- BACKGROUND: The TheraMon® microsensor is the most recent device developed to measure the wear-time of removable appliances. The accuracy has not been validated intraorally. OBJECTIVES: To determine 1) if the TheraMon® microsensor accurately records time when fixed intraorally, and 2) the effect of the intraoral location on the recorded time. METHODS: A prospective pilot study, using a convenience sample, was carried out in a UK hospital orthodontic department. Five non-patient volunteers wore microsensors positioned palatal to an upper molar, and buccal to a lower molar for 7 days. Differences between actual amount of wear and the wear recorded by each device were calculated. Differences between sites were also examined. RESULTS: The mean daily wear-time recorded by the upper and lower microsensors combined was 23 hours (95% CI 22.6-23.4), which is a mean under-recording of 4% (CI 2.5-5.8%). The maximum daily under-reporting of wear times was 5.5 hours. Microsensors in the lower buccal sulcus recorded wear-times that were closer to actual wear-times. CONCLUSIONS: Assumptions made by the TheraMon® microsensors software lead to under-reporting of intraoral wear-time, particularly when placed palatally. These discrepancies could be significant in both clinical practice and research. Adjustment of the microsensor software parameters would improve accuracy, irrespective of the intraoral location.