Assessment of operator-associated variability in thermal pulp sensibility tests: A simulation study using a custom-designed testing apparatus

Abstract

Objective:

Thermal pulp sensibility tests are critical, cost-effective tools for assessing pulp vitality and guiding disease prognosis. However, their accuracy and efficacy are often compromised by subjective patient responses and operator variability. This study evaluated operator-associated variability for the performance of hot and cold pulp sensibility tests using a custom-designed testing apparatus.

Materials and Methods:

In this cross-sectional study, 23 dentists performed heat and cold tests on the apparatus while thermal and temporal parameters were recorded. Key outcome measures included were tool heating/cooling time, heat dissipation time, tool temperature on tooth, maximum tooth temperature, and maximum tool temperature.

Results:

Metallic instrument (burnisher) used for heat testing exceeded temperatures of 400°C for both experienced (more than 5 years) and inexperienced operators. Heat application duration often surpassed 10 s, posing a risk. Conversely, cold testing using the Endo-Frost cold spray (−50°C) failed to attain sufficiently low temperatures to stimulate a pulpal response. Significant loss in tool temperature, particularly during cold tests, further compromised the efficacy.

Conclusion:

This study highlights considerable operator-induced variability in thermal pulp sensibility testing, with potential implications for diagnostic accuracy and patient safety. Study findings emphasize the necessity of standardized protocols to mitigate operator-related discrepancies and improve the diagnostic reliability.

INTRODUCTION

Thermal tests and electric pulp tests are among the most commonly used diagnostic tests relying on nerve stimulation of the dental pulp. In thermal sensitivity tests, changes in temperature trigger nerve response.[1] Although these tests share a common mechanism, they are conducted for different diagnostic purposes. A response to cold generally indicates a vital pulp, regardless of whether it is in a healthy or pathological state. Conversely, an exaggerated response to heat is suggestive of pulpal or periapical pathology, potentially necessitating endodontic intervention.[2] However, thermal sensitivity responses do not always accurately reflect pulpal health or integrity, as pulp vitality primarily depends on its blood supply. It has been proven that the pulp that has lost its innervation may still maintain adequate blood flow. The sensitivity of the pulp test is its ability to identify teeth with no pulp or diseased pulp, whereas the specificity of a pulp test is its ability to identify pulps without disease.[3] The interpretation of these tests can also be false negative in the traumatized tooth with intact blood supply but with stunned pulp, whereas it can be false positive in teeth with partial or complete necrosis.[4,5,6]

Laser Doppler Flowmetry (LDF) has demonstrated promising results for pulp vitality testing by directly measuring pulpal blood flow.[7,8] Several studies have reported the superiority of vitality tests over traditional sensibility tests.[7,9] However, Ghouth et al. highlighted that the LDF was not able to differentiate between the vital and non-vital pulps. In addition, widespread adoption of LDF remains a major challenge due to cost and lack of clinically usable commercial probes.[10]

Standardization of pulp testing procedures and minimization of operator-dependent variability are crucial for improving diagnostic accuracy. Despite this need, operator-related factors influencing thermal sensibility tests remain largely unexplored. Variability in test outcomes may be influenced by the operator’s knowledge, experience, and the frequency of performing these tests in practice. Therefore, this cross-sectional study aimed to investigate operator-related variability in traditional heat and cold testing methods and evaluate the adequacy of these procedures in eliciting the known thermal responses from the human dental pulp.

MATERIALS AND METHODS

Participants and experimental setup

After obtaining the informed consent, 23 dentists were enrolled in the study. Ethical clearance was obtained from the Institute Ethics Committee (IEC-774/07.10.2022). Participants were categorized into two groups based on their professional experience after graduation: those with <5 years of experience (n = 16) and those with more than 5 years of experience (n = 7). Among the experienced group, four dentists reported performing pulp sensibility tests at least 20–30 times per month, while the remaining three performed 10–20 tests monthly. In the less experienced group, nine participants performed fewer than 10 tests per month, six performed 10–20 times a month, and one carried out 20–30 tests monthly. Both groups were instructed to perform the thermal pulp sensibility tests (heat and cold) using the experimental apparatus as shown in Figure 1a and b. The validity and reliability of the experimental model were verified through repeated laboratory trials before being used by the participants. The experimental setup consisted of standard instruments used for heat and cold pulp sensibility tests consisting of a burnisher and tweezer equipped with a 0.3 mm K-type fine wire thermocouple (KA02, TME Thermometers, Sussex, UK) at the tip to record the tool temperature. These thermocouples were securely bonded to the tools using a temperature-resistant adhesive (Extremeheat Paste, J-B Weld, Marietta, USA).

Figure 1.

(a) The thermal sensibility experimental setup showing the tweezer and burnisher instrumented with thermocouple temperature sensors. The setup also shows an enlarged view of the simulated non-vital tooth and the associated temperature sensor. Burners and cold spray were kept in dedicated compartments to standardize the procedures. (b) Picture showing a participant using the setup for heat and cold sensibility test

The thermocouple outputs were connected to a MAX6675 thermocouple-to-digital converter (Analog Devices, Wilmington, USA) to digitize the output. To stimulate a non-vital tooth, a temperature sensor (LM35, Texas Instruments, Dallas, USA) was used, as replicating typical patient feedback obtained in clinical situations was not feasible. A microcontroller-based data logger recorded the temperature readings from all three sensors simultaneously at a sampling rate of 10 samples/s. Figure 1a illustrates a pulp sensibility test model, which included the compartments for a burner (Libral Traders, India) to heat the thermocouple-modified metallic burnisher and cold spray (Coltene, Waldent, Germany) to cool the tweezer. They were placed at specific positions to simulate a clinical workflow of handling such equipment while performing the thermal tests.

Step-by-step procedure

Participants were seated comfortably and provided a brief orientation to the experimental model and protocol. They were instructed to use the tools available in the pulp sensibility test kit to perform “heat” or “cold” tests as prompted. The simulated non-vital tooth represented the affected tooth in a clinical scenario. During the experiment, the participants were directed to adjust the temperature and application duration as they would during routine clinical practice. For ease and consistency, they were advised to use their dominant hand. Each participant performed 10 repetitions of both “hot” and “cold” tests in random order to minimize the effect of learning. To standardize the procedure, it was ensured that the burnishers and tweezers returned to room temperature before beginning a new repetition. Additionally, the cotton balls used for cold tests were discarded after each repetition to maintain procedural accuracy.

Outcome metrics

To compare the performance of both groups, the study utilized the following outcome metrics:

Tool heating time/tool cooling time

Tool heating time (t_{tool_heating}) or cooling time (t_{tool_cooling}) was regarded as the duration between the initiation of heating and the time when the burnisher reached its peak/desired temperature, while tool cooling time was the period from the start of cooling to the tweezer reaching its minimum temperature [Figure 2a and b]. These metrics quantify the time taken by users in applying heat or cold to the probe, offering insights into efficiency and proficiency.

Figure 2.

(a) Schematic of the temperature outputs obtained from the temperature sensor on the burnisher tool used for hot tests and the simulated non-vital tooth. (b) Schematic of the temperature outputs obtained from the temperature sensor on the tweezer tool used for cold tests and the simulated non-vital tooth. Thermal and temporal outcome metrics calculated from the temperature readings have been shown

t_{tool_heating} = t_{tool_peak} − t_{tool_initial}

Here t_{tool_peak} was the time at which the tool reached its peak heating or cooling temperature and t_{tool_initial} was the time at which the tool started heating as shown in Figure 2. Thermal dissipation time: Thermal dissipation time (t_{dissipation_heating} and t_{dissipation_cooling}) was considered as a metric that gauged the time spent by the operator in transporting the thermally charged tool to the tooth (heated/cooled). It specifically quantified the time difference between the moment the tool reached its maximum/minimum temperature and the subsequent application of heat/cold stimulus to the tooth by the user.

t_{dissipation_heating} = t_{tool_peak} − t_{tool_applied}

Here, t_{tool_applied} was the time at which the tool was touched or applied to the teeth.

Tool application time

Tool application time (t_{application_heating} and t_{application_cooling}) was a metric that quantified the duration for which the user applied heat or cold to the tooth. This measurement represented the time difference between the initiation of the application of heat/cold onto the tooth and the point at which the tooth reached its maximum/minimum temperature.

t_{application_heating} = t_{tooth_peak} − t_{tool_applied}

Here, t_{tooth_peak} was the time at which the teeth reached their peak temperature.

Tool peak temperature

The tool maximum/minimum temperature (T_tool__peak) refers to the highest (lowest for the cold test) temperature attained by the tool during the test procedures. This metric served to quantify the maximum heat or minimum cold temperatures of the tool.

Tool temperature on tooth

The assessment of tool temperature on tooth (T_tool__applied) quantified the temperature of the tool when it was applied to the tooth.

Tool temperature loss

Tool temperature loss (ΔT_loss) quantifies the thermal losses incurred by different users during the transition of the tool from the heating or cooling stage to its application on the tooth.

ΔT_loss = T_{tool_peak} − T_{tool_applied}

Peak tooth temperature

Maximum tooth temperature (T_{tooth_peak}) refers to the highest or the lowest temperatures reached by the tooth during thermal sensibility testing.

Statistical analysis

The Mann–Whitney U-test was conducted to compare the performance of two groups: those with <5 years of experience and those with more than 5 years of experience across all outcome measures. All statistical analyses were carried out using IBM SPSS Statistics (Version 28.0, IBM Corp, Armonk, USA). The effect size was calculated as the absolute value of the ratio between the z score and the square root of the total number of participants.[11] All analysis follows STROBE guidelines [Checklist in Supplementary Information].

RESULTS

The tool peak temperatures (T_{tool_peak}) during the heat and cold tests for experienced and inexperienced dentists are shown in Figure 3a and b respectively. T_{tool_peak} for the heat test for the experienced dentists and relatively inexperienced dentists were 728.70°C (95% confidence interval [CI]: 774.29, 683.12) and 615.81°C (95% CI: 652.34, 579.28) respectively. The results revealed a statistically significant difference in the maximum tool temperature during the heat test (P = 0.002, U = 1482, Z = −3.05, r = 0.63). For the cold test, T_{tool_peak} was −23.66°C (95% CI: −21.50, −25.82), and −20.66°C (95% CI: −19.35, −21.96) for the experienced and inexperienced dentists respectively. The difference in tool peak temperature for the cold test between the two groups was not statistically significant (P = 0.124, U = 5189, Z = −1.54). The tool temperature loss (ΔT_loss) for heat and cold is shown in Figure 3c and d. The experienced dentists demonstrated lower tool temperature loss of 119.19°C (95% CI: 147.71, 90.66) compared to the inexperienced group, 131.89°C (95% CI: 148.65, 115.12) during the heat test. The difference in tool temperature loss was not statistically significant for both groups (P = 0.201, U = 1899, Z = −1.28). During the cold test, experienced dentists demonstrated significantly lower ΔT_loss of 8.65 (95% CI: 10.52, 6.79])°C compared to inexperienced dentists 10.34 (95% CI: 11.37, 9.31)°C (P = 0.018, U = 4791, Z = −2.37, r = 0.49).

Figure 3.

Thermal outcome metrics derived from the tooth vitality experiment showing the influence of the operator’s clinical experience on (a and b) tool peak temperature, (c and d) tool thermal loss, (e and f) tool temperature on teeth and (g and h) peak tool temperature on teeth

The tool temperature on teeth (T_tool__applied) has been depicted in Figure 3e and f. There was a statistically significant difference in both heat tests (P < 0.001, U = 1100, Z = −4.67, r = 0.97) and cold tests (P < 0.001, U = 3478, Z = −5.14, r = 1.07) for the tool temperature on teeth between the two groups. The mean T_tool__applied inexperienced dentists for heat and cold test was 483.92°C (95% CI: 511.52, 456.32) and −10.85°C (95% CI: −9.82, −11.87)°C, respectively, and for experienced dentists was 609.52 (95% CI: 642.18, 576.85) and −15.58 (95% CI: −14.18, −16.97)°C, respectively.

Figure 3g and h depict the peak tooth temperature (T_{peak_tooth}) achieved by both inexperienced and experienced dentists for heat and cold tooth sensibility tests. The study revealed a statistically significant difference (P < 0.001, U = 648.50, Z = −6.60, r = 1.37), indicating that inexperienced dentists achieved notably lower T_{peak_tooth} (39.11°C [95% CI: 40.52, 37.70]) in contrast to the experienced ones with temperatures (54.61°C [95% CI: 58.13, 51.09]) for the heat test. Similarly, for the cold test, there was a statistically significant difference (P < 0.001, U = 3167.50, Z = −5.69, r = 1.18), indicating that inexperienced dentists attained notably higher T_{peak_tooth} (11.23°C [95% CI: 12.02, 10.44]) which is non-desirable compared to experienced dentist (6.73°C [95% CI: 7.90, 5.57]) during cold tests. Figure 4a and b show plots of tool heating (t_{tool_heating}) and cooling time (t_{tool_cooling}), respectively. The study found that experienced dentists had significantly higher t_{tool_heating} of 9.38s (95% CI: 10.23, 8.54) compared to the inexperienced group 7.37s (95% CI: 8.01, 6.72) (P < 0.001, U = 1298.50, Z = −3.83, r = 0.79). However, for the cold test, the experienced dentists had a lower t_{tool_cooling} of 9.71s (95% CI: 11.47, 7.96) compared to the inexperienced dentists 13.49s (95% CI: 17.97, 9.00). The difference was not statistically significant (P = 0.311, U = 5121, Z = −1.01).

Figure 4.

Outcome metrics derived from the tooth vitality experiment showing the influence of the experience on (a and b) tool heating time, (c and d) tool application time, (e and f) thermal dissipation time

Figure 4c and d shows that the mean thermal dissipation time (t_{dissipation_heating}) in heat tests for experienced dentists was 2.93s (95% CI: 3.71, 2.15) and 3.06s (95% CI: 3.48, 2.64) s for the inexperienced group. For cold tests, t_{dissipation_cooling} was 3.03s (95% CI: 3.75, 2.31) and 2.40s (95% CI: 2.74, 2.06) s for the experienced and inexperienced group, respectively. The difference in thermal dissipation times between the two groups was not statistically significant for both heat (P = 0.338, U = 1974.5, Z = −0.96) and cold tests (P = 0.882, U = 5849.5, Z = −0.15).

Figure 4e and f shows that there was no significant effect of operator experience on tool application time (P = 0.621, U = 2083.5, Z = −0.5, and P = 0.294, U = 5310, Z = −1.05) for heat and cold tests. The mean tool application time for the heat test (t_{application_heating}) was 17.80s (95% CI: 22.21, 13.39) s and 18.44 (95% CI: 21.05, 15.83) for experienced and inexperienced dentists, respectively. For the cold test (t_{application_cooling}), it was 45.53s (95% CI: 58.90, 32.16) and 53.82 (95% CI: 65.12, 42.5) s, respectively.

DISCUSSION

The assessment of pulp vitality remains a significant challenge in dentistry. While the conventional pulp sensibility tests (heat test and cold test) have notable limitations, they continue to be widely employed by clinicians.[12,13] The studies regarding their accuracy have demonstrated that these tests are better predictors of the absence of pulp disease than its presence. In other words, these pulp tests are more reliable in identifying vital teeth than necrotic ones.

The present study aimed to assess operator-related variability while performing thermal tests by analyzing various thermal and temporal outcome metrics. For heat tests, the mean tool temperature on the tooth was found to be 609.52°C (95% CI: 642.18, 576.85) for experienced operators and 483.92°C (95% CI: 511.52, 456.32) for inexperienced operators, demonstrating substantial variability between the two groups. Heated instruments, though commonly employed for thermal tests are considered an unreliable method due to the lack of reliability of stimulus and reproducibility. Methods for heat delivery include heated gutta-percha, warmed instruments, electrical heat sources, frictional heat, and hot water baths. However, challenges such as tooth isolation and obtaining a consistent heat stimulus often limit their use.[14] The findings of this study revealed that the thermal stimulus applied with a heated instrument often exceeded the recommended temperature limits. Such elevated temperatures can pose a risk to the dental pulp, as surface temperatures of up to 76°C have been reported to cause potential harm.[15] However, previous research suggests that shorter application times, such as 5 s or less, may not significantly compromise pulpal health, as the temperature increase at the Pulp Dentin Junction remains below 2°C.[16] This study observed that the temperature of the simulated tooth was a modest 39.11°C (95% CI: 40.52, 37.70) for the inexperienced group and 54.61°C (95% CI: 58.13, 51.09) for the experienced group. It is important to note that the simulated tooth (LM35 temperature sensor) may not precisely replicate the thermal properties of dental enamel, dentine, pulp, and thus the temperature rise observed in this study may not fully reflect clinical conditions. Further, the mean tool application time for the heat test was 17.80s (95% CI: 22.21,13.39) s and 18.44s (95% CI: 21.05,15.83) for the inexperienced and experienced groups, respectively, significantly exceeding the recommended duration of 5 s or less.[17] It is suggested that special care should be taken for not to damage the pulp tissue with an excessive or prolonged heat stimulus that can result in a biphasic stimulation, initially of the A-delta fibers and then subsequently of the C fibers, resulting in lingering pain.

For the cold test, the mean tool maximum temperature was −23.66°C (95% CI: −21.50, −25.82) for experienced dentists and −20.66°C (95% CI: −19.35, −21.96) for inexperienced dentists. However, thermal losses during cooling of the tool and transportation to the stimulated tooth resulted in a final tool temperature of −15.58°C (95% CI: −14.18, −16.97) for experienced dentists and −10.85°C (95% CI: −9.82, −11.87) for inexperienced dentists. While the manufacturer of the cold spray used in the study reported a temperature of −50°C, significant temperature losses occurred during the transfer process, particularly due to spraying on the cotton roll before application to the tooth surface. This resulted in a stimulus insufficient to reliably evoke a response from the dental pulp, increasing the likelihood of false-negative outcomes. While a strong stimulus may enhance diagnostic reliability, it also carries the potential harm to the dental pulp. Previous studies indicate that cold tests are generally safe and do not injure the pulp,[16] unlike heat tests, which have a greater potential to cause injury.[17] However, some studies have shown that cold tests can cause pulp degeneration if tissue freezing occurs, which only happens under extreme conditions such as maintaining a probe temperature below −10°C for 5–20 min.[18,19] This further necessitates the need for standardized devices to deliver consistent and clinically appropriate thermal stimuli for pulp sensibility testing.

The present study aimed to address the operator/clinician-related variability in thermal testing by using tools with integrated thermal sensors. While many limitations of thermal tests have been well-documented, operator-related variability has never been explored as a contributing factor to diagnostic subjectivity. The operator’s experience and knowledge have a large bearing on the understanding and execution of pulp vitality testing. Factors such as lack of clinical experience, frequency of performing vitality testing in their clinical or academic curriculum, and familiarity with the testing procedures have a significant influence on the reliability of these procedures. The results demonstrate that procedural variability stemming from lack of experience and practice may have a large bearing on the test results.

CONCLUSION

The thermal sensibility tests demonstrated significant variability in the intensity of heat and cold stimuli applied by different operators. The heat stimulus frequently exceeded the recommended temperature thresholds, posing a risk of tooth damage, while the cold stimulus was consistently insufficient to elicit a response from the dental pulp. Additionally, the duration of stimulus application during both heat and cold tests was often prolonged, potentially leading to pulpal damage in clinical settings. These findings underscore the critical need for the development of standardized devices for thermal testing, alongside enhanced training for dental practitioners to ensure safer and more accurate diagnostic practices.

Ethical approval

Ref no. IEC-774/07.10.2022.

Informed consent

A written informed consent was obtained from all the participants.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

The authors disclosed receipt of the following financial support for the research of this article: This research was funded Multi-Institutional Faculty Interdisciplinary Grant from the Industrial Research Development Unit (IRD), Indian Institute of Technology Delhi, and All India Institute of Medical Sciences New Delhi (MI02582G).