The narwhal (Monodon monoceros) cementum-dentin junction: a functionally graded biointerphase.

Area of Science:

• Biomaterials Science
• Biomineralization
• Tissue Engineering

Background:

• Biological interfaces often feature graded zones that provide unique functional properties at the organ level.
• The narwhal tooth's cementum-dentin junction serves as a prime example of such a biological interphase.

Purpose of the Study:

• To investigate the graded structural, mechanical, and chemical characteristics of the narwhal tooth's cementum-dentin junction layer.
• To understand how these properties contribute to resisting mechanical loads.

Main Methods:

• Light and electron microscopy to analyze structural properties.
• Compression testing and site-specific nanoindentation to assess mechanical behavior.
• Microindentation for hardness measurements.
• Raman spectroscopy and synchrotron-source microprobe X-ray fluorescence for chemical composition analysis.

Main Results:

• The cementum-dentin layer is a 1000-2000 μm graded zone with continuous collagen fiber bundles.
• The layer exhibits greater deformation under compression compared to cementum and dentin.
• Lower elastic modulus (2.2 ± 0.5 GPa) and hardness (0.3 ± 0.07 GPa) were observed in the interphase.
• Graded composition was confirmed, with decreasing mineral-to-matrix and phosphate-to-carbonate ratios, and Zn-containing bands.

Conclusions:

• The graded nature of the cementum-dentin junction layer is crucial for its mechanical resilience.
• Understanding these structure-function relationships in biological interphases can inform tissue engineering strategies.