Enamel distribution, structure and mechanical alterations in col1-caPPR mice molar.

Enamel mineralisation is a highly controlled process in which the deposition, growth, and maturation of inorganic crystallites are regulated by secreted matrix proteins at the molecular and cellular level. Maxillary and mandibular first molars from the col1-caPPR mutants as well as normal controls aged for 12 weeks were observed by SEM and nanoindentation, respectively. Several types of aberrations in enamel distribution and crystal organisation were encountered in the transgenic molars.

The mechanical anisotropy on a longitudinal section of human enamel studied by nanoindentation.

Nanoindentation has been widely used for probing the mechanical properties of tooth, especially for characterizing its complex hierarchical structures. Previous studies have confirmed the anisotropic mechanical behaviors caused by the alternated orientations of enamel rods and the alignment of fibril-like hydroxyapatite crystals, but the longitudinal section of enamel, which was composed of parallel-arranged rods, was regarded as a homogeneous continuum as always. In this study, nanoindentation combined with SEM was carried out with the indenter rotating on the longitudinal section of enamel to evaluate the relativity between the nano-mechanical properties and the orientation of indentation impressions.

Disturbed enamel biomineralization in col1-caPPR mouse incisor.

During the mineralization process of enamel, gene expression controls the activities of ameloblasts, the secretion and assembly of an extracellular protein matrix, affecting the final structure and functions. In this study, the enamel in the maxillary and mandibular incisors of wild-type and transgenic (col1-caPPR) mice, in which a constitutively active PTH/PTHrP receptor (PPR) was targeted to osteoblastic cells, was observed by scanning electron microscopy (SEM), Fourier transform infrared microscopy (FTIRM), and nanoindentation. The SEM studies showed that several different patterns of aberrations in crystal arrangement, disturbed prism organization without decussation, as well as abnormal enamel distribution were encountered in transgenic enamel.

The enamel softening and loss during early erosion studied by AFM, SEM and nanoindentation.

Enamel dissolution occurs when it contacts with acids produced by plaque bacteria, foods or drinks. There have been numerous and varied studies quantifying and characterizing the rate, extent and chemical aspects of enamel erosion; however, there is still hot debate about the amounts of enamel softening and loss. The objective of this study was to measure the enamel erosion process with high accuracy.