Local properties of a functionally graded interphase between cementum and dentin

Abstract The study of natural interfaces may provide information necessary to engineer functionally graded biomaterials for bioengineering applications. In this study, the mechanical, structural, and chemical composition variations associated with a region between cementum and dentin were studied with the use of nanoindentation, microindentation, optical microscopy, and Raman microspectroscopy techniques. Three‐millimeter‐thick transverse sections ( N = 5) were obtained from the apical one‐third of the roots of sterilized human molars. The samples were ultrasectioned at room temperature with the use of a diamond knife and an ultramicrotome. Longitudinal ground sections of 100 μm thickness were prepared and stained with von Kossa stain to determine the mineralized regions within the molar roots. Raman microspectroscopy was used to determine the relative inorganic content, mainly apatite (PO ν 1 mode at 960 cm −1 ) and organic content, mainly collagen (CH stretch at 2940 cm −1 ) between cementum and dentin bulk tissues. The microindentation and nanoindentation results indicated a gradual transition in hardness from cementum to dentin over a width ranging from 100 to 200 μm. However, the variation in hardness data for cementum and dentin by nanoindentation was larger (0.62 ± 0.21, 0.77 ± 0.14 GPa) than from microindentation (0.49 ± 0.03, 0.69 ± 0.07 GPa). Within the 100 to 200 μm region there was a 10 to 50 μm fibrillar hydrophilic cementum–dentin junction (CDJ) with mechanical properties significantly lower than either the cementum or the dentin side of CDJ. Light microscopy revealed a 100 to 200 μm translucent region between cementum and dentin. Raman microspectroscopy results showed a variation in organic and inorganic composition 80 to 140 μm wide. It was concluded that a morphologically and biomechanically different CDJ lies within a wider cementum–dentin interphase. Hence, cementum, dentin, and the interphase can be classified as a functionally graded dental tissue within the root of a tooth. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 480–489, 2004