Oral appliances (OAs) are frequently used in orthodontics and for the treatment of obstructive sleep apnea. Because OAs can be inserted and removed by patients themselves, the patient’s cooperation is a major component of effective treatment. In this review, we provide an overview of factors studied in the past that affect adherence to OA use in orthodontics and dental sleep medicine. We also describe future directions in adherence and the use of objective microsensor technology to measure adherence in these patients.
Because removable oral appliances (OAs) can be inserted and removed by patients themselves, their cooperation and adherence to therapy are necessary to achieve success.1,2 Removable OAs, such as headgear, removable retainers and functional appliances, are used in orthodontics to correct malocclusions. In the field of sleep medicine, removable OAs are increasingly used as an option in the treatment of patients with obstructive sleep apnea (OSA).
The gold standard for the treatment of moderate to severe OSA is continuous positive airway pressure (CPAP); however, adherence to this treatment has been found to be limited.3-5 Removable OAs, which reduce upper airway collapse by advancing the mandible, have emerged as a non-invasive treatment option for patients with OSA. These devices are similar in design to functional appliances used commonly for growth modification in orthodontics. They can be inserted and removed by patients, thus, placing responsibility on the patient to follow a prescribed wear schedule.
To date, many scientific publications have addressed the issue of adherence to treatment in orthodontics and dental sleep medicine to determine how to improve and monitor patient compliance.3,6-16 However, there is controversy over the factors that might predict adherence, mainly because, in the absence of objective monitors, information has been limited to self-reported use, which is often false or overestimated.17 Recently, objective compliance monitoring for removable OAs has become available.18,19 In this article, we present an overview of the factors that affect adherence to treatment in both orthodontics and sleep medicine. In addition, we review the use of objective microsensor technology to measure adherence in patients using removable OAs.17
Determinants of Adherence
Factors that are thought to be related to patient compliance and cooperation during therapy with removable OAs in orthodontics and dental sleep medicine include gender, age, socioeconomic status, psychosocial aspects, patient’s family and partner and the interaction between the dentist or physician and the patient.15,20 This multifaceted system leads to complex interactions in which each individual component as well as the interplay of factors should be studied.15,16
Patient gender is a factor commonly cited as a predictor of adherence to orthodontic treatment. Some reports suggest better adherence among female compared with male patients.21-24 Girls tend to take a more responsible attitude toward orthodontic therapy as they mature earlier than boys.23 On the other hand, more recent reports have failed to show gender as a significant factor in predicting adherence.6,22,25-30 Previous findings relied on subjective measures of adherence, such as orthodontists’ judgement, which may be more a reflection of social and gender stereotypes than a valid correlation.6 Studies using objective measures of adherence during orthodontic treatment, such as electronic sensors, have found no difference in overall wear time between genders.6,25,29,30
Although many studies in orthodontics have examined these issues, the correlation between gender and adherence has not been thoroughly assessed in OA treatment for OSA. However, long-term discontinuation of this therapy has not been found to be different between genders.31,32
Age is also often considered to be an influential factor in adherence to orthodontic therapy.33 Although some studies have found greater cooperation among younger patients (< 12 years),6,7,9,28,34-37 others have found no difference.7,22,25-27,30,38 The variation in reports on the effect of age on adherence may be confounded by variations in children’s individual psychological maturation. Teenage years are often associated with decreased parental influences and cooperation.7,36,37
Orthodontic studies focus on children, whereas OA therapy for OSA is mainly studied in adults. Although discontinuation of long-term OA therapy by OSA patients has not been found to be dependent on age, the effect of age on OA adherence has yet to be explored in this population.31,32
The potential influence of a patient’s socioeconomic status on adherence has been addressed and debated in the literature. Patients with higher socioeconomic status have been shown to be more cooperative orthodontic patients.7,21 A possible explanation is that higher socioeconomic groups perceive dentofacial appearance to be highly important for social and occupational success.22,39 On the other hand, another study reported greater adherence among patients from lower middle-class families compared with upper-class families.40 This may be attributed to a greater need for social acceptance, higher social aspiration, better child–parent relationships and greater emphasis on value for money seen in these socioeconomic groups. Some studies also report no difference in patient adherence based on socioeconomic status.22,38
In sleep medicine, patients with lower socioeconomic status are less likely to accept and commence CPAP therapy.15,41 Sleeping with a spouse or partner has been found to increase adherence as the partner may provide feedback regarding elimination of symptoms, such as snoring, which may increase CPAP use.42 Although these factors may be similar in OA therapy, this has not been assessed.
Considerable attention has been devoted to the examination of personality characteristics as a method to predict patients’ adherence to orthodontic treatment.1,2,6,22,25,36,43-46 In general, cooperative patients are characterized as enthusiastic, energetic, outgoing, self-controlled, responsible and hard working.33 These patients tend to have better grades and show less deviant behaviour in school.39 In contrast, uncooperative patients are described as hard headed, independent, temperamental, impatient, individualistic and intolerant of prolonged effort.33 Based on these findings, a patient’s performance in school may serve as a useful tool in determining adherence. However, children who are of below-average intelligence do not necessarily show poor adherence.39 Studies showing no correlation between personality questionnaires and adherence stated that treatment adherence and orthodontic cooperation is not reflective of a simple, single, monotonous dimension of cooperation, but rather a complex and interactive reaction.25,22,44,46,47 The use of psychological instruments44,45 to predict adherence has been shown to be useful, but these tools are not used in clinical practice.
In sleep medicine, OSA patients who display significantly more hypochondriasis and psychopathic deviation, presents a potentially higher rate of discontinuation and lower compliance. More specifically, OSA patients with a so-called type D (“distressed”) personality, defined as a combination of negative affectivity and social inhibition,48,49 show a significantly higher discontinuation rate for both CPAP and OA therapy.50,53
Measurement of Adherence
There are several approaches to measuring adherence. In orthodontics, the most common method relies on clinicians’ judgement. Typical clinical methods for estimating wear time of devices, such as headgear and removable OAs, include evaluation of patients’ oral hygiene, condition of the appliance, such as a worn-looking neck strap, mobility of molars, ease of patient use and missing or being late for scheduled orthodontic appointments.21 Unfortunately, these methods are unreliable. For example, adolescent patients brought to the orthodontist’s office by a parent or guardian reflect the punctuality of the parent, not the patient.2,6,28,52,53 As well, clinicians’ judgement is often influenced by therapeutic outcome. This is problematic because it assumes there is a direct link between the clinical outcome and the patient’s adherence to treatment, which is not necessarily the case.53
Another way to monitor adherence is through patients’ self-reports: interviews, questionnaires or log records. However, this can lead to false or overestimated compliance, largely because patients wish to appear more compliant than they actually are.8,29
The best way to assess compliance is by objective measures. Investigators have attempted to provide timers and microsensors to record accurate details of patient compliance, and the technology used in manufacturing these microsensors has been improving over many years.
Extraoral Compliance Timers
In 1974, Northcutt10 described the first extraoral orthodontic headgear with a timing mechanism to measure wear. It worked by simultaneously turning on 2 switches triggered by the pull of the strap and pressure on the back of the neck while the headgear is worn.10,54,55 Banks et al.56 found that the Northcutt timer was easily circumvented by the patient placing heavy objects on the pressure switch to activate the timer without actually wearing the headgear.
In 1991, Cureton et al.57 described a micro-electronic approach to measuring compliance using a small ladies’ quartz calendar watch with an accuracy level of 99.9% over 20 days of testing. A limitation of such an external headgear timer is that it is bulky and diminishes patient comfort when it is placed in a neck strap.58 The patient can also circumvent it by just stretching the band and, thereby, falsifying the wear data.52,59 In addition, many of these devices give only a cumulative overall measure of wear time and provide the orthodontist with intermittent headgear wear information and no easily accessible feedback to patients.6,53,59,60
Intraoral Compliance Timers
The ability to monitor intraoral appliance adherence is even more challenging because of the damaging effects of saliva. One of the first methods used was controlled-release glass discs60 composed of phosphates, borates and trace elements. A disc was fitted onto the surface of an orthodontic appliance and would dissolve in saline solution indicating wear. Problems with this method included disc separation from the appliance because of poor adhesion, surface grinding of the discs leading to fragmentation and dissolving of discs at different rates.60
More recently, a compliance indicator was introduced for aligner therapy. A food dye (erioglaucine disodium salt) is embedded in the OA and dissolves from the polymer when exposed to oral fluid.61,62 The clinician and the patient can evaluate 5 potential colour changes (from dark blue to clear) to obtain a graphic representation of wear time and have instant feedback on adherence. However, the rating on a 5-point scale involves subjective judgement and, thus, does not yield an objective wear time. In addition, the results can be easily falsified by patients, as the dye will fade in various aqueous solutions, for example, when left in the mouth while drinking, stored in water, cleaned with tablets containing oxidizing agents or cleaned in a dishwasher. A large variation in degree of fading was found among patients who strictly adhered to the prescribed wear times.57
In 1990, Sahm et al.11,63 created a reed-switch, which was embedded into a bionator functional appliance and was activated by a magnet system bonded to the lingual surface of the mandibular first permanent molar. The main problem noted with this device was its bulkiness and patient discomfort.
More recently, temperature sensitive microsensors have been used to objectively measure orthodontic OA use. These microsensors record temperature changes, assuming a difference between room and intraoral temperature. Schott and Göz64 assessed the accuracy of 2 temperature-sensitive microsensors: the Smart Retainer (discontinued production) and the TheraMon microsensor (IFT Handels und Entwicklungsgesellschaft GmbH, Handelsagentur Gschladt, Hargelsberg, Austria) using in vitro testing in a programmable water bath. They reported that the TheraMon microsensor is more accurate, with the Smart Retainer overestimating wear time by 1 h. However, the water bath was programmed to room temperature and oral temperature while not taking into account the time it takes for the water bath to heat or cool.
A year later, in vivo testing of the microsensor was conducted by Schott and Göz58 on patients fitted with upper and lower active plates, functional appliances or retention devices. However, they provide only 1 case report of a patient wearing an upper appliance and no statistical analysis of the accuracy of the device.
In 2013, Schott et al.30 published a study examining the adherence rate of patients fitted with retainers or functional appliances during the retention phase of their orthodontic treatment. Although patients were instructed to wear the appliances at least 8 h/day, the median wear time was 7 h/day. The report stated that adherence rates were influenced by age, sex and place of treatment, but these differences were not statistically significant.
Using the TheraMon microsensor, Pauls et al.29 found that orthodontic patients tended to overestimate their OA use by an average of 2.7 h/day. Informing and confronting the patients with their objectively measured OA use led to a more accurate subjective estimation, with an average overestimation of only 0.7 h/day.
The first report on intraoral recording of OA compliance during treatment for OSA was published by Lowe et al.65 This ceramic monitor had a memory system and temperature sensor that would monitor wear time based on temperature measured above 31°C. Several problems with this device were reported, including the damaging effect of saliva, heat intolerance of the electronic components and energy consumption over a long period.65
Vanderveken et al.18 were the first to assess the safety and feasibility of the TheraMon microsensor in vivo in dental sleep medicine. In their 3-month prospective clinical trial, they demonstrated that this compliance monitor could be used safely. No adverse effects, including oral burns, lesions or detachment of the microsensor were reported by the participants. Only 1 of 51 sensors was disqualified in this study because of technical problems. Recently, long-term results with the TheraMon microsensor in dental sleep medicine showed relatively high objective OA use on 1-year follow-up.66
To our knowledge, 3 microsensors that can be integrated into removable OAs for OSA are currently available commercially. These sensors differ in terms of data-recording interval, longevity, form of readout signals, size, weight, storage capacity and availability of a patient station, which permits patients to monitor their own adherence and upload their data remotely. Kirshenblatt et al.67 tested the accuracy of these thermosensitive microsensors in vitro using a water bath (34–37°C) to simulate OA wear time.
The TheraMon microsensor was accurate during both short and long durations of simulated OA wear, whereas the AIR AID SLEEP sensor (AIR AID GmbH & Co. KG, Frankfurt, Germany) significantly underestimated OA use during short durations by 3.67 ± 9.34 min./day, (mean and standard deviation) and the DentiTrac microsensor (Braebon Medical Corporation, Kanata, Canada) overestimated OA use during both short and long durations by 8.34 ± 3.62 min./day and 3.53 ± 2.42 min./day, respectively. However, these under- and overestimations were considered not clinically relevant.
Adherence to a prescribed treatment modality is of utmost importance in ensuring successful therapy. Lack of adherence can reduce the effectiveness of the best treatment plan and the most promising treatment mechanisms.5 This literature review shows that several factors have been thought to affect adherence in the fields of both orthodontics and dental sleep medicine. Studies indicating that adherence may be influenced by gender, age, psychosocial and socioeconomic factors have found wide variation among individuals.1,25 Other factors may also be found to be important, such as cultural background and severity of malocclusion/disease. Although the studies have tried to pinpoint which factors are determinants of patient adherence, this review shows that, in reality, it is difficult and challenging for clinicians to predict which patients will be cooperative. This can be explained by the fact that human behaviour is multifactorial and includes complex interactions in which each individual component, as well as the interplay of factors, should be studied.15
Another important finding is that patients’ adherence significantly increases when there is some objective feedback or when they are aware of being monitored objectively.10,34,68,69 Because patients are more motivated to change their behaviour when they know it is being monitored, there is a strong need for and interest in an objective compliance monitor for OA therapy in both orthodontics and dental sleep medicine. The use of such monitors alone may improve adherence.
However, the use of such devices is not part of routine daily clinical practice. A major problem with these monitors for removable OAs is accuracy. Besides the technical and functional factors, additional requirements must be met to achieve a high level of product acceptance by patients and health care professionals. Compliance monitors must be safe and small without altering the dimensions of the OA or affecting patients’ comfort; read-outs and monitoring must be easy and fast; and the sensors’ unit price must be reasonable.70
Microsensors that have recently become available can assist with monitoring patient adherence to orthodontics treatment and OA therapy for patients diagnosed with OSA.19 Such microsensors will give clinicians a better understanding of their patients and will allow them to tailor appointment schedules to best meet patients’ individual treatment needs. These microsensors can be used as a tool to motivate patients. In addition, the availability of objective compliance data will eliminate inconsistencies in patients’ subjective reports if the data prove to be accurate.
Furthermore, it is difficult to compare tolerance to various OA devices based on subjective compliance data without proof that patients are actually wearing them. In the field of sleep medicine, objective monitoring will allow for calculation of mean disease alleviation, which depends on both efficacy and compliance for therapeutic effectiveness.18 Calculation of real therapeutic effectiveness allows for comparison of different treatment modalities, such as CPAP therapy, surgery and oral appliances. For example, in the literature, CPAP therapy and oral appliances have been comparable in terms of mean disease alleviation.18,71 It has been suggested that the greater efficacy of CPAP therapy is being offset by inferior CPAP adherence compared with OA adherence, possibly resulting in equal effectiveness.72,73
In orthodontics, objective microsensors will increase the strength of evidence from studies comparing various appliances and retainer designs. Future studies using these monitors may also help identify the most appropriate wear pattern clinicians should be prescribing for the most effective treatment results.
Removable OAs are frequently used in both orthodontics and the treatment of OSA. Many of the appliances used in orthodontic practice rely on patients wearing the devices as prescribed. Adherence is of utmost importance in ensuring successful treatment. This literature review shows that, although several factors have been thought to affect adherence, human behaviour is complex and open to multifactorial influences. Therefore, there is a strong need for and interest in objective adherence monitors for OA therapy. The availability of such monitors will allow clinicians to track patient adherence, motivate patients and improve research that compares treatment outcomes.
Correspondence to: Dr. Fernanda Almeida, 2199 Wesbrook Mall, V6T 1Z3 Vancouver, British Columbia. Email: firstname.lastname@example.org
The authors have no declared financial interests in any company manufacturing the types of products mentioned in this article.
This article has been peer reviewed.
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