This involves applying either heat or cold to a tooth, but neither test is particularly reliable and may produce either false-positive or falsenegative results.
Heat
There are several different methods of applying heat to a tooth. The tip of a gutta-percha stick may be heated in a flame and applied to a tooth. Take great note that hot gutta-percha may stick fast to enamel, and it is essential to coat the tooth with vaseline to prevent the gutta-percha sticking and causing unnecessary pain to the patient. Another method is to ask the patient to hold warm water in the mouth, which will act on all the teeth in the arch, or to isolate individual teeth with rubber dam and apply warm water directly to the suspected tooth. This is explored further under local anaesthesia.
Cold
Three different methods may be used to apply a cold stimulus to a tooth. The most effective is the use of a –50°C spray, which may be applied using a cotton pledget (Fig. 7). Alternatively, though less effectively, an ethyl chloride spray may be used. Finally, ice sticks may be made by filling the plastic covers from a hypodermic needle with water and placing in the freezing compartment of a refrigerator. When required for use one cover is warmed and removed to provide the ice stick. However, false readings may be obtained if the ice melts and flows onto the adjacent tissues.
Local anaesthetic
In cases where the patient cannot locate the pain and routine thermal tests have been negative, a reaction may be obtained by asking the patient to sip hot water from a cup. The patient is instructed to hold the water first against the mandibular teeth on one side and then by tilting the head, to include the maxillary teeth. If a reaction occurs, an intraligamental injection may be given to anaesthetise the suspect tooth and hot water is then again applied to the area; if there is no reaction, the pulpitic tooth has been identified. It should be borne in mind that a better term for intraligamental is intra-osseous, as the local anaesthetic will pass into the medullary spaces round the tooth and may possibly also affect the proximal teeth.