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Can mandibular advancement devices be a

satisfactory substitute for short term use in patients
on nasal continuous positive airway pressure?
D M Smith and J R Stradling
Thorax 2002;57;305-308
doi:10.1136/thorax.57.4.305

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305

ORIGINAL ARTICLE

Can mandibular advancement devices be a satisfactory

substitute for short term use in patients on nasal
continuous positive airway pressure?
D M Smith, J R Stradling
.............................................................................................................................

Thorax 2002;57:305308

See end of article for

authors affiliations

.......................
Correspondence to:
Professor J Stradling,
Oxford Centre for
Respiratory Medicine,
Oxford Radcliffe Trust,
Churchill Campus, Oxford
OX3 7LJ, UK;
john.stradling@orh.nhs.uk
Revised version received
16 July 2001
Accepted for publication
13 September 2001

.......................

Background: Mandibular advancement devices (MADs) can successfully control both snoring and
obstructive sleep apnoea (OSA). Many patients on nasal continuous positive airway pressure (NCPAP)
for OSA would like a more portable alternative, even if only temporarily. This study assesses what proportion of patients with OSA already on NCPAP can successfully use a MAD for short periods (up to 1
month) as a temporary alternative to NCPAP.
Methods: Fifty patients with OSA, already on NCPAP for at least 3 months, were recruited by invitation. They were provided with a simple fixed MAD estimated to provide 75% of maximum mandibular
protrusion. Sleep studies using a portable home recorder were performed on and after three nights
without NCPAP to provide control data. Following acclimatisation to the MAD, sleep studies were also
planned after 3, 7, and 28 days while using the MAD. If their overnight >4% SaO2 dips per hour deteriorated to >20 or the Epworth sleepiness score (ESS) rose to >9 (or increased by >4 over baseline) on
nights 3 or 7, they were then deemed to have failed the trial and were withdrawn.
Results: Of the 50 patients entered, one had inadequate teeth for a MAD and 31 gave up trying to
use the device during the acclimatisation period because of side effects. Of the 18 prepared to use the
device, two patients failed at night 3, five at night 7, and two at night 28. Thus, nine patients remained
controlled by our criteria at night 28. On average, sleep study indices while using the MAD were poor
compared with the night on NCPAP.
Conclusions: Simple MADs are poorly tolerated by patients with OSA already on NCPAP. OSA was
adequately controlled by our criteria in 32% of those recruited for the equivalent of a weekend, in 22%
for 1 week, and in 18% for up to 1 month. Better tolerated devices would be likely to improve on these
figures.

andibular advancement devices (MADs) have been

used successfully to control both snoring1 and
obstructive sleep apnoea (OSA).2 It is assumed that
they work by increasing the volume of the pharynx and
rendering it less collapsible during sleep.3 It is clear they do not
work for all patients, and are probably more successful for less
obese patients with milder disease.4 There are many patients
with OSA on nasal continuous positive airway pressure
(NCPAP) who find their treatment inconvenient while away
from home who would like a more portable alternative, even if
only temporarily.
The purpose of this study was to assess what proportion of
a group of patients with OSA already on NCPAP could
successfully use a MAD for short periods (up to 1 month) as a
temporary alternative to NCPAP.

Table 1 Baseline data on the 50 patients entering

the study

Age (years)
Time on NCPAP (months)
Body mass index (kg/m2)
Original pretreatment >4% SaO2 dips/h
Original pretreatment Epworth sleepiness score
NCPAP compliance before study (h/night)
NCPAP pressure (cm H2O)

Mean

SD

47.5
31.8
34.1
34.7
17.3
5.9
10.0

9.8
27.9
6.4
19.2
3.8
1.5
2.1

METHODS
Patients
To be eligible for the study patients needed to have been on
NCPAP for at least 3 months, to have an average NCPAP compliance of >4 hours per night, a pretreatment Epworth sleepiness score (ESS) of >10, a diagnostic pretreatment rate of
>4% dips in oxygen saturation (SaO2) overnight of >15/hour,
and to have sound teeth. Patients were recruited by invitation
from the NCPAP follow up clinic and via the patients association quarterly newsletter. Characteristics of the patients
included in the study are shown in table 1.
Techniques

Sleep studies
Sleep studies were performed in the subjects own homes
using RM50 portable monitors (DeVilbiss, London, UK). These
devices record for 8 hours and can be programmed to turn on
and off at particular times (usually 23.00 and 07.00 hours,
respectively). The RM50 records oxygen saturation from a finger probe, snoring via a throat microphone, body position via
a sensor in a chest box (held on by one chest band), chest
movements, heart rate (from three ECG electrodes), and pulse
transit time (PTT). The latter is the time delay between the
ECG R wave and the arrival of the pulse wave at the finger
detected from the transmittance signal of the oximeter probe.
This value is typically about 250 ms and varies inversely with
blood pressure. As the blood pressure falls, tension in the
arterial wall falls and PTT increases, and vice versa.
Beat to beat measures of PTT therefore provide an estimate
of the beat to beat changes in blood pressure5 6 that occur both

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306

Smith, Stradling

50 patients recruited
1 patients teeth
too decayed

31 patients gave up
due to intolerable
side effects
18 entered the
study

Failures

2 patients at
3rd night
16
5 patients at
7th night
11
2 patients at
28th night
9 were satisfactorily
controlled on the 28th night
Figure 1 Flow diagram of patients entered into the study.

during every inspiratory effort (pulsus paradoxus)7 and

following a transient arousal from sleep.8 By chance, a change
of 1 ms is about equivalent to a change of 1 mm Hg in blood
pressure. It has been shown that respiratory swings in PTT
quantitatively reflect swings in oesophageal pressure,9 10 and
that falls in PTT over a slower time course of 20 s or so reflect
the rise in bllod pressure following arousing stimuli, even
when there are no discernible changes on the EEG (so called
subcortical arousals).11
Analysis of the RM50 signals thus provided the following
derivatives: number of >4% dips in SaO2 per hour of the
study,12 number of rises in blood pressure per hour of the
study,11 13 14 15 and the mean fall in blood pressure due to each
inspiration (pulsus paradoxus) across the whole study.9 10 16 17
The units for the latter are in milliseconds and the overnight
mean could represent up to 7000 or more breaths.
Previous work from this unit to assess the reproducibility of
these two PTT derivatives compared two separate overnight
recordings in 40 adult patients with a wide range of severity of
sleep disordered breathing. Both blood pressure arousals
and mean all night inspiratory effort showed good reproducibility with correlation coefficients between nights 1 and 2 of
0.81 and 0.87, respectively.15

Epworth sleepiness score

The Epworth sleepiness score (ESS) is the most widely used
subjective index to quantify sleepiness.18 It consists of eight
questions about the tendency to fall asleep in situations of
differing stimulation such as watching television or talking to
someone. Each question is scored 0, 1, 2, or 3 indicating an
increasing tendency to fall asleep in each situation; the total
score can thus vary from 0 (no sleepiness) to 24 (extremely
sleepy) with 9 being the upper limit of normal.19 Previous
uncontrolled studies have shown that this index improves significantly following NCPAP for OSA.20 The ESS is designed to
assess sleepiness retrospectively over a period of time in
recent times. When using the questionnaire to assess sleepiness over a shorter period, the patients were asked to confine
their rating to this shorter period.

Mandibular advancement device

The mandibular advancement device used in this study essentially consists of two customised sports-type mouth guards

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(one for the top teeth and one for the bottom teeth) fused
together in such a way that, when the appliance is bitten into,
the mandible is held passively in a protruded position.1
Construction of the appliance requires upper and lower dental
impressions from which plaster models are cast. A wax
interocclusal record is taken with the patient posturing the
lower jaw forward to about 75% of the maximum possible.
Thermoplastic polyvinyl acetate/polyethylene blanks are
moulded onto the models and trimmed. The models are then
placed on a dental articulator in the previously recorded protrusive relationship and the upper and lower parts of the
device are heat sealed together in this position. Finally, this
bond is reinforced by heat moulding a thin layer of the
thermoplastic material over the inner and outer surfaces. Both
the clinical and laboratory stages of construction are straightforward, using inexpensive materials and widely available
techniques.
Protocol
Following recruitment, patients were seen by one of two dentists (at no cost to themselves) for the dental impressions
required for the MAD. Following construction, they were fitted
at a second visit or occasionally they were sent directly to the
patient and a second appointment was organised only if necessary and by patient request. Patients were then given as long
as necessary to acclimatise to wearing their MAD overnight at
home. During this acclimatisation period one home sleep
study was performed on NCPAP. If they were happy to
continue they were randomised to one of two pathways: MAD
trial followed by an assessment of OSA severity off all
treatment for three nights or vice versa. During the trial of
MAD usage an assessment was made after each sleep study
(at 3, 7, and 28 days) as to whether or not the device was successfully controlling the patients OSA. This is necessarily
arbitrary and the following criteria were used to define
continuing control: >4% SaO2 dip rate <20 per hour; ESS <10
(or not increased by >4 over baseline). If these criteria were
not met, the patient was withdrawn and the MAD deemed to
have failed at that particular time interval.

RESULTS
Figure 1 is a flow diagram showing the outcomes stage by
stage. Despite our assessment of sound teeth, the dentist disagreed in one patient. Thirty one subjects (62%) gave up
because of intolerable side effects which included excessive
salivation, sore gums, and painful masseter muscles or temporomandibular joints. Patients were often unwilling to persevere because they felt insecure without their NCPAP machines, having lack of faith in the efficacy of the MAD. In 32%
of patients their OSA and symptoms were controlled for the
equivalent of a weekend, in 22% for up to 1 week, and in 18%
for up to 1 month. If these data are quoted for the 18 patients
able to tolerate the MAD, then 89% were controlled for a
weekend, 61% for 1 week, and 50% for up to 1 month.
Control data when on and off NCPAP are shown in table 2
(columns 2 and 3). On NCPAP the results were normal and the
PTT derivatives (arousals and inspiratory effort) were in the
normal range established in earlier studies.21 22 After no treatment for 3 nights there was a clear deterioration in all measures, even after such a short time; these latter data were only
available in 34 of the original 50 as some patients declined to
be studied further when they realised they were not going to
be able to tolerate the MAD. Data at each of the stages while
using the MAD are shown in in table 2 (columns 4, 5 and 6),
including the results for the patients subsequently withdrawn
when they failed to fulfil the criteria for continuing control of
their OSA (two on night 3, five on night 7). Despite control of
OSA symptoms and only a slightly raised >4% SaO2 dip rate,
the arousal index and measure of inspiratory effort were considerably worse than during treatment with NCPAP, approaching the severity when on no treatment.

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Mandibular advancement devices instead of NCPAP?

307

Table 2 Mean (SD) ESS and sleep data when on and off NCPAP and at each stage
during MAD usage

ESS
>4% SaO2 dips/h
Autonomic arousals/h (via PTT)
Respiratory effort in ms (via PTT)

On CPAP
(n=50)

During MAD usage

On third night
off CPAP
Night 3
Night 7
(n=34)
(n=18)
(n=16)

Night 28
(n=11)

4.9 (3.2)
1.0 (2.3)
19.1 (12.8)
9.9 (2.4)

13.0 (5.1)
29.0 (25.0)
50.1 (23.8)
16.8 (4.8)

7.7 (5.1)
4.0 (5.5)
28.1 (12.2)
12.7 (4.0)

8.1 (3.6)
6.7 (5.5)
32.8 (15.4)
16.6 (5.5)

8.9 (5.4)
7.2 (8.6)
29.2 (10.2)
14.3 (5.0)

ESS=Epworth sleepiness score; PTT=pulse transit time; MAD=mandibular advancement device.

DISCUSSION
This study has shown that simple MADs can replace NCPAP
and control OSA for short periods of time in some patients.
The acceptance rate was poor and in over 60% the cost of the
device was essentially wasted. Most of the patients acclimatising to the device found it useful for a weekend, and many for
longer. In the UK the cost of these devices is about 200, so the
effective cost per patient able to use a device is nearer 600.
The cost is therefore more than the original NCPAP machine.
The definition of control is, of necessity, arbitrary. Had we
set higher or lower criteria to define control, then our percentage success rates would have been altered accordingly. The
definition we used was a pragmatic one, agreed by several staff
working with patients with OSA, and seemed to accord with
the patients view of control. It is interesting that, despite
apparently keeping the ESS and SaO2 dip rate down, these
devices were far less successful at controlling sleep fragmentation (as measured by transient blood pressure rises via PTT)
and inspiratory effort (as measured by respiratory blood pressure swings via PTT). This would suggest that MADs are only
partially controlling the upper airway obstruction and perhaps
are converting apnoeas to upper airway resistance events.
The use of MADs has been explored as a treatment for
snoring in the absence of sleep apnoea, and there are controlled data to show that they clearly work.1 In OSA their success
is somewhat less and variable. For example, the Vancouver
group23 studied 24 patients with mild to moderate OSA, comparing an adjustable MAD with NCPAP (4 months each) in a
randomised crossover design. The mean apnoea/hypopnoea
index (AHI) was about 25 and fell to 4 on NCPAP but only to
14 with the MAD. Furthermore, some patients derived no
benefit or even deteriorated using a MAD, whereas all
improved on NCPAP. Despite the superior physiological
improvement from NCPAP, there was greater improvement in
subjective sleepiness using the MADs and more patients preferred them. Half of the patients were, of course, started on the
MAD first, rather than having already been established
successfully on NCPAP for a period of time, as in our study.
There were no variables such as cephalometric measurements
that predicted a better response to the MAD.
Our low acceptance rate was disappointing and may have
been due to a variety of reasons. Had we used adjustable
devices, with a gradual increase in the degree of protrusion,
we might have avoided some of the unpleasant side effects.
However, there is no good evidence that this is so. Our device
covers the teeth and gums to spread the load, but this encourages gum discomfort and there are MADs that only clip onto
the teeth. Again, there is no work available to suggest the
superiority of one type of device over another. In a recent
questionnaire survey of the long term usage of carefully fitted
adjustable MADs (Silensor and Herbst appliances) on an
intention to treat basis, only 47 of 166 (28%) were using it
every night, and only 69 (42%) were using it at least once a
week.24 Our own view from talking to patients was that,
although they were keen to try an alternative to NCPAP, when
they actually tried to come off it they felt insecure and were

aware of sleeping badly. Had they been introduced to the MAD

before NCPAP, the outcome might have been different. Whatever the reason, the eventual success rate was not as good as
we had hoped. Given the simplicity of the device used, it is
likely that our results represent a worst case scenario with
more modern devices perhaps likely to achieve greater
success. These data have at least allowed us to inform patients
currently on NCPAP of the approximate success rate should
they choose to try a MAD as an alternative.

ACKNOWLEDGEMENTS
The authors thank Jill Adam and Paul Fuller, the two dentists who
made all the MADs for our patients. The Sleep Apnoea Trust supported
the study through the purchase of the MADs.
.....................

Authors affiliations
D M Smith, J R Stradling, Oxford Centre for Respiratory Medicine,
Oxford Radcliffe Trust, Oxford OX3 7LJ, UK

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