Behaviour of Human Oral Epithelial Cells Grown on Invisalign® SmartTrack® Material

Clinical outcomes of arch expansion with Invisalign: a systematic review

OBJECTIVE

This study aims to assess the scientific evidence regarding the clinical outcomes of Invisalign therapy in controlling orthodontic tooth movement.

MATERIALS AND METHODS

An electronic search was conducted on PubMed, Cochrane Library, Web of Science, Embase, and Scopus from November 2015 to November 2022 to identify relevant articles. Methodological shortcomings were highlighted, and an evaluation of the quality of the included studies was completed using the Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) tool.

RESULTS

Fifteen non-randomized controlled trials were included in the analysis. Most non-randomized controlled trials (n=11; 73%) were rated with a moderate risk of bias according to the ROBINS-I tool. There were statistically significant differences between the pretreatment and posttreatment arches. The average expansion was significantly different from that predicted for each type of tooth in both the maxilla and mandible. Furthermore, the efficiency decreased from the anterior area to the posterior area in the upper arch.

CONCLUSION

Despite the fact that arch expansion with Invisalign® is not entirely predictable, clear aligner treatment is a viable option for addressing dentition crowding. The efficacy of expansion is greatest in the premolar area. More research focusing on treatment outcomes with different materials of aligners should be conducted in the future. Overcorrection should be considered when planning arch expansion with Invisalign. In the maxilla, the expansion rate decreases from the anterior to the posterior, and presetting sufficient buccal root torque of posterior teeth may result in improved efficiency of expansion.

The incidence and severity of open gingival embrasures in adults treated with clear aligners and fixed appliances: a retrospective cohort study

BACKGROUND

To evaluate the incidence and severity of open gingival embrasures (OGEs) in adult patients treated with clear aligners and fixed appliances.

METHODS

Two hundred non-extraction adult subjects with less than 5 mm of crowding (mean age, 24.6 ± 3.8 years) were enrolled in this retrospective study. The subjects were divided into the clear aligner (n = 100) and fixed appliance group (n = 100). The intraoral photographs were utilized to determine the incidence of OGEs in the upper arch between maxillary central incisors, as well as the lower arch between mandibular central incisors. Crown overlap, crown shape, posttreatment root angulation, the distance from the interproximal contact point (ICP) to the alveolar bone crest (ABC) after treatment and interproximal enamel reduction (IPR) were determined in the two groups.

RESULTS

The incidence of OGEs between maxillary and mandibular central incisors after orthodontic treatment was 35.0% and 38.0% in the clear aligner group, respectively, significantly higher than that (18.0% and 24.0%) in the fixed appliance group (P < 0.05). The average area of an OGE after clear aligner treatment was larger both in the maxilla (0.16 ± 0.12mm²) and mandible (0.21 ± 0.24mm²) compared with that (0.05 ± 0.03mm² and 0.05 ± 0.06mm²) after fixed appliance treatment (P < 0.05). No difference was found regarding pretreatment crown overlap, crown shape, treatment duration, posttreatment root angulation, amount and distribution of IPR and the distance from ICP to ABC.

CONCLUSIONS

The incidence and severity of OGEs were higher in adults treated with clear aligners. Clinicians should be aware of the risk of OGEs during treatment with clear aligners.

A systematic review of biocompatibility and safety of orthodontic clear aligners and transparent vacuum-formed thermoplastic retainers: Bisphenol-A release, adverse effects, cytotoxicity, and estrogenic effects

Background

An ever-increasing demand is seen for clear aligners and transparent vacuum-formed retainers. They are esthetic and convenient. However, the biomaterials used in these appliances might pose biological safety and biocompatibility threats in terms of their bisphenol-A (BPA) release, cytotoxicity, adverse effects, and estrogenic effects. Due to the controversial results and the lack of any systematic reviews in this regard, we conducted this systematic review.

Materials and Methods

Web of Science, PubMed, Cochrane, Scopus, and Google Scholar as well as references of the found articles were searched (independently by 3 researchers) up to December 22, 2021, to find studies relevant to the biocompatibility of clear aligners and thermoplastic retainers. The search keywords were a combination of the following (and more): Essix, vacuum-formed aligner, thermoplastic aligner, clear aligner, Invisalign, vacuum-formed retainer, BPA release, monomer release, cytotoxicity, estrogenicity, biocompatibility, chemical properties, and oral epithelial cell. As eligibility criteria, articles in all languages would be included as long as their text could be translated clearly using online translators or by professional translators; all types of publications (article, book, and thesis) would be included if containing relevant studies and information; they should have been on clear liners or thermoplastic retainers; and they should have been on biocompatibility, safety, cytotoxicity, or estrogenicity of clear aligners or thermoplastic retainers. There were no restrictions on the type of study (randomized clinical trials, experimental in vitro studies). Studies focusing merely on the mechanical properties of clear aligners or thermoplastic retainers (without examining their chemical properties) would be excluded. The risk of bias was assessed.

Results

The risk of bias was rather low. However, the methodologies of the studies were quite different. Overall, 16 articles (1 randomized clinical trial and 15 in vitro studies) were identified. The data for BPA release were reported in four articles (1 clinical trial and 3 in vitro studies). Quantitatively speaking, the amount of released BPA reported by in vitro studies was very low, if not zero. However, the BPA level was very high in the only randomized clinical trial. Many adverse effects were linked to using clear aligners or transparent retainers, including pain and soft-tissue issues such as burning, tingling, sore tongue, lip swelling, blisters, ulceration, dry mouth, periodontal problems, and even systemic problems such as difficulty in breathing. Besides these biological adverse effects, oral dysfunctions and speech difficulties and tooth damage may be associated with clear aligners and should as well be taken into consideration.

Conclusion

Given the very high levels of BPA leach observed in the only clinical trial and considering other possible dangers of small traces of BPA (even at low doses) and also given the numerous adverse events linked to clear aligners or transparent retainers, it seems that safety of these appliances might be questionable and more clinical studies of biocompatibility are needed in this regard.

A spectroscopic study on orthodontic aligners: First evidence of secondary microplastic detachment after seven days of artificial saliva exposure

Clear orthodontic aligners have recently seen increasing popularity. The thermoplastic materials present several advantages, even if it is known that all plastic products can be subjected to environmental and mechanical degradation, leading to the release of microplastics (MPs). Their ingestion could cause oxidative stress and inflammatory lesions. This study aims to evaluate the potential detachment of MPs by clear aligners due to mechanical friction simulated with a 7-day protocol in artificial saliva. The study was performed on orthodontic clear aligners from different manufacturers: Alleo (AL); FlexiLigner (FL); F22 Aligner (F22); Invisalign® (INV); Lineo (LIN); Arc Angel (ARC), and Ortobel Aligner (OR). For each group, two aligners were immersed in artificial saliva for 7 days and stirred for 5 h/day, simulating the physiological teeth mechanical friction. After 7 days, the artificial saliva was filtered; then, filters were analyzed by Raman Microspectroscopy (RMS) and Scanning Electron Microscopy (SEM), respectively to chemically identify the polymeric matrix and to measure the number and size of the detected MPs. RMS spectra revealed that AL, FL, LIN, ARC, and OR aligners were composed by polyethylene terephthalate, while F22 and INV ones by polyurethane. SEM analysis showed that the highest number of MPs was found in ARC and the lowest in INV (p < 0.05). As regards MPs' size, no statistically significant difference was found among groups, with most MPs ranging from 5 to 20 μm. Noteworthy, a highly significant correlation (p < 0.0001) was highlighted between the distribution of MPs size and the different typologies of aligners. This in vitro study highlighted for the first time the detachment of MPs from clear aligners due to mechanical friction. This evidence may represent a great concern in the clinical practice since it could impact human general health.

New Materials and Techniques for Orthodontics

Orthodontics is a specialty of dentistry dealing with the prevention, diagnosis, and treatment of mispositioned jaws and teeth [...].

Effect of Titanium and Zirconia Nanoparticles on Human Gingival Mesenchymal Stromal Cells

Nano- and microparticles are currently being discussed as potential risk factors for peri-implant disease. In the present study, we compared the responses of human gingival mesenchymal stromal cells (hG-MSCs) on titanium and zirconia nanoparticles (<100 nm) in the absence and presence of Porphyromonas gingivalis lipopolysaccharide (LPS). The primary hG-MSCs were treated with titanium and zirconia nanoparticles in concentrations up to 2.000 µg/mL for 24 h, 72 h, and 168 h. Additionally, the cells were treated with different nanoparticles (25−100 µg/mL) in the presence of P. gingivalis LPS for 24 h. The cell proliferation and viability assay and live−dead and focal adhesion stainings were performed, and the expression levels of interleukin (IL)-6, IL-8, and monocyte chemoattractant protein (MCP)-1 were measured. The cell proliferation and viability were inhibited by the titanium (>1000 µg/mL) but not the zirconia nanoparticles, which was accompanied by enhanced apoptosis. Both types of nanoparticles (>25 µg/mL) induced the significant expression of IL-8 in gingival MSCs, and a slightly higher effect was observed for titanium nanoparticles. Both nanoparticles substantially enhanced the P. gingivalis LPS-induced IL-8 production; a higher effect was observed for zirconia nanoparticles. The production of inflammatory mediators by hG-MSCs is affected by the nanoparticles. This effect depends on the nanoparticle material and the presence of inflammatory stimuli.