Ultrastructure and nanomechanical properties of cementum dentin junction

Abstract

The attachment between cementum and dentin has been given several definitions and nomenclature, including: interzonal layer, intermediate cementum, collagen hiatus, Hopewell-Smith's hyaline layer, and more commonly, cementum-dentin junction (CDJ). Understanding the attachment of two structurally dissimilar hard tissues such as cementum and dentin defined by a junction may provide information necessary to engineer functionally graded materials that can be used for efficient tooth restorations in clinical dentistry and other bioengineering applications. Hence, in this study, as a first step toward understanding the CDJ using a biomechanical approach, it was hypothesized that the CDJ between cementum and dentin is a wide zone with mechanical properties significantly lower than the neighboring tissues. The structure of the CDJ was studied using an atomic force microscope (AFM), and site-specific mechanical response of the three regions; cementum, CDJ, and dentin were determined using an AFM-nanoindenter under dry and wet conditions. The AFM results of the CDJ demonstrated a valley under dry conditions and a peak under wet conditions. The magnitude of the depth of the valley was approximately the same as the height of the peak of the CDJ, ranging from 10 to 40 microm. The nanomechanical properties under dry conditions indicated no significant difference (p > 0.05) in elastic modulus and hardness of the CDJ (Er = 17.5 +/- 2.7 GPa, H = 0.6 +/- 0.1 GPa) and cementum (Er = 18.7 +/- 2.5 GPa, H = 0.6 +/- 0.1 GPa). The mechanical properties of the CDJ were significantly lower (p << 0.05) than dentin (Er = 19.9 +/- 2.9 GPa, H = 0.6 +/- 0.1 GPa) under dry conditions. However, under more relevant hydrated conditions, the mechanical properties of CDJ (Er 3.0 +/- 0.7 GPa, H = 0.1 +/- 0.0 GPa) were significantly lower (p << 0.05) than those of cementum (Er 6.8 +/- 1.9 GPa, H = 0.2 +/- 0.1 GPa) and dentin (Er 9.4 +/- 2.3 GPa, H = 0.3 +/- 0.1 GPa). Based on the results from this study, it can be concluded that the CDJ can be regarded as a wide zone containing large quantities of proteins including collagen that contribute to hydration and significantly reduce mechanical properties, compared with the adjacent hard tissues, cementum, and dentin. The lower mechanical properties of the CDJ may make it possible for it to redistribute occlusal loads to the alveolar bone.

The tooth attachment mechanism defined by structure, chemical composition and mechanical properties of collagen fibers in the periodontium

“…Collagen fibers are continuous from cementum through the CDJ to root mantle dentin-The AFM micrograph shown in Figure 1e illustrates continuous collagen fibers from the root surface through the CDJ into mantle dentin. Notice the previously reported [8] valley-like CDJ under dry conditions (Fig. 1e).…”

“…Nanomechanical tests on dry and wet specimens were performed using an AFM, to which a load-displacement transducer (Triboscope Micromechanical Test Instrument, Hysitron Incorporated, MN) was attached [8]. A sharp diamond Berkovich indenter with a radius of curvature less than 100 nm (Triboscope Micromechanical Test Instrument, Hysitron Incorporated, Minneapolis, MN) was fitted to the transducer.…”

“…Cementum is attached to root dentin via a hydrophilic fibrous cementum-dentin junction (CDJ) [8]. The CDJ is also known as the innermost cementum layer, intermediate cementum or collagen hiatus and consists of collagen fibrils and remnants of epithelial cells of Hertwig's Epithelial root sheath (HERS) [9].…”

“…In this study the attachment of bulk cementum to root mantle dentin was investigated with respect to the periodontal ligament (PDL) and previously reported hydrophilic CDJ [8]. This study sought to demonstrate that the collagen fibers within the CDJ are continuous with the Sharpey's fibers in human cellular cementum, using various high-resolution imaging techniques and histology.…”

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

“…Others have shown that enamel crystals are formed at a given distance from the dentine surface (Simmer and Fincham 1995;Diekwisch et al 1995;Aoba 1996;Bodier-Houllé et al 2000) and could either reach dentine crystals by a subsequent growth (Takano et al 1996) or remain distant (Bodier-Houllé et al 2000;Dong and Warshawsky 1996). In addition, there are both a cementum-enamel junction (CEJ) (Wang et al 2006b), which is quite similar to DEJ, and a cementumdentine junction (CDJ) (Ho et al 2004(Ho et al , 2005Jang et al 2014).…”