Recent advances in pulp vitality testing
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Endodontology, Vol. 15, 2003
Recent advances in pulp vitality testing
*Samraj RV **Indira R **Srinivasan MR ***Kumar A
ABSTRACT
Pulp vitality test is crucial in monitoring the state of health of dental pulp,
especially after traumatic injuries. The traditional pulp testing methods such
as thermal and electric pulp testing methods depend on the innervation and
often yield false positive and negative response. The newer pulp testing
devices, some of which are still under development stage, detect the blood
supply of the pulp, through light absorption and reflection, are considered
to be more accurate and non-invasive. The article attempts to discuss issues
related to pulp vitality testing in clinical endodontic practice and describes
the principle on which these newer pulp testing devices are based and its
mode of working.
Key words: Pulp vitality, Pulse oximetry, Laser Doppler flowmetry, Pulpal circulation,
Revascularizaton, Light transmission.
Introduction vitality 3,4 as it provides an objective
differentiation between necrotic and vital pulp
The assessment of pulp vitality is a crucial tissue. This article highlights tests relying on
diagnostic procedure in the practice of the passage of light through the tooth to detect
dentistry1. Current routine methods rely on pulp vitality with greater objectivity. They rely
stimulation of Ad nerve fibers and give no direct either on the detection of changes in the light
indication of blood flow within the pulp. These absorption as it passed through the tooth, as
include thermal stimulation, electrical or direct in photoplethysmography, pulse oximetry and
dentine stimulation. These testing methods dual wavelength spectrophotometry5 or the
have the potential to produce an unpleasant shift in light frequency as it is reflected back
and occasionally painful sensation and from a tooth, as in laser Doppler flowmetry6.
inaccurate results (false positive or negative This paper attempts to review the newer pulp
can be obtained in many instances). In addition,
vitality testing methods.
each is a subjective test that depends on the
patient's perceived response to a stimulus as Pulse Oximetry
well as the dentist's interpretation of that
response2. Recent studies have shown that The pulse oximeter is a non-invasive
blood circulation and not innervation is the most oxygen saturation monitoring device widely
accurate determinant in assessing pulp used in medical practice for recording blood
oxygen saturation levels during the
* Post Graduate Student administration of intravenous anesthesia. It
** Professor contributes to the increased safety of general
*** Lecturer
Department of Conservative Dentistry and
anesthesia. Pulse oximeter is a standard
Endodontics, Ragas Dental College equipment in operating rooms and is routinely
Chennai-600119 being used in other acute care settings,
14Samraj RV et al. Pulp vitality testing...
including intensive care units, emergency of pulp tissue is present for adequate detection
rooms and endoscopy suites where sedation of the pulse.
and analgesia are provided 8 . Its wide
A number of clinical studies have proved
acceptance in the medical field results from
that the pulse oximetry is an effective and
its ease of application and its capability of
objective method of evaluating dental pulp
providing vital information about the patient's
vitality. Though the surrounding insulation of
status.
the enamel and dentine are hindrances to the
This device is currently under investigation detection of a pulse in the pulp, it has proved
in dental practice to detect pulpal blood to be a successful method in 70% of the clinical
circulation by virtue of its non-invasive and trials and further work is still in progress. It is
atraumatic nature. Specific objectives were to also useful in cases of impact injury where the
develop a design for a. dental sensor (a blood supply remains intact but the nerve
modified finger probe) that can be successfully supply is damaged12. Also current results
applied and adapted to the tooth and well suited indicate that pulpal circulation can be detected
to detect pulsatile absorbance. by the pulse oximeter independent of gingival
circulation. Signal filtration is now employed to
The principle of this technology is based
make it easier to reproduce pulp pulse
on a modification of Beer's law, which relates
readings. Smaller and cheaper commercial
the absorption of light, by a solute to its
oximeters are now available for routine clinical
concentration and optical properties at a given
use in an average dental office.
light wavelength9. It also depends on the
absorbance characteristics of haemoglobin in Despite its advantages, limitations include
the red and infra-red range. In the red region, background absorption associated with venous
oxyhaemoglobin absorbs less light than blood and tissue constituents, which should be
deoxyhaemoglobin and vice versa in the infra- differentiated. In addition to the absorption,
red region. Hence one wavelength was refraction and reflection also occur as in
sensitive to changes in oxygenation and the Penumbra effect, which is seen in patients with
second was insensitive to compensate for strong tissue pulsations, where some of the
changes in tissue thickness, haemoglobin light reaches the photo detector diode without
content and light intensity. passing through the tissue bed13. The oxygen
saturation values from the teeth routinely
The system consists of a probe containing
register lower than the readings from the
a diode that emits light in two wavelengths:
patient's finger. This may be due to the
I. Red light of approximately 660 nm limitations of using a probe designed for other
body parts, not specifically for the anatomy of
II. Infra-red light of approximately 850 nm
a tooth14.
A silicon photo detector diode is placed
on the opposing surfaces of the tooth, which Dual Wavelength
is connected to a microprocessor. Spectrophotometry
The probe is placed on the labial surface Dual wavelength spectrophotometry
of the tooth crown and the sensor on the palatal (DWLS) is a method independent of a pulsatile
surface. Ideal placement of the probe is in the circulation. The presence of arterioles rather
middle third of the crown. If placed in the than arteries in the pulp and its rigid
gingival third, disturbances from gingival encapsulation by surrounding dentine and
circulation or any gingival trauma or bleeding enamel make it difficult to detect a pulse in the
will interfere with the readings. Incisally, less pulp space. This method measures
15Endodontology, Vol. 15, 2003
oxygenation changes in the capillary bed rather instrument is small, portable, relatively
than in the supply vessels and hence does not inexpensive and should be suitable for use in
depend on a pulsatile blood flow. Pulse a private dental office.
oximetry is a method based on DWLS.
Laser doppler flowmetry
DWLS detects the presence or absence
of oxygenated blood at 760 nm and 850nm. Laser Doppler Flowmetry (LDF) is a non-
The blood volume or concentration channel invasive, electro optical technique, which
(760 nm plus 850 nm) is arranged to respond allows the semi-quantitative recording of pulpal
linearly to the increase in light absorption. The blood flow16. The Laser Doppler technique
oxygenation channel (760 nm minus 850 nm) measures blood flow in the very small blood
senses the oxygenated blood because of the vessels of the microvasculature.
greater absorption at 850 nm as compared to The technique depends on the Doppler
760 nm. In vivo and in vitro studies were principle whereby light from a laser diode
conducted to differentiate between pulp incident on the tissue is scattered by moving
chambers that were empty, filled with RBC's and as a consequence, the frequency
oxygenated blood or fixed pulp tissue. DWLS broadened.
was able to differentiate with reproducible
readings between a pulp chamber of a vital The frequency broadened light, together
and non-vital tooth in vivo. with laser light scattered from static tissue is
photo detected and the resulting photocurrent
In young children, in cases of avulsed and processed to provide a blood flow
replanted teeth with open apices, the blood measurement. The Doppler shifted laser light,
supply is regained within the first 20 days after back- scattered out of the tooth is detected by
replantation but nerve supply lags behind15. a photocell on the tooth surface. The output is
Repeated spectrophotometric readings taken proportionate to the number and velocity of the
at the start of the replantation and continuing blood cells.
upto 40 days later revealed an increase in blood
oxygenation levels indicating a healing process Over the past decade LDF technology has
and that the pulp of the avulsed tooth was been used experimentally to monitor blood flow
recovering. Hence endodontic treatment need in the pulps of both, the animals and the
not be undertaken. humans17,18. LDF has been shown to be
valuable in monitoring revascularization of
Even though the instrument was not immature incisors following severe dental
specifically designed for dental use, it was easy trauma. During follow-up examination the
to use and can be developed as a pulp tester. traumatized tooth was unresponsive to
A major advantage is that it uses visible light traditional vitality testing during the first 6
that is filtered and guided to the tooth by months. However LDF indicated that
fibreoptics. Thus unlike Laser light, added eye revascularization had occurred much sooner19.
protection is unnecessary for the patient and
the operator. The primary issues in pulp-vitality testing
as follows:
Still in vivo tests of this hypothesis are in
progress. Influence of the gingival circulation • A non-vital post-traumatized incisor has a
cannot be ruled out and data on how large a better long-term prognosis if root canal
mass of pulp tissue is needed for accurate therapy is completed before the necrotic
readings must be determined. The test is non- pulp gets infected.
invasive and yields objective results. The • The best outcome for the post-traumatized
16Samraj RV et al. Pulp vitality testing...
immature incisor is for it to revascularize temperature, distinct differences in vital and
and continue normal root development, nonvital teeth. He used a Thermistor unit
including increased root wall thickness, consisting of 2 matched thermistors connected
which is not possible to assess with back to back, one measuring the surface
conventional electrical and thermal temperature of the crown (measuring
testing20. thermistor) while the other acting as a
reference thermistor23. The tooth to be tested
• Watching and hoping for revascularization
was dried with gauze and the thermistor unit
using sensitivity testing may lead to
was positioned so that the measuring
infection in the post-trauma observation
thermistor contacted the center of the buccal
period.
surface of the crown. The reference thermistor
Studies were carried out to compare LDF was suspended in air, close to it, but not
with conventional pulp tests, EPT (electric pulp touching either the measuring thermistor or the
testing) and thermal tests, in children with enamel surface.
certain dental injuries. At the initial assessment
An equilibrium was next achieved between
at presentation, all tests had poor sensitivity
the temperatures of the thermistors, the crown
and specificity; however at 3, 6, and 12 months,
surface and the immediate environment by
LDF was significantly better than the other
holding the measuring unit in the described
tests21. There was no difference between tests
position until a steady state was established
at the later time periods, 18 months and 2
for at least 20 seconds22. Stimulation of the
years. It was concluded that LDF identified
crown surface was carried out by means of a
more vital and non-vital teeth correctly at earlier
rubber-polishing cup fitted to a dental contra-
time periods following injury than conventional
angle handpiece. The recordings were.
tests.
continued for a period of time following the
The limitations of this method include a too stimulation period. It was found that a difference
expensive device for use in a dental office. The was obtained between the critical period for
sensor should be maintained motionless and vital and non-vital teeth and the difference
in constant contact with the tooth for accurate corresponded with a specific temperature
readings. Also the laser beam must interact change.
with the moving cells within the pulpal
The feasibility of temperature
vasculature. However, it is useful in young
measurement as a diagnostic procedure in
children whose responses are unreliable and
human teeth was again demonstrated in 1986
its non-invasive nature helps to promote patient
by Fanibunda in another clinical study, using
co-operation and acceptance.
the time-temperature relationship method.
Other Testing Modalities Graphs were constructed from temperature
readings of teeth at 15 seconds intervals. At
The concept of diagnosing tooth vitality by the end of the cooling period, vital teeth
temperature measurement can provide illustrated a rise in temperature and following
valuable information on the integrity of the this a steady state was reached. Non-vital
underlying pulp. Howell et al used liquid teeth, at the end of the cooling period did not
cholesteric crystals and found that non-vital show any rise in temperature before it reached
teeth have lower temperature than vital teeth22. a steady state. The temperature remained at a
Fanibund in 1985 concluded from a steady level or decreased further. Information
laboratory study that it is possible to in respect of tooth vitality can be gained from
differentiate by means of crown surface the time-temperature relationship method.
17Endodontology, Vol. 15, 2003
Recently, computerised infrared 4. Bhasker SN and Rapport HR. Dental vitality test and
thermographic imaging (TI)24,25 for human pulp status. J. Am. Dent. Assoc. 1973; 86: 405-11.
teeth is under investigation to assess pulp 5. Nissan R, Trope M, Zharg CD and Chance B. Dual
vitality. wavelength spectrophotometry as a diagnostic test of the
pulp chamber contents. Oral Surg. Oral Med Oral Patho.
Further research is being undertaken with 1992; 86: 405-11.
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difference between vital and non-vital teeth, so invasive recording of blood flow in human dental pulp.
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may be evolved which is of diagnostic 7. Trope M, Jaggi J, Bennet F and Transtad L. Vitality
significance under routine clinical conditions. testing of teeth with a radiation probe using 133 xenon
radioisotope. Endod. Dent. Traumatol. 1986; 2: 215-8.
Conclusion 8. Severinghans JW and Kelleher JF. Recent
developments in pulse oximetry. Anesthesiology 1992;
The unreliability of testing tooth pulp nerve 76: 1918-38.
response is well documented. When nervous
sensations are inhibited or abolished in the 9. Weddington T, Alexander CM and Gross JB. Principles
of pulse oximetry. Anesthesia Equipment Manual 1997:
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transplantation procedures or during a general
10. Kahan RS, Gulabivala K, Snook M and Setchell DJ.
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vascular response of the pilip need not be
11. Shoher I, Mahler Y and Samueloff S. Dental pulp
restricted under such conditions. Recording the photoplethysmography in human beings. Oral Surg. 1973;
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probe malposition. Anesthesiology 1989; 71: 787-91.
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16. Evans D, Reid J, Strang R and Stirrups D. A
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