Thermal stimulation causes tooth deformation: A possible alternative to the hydrodynamic theory?

Abstract

Objectives To investigate the relationship between temperature distribution and tooth structure deformation during and after localised application of thermal stimuli used during pulp vitality testing. Methods Strains and temperature changes within tooth structures were recorded when three different thermal stimuli, namely heated gutta percha (120–140 °C), carbon dioxide dry ice (−72 °C) and refrigerant spray (−50 °C), were applied to extracted bovine incisors. Each stimulus was applied for 5 s on the labial enamel surface in a random order, with a 30-min interval between tests. Finite element analysis was performed on basic geometrical shapes to investigate structural deformation in relation to temperature change. Results Application of thermal stimuli to the labial enamel surface resulted in rapid development of strain at the pulpal dentine surface before any temperature change was detected at the dentino-enamel junction. The strain pattern was biphasic; heat produced an initial contraction of the pulpal surface, followed by an expansion, and the reverse pattern was found with cold stimulation. Finite element analysis confirmed that the initially pronounced thermal gradient across the enamel and dentine caused rapid flexural deformation before temperature changes reached the dentino-enamel junction. When the temperature changes reached the pulpal dentine and thus reduced the thermal gradient, the direction of the strain was reversed. Conclusion These results indicate possible alternatives to the hydrodynamic theory for thermal stimuli applied to intact teeth. Mechanically induced dentine deformation may trigger nerve impulses directly, or may exert mechanically induced dentinal fluid flow that triggers nerve activity.