Enamelin Directs Crystallite Organization at the Enamel-Dentine Junction

Abstract

Enamel is an acellular material formed by the intricate process of amelogenesis. Disruption caused at the initial stages of development, by means of mutations in the ENAM gene encoding the enamelin protein, results in enamel hypoplasia. Little is known about the consequence of ENAM mutation on the enamel structure at a crystallographic level. The aim of this study was to characterize the structure of ENAM-mutated enamel to develop a deeper understanding of the role of enamelin protein during formation with regard to crystal organization. Synchrotron X-ray microdiffraction (SXRD) and scanning electron microscopy (SEM) have been used to measure and correlate enamel crystallography and microstructure in hypoplastic and healthy enamel. Rietveld refinement carried out on 2-dimensional diffraction patterns, collected from the Advanced Photon Source, were used to quantify changes in the preferred orientation (crystallographic texture) within the labial regions of each tooth slice and then correlated with the local microstructure. In general, healthy deciduous incisors displayed a higher degree of crystal organization across the labial surface in comparison with the hypoplastic enamel. ENAM plays the greatest functional role at the enamel-dentine junction (EDJ), as it was the region that exhibited lowest texture relative to unaffected controls. Other areas within the tooth, however, such as the cusp tip, displayed greater organization in line with healthy enamel, suggesting its effects are restricted to the early stages of enamel secretion. Observed clinically, the surface of ENAM-mutated hypoplastic enamel can appear to be normal, yet severe sub-nano and microstructural defects appear beneath the subsurface layer. Quantitative characterization of the crystallographic properties from enamel with known genotype expands the understanding of enamel formation processes and can aid better clinical diagnosis and tailor-made treatment.

Biomimetic mineralisation systems for in situ enamel restoration inspired by amelogenesis

“…The surface of ENAM-mutated hypoplastic enamel appears to be normal. However, severe sub-nano and micro-structural defects appear beneath the subsurface layer [ 60 ]. The ~32 kDa cleavage product of ENAM is a functional fragment.…”

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

“…WAXS experiments have been used to study human enamel at different stages of mineralisation with analysis of the texture of HAp crystallites in various regions of the enamel and observation of the presence of two orientation populations [ 378 ]. WAXS was also used for the study of crystallographic texture in the enamel of diseases other than caries: ENAM -mutated enamel was found with a lower texture compared to normal enamel [ 399 ]; in mucopolysaccharidosis, where crystallites were less oriented than in normal enamel [ 403 , 463 ]; and erythroblastosis fetalis (texture and size of the crystallites) [ 414 ]. In a comparative study of a human tooth and animal rostrum in a whale, more texture was present in human enamel, suggesting a different biomineralisation process [ 266 ].…”

“… Timeline of the synchrotron studies carried out on human teeth. Timeline showing studies that have been performed on human teeth, with the details of some research done over the past decades covering different modalities and applications, e.g., WAXS, SAXS, tomography, X-ray fluorescence spectroscopy, and PIC mapping, the details in the figure are from these references [ 31 , 39 , 56 , 57 , 77 , 78 , 89 , 121 , 169 , 170 , 171 , 172 , 175 , 193 , 195 , 303 , 304 , 310 , 318 , 327 , 328 , 333 , 338 , 344 , 348 , 349 , 353 , 354 , 361 , 363 , 368 , 372 , 376 , 380 , 385 , 392 , 399 , 403 , 404 , 407 , 412 , 413 , 414 , 416 , 419 , 420 , 423 , 425 , …”

Enam expression is regulated by Msx2

“…The functional ameloblasts express numerous proteins, including enzymes, signaling molecules, cell–cell adhesion molecules, transcription factors, and several secreted proteins, such as ameloblastin , amelogenin , enamelin , tuftelin , DSPP , apin , and amelotin 1‐3 . Of all secreted proteins, amelogenin, enamelin, and ameloblastin are the major secretory products of ameloblasts that contribute to enamel formation 4,5 . Amelogenin is the most abundant one, while ameloblastin and enamelin are less abundant and degrade rapidly during enamel formation 6 …”

“…[1][2][3] Of all secreted proteins, amelogenin, enamelin, and ameloblastin are the major secretory products of ameloblasts that contribute to enamel formation. 4,5 Amelogenin is the most abundant one, while ameloblastin and enamelin are less abundant and degrade rapidly during enamel formation. 6 Enam is uniquely expressed by the ameloblasts and is expressed during the secretory, transition, and early maturation stages of ameloblast life cycle.…”