Effect of hydration on the strain gradients in dental hard tissues after heat and cold application.

Introduction: This study was aimed to investigate the thermal strain gradients on dental hard tissues to localized heat and cold applications, applied to assess the vitality of pulp. The role of hydration on the thermal strain distribution within the enamel, dentin, and dentino-enamel junction (DEJ) was examined by using a digital moiré interferometry.

Methods: Extracted bovine incisors were prepared, and high-frequency diffraction gratings were replicated on one surface. Heat (120°C-140°C) and cold (-50°C) stimuli were applied on the external surface, and the strain patterns were recorded and analyzed for the first 3 seconds. The specimens were tested under fully hydrated and partially dehydrated conditions (72 hours at 24°C, 60% relative humidity).

Results: Distinct thermal strain gradient was observed in the enamel, dentin, and DEJ after the application of heat and cold stimuli. Application of both heat and cold resulted in significantly higher strains in the partially dehydrated teeth than in the fully hydrated teeth (P < .05). There was only a marginal increase in strains at the location of application of stimuli in hydrated teeth. The DEJ in both the fully hydrated and partially dehydrated teeth showed the highest strains.

Conclusions: There was a marked difference in the thermal strain gradients within dental hard tissues after the application of heat/cold stimuli, depending on the level of tissue hydration. The findings from this study highlighted the role of free water and structural characteristics of enamel, dentin, and DEJ in dissipating the thermal strains in the tooth.