A simple stimulator for periodontal mechanoreceptors in human subjects

Mechanoreceptors in the periodontal ligament are activated by tooth movements as little as 1-3 microns. It has been difficult in the past to move a tooth only over this small distance in order to activate the periodontal receptors without at the same time activating other receptors in related structures. This paper describes a simple solution to this problem based on the use of von Frey hairs (in the form of nylon filaments) rather than a rigid probe, to move the tooth. Filaments of different stiffness are mounted on the moving coil of a loudspeaker to apply different forces to the tooth. The timing of the contact of the filament with the tooth is measured precisely with a simple impact detector. The sensation elicited by this stimulator is abolished by local alveolar anaesthesia, indicating that the stimulation was localised to the periodontal area. The flexible probe is an important safety feature, as it limits the force applied to the tooth, and therefore the distance that the tooth can be displaced. The stimulator, suitable for psychophysical studies on the thresholds of periodontal receptors, on the reflex responses to stimulation of periodontal mechanoreceptors, and teaching applications, can be constructed from readily available components at minimal cost.