Changes in pulp temperature during thermostimulation of human teeth by a simple electrically controlled thermode

MATHEMATICAL MODELING FOR THE PREDICTION AND IMPROVEMENT OF TOOTH THERMAL PAIN: A REVIEW

Tooth pain, especially tooth thermal pain, is one of the most important symptoms and signs in dental clinic and daily life. As a special sensation, pain has been studied extensively in both clinic and experimental research aimed at reducing or eliminating the possible negative effects of pain. Unfortunately, the full underlying mechanism of pain is still unclear, because the pain could be influenced by many factors, including physiological, psychological, physical, chemical, and biological factors and so on. Besides, most studies on pain mechanisms in the literature are based on skin pain sensation and only few are based on tooth pain. In this paper, we present a comprehensive review on both neurophysiology of tooth pain mechanism, and corresponding thermal, mechanical, and thermomechanical behaviors of teeth. We also describe a multiscale modeling approach for quantifying tooth thermal pain by integrating the mathematic methods of engineering into the neuroscience. The mathematical model of tooth thermal pain will enable better understanding of thermal pain mechanism and optimization of existing diagnosis and treatment in dental clinic.

Effect of interstimulus interval on perceived sensation and intradental nerve activity during thermal tooth stimulation in man

The effect of interstimulus interval on nerve responses and subjective sensory ratings evoked by thermal stimulation of the teeth were studied in man. A total of 30 unitary discharges during heat stimulation of the lower incisor teeth were recorded from the inferior alveolar nerves using microneurographic technique. Fifteen of them had threshold sensory ratings above 3 (pain related-units) and 15 had ratings of less than 2 (non-pain-related units). Repetitive heat stimulation was applied to the teeth with interstimulus intervals of 180 s (ISI 180) and 30 s (ISI 30). Repetitive (ISI 180 and ISI 30) non-painful heat stimulation of the teeth did not alter either the intensity ratings or unitary discharge activities of non-pain-related units (P > 0.05). Repetitive painful heat stimulation of the teeth with ISI 180 did not alter the intensity ratings of pain-related units (P > 0.05), whereas that with ISI 30 significantly reduced the intensity ratings of pain-related units during a second session of heat trials (P < 0.05). On the other hand, repetitive heat stimulation of the teeth with ISI 180 caused a slight reduction in the firing frequency of pain-related units (P > 0.05). Repetitive painful heat stimulation with ISI 30 significantly reduced the firing frequency of pain-related units (P < 0.05).

Pain sensation during cold stimulation of the teeth: differential reflection of A delta and C fibre activity?

Cold stimuli of varying intensities were randomly applied to upper middle incisors of 12 healthy young subjects for a mean duration of 2 min by individually adapted thermodes the temperatures of which ranged from +30 degrees C to -30 degrees C. The subjects were asked to rate the magnitude of their pain sensations during application of the stimuli by means of a linear potentiometer according to a category scale. After each stimulus, they were asked to describe the quality of their pain sensations. Cold stimulation of the teeth evoked pain sensations were reproducible that in subsequent trials and could be graded according to stimulation intensity. Below certain individually different threshold thermode temperatures the onset of a stimulus was followed, after a short latency (1.6 +/- 1 sec), by a sharp and shooting pain sensation which immediately decreased after reaching its maximum value while the stimulus was still present. The mean maxima of the pain intensities were correlated to the thermode temperature. In general, this first pain component was followed by a second one (latency: 29.9 +/- 6.3 sec) with a lower threshold temperature, less of an increase in rate and lower magnitude. This was described as a dull, burning pain which was difficult to localize. The human pain ratings are compared to recordings of intradental nerve fibres in the cat and, under the assumption that the response behaviour of human pulpal nerve fibres is comparable to that of the cat, we hypothesize that the first pain component is evoked by intradental A delta fibres exhibiting their typical phasic response behaviour and firing during the initial steep temperature decrease. After some seconds, intradental temperature reached values sufficient to evoke C-fibre activity associated with the second pain component.

Heat generated by grinding during removal of ceramic brackets

When ceramic brackets fracture during treatment or at the time of debonding, it may become necessary to remove residual fragments by grinding with a handpiece. However, the grinding of ceramic surfaces may generate temperatures high enough to have detrimental effects on dental pulp. Intrapulpal temperature measurements were made on extracted teeth during bracket grinding with a small thermocouple probe fixed to the pulpal wall subjacent to the bracket position. These measurements were then compared with established threshold temperatures that have been reported to cause pulpal pathosis. We removed 122 ceramic brackets (A-Company Starfire, GAC Allure, and Unitek Transcend) from eight extracted teeth by grinding with high-speed diamond burs or low-speed green stones, both with and without air or water coolant. It was determined that low-speed grinding without coolant resulted in a significant (p less than 0.001) increase in pulp chamber temperature for all three types of brackets. Neither high-speed nor low-speed grinding during bracket removal caused a rise in pulp chamber temperature when combined with air or water coolant.

Psychophysical experiments of thermoperception in human teeth

Clinically inconspicuous anterior teeth of subjects 18-53 years of age were stimulated by means of an electrically controlled thermode of 0.5 degree C, 35 degrees C and 71 degrees C for 60 s. In two sets of experiments testing vital anterior teeth the cold stimuli were correctly identified significantly above chance level, making the existence of cold receptors inside the tooth probable. No evidence of a corresponding warm perception in human anterior teeth was found. These results were corroborated in a third experiment by comparative testing of 75 anterior teeth--25 devital and 50 vital--for a possible stimulus spread to other than intradental neural structures. Local surface anaesthesia of the tissues adjacent to the teeth significantly reduced the subject's ability to correctly identify cold stimuli. Investigating the effect of cold stimulus temperatures (0.5 degree C, 15 degrees C and 25 degrees C), no significant difference in correct cold perception was found when the two lower temperatures were applied, while with the 25 degrees C stimulus correct cold perception was at chance level. The latency of correct cold responses increased significantly when stimuli of 15 degrees C instead of 0.5 degree C were applied (t-test p less than 0.05). The latency of correct cold responses (0.5 degrees C) was not significantly influenced by surface anaesthesia. It increased significantly, however, when devital teeth were tested with the 0.5 degree C stimulus (t-test; p less than 0.01).

Age-dependent changes in thermoperception in human anterior teeth

Subjects (110) divided into three different age groups participated in a follow-up study investigating thermoperception in human anterior teeth. Deciduous teeth (51) were tested in 17 children (3.7 +/- 0.5 yr) and a total of 531 permanent teeth in two other groups of subjects: older children with an average age of 12.4 +/- 1.9 yr and adults with an age of 44.7 +/- 11.7 yr. In all three populations, the subjects' ability in cold perception in teeth was determinable. No data were obtained, however, to prove the existence of a corresponding warm perception. The differences in percentages of correctly-identified cold stimuli and in recorded mean latencies proved to be age-dependent. Variations in degree of dental decay and prior dental therapy did not show a significant effect on cold perception. No differences were found in the data obtained from female and male volunteers.