Nano-scale structure and mechanical properties of the human dentine-enamel junction

Despite being an interface between two mechanically mismatched phases of the soft dentine and hard enamel, the dentine-enamel junction (DEJ) in a human tooth is in general capable of withstanding a long working life of repeated dynamic loading. The current poor understanding of the structure and properties of the DEJ has presented a major obstacle to designing better therapeutic protocols for complications concerning the DEJ. In this investigation, it was discovered that the DEJ is a thin, but gradual interface with characteristics transiting from those of dentine to those of enamel. The collagen fibres in dentine enter into the enamel side of the DEJ and terminate in a region in which the hydroxyapatite crystals begin to show enamel characteristics. Using focused ion beam machining, micro-beams were fabricated from regions within 50 μm of the DEJ and were subjected to bend tests. In spite of the similarity in the flexural strength of the DEJ and enamel, fractographs revealed cracks in the DEJ that propagated along structures with dentine characteristics. To the best of our knowledge, this is the first report on the testing of the mechanical properties of the DEJ.