|
Method 1: The Profile Technique
First establish the patient's 'rest position'. With reference to Fig
1 and with the patient sitting upright with the head unsupported, relaxed
and breathing quietly, locate the two divider arms as illustrated: the
upper and moveable divider arm touching the underside of the nose, the
lower fixed arm touching the underside of the mandible. Record the distance
from the mm scale.
Repeat the exercise after asking the patient to close the teeth together.
Record the new distance from the scale. Repeat both measurements once
or twice. With the Alma Bite Gauge this takes only a few seconds.
Calculate the averages of RVD and OVD readings and then the difference
between the averages. This is the freeway space (nose-chin approximation;
the distance between the teeth or rims is less).
The accuracy of Method 1 measurements is assured because with the upper
arm reversed, the location of the measuring arrow compensates for the
height of the arm itself.
Method 2: The Two Dots Technique
Using a fine tip pen with water-based ink, mark a small dot on the tip
of the patient's nose and another on the patient's chin. With the patient
sitting upright as described in Method 1, slide the upper divider arm
so that the points of the upper and lower arms line up with the dots.
Read off the distance between the two points from the scale and record
it.
Then measure the distance between the same points with the teeth closed
together. Repeat the measurements, average them and calculate the freeway
space as before (Method 1). You don't need to place the dots in exactly
the same places if measuring the vertical dimensions on another occasion
because it is only the difference between RVD and OVD that matters (RVD
- OVD = FWS). Don't forget to remove the dots before the patient leaves.
Tips
For either method, it is important to have your patient completely relaxed,
sitting in a comfortable upright position with the head OFF the head-rest
and with the mandible in its postural position. A useful tip is to request
the patient to hum (Make the sound of the letter 'm') while relaxing.
Licking the lips or sipping and swallowing water may also prepare the
mandible for assuming its usual rest position.
With Method 1, errors may be caused by the instrument touching the patient's
face and causing jaw movement.
With method 2 errors may arise by unconscious movement of the soft tissues
of the chin by the patient. This is a habitual compensation in people
whose lips do not naturally close at rest (incompetent lips). Care must
be taken to ensure that the mentalis muscle is relaxed (and the skin of
the chin not puckered) or else the lower spot can move up or down in an
unpredictable way.
Make RVD and OVD measurements at least twice to reduce error; while the
occluding position is usually constant and reproducible, the rest (postural)
position may vary from time to time and repeated readings should isolate
an unusual one.
With edentulous patients, at least one reading should be taken with
one of the dentures out, preferable the upper. This will allow a more
normal rest position to be assumed where the OVD of the dentures is too
great, and a false FWS has occurred.
Asden Limited
Astek House
Atlantic Street
Altrincham
Cheshire
WA14 5DH
ENGLAND
Tel: +44 (0)161 942 3920
Fax: +44 (0)161 942 3921
info@asden.co.uk
|
