Clear Aligners as a Prescribed Source of Unmeasured Intra-Oral Micro- and Nanoplastic Exposure: Release Mechanisms, Human Evidence, Salivary Biomonitoring and the EU Regulatory Context.

Clear orthodontic aligners are removable polymer devices worn about 22 h a day for 12 to 24 months, increasingly by children. A growing in vitro literature shows that thermoformed and 3D-printed aligners shed micro- and nanoplastics and co-release elemental or organic constituents under oral, gastric and mechanical conditions, yet aligner-derived particle burden and systemic dose in wearers have not been measured. This review sets aligner-derived release against the wider human micro- and nanoplastic record and evaluates saliva as a biomonitoring matrix. Directly printed devices release more and larger microplastics under mechanical stress, whereas thermoformed materials show acid-related degradation, with Sb/Sn release and nanometre-scale particles reported in a single, not yet replicated in vitro study. Particles below 5 microns, especially below 1 micron, are plausible translocation candidates, but translocation of aligner-derived particles has not been demonstrated. In vitro work reports macrophage and oxidative responses, whereas detections in blood, placenta and atheroma are not source-specific and remain associative. The EU amalgam phase-out does not regulate aligners but highlights a substitution question, because device and chemicals law addresses intentionally added microplastics, not wear-generated secondary particles. ICP-MS for antimony and tin, with Raman, micro-FTIR and electron microscopy, forms a plausible analytical toolbox. We propose harmonised release testing and validated salivary biomonitoring, prioritising children, to characterise source-proximal exposure before use expands.