Does interproximal reduction during clear aligner treatment increase the risk of caries? A retrospective cohort study

AIM: This study aimed to evaluate the potential risk of caries in patients who underwent interproximal enamel reduction (IPER) in the maxillary and mandibular teeth during clear aligner orthodontic treatment. METHODS: A total of 344 patients treated with clear aligners were included. Samples were categorised into four groups based on IPER site: maxillary posterior (MxP), maxillary anterior (MxA), mandibular posterior (MdP) and mandibular anterior (MdA). The amount of IPER was classified according to the total reduction performed at each interproximal contact area involving two adjacent tooth surfaces, rather than per individual tooth surface, into four subgroups: (1) 0.1-0.3 mm, (2) 0.4-0.5 mm, (3) 0.6-0.8 mm and (4) 0.9-1.0 mm. Clinical and radiographic caries assessments were performed, and longitudinal data were analysed using Generalised Estimating Equations (GEE) models at the proximal tooth-surface level, with clustering of surfaces within patients taken into account. RESULTS: A total of 4800 proximal surfaces were evaluated, with caries detected on 66 surfaces in 36 patients. Overall incidence remained low across all groups. Site- and amount-related differences were observed in the GEE analysis; however, these findings should be interpreted cautiously because of the low absolute event rate and limited number of carious surfaces. CONCLUSION: Within this low-risk, highly compliant cohort, IPER up to 1.0 mm (0.5 mm per tooth surface) was associated with a very low observed incidence of caries when combined with proper polishing, oral hygiene and follow-up care. However, this study does not show that IPER increases caries compared with untreated teeth.