PGO Scientific journal

Sleep Disordered Breathing (SDB) affects adults worldwide.¹ SDB has a high prevalence with 49.7% of men and 23% of women having an Apnoea-Hypopnoea Index (AHI) greater than 5.² A high percentage of people have undiagnosed or untreated moderate to severe Obstructive Sleep Apnoea Syndrome (OSA).^3,4 The main problem in patients with OSA is the collapse of the airway at the pharyngeal level that occurs in hypoapnoea (reduced ventilation) or apnoea (complete cessation of breathing) ⁵.Increased carbon dioxide levels (hypercapnia) and low oxygen concentration (hypoxaemia) in the blood can lead to hypertension, heart disease and even death.^3,5TRS is also associated with mood disturbance, disruptive behaviour, snoring, and decreased quality of life.^1,3,6,7

Continuous positive airway pressure (CPAP) therapy is primarily used by sleep physicians and remains the gold standard for the treatment of OSA.¹ Another alternative indicated to treat TRS in adults is the mandibular advancement device (MAD),⁶ which aims to advance the mandible and associated soft tissues to open the airway and reduce the apnoea-hypopnoea index (AHI) ⁹.

DAMs were introduced in the 1980s and since then interest in this therapeutic alternative has been growing. There are currently more than 500 patents for different devices and more than 50 have FDA approval. The scientific evidence is growing, as is the large number of devices available on the market. It is therefore important to be familiar with their characteristics and clinical management.

The design of MADs is important and plays a key role in the efficacy of the treatment, the proper use of the device by the patient, and the prevention of possible adverse effects ¹⁰. So far, few articles highlight the importance of design in the efficacy of MADs. Elements such as the analysis of the materials used to manufacture the device, the extension that the two splints should have, the retention associated with both the extension and the materials are relevant. Also the mechanism of union between the upper and lower splint, the advance regulation system, the control of the opening and the freedom of movement. And finally, the initial position of the device, with the appropriate level of advancement and control of the level of opening, as well as occlusal stability.

The aim of this review is to highlight the main design features of a DAM. The analysis will be divided into three points: 1) the upper and lower splints separately (Materials, Extension and Retention); 2) the attachment mechanism (Titration, Freedom of Movement and Opening Control); 3) the initial position (Opening, Advancement and Occlusal Support) (Figure 1).

Materials:

The materials of commercially available devices are diverse, and include thermoformed plastic, double laminated material, acrylic material and 3D printed nylon (Figure 2). It is important to know the strength, flexibility and hardness characteristics of the DAM to avoid possible adverse consequences such as tooth movement if the material is too flexible or soft¹⁰. The nature of flexible materials, teeth or part of teeth NOT covered and/or imprecise fitting of oral appliances cause teeth to move more during therapy¹¹. Although it is believed that the material from which the DAM is made may influence clinical outcomes, no clear deductions can be made at this time as to whether the materials used in the manufacture of the appliances influence the treatment outcome, as there are no studies specifically investigating this issue¹².

Extension:

The device must cover all teeth present in the mouth to avoid possible lateral or extrusive movements (Figure 3). If a tooth is not supported by the appliance, it may move during the 6-8 hours it is used, causing harm to the patient and loss of continuity of treatment.

Retention:

All DAMs require retention in the teeth to maintain protrusion of the mandible during sleep¹³. The retentive area of each is determined by its equator, length, shape and inclination (Figure 4). These factors influence good or poor retention of the DAM. Poor retention causes loosening of the DAM, reduced treatment efficacy, patient complaints about poor fit, and an increased risk of side effects. Knowledge of the retentive characteristics of a particular DAM is therefore essential for the selection of an appropriate DAM for clinical use.

Factors influencing the retention of a DAM

Device:

• DAM extension
• Materials
• Design
• Time elapsed

Device construction:

• Progress level
• Opening level
• Route of insertion or removal

Patient

• Shape and size of teeth
• Saliva
• Facial biotype

Dynamics and functioning

• Rotation and translation of the mandible and condyle
• Direction and vectors of muscular action

Subject’s opening strength.

Linking mechanism:

All DAMs require a system of attachment between the upper brace and the lower brace¹⁴. There are monoblock devices in which the upper and lower ferrule are joined together to form a single block without the possibility of adjustment or adjustment of the advancement (Figure 5). Adjustable devices have two separate splints that are joined by different connecting elements such as elastic or rigid connecting rods, screws, hooks, straight or inclined contact surfaces, chambers or contact points.

• There are three important aspects to consider among the different joining mechanisms: 1) the freedom of movement they allow, 2) the control or limitation of opening and 3) the titling mechanism. In terms of freedom of movement, some do not allow any mobility and others do. Studies recommend devices with some freedom of movement, which makes them more physiological and limits or reduces the risk of adverse effects. Limitation or control of opening is important to avoid jaw opening during sleep and subsequent airway collapse. Certain devices include in their manufacture or design a system that limits and controls opening and others that may incorporate vertical elastics for vertical control¹⁵. Especially in supine dependent OSA the usefulness of opening control and limitation has been seen¹⁵. The titling mechanism differs from device to device. There are those with screws that are activated by turning them, those with interchangeable elastic rods of different lengths, and those with different lower splints with varying degrees of advancement. In each case it is important to know the mechanism and to apply it correctly.

Starting position:

All DAMs require an initial position to be determined by the MDS-trained dentist¹⁷. According to Sheats et al 2020 the definition of initial position is the initial position of the mandible when the appliance is delivered at the start of treatment. The initial position is recorded by a constructive bite by the qualified dentist (Figure 6).

Factors influencing the initial position

• The DAM used
• The gauge or measuring method used
• The reference point used
• The patient’s spee curve
• The patient’s overbite
• Appropriate level of progress
• The appropriate level of vertical opening

The device used influences the initial position as some require greater thickness to manufacture and comparison between devices can be difficult. The gauge used also makes a difference, as some thicker gauges open the vertical dimension more than others. Another point that conditions the initial position and its comparison between studies or subjects is the reference point used; it can be maximum intercuspidation or maximum retrusion. In this respect, it is advisable to follow the indications of 2020 Sheats, who recommend maximum retrusion as the reference point¹⁷. The spee curve and overbite can also influence the initial position, as they can condition the increase of the vertical dimension in the device.

Vertical dimension:

All DAMs require a certain level of openness to manufacture the device. A certain level of opening is good because it gives more space for the tongue. If the mandible was advanced and the vertical dimension was not increased, the tongue would be compacted against the bony palate and pushed backwards, thus decreasing the space for the upper airway¹⁸.

Excessive opening of the mandible pulls back and down the mentonian symphysis, in particular the area of the geniculate process where the genioglossus inserts, resulting in displacement of the tongue downwards and backwards and narrowing of the airway¹⁹. This is the opposite of what is intended by the use of the device.

The impact of vertical dimension on the initial position of the devices has been studied by 2019 Mayoral¹⁸ and demonstrates that increasing the vertical dimension results in postero-rotation of the mandible and therefore of the point of maximum retrusion measured with the George gauge, while reducing the range of protrusive movement of the mandible by approximately 0.3 mm for every millimetre of opening (Figure 7). This causes the mandible to be more backward with increased aperture and less total forward range of movement.

Mandibular advancement:

All DAMs require a certain level of advancement when fabricating the device. The initial advancement of the mandible with the device varies depending on the device used, the amount of opening required to fabricate the device, and the clinical judgement of the dentist. The level of advancement is typically set between 25% to 75%, with 50% of the total jaw advancement being recommended (Figure 8).

Once it is determined whether the initial advancement is effective, the process of titrating the advancement until the therapeutically effective position is achieved. Therapeutically effective position is defined as the jaw position that improves the objective signs, symptoms or indices of sleep-related breathing disorders. The patient, dentist and medical provider agree on the determination of improvement through clinical experience and, where available, evidence-based approaches. In this position, the appliance can be used comfortably every night¹⁷.

Occlusal support:

All DAMs require correct occlusal support between the two splints when fabricating the device. It is important to give good occlusal stability to the devices in order to avoid muscular, dental and TMJ discomfort²⁰ (Figura 9). In the field of occlusal splints, occlusal stability is always checked. Sheats in 2017²¹ points out that the verification and correction of occlusion is an effort to keep the occlusal forces in the appliance balanced in both the transverse and anterior-posterior directions. This balance can be altered during titration of the appliance, as well as when muscles contract or relax with use.

The design of mandibular advancement devices is a key element in treatment. Special attention must be paid to each and every detail of the design to allow correct positioning of the mandible, correct control of this position during sleep and to ensure that the patient finds it both effective and comfortable to use.

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