A Note On Pulp Vitality Testing In Endodontics

VITAL PULP TESTING

The clinical and radiographic steps of the examination often-times cast suspicion of endodontic involvement of a specific tooth. Vital pulp tests (VPT) are essential components of the endodontic examination and serve to disclose the status of the dental pulp.

Frequently, patients present reporting pain to a thermal stimulus in a specific quadrant. In these instances, vital pulp testing schemes should be performed first on presumably “pain-free” teeth, away from the area of the chief complaint. Specifically, the preferred sequence is to test contralateral teeth first, opposing teeth second, then presumably healthy teeth within the thermally painful quadrant, and finally, the most suspicious tooth last. This strategy of sequencing the vital pulp tests allows both the doctor and the patient to appreciate the range of “normal” pulpal responses exhibited by asymptomatic teeth.

Importantly, performing repetitive pulp tests, as described, will tend to relax the patient, build confidence and reduce the probability of a false positive or false negative report.  VPT procedures are initially performed to establish a normal “baseline” for any given tooth on any single patient. Once a baseline has been established then, and only then, should the appropriate VPT be performed in the quadrant where the patient is experiencing symptoms. Performing VPT on asymptomatic teeth establishes the baseline for testing and comparing an “abnormal” response in a symptomatic tooth.

In fact, when VPT schemes are conducted in this manner, patients will frequently question why another tooth is either overreactive or nonreactive to the specific test. In these instances, additional diagnostic evaluation may be required to clarify the endodontic status of any given tooth.

When pulpal inflammation is confined to the root canal space, diagnosticians should be skeptical when patients attempt to identify a specific tooth they perceive as the source of their pain. This doubt is justified since the dental pulp does not have proprioceptive nerve fibers. On the contrary, the attachment apparatus has proprioceptive nerve fibers that allow a patient to identify a tooth that is sensitive to biting pressure. As such, inflammatory conditions involving the dental pulp are diagnosed by reproducing the patient’s chief complaint as this is diagnostic. Thermal pain is pulpal in origin whereas biting or chewing pain is related to injuries involving the periodontal attachment apparatus. The origins of attachment apparatus injuries are multifactorial and, as examples, could be periodontal or endodontic in etiology or attributable to a recently placed restoration in hyperocclusion.

In summary, it is wise to appreciate that a symptomatic patient can present with two separate, distinct and unrelated problems and, as an example, the tooth that is symptomatic to biting pressure may not be the tooth that is symptomatic to a thermal stimulus. 

This radiograph suggests the mandibular first bicuspid has a carious pulp exposure and reveals a endo lesion associated with the mesial root of the molar.

There are four methods that may be employed to determine the vitality of the dental pulp: the cold, hot, electric, and cavity tests. Selection of the cold test or the hot test is based on the patient’s chief complaint. If a patient does not report any history of thermal pain then, for ease, the cold test is selected.

However, it should be recognized that once the pulp is stimulated with cold, there is a refractory period of several minutes before a second cold or hot test can be accurately conducted. The electric pulp test is more technique sensitive, requires a dry field and is oftentimes impractical to utilize in teeth with full restorative coverage. The cavity test is rarely used, and only considered when the clinical and radiographic information and pulp test results prove inconclusive. In these instances and, when the patient situation supports intervention, then the cavity test could be considered as a last resort. If employed, the cavity test is initiated on a suspicious tooth, without anesthetic, and involves drilling a small window through either enamel or a restoration to dentin. The cavity test will stimulate a vital pulp and provoke a painful response when dentin is invaded. In the event of a vital response, a simple restoration is placed. On the contrary, the cavity test will not stimulate a partially necrotic pulp to the same extent as a vital pulp. In this situation, the dentist initiates the access cavity, invades progressively deeper into dentin and often reaches the pulp chamber uneventfully.

Thermal tests should be conducted on the cervical aspect of a tooth, and as close as possible to the free gingival margin. This location represents the thinnest aspect of enamel or a restoration and, importantly, the closest distance to the pulp chamber. When performing a thermal test, the clinician is evaluating the “immediacy”, the “intensity”, and the “duration” of the response. The immediacy and intensity of a response to thermal testing can vary significantly depending on, as examples, the depth of a carious lesion, the placement of a new restoration, or recent periodontal surgery. It is useful to have the patient subjectively rate the intensity of a response utilizing a zero to ten (0-10) scale where zero (0) is a no response and ten (10) represents maximum pain. Regardless of the immediacy and intensity, if the response rapidly dissipates upon removing the thermal stimulus, then although the pulp may have tested inflamed, this may be a reversible condition. Importantly, it is the “duration” of the response, compared to the baseline that was established by testing other teeth, that is most diagnostic.

In certain instances, a tooth tested with a thermal stimulus may elicit a “no response” which could infer the pulp is necrotic. It should be recognized a patient may not respond to a thermal test if the pulp chamber has significantly calcified or receded apical to the crest of bone. Further, a no response to a thermal test could imply a tooth has been involved in a recent episode of trauma, has an immature apex, or the patient may have premedicated. Additionally, a patient will not generally respond to a thermal stimulus on a tooth that has had root canal treatment. However, an endodontically failing tooth with a missed canal will, at times, illicit a painful response when tested with a hot stimulus.

COLD TEST

When a patient presents and reports a history of pain to a cold stimulus, then the clinician should logically conduct the “cold test”. Although there are a few different methods that may be selected to apply a cold stimulus, one reliable source is to utilize an ice pencil.

A pencil of ice is easily formed by first purging all the anesthetic from an unused carpule. Dental floss may then be cut about one (1) inch longer than the length of the carpule and inserted into this glass tube. Several of these carpules are filled with water, held upright in a cup and then placed in a freezer. When a pencil of ice is needed, a frozen carpule is briskly rolled between the gloved palms of the hands. This action serves to warm and contract the ice pencil which may then be liberated by gently pulling the floss. The pencil of ice is placed in a 2x2 gauze to prevent warmth from the fingers from prematurely melting the ice.

Before initiating any thermal pulp test the diagnostician needs to establish reliable hand signals. The patient is instructed to raise their hand when they first feel the sensation from the thermal stimulus in the tooth, to keep their hand up as long as this sensation lingers, and to lower their hand when the sensation dissipates. It is wise to repeat and clarify these instructions as both asymptomatic and, especially, symptomatic patients are frequently nervous and may inadvertently not follow directions. This is precisely why thermal pulp tests should not be initially performed on suspicious or symptomatic teeth. As such, before instituting any pulp test, advise the patient how this test works, ask permission to test, and then initiate the test on pain-free teeth.

The specific technique for pulp testing is straightforward.  The ice stick is placed towards the cervical aspect of a tooth on either the buccal or lingual aspect of a crown and quickly moved back and forth. 

A clinical photograph demonstrates a reliable method and technique for performing the cold test.

This action creates a slurry of cold water which will effectively bathe, conduct and penetrate into a tooth. To prevent a false positive result, a cotton pellet should be placed just distal to the tooth being tested to prevent ice water from potentially contacting a more posterior tooth.

When the patient signals they feel cold in the tooth being tested, the ice is immediately removed. However, the patient is reminded to keep their hand up as long as the cold sensation lingers in the tooth. When testing teeth with healthy pulps, once the patient has signaled they feel cold in a tooth, their hand will generally remain raised approximately 2-5 seconds after the stimulus is removed. As mentioned, the diagnostician is observing the immediacy, intensity, and importantly, the duration of the response. At times, the ice pencil and resultant slurry of cold water will not elicit a response and reproduce the patient’s chief complaint. In these instances, a tooth or group of teeth may be individually isolated with a rubber dam, and ice water syringed onto each tooth. Although more time consuming, this method of testing is very effective at simultaneously bathing the entire clinical crown of a tooth and stimulating an inflamed pulp. Astute clinicians appreciate that a test that elicits a lingering response is diagnostic and separates the reversible pulpal conditions from the irreversible conditions.

HOT TEST

When a patient reports a history of pain to a hot stimulus, then the clinician should logically conduct the “hot test”. A “toothache” precipitated by hot liquids or foods usually suggests an acutely inflamed or partially necrotic pulp. Necrotic tissue frequently harbors bacteria which can pro-duce gasses that potentially expand against tissue encased inside unyielding dentinal walls. This phenomenon causes sensory fibers of the pulp to transmit pain.

There are a few different devices that may be selected to apply a hot stimulus, including the Touch ‘n’ Heat or System B (SybronEndo; Orange, California). Either device has a handpiece which is designed to receive various inserts such as the Hot Pulp Test Tip (SybronEndo; Orange, California). Regardless of the device chosen, the continuous mode is selected and the intensity is set at the manufacturer’s recommendation for performing the hot pulp test. Within a few seconds, the insert tip’s metallic end becomes sufficiently hot.

The clinician may use the heat from the insert tip to thermosoften a gutta percha cone into a round ball, which is then attached to the Hot Pulp Test Tip. A thermosoftened ball of gutta percha will readily adapt to the morphological contour of a tooth, which results in achieving better conductivity into the pulp chamber. As with the cold test, the diagnostician must first establish a baseline by testing asymptomatic teeth. The hot test and related hand signals are performed as described for the cold test. Thermosoftened gutta percha is placed towards the cervical aspect of a moist or lubricated tooth, on either the buccal or lingual aspects of the crown.

A clinical photograph shows the Hot Pulp Test Tip with thermosoftened gutta percha contacting the cervical aspect of a maxillary lateral incisor.

When the patient raises their hand, the diagnostician should immediately remove the hot stimulus. In the event the patient does not perceive any heat sensation in their tooth after 5-6 seconds, then the stimulus should be removed. However, certain pulpally involved teeth may not initially be stimulated by the hot test, then after several seconds, elicit significant pain. For this reason, it is advisable to wait several seconds before placing a hot stimulus on the next tooth. Some teeth with irreversible pulpitis require a repeated hot stimulus over time to reach a threshold that provokes pain. Therefore, when a patient reports pain upon drinking hot coffee, it is informative to inquire if the pain is experienced on the first sip or after repeated sips. This information may be useful when performing and sequencing the hot pulp test. At times, after carefully conducting the hot test as described, the diagnostician may not be able to reproduce the patient’s chief complaint. An alternate method of heat testing involves isolating the crown of a tooth with a rubber dam, and then applying hot water with a syringe.

The advantage of this method is that hot water instantaneously bathes the entire clinical crown, improves conductivity, and more closely replicates the way heat naturally contacts the tooth during the ingestion of hot foods and liquids.

A clinical photograph demonstrates syringing 60°C hot water onto a tooth that has been carefully isolated with a rubber dam.

The disadvantage of this test is the cooperation required to comfortably place a clamp on a tooth, then the time required to perform this test on several teeth. Regardless of which hot pulp test method was utilized, the clinician is assessing the immediacy, intensity and duration of each response. As with the cold test, the response that lingers disproportionately, as compared to contralateral, opposing and adjacent teeth, is diagnostic. On occasion, certain patients present with a glass of cold water tightly grasped in their hand. These patients typically have a necrotic pulp and the attendant pain can be “turned off” when they drink cold water or when the diagnostician places an ice pencil on the offending tooth. Provoking a “toothache” with a hot stimulus then turning off the pain with a cold stimulus is profoundly diagnostic.

On occasion, after conducting a thorough clinical and radiographic examination and performing VPT, there may be a diagnostic dilemma, such as when a patient reports acute, radiating or diffuse pain that cannot be localized. In these situations, it may be helpful to remove a specific crown or administer block anesthesia in either the maxillary or the mandibular arches to help localize the source of the chief complaint. Clinicians should recognize that in spite of performing a thorough and comprehensive endodontic examination, there will be times when a definitive diagnosis cannot be made. It is wise to remember the Hippocratic oath which states, “Do no harm while doing good.” In these instances, it is appropriate to dismiss the patient and reschedule when their symptoms can be localized.