Factors that affect the magnitude and the direction of incisal bite forces: A possible role for pulpal mechanoreceptors

It is generally accepted that pain is the only sensation aroused when pulpal nerves are stimulated. The stimuli used to evoke the sensation have always been artificial such as drilling a tooth, blowing air on exposed dentine or applying an electrical shock. Pain has never been evoked in response to the type of stimulus that would normally be experienced. It is very difficult to understand the functional advantage of encasing sensory nerves inside a tooth with the only function of registering pain in response to abnormal stimuli. It is postulated here that dentine and its contained nerves act as a "stress sensor." A transducer was designed that, when clenched between upper and lower teeth, could be used to measure the magnitude and direction of a bite force. The role of the putative mechanoreceptors was tested by varying the stress on incisors while measuring the maximum force subjects could develop when clenching on them. The force was increased as the stress was decreased. No nerves other than those in the pulp could have been used to detect the stress. In a situation which precluded the use of any other receptors than those in the incisor pulp it was found that subjects could discriminate between the hardness of materials clenched between upper and lower incisors. Finally when loads within the normal physiological range were applied to extracted human teeth, an amount of fluid was displaced sufficient to stimulate pulpal nerves. It is suggested that pulp may contain mechanoreceptors. The receptors may be subconsciously used to protect teeth from potentially harmful bite forces and probably help establish a precise cuspal interdigitation. They can also be consciously used to discriminate between the hardness of harder food. Forces applied to a tooth deform dentine, displace dentinal fluid into the pulp and subsequently activate mechanoreceptors inside the tooth either in dentine, predentine or pulp proper.