Single Enamel Research Articles

Mesoscale structural gradients in human tooth enamel

The outstanding mechanical and chemical properties of dental enamel emerge from its complex hierarchical architecture. An accurate, detailed multiscale model of the structure and composition of enamel is important for understanding lesion formation in tooth decay (dental caries), enamel development (amelogenesis) and associated pathologies (e.g., amelogenesis imperfecta or molar hypomineralization), and minimally invasive dentistry. Although features at length scales smaller than 100 nm (individual crystallites) and greater than 50 µm (multiple rods) are well understood, competing field of view and sampling considerations have hindered exploration of mesoscale features, i.e., at the level of single enamel rods and the interrod enamel (1 to 10 µm). Here, we combine synchrotron X-ray diffraction at submicrometer resolution, analysis of crystallite orientation distribution, and unsupervised machine learning to show that crystallographic parameters differ between rod head and rod tail/interrod enamel. This variation strongly suggests that crystallites in different microarchitectural domains also differ in their composition. Thus, we use a dilute linear model to predict the concentrations of minority ions in hydroxylapatite (Mg2+ and CO32-/Na+) that plausibly explain the observed lattice parameter variations. While differences within samples are highly significant and of similar magnitude, absolute values and the sign of the effect for some crystallographic parameters show interindividual variation that warrants further investigation. By revealing additional complexity at the rod/interrod level of human enamel and leaving open the possibility of modulation across larger length scales, these results inform future investigations into mechanisms governing amelogenesis and introduce another feature to consider when modeling the mechanical and chemical performance of enamel.

Damage mechanisms in uniaxial compression of single enamel rods

Enamel possesses a complex hierarchical structure, which bestows this tissue with unique mechanical properties. In this study, the mechanical behavior of single enamel rods was investigated under uniaxial compression. Numerical simulations were also performed using micromechanics models for individual enamel rods to identify the damage mechanisms contributing to the constitutive behavior. Experimental results showed that the single rods exhibited an elastic modulus ranging from 10~31GPa, and that they undergo post-yield strain-hardening. The primary damage mode consisted of delamination within the assembly of mineral crystals. Results from numerical simulations suggest that strain localization within individual rods is responsible for the observed delamination, which is believed to arise from the non-uniform arrangement of mineral crystals. This mechanism was independent of mineral morphology and properties. The non-uniform crystal arrangement results in friction between crystals with different inclination angles and is believed to be responsible for the post-yield strain hardening behavior.

Flower Shaped Geminated Maxillary Nolar – Report of A Typical Case

Gemination and Fusion are irregularities in tooth development. Gemination is the attempted formation of two teeth from a single enamel organ, it has an incidence of 0.47% without sex predilection1, and it is a rare anomaly that arises when the tooth bud of a single tooth attempts to divide. Geminations more frequently affect the primary teeth, but it may occur in both dentitions, usually in the incisor region. This article reports a typical case of geminated maxillary molar giving appearance of flower radiographically.

Enamel Defect Restoration of the Left Mandibular First Molar Tooth

Restorative dentistry is often performed to treat defects including caries, fractures, access sites for endodontic therapy, and enamel lesions. Restorative materials can reestablish tooth function, restore esthetics, or do both. The objectives of restorative dentistry are to return (restore) teeth to optimum form and function, prevent further breakdown of the remaining tooth structure, to protect pulp tissue from thermal, mechanical, and bacterial insult, and to create a proper or aesthetic tooth appearance. Enamel defects in dogs can affect one or multiple teeth. This case report will focus on a single enamel defect affecting the non-occlusal surface of a mandibular first molar tooth. This case report includes descriptions of proper defect preparation and application of a flowable composite, and a review of composite materials used in restorative dentistry.

Sub-10-micrometer toughening and crack tip toughness of dental enamel

In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R -curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip’s toughness ( K I0 , K III0 ), the crack’s closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K I0 of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K I0,Ir = 0.5 – 1.6 MPa m 0.5 (based on Irwin’s ‘near-field’ solution) and K I0,cz = 0.8 – 1.5 MPa m 0.5 (based on the cohesive zone solution of the Dugdale–Muskhelishvili (DM) crack model). The mode III crack tip toughness K III0,Ir was computed as 0.02 – 0.15 MPa m 0.5 . The crack-closure stress at the crack tip was computed as 163–770 MPa with a cohesive zone length and width 1.6 – 10.1 μ m and 24–44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified.

Nanomechanical properties and microtribological behaviours of human tooth enamel

Nanomechanical properties and microtribological behaviours of human tooth enamel have been investigated using the nanoindentation and nanoscratch techniques. Nanoscratch tests were conducted along different directions in the occlusal and axial sections of enamel under different normal loads. The results showed that for a single enamel rod, the hardness and Young's modulus were higher in the central head area and tended to be lower in the edge area, especially in the tail area. In the occlusal section, the enamel presented higher wear resistance at low loads owing to the compact alternate arrangement of mineral and organic phases within the enamel and the heterogeneous mechanical properties of enamel rods. No obvious material removal occurred, and the surface lesion of enamel was characterized mainly by plastic deformation. As the load increased, significant material removal occurred as a result of brittle delamination, and the coefficient of friction increased and fluctuated. The wear resistance of the axial section was inferior to that of the occlusal section, and moreover, the enamel demonstrated anisotropic microtribological properties in the axial section. Both the friction coefficient and wear loss were higher when the scratches were conducted along the direction of enamel rods.

Nanotribological characterization of tooth enamel rod affected by surface treatment

Tooth enamel is a hybrid organic–inorganic bionanocomposite comprised predominantly of enamel rods. Understanding the effects of anti-caries treatment on the biomechanical properties of these rods is essential in developing effective caries prevention strategies. Calcium fluoride-like deposits play an important role in caries prevention and their nanotribological properties have a direct effect upon their long-term effectiveness. Accordingly, this study utilizes a variety of techniques, namely nanoindentation, nanoscratch tests, nanowear tests and atomic force microscopy (AFM), to characterize the mechanical and tribological properties of single enamel rods before and after topical fluoride application. The results show that the CaF2-like deposits formed on the enamel surface following fluoride application increase the coefficient of friction of the enamel rods, but decrease their critical load and nanohardness. As a result, the nanowear depth of the treated enamel surface is around six times higher than that of the native enamel surface under an applied load of 300μN. Following the removal of the surface deposits, however, the modulus of elasticity and wear depth of the underlying enamel surface are found to be similar to those of the original enamel surface. However, a notable increase in the surface roughness is observed.

Nanomechanical Properties of Tooth and Bone Revealed by Nanoindentation and AFM

In this paper, an overview on nanoindentation and its combination with AFM is presented with regard to current instrument technology and applications on dental and bony tissues. Nanoindentation has been a widely used technique to determine the mechanical properties such as nanohardness and Young’s modulus for nanostructured materials. Especially, atomic force microscopy (AFM) combined with nanoindentation, with the pit positions controlled accurately, become a powerful technique used to measure mechanical properties of materials on the nanoscale, and has been applied to the study of biological hard tissues, such as bone and tooth. Examples will be shown that significantly different nanohardness and modulus in the isolated domains within single enamel, the prisms, interprisms, the surrounding sheaths and the different parts of skeletal bone, could been distinguished, while such information was unable to be obtained by traditional methods of mechanical measurements.

Apparatus for Automatically Recording Strains Between Enamel and Metal

The construction and operation of a mechanism for converting the movement of an enameled split ring into a suitable electrical signal to be automatically recorded is described. Strain curves are presented for a single enamel when applied to several metals. These data were used to determine the relationship between the strains recorded and the properties of the metals to which the enamel was applied.

Quantitatively Studying Nano-mechanical Properties within the Prism and Organic Sheath of Enamel

AbstractEnamel is made up of enamel prisms separated by thin layer of organic sheaths. The mechanical properties of the prisms and the organic sheaths are obviously different from each other due to different compositions and microstructures. However, quantitative measurements of such differences have been a challenge in the past. The objective of this study is to accurately study the mechanical properties in the isolated domains within single enamel prism. The technique of nanoindentation combined with Atomic Force Microscopy (AFM) was employed to test the enamel specimens from mature human maxillary third molar. It was revealed that the nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms. AFM topographies of the residual indent impressions also visually confirmed the differences. In addition to nanoindentation tests, the microstructures of enamel were carefully investigated in terms of hierarchical levels of organization to understand the structural reasons of the mechanical differences. We found a close relation between the variations of mechanical properties of enamel and its hierarchical structure. The analysis of the mechanical properties within enamel upon hierarchy is not only helpful to understand its unique property, but may also inspire ideas for the design of novel synthetic materials.

Property variations in the prism and the organic sheath within enamel by nanoindentation

Atomic force microscopy (AFM) combined with nanoindentation technique was used to definitely, site-specifically, test the nanomechanical properties, including nanohardness and elastic modulus, of the isolated domains within single enamel, the prisms and the surrounding sheaths, of mature human maxillary third molars. In this way, it is for the first time that evident differences of nanomechanical properties were revealed between these domains. The nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms, respectively. Measuring the residual impressions with AFM supported the similar conclusion. The variations of mechanical properties in these domains are considered to be mainly relative to their different component and fibrils arrangement.

Enamel structure properties controlled by engineered proteins in transgenic mice.

Amelogenin protein has regulatory effects on enamel biofabrication in mammalian tooth. Using teeth obtained from transgenic mice that express two separate protein-engineered versions of amelogenins, we made structure-nanomechanical properties correlations and showed 21% hardness and 24% elastic modulus degradation compared with the age-matched wildtype littermates. We attribute the inferior properties to the disorganization of the protein matrix resulting in defective mineral formation. Enamel is a bioceramic initiated by the biosynthesis of a complex mixture of proteins that undergoes self-assembly to produce a super molecular ensemble that controls the nucleation and habit of the crystalline mineral phase. Ultimately, the inorganic crystals grow to almost fully replace the organic phase. This biofabrication process occurs at physiologic conditions of pH, temperature, pressure, and ion concentration and results in the hardest tissue in the vertebrate body, with the largest and longest substituted-hydroxyapatite crystals known to biomineralizing systems. The most abundant protein of forming mammalian enamel, amelogenin, has been shown to have a significant regulatory effect on this complex process. In this work, we present the effect of protein engineering of amelogenin on the mechanical properties of the resultant mouse enamel. We have produced two types of transgenic animals that express separate versions of amelogenin proteins that lack the required self-assembly domains. The resultant matured enamel was extensively characterized for its mechanical properties at the nanoscale by means of nanoindentation and atomic force microscopy (AFM). These techniques have enabled us to probe the mechanical properties that are representative of a single enamel rod. Our nanoindentation measurements have revealed that the altered amelogenin with dysfunctional self-assembly properties resulted in a degradation by as much as 21% in hardness and 24% in elastic modulus compared with the age-matched wildtype littermates. Furthermore, the enamel formed by these defective proteins is found to display a decrease in indentation surface pile-up volume by up to 32%. We attribute these inferior mechanical properties for the enamel grown by the engineered amelogenins to result from the disorganization of the nanospheres formed in the protein matrix starting at the mineral nucleation stage with a consequential alteration to the fully grown mineral component. By engineering the properties of proteins that contribute to the nanoscale level of hierarchy in enamel biomineralization, it is possible to regulate the properties of the resulting bioceramic at the mesoscale level of the tissue.

Mechanical properties of human dental enamel on the nanometre scale

Atomic force microscopy (AFM) combined with a nano-indentation technique was used to reveal the structure and to perform site-specific mechanical testing of the enamel of third molars. Nano-indentations (size<500 nm) were made in the cusp area to measure the mechanical properties of single enamel rods at different orientations. The influence of etching on the physical properties was studied and etching conditions that did not significantly alter the plastic–elastic response of enamel were defined. Elasticity and hardness were found to be a function of the microstructural texture. Mean Young's moduli of 87.5 (±2.2) and 72.2 (±4.5) GPa and mean hardness of 3.9±0.3 and 3.3±0.3 GPa were measured in directions parallel and perpendicular to the enamel rods, respectively. Analysis of variance showed that the differences were significant. The observed anisotropy of enamel is related to the alignment of fibre-like apatite crystals and the composite nature of enamel rods. Mechanical properties were also studied at different locations on single enamel rods. Compared to those in the head area of the rods, Young's moduli and hardness were lower in the tail area and in the inter-rod enamel, which can be attributed to changes in crystal orientation and the higher content of soft organic tissue in these areas.

The Function and Structure of the Marsupial Enamel

The aims of this study are to clarify the structure of tubular enamel and the function of enamel tubules on the marsupial of opossum (Monodelphis domestica). Almost all enamel prisms, surrounded by interprismatic enamel, ran obliquely from the dentinoenamel junction (DEJ), and bent near the enamel surface. The enamel tubules are distributed in both enamel prisms and the interprismatic enamel near the DEJ. From the middle to the surface of the enamel, one enamel tubule ran within a single enamel prism. Most of enamel tubules continued from the DEJ to near the enamel surface. It is suggested that each enamel tubule developed in relation to one ameloblast. The fibers of odontoblastic process penetrated the DEJ from the dentinal tubules into the enamel tubules, and some branched across the enamel prisms. The odontoblastic process may be actively cross into the ameloblastic layer and may be involved in the formation of enamel tubules. After in vivo injection of tetracycline, tetracycline labeling showed that the odontoblastic tubules continued to enamel tubules. And strontium was detected in enamel tubules from the DEJ to the enamel surface, as was the dentinal tubules. In conclusion, there was active transport by the odontoblast and it's process through the enamel tubules.

Computer-assisted reconstruction of enamel fissures and carious lesions of human premolars.

The origin of cariogenesis in occlusal fissures remains elusive because of limited information about both the fissure structure and the morphologic details of carious lesions occurring there. The present study was aimed at reconstructing the coronal structure of human premolars with the aid of computer-assisted image analysis and, on the basis of the reconstructed structures, investigating the configuration of fissures, their proximity to the enamel-dentin junction (EDJ), and the occurrence and extension of carious lesions around the fissure walls. The coronal portions of the teeth were embedded in polyester resin and then ground off stepwise by hand. Serial images of the enamel contour on successive ground planes were recorded by objective microscopy after it was distinctly demarcated with either 0.5 w/v% carbol fuchsin or 1 w/v% basic fuchsin. Usually, from 150 to 250 photoprints were collected from a single enamel crown to reproduce the details of the fissure structures. The enamel outline (the occlusal and lateral surfaces, fissure walls, and EDJ) and, if present, the outline of caries-attacked areas were traced accurately on those photoprints by means of a digitizing system. The enamel contour data in series were input into an image analyzing system (Nikon COSMOZONE, 2SA). Observation of the computer-drawn coronal enamel allowed us to view the morphologic features of the fissures (shape, divarication, and proximity to EDJ) and to scrutinize the pathway of enamel caries along fissure walls.(ABSTRACT TRUNCATED AT 250 WORDS)

A quasi-constant composition method for studying the formation of artificial caries-like lesions.

Caries-like lesions were formed in human tooth enamel in a quasi-constant composition titration system without the use of surface dissolution inhibitors or weak acids. The titration system maintained the composition of the demineralizing solution constant to within 6% on the average. Thus, the rate of lesion formation may be quantitatively assessed from the rate of titration. The system has sufficient sensitivity for measuring the rate of lesion formation in a small area, e.g., 15 mm2, of a single human enamel specimen.

Single bovine enamel particles examined by electron optics.

Whole enamel scrapings from teeth of embryonic calves have been separated by density gradient centrifugation in organic solvents into fractions (1.6 less than p less than 2.4 g/cm3) representing progressive stages of mineral phase maturation. Single enamel particles or their small aggregates from such fractions were examined by transmission electron microscopy, electron diffraction, and high-spatial-resolution electron probe micro-analysis. The electron optical methods demonstrated the presence of poorly crystalline hydroxyapatite as the only detectable solid phase in all fractions. Octacalcium phosphate and brushite were not identified in the fractions. Changes in electron diffraction patterns were indicative of a progressive increase in apatite crystallinity with enamel maturation. Molar Ca/P ratios were found to range from 1.48 to 1.70, with a higher mean value obtained for lower-density fractions (p less than 2.0 g/cm3). Lower-density fractions contained some particles with high ratios (approximately equal to 2.0-4.0) and a non-uniform distribution of Ca and P, as revealed by electron probe mapping. These characteristics are suggested as possibly being related to carbonate phases in early enamel.

Observations on the aetiology of supernumerary upper incisors in the albino ferret ( Mustela putorius)

An histological investigation was undertaken to study the development of deciduous and permanent supernumerary upper incisors in the albino ferret ( Mustela putorius). Twenty-one specimens, aged between 35 and 47 days following fertilization, which exhibited supernumerary teeth were serially sectioned and the developing teeth graphically reconstructed. Twenty-seven deciduous supernumerary incisors, each occupying the second incisor tooth position, were studied; 17 of these were completely separate teeth, a further nine had separate pulp chambers but were contained within a single enamel organ common to that of the medially situated deciduous first incisor, while the remaining specimen showed evidence of a supernumerary tooth sharing a common pulp chamber with that of the first incisor. Thirteen permanent supernumerary upper incisors were observed and all were associated with the presence of the corresponding deciduous supernumerary. In six cases, the permanent supernumerary was present as a completely separate tooth while the remaining seven specimens showed varying degrees of fusion with the medially situated permanent first incisor tooth germ. The evidence suggests that the deciduous supernumerary incisor arose as a result of dichotomy of the medially situated deciduous first incisor tooth germ. It was further suggested that permanent supernumerary incisor teeth may be lost from the functional adult dentition as a result of fusion with the medially situated permanent first incisor during tooth development.

DETERMINATION OF THE ALKALIS IN VITREOUS ENAMEL1

Sodium and potassium comprise from 5 to 25%, of the total composition of vitreous enamels. The other 75% is comprised of a wider variety of other elements than is found usually in materials which are analyzed for their alkali content. No less than twentyfive oxides are used commonly in enamel glass, and often fifteen of these are in a single enamel. The task of removing all interfering elements from the alkalis is an analytical problem of more than ordinary difficulty. The process is necessarily long and tedious. It calls for the most exact attention to detail and the most careful manipulation. This article tells of attempts to use the usual methods for determination of alkalis in vitreous enamel, and also the procedures found to be most useful and accurate for all classes of enamels.