|
Oral Appliances.
Currently
there are in excess of 200 different types of appliances available.
Universally they all have similar effect of repositioning and
holding the mandibular (lower jaw) in a protruded position during
sleep. This concept was first published and reported back in the
early 1980's ( Pancherez et al , Clarke et al, Halstrom et al,
Lowe et al ). Earlier patents and published evidence
confirmed the efficacy of this.
By holding the
lower jaw forward tends to also bring the tongue forward and exert
tension on the muscles of the tongue making it more rigid and less
floppy overcoming obstruction of the throat.
Of these 200
appliances they tend to fall into 5 categories, defined by their
individual design application.
The real
question is which is best for each patient and which have medical
evidence to support their claims.
Unfortunately
as most research studies define the appliance used in the generic
of MAS or MAD all appliances tend to reference any study published
as applicable to their product.
Why? It’s essential
to select the right oral appliance for each patient to ensure
compliance and improved patient outcomes.
Studies have
shown that changes occur in the upper airway at several levels when
the mandible is pulled forward.
A study by Isono et al (1)
used video endoscopy to examine the effects of advancing the
mandible on the pharyngeal airway of 13 patients with OSA who were
under general anesthesia with total muscle paralysis. They found
that advancing the mandible widened the retropalatal airway as well
as that at the base of the tongue. They applied negative pressures
to the airway and showed that a more negative pressure was required
to cause collapse of the airway when the mandible has been
advanced. In their discussion, they postulated that one of the
mechanisms by which mandibular advancement stabilizes the soft
palate and retropalatal airway is through tension transmitted along
the palatoglossus muscles to the soft palate.
A study by Schwab et al (2)
using MRI on snorers while they were awake showed that advancing
the mandible resulted in a greater increase in the lateral than the
A-P dimension of the airway. CPAP produces a similar change
(3).
Wearing an appliance will
also prevent the mouth from falling open during sleep. A study by
Meurice et al (4) showed that upper airway collapsibility was
increased in normal subjects while awake when their mouths were
opened.
Therefore, wearing a
dental appliance that advances the mandible stabilizes the upper
airway by:
1.
pulling the base of the tongue forward,
2. pulling the soft
palate forward and putting the walls of the upper airway under
tension
3. keeping the mouth from
falling open during sleep.
These are primarily
passive mechanical effects that can be explained by applying simple
physical principles to what is known about the anatomy of the upper
airway.
The critical anatomic
relationships in terms of improving the sleeping airway with
mandibular advancement are as follows:
It is important to keep the
mouth closed. If the mouth is opened more than 10mm
tensile forces that are produced by advancing the mandible are
directed partly downwards towards the feet. This increases the
longitudinal tension in the pharynx and promotes
collapse.
However, there are situations in
which combining advancement of the mandible with a slight increase
in the opening of the jaw will help to further stabilize the soft
palate without promoting collapse of other portions of the upper
airway.
It is tension that
stabilises the structures in the upper airway. When you are awake,
upper airway muscles are activated to produce this
tension.
When you are asleep, these
muscles become less active and tension is lost.
CPAP restores this tension
by applying an intraluminal pressure. When the anatomy is
favorable, mandibular advancement can be as effective as CPAP in
tensing and stabilizing the structures of the upper
airway.
Study by Oshima et al (5)
demonstrates that mandibular advancement in properly selected
patients with OSA results in a decrease in genioglossal EMG
activity during sleep as has been observed in patients with OSA who
use CPAP (6).
CPAP applies pressure to
the inside of the upper airway that stretches the tissues and
prevents their collapse.
This pressure also acts as
a counter-pressure to the pressure exerted by the tissues
surrounding the upper airway. Advancing the mandible decompresses
these same tissues. Either way, the net pressure in the tissues
surrounding the upper airway is lowered resulting in widening of
the upper airway.
CPAP
accomplishes these goals by applying pressure to the inside of the
upper airway.
When the anatomy is
favorable, mandibular advancement with a dental appliance can
achieve the same goals.
References
1.Isono S,
Tanaka A, Sho Y, Konn A, Nishino T: Advancement of the Mandible
Improves Velopharyngeal Airway Patency. J Appl Physiol 1995;
79:2132-2138
2.Schwab RJ, Gupta KB,
Duong D, Schmidt-Nowara WW, Pack AI, Gefter WB: Upper Airway Soft
Tissue Structural Changes with Dental Appliances in Apneics. Am J
Respir Crit Care Med 1996; 153 (part 2 of 2 parts):
A719
3.Schwab RJ, Pack AI,
Gupta KB, Metzger LJ, Oh E, Getsy JE, Hoffman EA, Gefter WB: Upper
Airway and Soft Tissue Structural Changes Induced by CPAP in Normal
Subjects. Am J Respir Crit Care Med 1996;
154:1106-1116
4.Meurice J, Marc I,
Carrier G, Series F: Effects of Mouth Opening on Upper Airway
Collapsibility in Normal Sleeping Subjects. Am J Respir Crit Care
Med 1996; 153:255-259
5.Oshima T, Tsai WH,
Hadjuk EA, Remmers JE: Mandibular Protrusion Decreases Genioglossal
EMG. Am J Crit Care Med 1998; 157(3):A655
6.Strohl KP, Redline S:
Nasal CPAP Therapy, Upper Airway Muscle Activation and Obstructive
Sleep Apnea. Am Rev Resp Dis 1986; 134:555-558
| 