Clear aligner therapy (CAT) has become a popular orthodontic option, driven by advances in digital workflows, increasing aesthetic demands, and perceived benefits in comfort and oral hygiene. Although its clinical effectiveness has been well documented, a thorough review of its biological and environmental effects remains incomplete. This narrative review consolidates current evidence on CAT, exploring their history, material makeup, impact on oral health, and emerging environmental concerns. Recent clinical and microbiological research indicates that CAT may improve plaque control and periodontal health compared with fixed appliances; however, these benefits are heavily influenced by patient behavior, baseline caries risk, treatment duration, and adherence to hygiene and dietary guidelines. Evidence shows that aligner materials can support bacterial and fungal biofilm growth and, under certain conditions, may lead to enamel demineralization or erosion, emphasizing the need for personalized risk assessments and proper aligner maintenance. From a materials standpoint, modern aligners are primarily made from thermoplastic and polyurethane polymers, designed to exert controlled orthodontic forces and ensure durability. While beneficial clinically, these materials are poorly degradable and have limited recyclability. Life cycle analyses reveal that the environmental impact of CAT extends beyond disposal to include polymer production, energy-intensive manufacturing, packaging, and distribution. Additionally, emerging research suggests that aligners may release microplastics during use, adding to concerns about plastic pollution beyond solid waste. Given the rapid growth of the global clear aligner market, even small amounts of material per patient can result in a significant environmental impact. Overall, the evidence indicates that clear aligner therapy involves a complex interplay among biomechanics, patient care, materials science, and environmental sustainability. An integrated, life–cycle–based strategy is crucial to guiding clinicians, researchers, and manufacturers toward treatments that are both effective and environmentally responsible.
Martínez-Hernández et al. (Tue,) studied this question.