Discipline of Endodontics, University of Toronto, Toronto, Ontario, Canada.
J Endod. 2010 Oct;36(10):1643-7. doi: 10.1016/j.joen.2010.06.027. Epub 2010 Aug 12.
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.
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).
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.
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.
本研究旨在探讨牙体硬组织在局部热和冷应用下的热应变梯度，以评估牙髓活力。通过数字云纹干涉法研究了水合作用对牙釉质、牙本质和牙本质-釉质交界处（DEJ）内热应变分布的影响。
从牛牙中提取牙，在一个表面复制高频衍射光栅。在外部表面施加热（120°C-140°C）和冷（-50°C）刺激，记录并分析最初 3 秒的应变模式。将标本在完全水合和部分脱水条件下（24°C，60%相对湿度下 72 小时）进行测试。
在施加热和冷刺激后，牙釉质、牙本质和 DEJ 中观察到明显的热应变梯度。与完全水合的牙齿相比，部分脱水的牙齿在应用热和冷刺激时产生的应变明显更高（P<.05）。在水合牙齿中，刺激应用位置的应变仅略有增加。在完全水合和部分脱水的牙齿中，DEJ 显示出最高的应变。
牙体硬组织在应用热/冷刺激后，其热应变梯度存在显著差异，这取决于组织水合水平。本研究的结果强调了自由水和牙釉质、牙本质和 DEJ 的结构特征在牙齿中耗散热应变的作用。
