Objective: To investigate if the alternating current impedance spectroscopy (ACIS) technology could be used to monitor remineralization of post-orthodontic white spot lesions (WSLs) after debonding of fixed orthodontic appliances.

Material and methods: The study group consisted of 28 adolescents (aged 12-16 years) with at least two WSLs on their maxillary incisors, canines, or first premolars at debonding. Buccal surfaces (n = 194) were visually examined and scored with modified International Caries Detection and Assessment System (ICDAS) criteria and with the CarieScan Pro device by three examiners according to manufactures manual (test method). In addition, 31 surfaces with ICDAS = 0 were monitored by ACIS, serving as controls. Follow-up examinations were carried out after 8 and 16 weeks. Modified ICDAS scores, captured from digital photographs by three independent examiners, served as reference method. Four patients were lost to follow-up. Data were analysed in a mixed statistical model considering systematic effects of visit, tooth and observer, random effects of patients, and visits within patients.

Results: Over 50 per cent of all surfaces had marked WSL at baseline and the corresponding values at 8 and 16 weeks were 33 per cent and 22 per cent. The ACIS readings mirrored the visual scores; the baseline estimate (56.3) was significantly decreased after 8 weeks (P < 0.05). The lateral incisors exhibited the highest values whereas the lowest were recorded for the central incisors.

Limitations: ICDAS is not the same as a 'true' gold standard. The high prevalence of WSL may jeopardize the external validity.

Conclusion: The ACIS technology may to some extent be used to monitor the regression of post-orthodontic WSLs.