Dental pulp test

Dental pulpal testing is a clinical and diagnostic aid used in dentistry to help establish the health of the dental pulp within the pulp chamber and root canals of a tooth. Such investigations are important in aiding dentists in devising a treatment plan for the tooth being tested. There are two major types of dental pulp tests. "Vitality testing" assesses the blood supply to the tooth, whilst "sensitivity testing" tests the sensory supply.

Clinical Application

Dental pulp tests are valuable techniques used to establish the pulpal health status of a tooth in dentistry. The diagnostic information obtained from pulpal testing is then used alongside a patient's history, clinical and radiographic findings to determine a diagnosis and prognosis of the tooth.

Pulp tests are useful for the following procedures in dentistry:

a) diagnosis of endodontic pathology,

b) localisation of tooth pain,

c) differentiating between odontogenic and non-odontogenic pain,

d) assessing pulpal status following dental trauma,

e) establishment of pulpal health prior to prosthodontic treatment.

Pulpal tests may be conducted via stimulation of the sensory fibres within the pulp (sensibility testing) or by assessing pulpal blood flow (vitality testing). All available techniques are reported to have limitations in terms of accuracy and reproducibility and therefore require careful interpretation in clinical practice.

Sensitivity testing

Sensitivity tests assess the sensory response of a tooth to an external stimulus, results which may be extrapolated to indirectly determine pulpal health status. Sensory stimuli, such as heat, cold or an electrical current, are applied to the tooth in question in order to stimulate the nocireceptors within the pulp. The type of sensory fibres activated and therefore the response felt by the patient depends on the stimulus used. Sensibility testing is based on Brännström's Hydrodynamic Theory, which postulates that the activation of nocireceptors is caused by fluid movement within the dentinal tubules in response to thermal, electrical, mechanical or osmotic stimuli.

Responses To Sensitivity Testing

There are three primary outcomes of a pulp sensitivity test, as described.

a)Normal Response: Healthy pulps are expected to respond to sensitivity testing by eliciting a short, sharp pain which subsides when the stimulus is removed, indicating that the nerve fibres are present and responsive.

b) A Heightened or Prolonged Response: An exaggerated or lingering response to sensitivity testing indicates some degree of pulpal inflammation. If the pain is pronounced yet subsides once the stimulus has been removed, a diagnosis of reversible pulpitis may be probable. However, a lingering pain which continues despite the removal of the stimulus is indicative of irreversible pulpitis.

c) No Response; A lack of response to sensitivity testing suggests that the nerve supply to the tooth has been diminished, as in the case of pulpal necrosis or in previously root treated canals.

1. Thermal Tests

Thermal testing, which involves the application of either a hot or cold stimuli to the tooth, is the most common form of sensibility test.

A number of products are available for cold testing, each with varying melting points. Although household ice (0°C) is cheap and easy to obtain, it is not as accurate as colder products. Dry ice (-78°c) can be used, however there have been concerns regarding the damaging effects of using something so cold in the oral cavity despite evidence to suggest that dry ice has no negative impact on mucosal or tooth structure . Refrigerant sprays, such as ethyl chloride (-12.3°C), 1,1,1,2-tetrafluoroethane (-26.5°C) or a propane/butane/isobutane gas mixture are further commonly used cold tests. Cold testing is thought to stimulate Type Aδ fibres in the pulpal tissue, which elicit a short, sharp pain.

Heat tests include using heated instruments, such as a ball-ended probe or gutta-percha, a rubber commonly used in root canal procedures. Such tests are less commonly used as they are thought to be less accurate than cold tests, but may be more likely to cause damage to the teeth and surrounding mucosa .

2. Electric Pulp Testing (EPT)

An electrical current can be applied to the tooth in order to generate an action potential in the Type Aδ fibres within pulp, eliciting a neurological response. Such tests are conducted by applying a conducting medium (e.g. toothpaste) on a dried tooth and placing the probe tip of an electric pulp tester on the surface of the tooth closest to the pulp horn(s). The patient is then directed to hold the end of the conducting probe to complete the circuit and asked to let go of the probe when a ‘tingling’ sensation is felt. The use of electric pulp testing has been questioned in patients with traditional cardiac pacemakers despite no evidence of interferences in humans, particularly with more modern devices . Care must be taken if using an electric pulp test on a tooth adjacent to metallic restorations, as these can create electrical conduction and yield false negative results.

3. Bite test

The patient is asked to bite on a hard object such as cotton swab, tooth pick, or an orange wood stick. Pain on biting may indicate a fractured tooth.

4. Anaesthesia Testing

A single tooth is anaesthetised until the pain is diminished. If the pain continues, the procedure is repeated to the tooth mesial to it. This procedure is continued until the pain is gone. If the source of pain cannot be determined, the same technique on the opposite arch is repeated.

5. Test cavity

This technique is only used when the results produced by all other methods above are inconclusive and is regarded as the last resort. High speed burs are used, without anaesthetic, to drill a small window through either enamel or a restoration to dentine. The patient is asked whether a painful sensation is experienced during drilling, indicating pulpal vitality. In the event of a vital pulp, a painful response is provoked when dentin is invaded and a simple restoration will then be placed. On the contrary, a partially necrotic pulp will not be stimulated to the same extent as a vital pulp. In this case, the dentist would initiate access and invade progressively deeper into dentine, without a sensory response. This invasive method can be influenced by the anxiety levels of the patient, and therefore is generally avoided.

Limitations of Sensitivity Testing

Sensitivity testing is routinely used to establish pulpal status in clinical dentistry and is an invaluable diagnostic aid. Nevertheless, all tests have some limitations and therefore the results should be interpretated by an experienced dentist in light of clinical and radiographic symptoms. Sensitivity tests only indicate the presence or absence of the nerve supply to a chosen tooth and, although a prolonged response to such tests indicate pulpal inflammation, the degree of inflammation or innervation cannot be inferred from these tests.

False positive or false negative results are possible when performing a sensitivity testing. A false positive response occurs when a patient responds to sensitivity testing despite the lack of sensory tissue in the test tooth. Such responses may occur due to innervation of adjacent teeth due to inadequate isolation of the test tooth, in anxious patients who perceive pain despite no sensory stimulus, or in multi-rooted teeth which still have residual pulpal tissue in one canal . False negative results, which refer to innervated teeth which do not respond to sensibility testing, can occur in teeth which have been recently traumatised, those which have incomplete root development, are heavily restored or have a significantly reduced pulp size due to the production of tertiary or sclerotic dentine .

Pulpal sensitivity testing may be regarded as inferior to vitality testing as they do not definitively prove that the tooth has a blood supply and is vital. Nevertheless, electric pulp testing and cold testing, particularly with Endo-Ice, have been found to be accurate and reliable methods of assessing pulpal health, especially when used in combination . However, cold testing is more accurate than electric pulp testing in immature or traumatised teeth.

Vitality testing

Vitality tests assess the vascular supply of a tooth. Vascular supply is a more accurate and reliable indicator of pulpal health than sensibility testing; however their use in clinical practice is hindered due to cost, time and equipment requirements . The diagnostic methods to assess the vascular response of the pulp include:

1. Laser-Doppler Flowmetry

A laser beam directed onto the tooth follows the path of dentinal tubules to the pulp. The viability of the vascular supply of the pulp is determined by the output signal generated by the backscattered reflected light from circulating blood cells. The reflected light is Doppler-shifted and has a different frequency to those reflected by the surrounding tissues which are static. An arbitrary unit of measurement, ‘perfusion unit’ (PU, is used to measure the concentration and velocity (flux) of blood cells. The output of laser doppler flowmetry may be influenced by the blood flow in surrounding tissues, and therefore the test tooth must be adequately isolated to avoid inaccuracies .

2. Pulse Oximetry

This method utilises the difference in red and infrared light absorption by oxygenated and deoxygenated red blood cells within blood circulation to determine the oxygen saturation level (SaO2) .

3. Dual Wavelength Spectrophotometry

The use of dual wavelength light establishes the contents within the pulp chamber.

See Also

• Dental pulp
• Pulpitis
• Endodontics