Influence of temperature and foil hardness on interocclusal tactile threshold

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Abstract
Determinations of interocclusal tactile threshold levels so far have involved neither appropriate psychophysical approaches nor an assessment of the mechanical and thermal properties of the foils used. Twenty subjects (12 females) aged 18 to 50 (mean age 35) were tested for their absolute threshold level (RL). Both the method of limits and the staircase method were applied to determine the active or passive RL. For the active RL assessment, foils of different thicknesses were placed between edge‐to‐edge opposed incisors during gentle biting. Inner ear receptors of the blindfolded subjects were blocked by broad band noise applied through earphones, because vibrations induced by occlusal contact and conducted through bone might be perceived by these receptors. The foils presented were aluminum (Al), tin (Sn), polyester (PE) and calibrated steel (St) (thickness ranging from 8 to 50 μm) which offer different physical and thermal properties. The range of RL of the group varied between 8 μm for aluminum to 46 μm for polyester for 50% correct assessments. Increasing the foil temperature from room temperature (20°C) to body temperature (35°C) significantly increased the RL for conducting materials (one‐way blocked ANOVA). These results indicate that temperature exchange takes place while presenting conducting foils at 20°C (cold stimulus) interocclusally, which influences the RL by activating thermosensitive receptors. The passive RL determination with classical von Frey‐hairs resulted in a mean axial RL of 3.0 g. Both psychophysical RL assessments (method of limits, staircase method) gave reproducible and similar results as ascertained by ANOVA. Furthermore, a positive correlation was established between active and passive RL (Pearson correlation test). It is concluded that the physical and thermal properties of the foils need careful consideration in future experiments on threshold determination. Although active RL determination may involve the activation of non‐periodontal receptors, it remains a realistic parameter to monitor tactile function of teeth.