Objectives The objectives of this study were to quantify the dimensional changes in dentin and enamel during dehydration, and to determine if there are differences between the responses of these tissues from young and old patients. Methods Microscopic Digital Image Correlation (DIC) was used to evaluate deformation of dentin and enamel as a function of water loss resulting from free convection in air. Dimensional changes within both tissues were quantified for two patient age groups (i.e. young 18≤age≤30 and old 50≤age) and in two orthogonal directions (i.e. parallel and perpendicular to the prevailing structural feature (dentin tubules or enamel prisms)). The deformation histories were used to estimate effective dehydration coefficients that can be used in quantifying the strains induced by dehydration. Results Both dentin and enamel underwent contraction with water loss, regardless of the patient age. There was no significant difference between responses of the two age groups or the two orthogonal directions. Over one hour of free convection, the average water loss in dentin was 6% and resulted in approximately 0.5 % shrinkage. In the same time period the average water loss in the enamel was approximately 1% and resulted in 0.03% shrinkage. The estimated effective dehydration coefficients were -810 µm/m/(% weight loss) and -50 µm/m/(% weight loss) for dentin and enamel, respectively. Significance The degree of deformation shrinkage resulting from dehydration is over a factor of magnitude larger in dentin than enamel.

No abstract

No abstract

No abstract

Fish scales serve as a dermal armor that provides protection from physical injury. Due to a number of outstanding properties, fish scales are inspiring new concepts for layered engineered materials and next-generation flexible armors. While past efforts have primarily focused on the structure and mechanical behavior of ontogenetic scales, the structure-property relationships of regenerated scales have received limited attention. In the present study, common carp (Cyprinus carpio) acquired from the wild were held live in an aquatic laboratory at 10° and 20°C. Ontogenetic scales were extracted from the fish for analysis, as well as regenerated scales after approximately 1 year of development and growth. Their microstructure was characterized using microscopy and Raman spectroscopy, and the mechanical properties were evaluated in uniaxial tension to failure under hydrated conditions. The strength, strain to fracture and toughness of the regenerated scales were significantly lower than those of ontogenetic scales from the same fish, regardless of the water temperature. Scales that regenerated at 20°C exhibited significantly higher strength, strain to fracture and toughness than those regenerated at 10°C. The regenerated scales exhibited a highly mineralized outer layer, but no distinct limiting layer or external elasmodine; they also possessed a significantly lower number of plies in the basal layer than in the ontogenetic scales. The results suggest that a mineralized layer develops preferentially during scale regeneration with the topology needed for protection, prior to the development of other qualities.