Influences of the sample shape and compression temperature on the deformation behavior and mechanical properties of human dentin

Deformation behavior and mechanical properties of samples of human dentin having different geometries were studied under compression in liquid nitrogen. In this case, the plastic response of the collagen fibers in dentin was excluded. The findings were compared with the mechanical properties of dentin at room temperature. Such a comparison allows the plastic contribution of collagen in human dentin to be estimated for samples of different shapes. It was shown that the deformation behavior of human dentin under compression is similar at 77 K and 300 K. The dentin samples with low aspect ratio exhibited almost brittle behavior, whereas those with high aspect ratio were prone to considerable deformation. SEM study of the fracture surfaces of samples tested at room and liquid nitrogen temperatures has shown that they are similar. Examination of cracks on the compression surface of samples agrees with this conclusion. However, the mechanical characteristics of dentin depended on the temperature of testing. The compression strength and elastic deformation of dentin at 77 K are higher than these parameters at room temperature, while the plasticity of dentin at 77 K is lower. The plastic contribution of collagen fibers at room temperature was estimated on the basis of this comparison. The total plasticity of dentin is the sum of the contributions of both collagen and the geometry of the sample. The plasticity of dentin samples having a low aspect ratio is provided by collagen fibers only, while geometric factors are dominant for samples with a high aspect ratio. The contribution of collagen fibers to the plasticity of dentin depends on the geometry of samples with an intermediate aspect ratio.