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Reliability and validity of a digital pulp tester as a test standard for measuring sensory perception
0099-2399/88/1407-0352/$02.00/0 JOURNAL OF ENDODONTIO$ Copyright 9 1988 by The American Association of Endodontists
Printed in U.S.A.
VOL. 14, No. 7, JULY 1988
CLINICAL ARTICLE Reliability and Validity of a Digital Pulp Tester as a Test Standard for Measuring Sensory Perception Ernest A. Lado, DDS, Arthur F. Richmond, and Ronald G. Marks, PhD
A study of eight subjects was conducted to determine the reliability of a digital pulp tester as a test standard in measuring pulp responses in healthy teeth. The maxillary anterior incisors of four males and four females were electrically stimulated in a randomized experimental design and readings were recorded at three levels of perception (threshold, localization, and tolerance). Voltage and digital readings were recorded at each level of stimulation. Pearson correlation coefficients between voltage and digital readings were computed and found to range from 0.51 to 0.99. Correlation coefficients for perception indices ranged from 0.17 to 0.90 between trials for digital readings and from 0.05 to 0.93 for voltage readings. These large differences in correlation coefficients indicate that in spite of the digital pulp tester being a reliable tool for evaluating pulp vitality, it is of little value in measuring nervous perception in healthy teeth over repeated trials.
old and tolerance. Standard clinical pulp testing methods were used and the digital readout served as the data (S. Seltzer, personal communication). The digital readings are not a measurement of standard physical units but do represent relative changes in voltage as proposed by Mumford (4). The purpose of this study was to test the reliability of the digital pulp tester as a test standard in measuring perception levels of threshold, localization, and tolerance in healthy teeth. Two specific questions to be answered were: What was the correlation between digital and voltage measurements and were the measurements reproducible over time on the same subject?
E X P E R I M E N T A L DESIGN The maxillary incisors of eight subjects were electrically challenged at three separate sessions (trials) 1 wk apart. At each session, the subjects were asked to identify three levels of perception for each incisor as follows: 1: threshold stimuhis--lowest value at which the stimulus was perceived; 2: localization--lowest value at which the subject attempted to identify the challenged tooth; and 3: tolerance--highest value the subject was able to withstand. Subjects were junior and senior dental students (four females and four males) that had unrestored or minimally restored healthy maxillary incisors. Institutional Review Board approval was attained and all subjects were financially compensated at the end of the final (third) session. Health histories, oral examinations, and pulp tests as well as periodontal probings and radiographs were made and found to be within normal limits on all subjects. Subjects were required to be in excellent health and were instructed to refrain from any medications, especially analgesics, 24 h prior to each session. Individualized, clear acrylic stints, made from alginate impressions, were used throughout the study to ensure that the location of the electrical contacts remained constant between trials. The stints extended from cuspid to cuspid and were trimmed so as not to contact the gingiva. Electrical contacts were made with toothpaste through "windows" the size of a #8 round bur and were centrally located on the facial aspect of each tooth.
Numerous investigators have attempted to correlate pulp pathosis and nerve responses to electrical stimulation with varying degrees of success. Vargas and Vivaldi (1) concluded that there is a high correlation of the accommodation index with pulp histology, while clinical diagnosis showed a low correlation. Reynolds (2), on the other hand, found no correlation between pulp pathosis and dial position on a vitalometer in teeth with vital pulps but reported a 100% accuracy in diagnosing teeth with nonvital pulps. Others (3) have concluded that the degree of pulpal health cannot be determined by electrical stimulation. Mumford (4) proposed that pulp testing would be a more dependable diagnostic method if pain threshold values could be established for normal teeth. He said it would be better if results were reported in standard physical units and expressed an opinion that relative changes in the threshold values could be of value in determining the efficacy of analgesics. In a recent study (5), a digital electric pulp tester was used to measure the effects of dietary manipulation on pain thresh-
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Vol. 14, No. 7, July 1988
Electric Pulp Tester as a Test Standard
The incisors were connected, from the stints, to a control panel by a four-strand insulated copper wire. At the control panel, a digital pulp tester (Analytic Technology Co., Redmond, WA) was randomly connected to one of four male prongs (each corresponding to a specific incisor) without the subjects knowledge as to which tooth was to be challenged. A ground plate (coated with a conduction jel) was strapped to the left arm rest of the chair. This plate was connected to the handle of the pulp tester so as to complete the circuit when the subject placed his left hand on the ground plate. Thus, the subject had control over the completion of the circuit and could break it at will by raising his left hand (Fig. 1). Prior to inserting the stint, a rubber dam was placed to ensure a dry field. An oscilloscope was connected in parallel and used to record the actual voltage at any point in time. The pulp tester is reported to have an integrated circuit that automatically increases the output voltage from 0 to 230 V at an output impedance of 140K ohms, once the circuit is closed. In this study the dial that controlled the rate at which the output voltage increased was set at its lowest setting and it took about 26 s for the maximum output voltage to be reached. The relationship between the output voltage and digital reading took on a mild S shape with the greatest slope being found in the middle ranges (30 to 60), while the low and high range of the light-emitting diode (LED) display tended to be fiat. That is, the change in voltage at the midrange was greater than at the low or high end for a corresponding change in the digital LED reading. These findings were consistent with reported characteristics of the pulp tester used in this study (6).
353
Subjects were given standard instructions at the beginning of each session. Once the apparatus was in place, each subject was told that upon contacting the ground plate with his left hand, the circuit would be completed. They were instructed to indicate three levels of perception as follows: 1. Threshold stimulus: The subject was asked to raise his right hand as soon as he thought he felt a stimulus. 2. Localization: The subject was asked to point to the tooth or quadrant when he thought he could identify the tooth. 3. Tolerance: The subject was asked to lift his left hand when he could no longer stand the stimulus, thus breaking the circuit. One investigator (E. L.) placed the rubber dam, connected the circuit, and recorded the readings from the digital LED display of the pulp tester while a second investigator (A. R.) recorded the voltages from the oscilloscope. An independent recorder was not used due to limited space. Also since recording the values involved minimal interpretation, it was felt that an independent recorder was not necessary. STATISTICAL M E T H O D S Descriptive statistics of the raw data are given and analyses of the raw data were performed using Pearson's product moment correlation coefficients (r) to determine the relationship between the digital and voltage measurements and the reproducibility of all measurements over time (7). Although the sample sizes were small, correlations were also computed to determine differences according to gender. RESULTS
~
',
SUBJECT
Table 1 details the means, ranges, and confidence intervals calculated for threshold readings by sex. Table 2 details the same readings for threshold when grouped by trial. Table 3 details the threshold readings when grouped by tooth. Table 4 presents the correlations between digital and voltage measurements for threshold, localization, and tolerance data for each tooth at three different times and for the average of the three times. The correlations between voltage and digital readings for males and females combined ranged from 0.71 to 0.99 (p < 0.05) for all but two calculations. The two nonsignificant correlations were for threshold data (the second replicate for the central incisor (r = 0.64, p = 0.09) and the third replicate for the lateral teeth (r = 0.5 l, p = 0.21)). The most consistently high correlations were for the left lateral incisors in that all correlations were over 0.90, except for a single nonsignificant correlation. The correlations were very similar for both left and right central incisors and the correlations for the right lateral incisors seemed slightly less than those for the central incisors. TABLE 1. Threshold according to sex Mean
FIG 1. A control panel provided a means of connecting the pulp tester probe to any one of four incisors without the awareness of subjects as to the tooth being stimulated. Subjects could break the circuit at will by removing their left hand from the ground plate. An oscilloscope was wired in parallel so as to provide actual voltages that were recorded and correlated to the digital reading on the electric pulp tester.
Digital Males Females Voltage Males Females
Range
2 x SD*
29.6 23.0
12-51 11-38
20.2 14.2
55.8 36.2
18-170 12-95
77.1 29.3
* Two times the standarddeviation(confidence interval).
354
Lado et al.
Journal of Endodontics
Table 4 also presents the correlations computed for males and females separately. There were only four males and four females so statistical significance would normally be difficult to obtain. The results for males alone parallel the overall
results for the whole group except that fewer correlations are significant, possibly due to the reduced sample size. It is interesting to note, however, that the correlations for females alone were consistently higher than for males and most exceed 0.90. Table 5 presents a comparison of digital measurements between trials (1 and 2; 1 and 3; 2 and 3). The majority of correlations were less than 0.70 and were not statistically significant (p > 0.05) for the combined male-female group. However, when the males and females were examined separately, the females have more reproducible results than males in that there were more correlations above 0.85. Table 6 presents a comparison of voltage measurements between trials (1 and 2; 1 and 3; 2 and 3). Again, the majority of correlations were less than 0.70 (p > 0.05) for the combined group and females had more reproducible results than males. A second parameter examined was the subjects's ability to localize the challenged tooth. Subjects identified the tooth by pointing and overall they were able to localize accurately the simulated tooth only 60.4% of the time. The stimulated quadrant was correctly identified 95.8% of the time. In four instances the contralateral side was mistakenly identified. Each of these cases of identifying the wrong quadrant occurred with central incisors, and one individual (male) accounted for two of the four misses.
TABLE 2. Thresholds grouped by tdal
Digital Trial 1 Trial 2 Trial 3 Voltage Trial 1 Trial 2 Trial 3
Mean
Range
2 x SD*
26.7 24.7 27.7
13-49 11-45 12-51
15.1 15.8 23.7
45.2 40.0 52.8
20-148 18-125 12-170
48.9 47.9 80.4
* Two times the standard deviation (confidence interval).
TABLE 3. Thresholds grouped by tooth Mean Digital L L t incisors LC incisors RC incisors RL incisors Voltage LL incisors LC incisors RC incisors RL incisors
Range
2 x SD*
25.5 26.1 25.4 28.3
13-38 14-50 12-51 11-45
13.6 18.2 22.2 19.8
42.0 42.8 48.6 50.5
20-95 20-125 12-170 18-110
38.6 52.8 88.4 56.2
DISCUSSION It should be evident from Tables 1 to 3 that the readings (both digital and voltage) vary considerably not only between
* Two times the standard deviation (confidence interval). t LL, left lateral; LC, left central; RC, right central; RL, right lateral.
TABLE 4. Correlations of digital and voltage readings Right Trials
Lateral
1 Threshold
Left
2
0.74* 0.72 0.04t 0.05
Localization 0.83 0.01
0.87 0.006
3
Central
X
1
2
3
Central
X
1
2
Lateral
3
X
1
2
3
0.84 0.01
0.96 0.86 0.0002 0.01
Males and females combined 0.95 0.73 0.97 0.92 0.64 0.88 0.89 0.94 0.91 0.0003 0.04 0.0001 0.001 0.09 0.003 0.0003 0.0006 0.002
0.74 0.04
0.84 0.008
0.99 0.72 0.0001 0.05
0.98 0.96 0.0001 0.0002
0.83 0.01
0.82 0.02
0.93 0.93 0.96 0.96 0.95 0.0007 0.0009 0.0002 0.0002 0.0004
0.93 0.82 0.0009 0.02
0.97 0.95 0.99 0.94 0.98 0.0001 0.0003 0.0001 0.0004 0.0001
0.49 0.51
0.97 0.04
0.97 0.03
0.99 0.007
0.99 0.02
0.45 0.55
0.98 0.02
0.98 0.03
0.98 0.02
0.99 0.009
0.99 0.02
0.98 0.02
0.86 0.007
0.51 0.21
0.96 0.0002
Tolerance
0.89 0.96 0.71 0.003 0.0001 0.05
0.94 0.95 0.99 0.82 0.0005 0.0003 0.0001 0.02
0.98 0.99 0.0001 0.0001
Threshold
0.66 0.36
0.45 0.55
0.79 0.21
0.99 0.01
0.81 0.19
0.98 0.02
0.67 0.33
0.97 0.03
Localization 0.77 0.24
0.53 0.47
0.68 0.33
0.96 0.05
0.84 0.16
0.99 0.007
0.68 0.32
0.98 0.02
0.96 0.05
-0.35 0.65
0.98 0.02
Tolerance
0.97 0.04
0.77 0.24
0.46 0.54
0.87 0.13
0.96 0.04
0.98 0.02
0.73 0.27
0.94 0.06
0.99 0.009
-0.17 0.83
0.99 0.99 0.008 0.02
0.99 0.008
0.99 0.005
0.99 0.004
0.99 0.0007
Threshold
0.98 0.03
0.99 0.02
0.97 0.03
0.96 0.04
0.96 0.04
0.79 0.21
Females only 0.99 0.98 0.98 0.88 0.003 0.03 0.02 0.12
0.13 0.87
0.99 0.01
0.97 0.03
0.95 0.05
0.49 0.51
0.99 0.005
Localization 0.98 0.02
0.97 0.03
0.99 0.98 0.009 0.02
0.94 0.06
0.99 0.02
0.98 0.03
0.99 0.003
0.99 0.004
0.77 0.24
0.99 0.002
0.95 0.05
0.95 0.05
0.92 0.08
0.99 0.0009
Tolerance
0.99 0.99 0.99 0.0002 0.007 0.002
0.98 0.02
0.99 0.004
0.99 0.99 0.99 0.008 0.0005 0.007
0.99 0.002
0.98 0.03
0.99 0.97 0.0001 0.04
0.99 0.002
0.99 0.004
0.99 0.003
0.94 0.07
* Correlation coefficient. t Level of statistical significance.
Males only 0.94 0.06
0.99 0.005
Electric Pulp Tester as a Test Standard
Vol. 14, No. 7, July 1988
355
TABLE 5. Correlations of digital readings between trials Right Trials
Left
Lateral 1-2
1-3
Central 2-3
1-2
1-3
Central 2-3
1-2
1-3
Lateral 2-3
1-2
1-3
2-3
0.31 0.46
0.51 0.20
0.84 0.009
0.69 0.06
0.31 0.45
0.89 0.003
0.53 0.18
Males and females combined 0.84 0.86 0.63 0.87 0.008 0.007 0.09 0.006
-0.17 0.70
0.35 0.40
0.36 0.38
0.45 0.26
0.81 0.02
0.78 0.03
0.43 0.29
0.86 0.007
0.48 0.23
0.24 0.57
0.60 0.12
0,56 0.15
Tolerance
0.54 0.17
0.32 0.44
0.21 0.61
0.56 0,14
0.80 0.02
0.87 0.005
0.54 0,17
0.90 0.002
0.69 0.06
0.42 0.29
0.78 0.02
0.65 0.09
Threshold
-0.24 0.76
-0.45 0.55
0.92 0.08
0.67 0.33
0.94 0.06
Females only 0.85 0.98 0.15 0.02
0.65 0.35
0.76 0.24
0.53 0.47
0.88 0.12
0.73 0.27
Localization
-0.94 0.06
-0.84 0.16
0.69 0.31
0.83 0.17
0.98 0.02
0.84 0.16
0.89 0.11
0.72 0.28
0.92 0.08
0.40 0.60
0.61 0.39
0.60 0.40
Tolerance
0.56 0.44
0.75 0.25
0.92 0.08
0.92 0.08
0.97 0.03
0.98 0.02
0.88 0.12
0.85 0.15
0.99 0.01
0.71 0.29
0.78 0.22
0.93 0.07
Threshold
0.82 0.18
0.97 0.03
0.79 0.21
0.43 0.57
0.83 0,17
Males only 0.85 0.72 0.15 0.29
0.92 0.08
0.40 0.60
0.24 0.76
0.80 0.20
0.57 0.43
Localization
0.79 0.21
0.84 0.16
0.36 0.64
0.19 0,81
0.76 0.24
0.77 0.24
0.55 0,46
0.90 0.11
0.41 0,59
0.06 0.94
0.67 0.33
0.51 0.49
Tolerance
0.92 0.09
0.23 0.79
-0.13 0.87
0,11 0.89
0.68 0.32
0.69 0.31
0.25 0.75
0.95 0.05
0.08 0.92
-0.46 0.54
0.86 0.14
-0.01 0.99
Threshold Localization
0.35* 0.40t
* Correlation coefficient. t Level of statistical significance.
TABLE 6. Correlations of voltage readings between trials Left
Right Trials
Lateral 1-2
1-3
Central 2-3
1-2
1-3
Central 2-3
1-2
1-3
Lateral 2-3
1-2
1-3
2-3
0.13 0.77
0.22 0.60
-0.05 0.91
Males and females combined 0.74 0.21 -0.08 0.65 0.04 0.63 0.86 0.08
-0.46 0.25
0.08 0.86
0.63 0.09
-0.17 0.70
0.85 0.008
0.11 0.80
0.06 0.89
0.78 0.03
Tolerance
0.29 0.49
0.55 0.17
0.52 0.19
0.21 0.61
0.93 0.0009
0.41 0.32
0.45 0.26
0.86 0.006
0.13 0.77
0.19 0.66
0.82 0.02
0.45 0.26
Threshold
-0.45 0.54
-0.61 0.31
0.71 0.29
0.86 0.14
0.90 0.10
0.73 0.27
0.57 0.43
0.48 0.52
0.89 0.11
0.44 0.56
Localization
-0.88 0.12
-0.78 0,22
0.85 0.15
0.60 0.40
0.87 0.13
0.76 0.24
0.89 0.11
0.18 0.82
0.45 0.55
-0.01 0.99
0.01 0,99
0.18 0.82
Tolerance
0.46 0.54
0.74 0.26
0.94 0.06
0.93 0.07
0.89 0.11
0.99 0.01
0.93 0.07
0.81 0.19
0,93 0.07
0.66 0.34
0.57 0.43
0.94 0.06
Threshold
-0.23 0.77
0.98 0.02
-0.20 0.80
-0.27 0.73
0.90 0.10
Males only 0.03 0.11 0.97 0.89
0.62 0.38
-0.57 0.43
0.09 0.91
0.85 0.15
0.43 0.57
Localization
0.11 0.89
0.93 0.07
0.24 0.76
-0.43 0.57
0.90 0.10
-0.04 0.96
-0.79 0.21
0.77 0.23
-0.98 0.02
0.01 0.99
0.82 0,18
0.35 0.65
Tolerance
0.50 0.50
0.86 0.14
0.12 0.88
-0.32 0.68
0.94 0.06
-0.05 0.95
0.06 0.94
0.97 0.03
0.25 0.75
-0.48 0.57
0.93 0.07
-0.15 0.85
Threshold Localization
0.27* 0.51 t
* Correlation coefficient, t Level of statistical significance.
Females only 0.92 0.77 0.08 0.23
-0.58 0.14
0.28 0.50
0.90 0.003
0.50 0.21
-0.26 0.53
0.09 0.83
0.70 0.06
0.36 0.38
356
Lado et al.
teeth but also between individuals and trials. Several studies have shown arbitrary units or voltages to be unsatisfactory in measuring pain perception (4, 8-10). The wide variation in our readings may be attributed to the impedance of enamel and dentin. Mumford (4) has reported the resistivity of enamel to range from 2.67 x l06 to 6.9 x 106 ohms/cm 2 and dentin from 11 x 103 to 52 x l 0 3 ohms/cm 2. Specimens that were allowed to dry exhibited considerably higher resistances (11). Since a rubber dam was used to ensure a dry field and thus prevent shorting the stimulus through the periodontium or adjacent teeth, it was impossible to maintain a uniform hydration between teeth/trials. The increased resistance, that results from desiccation, may very well have contributed to the wide confidence intervals found in this study. An examination of the difference in means between males and females (Table 1) shows a 65% higher average voltage for males. This could be interpreted as a significant difference but when Student's t test was applied to the raw data, chance could not be ruled out (p = 0.18). The apparent differences might be attributed to variations in thickness of enamel but with a sample size of only four subjects per group it is not possible to draw any definitive conclusions regarding variations due to sex. Although the means for threshold values grouped by trial and tooth (Tables 2 and 3) are relatively similar, the range and standard deviations are so large that the pulp tester cannot be considered to be a reliable test standard in measuring levels of stimulation. The results presented in Table 4 indicate a relatively high correlation between digital and voltage readings. Care must be taken not to attach too much significance to this finding in clinical diagnosis. Although one tooth may respond at a much higher or lower level than a contralateral or test tooth, there can be many other factors other than the status of the pulp causing this difference. The results presented in Tables 5 and 6 indicate low correlations between trials for both digital and voltage readings. If the pulp tester was a reliable test standard, high correlations between trials would have been found. As mentioned, dehydration of enamel causes a considerable increase in resistance and thus may have been the cause of the low correlations found between trials. The ability to localize an electrical stimulus to a given quadrant was high but the ability to localize the specific tooth was little better than guesswork (60%). Results similar to these were reported by Friend and Glenwright (12) when they found the central incisor (when electrically stimulated) could be correctly identified 62.5% of the time. They also found a decreasing accuracy as teeth away from the midline were stimulated. This inability to localize pulpal pain is evidenced in clinical experience and has been attributed to the anatomical convergence of first- and second-order fibers of the trigeminal system (13, 14).
Journal of Endodontics
CONCLUSIONS It was determined that a high correlation exists between voltage and digital measurements; however, individual recordings are not reproducible over time on the same subject. Of clinical relevance is the notion that comparing digital readings for teeth with suspected diseased pulps to "normal" pulps may be of minimal value since many factors other than the status of the pulp have an effect upon impedance and thus affect the reading obtained. It has been previously reported that the pulp tester should be used only to establish the presence of vital pulp tissue and high or low readings should not be used to determine the overall health of that tissue (15). Furthermore, although the digital pulp tester may be an excellent tool to determine pulp vitality on fully developed permanent teeth, the results of this study do not show it to be a reliable test standard for measuring pain perception. This study was supported by a Biomedical Research Grant from the University of Florida, Gainesville, FL. Dr. Lade is assistant professor, Department of Oral Diagnostic Sciences, College of Dentistry, University of Florida, Gainesville, FL. Mr. Richmond is a research assistant, Department of Oral Biology, College of Dentistry, University of Florida. Dr. Marks is associate professor, Division of Biostatistics, Department of Statistics, University of Florida.
References 1. Vargas FF, Vivaldi LM. Correlation between nervous eccomodation, symptomatology, and histology of normal and pathologic tooth pulp; Its application to electrodiagnosis. J Dent Res 1959;38:866-80. 2. Reynolds RL. THe determination of pulp vitality by means of thermal and electric stimuli. Oral Surg 1986;22:231-40. 3. Matthews B, Searle BN, Adams D, Linden R. Thresholds of vital and non-vital teeth to stimulation with electric pulp testers. Br Dent J 1974;137:3535. 4. Mumford JM. Pain threshold of normal human anterior teeth. Arch Oral Biol 1963;8:493-501. 5. Seltzer S, Marcus R, Stoch R. Perspectives in the control of chronic pain by nutritional manipulation. Pain 1981 ;11:141-8. 6. Kitamura T, Takahashi T, Horiuchi H. Electrical characteristics and clinical application of a new automatic pulp tester. Quint Int 1983;1:45-53. 7. Mendenhall W. Introduction to probability and statistics. Belmont, CA: Duxbury Press, 1979:350-3. 8. Matthews B, Horiuchi H, Greenwood F. The effects of stimulus polarity and electrode area on the threshold to monopolar stimulation of teeth in human subjects, with some preliminary observations on the use of a bipolar pulp tester. Arch Oral Bio11974;19:35-42. 9. Mumford JM, Lewis DG. Electronic tooth stimulator for pain research. Biomed Eng (Bed) 1976;11:22-3. 10. McGrath PA, Gracely RH, Dubner R, Heft MW. Nonpain and pain sensations evoked by tooth pulp stimulation. Pain 1983;15:377-88. 11. Mumford JM. Resistivity of human enamel and dentine. Arch Oral Biol 1967;12:925-7. 12. Friend LA, Glenwright HD. An experimental investigation into the localization of pain from the dental pulp. Oral Surg 1968;25:765-74. 13. Mumford JM, Newton AV. Convergence in the trigeminal system following stimulation in human teeth. Arch Oral Bio11971 ;16:1089-97. 14. Mumford JM, Newton AV. Trigeminal convergence from human teeth influence of contralateral stimulation and stimulus frequency on pain perception threshold. Arch Oral Bio11974;19:145-9. 15. Lade EA. Use, abuse and misuse of the electric pulp tester. Oper Dent 1983;8:140-1.
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VOL. 14, No. 7, JULY 1988
CLINICAL ARTICLE Reliability and Validity of a Digital Pulp Tester as a Test Standard for Measuring Sensory Perception Ernest A. Lado, DDS, Arthur F. Richmond, and Ronald G. Marks, PhD
A study of eight subjects was conducted to determine the reliability of a digital pulp tester as a test standard in measuring pulp responses in healthy teeth. The maxillary anterior incisors of four males and four females were electrically stimulated in a randomized experimental design and readings were recorded at three levels of perception (threshold, localization, and tolerance). Voltage and digital readings were recorded at each level of stimulation. Pearson correlation coefficients between voltage and digital readings were computed and found to range from 0.51 to 0.99. Correlation coefficients for perception indices ranged from 0.17 to 0.90 between trials for digital readings and from 0.05 to 0.93 for voltage readings. These large differences in correlation coefficients indicate that in spite of the digital pulp tester being a reliable tool for evaluating pulp vitality, it is of little value in measuring nervous perception in healthy teeth over repeated trials.
old and tolerance. Standard clinical pulp testing methods were used and the digital readout served as the data (S. Seltzer, personal communication). The digital readings are not a measurement of standard physical units but do represent relative changes in voltage as proposed by Mumford (4). The purpose of this study was to test the reliability of the digital pulp tester as a test standard in measuring perception levels of threshold, localization, and tolerance in healthy teeth. Two specific questions to be answered were: What was the correlation between digital and voltage measurements and were the measurements reproducible over time on the same subject?
E X P E R I M E N T A L DESIGN The maxillary incisors of eight subjects were electrically challenged at three separate sessions (trials) 1 wk apart. At each session, the subjects were asked to identify three levels of perception for each incisor as follows: 1: threshold stimuhis--lowest value at which the stimulus was perceived; 2: localization--lowest value at which the subject attempted to identify the challenged tooth; and 3: tolerance--highest value the subject was able to withstand. Subjects were junior and senior dental students (four females and four males) that had unrestored or minimally restored healthy maxillary incisors. Institutional Review Board approval was attained and all subjects were financially compensated at the end of the final (third) session. Health histories, oral examinations, and pulp tests as well as periodontal probings and radiographs were made and found to be within normal limits on all subjects. Subjects were required to be in excellent health and were instructed to refrain from any medications, especially analgesics, 24 h prior to each session. Individualized, clear acrylic stints, made from alginate impressions, were used throughout the study to ensure that the location of the electrical contacts remained constant between trials. The stints extended from cuspid to cuspid and were trimmed so as not to contact the gingiva. Electrical contacts were made with toothpaste through "windows" the size of a #8 round bur and were centrally located on the facial aspect of each tooth.
Numerous investigators have attempted to correlate pulp pathosis and nerve responses to electrical stimulation with varying degrees of success. Vargas and Vivaldi (1) concluded that there is a high correlation of the accommodation index with pulp histology, while clinical diagnosis showed a low correlation. Reynolds (2), on the other hand, found no correlation between pulp pathosis and dial position on a vitalometer in teeth with vital pulps but reported a 100% accuracy in diagnosing teeth with nonvital pulps. Others (3) have concluded that the degree of pulpal health cannot be determined by electrical stimulation. Mumford (4) proposed that pulp testing would be a more dependable diagnostic method if pain threshold values could be established for normal teeth. He said it would be better if results were reported in standard physical units and expressed an opinion that relative changes in the threshold values could be of value in determining the efficacy of analgesics. In a recent study (5), a digital electric pulp tester was used to measure the effects of dietary manipulation on pain thresh-
352
Vol. 14, No. 7, July 1988
Electric Pulp Tester as a Test Standard
The incisors were connected, from the stints, to a control panel by a four-strand insulated copper wire. At the control panel, a digital pulp tester (Analytic Technology Co., Redmond, WA) was randomly connected to one of four male prongs (each corresponding to a specific incisor) without the subjects knowledge as to which tooth was to be challenged. A ground plate (coated with a conduction jel) was strapped to the left arm rest of the chair. This plate was connected to the handle of the pulp tester so as to complete the circuit when the subject placed his left hand on the ground plate. Thus, the subject had control over the completion of the circuit and could break it at will by raising his left hand (Fig. 1). Prior to inserting the stint, a rubber dam was placed to ensure a dry field. An oscilloscope was connected in parallel and used to record the actual voltage at any point in time. The pulp tester is reported to have an integrated circuit that automatically increases the output voltage from 0 to 230 V at an output impedance of 140K ohms, once the circuit is closed. In this study the dial that controlled the rate at which the output voltage increased was set at its lowest setting and it took about 26 s for the maximum output voltage to be reached. The relationship between the output voltage and digital reading took on a mild S shape with the greatest slope being found in the middle ranges (30 to 60), while the low and high range of the light-emitting diode (LED) display tended to be fiat. That is, the change in voltage at the midrange was greater than at the low or high end for a corresponding change in the digital LED reading. These findings were consistent with reported characteristics of the pulp tester used in this study (6).
353
Subjects were given standard instructions at the beginning of each session. Once the apparatus was in place, each subject was told that upon contacting the ground plate with his left hand, the circuit would be completed. They were instructed to indicate three levels of perception as follows: 1. Threshold stimulus: The subject was asked to raise his right hand as soon as he thought he felt a stimulus. 2. Localization: The subject was asked to point to the tooth or quadrant when he thought he could identify the tooth. 3. Tolerance: The subject was asked to lift his left hand when he could no longer stand the stimulus, thus breaking the circuit. One investigator (E. L.) placed the rubber dam, connected the circuit, and recorded the readings from the digital LED display of the pulp tester while a second investigator (A. R.) recorded the voltages from the oscilloscope. An independent recorder was not used due to limited space. Also since recording the values involved minimal interpretation, it was felt that an independent recorder was not necessary. STATISTICAL M E T H O D S Descriptive statistics of the raw data are given and analyses of the raw data were performed using Pearson's product moment correlation coefficients (r) to determine the relationship between the digital and voltage measurements and the reproducibility of all measurements over time (7). Although the sample sizes were small, correlations were also computed to determine differences according to gender. RESULTS
~
',
SUBJECT
Table 1 details the means, ranges, and confidence intervals calculated for threshold readings by sex. Table 2 details the same readings for threshold when grouped by trial. Table 3 details the threshold readings when grouped by tooth. Table 4 presents the correlations between digital and voltage measurements for threshold, localization, and tolerance data for each tooth at three different times and for the average of the three times. The correlations between voltage and digital readings for males and females combined ranged from 0.71 to 0.99 (p < 0.05) for all but two calculations. The two nonsignificant correlations were for threshold data (the second replicate for the central incisor (r = 0.64, p = 0.09) and the third replicate for the lateral teeth (r = 0.5 l, p = 0.21)). The most consistently high correlations were for the left lateral incisors in that all correlations were over 0.90, except for a single nonsignificant correlation. The correlations were very similar for both left and right central incisors and the correlations for the right lateral incisors seemed slightly less than those for the central incisors. TABLE 1. Threshold according to sex Mean
FIG 1. A control panel provided a means of connecting the pulp tester probe to any one of four incisors without the awareness of subjects as to the tooth being stimulated. Subjects could break the circuit at will by removing their left hand from the ground plate. An oscilloscope was wired in parallel so as to provide actual voltages that were recorded and correlated to the digital reading on the electric pulp tester.
Digital Males Females Voltage Males Females
Range
2 x SD*
29.6 23.0
12-51 11-38
20.2 14.2
55.8 36.2
18-170 12-95
77.1 29.3
* Two times the standarddeviation(confidence interval).
354
Lado et al.
Journal of Endodontics
Table 4 also presents the correlations computed for males and females separately. There were only four males and four females so statistical significance would normally be difficult to obtain. The results for males alone parallel the overall
results for the whole group except that fewer correlations are significant, possibly due to the reduced sample size. It is interesting to note, however, that the correlations for females alone were consistently higher than for males and most exceed 0.90. Table 5 presents a comparison of digital measurements between trials (1 and 2; 1 and 3; 2 and 3). The majority of correlations were less than 0.70 and were not statistically significant (p > 0.05) for the combined male-female group. However, when the males and females were examined separately, the females have more reproducible results than males in that there were more correlations above 0.85. Table 6 presents a comparison of voltage measurements between trials (1 and 2; 1 and 3; 2 and 3). Again, the majority of correlations were less than 0.70 (p > 0.05) for the combined group and females had more reproducible results than males. A second parameter examined was the subjects's ability to localize the challenged tooth. Subjects identified the tooth by pointing and overall they were able to localize accurately the simulated tooth only 60.4% of the time. The stimulated quadrant was correctly identified 95.8% of the time. In four instances the contralateral side was mistakenly identified. Each of these cases of identifying the wrong quadrant occurred with central incisors, and one individual (male) accounted for two of the four misses.
TABLE 2. Thresholds grouped by tdal
Digital Trial 1 Trial 2 Trial 3 Voltage Trial 1 Trial 2 Trial 3
Mean
Range
2 x SD*
26.7 24.7 27.7
13-49 11-45 12-51
15.1 15.8 23.7
45.2 40.0 52.8
20-148 18-125 12-170
48.9 47.9 80.4
* Two times the standard deviation (confidence interval).
TABLE 3. Thresholds grouped by tooth Mean Digital L L t incisors LC incisors RC incisors RL incisors Voltage LL incisors LC incisors RC incisors RL incisors
Range
2 x SD*
25.5 26.1 25.4 28.3
13-38 14-50 12-51 11-45
13.6 18.2 22.2 19.8
42.0 42.8 48.6 50.5
20-95 20-125 12-170 18-110
38.6 52.8 88.4 56.2
DISCUSSION It should be evident from Tables 1 to 3 that the readings (both digital and voltage) vary considerably not only between
* Two times the standard deviation (confidence interval). t LL, left lateral; LC, left central; RC, right central; RL, right lateral.
TABLE 4. Correlations of digital and voltage readings Right Trials
Lateral
1 Threshold
Left
2
0.74* 0.72 0.04t 0.05
Localization 0.83 0.01
0.87 0.006
3
Central
X
1
2
3
Central
X
1
2
Lateral
3
X
1
2
3
0.84 0.01
0.96 0.86 0.0002 0.01
Males and females combined 0.95 0.73 0.97 0.92 0.64 0.88 0.89 0.94 0.91 0.0003 0.04 0.0001 0.001 0.09 0.003 0.0003 0.0006 0.002
0.74 0.04
0.84 0.008
0.99 0.72 0.0001 0.05
0.98 0.96 0.0001 0.0002
0.83 0.01
0.82 0.02
0.93 0.93 0.96 0.96 0.95 0.0007 0.0009 0.0002 0.0002 0.0004
0.93 0.82 0.0009 0.02
0.97 0.95 0.99 0.94 0.98 0.0001 0.0003 0.0001 0.0004 0.0001
0.49 0.51
0.97 0.04
0.97 0.03
0.99 0.007
0.99 0.02
0.45 0.55
0.98 0.02
0.98 0.03
0.98 0.02
0.99 0.009
0.99 0.02
0.98 0.02
0.86 0.007
0.51 0.21
0.96 0.0002
Tolerance
0.89 0.96 0.71 0.003 0.0001 0.05
0.94 0.95 0.99 0.82 0.0005 0.0003 0.0001 0.02
0.98 0.99 0.0001 0.0001
Threshold
0.66 0.36
0.45 0.55
0.79 0.21
0.99 0.01
0.81 0.19
0.98 0.02
0.67 0.33
0.97 0.03
Localization 0.77 0.24
0.53 0.47
0.68 0.33
0.96 0.05
0.84 0.16
0.99 0.007
0.68 0.32
0.98 0.02
0.96 0.05
-0.35 0.65
0.98 0.02
Tolerance
0.97 0.04
0.77 0.24
0.46 0.54
0.87 0.13
0.96 0.04
0.98 0.02
0.73 0.27
0.94 0.06
0.99 0.009
-0.17 0.83
0.99 0.99 0.008 0.02
0.99 0.008
0.99 0.005
0.99 0.004
0.99 0.0007
Threshold
0.98 0.03
0.99 0.02
0.97 0.03
0.96 0.04
0.96 0.04
0.79 0.21
Females only 0.99 0.98 0.98 0.88 0.003 0.03 0.02 0.12
0.13 0.87
0.99 0.01
0.97 0.03
0.95 0.05
0.49 0.51
0.99 0.005
Localization 0.98 0.02
0.97 0.03
0.99 0.98 0.009 0.02
0.94 0.06
0.99 0.02
0.98 0.03
0.99 0.003
0.99 0.004
0.77 0.24
0.99 0.002
0.95 0.05
0.95 0.05
0.92 0.08
0.99 0.0009
Tolerance
0.99 0.99 0.99 0.0002 0.007 0.002
0.98 0.02
0.99 0.004
0.99 0.99 0.99 0.008 0.0005 0.007
0.99 0.002
0.98 0.03
0.99 0.97 0.0001 0.04
0.99 0.002
0.99 0.004
0.99 0.003
0.94 0.07
* Correlation coefficient. t Level of statistical significance.
Males only 0.94 0.06
0.99 0.005
Electric Pulp Tester as a Test Standard
Vol. 14, No. 7, July 1988
355
TABLE 5. Correlations of digital readings between trials Right Trials
Left
Lateral 1-2
1-3
Central 2-3
1-2
1-3
Central 2-3
1-2
1-3
Lateral 2-3
1-2
1-3
2-3
0.31 0.46
0.51 0.20
0.84 0.009
0.69 0.06
0.31 0.45
0.89 0.003
0.53 0.18
Males and females combined 0.84 0.86 0.63 0.87 0.008 0.007 0.09 0.006
-0.17 0.70
0.35 0.40
0.36 0.38
0.45 0.26
0.81 0.02
0.78 0.03
0.43 0.29
0.86 0.007
0.48 0.23
0.24 0.57
0.60 0.12
0,56 0.15
Tolerance
0.54 0.17
0.32 0.44
0.21 0.61
0.56 0,14
0.80 0.02
0.87 0.005
0.54 0,17
0.90 0.002
0.69 0.06
0.42 0.29
0.78 0.02
0.65 0.09
Threshold
-0.24 0.76
-0.45 0.55
0.92 0.08
0.67 0.33
0.94 0.06
Females only 0.85 0.98 0.15 0.02
0.65 0.35
0.76 0.24
0.53 0.47
0.88 0.12
0.73 0.27
Localization
-0.94 0.06
-0.84 0.16
0.69 0.31
0.83 0.17
0.98 0.02
0.84 0.16
0.89 0.11
0.72 0.28
0.92 0.08
0.40 0.60
0.61 0.39
0.60 0.40
Tolerance
0.56 0.44
0.75 0.25
0.92 0.08
0.92 0.08
0.97 0.03
0.98 0.02
0.88 0.12
0.85 0.15
0.99 0.01
0.71 0.29
0.78 0.22
0.93 0.07
Threshold
0.82 0.18
0.97 0.03
0.79 0.21
0.43 0.57
0.83 0,17
Males only 0.85 0.72 0.15 0.29
0.92 0.08
0.40 0.60
0.24 0.76
0.80 0.20
0.57 0.43
Localization
0.79 0.21
0.84 0.16
0.36 0.64
0.19 0,81
0.76 0.24
0.77 0.24
0.55 0,46
0.90 0.11
0.41 0,59
0.06 0.94
0.67 0.33
0.51 0.49
Tolerance
0.92 0.09
0.23 0.79
-0.13 0.87
0,11 0.89
0.68 0.32
0.69 0.31
0.25 0.75
0.95 0.05
0.08 0.92
-0.46 0.54
0.86 0.14
-0.01 0.99
Threshold Localization
0.35* 0.40t
* Correlation coefficient. t Level of statistical significance.
TABLE 6. Correlations of voltage readings between trials Left
Right Trials
Lateral 1-2
1-3
Central 2-3
1-2
1-3
Central 2-3
1-2
1-3
Lateral 2-3
1-2
1-3
2-3
0.13 0.77
0.22 0.60
-0.05 0.91
Males and females combined 0.74 0.21 -0.08 0.65 0.04 0.63 0.86 0.08
-0.46 0.25
0.08 0.86
0.63 0.09
-0.17 0.70
0.85 0.008
0.11 0.80
0.06 0.89
0.78 0.03
Tolerance
0.29 0.49
0.55 0.17
0.52 0.19
0.21 0.61
0.93 0.0009
0.41 0.32
0.45 0.26
0.86 0.006
0.13 0.77
0.19 0.66
0.82 0.02
0.45 0.26
Threshold
-0.45 0.54
-0.61 0.31
0.71 0.29
0.86 0.14
0.90 0.10
0.73 0.27
0.57 0.43
0.48 0.52
0.89 0.11
0.44 0.56
Localization
-0.88 0.12
-0.78 0,22
0.85 0.15
0.60 0.40
0.87 0.13
0.76 0.24
0.89 0.11
0.18 0.82
0.45 0.55
-0.01 0.99
0.01 0,99
0.18 0.82
Tolerance
0.46 0.54
0.74 0.26
0.94 0.06
0.93 0.07
0.89 0.11
0.99 0.01
0.93 0.07
0.81 0.19
0,93 0.07
0.66 0.34
0.57 0.43
0.94 0.06
Threshold
-0.23 0.77
0.98 0.02
-0.20 0.80
-0.27 0.73
0.90 0.10
Males only 0.03 0.11 0.97 0.89
0.62 0.38
-0.57 0.43
0.09 0.91
0.85 0.15
0.43 0.57
Localization
0.11 0.89
0.93 0.07
0.24 0.76
-0.43 0.57
0.90 0.10
-0.04 0.96
-0.79 0.21
0.77 0.23
-0.98 0.02
0.01 0.99
0.82 0,18
0.35 0.65
Tolerance
0.50 0.50
0.86 0.14
0.12 0.88
-0.32 0.68
0.94 0.06
-0.05 0.95
0.06 0.94
0.97 0.03
0.25 0.75
-0.48 0.57
0.93 0.07
-0.15 0.85
Threshold Localization
0.27* 0.51 t
* Correlation coefficient, t Level of statistical significance.
Females only 0.92 0.77 0.08 0.23
-0.58 0.14
0.28 0.50
0.90 0.003
0.50 0.21
-0.26 0.53
0.09 0.83
0.70 0.06
0.36 0.38
356
Lado et al.
teeth but also between individuals and trials. Several studies have shown arbitrary units or voltages to be unsatisfactory in measuring pain perception (4, 8-10). The wide variation in our readings may be attributed to the impedance of enamel and dentin. Mumford (4) has reported the resistivity of enamel to range from 2.67 x l06 to 6.9 x 106 ohms/cm 2 and dentin from 11 x 103 to 52 x l 0 3 ohms/cm 2. Specimens that were allowed to dry exhibited considerably higher resistances (11). Since a rubber dam was used to ensure a dry field and thus prevent shorting the stimulus through the periodontium or adjacent teeth, it was impossible to maintain a uniform hydration between teeth/trials. The increased resistance, that results from desiccation, may very well have contributed to the wide confidence intervals found in this study. An examination of the difference in means between males and females (Table 1) shows a 65% higher average voltage for males. This could be interpreted as a significant difference but when Student's t test was applied to the raw data, chance could not be ruled out (p = 0.18). The apparent differences might be attributed to variations in thickness of enamel but with a sample size of only four subjects per group it is not possible to draw any definitive conclusions regarding variations due to sex. Although the means for threshold values grouped by trial and tooth (Tables 2 and 3) are relatively similar, the range and standard deviations are so large that the pulp tester cannot be considered to be a reliable test standard in measuring levels of stimulation. The results presented in Table 4 indicate a relatively high correlation between digital and voltage readings. Care must be taken not to attach too much significance to this finding in clinical diagnosis. Although one tooth may respond at a much higher or lower level than a contralateral or test tooth, there can be many other factors other than the status of the pulp causing this difference. The results presented in Tables 5 and 6 indicate low correlations between trials for both digital and voltage readings. If the pulp tester was a reliable test standard, high correlations between trials would have been found. As mentioned, dehydration of enamel causes a considerable increase in resistance and thus may have been the cause of the low correlations found between trials. The ability to localize an electrical stimulus to a given quadrant was high but the ability to localize the specific tooth was little better than guesswork (60%). Results similar to these were reported by Friend and Glenwright (12) when they found the central incisor (when electrically stimulated) could be correctly identified 62.5% of the time. They also found a decreasing accuracy as teeth away from the midline were stimulated. This inability to localize pulpal pain is evidenced in clinical experience and has been attributed to the anatomical convergence of first- and second-order fibers of the trigeminal system (13, 14).
Journal of Endodontics
CONCLUSIONS It was determined that a high correlation exists between voltage and digital measurements; however, individual recordings are not reproducible over time on the same subject. Of clinical relevance is the notion that comparing digital readings for teeth with suspected diseased pulps to "normal" pulps may be of minimal value since many factors other than the status of the pulp have an effect upon impedance and thus affect the reading obtained. It has been previously reported that the pulp tester should be used only to establish the presence of vital pulp tissue and high or low readings should not be used to determine the overall health of that tissue (15). Furthermore, although the digital pulp tester may be an excellent tool to determine pulp vitality on fully developed permanent teeth, the results of this study do not show it to be a reliable test standard for measuring pain perception. This study was supported by a Biomedical Research Grant from the University of Florida, Gainesville, FL. Dr. Lade is assistant professor, Department of Oral Diagnostic Sciences, College of Dentistry, University of Florida, Gainesville, FL. Mr. Richmond is a research assistant, Department of Oral Biology, College of Dentistry, University of Florida. Dr. Marks is associate professor, Division of Biostatistics, Department of Statistics, University of Florida.
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