Novel Handheld Device to Determine Physical Properties of Hydrated Dentin

Introduction: Standardized minimally invasive caries-excavation aims at selective caries removal of infected, carious dentin, resulting in an irregular cavity floor of remineralizable, affected dentin.

Objectives: To determine the in-vitro microhardness and Young's modulus of wet affected dentin at the cavity floor.

Methods: Extracted human teeth (N=8) with extensive carious lesions into inner third of dentin were excavated using standardized procedures for selective caries removal. Material properties of healthy and irregularly shaped, affected dentin at the cavity floor were determined using a novel handheld diagnostic instrument. The device, which measures the hardness and elastic modulus of dentin by indenting the surface on the order of 50-100 µm, has a sharpened test probe which slides inside a hypodermic syringe that serves as a local reference.

Results: The surface of healthy occlusal dentin and deeper affected dentin showed a mean indentation hardness of 0.5 GPa, and 0.1 to 0.2 GPa, respectively. These hardness values were comparable to the hardness recently reported with nanoindentation of wet dentin (0.3 GPa). The mean elastic modulus measured was 12 GPa and 3 GPa, respectively, comparable to the elastic modulus recently reported with nanoindentation of wet dentin (12 GPa).

Conclusion: The device enabled determination of microhardness and elastic modulus in irregularly shaped, fully-hydrated dentin cavities. The hardness and elastic modulus of healthy and affected wet dentin demonstrated significantly different values, while being close to the range of wet-environment values reported in literature. The novel device demonstrated great potential to facilitate measuring of in-vivo hydrated material properties of irregularly-shaped, mineralized tissues (dentin, bone etc.).

Supported in part by DoD/US Army DAMD17-03-1-0556 and NIH/RO1 GM65354.