for the future delivery to the craniofacial complex are presented.

Wearable Orofacial Technology and Orthodontics

Wearable technology to augment traditional approaches are increasingly being added to the arsenals of treatment providers. Wearable technology generally refers to electronic systems, devices, or sensors that are usually worn on or are in close proximity to the human body. Wearables may be stand-alone or integrated into materials that are worn on the body. What sets medical wearables apart from other systems is their ability to collect, store, and relay information regarding an individual's current body status to other devices operating on compatible networks in naturalistic settings. The last decade has witnessed a steady increase in the use of wearables specific to the orofacial region. Applications range from supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and better understanding the jaw's functional and parafunctional activities. Orofacial wearable devices may be unimodal or incorporate multiple sensing modalities. The objective data collected continuously, in real time, in naturalistic settings using these orofacial wearables provide opportunities to formulate accurate and personalized treatment strategies. In the not-too-distant future, it is anticipated that information about an individual's current oral health status may provide patient-centric personalized care to prevent, diagnose, and treat oral diseases, with wearables playing a key role. In this review, we examine the progress achieved, summarize applications of orthodontic relevance and examine the future potential of orofacial wearables.

Dynamics and observations of long-term orthodontic tooth movement and subsequent relapse in C57BL/6 mice

The risk of relapse associated with orthodontic treatment is a major problem. Despite extensive research and discussion regarding the risk of orthodontic relapse, the underlying mechanisms remain to be elucidated. This study aimed to evaluate relapse following orthodontic treatment in mice (C57BL/6) tested via the coil spring method based on tooth movement at 21 days and mechanical retention at 7 days after completion of the procedure. During the experiment, relapse was observed and evaluated over 7 days. At the end of orthodontic tooth movement, the average distance was 259.6 (± 10.9) µm, and tooth movement was observed in all mice. No significant differences in distance were observed at the end of the experimental treatment period or after 7 days of mechanical retention. The distance at the start of observation was 258.6 (± 10.4) µm, whereas that at the end was 155.4 (± 12.4) µm, indicating that the distance had decreased significantly. Relative to the total relapse distance over the 7-day period, 45.7 (± 4.3)% of the relapse was observed on Day 0-1. The mouse model established in the current study provides an effective and reproducible method for the optimal evaluation of relapse. Our findings clarified that most of the relapse occurs within 7 days during the initial observation stage.