Investigations on the dynamics of water in the macrostructural dentine

Abstract

The purpose of this study was twofold: (1) to investigate the nature and degree of water loss at 21 degrees C, 60% relative humidity (dehydration) and at 105 degrees C (desiccation), and to relate these findings with (2) the strains produced in the dentine structure during dehydration and rehydration processes. In stage 1, digital moire interferometry (DMI) was used to study the strain distribution pattern during dehydration and rehydration at 21 degrees C. In stage 2, the nature and degree of water loss was determined using gravimetric analysis and nuclear magnetic resonance spectroscopy. DMI showed that dehydration produced strains in the dentine structure after an initial latent period. Gravimetric analysis showed that dentine exhibited an initial rapid water-loss phase followed by a slow and steady water-loss phase. Though the major portion of water loss occurred in the initial 2 h of dehydration (rapid water-loss phase), no obvious strains were produced during this period. Rehydration lead to the major reversal of dehydration-induced water loss and strains in dentine. Heating at 105 degrees C resulted in further substantial loss of water from dentine. These experiments highlighted that the free water in the dentine surface, porosities and tubules are lost rapidly and constitute the major water lost when dehydrated at 21 degrees C.

Effect of Hydration on the Strain Gradients in Dental Hard Tissues after Heat and Cold Application

“…During experiments specimens were placed in a very stable, specially designed jig. DMI has been used in previous studies to characterize and investigate the biomechanical properties of dental hard tissues (11,12). Heat stimuli were applied by using heated gutta-percha sticks (z135 C), and cold stimuli were applied by using refrigerant spray on a cotton pellet (z-50 C) in the middle third of the labial surface of the crown (6,13).…”

“…The level of hydration, in particular the free water, has been shown to influence the mechanical stress-strain behavior of dentin (12). It was also shown that the free water is lost rapidly within the first 2 hours of exposure to room conditions as a result of evaporation from the dentinal tubules and dentin surface (11). These findings suggest that care should be exercised during sample preparation and while comparing findings from different studies.…”

“…Digital moiré interferometry (DMI) is a highly sensitive and high-resolution approach that uses the principles of optical interferometry to measure in-plane, whole-field deformation from entire surface of interest (11,12,16,17). DMI records the real-time strain response from surface of a specimen in both the x and y directions simultaneously.…”

“…Keeping in mind the gradients in thermal/mechanical properties of dental hard tissues, the purpose of this in vitro study was to evaluate the pattern of thermal strain gradients within the tissues/interfaces quantitatively under different levels of hydration. The DMI system used in the study has been previously calibrated and tested as described in earlier experiments (11,12).…”

Importance of aging to dehydration shrinkage of human dentin

“…During the convection of fully mineralized tissues in air, the free water is lost rapidly and the strains are small, generally < 1% [17] . Therefore, quantifying dehydration shrinkage in hydrated and highly mineralized tissues requires an approach with adequate measurement resolution, which can not be hindered by the moisture changes.…”