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JOURNAL OF ENDODONTICS ] VOL 2, NO 5, MAY 1976 Measurement of tooth temperature as a means of determining pulp vitality Larry C. Stoops, DMD, and Donald Scott, Jr., PhD, Philadelphia Two groups of 23 patients each were selected for this study. A test group was selected from 115 patients who required endodontic therapy. Another group of 23 patients who did not require endodontic therapy and who had homologous contralateral teeth with vital pulps acted as a control group. In both groups the same procedures were used; the teeth were cooled to below body temperature and the surface temperatures were recorded by a thermistor as the teeth approached body temperature during rewarming at selected time intervals. The results of this study indicate that there is a relationship between pulp vitality and tooth temperature and this relationship may provide a useful means of determining pulp vitality. Current methods for the determin- ation of pulp vitality of pulp patho- logic conditions include the use of de- vices such as the electric pulp tester, application of a segment of ice or hot gutta-percha, palpation, and percus- sion. These tests can be very painful-- regardless of whether the pain is real or imagined. An incorrect diagnosis may result when the pain causes a periapical vascular reflex response. Anxiety caused by these procedures commonly results in a powerful excita- tion of the vasomotor efferent nerve fibers of the sympathetic nervous sys- tem causing pronounced and rapid decreases in peripheral microcircula- tion of the pulp. 1 It also has been shown that such dramatic decreases in local circulation may lead to almost complete inhibition of pulpal blood flow in as little as 11 seconds. When such a major decrease in capillary cir- culation occurs, the excitability of the sensory neurons in the pulp and their ability to conduct impulses decreases rapidly and may fail in a period of two to three minutesY A more reliable method of diagnosis would be obtained if a technique could be found for determining pulp vitalty without enhancing the fears of the apprehensive patient. A method based on the simple measurement of tooth surface temperature might prove to be of diagnostic value. Infrared thermographic equipment has been used in the detection of breast cancer and certain cardiovascu- lar diseases for a number of yearsY -7 In 1966, Crandell and Hill 8 at- tempted to use thermography in dental diagnosis. They made a scan of a patient with a known periapical abscess and then compared the results from infrared thermography with the results obtained by the use of the elec- tric pulp tester. The results were in- conclusive. In 1970, Howell, Duell, and Mullany ~ evaluated pulp Vitality by thermographic means using choles- teric liquid crystals. Ten teeth in eight patients gave negative responses. Six teeth gave a temperature reading that was lower than that of control teeth. The remaining four teeth gave tem- perature readings that were either the same as or higher than those of the control group. Three of these teeth were opened and granulation tissue or pulplike tissue was found in a portion of the canal. The results of the inves- tigation implied that vital tissue in the 141

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JOURNAL OF ENDODONTICS ] VOL 2, NO 5, MAY 1976

M e a s u r e m e n t of t o o t h t e m p e r a t u r e as a m e a n s of d e t e r m i n i n g pu lp v i t a l i t y

Larry C. Stoops, DMD, a n d Dona ld Scott, Jr., PhD, Phi lade lphia

Two g r o u p s of 23 p a t i e n t s e a c h w e r e s e l e c t e d for this s tudy . A

test g r o u p w a s s e l e c t e d f rom 115 p a t i e n t s w h o r e q u i r e d e n d o d o n t i c

t h e r a p y . A n o t h e r g r o u p of 23 p a t i e n t s w h o d i d not r e q u i r e e n d o d o n t i c t h e r a p y a n d w h o h a d h o m o l o g o u s c o n t r a l a t e r a l tee th wi th v i ta l p u l p s a c t e d a s a control g roup . In bo th g r o u p s the s a m e p r o c e d u r e s w e r e u s e d ; the tee th w e r e c o o l e d to b e l o w b o d y t e m p e r a t u r e a n d the s u r f a c e t e m p e r a t u r e s w e r e r e c o r d e d b y a t he rmis to r a s the tee th a p p r o a c h e d b o d y t e m p e r a t u r e d u r i n g r e w a r m i n g a t s e l e c t e d t ime in te rva l s . The resu l t s of this s t u d y i n d i c a t e tha t the re is a r e l a t i o n s h i p b e t w e e n p u l p v i t a l i ty a n d tooth t e m p e r a t u r e a n d this r e l a t i o n s h i p m a y p r o v i d e a usefu l m e a n s of d e t e r m i n i n g p u l p v i ta l i ty .

Current methods for the determin- ation of pulp vitality of pulp patho- logic conditions include the use of de- vices such as the electric pulp tester, application of a segment of ice or hot gutta-percha, palpation, and percus- sion. These tests can be very painful - - regardless of whether the pain is real or imagined. An incorrect diagnosis may result when the pain causes a periapical vascular reflex response. Anxiety caused by these procedures commonly results in a powerful excita- tion of the vasomotor efferent nerve fibers of the sympathetic nervous sys- tem causing pronounced and rapid decreases in peripheral microcircula- tion of the pulp. 1 It also has been shown that such dramatic decreases in local circulation may lead to almost complete inhibition of pulpal blood

flow in as little as 11 seconds. When such a major decrease in capillary cir- culation occurs, the excitability of the sensory neurons in the pulp and their ability to conduct impulses decreases rapidly and may fail in a period of two to three minutesY

A more reliable method of diagnosis would be obtained if a technique could be found for determining pulp vitalty without enhancing the fears of the apprehensive patient. A method based on the simple measurement of tooth surface temperature might prove to be of diagnostic value.

Infrared thermographic equipment has been used in the detection of breast cancer and certain cardiovascu- lar diseases for a number of yearsY -7

In 1966, Crandell and Hill 8 at- tempted to use thermography in

dental diagnosis. They made a scan of a patient with a known periapical abscess and then compared the results from infrared thermography with the results obtained by the use of the elec- tric pulp tester. The results were in- conclusive. In 1970, Howell, Duell, and Mullany ~ evaluated pulp Vitality by thermographic means using choles- teric liquid crystals. Ten teeth in eight patients gave negative responses. Six teeth gave a temperature reading that was lower than that of control teeth. The remaining four teeth gave tem- perature readings that were either the same as or higher than those of the control group. Three of these teeth were opened and granulation tissue or pulplike tissue was found in a portion of the canal. The results of the inves- tigation implied that vital tissue in the

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JOURNAL OF ENDODONTICS I VOL 2, NO 5, MAY 1976

apical third or more of .,the pulp canal can maintain .the temperature of a tooth within levels close to that of a normal control tooth.

Since a pulpless tooth would be ex- pected to have an impaired blood sup- ply, a lowering of the tooth's tem- perature would be observed when it was exposed to room air and was not warmed by adjacent tissues except via the apical contacts with the gingiva.

When a ,tooth is fully exposed to room air, its temperature is strongly influenced by its blood flow. Although evaporation of saliva will cool moist teeth and the heat gained from adja- cent tissues will raise tooth .tempera- ture, these changes will be equal for symetrically placed teeth. Thus, it is speculated that the surface temperature of a tooth suspected of being pulpless can be compared with that o.f its con- tralateral homologue when the surfaces of both are dry; the observed tempera- ture difference should be an indicator of the difference in the local circula- tion. The current study was under- taken to determine whether measuring the tooth surface temperature could aid in determining pulp vi,talrity.

M a t e r i a l s a n d M e t h o d

The accurate measurement of the temperature of the intact tooth re- quires a precise measuring device and a carefully determined set of repro- ducible conditions during observation to avoid errors from changes in the environment. For this purpose a thermistor was selected for measure- ment because of its high level of sen- sitivity and the availability of extreme- ly small sensory units with ,a very low thermal inertia.

For this purpose VECO model 32A7 thermistors* were used since they weighed only 0.5 mg each and could easily be protected with a thin coat of insulating varnish to prevent electrical or mechanical damage (Fig I). The resistance of these units

Fig 1- -VECO model 32A7 thermistor.

Fig 2--Bridge circuit with adjustments [or calibrations.

varied from 1.0 to 1.8 • l0 :~ ohms depending on the temperature. Each of these units was incorporated into an appropriate bridge circuit that in- cluded adjustments for setting the calibrated reference temperature and for adjusting the sensitivity (Fig 2). Once a given unit was in active use these controls were locked in position so that a direct temperature reading scale could be placed on the face of the recording galvanometer (Fig 3). At this point, the reference tempera- ture was calibrated against a precision constant temperature bath. The indi- cating instrument was .a galvanometer with a sensitivity of 1.94 /zA/em. (Fig 4). The reproducibility of meas- urements with this unit at the sensi- tivity used in this study was +0.07C on the galvanometer scale between a temperature range of 27.0 and 31.0C.

The technique for determining the relative tooth temperature of the test and control teeth involved only a few minutes. The ,tooth suspected of be- ing pulpless and its contralateral

homologue were cooled simultaneous- ly by covering both teeth with a piece of gauze that had been saturated with cold tap water (10C). After cooling for one minute, the teeth were isolated with cotton rolls and air dried. Tooth temperature was monitored with the thermistor and after a period of three to five minutes it was revcarmed so as to be wi,thin the range of the recording instrument. Once that range was reached the thermistor was alternately applied to each tooth. A series of com- parative readings from the two ,teeth was thus obtained over a period of one minute and the average tempera- ture of each tooth was recorded.

Before attempting to evaluate .the relative differences in temperature be- tween a vital and a pulpless tooth, control observations must be made to determine the possible differences in temperature between two healthy, vital, symmetrical teeth. For this purpose, in the first phase of our study 23 subjects were selected with vi.tal, asymptomatic, contralateral teeth of the types rep-

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JOURNAL OF ENDODONTICS ] VOL 2, NO S, MAY 1976

40 30 20 10 0 10 20 30 40

27 28 29 30 31

Fig 3--Top: Direct tempera- ture reading scale on [ace o/ recording galvanometer. Bot- tom: diagrammatic represen- tation of direct temperature reading scale.

Fig 4---Indicating instrument: galva- nometer.

resented by those of the test patients and the same procedure was applied to their teeth.

The subjects for the second phase of our study, lhose with pulpless teeth, were selected from among 115 patients. The 23 chosen were limited to those patients who were suspected of having a pulpless tooth as determined by the use Of radiographs, and who had a homologous contralateral vital tooth. So that the results would be significant and suitable for statistical analysis, it was important that no differences existed in the two teeth whose tempera- tures were compared in a given patient. Care was taken to be sure that if the test tooth contained a large composite restoration or was fractured, the con- trol tooth also had a similar size com- posite restoration or fracture.

R e s u l t s

Table I shows the temperature dif- ferences between 23 pairs of vital con- tralateral teeth. In all cases the teeth were free from restorations, had no history of trauma, gave negative radiographic findings, and gave a posi- tive response to the electric pulp tester. The temperature difference between the pairs of teeth was zero in half of the teeth tested and varied among the remainder up to a single result of 0.38C with a mean value of 0.06C.

Table 2 presents the data from the 23 patients whose selection was deter- mined by an apparent need for root canal therapy. Differences between tooth temperatures in these patients ranged from a low of 0.13C to as much as 0.75C, with a mean value of 0.55C. In three patients there was a reversal of temperature difference in which the pulpless tooth showed a greater rise in temperature after cool- ing than did the vital control tooth within the given time period. In one of these the canal hemorrhaged and was noted to contain granulationlike tissue in the apical portion. This pa- tient required anesthesia to perform endodontic therapy. When the sus- pected teeth were opened for endodon- tic therapy, all teeth appeared to be pulpless except for the one tooth prev- iously mentioned.

D i s c u s s i o n

The consistent data shown in the re- sults were obtained after experiende had shown the need for precautions in the use of the thermistor and the preparation of the teeth for tempera- ture determination. The thermistor proved to be so temperature sensitive that the presence of a small amount of saliva on the tooth or the disturb- ance of local air current in the room could influence the results. Error from

evaporative cooling could be avoided by careful drying of the tooth and by shielding from ambient air move- ments. Relative ease of use came with experience. Most of these technical problems are being eliminated in more recent models of the testing equipment.

This study was conducted on the predicate that a pulpless tooth has a seriously impaired internal blood sup- ply. If a pulpless tooth and a vital contralateral tooth are cooled simul- taneously to below body temperature, the pulpless tooth should have a slower rate of return to body temperature be- cause of its reduced circulation.

Table 1 demonstrates the small dif- ference in tooth temperature between" : two vital contralateral teeth within the same individual. The sample teeth listed in Table 1 were selected care- fully to compare with those of the test group in Table 2 (for example, similar numbers and varieties of teeth from selected areas of the dentition). Table 1 shows that vital contralateral teeth do have a variable range of tem- perature difference, but the range is small when compared with that of the test patients in Table 2.

Table 2 indicates that in 20 pa- tients, the temperature difference be- tween the tooth suspected of being pulpless and its vital counterpart had a range of from 0.13 to 0.75C. These

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JOURNAL OF ENDODONTICS 1 VOL 2, NO 5, MAY 1976

Patient No.

Table I * Comparison of control patients.

Temperature comparison between vital contralateral teeth

Age No. Degrees(C) No. Degrees(C)

I 18 8 27.5 9 27.5 2 20 8 27.75 9 27.62 3 32 8 28.0 9 28.38 4 31 8 27.38 9 27.38 5 30 8 28.25 9 28.38 6 19 7 28.75 10 28.87 7 26 7 28.5 10 28.63 8 27 6 29.25 11 29.12 9 28 21 31.0 28 31.0

10 30 22 29.25 27 29.25 11 18 22 31.0 27 31.0 12 36 23 30.5 26 30.5 13 32 23 29.25 26 29.37 14 20 24 28.75 25 28.75 15 19 7 29.0 10 29.0 16 23 6 29.5 11 29.63 17 30 24 28.5 25 28.63 18 27 23 30.0 26 30.0 19 28 21 30.5 28 30.63 20 36 6 28.75 11 28.75 21 20 7 28.0 10 29.0 22 23 8 27.75 9 27.87 23 27 24 29.0 25 29.0

Temperature differential

0 0.13 0.38 0 0.13 0.12 0.13 0.13 0 0 0 0 0.12 0 0 0.13 0.13 0 0.13 0 0 0.12 0

Patient No. Age

Table 2 �9 Comparison of test patients.

Temperature comparison of involved vs contralateral control

Canal contents Normal-vital Involved Temperature of involved

No. Degrees(C) No. Degrees(C) differential tooth

1 17 8 28.25 9 27.50 2 62 7 31.0 10 30.5 3 23 9 29.25 8 28.25 4 27 8 27.25 9 27.5 5 19 8 30.50 9 30.0 6 29 I0 28.0 7 27.87 7 32 8 28.25 9 27.5 8 53 I0 29.25 7 28.75 9 16 7 29.25 10 28.50

10 29 9 30.50 8 31.0 1I 27 24 29.50 25 30.0

12 56 6 28.0 11 27.5 13 15 9 30.5 8 30.0 14 48 6 30.62 11 30.0 15 39 25 30.13 24 29.63 16 23 24 30.5 25 29.87 17 27 25 28.25 24 27.63 18 30 26 28.25 22 27.75 19 22 28 28.25 21 27.63 20 49 9 30.25 8 29.63 21 53 7 29.0 10 28.5 22 36 11 31.0 6 30.5 23 21 10 30.87 7 30.25

-0 .75 -0 .50 -0 .50 +0.25 -0 .50 -0 .13 -0 .75 -0 .50 -0 .75 + 0.50 +0.50

-0 .50 -0 .50 -0 .62 -0 .50 -0 .63 -0 .63 -0 .50 -0 .62 -0 .63 -0 .50 -0 .50 -0 .62

Wet, necrosis Calcified Wet, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Wet, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Hemorrhage, Granulationlike tissue in apical third Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis Dry, necrosis

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JOURNAL OF ENDODONTICS I VOL 2, NO 5, MAY 1976

temperature differences were always greater than the average in the control patients. In the remaining three pa- tients of the test group, a temperature reversal was observed in which the endodontically involved tooth returned to a higher temperature than did the vital control tooth within a given period of time (3'A to 5 minutes). In one of these three teeth, the contents of the canal hemorrhaged and re- sembled granulationlike tissue, so it was not avascular.

The data from Tables 1 and 2 were analyzed statistically and results showed that there is a statistically significant difference in .temperature between a vital and a pulpless tooth in the same individual when taking normal variation into account. A matched t test disclosed: t22 = 5.71.

The advantages of this method in- clude the following: It avoids false diagnosis as a result of peripheral vasoconstriction arising from patients' reflex response to apprehension. It is well suited to special diagnostic prob- lems such as pedodontic patients in whom neurologic maturation has not as yet taken place and in cases where the electric pulp test is inconclusive following a traumatic blow to the dentition. Another example is a frac- tured mandible or mandibular resection where innervations to the teeth may be impaired.

S u m m a r y

A test group of 23 patients was selected from 115 patients who re- quired endodontic therapy. Another group of 23 patients who did not re- quire endodontic therapy and who possessed vital, homologous contrala- teral teeth acted as a control group. In both groups the same procedures were used; the teeth were cooled to below body temperature and the sur- face temperatures were recorded by a thermistor as the teeth approached body temperature during rewarming at selected time intervals. The results were analyzed statistically and the data were found to be statistically significant. The results of this study indicate that there is a relationship between pulp vitality and tooth temp- erature and this relationship may provide a useful means of determining pulp vitality.

*Victory Engineering Corp., Victory Road, Springfield, NJ.

The authors express their appreciation to Dr. Larry L. Laster for performing the statistical evaluations.

From a paper submitted by Dr. Stoops in partial fulfillment of the requirements for the Certificate of Endodontics, Uni- versity of Pennsylvania School of Dental Medicine, Philadelphia.

Dr. Stoops is in private practice in Westlake Village, Calif, and is on the teaching staff, department of endodontics, UCLA School of Dentistry. Dr. Scott is

in the department of physiology, Uni- versity of Pennsylvania Medical School, Philadelphia. Reprint requests should be directed to Dr L.C. Stoops, 1672 Devon- shire Court, Westlake Village, Calif 91361.

References

1. Scott, D. Jr.; Scheinen A.; Karjalain- en, S.; and Edwall, L. Influence of sym- pathetic nerve stimulation of flow veloci- ty in pulpal vessels. Acta Odontol Scand 30:227 May 1972.

2. Edwall, L., and Scott, D. Jr. In- fluence of changes in microcirculation on the excitability of the sensory unit in the tooth of the cat. Acta Physiol Scand 82:555 Sept 1971.

3. Williams, K.L.; Williams, F.L.; and Handley, R.S. Infra-red radiation ther- mometry in clinical practice. Lancet 2:959 Oct 1960.

4. Barnes, R.B. Thermography of the human body. Science 140:870 May 1963.

5. Barnes, R.B., and Gershon-Cohn, J. Clinical Thermography. JAMA 185:949 Sept 1963.

6. Gershon-Cohn, J., and Haberman, J.D. Medical thermography. Am J Roent- gen 94:735 July 1965.

7. Whipple, H.E. Thermography and its clinical applications. Ann NY Acad Sci 121:99 June 1964.

8. Crandell, C.E., and Hill, R.P. Ther- mography in dentistry: a pilot study. Oral Surg 21:316 March 1966.

9. Howell, R.M.; Duell, R.C.; and Mullaney, T.P. The determination of pulp vitality by thermographic means using cholesteric liquid crystals. A pre- liminary study. Oral Surg 29:763 May 1970.

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