Finding the Starting Jaw Position
One challenge, and point of many discussions, is the starting position for oral appliance therapy in the management of obstructive sleep apnea (OSA). A question that often comes up is “where do I set the first jaw position?” If I had the answer to this question, I would look like a genius. We seem to forget that our bite position, whether it be a phonetic bite, George gauge, ProGauge, pharyngometry, or any other method, is a relative starting position. This bite position allows us to start at some point in space while considering a comfortable position for the patient.
The Oral Appliance – How it Works
Oral appliances (OA) are designed to improve upper airway configuration and prevent collapse through alteration of jaw and tongue position. These appliances are often termed “mandibular advancement devices (MAD),” “mandibular advancement splints (MAS),” or “mandibular repositioning appliances (MRA).”
The posterior airway is opened with an OA by advancing the mandible relative to the maxilla, and repositioning the many connected soft tissues in a forward position. While these devices are thought to increase upper airway caliber, activate upper airway dilator muscles, and decrease upper airway compliance, their precise mode and site of action are unknown.
The velopharynx was revealed to be a principal site of enlargement by the action of MAD by many authors using cephalometric analysis,1,2 or fiber-optic video-endoscopy.3 Choi et al showed that both the retropalatal (velo-pharynx) and the retroglossal areas of the oropharynx are significantly enlarged with mandibular advancement in most patients with obstructive sleep apnea.4
Imaging studies show that mandibular advancement with OA enlarges the upper airway space, most notably in the lateral dimension of the velopharynx.5 Lateral expansion of the airway space is likely mediated through tissue movement via direct connections between the lateral walls of the pharynx and the ramus of the mandible.6
The Treatment Outcome
Various patient factors have often been associated with the treatment outcome. Less severe disease and supine-predominant OSA (a higher AHI in supine compared to lateral sleeping position), have been considered favorable predictors for treatment success.7,8 Younger age, female gender, and less obesity (lower BMI and neck circumference) can even be positive predictors of treatment success.7,9
Craniofacial features assessed by lateral cephalometry, including shorter soft palate length, lower hyoid bone position, greater angle between the cranial base and mandibular plane, and a retrognathic mandible, are also associated with favorable treatment outcome.7,10,11 Although various patient phenotypes have been related to a higher likelihood of treatment success, these are not universal, meaning that patient response is not predictable using phenotype details. If we can’t predict where the jaw needs to be at the end, it means we have to randomly choose where to start, also.
OA Design Parameters
Even the most experienced clinician universally uses titratable appliances, because of this need to select among the many start position choices. Numerous prefabricated or custom-made MAD have been designed and developed for OSA patients that allow adjustment after delivery.12-14 While there are many different design parameters, we must determine the degree of mandibular protrusion and vertical opening. These crucial design parameters have been extensively investigated, but the ideal amount of therapy has not yet been defined.4,15,16 I’m sure we will get to a better definition, but for now it is left to our interpretation.
A dose-dependent effect of mandibular advancement was demonstrated using 4 randomized levels of advancement (0%, 25%, 50%, and 75% maximum), with the efficacy of 50% to 75% advancement greater than 25%, and 25% greater than 0%.3 However above 50% of patient’s advancement range,, there was an associated increase in reported side effects. A titration approach to determine optimal level of advancement with gradual increments over time is thought to optimize treatment outcome.17
Titration can be guided by subjective symptomatic improvement, consumer-level devices and apps, and objective monitoring by overnight oximetry, all the while limited by patient comfort, to (unofficially) find the optimally effective advancement level. 17
Assessment of pharyngeal collapsibility during mandibular advancement has also shown a dose-dependent effect in improvement of upper airway closing pressures.18 Gao et al.19 reported an expansion of 7.5% in the upper airway for every 25% increase in mandibular protrusion after 50% mandibular protrusion.
Generally, the greater the level of advancement, the better the treatment effect. However, it is vital that this is balanced against a potential increase in side effects. We can’t say what the perfect starting jaw position is, but we can take proactive steps in helping us find an optimal solution for each individual patient.