The pulse oximeter is a non-invasive
oxygen saturation monitoring device widely
used in medical practice for recording blood
oxygen saturation levels during the
administration of intravenous anesthesia. It
contributes to the increased safety of general
anesthesia. Pulse oximeter is a standard
equipment in operating rooms and is routinely
being used in other acute care settings,
including intensive care units, emergency
rooms and endoscopy suites where sedation
and analgesia are provided8. Its wide
acceptance in the medical field results from
its ease of application and its capability of
providing vital information about the patient’s
status.
This device is currently under investigation
in dental practice to detect pulpal blood
circulation by virtue of its non-invasive and
atraumatic nature. Specific objectives were to
develop a design for a. dental sensor (a
modified finger probe) that can be successfully
applied and adapted to the tooth and well suited
to detect pulsatile absorbance.
The principle of this technology is based
on a modification of Beer’s law, which relates
the absorption of light, by a solute to its
concentration and optical properties at a given
light wavelength9. It also depends on the
absorbance characteristics of haemoglobin in
the red and infra-red range. In the red region,
oxyhaemoglobin absorbs less light than
deoxyhaemoglobin and vice versa in the infrared
region. Hence one wavelength was
sensitive to changes in oxygenation and the
second was insensitive to compensate for
changes in tissue thickness, haemoglobin
content and light intensity.
The system consists of a probe containing
a diode that emits light in two wavelengths:
I. Red light of approximately 660 nm
II. Infra-red light of approximately 850 nm
A silicon photo detector diode is placed
on the opposing surfaces of the tooth, which
is connected to a microprocessor.
The probe is placed on the labial surface
of the tooth crown and the sensor on the palatal
surface. Ideal placement of the probe is in the
middle third of the crown. If placed in the
gingival third, disturbances from gingival
circulation or any gingival trauma or bleeding
will interfere with the readings. Incisally, less
of pulp tissue is present for adequate detection
of the pulse.
A number of clinical studies have proved
that the pulse oximetry is an effective and
objective method of evaluating dental pulp
vitality. Though the surrounding insulation of
the enamel and dentine are hindrances to the
detection of a pulse in the pulp, it has proved
to be a successful method in 70% of the clinical
trials and further work is still in progress. It is
also useful in cases of impact injury where the
blood supply remains intact but the nerve
supply is damaged. Also current results
indicate that pulpal circulation can be detected
by the pulse oximeter independent of gingival
circulation. Signal filtration is now employed to
make it easier to reproduce pulp pulse
readings. Smaller and cheaper commercial
oximeters are now available for routine clinical
use in an average dental office.
Despite its advantages, limitations include
background absorption associated with venous
blood and tissue constituents, which should be
differentiated. In addition to the absorption,
refraction and reflection also occur as in
Penumbra effect, which is seen in patients with
strong tissue pulsations, where some of the
light reaches the photo detector diode without
passing through the tissue bed13. The oxygen
saturation values from the teeth routinely
register lower than the readings from the
patient’s finger. This may be due to the
limitations of using a probe designed for other
body parts, not specifically for the anatomy of
a tooth
.
