# Factors Influencing Appliance Wearing Time during Orthodontic Treatments: A Literature Review
## 4 Results and Discussion
### Compliance Monitoring: Physical Devices and Chemical Indicators  
[PERSON] et al. reported that, to achieve an orthodontic treatment goal, functional appliances should be worn at least 12.8 h per day, and active plates should be worn for 13.9 h per day [34]. The literature agrees on the fact that compliance never exceeds 7 to 9 h of the prescribed 8 to 15 h per day [11; 12; 34]. It is very poor at 65% of the 13 h prescribed and is likely to compromise the efficacy of the orthodontic treatment [12]. Patients are used to cheating, declaring that they wear orthodontic appliances for more hours than the real time of wearing [15]. The awareness of being monitored by monitoring devices leads patients to be more realistic about their wear-time. When confronted with the objective and real measurement of the wear-time of the removable appliances, patients start to provide more accurate subjective estimations, with better transparency about their behavior, which may help in understanding possible failures of the treatment [34; 55]. Yet, the evidence reported that wear-time monitoring by clinicians and caregivers does not necessarily boost compliance or increase the general amount of time spent wearing removable appliances [12]: if patients are informed that their wear-time is recorded, they tend to be more compliant but still wear the appliances for a shorter period than that prescribed by the given instructions [14; 36]. Physical compliance devices have been developed to associate the wear-time with intraoral environmental factors (e.g., pressure, body temperature) [56]. The first timing device was a piece of headgear introduced by [PERSON] (1974) which was activated by pressure switches on the neckstrap, but it was easy to cheat by just activating the timer by placing heavy objects on the pressure switch [57]. A timer monitor designed by [PERSON] (1982) used a soluble controlled-release glass timing disc incorporated into the removable appliance [58], and [PERSON] et al. (1991) developed a device with a small quartz calendar wristwatch [59]. These devices were innovative, but they never spread for clinical purposes, not even for research, because of the inadequate characteristics such as the elevated costs, the complicated use, and the uncomfortable size affecting the acceptance among patients and orthodontists [26; 40; 56; 60]. Low reliability and poor accuracy in the measurements were also reported [40; 60]. More recently, environmental microsensors which can be embedded in appliances and automatically measure and record temperature changes between the oral cavity and surrounding area were introduced. The TheraMon(r) System (Handelsagentur Gschladt, Hargelsberg, Austria or Forestadent, Pforzheim, Germany) is a small device (13 \(\times\) 9 \(\times\) 4.5 mm) that measures the intraoral wear time: it works as a recording thermometer by measuring the temperature of the surrounding area of the patient's orthodontic appliance. The system is a useful tool to briefly ascertain the time for which patients wear removable appliances, but it does not allow for the objectification of the effective wear-time due to the several confounders (starting from temperature variations in an individual's mouth) that affect the data recordings [16; 61]. The Smart Retainer(r) (Scientific Compliance, Atlanta, GA, USA) gathers several pieces of data from the environment (light, vibration, temperature) and consists of a button-size environmental microsensor that can be easily embedded into many types of orthodontic devices. At preset intervals, the microsensors automatically monitor any change in the environmental surroundings and store the data in an encrypted form. When the retainer is plugged in the proprietary USB-powered Smart Reader, the data are analyzed using proprietary algorithms for trends and use pattern periods [26]. Chemical indicators were also introduced to monitor the wear-time of clear aligners by Align Technology [41].