Thresholds of vital and non-vital teeth to stimulation with electric pulp testers

Review of pulp sensibility tests. Part II: electric pulp tests and test cavities

The electric pulp test (EPT) is one type of pulp sensibility test that can be used as an aid in the diagnosis of the status of the dental pulp. However, like thermal pulp sensibility tests, it does not provide any direct information about the vitality (blood supply) of the pulp or whether the pulp is necrotic. The relevant literature on pulp sensibility tests in the context of endodontics up to January 2009 was reviewed using PubMed and MEDLINE database searches. This search identified articles published between November 1964 and January 2009 in all languages. The EPT is technique sensitive, and false responses may occur. Various factors can affect the test results, and therefore it is important that dental practitioners understand the nature of these tests and how to interpret them. Test cavities have been suggested as another method for assessing the pulp status; however, the use of this technique needs careful consideration because of its invasive and irreversible nature. In addition, it is unlikely to be useful in apprehensive patients and should not be required because it provides no further information beyond what thermal and electric pulp sensibility tests provide - that is, whether the pulp is able to respond to a stimulus. A review of the literature and a discussion of the important points regarding these two tests are presented.

Assessment of pulp vitality: a review

BACKGROUND

One of the greatest diagnostic challenges in clinical practice is the accurate assessment of pulp status. This may be further complicated in paediatric dentistry where the practitioner is faced with a developing dentition, traumatized teeth, or young children who have a limited ability to recall a pain history for the tooth in question. A variety of pulp testing approaches exist, and there may be confusion as to their validity or appropriateness in different clinical situations.

AIM

The aim of this paper is to provide the clinician with a comprehensive review of current pulp testing methods. A key objective is to highlight the difference between sensitivity testing and vitality testing. A biological basis for pulp testing is also provided to allow greater insight into the interpretation of pulp testing results. The rationale for, and methods of, assessing pulpal blood flow are described.

Differences between inhibitory jaw reflexes evoked by stimulation of tooth pulp and across the adjacent alveolar process in man

OBJECTIVE

In humans, stimulation of nerves in or around teeth can evoke inhibitory jaw reflexes. Previous studies had suggested that there may be subtle differences in the timings of the responses. The aim of the present study was to investigate this by comparing reflexes evoked by electrical stimulation of a tooth and of the adjacent tissues in individual subjects.

DESIGN

Experiments were performed on 9 volunteers (3 male, 6 female). EMG recordings were made from the masseter muscle ipsilateral to the stimuli, whilst the subjects maintained a steady level of activity in the muscle. Reflexes were evoked by applying stimuli to an incisor tooth (pulpal stimuli) or across the adjacent alveolar process (transalveolar stimuli), using bipolar electrodes.

RESULTS

Two inhibitory responses were evoked in most (8/9) subjects. The first occurred at a shorter latency after transalveolar than after pulpal stimulation (12.3+/-0.5 ms vs 19.4+/-1.5 ms; P=0.0014, paired t-test). For technical reasons, it was not possible to make such comparisons for the second inhibitory responses in all the subjects. In 5 subjects where such a comparison was possible, the mean latency of the transalveolar-evoked response was again shorter than that of the pulpal-evoked response (56.4+/-2.8 ms and 58.8+/-5.3 ms, respectively), but this difference was not significant (P=0.5).

CONCLUSIONS

It appears that inhibitory jaw reflexes evoked from around the teeth are faster than those from the dental pulp. This observation could be due to differences between the peripheral afferent and/or the central pathways mediating the reflexes.

Sensory experiences in relation to pulpal nerve activation of human teeth in different age groups

There are no data on the correlation of intradental nerve activity and sensation from intact human teeth. We used microneurography to examine this relation and to determine whether it changes with age. Fifteen informed and healthy male volunteers were divided into three age groups: group A (18.6+/-1.82 years, mean+/-standard deviation (S.D.)), group B (38.4+/-2.70 years) and group C (64.0+/-4.06 years). Ratings of perceived pain intensity to thermal stimulation were obtained using a visual analogue scale (VAS). In addition, each subject chose one or two words from the short-form McGill Pain Questionnaire to describe perceived pain. A total of 90 single pulpal axons were studied with microneurography at the same time as the sensory experiences were recorded. Mean conduction velocities and variance estimates correlated closely with age. With advancing age, first, the percentage of teeth from which the subjects did not perceive any sensations to thermal stimulation increased, second, units responding to heat stimulus decreased, and third, latencies of sensation induced by thermal stimulation increased. In addition, a burst of afterdischarges following thermal stimulation and neural discharges evoked by thermal stimulation produced no sensation only in some of group B and C units. In contrast, no significant difference was found among three groups in VAS scores and words to describe the perceived pain to thermal stimulation. These results suggest that pulpal afferents were activated by the same mechanism(s); the hydrodynamic mechanism works immediately after thermal stimulation and is possibly followed by direct activation of some nerves, especially slow conducting fibres. In older tooth pulps, the decrease in the number of fast conducting afferents and mineral apposition of dentinal tubules impaired the nerve activation, especially by heat, as per the hydrodynamic mechanism. Spike discharges without sensation in older individuals were suggested to be due to insufficient spatial and temporal summation and may be involved with abnormal uncomfortable sensations.

Subjective sensation and objective neural discharges recorded from clinically nonvital and intact teeth

The aim of this study was to compare subjective sensation with objective neural discharges recorded by microneurography. We examined human teeth that did not respond to pulp vitality testing, but that responded to cavity preparation for endodontic treatment (pathophysiological). Intact teeth and endodontically obturated teeth were used as controls. Pulpal blood flow in the clinical crown and histological examination were also used. Most teeth, both in normal and pathophysiological conditions, did not respond to all pulp vitality tests. Even when teeth in the pathophysiological group showed spike discharges evoked by pulp vitality tests or from spontaneous activity no sensation was elicited. These results confirmed the usefulness of microneurography for research on pulpal sensation and the significance of summation in the perception of sensation in chronically inflamed tooth pulp.

An assessment of the reliability of pulp testing deciduous teeth

The aim of this study was to assess the reliability of children's responses to pulp testing of deciduous teeth. The maxillary canine was chosen as the test tooth. One hundred children aged 7-10 years were selected who had at least one non-carious maxillary canine with an intact root showing only early radiographic signs of resorption. Using a minimization sampling technique, the children were allocated to one of two groups, for pulp testing with ethyl chloride (EC) or with an electric pulp tester (EPT). True and sham tests for both pulp testing methods were applied. The tests were repeated following an application of 5% lignocaine paste to the gingival margin around the tooth to prevent gingival detection of the stimulus. Children were asked to record their responses to each of the four tests on a visual analogue scale (VAS) of 1-10. Significantly higher mean scores were obtained with true tests than with sham tests, for both EC and EPT. The application of lignocaine to the gingival margin did not significantly affect the responses to either EC or EPT. It was concluded that pulp testing of intact maxillary deciduous canines with no or only early signs of radiographic root resorption, using EC or EPT, results in reliable responses in 7-10-year-olds, suggesting that pulp testing is valid in the deciduous dentition. The VAS was a useful tool for the evaluation of the children's responses.

Reproducibility of data from a hand-held digital pulp tester used on teeth and oral soft tissue

Controlled studies of the reproducibility of data from electronic pulp testing instruments are limited and contain few statistical analyses. The reproducibility of these readings is important if the instrument is to be used for determining differences in sensitivity. Twenty human subjects (16 male) were used in this study. One incisor, one premolar, one molar tooth with small or no restorations, and two gingival soft tissue positions from each upper and lower arch of each subject were stimulated with the Analytic Technology vitality scanner. This procedure was repeated twice with a 5-minute rest between each trial, for a total of three trials. Each subject was then seen again after a period of at least 3 days, at which time the trials were repeated. The collected data were grouped by trial, tooth position, and day. Paired t test analysis of both the absolute difference between any two trials on the same day and the average of the absolute differences between corresponding trials on days 1 and 2 showed no statistically significant differences (p greater than 0.05). Accommodation to the stimulus was evaluated by examining differences in the mean values between the three same-day trials. The Analytic Technology vitality scanner was found to be reproducible both for consecutive same-day trials and for corresponding trials on different days. No same-day trends in meter readings were noted.

The optimum placement-site of the electrode in electric pulp testing of the 12 anterior teeth

The present study of 2,387 recordings of 12 anterior teeth in 53 patients indicates that the incisal edge is the optimal placement-site for the electric pulp tester to determine the lowest response threshold. The results show significant individual variations in the lowest threshold responses of the cervical-third, middle-third, incisal one-third, and incisal edge sites on a tooth, with a confidence level of 99%, according to the analysis of variance. The maxillary teeth gave a higher response threshold than the mandibular teeth and different types of teeth (canines and incisors) had statistically significant different response thresholds. The application of the electric pulp tester to the incisal-edge region with exposed dentin produced the most significant decrease in the threshold response.

A comparison of monopolar and bipolar electrical stimuli and thermal stimuli in determining the vitality of human teeth

The sensory threshold was determined for 50 teeth in 31 patients using constant-current stimuli of 0.1, 1.0 and 10 ms duration at 10 Hz through both monopolar and bipolar electrodes. The teeth were also tested with a cold stimulus (ethyl chloride on cotton wool), then extracted, processed and examined by light microscopy. Histologically, 38 teeth were vital and 7 non-vital. The best prediction of vitality was from ethyl chloride (80% correct) or bipolar stimuli of 10 ms duration and up to 200 microA (73% correct). The remaining 5 teeth had vital radicular pulps and necrotic tissue coronally, but a comparison between the results of monopolar and bipolar stimulation did not permit the detection of this group. There was no correlation between the electrical threshold and presence of caries, restorations, pulp stones or diffuse pulpal mineralization.

A comparison of monopolar and bipolar electrical stimuli and thermal stimuli in determining the vitality of autotransplanted human teeth

Of 33 autotransplanted maxillary canines, 13 responded to cathodal monopolar stimuli, 15 to bipolar stimuli and nine to a cold stimulus. Responses returned between seven weeks and 26 months after transplantation and indicated that the coronal pulp was reinnervated. There was no evidence that comparison of monopolar and bipolar stimulation might distinguish between the vitality of the coronal and radicular pulp, probably because monopolar stimuli did not excite nerves within the root. The thresholds to both forms of electrical stimulation were raised; the bipolar threshold was significantly higher than the monopolar. No transplanted teeth which responded to a cold stimulus did not also respond to an electrical stimulus.

Probe placement during electric pulp-testing procedures

Electrode placement sites during electric pulp-testing procedures on the crown of a tooth were evaluated in a laboratory setting using thirty-one extracted teeth, an oscilloscope, and a new electric pulp tester (Digital Analytical Pulp Tester). This study showed that the lowest resistance occurred on the occlusal two-thirds electrode sites of the labial or buccal surfaces of maxillary incisors and premolars. More specifically, the middle-third electrode sites of the incisors and the occlusal-third electrode sites of the premolars were shown to have the least resistance. The electrode placement area on the crown where the pulp nerve is first excited to threshold must be identified to avoid false-positive stimulation of surrounding periodontal nerves. This will decrease nerve damage and ensure the patient's cooperation and acceptance.

Electronic and clinical comparison of pulp testers

Electronic and clinical comparisons of three commercially available pulp testers were investigated using oscilloscopes and a clinical trial. The three devices varied in wave-form characteristics and showed statistically significant differences in patient responses.

Rationalization of electric pulp-testing methods

A new electric pulp-testing system, the Testark, was developed in order to assess the potential of a different way of testing pulp sensitivity, thus making this electric pulp test more dependable than the conventional electric pulp-testing method. A study was conducted to evaluate the potential of the Testark system in comparison with a commercially available pulp tester. This pilot study consisted of application of three different desensitizing agents (sodium fluoride, test product. 'A', and test product 'B') to the cervical areas of hypersensitive teeth. The results were recorded with both the Testark and the conventional pulp tester simultaneously, and the sodium fluoride and test product 'B' proved to yield a beneficial effect by desensitizing the teeth after a single application. The level of desensitization with these agents was higher than the level obtained with the test product 'A' paste, which was utilized daily for 14 days. The results obtained with the conventional pulp tester differed by way of interpretation from those obtained with the Testark system. The Testark system proved to be easy to use and highly accurate in the data readings because of its high resolution. The Testark systemwas found to be more dependable than the commerical pulp tester, since it reduced the subjective errors which are inevitable when a commerical pulp tester is used. The Testark system is being developed further, and more studies are being conducted at the present time, in order to assess the full potential of the instrument.

Electrical stimulation of teeth

The technical problems of stimulating intact teeth in clinical diagnosis and in pain research are discussed. Bipolar stimulation has no advantage over monopolar stimulation for most applications. A 100 V constant current stimulator is suitable for monopolar stimulation of healthy teeth with a large electrode at about threshold intensity, but, for monopolar stimulation up to 150 micronA and for bipolar stimulation, very much higher voltages are required and no suitable instrument is available. Circuits are given for isolated 100 V and 1kV constant current stimulators.

Sensory and reflex responses to tooth pulp stimulation in man

Experiments have been carried out to investigate whether all tooth pulp afferent nerves are capable of producing pain. Monopolar and bipolar stimuli were applied to teeth in human subjects and sensory thresholds determined. EMGs were recorded from the masseter and the anterior digastric muscles. With stimuli up to three times the sensory threshold, no response could be detected in the digastric but at, or just above, the sensory threshold, inhibitory effects were produced in masseter muscle. The latency of the muscle response with bipolar stimulation was 18-22 msec. There was no evidence of stimulus spread to nerves outside the teeth. Bipolar and monopolar stimulation both produced the same sensation but this was not described as painful. It is concluded that some pulpal afferent nerves may not be capable of producing pain, and that the sensory and reflex responses at threshold were probably produced by the same fibres.