Factors associated with treatment adherence to mandibular advancement devices: a scoping review

Obstructive sleep apnea (OSA) is a common condition that affects approximately 17% of women and 34% of men in the general adult population [1]. People with untreated OSA are at risk of diabetes type 2 [2], hypertension [3], and cardiovascular disease [4] and have a higher risk of traffic accidents [5]. Due to not only the high prevalence of OSA, but also personal health concerns and socioeconomic healthcare issues associated with OSA, effective treatment is essential.

The severity of OSA is determined by the apnea-hypopnea index (AHI) measured during a polysomnography (PSG). OSA severity is classified into mild (AHI ≥5 to <15), moderate (AHI ≥15 to <30), or severe (AHI ≥30) [6]. While the current standard treatment for patients with severe OSA is continuous positive airway pressure (CPAP) [7], oral appliance therapy is indicated for patients with mild to moderate OSA and for patients with severe OSA who cannot tolerate CPAP [8, 9]. Oral appliances advance the mandible and the tongue during sleep and thereby prevent obstruction of the upper airway. Such oral appliances are known as mandibular advancement devices (MADs). As neither CPAP nor MAD eliminate the underlying causes of upper airway collapsibility, lifelong treatment is necessary.

Although CPAP reduces OSA severity more than MAD therapy in patients with mild to severe OSA [10‐12], its clinical effect is often compromised by low adherence [13, 14]. Adherence is commonly defined as behaving exactly according to rules or beliefs, which, in healthcare, usually involves conformity to treatment or medication [15, 16]. Another common related term is compliance, which is defined as obeying a particular law or rule or acting according to an agreement [15, 16]. Although the terms “compliance” and “adherence” are used synonymously, they are different in terms of the quality of healthcare, as the first term implies passively following of the instructions of the physician, while the second term implies active participation of the patient in the development of the treatment plan. The World Health Organization (WHO) prefers adherence to treatment over compliance [17]. Adherence to medical therapy is of utmost importance in the management of chronic conditions such as OSA. Studies on MAD therapy show varying results for long-term treatment adherence, which likely relate to many factors. Although numerous factors underlying poor adherence have been identified for CPAP therapy (Appendix 1) [13, 18‐43], little is known about MAD adherence. Therefore, the aim of this scoping review was to assess the factors that may be associated with MAD adherence and to compare them with those related to CPAP adherence.

We hypothesized that patient-related factors associated with adherence to CPAP therapy — such as psychological status, perception of side effects, and social support [18, 33‐36, 38] — also have an impact on adherence to MAD therapy. On the other hand, we also expected to find differences between adherence to both therapies regarding factors related to the device itself, such as effectivity and comfort. We expected to find that educational and behavioral interventions, as with CPAP [13, 26, 32], improve adherence to MAD.

The search resulted in 1202 articles (376, PubMed; 414, Embase.​com; 139, Cochrane Library; 273, Web of Science). After removal of duplicate articles and screening of titles and abstracts, 114 articles remained for full-text screening (Fig. 1). Ultimately, we identified 40 primary studies for this scoping review that addressed factors associated with MAD adherence in adults. These studies were published between 2001 and 2022. The types of factors found to be associated with MAD adherence were grouped according to the following categories: physical and psychological status of patients, effectiveness of MAD therapy, type of MAD, professional guidance during MAD treatment, side effects during MAD therapy, dental treatments during MAD therapy, previous treatments of OSA, and quantity of factors of non-adherence. Table 1 gives an overview of all the included papers and which positive and negative adherence factors they have described. The column “categories” indicates under which subheading of the “Results” section the findings from the articles are classified. In the last two columns, we described how the data was obtained (based on scientific research (fact) or by expert opinion) and how the adherence was measured (objective, subjective (self-reported), or not applicable). Side effects during MAD therapy, effectiveness of MAD therapy, and type of MAD are the most frequently described factors related to adherence in the literature (Fig. 2).

Sometimes, patients with OSA start with another treatment modality before being referred for MAD therapy. When patients are previously treated with another treatment modality, they come from a situation of treatment failure, so Amoric et al. stated that there is a likelihood this category of patients will be more inclined to abandon this new treatment as well, because of their poor psychological acceptance ability [60]. Friedman et al. found that adherence to a custom (50.9%) or a self-molded (32.5%) MAD was poor after 6 months, but explained that this adherence rate was acceptable because all patients in this study had previously failed OSA therapy (e.g., CPAP and/or upper airway surgery) [74]. MAD-therapy as a first-line therapy was one of the predictors of long-term use of MAD [61]. In contrast to this conclusion, Vuorjoki-Ranta et al. found that many of their patients were still using their MAD after receiving CPAP therapy or surgery 5 years earlier [69].

This scoping review aimed to identify the various factors associated with MAD adherence and compare them to the factors associated with CPAP adherence. The available literature described that several factors may have an association with adherence to MAD treatment. Factors that may have a positive impact on MAD adherence include good effectiveness of therapy, custom-made MAD, good communication skills of the practitioner, early recognition of side effects, stepwise titration of the MAD, and positive first experience with MAD. Main factors with a possible negative influence on the adherence to MAD treatment are personality aspects like a type D personality; failing effectiveness of MAD; occurrence of side effects during MAD therapy, such as patient discomfort or dental pain; usage of a thermoplastic MAD instead of a custom-made one; dental treatments during MAD therapy; and a poor first experience with the MAD with inadequate guidance by professionals. Side effects during MAD therapy, effectiveness of MAD therapy, and type of MAD are the most frequently described factors related to adherence in the literature (Fig. 2). This does not imply that these factors in fact have the greatest influence on adherence. Therefore, in this scoping review, all potential factors were examined.

A distinction can be made between MAD-specific factors and general factors of OSA therapy adherence. MAD-specific factors include occurrence of side effects during MAD therapy; the type of MAD; and dental treatments during MAD therapy. General factors include personality aspects of patients; failing effectiveness of treatment; poor experience of initial treatment with inadequate guidance by professionals; and poor experience with previous treatment modalities. The distinction between both factors is relevant for the purpose of achieving patient’s adherence.

As to enable the comparison between factors influencing adherence to MAD and to CPAP, a search was performed in PubMed with the aim to retrieve factors known to influence adherence to CPAP from systematic reviews (see Appendix 1). Patients with mild OSA are less likely to be compliant with CPAP therapy than patients with moderate to severe OSA[31]. Also, Holley et al. found that there was no significant difference in mild OSA patients between CPAP and MAD treatment in achieving their target AHI [89]. The factors listed above associated with MAD adherence in the treatment of OSA indicate that there are both similarities and differences in physical and psychological status of patients, type of device, and professional guidance during treatment between MAD and CPAP. Both treatments cause different side effects, but for each device, a high frequency or severity of side effects negatively affects adherence [18, 60]. Unlike CPAP, in the case of MAD treatment, TMD is also a reason for poor adherence [55], although a case report has described TMD-related side effects in association with CPAP as well [90]. It is noteworthy that patients with mild OSA are likely to have better adherence with MAD, and patients with severe OSA with CPAP [31, 54]. Lack of support from a partner or family, when no change is noticed by them, has a negative impact on adherence with both MAD and CPAP [18, 36]. Factors related to psychological status also affect both treatments. For example, in both CPAP and MAD treatment, type D personality and a poor perception of their general and mental state of health are of influence [38, 47, 59, 60]. However, for CPAP only, a psychological comorbidity, such as PTSD, influences adherence [33‐35, 91, 92]. To our knowledge, however, this has not yet been researched for MAD in the current literature. When looking at device-related factors in MAD and CPAP therapy, for both treatments, the design of the device is a topic that has been extensively studied and can affect adherence. For example, for CPAP, the type of mask is of influence, while for MAD, there is a difference between custom-made or thermoplastic devices [11, 20, 21, 64, 80, 93]. For both CPAP and MAD, adherence is improved when using feedback services by ICT [21‐25, 43, 84]. It is important to improve and enhance these technologies in the future. Also, MAD and CPAP adherence are both affected by the practitioner in terms of their communication skills or the use of behavioral interventions [13, 18, 26, 32, 60, 64, 69].

Although many interventions have been described in the literature on improving CPAP adherence, such as behavioral interventions like motivational interviewing, few interventions have been described for improving MAD adherence [18]. However, Dioguardi et al. described that patients who are included in the decision-making process of choosing a therapy have better treatment adherence [83]. Also, De Ruiter et al. described that stepwise titration of protrusion of the mandible improves MAD adherence [86].

Only 40 articles were included in this study, despite including all publication types being accepted. Therefore, our findings for this scoping review indicate a scarcity of literature specifically addressing MAD adherence in OSA therapy. Clearly, more research is needed to adequately reveal the associated factors with MAD adherence.

When looking at the type of MAD, it is noteworthy that Uniken Venema et al. described that mono-bloc appliances, compared to bi-bloc appliances, performed more favorable when examining AHI reduction. However, there were no clinically relevant differences in reduction of the Epworth Sleepiness Scale (ESS), preference, side effects, and cost-effectiveness, and in contrast to Dieltjens et al. and Lee et al., in the study by Uniken Venema et al., there were no differences between mono-bloc or bi-bloc MADs in adherence [59, 80, 81].

When comparing our scoping review to the systematic review and meta-analysis of Tallamraju et al., both studies found no significant correlation between adherence and patient or disease characteristics. Patients who did not adhere to the therapy reported experiencing more side effects and were more likely to discontinue the treatment within the first three months. Additionally, custom-made oral appliances were found to be preferred and associated with higher adherence compared to self-molded appliances. However, further research is needed to investigate the relationship between psychosocial factors and adherence to oral appliance therapy [58].

This scoping review described several factors that may have an association with adherence to MAD therapy, such as physical and psychological status of patients, effectiveness of MAD therapy, type of MAD, side effects during MAD therapy, professional guidance during MAD treatment, dental treatments during MAD therapy, previous treatments of OSA, and quantity of factors of non-adherence. When comparing the factors associated with MAD adherence to those associated with CPAP adherence, there are both similarities and differences in the categories physical and psychological status of patients, type of device, and professional guidance during treatment. These results show that MAD adherence does not depend on the same factors as CPAP adherence, but there is some overlap.

The knowledge of the factors found in this study associated with MAD adherence can be used for further research to make recommendations to improve adherence. Ultimately, further studies would be useful to detect non-adherent patients before starting treatment and to provide proper guidance in the early stages of treatment. Matching patients to treatments in a personalized manner may contribute to the efficacy of OSA management. To facilitate clinical decision-making, more prospective randomized studies are needed.