Enamel Prisms Research Articles

Comparative assessment of the rate and quality of enamel mineral component maturation of human teeth with connective tissue dysplasia in the early postpartum period

Objective. It is necessary to study the human enamel prisms size at different periods of postpartum ontogenesis in connective tissue dysplasia by atomic force microscopy. Materials and methods. The study involved 150 males divided into a group with and without connective tissue dysplasia (each additionally by age: 15—20, 21—30, 31—40 years). Each examined was removed one of the low wisdom teeth (3.8 or 4.8 by ISO). Prepared thin sections of human tooth enamel samples up to grade 14, with maximum preservation of the edges of the enamel prisms within the surface layer. The Image Analysis NT-VDT software was used to analyze the number of faces, shape, length, and width of enamel prisms. Results. It was found that at 15—30 years old there is an ordered structure of enamel prisms, a large number of 5-sided forms (50—60%). A permanent form of enamel prisms at 31—40 years old, where the share of 6-sided figures is 30%. With CTD, the growth rate on the plane, which increases the width of the prism, is very similar to the growth rate of length up to 30 years, which leads to a violation of their spatial configuration relative to the organic matrix. Conclusions. The maturation of human enamel is strictly individual, depending on the connective tissue dysplasia, which has a negative effect on the rate of maturation, and after eruption can lead to pathological conditions of hard dental tissues.

Crocodile Tooth Histology from a Pliocene Deposit in Chinchilla, Queensland

Chinchilla in the Western Downs Region of Queensland is home to the Chinchilla Rifle Range, a palaeontological site that has produced a significant well-preserved Pliocene vertebrate assemblage. Here, we describe and discuss the histology of a crocodile tooth recovered from the ca 3.5-million-year-old Chinchilla Sand deposit in the Rifle Range. The tooth is from the posterior jaw and likely belongs to a species of Paludirex. We discuss the tooth micro-morphology in relation to what is known about tooth histology in extant and extinct crocodylians with brevirostine and platyrostral skull morphology. We hypothesised that there should be several similarities in the tooth micro-structures between related extinct and extant taxa. We found that the Chinchilla Sand fossil tooth is characterised by thin enamel that is likely prismless but shows incremental striations (also seen in dentine), similar to other crocodylians. This short study highlights the importance of microscopic techniques applied to fossil material. With further fossil evidence emerging from Chinchilla, and application of three-dimensional microscopy techniques to understand the nature of Paludirex enamel prisms, a better understanding of reptile palaeobiology can be developed for Queensland and Australia.

Language And Teeth Information Carriers State Of Internal Organs

As a result of electron-microscopic examinations, enamel prisms in the transverse position, they look like arches and roofs. When we cross the enamel prisms, we see diagonals, polygonal prisms. When they are parallel, when they are cut lengthwise, we see the planes, the fibers parallel to each other. Because enamel prisms are curved in an S-shape, some appear transverse and others parallel when cut. The result is light and dim roads, called Schroeder roads

Dental enamel structure in long-nosed armadillos (Xenarthra:Dasypus) and its evolutionary implications

AbstractMost xenarthrans have a reduced and simplified dentition that lacks enamel. However, the presence of prismatic enamel has been recorded in the Eocene armadillos Utaetus buccatus (Euphractinae) and Astegotherium dichotomus (Astegotheriini). Among extant xenarthrans, the occurrence of enamel has been recognized only in the long-nosed armadillo, Dasypus novemcinctus (Dasypodinae), but its microstructure has never been described. In this contribution, we analyse the enamel microstructure in deciduous and permanent teeth of four Dasypus species. In deciduous molariform teeth of some species, we identify an apical cap of vestigial enamel (without crystalline structure), interpreted as an amorphous ameloblastic secretion. In permanent teeth, a thin layer of true enamel is found in the apical portion of unworn molariforms. The enamel is prismatic in D. novemcinctus, but in Dasypus hybridus, Dasypus sabanicola and Dasypus punctatus it is prismless. Taking into account the Eocene species of armadillos, the ancestral condition of enamel in cingulates could have been more complex (as in other placentals) and undergone progressive reduction, as shown in the Dasypus lineage. In light of previous genetic and developmental studies, we review and briefly discuss the processes that can account for the reduction/loss of enamel in extant and extinct armadillos. The retention of enamel and the fact that this genus is the only living xenarthran with two functional generations of teeth support the early divergence of the Dasypus lineage among living cingulates. This is in agreement with morphological and molecular analyses.

Effect of enamel regions and prisms orientation on the microshear bond strength of a multimode and a two-step self-etch adhesives applied with different adhesion protocols

Multi-mode adhesives (MMA) with different adhesion protocols are postulated to improve bonding to enamel. Thus, this study compared the microshear bond strength (μSBS) of (MMA) and self-etch adhesive (SEA) to different regions and prism orientations of enamel. Materials and methodsThirty premolars were assigned for preparing 160 specimens for μSBS. Specimens were equally divided (n = 80) according to the enamel region evaluated: cuspal, and mid coronal enamel. Each group was divided into two subgroups according to the direction of tooth sectioning: axial, or tangential. Each subgroup was divided into two classes according to the applied adhesive system; either MMA or SEA. Finally; each class was divided into two subclasses (n = 10) according to the adhesion protocol utilized; self-etch adhesion protocol or with etch-and-rinse (pre-etching) adhesion protocol. Nano-filled flowable composite was used to prepare μSBS specimens. μSBS was measured using universal testing machine at a cross head speed of 0.5 mm/min until failure. Statistical analysis was carried out using four-way ANOVA test. ResultsDifferent enamel regions had no statistically significant effect at P-value 0.491. Direction of sectioning had a statistically significant effect at P-value <0.001. Adhesive systems had a statistically significant effect at P-value <0.001. Adhesion protocols had a statistically significant effect at P-value 0.001. ConclusionPre-etching of enamel before the application of the MMA improves the resin-enamel μSBS, while there was no advantage of the pre-etching step with the SEA. The μSBS of the tested adhesive systems were influenced by the direction of enamel prisms. The μSBS of the tested adhesive systems were not influenced by the enamel regions tested.

Morphological, optical, and elemental analysis of dental enamel after debonding laminate veneer with Er,Cr:YSGG laser: A pilot study.

Laminate veneer removal is becoming a routine procedure at the dental clinic and the use of laser can facilitate its removal. This work aimed to evaluate the morphological, elemental, and optical changes in the remaining enamel after veneer removal using Er,Cr:YSGG laser. Forty-four enamel slabs were prepared and randomly distributed into nine experimental groups, for bonding using lithium disilicate laminates with three different luting agents (Variolink Veneer, RelyX U200, and RelyX Veneer). Then each agent was debonded using Er,Cr:YSGG laser (2.78 μm) using two different protocols:3.5 W, 48.14 J/cm2 , 20 Hz non-contact and 3.0 W, 48.14 J/cm2 , 20 Hz non-contact. The morphological, optical, and elemental analysis of enamel was performed before cementation and after laser debonding, using scanning electron microscopy (SEM), optical coherence tomography (OCT), and energy-dispersive X-ray spectroscopy (EDS). The level of statistical significance adopted was 5%. The EDS analysis of enamel after debonding revealed a significant increase in silane and carbon, as well as a decrease in calcium and phosphate contents. Analysis showed the presence of residual cement in most experimental groups but the morphological analysis showed alteration of the enamel's prisms only in the groups that used RelyX Veneer and Variolink Veneer cements. There was no evidence of deleterious morphological changes resulting from irradiation. However, an increase in the optical attenuation coefficient by the OCT was observed due to the presence of the remaining cement. It can be concluded that the Er,Cr:YSGG laser, in the mean powers used, is efficient for veneer removal without causing deleterious effects for the enamel.

Deficiency of the SMOC2 matricellular protein impairs bone healing and produces age-dependent bone loss

Secreted extracellular matrix components which regulate craniofacial development could be reactivated and play roles in adult wound healing. We report a patient with a loss-of-function of the secreted matricellular protein SMOC2 (SPARC related modular calcium binding 2) presenting severe oligodontia, microdontia, tooth root deficiencies, alveolar bone hypoplasia, and a range of skeletal malformations. Turning to a mouse model, Smoc2-GFP reporter expression indicates SMOC2 dynamically marks a range of dental and bone progenitors. While germline Smoc2 homozygous mutants are viable, tooth number anomalies, reduced tooth size, altered enamel prism patterning, and spontaneous age-induced periodontal bone and root loss are observed in this mouse model. Whole-genome RNA-sequencing analysis of embryonic day (E) 14.5 cap stage molars revealed reductions in early expressed enamel matrix components (Odontogenic ameloblast-associated protein) and dentin dysplasia targets (Dentin matrix acidic phosphoprotein 1). We tested if like other matricellular proteins SMOC2 was required for regenerative repair. We found that the Smoc2-GFP reporter was reactivated in adjacent periodontal tissues 4 days after tooth avulsion injury. Following maxillary tooth injury, Smoc2−/− mutants had increased osteoclast activity and bone resorption surrounding the extracted molar. Interestingly, a 10-day treatment with the cyclooxygenase 2 (COX2) inhibitor ibuprofen (30 mg/kg body weight) blocked tooth injury-induced bone loss in Smoc2−/− mutants, reducing matrix metalloprotease (Mmp)9. Collectively, our results indicate that endogenous SMOC2 blocks injury-induced jaw bone osteonecrosis and offsets age-induced periodontal decay.

On the vital role of enamel prism interfaces and graded properties in human tooth survival.

Teeth of omnivores face a formidable evolutionary challenge: how to protect against fracture and abrasive wear caused by the wide variety of foods they process. It is hypothesized that this challenge is met in part by adaptations in enamel microstructure. The low-crowned teeth of humans and some other omnivorous mammals exhibit multiple fissures running longitudinally along the outer enamel walls, yet remain intact. It is proposed that inter-prism weakness and enamel property gradation act together to avert entry of these fissures into vulnerable inner tooth regions and, at the same time, confer wear resistance at the occlusal surface. A simple indentation experiment is employed to quantify crack paths and energetics in human enamel, and an extended-finite-element model to evaluate longitudinal crack growth histories. Consideration is given as to how tooth microstructure may have played a vital role in human evolution, and by extension to other omnivorous mammals.

Dental Treatment of White Spots and a Description of the Technique and Digital Quantification of the Loss of Enamel Volume

The prevalence of white spots on teeth has increased in recent years. Regardless of their etiology, these lesions are characterized by a reduction in the enamel’s mineral phase, which is replaced by organic fluids. This causes an alteration of its chemical composition that affects its optical characteristics. Subsurface demineralization increases the pore volume of enamel, which in turn changes its optical refraction and results in the opaque color of white spot lesions. Here, we examined a non-invasive clinical technique used for eliminating these white spot lesions from enamel via two HCl-based products at different concentrations (6.6% and 15%). We used a digital method for evaluating the volumetric changes produced in dental enamel by the application of both products, one of which involved chemical erosion and the other, abrasive erosion. The mean volume of the enamel eliminated was −0.042 mm in 15% HCl, and −0.12 mm in 6.6% HCl. Thus, both 15% HCl and 6.6% HCl are capable of eroding the surface of the tooth enamel without reaching dentin. Moreover, 6.6% HCl produced a greater erosion of the dental enamel and left the surface a texture typical of an abrasive chemical-erosive product. The 15% HCl, however, produced an etching pattern typical of an erosive chemical with open enamel prisms prepared for subsequent adhesive procedures and restorers.

Comparative evaluation of the effect of chemical and diode laser activated bleaching techniques on enamel surface and subsurface

Objective: The aim of this study was to compare diode laser-activated bleaching effect versus chemical bleaching on enamel surface and subsurface of human mandibular incisors concerning morphology and chemical profile.Materials and Methods: Forty extracted human, caries and defect-free mandibular incisors were divided into four groups by dividing their labial surface longitudinally into two halves. The distal halves of 20 teeth were assigned for chemical bleaching protocol using 38% hydrogen peroxide, their mesial halves represented their control. The other 20 teeth were assigned by the same method into laser-activated bleaching group and its control. The morphology and chemical profile of the surface and subsurface of the labial enamel were investigated, chemical profile of the subsurface was investigated at 50 and 100 μm depth.Results: The enamel surface of chemically bleached group showed surface irregularities, porosities and erosive areas, ternary diagram of its chemical profile presented a slight shift to an area of less mineralized enamel. Morphology of the subsurface of chemically bleached enamel showed structural defects in prisms configuration and channels extending from surface defects through the enamel, its ternary diagram presented a shift to a demineralized area at both depths examined. Enamel surface of laser-bleached teeth appeared as a molten glazed surface and presented almost no shift in the ternary diagram. Subsurface of laser-bleached teeth showed loss of prismatic enamel integrity and presented a shift to a more mineralized area at 50μm depth and to a demineralized area at 100μm depth.Conclusion: Laser-activated bleaching caused less enamel surface irregularities than chemical bleaching, but its effect was more deleterious on the morphology of the enamel subsurface. Concerning enamel chemical profile, subsurface enamel of chemically bleached teeth was more affected than that of the laser-bleached teeth.

Does etching time affect the in vitro performance of a sealant material?

This in vitro study evaluated the shear bond strength (SBS), failure mode and microleakage of fissure sealing materials in relation to different etching times on aprismatic and prismatic enamel. Ninety-six healthy human third molars were randomly allocated to the following groups: 1) prismatic or aprismatic enamel; 2) etching: 15, 30, 45, 60 s. After 5,000-fold thermocycling SBS, failure mode and microleakage were measured. Statistical evaluation included Mann-Whitney-U-test and linear regression analysis. In the aprismatic enamel group, an increasing etching time resulted in higher SBS. The linear regression model revealed that 60 s of etching time led to a significant increase in SBS. Microleakage was found to be low in all test groups. This study indicated that 60 s of etching time showed to a significantly better SBS. When considering the small differences of SBS, failure modes and microleakage between 30 and 60 s etching time, 30 s acid etching seems to also be justifiable.

Acid-induced demineralisation of human enamel as a function of time and pH observed using X-ray and polarised light imaging

Acid-induced enamel demineralisation affects many individuals either by exposure to acidic diets, acidic gas pollution (dental erosion) or to dental plaque acids (dental caries). This study aimed to develop in situ X-ray and light imaging methods to determine progression of enamel demineralisation and the dynamic relationship between acid pH and mineral density.Hourly digital microradiograph time-lapse sequences showed the depth of enamel demineralisation in 500 µm thick sections progressed with time from the surface towards the dentine following a power-law function, which was 21% faster than the lateral demineralisation progression after exposure for 85 h to lactic acid (10%, pH 2.2). The minimum greyscale remaining (mineral content) within the induced enamel lesion followed an exponential decay, while the accumulated total greyscale loss with time was linear, which showed a constant anisotropic mineral release within the enamel architecture. This 85 h demineralisation method studied by polarised light microscopy time-lapse sequences showed that once the demineralisation front reached the enamel Hunter-Schreger bands, there was preferential demineralisation along those bands.Mineral density loss was linear with increasing pH acidity between pH 5.2 and pH 4.0 (with 0.4 pH increments) when incubated over a 3-week period exposed to 0.5% lactic acid. At pH 4.0, there was complete mineral loss in the centre of the demineralised area after the 3-week period and the linear function intercepted the x-axis at ~ pH 5.5, near the critical pH for hydroxyapatite (HAp). These observations showed how intrinsic enamel structure and pH affected the progression of demineralisation. Statement of SignificanceHydroxyapatite crystallites (HAp) in human enamel dissolve when exposed to an acidic environment but little is known about how the intrinsic structures in enamel and pH influence the demineralisation kinetics. We have developed a time-lapse in situ microradiography method to quantify microscopic anisotropic mineral loss dynamics in response to an acid-only caries model. Correlation with polarised light microscopy time-lapse sequences showed that larger structures in enamel also influence demineralisation progression as demineralisation occurred preferentially along the Hunter-Schreger bands (decussating prismatic enamel). The pH-controlled enamel mineral release in a linear manner quantifying the relationship between HAp orientation and acid solubility. These findings should direct the development of improved anti-demineralisation/ remineralisation treatments to retain/ restore the natural intrinsic enamel structure.

Protective Effects of GIC and S-PRG Filler Restoratives on Demineralization of Bovine Enamel in Lactic Acid Solution

This study was aimed at investigating the protective effects of glass ionomer cement (GIC) and surface pre-reacted glass ionomer (S-PRG) fillers used as dental restorative materials on demineralization of bovine enamel. GlasIonomer FX ULTRA (FXU), Fuji IX GP Extra (FIXE), CAREDYNE RESTORE (CDR) were used as GICs. PRG Barrier Coat (BC) was used as the S-PRG filler. They were incubated in a lactic acid solution (pH = 4.0) for six days at a temperature of 37 °C. The mineral was etched from the enamel surface, and a large number of Ca and P ions were detected in solution. The Al, F, Na, Sr, and Sr ions were released in GICs and S-RPG fillers. The Zn ion was released only in CDR and the B ion was released only in BC. The presence of apparent enamel prism peripheries was observed after six days of treatment for the group containing only enamel blocks. pH values for the FXU, FIXE, CDR, BC, and enamel block groups after six days were 6.5, 6.6, 6.7, 5.9, and 5.1, respectively. Therefore, the observed pH neutralization effect suppressed progression of caries due to the release of several ions from the restoratives.

Evolution: Herbivore-Type Teeth in a Cretaceous Tuatara Relative.

In a new study, LeBlanc and co-workers have discovered an unusually complex dentition in a fossil relative of the modern-day tuatara that features compound occlusal surfaces, thick and prismatic enamel, and a novel enamel-to-bone tooth attachment. This finding suggests that complex dentitions arose independently in several reptilian lineages.

Variation in the timing of enamel formation in modern human deciduous canines

ObjectivesDeciduous canines are now used increasingly in archaeological and forensic studies to establish the time of birth and as a retrospective source of trace elements incorporated into enamel before and after birth. However, data on the variability of deciduous enamel formation times are scarce. Our objectives were to use daily incremental markings to estimate daily secretion rates, the timing of prenatal, postnatal and total enamel formation and any changes in enamel coverage or prism and stria orientation that occur during enamel formation. Materials and MethodsLongitudinal ground sections of 81 deciduous canines were studied with transmitted light microscopy. High-resolution digital images were imported from an Olympus VS-120 virtual slide scanning system into a geographic information system (ArcGIS, ESRI USA) for quantitative and statistical analyses of linear, angular and area measurements of buccal enamel. ResultsDaily rates of enamel secretion close to the EDJ were faster than in permanent enamel (3.23 μm/day, SD = 0.54). Prism and stria angles subtended to the EDJ both increased through crown formation. Enamel coverage was low in the cusp and cervix but maximal ∼150 days after birth. The mean prenatal enamel formation time was 118 days (range 60−150, SD, 29.2, n = 24). The overall mean postnatal enamel formation time was 319 days (range 210–420, SD 50.6, n = 67). ConclusionsDaily enamel secretion rates compared well with previous studies of deciduous enamel, however, enamel extension rates in deciduous cuspal enamel were notably lower. The variability of both prenatal and postnatal deciduous enamel formation times was greater than previously reported.

Complex Dental Structure and Wear Biomechanics in Non‐Avian Dinosaurs and Pleistocene Mammals

Reptiles rarely approached the biomechanical sophistication for feeding or dietary diversity seen in mammals. Their teeth are typically non‐occluding, semi‐conical structures with simplistic parallel‐crystallite enamel surrounding an orthodentine core. Conversely, most mammals possess multi‐cusped teeth that are drawn across one another during mastication and self‐wear to their functional morphology. The most complex dental architectures are seen in herbivorous mammals. Their teeth are composed of up to four constituents (incl. prismatic enamel) that strategically wear creating coarse grinding or slicing surfaces. These allow them to comminute tough and/or abrasive plants and liberate nutrients inaccessible to other animals. Non‐avian dinosaurs stand out among reptiles in that precise, mammal‐like dental occlusion and self‐wearing teeth evolved on at least four occasions. These topographies enabled access to myriad floral types and facilitated their respective ecological diversifications. My research group and colleagues showed that the teeth of these dinosaurs are histologically more complex than formerly appreciated. Using cutting‐edge material science and tribological engineering indentation techniques we discovered that wear and fracture relevant material properties are preserved in the fossil dental tissues of dinosaurs and Pleistocene mammals. This led to development of a 3D Archard’s wear model from which we determined how horse‐like occlusal surfaces for the grinding of plant matter occurred in hadrosaurids, and fuller‐like slicing surfaces developed and functioned in ceratopsians. In current research we are studying how the grinding dentitions of mammoths similarly formed through self‐wear. Notably our paleontologically‐inspired wear model is seeing broad industrial applications.Support or Funding InformationNSF CMMI (Civil, Mechanical and Manufacturing Innovation) Eager and AFOSR (Air Force Office of Scientific Research) to GME, SP and BAK

Unique Tooth Morphology and Prismatic Enamel in Late Cretaceous Sphenodontians from Argentina.

Mammals and reptiles have evolved divergent adaptations for processing abrasive foods. Mammals have occluding, diphyodont dentitions with taller teeth (hypsodonty), more complex occlusal surfaces, continuous tooth eruption, and forms of prismatic enamel that prolong the functional life of each tooth [1, 2]. The evolution of prismatic enamel in particular was a key innovation that made individual teeth more resilient to abrasion in early mammals [2-4]. Incontrast, reptiles typically have thin, non-prismatic enamel, and shearing, polyphyodont dentitions with multi-cusped or serrated tooth crowns, multiple tooth rows, rapid tooth replacement rates, or batteries made of hundreds of teeth [5-9]. However, there are rare cases where reptiles have evolved alternative solutions to cope with abrasive diets. Here, we show that the combined effects of herbivory and an ancestral loss of tooth replacement in a lineage of extinct herbivorous sphenodontians, distant relatives of the modern tuatara (Sphenodon punctatus) [10], are associated with the evolution of wear-resistant and highly complex teeth. Priosphenodon avelasi, an extinct sphenodontian from the Cretaceous of Argentina, possesses a unique cone-in-cone dentition with overlapping generations of teeth forming a densely packed tooth file. Each tooth is anchored to its predecessor via a rearrangement of dental tissues that results in a novel enamel-to-bone tooth attachment. Furthermore, the compound occlusal surfaces, thickened enamel, and the first report of prismatic enamel in a sphenodontian are convergent strategies with those in some mammals, challenging the perceived simplicity of acrodont dentitions [11-15] and showcasing the reptilian capacity to produce complex and unusual dentitions.

The effect of shape and size distribution of abrasive particles on the volume loss of enamel using micro-abrasion

Wear of enamel during tooth brushing is a complex phenomenon with many variables affecting the level of loss. Toothpastes contain angular abrasive particles at a concentration of 12%–15% v/v abrasive designed to remove biofilm and extrinsic stains that also have the potential to harm the tooth enamel resulting in wear. Toothpastes contain multi-modal particles in the size range of 4μm–12μm. The aim of this paper is to develop an understanding of the relationship between the combined effects of particle shape, size, size distribution and load on the volume loss of enamel under abrasive testing. Micro-abrasion testing using a Nylon ball, to simulate the toothbrush, was undertaken on hydrated bovine enamel disks using volume concentrations of 5% – 20% v/v alumina and silica. Post experimental surface analysis was performed to analyse the wear scar morphology and groove analysis. The synergistic effects were calculated of bimodal particles vs. mono sized particles. Mono-sized particles as compared to bimodal, appeared to give the best outcome and least wear of enamel. A positive synergy existed for the alumina and silica bimodal tests, indicating the bimodal particle distribution was causing more wear than the mono-sized particles. The mechanism of material removal was a combination of crushing and fracture of the enamel prisms (rods), followed by micro-chipping and removal of enamel. The magnitude and the distribution of the particle sizes is the most dominant factor in determining the levels of wear, with smaller particles and narrow distributions of the particle size reducing the magnitude of wear. The shape of the particles is also a major factor influencing wear, with the spherical tests generating lower wear rates than the angular tests.

The geometrical structure of interfaces in dental enamel: A FIB-STEM investigation

In this study a high resolution structural analysis revealed that enamel prisms are surrounded by an interface that is discontinuous with frequent mineral to mineral contact separated by gaps. This contact manifests either by crystallites bridging the boundary between prismatic and interprismatic enamel or continuous crystallites curving and bridging the interprismatic enamel to the prisms. The geometrical resolution of this TEM investigation of the interfaces is ≤2 nm as a basis for micromechanical models. Within this resolution, contrary to existing structural descriptions of dental enamel structure in materials science literature, here the crystallites themselves are shown to be either in direct contact with each other, sometimes even fusing together, or are separated by gaps. Image analysis revealed that on average only 57 ± 15% of the interface consists of points of no contact between crystallites. This work reveals structural features of dental enamel that contribute important understanding to both the architecture and mechanical properties of this biological material. A new structural model is proposed and the implications for the mechanical properties of dental enamel are discussed. Statement of significanceIn this study a high resolution structural analysis, employing focused ion beam and transmission electron microscopy revealed that enamel prisms are surrounded by interfaces that are discontinuous with frequent mineral to mineral contact separated by gaps. Although the interfaces in enamel have been investigated previously, existing studies are lacking in detail considering the geometry and morphology of the interfaces. We think that this result is of great importance when it comes to the understanding of the mechanical properties. In our opinion the concept of soft sheaths is no longer feasible. The resulting observations are included in a new structural model which provides new qualitative insights into the mechanical behavior. Existing analytical models were applied to simulate the new geometrical structure.

Research of the structure of teeth enamel mineral component in connective tissue dysplasia by densitometry and atomic force microscopy in the late postpartum ontogenesis period

Цель работы — дать количественную и качественную характеристику структуре минерального компонента эмали ретинированных зубов при дисплазии соединительной ткани и без нее в различные периоды позднего постнатального онтогенеза человека методами денситометрии и атомно-силовой микроскопии. Материалы и методы. Удаляли 3.8, 4.8 зубы, не имеющие контакта с ротовой жидкостью, у 60 мужчин с дисплазией соединительной ткани и без нее (возрастные группы: 31—40, 41—50, 51—60 лет). Денситометрическую оценку плотности неорганического компонента эмали проводили в программе Kodak Dental Systems. Форму, упаковку, расстояние между эмалевыми призмами анализировали в программе Image Analysis NT—VDT. Результаты. Установлено, что после 30 лет в ретинированных зубах наблюдается выраженный эмалевый метаболизм, характеризующийся изменением формы, плотности упаковки и расстоянием между эмалевыми призмами. Показано, что при дисплазии соединительной ткани темпы созревания эмалевых призм в позднем постнатальном периоде онтогенеза снижены. Заключение. При дисплазии соединительной ткани наблюдается картина незавершенного амелогенеза с низкой плотностью упаковки и большим расстоянием между эмалевыми призмами.