on the stimulation of sensory nerves in the pulp. it does not provide information on vascular supply to the pulp. the probe tip of the test device is placed directly onto the tooth surface and an electrical stimulus is produced. this stimulus causes an ionic change across the neural membrane, inducing an action potential in the myelinated nerves. the threshold of pain is determined by increasing the voltage. a tingling sensation is felt once the voltage reaches the pain threshold. this threshold level varies between patients, and is affected by factors such as age, pain perception, tooth surface conduction and resistance. the requirements of an ept are appropriate application method, careful interpretation of the results, and an appropriate stimulus. ept must be done with tooth isolation and conduction media. key factors in pulp testing are the enamel and dentine thickness, and the number of nerve fibers in the underlying the pulp. ept is not used in patients with orthodontic bands or crowned teeth, as the current may be conducted to adjacent teeth, resulting in false-positive responses. pulp nerve fibers also respond to lower current intensities and only a small number of pulpal nerves are required to create responses when electrical stimulation is applied. this means that ept may result in false-positive responses in teeth with pulpal necrosis. furthermore, as pulpal and periodontal nerve thresholds overlap, the periodontal nerves may give a false indication of tooth sensibility. possible explanations for false-positives include: response caused by conduction of the current because of periodontal or gingival issues breakdown products associated with pulp necrosis may be able to conduct electric current next to infected and hypersensitive pulp tissue inflamed pulp tissue may still be present metallic restorations or orthodontic gear are still present studies have indicated that there is little correlation between histopathological status of the pulp and clinical information. a negative ept response showed localized necrosis in 25.7% of cases and 72% of cases. thus, 97.7% of cases with a negative response to ept indicated that a root canal treatment should be carried out. test cavity: the preparation of a test cavity involves cutting into the dentine of a tooth to determine whether the sensory element of the pulp is still functioning. test cavity preparation is a last resort as this method is considered invasive and irreversible. it is also unlikely that this procedure would provide any more information than thermal and electric pulp sensibility tests. therefore, test cavities are not generally used in practice as a means of testing pulp sensibility. treatment once the pulp has become inflamed, the tooth can be diagnostically divided into two categories: reversible pulpitis and irreversible pulpitis reversible this is the condition where the pulp is inflamed and is actively responding to an irritant. this may include a carious lesion that has not reached the pulp. symptoms include transient pain or sensitivity resulting from many stimuli, notably hot, cold, sweet, water and touch. the pulp is still considered to be vital. this means that once the irritant is eliminated, usually by removal of decay and the placement of a restoration, that the pulp will return to its normal, healthy state. when it becomes painful and decayed the tooth may become known as a "hot tooth" and local anesthetic may not work as well. irreversible this is the condition where the pulp is irreversibly damaged. the pulp cannot recover from the insult and damage. for example, decay that has reached the pulp of the tooth introduces bacteria into the pulp. the pulp is still alive, but the introduction of bacteria into the pulp will not allow the pulp to heal and it will ultimately result in necrosis, or death, of the pulp tissue. symptoms associated with irreversible pulpitis may include dull aching, pain from hot or cold (though cold may actually provide relief) lingering pain after removal of a stimulus, spontaneous pain, or referred pain. clinical signs may include reduced response to electronic pulp testing and painful response to thermal stimuli. today electronic pulp testers are rarely used for diagnosis of the reversibility of pulpitis due to their unreliable nature. instead they should only be used to test the vitality of teeth. the pulp of a tooth with irreversible pulpitis may not be left alone to heal. that is at least the general viewpoint of the dental profession, and not every dentist would agree that a dead tooth must be treated. no statistics are known but it is possible to have a trouble-free tooth after irreversible pulpitis, albeit a dead tooth. the tooth may be endodontically treated whereby the pulp is removed and replaced by gutta percha. an alternative is extraction of the tooth. this may be required if there is insufficient coronal tissue remaining for restoration once the root canal therapy has been completed.