The aim of this in vivo pilot study was to record variations in temperature at various sites in a subject's mouth in response to a standardised thermal challenge and to determine a more realistic thermocycling regimen for future use. A volunteer who suffered from no dentinal hypersensitivity had modified study models prepared for constructing vacuum-formed PVC splints. Perforations 2 mm in diameter were placed for thermocouples facially and lingually in the midcoronal sites of the upper and lower central incisors, canines, second premolars, and second molars to measure temperatures at these sites. A standardised drinking regimen was followed of hot black coffee (72.5 degrees C) followed by cold orange juice (6.0 degrees C). Contralateral sites experienced similar temperature changes of short duration. A maximum of 68.0 degrees C and a minimum of 15.4 degrees C were recorded. Less extreme temperatures were experienced posteriorly, and little or no discernible changes were noted at the facial aspects of the upper second molars or lingually on the lower second molars. Most commonly used thermocycling regimens are clinically unrealistic, and temperatures vary widely throughout the mouth when hot or cold drinks are taken.