Current opinions and clinical practice in the titration of oral appliances in the treatment of sleep-disordered breathing

Summary

Obstructive sleep apnea is characterized by recurrent obstruction of the upper airway during sleep, resulting in episodic reductions in blood oxygen saturation and arousals from sleep. Mandibular repositioning appliances (MRAs) which are worn intra-orally at night, mechanically advance the mandible to help maintain a patent oropharygeal airway and have been proven to be an effective alternative for continuous positive airway pressure in the treatment of obstructive sleep apnea. Titratable MRAs are designed to gradually protrude the mandible applying an easy-to-use mechanical advancing mechanism, until a protrusive position with positive effect on sleep apnea is reached. Considering the relatively low-tech approach of the basic advancement mechanism, the interest in the mechanistic element of the dental treatment of obstructive sleep apnea has increased.

The present paper provides an overview of the different titration protocols described in the recent literature together with a discussion of both the clinical and mechanical aspects of treatment. At present, a consensus exists that an optimal titration protocol is of primary importance to achieve a successful treatment outcome with an MRA. To date however, there is no consensus on how to define the optimal titration protocol.

Introduction

Sleep-disordered breathing (SDB) is a pathophysiological continuum ranging from intermittent snoring to the full-blown sleep apnea–hypopnea syndrome.1, 2

Obstructive sleep apnea (OSA) is a common type of SDB, affecting an estimated 2% of middle-aged women and 4% of middle-aged men.³ Loud snoring, a precursor to OSA, and one of the most commonly reported sleep-related complaints, is even more prevalent, affecting 40–60% of all adults.⁴

OSA is characterized by recurrent obstructions of the upper airway during sleep, resulting in episodic reductions in blood oxygen saturation (hypoxemia) and causing arousals from sleep and sleep fragmentation.⁵ The clinical daytime consequences associated with an undiagnosed or untreated OSA include excessive daytime sleepiness, impaired cognitive performance and reduced quality of life. Many scientific studies show conclusive evidence that OSA is a strong and independent risk factor for cardiovascular and cerebrovascular diseases.*6, 7, 8, 9

The diagnosis of OSA follows both subjective and objective appraisal.¹⁰ A clinical and comprehensive sleep history includes the evaluation of subjective symptoms such as habitual snoring, excessive daytime sleepiness, nocturnal witnessed apneas, and a physical examination. Overnight polysomnography (PSG) remains the gold standard for the objective measurement of SDB.10, 11, 12 The severity of OSA is expressed by the apnea–hypopnea index (AHI), the number of apneas and hypopneas per hour of sleep, or the respiratory disturbance index (RDI), the number of apneas, hypopneas and respiratory effort-related arousals.5, 10 The diagnosis of OSA is confirmed if the AHI is greater than 5 events per hour of sleep. Based on the AHI the following levels of severity are defined: mild OSA (5 < AHI ≤ 15/h), moderate OSA (15 < AHI ≤ 30/h) and severe OSA (AHI > 30/h).5, 10

Continuous positive airway pressure (CPAP) is the treatment of choice for moderate to severe OSA. CPAP produces a ‘pneumatic splint’ preventing sleep-related upper airway collapse.¹³ Since its initial description, the effectiveness of CPAP has been demonstrated in several studies.14, 15, 16 Consistent CPAP treatment has proven to be effective in improving the cardiovascular morbidity in OSA patients.⁸ However, despite the potentially high effectiveness of CPAP, the compliance and long-term acceptance is relatively low, resulting in a limited clinical effectiveness.17, 18, 19 Therefore, there is a need for other treatment options.

Oral appliance therapy has emerged as a conservative, non-invasive treatment option for patients with OSA.*6, *20, 21 The most common type of oral appliances currently used in the treatment of OSA are the mandibular repositioning appliances (MRAs), which are worn at night to advance the mandible (Fig. 1) in order to reduce the collapsibility of the upper airway during sleep.*6, 18, 22 It is assumed that MRAs work by increasing the upper airway volume, predominantly by widening of the lateral dimensions of the velopharynx.²³ This increased volume is associated with an anterior displacement of the tongue, whose major muscle, the m. genioglossus, is attached to the lingual surface of the anterior mandibular arch, the epiglottis and the soft palate.⁶

It has been reported that MRAs reduce the severity of OSA to a lesser or a similar degree than CPAP.¹⁸ Nevertheless, it has been shown that MRA therapy has a higher self-reported compliance rate and a higher patient preference when compared with CPAP therapy.24, 25 There is growing evidence that MRA therapy could also be effective at improving the adverse health consequences of OSA.*20, 24 MRA therapy could lead to similar-sized reductions in hypertension as CPAP therapy.8, 26, 27 In one study, the nocturnal diastolic blood pressure improved with MRA but not with CPAP therapy. Furthermore, the MRA therapy significantly increased the proportion of patients exhibiting normal nighttime dips in blood pressure.²⁸

There is a huge variety of commercially available MRAs, all with different design features.²⁹ The concept of a custom-made MRA has evolved from the ‘mono-bloc’ type of device where upper and lower parts are rigidly connected, towards the current ‘duo-bloc’ types. These so-called titratable MRAs (tMRAs) allow for fine-tuning of the mandibular advancement as the upper and lower parts are separate but dynamically interconnected. The rigid mono-bloc MRA restricts mandibular movements which sometimes produces temporomandibular discomfort.³⁰