Adverse Effects

All oral appliances, regardless of design, have potential short- and long-term side effects. Most MAS are modified or similar to orthopedic appliances used routinely in the treatment of mandibular deficiencies for growth modification. Dental and bony changes associated with the use of orthopedic appliances in growing patients are well-documented, and are a desirable effect of treatment (46,47). However, MAS are largely prescribed to adult OSA patients for use during sleep only, and dental and skeletal changes would be considered undesirable. The main action of MAS is to increase the airway space by providing a stable anterior position of the mandible and advancement of the tongue, soft palate, and related tissues. This action of the MAS mediates posteriorly directed pressure on the upper dentition and anteriorly directed pressure on the lower dentition and causes immediate bite and jaw posture changes. Since there are no adaptive growth and/or major remodeling changes in adults, postural jaw modification may trigger dental and temporomandibular joint (TMJ) discomfort.

Most patients experience acute side effects during the initial phase of treatment. Excessive salivation (38-50%) and transient dental discomfort (33%), particularly of the upper and lower front teeth, for a brief time after awakening, are commonly reported with initial use and may prevent early acceptance of an oral appliance (19). TMJ discomfort (12.5-33%), dryness of the mouth (28-46%), gum irritation (20%), headaches and bruxism (12.5%) are other side effects that have been reported (12,19,48). Although these acute side effects are common, for most patients these are minor and transient, subsiding with continued use of the oral appliance.

Potential long-term adverse effects can be broken and / or loosened teeth, dislodgement of existing dental restorations, tooth mobility, periodontal complications, muscle spasms, and otalgia (49-53). These complications can often be avoided by simple recognition and appropriate early response to initial complaints. To monitor for these potential problems, it is suggested that patients with oral appliances should make periodic visits to the treating dental clinician. There are now published studies assessing long-term adverse effects out of seven years of use. Occlusal changes are predominantly characterized by a reduction in overjet and overbite, that is, backward movement of the upper front teeth, forward movement of the lower front teeth, and mandible and an increase in lower facial height (Fig. 5) (51-54). Even though the degree of overjet reduction is generally small, ranging from 0.4 mm to 3 mm (51), these changes can be clinically important. However, these changes uncommonly warrant cessation of treatment, and have to be weighed against the benefit provided by the oral appliance and the desirability of alternative treatments.

Previous studies have suggested that changes occur within the first two years of MAS use, after which they appear to stabilize (55). However, such studies have had methodological problems. More recently, a seven-year follow-up study reported progressive changes over time and also found that the magnitude of reduction in overjet was correlated with the magnitude of the initial overbite (56,57). Even though the influence of oral appliance design on side effects is not yet well-studied, the use of soft elastomeric devices, even if less durable, appears to provide some relative protection from large reductions in overjet (58). Predictably, the prevalence of side effects increases with more frequent use of the device (58). Whilst the literature suggests that the changes in the occlusion are largely temporary and revert after cessation of MAS use, permanent dental side effects requiring orthodontic treatment have been reported in a minority of cases (48). Hence it is important that patients are fully informed about these potential risks before commencing treatment. Whilst not yet investigated, it may be possible to avoid such side effects with the use of prosthetic and/or auxiliary implants as anchorage units on the upper and lower jaws. These types of anchorage units are currently successfully used to avoid unwanted effects of orthodontic forces.

FIGURE 5 Close-up cephalometric radiographs of a 44-year-old female patient before, after 1.5 years, and after four years of mandibular advancement splint use, showing considerable reduction in overjet and overbite during that time.
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