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Structure of Mature Enamel
Published in Colin Robinson, Jennifer Kirkham, Roger Shore, Dental Enamel, 2017
Roger C. Shore, Colin Robinson, Jennifer Kirkham, Steven J. Brookes
Beneath the incisal edge of anterior teeth and the cusps of posterior teeth, the path of the prisms becomes much less ordered giving rise to a very confused arrangement — the so-called gnarled enamel. Boyde,5 however, doubted that there was any real increase in complexity and that the appearance arose because "the standard histological section planes intercept the structure in a greater variety of directions." A section taken through the cusp center would possess intact Hunter-Schreger bands radiating around the apex of the cusp. In cats and dogs the Hunter-Schreger bands may present a spiral appearance, the center of the spiral being the cuspal tip.13 This would be consistent with groups of prisms spiralling around a central axis running from dentinal cornua to cusp tip.7
A step toward bio-inspired dental composites
Published in Biomaterial Investigations in Dentistry, 2023
Janine Tiu, Renan Belli, Ulrich Lohbauer
The current selection of dental restorative resin composites for computer-aided design and manufacturing (CAD/CAM) continues to expand with advances in technology. While restorative dentistry sets its bounds with mechanical, biological and esthetical demands, it is imperative that materials development does not stagnate. Instead, development should intently move toward replicating the mechanical properties of the natural tissues they aim to restore. As the human enamel is a highly textured structure composed of high aspect-ratio reinforcing units, the reinforcing concept is optimized for intraoral loading and maximum damage resistance. Nacre presents a similar concept that should guide us in development of more naturally inspired reinforcing concepts. At this stage, the three-dimensional replication of structures in the micrometric scale remains too high a feat for current CAD/CAM technologies. However, incremental strides can be taken to ensure progress toward bio-inspired materials. Innovative attempts are seen in polymer-infiltrated ceramic scaffolds [1,2]. While exhibiting Young’s modulus matching with dentin, these infiltrated structures fall short in resembling the structural organization and other critical mechanical behavior seen in natural dental tissues [3]. Hence, the basic mechanical principles are often overlooked. This includes the required arranged configuration of high aspect-ratio microstructural units responsible for complex crack-particulate interactions. Noteworthy innovation is seen with the inclusion of short glass fibers in dental resin composites [4]. The fibers offer an efficient means of inducing crack bridging toughening mechanisms similar to those seen in human enamel [5,6]. Prism orientation, especially in the inner region of the enamel layer (called Hunter-Schreger-Bands), account for effective energy absorption and toughening during crack propagation from the surface toward the dentin-enamel junction [7]. The orientation of high aspect-ratio elongated microstructural units, be it fibers in composites or crystal phases in glass-ceramics [8,9], provide the large-scale anisotropic architecture that leads growing cracks to deflect into high-energy-consuming shear loading (mode-II) states [10].