Recent Advances in Pulp Vitality Testing

14

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 suchas thermal and electric pulp testing methods depend on the innervation andoften yield false positive and negative response. The newer pulp testingdevices, some of which are still under development stage, detect the bloodsupply of the pulp, through light absorption and reflection, are consideredto be more accurate and non-invasive. The article attempts to discuss issuesrelated to pulp vitality testing in clinical endodontic practice and describesthe principle on which these newer pulp testing devices are based and itsmode of working.

Key words: Pulp vitality, Pulse oximetry, Laser Doppler flowmetry, Pulpal circulation,Revascularizaton, Light transmission.

IntroductionThe assessment of pulp vitality is a crucial

diagnostic procedure in the practice ofdentistry1. Current routine methods rely onstimulation of Ad nerve fibers and give no directindication of blood flow within the pulp. Theseinclude thermal stimulation, electrical or directdentine stimulation. These testing methodshave the potential to produce an unpleasantand occasionally painful sensation andinaccurate results (false positive or negativecan be obtained in many instances). In addition,each is a subjective test that depends on thepatient's perceived response to a stimulus aswell as the dentist's interpretation of thatresponse2. Recent studies have shown thatblood circulation and not innervation is the mostaccurate determinant in assessing pulp

vitality3,4 as it provides an objectivedifferentiation between necrotic and vital pulptissue. This article highlights tests relying onthe passage of light through the tooth to detectpulp vitality with greater objectivity. They relyeither on the detection of changes in the lightabsorption as it passed through the tooth, asin photoplethysmography, pulse oximetry anddual wavelength spectrophotometry5 or theshift in light frequency as it is reflected backfrom a tooth, as in laser Doppler flowmetry6.This paper attempts to review the newer pulpvitality testing methods.

Pulse OximetryThe pulse oximeter is a non-invasive

oxygen saturation monitoring device widelyused in medical practice for recording bloodoxygen saturation levels during theadministration of intravenous anesthesia. Itcontributes to the increased safety of generalanesthesia. Pulse oximeter is a standardequipment in operating rooms and is routinelybeing used in other acute care settings,

* Post Graduate Student** Professor*** Lecturer

Department of Conservative Dentistry andEndodontics, Ragas Dental CollegeChennai-600119

15

including intensive care units, emergencyrooms and endoscopy suites where sedationand analgesia are provided8. Its wideacceptance in the medical field results fromits ease of application and its capability ofproviding vital information about the patient'sstatus.

This device is currently under investigationin dental practice to detect pulpal bloodcirculation by virtue of its non-invasive andatraumatic nature. Specific objectives were todevelop a design for a. dental sensor (amodified finger probe) that can be successfullyapplied and adapted to the tooth and well suitedto detect pulsatile absorbance.

The principle of this technology is basedon a modification of Beer's law, which relatesthe absorption of light, by a solute to itsconcentration and optical properties at a givenlight wavelength9. It also depends on theabsorbance characteristics of haemoglobin inthe red and infra-red range. In the red region,oxyhaemoglobin absorbs less light thandeoxyhaemoglobin and vice versa in the infra-red region. Hence one wavelength wassensitive to changes in oxygenation and thesecond was insensitive to compensate forchanges in tissue thickness, haemoglobincontent and light intensity.

The system consists of a probe containinga 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 placedon the opposing surfaces of the tooth, whichis connected to a microprocessor.

The probe is placed on the labial surfaceof the tooth crown and the sensor on the palatalsurface. Ideal placement of the probe is in themiddle third of the crown. If placed in thegingival third, disturbances from gingivalcirculation or any gingival trauma or bleedingwill interfere with the readings. Incisally, less

of pulp tissue is present for adequate detectionof the pulse.

A number of clinical studies have provedthat the pulse oximetry is an effective andobjective method of evaluating dental pulpvitality. Though the surrounding insulation ofthe enamel and dentine are hindrances to thedetection of a pulse in the pulp, it has provedto be a successful method in 70% of the clinicaltrials and further work is still in progress. It isalso useful in cases of impact injury where theblood supply remains intact but the nervesupply is damaged12. Also current resultsindicate that pulpal circulation can be detectedby the pulse oximeter independent of gingivalcirculation. Signal filtration is now employed tomake it easier to reproduce pulp pulsereadings. Smaller and cheaper commercialoximeters are now available for routine clinicaluse in an average dental office.

Despite its advantages, limitations includebackground absorption associated with venousblood and tissue constituents, which should bedifferentiated. In addition to the absorption,refraction and reflection also occur as inPenumbra effect, which is seen in patients withstrong tissue pulsations, where some of thelight reaches the photo detector diode withoutpassing through the tissue bed13. The oxygensaturation values from the teeth routinelyregister lower than the readings from thepatient's finger. This may be due to thelimitations of using a probe designed for otherbody parts, not specifically for the anatomy ofa tooth14.

Dual WavelengthSpectrophotometry

Dual wavelength spectrophotometry(DWLS) is a method independent of a pulsatilecirculation. The presence of arterioles ratherthan arteries in the pulp and its rigidencapsulation by surrounding dentine andenamel make it difficult to detect a pulse in thepulp space. This method measures

Samraj RV et al. Pulp vitality testing...

16


oxygenation changes in the capillary bed ratherthan in the supply vessels and hence does notdepend on a pulsatile blood flow. Pulseoximetry is a method based on DWLS.

DWLS detects the presence or absenceof oxygenated blood at 760 nm and 850nm.The blood volume or concentration channel(760 nm plus 850 nm) is arranged to respondlinearly to the increase in light absorption. Theoxygenation channel (760 nm minus 850 nm)senses the oxygenated blood because of thegreater absorption at 850 nm as compared to760 nm. In vivo and in vitro studies wereconducted to differentiate between pulpchambers that were empty, fil led withoxygenated blood or fixed pulp tissue. DWLSwas able to differentiate with reproduciblereadings between a pulp chamber of a vitaland non-vital tooth in vivo.

In young children, in cases of avulsed andreplanted teeth with open apices, the bloodsupply is regained within the first 20 days afterreplantation but nerve supply lags behind15.Repeated spectrophotometric readings takenat the start of the replantation and continuingupto 40 days later revealed an increase in bloodoxygenation levels indicating a healing processand that the pulp of the avulsed tooth wasrecovering. Hence endodontic treatment neednot be undertaken.

Even though the instrument was notspecifically designed for dental use, it was easyto use and can be developed as a pulp tester.A major advantage is that it uses visible lightthat is filtered and guided to the tooth byfibreoptics. Thus unlike Laser light, added eyeprotection is unnecessary for the patient andthe operator.

Still in vivo tests of this hypothesis are inprogress. Influence of the gingival circulationcannot be ruled out and data on how large amass of pulp tissue is needed for accuratereadings must be determined. The test is non-invasive and yields objective results. The

instrument is small, portable, relativelyinexpensive and should be suitable for use ina private dental office.

Laser doppler flowmetryLaser Doppler Flowmetry (LDF) is a non-

invasive, electro optical technique, whichallows the semi-quantitative recording of pulpalblood flow16. The Laser Doppler techniquemeasures blood flow in the very small bloodvessels of the microvasculature.

The technique depends on the Dopplerprinciple whereby light from a laser diodeincident on the tissue is scattered by movingRBC's and as a consequence, the frequencybroadened.

The frequency broadened light, togetherwith laser light scattered from static tissue isphoto detected and the resulting photocurrentprocessed to provide a blood flowmeasurement. The Doppler shifted laser light,back- scattered out of the tooth is detected bya photocell on the tooth surface. The output isproportionate to the number and velocity of theblood cells.

Over the past decade LDF technology hasbeen used experimentally to monitor blood flowin the pulps of both, the animals and thehumans17,18. LDF has been shown to bevaluable in monitoring revascularization ofimmature incisors following severe dentaltrauma. During follow-up examination thetraumatized tooth was unresponsive totraditional vitality testing during the first 6months. However LDF indicated thatrevascularization had occurred much sooner19.

The primary issues in pulp-vitality testingas follows:

• A non-vital post-traumatized incisor has abetter long-term prognosis if root canaltherapy is completed before the necroticpulp gets infected.

• The best outcome for the post-traumatized

17

immature incisor is for it to revascularizeand continue normal root development,including increased root wall thickness,which is not possible to assess withconventional electrical and thermaltesting20.

• Watching and hoping for revascularizationusing sensitivity testing may lead toinfection in the post-trauma observationperiod.

Studies were carried out to compare LDFwith conventional pulp tests, EPT (electric pulptesting) and thermal tests, in children withcertain dental injuries. At the initial assessmentat presentation, all tests had poor sensitivityand specificity; however at 3, 6, and 12 months,LDF was significantly better than the othertests21. There was no difference between testsat the later time periods, 18 months and 2years. It was concluded that LDF identifiedmore vital and non-vital teeth correctly at earliertime periods following injury than conventionaltests.

The limitations of this method include a tooexpensive device for use in a dental office. Thesensor should be maintained motionless andin constant contact with the tooth for accuratereadings. Also the laser beam must interactwith the moving cells within the pulpalvasculature. However, it is useful in youngchildren whose responses are unreliable andits non-invasive nature helps to promote patientco-operation and acceptance.

Other Testing ModalitiesThe concept of diagnosing tooth vitality by

temperature measurement can providevaluable information on the integrity of theunderlying pulp. Howell et al used liquidcholesteric crystals and found that non-vitalteeth have lower temperature than vital teeth22.

Fanibund in 1985 concluded from alaboratory study that it is possible todifferentiate by means of crown surface

temperature, distinct differences in vital andnonvital teeth. He used a Thermistor unitconsisting of 2 matched thermistors connectedback to back, one measuring the surfacetemperature of the crown (measuringthermistor) while the other acting as areference thermistor23. The tooth to be testedwas dried with gauze and the thermistor unitwas positioned so that the measuringthermistor contacted the center of the buccalsurface of the crown. The reference thermistorwas suspended in air, close to it, but nottouching either the measuring thermistor or theenamel surface.

An equilibrium was next achieved betweenthe temperatures of the thermistors, the crownsurface and the immediate environment byholding the measuring unit in the describedposition until a steady state was establishedfor at least 20 seconds22. Stimulation of thecrown surface was carried out by means of arubber-polishing cup fitted to a dental contra-angle handpiece. The recordings were.continued for a period of time following thestimulation period. It was found that a differencewas obtained between the critical period forvital and non-vital teeth and the differencecorresponded with a specific temperaturechange.

The feasibility of temperaturemeasurement as a diagnostic procedure inhuman teeth was again demonstrated in 1986by Fanibunda in another clinical study, usingthe time-temperature relationship method.Graphs were constructed from temperaturereadings of teeth at 15 seconds intervals. Atthe end of the cooling period, vital teethillustrated a rise in temperature and followingthis a steady state was reached. Non-vitalteeth, at the end of the cooling period did notshow any rise in temperature before it reacheda steady state. The temperature remained at asteady level or decreased further. Informationin respect of tooth vitality can be gained fromthe time-temperature relationship method.


18


Recently, computerised infraredthermographic imaging (TI)24,25 for humanteeth is under investigation to assess pulpvitality.

Further research is being undertaken withthe sole aim of increasing the detectabledifference between vital and non-vital teeth, sothat a method of temperature measurementmay be evolved which is of diagnosticsignificance under routine clinical conditions.

ConclusionThe unreliability of testing tooth pulp nerve

response is well documented. When nervoussensations are inhibited or abolished in thetooth, for example following trauma, toothtransplantation procedures or during a generalanaesthetic, conventional tests are of littlevalue. However, a method based on thevascular response of the pilip need not berestricted under such conditions. Recording thepulpal blood flow would be an objectiveassessment of the status of the pulpal bloodcirculation, a true indicator of pulp vitality.Optical devices that exploit the variousabsorbance properties of different substanceswithin the dental pulp are being studied todetermine pulsation and blood volume. Theyoffer the advantages of being objective, non-invasive and atraumatic testing modalities,which result in greater patient acceptance andco-operation. Currently, the significance andreliability of these methods are being studied.It is hoped that newer technology will enable amore thorough study of the pulpal vasculatureand define its role in pulp vitality testing.

References1. Noblett WC, Wilcox LR, Scammon F, Johnson WT andDiaZ-Arnol AM. Detection of pulpal circulation in vitro bypulse oximetry. J. Endod. 1996; 22:1-5.

2. Ehrmann EH. Pulp testers and pulp testing withparticular reference to the use of dry ice. Austral. Dent. J.1977; 22: 272-9.

3. Chambers IG. The role and methods of pulp testing inoral diagnosis: A review. Int. Endod. J. 1982; 15: 1-15.

4. Bhasker SN and Rapport HR. Dental vitality test andpulp status. J. Am. Dent. Assoc. 1973; 86: 405-11.

5. Nissan R, Trope M, Zharg CD and Chance B. Dualwavelength spectrophotometry as a diagnostic test of thepulp chamber contents. Oral Surg. Oral Med Oral Patho.1992; 86: 405-11.

6. Gazelius B, Olgart L, Edwall B and Edwall L. Non-invasive recording of blood flow in human dental pulp.Endod. Dent. Traumatol. 1986; 2; 219-21.

7. Trope M, Jaggi J, Bennet F and Transtad L. Vitalitytesting of teeth with a radiation probe using 133 xenonradioisotope. Endod. Dent. Traumatol. 1986; 2: 215-8.

8. Severinghans JW and Kelleher JF. Recentdevelopments in pulse oximetry. Anesthesiology 1992;76: 1918-38.

9. Weddington T, Alexander CM and Gross JB. Principlesof pulse oximetry. Anesthesia Equipment Manual 1997:147-55.

10. Kahan RS, Gulabivala K, Snook M and Setchell DJ.Evaluation of a pulse oximeter and customized probe forpulp vitality testing. J. Endod. 1996; 22: 105-9. .

11. Shoher I, Mahler Y and Samueloff S. Dental pulpphotoplethysmography in human beings. Oral Surg. 1973;36: 915-21.

12. Andreasan FM, Yu Z, Thomsen B and Andreasan P.Occurrence of pulp canal obliteration after luxation injuriesin the permanent dentition. Endod. Dent. Traumatol. 1987;3: 103-15.

13. Kelleher JF and Ruff RH. The penumbra effect;vasomotion dependent pulse oximeter artifact due toprobe malposition. Anesthesiology 1989; 71: 787-91.

14. Goho C. Pulse oximetry evaluation of vitality in primaryand immature permanent teeth. Pediatric. Dent. 1999; 21:125-7.

15. Skoglund A, Tronstad L and Wallenius KA.Microangiographic study of vascular changes in replantedand auto transplanted teeth of young dogs. Oral Surg.Oral Med. Oral Path. 1978; 45: 17-28.

16. Evans D, Reid J, Strang R and Stirrups D. Acomparison of laser Doppler flowmetry with other methodsof assessing the vitality of traumatized anterior teeth.(Abstract) Endod. Dent. Traumatol. 1999; 15: 284-90.

17. Gazelius B, Olgart L, Edwall B and Edwall L. Non-invasive recording of blood flow in human dental pulp.Endod. Dent. Traumatol. 1986; 2: 219-21.

18. Olgart L, Gazelius B and Lindh-Stromberg U. LaserDoppler flowmetry in assessing vitality in luxatedpermanent teeth. Int. Endod. 1. 1988; 21: 300-6.

19

19. Wee JY, Yanpiset K, Sigurdsson A and Vann In WF.Laser Doppler flowmetry for monitoring traumatized teeth.Dent. Traumatol. 2001; 17: 231-5.

20. Kerekes K, Heide S and Jacobson I. Follow-upexamination of endodontic treatment in traumatizedjuvenile incisors. J. Endod. 1980; 6:744-8.

21. Odor TM, Pitt Ford TR and McDonald F. Laser Dopplerflowmetry as a vitality test in injured teeth (Abstract). Int.Endod. J. 2000; 33: 160.

22. Fanibunda KB. The feasibility of temperaturemeasurement as a diagnostic procedure in human teeth.J. Dent. 1986; 14; 126-9.

23. Fanibunda KB. Diagnosis of tooth vitality by crownsurface temperature measurement; a clinical evaluatfon.J. Dent. 1986; 14: 160-4.

24. Kells BE, Kennedy J G Biagioni PA and Lamey PJ.Computerised infrared thermographic imaging and pulpalblood flow; Part 1. A protocol for thermal imaging of humanteeth. Int. Endod.J. 2000; 33: 442-7.

25. Kells BE, Kennedy JG, Biagioni PA and Lamey PJ.Computerised infrared thermographic imaging and pulpalblood flow; Part 2. Rewarming of healthy human teethfollowing a controlled cold stimulus. Int. Endod J. 2000;33: 448-62.


Documents

Recent Advances in Pulp Vitality Testing