Safety Considerations for Thermoplastic-Type Appliances Used as Orthodontic Aligners or Retainers. A Systematic Review and Meta-Analysis of Clinical and In-Vitro Research

Abstract

Use of thermoplastic material in orthodontics, either as aligner or as retainer appliances, is common practice and is likely to increase in the years to come. However, no systematic assessment on safety considerations of these adjuncts has been implemented up to date. The aim of this systematic review was to collectively appraise the existing evidence from both clinical and laboratory studies, on whether these appliances are associated with any estrogenic/cytotoxic effects or bisphenol-A (BPA) and monomer leaching. Eight electronic databases were searched with no limits in December 22, 2019, for published and unpublished research. Eligibility criteria comprised of studies of any design, describing use of any type of thermoplastic aligner. Study selection, data extraction and risk of bias (RoB) assessment was done independently, either in duplicate or confirmed by a second reviewer. Random effects meta-analyses of weighted mean differences (WMD) with associated 95% Confidence Intervals (CIs) were planned. Quality of the evidence was evaluated with Grading of Recommendations Assessment, Development and Evaluation (GRADE). A total of 58 articles were initially identified, while 5 were included in qualitative synthesis and 2 of those contributed to the quantitative syntheses. Four studies were in-vitro, while one was a randomized controlled trial; all assessed some type of orthodontic aligner or retainer, either as-received or retrieved. Risk of bias recordings ranged between unclear and high for all studies. Proliferation induction capacity of thermoplastic appliances’ eluents on MCF-7 cells failed to be confirmed compared to beta-estradiol (2 studies: 5% v/v, WMD: −182.08; 95% CI: −198.83, −165.33; p-value < 0.001; and 20% v/v, WMD: −184.53; 95% CI: −206.17, −162.88; p-value < 0.001). No cytotoxic activity was detected as well. In addition, although evidence from in-vitro studies was indicative of no traceable detection of BPA or other monomers, the findings from a single clinical trial were allied to increased levels of BPA in whole stimulated saliva, after up to 30 days of thermoplastic retainer usage, compared to standard Hawley retainer. The quality of the evidence overall was low to medium. Current data from in-vitro research are indicative of an absence of an estrogenic or cytotoxic effect of thermoplastic aligners or retainers. Regarding BPA or monomer release, evidence from clinical and laboratory studies appear inconsistent.

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

“…Biocompatibility and application material safety are essential factors, which should be considered during aligner therapy. However, a recent meta-analysis on safety considerations of orthodontic aligners revealed that the current evidence is inconsistent, and further laboratory and clinical studies are needed [ 10 ]. A potential cytotoxic effect of aligners’ eluates was tested in several in vitro studies, reporting rather weak cytotoxic activity of aligner eluates toward gingival fibroblasts, keratinocytes, and breast cancer cells [ 11 , 12 , 13 ].…”

Interventions to Reduce Aerosolized Microbes in Dental Practice: A Systematic Review with Network Meta-analysis of Randomized Controlled Trials

“…In all, adoption of occupational measures in dental practice against potentially hazardous aerosol-forming procedures should be considered in a universal basis, and standard precaution procedures should involve more skeptical application and even reduction in the use of aerosol-forming instrumentation in everyday practice. These constitute not only ultrasonic scaling but also restorative procedures (Purohit et al 2009), enamel cleanup after fixed appliance orthodontic treatment (Dawson et al 2016), and massive attachment removal following aligner treatment (Iliadi et al 2020). To this respect, founding recommendations from the US Centers for Disease Control and Prevention (2016) involve a range of safety considerations, as documented by aerosol and waterline precautions, personal protective equipment, and ventilation management.…”

“…Aerosolized microorganisms, including potentially airborne pathogens, may come as a result of the active performance of high-powered handpiece utilization during standard dental procedures. Tooth grinding for restorations, material grinding, composite removal after orthodontic debonding, attachment grinding after aligner treatment (Iliadi et al 2020), and routine practice professional oral prophylaxis with high-speed ultrasonic scalers are adequately matched for an increased dynamic for spatter-related contamination within the dental practice environment and across the practices’ personnel (Laheij et al 2012).…”

Behavior of Primary Human Oral Keratinocytes Grown on Invisalign® SmartTrack® Material

“…Clear aligners, a series of clear plastic appliances, represent an esthetic and removable alternative to conventional fixed orthodontic treatment. Reinforced by the patients' request for less visible orthodontic devices and a systematic promotion policy of aligner companies, an increased demand for clear aligner treatment took place in the last decade [1][2][3]. This led to an intensified development and application of this orthodontic treatment modality [4].…”