Transmission electron microscope observations on enamel following silver methenamine staining.

Transmission electron microscope observations on porcine enamel and secretory ameloblasts showed that silver methenamine material was located inside secretory vesicles in secretory ameloblasts and along the enamel crystals inside immature enamel. It is concluded that silver methenamine is able to stain enamel proteins selectively inside these tissues.     

Uncoated specimen of human enamel obeerved in the scanning electron microscope

Abstract – A1-mm-thick section of human premolar was acid etched and observed uncoated in the SEM at accelerating voltages of 3, 5, 10 and 15 k v . Prisms and interprismatic substance were easily distinguishable. Low-voltage operation (3 and 5 k v ) gave the best results. Specimen charging was detectable at 5 k v and caused reduced image quality at 10 and 15 k v . Application of silver paste did not reduce charging appreciably. Prolonged observation at high magnification (x 10 000) resulted in contamination of the specimen with consequent charging and reduced resolution. Dental enamel seems to be a material which is well suited when uncoated for obervation in the SEM. This may be due both to the high content of the relatively heavy atom calcium, giving good secondary electron emission, and possibly to a certain degree of conductivity caused by diffusible icons.     

A scanning electron microscope study of the three-dimensional extent of Retzius lines in human dental enamel

A method involving carefully planned sectioning and grinding of human maxillary first premolars, allowing enamel structure to be studied with the SEM in more than one plane at the same time, was employed to demonstrate the extent of Retzius lines within the confines of the three-dimensional enamel cap. It was found that the Retzius lines behaved as could be predicted by the theory stating that the striae represent one-dimensional cuts of two-dimensional, curved growth planes. Retzius lines in adjoining planes were continuous across the edge where the two planes met. In a supernumerary tooth, the surface of its hypoplaslic tooth tip was continuous with distinct Retzius lines. The present observations provide for the first time direct morphologic verification of the supposed nature of Retzius lines, with reference to extent and continuity in three-dimensional space.     

Scanning electron microscopy of fluorideinduced disturbances on the enamel surface of rat molars

Abstract — Rats were given a single high dose of fluoride at the age of 5 days and killed after 24 h, 10 or 15 days. The maxillary Erst molars were prepared for scanning electron microscopic examination. It was concluded that a single dose of fluoride, preferentially affecting ameloblasts with a high secretory activity, leads to the formation of subameloblastic cysts and enamel hypoplasias covered with granular deposits.     

Scanning electron microscopic observations of early plaque formation in vivo on enamel specimens treated with delmopinol

Abstract The aim of this double blind, cross-over, scanning electron microscopic (SEM) study was to compare the effect of topical application of 0.5% delmopinol HCl (aqueous solution) with placebo on early supragingival plaque formation on enamel specimens attached to a maxillary premolar. 3 subjects underwent 2 × (placebo and delmopinol treatment, respectively) 7 treatment periods (1/2, 1, 2, 8, 24 hours; 3, 7 days) of undisturbed dental plaque accumulation, during which 2 ml of placebo and delmopinol HCl 0.5%, respectively, were applied topically to all teeth 2 × daily. At the end of each period, the specimen was retrieved and processed for SEM. For the specimens obtained after 24 h or less, the number of visible micro-organisms was estimated. For the 3- and 7-day specimens, the area covered by plaque was calculated planimetrically. Large inter-individual differences were observed in the number of bacteria attaching during the first 24 h, with apparently no major differences between delmopinol and placebo. 1 subject showed a bacterial colonization predominated by curved rods throughout the first 8 h. Compared to placebo, the area of the specimens covered by plaque was reduced after 3 and 7 days of delmopinol use, with coccoid cells as the predominant morphotype. Plaque maturity, characterized by the appearance of corncob formations and high numbers of different morphotypes, was not observed on the delmopinol specimens, in contrast to the placebo specimens. The study shows that topical application of 0.5% delmopinol HCl delays and interferes with dental plaque maturation.     

Circumferential continuity of perikymata in human dental enamel investigated by scanning electron microscopy

Abstract – Theoretically the perikymata may represent one of two possible configurations: closed circles or continuous spirals. In the present study one randomly selected perikyma groove in one randomly selected tooth (the mandibular first premolar of a 12-yr-old girl) was tracked around the circumference of the crown in the scanning electron microscope. It was found that the perikymata geometrically represented closed circles. The possibility of methodologic error was excluded.     

The ultrastructure of fluorosed human dental enamel

abstract — More than 80 specimens of enamel from 20 ground sections of eight teeth showing severe dental fluorosis have been examined in the transmission electron microscope. The study has shown that the prisms have normal size and form, but are surrounded by large periprismatic gaps. The individual crystals commonly appear in cross sections as regular, flattened hexagons with an average width of 91 nm and average thickness of 45 nm. Particularly in the tail regions and at prism peripheries, extensive intercrystalline spaces were found. The crystal lattice demonstrated a spacing of 0.82 nm. Demineralization of thin sections with PTA showed a preferential dissolution of the crystal centers. Based on the ultra-structural observations it is proposed that the hypomineralized regions of fluorosed enamel are produced by an arrest of enamel maturation, possibly due to toxic damage to the ameloblasts in the absorptive or maturative phase of their life cycle.     

Contralateral symmetry of acid etched enamel surfaces

abstract — Scanning electron microscopy (SEM) of phosphoric acid etched labial enamel surfaces of human permanent incisors and canines showed that the etch pattern, including the depth of the etched relief, may vary significantly from tooth to tooth and between different areas of the same tooth. On the other hand, pairs of contralateral teeth showed a very similar etch pattern symmetrically along the midline. No difference in the pattern could be found in enamel etched with three different orthophosphoric acids: 50% with 7% ZnO, 37%, and 35%. Therefore, when comparing the depth of penetration of different coldcuring restorative resins, composite or non-composite, into the etched enamel relief, it seems appropriate to study these materials two-by-two on pairs of contralateral teeth.     

Multiangular viewing of dental enamel in the SEM: a simple specimen holder system

Abstract – The specimen holder system described here has beet) found very useful when studying the three-dimensional organization of dental enamel in the SEM, The system includes small brass cylinders on which die specimens are mounted. The cylinders can be placed both vertically and horizontally in a specially designed holder. With this holder and a tilling capacity of 45° all specimen aspects deviating as much as 135° from the top surface can be studied.     

Inter-crystallite nanoretention of self-etching adhesives at enamel imaged by transmission electron microscopy

The purpose of this in vitro study was to analyse the mode of action of self-etching adhesive systems when applied for resin-to-enamel bonding. Transmission electron microscopy was used to investigate the enamel-resin interface after application of non-rinsing self-etching adhesive systems based on phosphoric acid estered methacrylates (Clearfil Liner Bond 2, Clearfil SE Bond, Etch & Prime 3.0 and Resulcin AquaPrime) compared with conventional phosphoric acid etching and bonding (Heliobond). Non-decalcified ultrathin sections from the interface between enamel and self-etching adhesive systems revealed a 1.5-3.2-microm deep enamel surface layer characterized by a less-dense arrangement of enamel crystallites separated from each other by nanometer-sized spaces. A 1.5-3.2-microm wide, netlike resinous structure was observed in corresponding decalcified specimens, indicating that self-etching priming agents dissolve the peripheral and central part of the enamel crystallites, while simultaneously promoting inter- and intra-crystallite monomer infiltration. A similar pattern, but greater depth (6.9 microm) of enamel surface hybridization was found in the phosphoric acid-etched and bonded specimens. The nanoretentive interlocking between enamel crystallites and resin could explain the potential of self-etching adhesive systems in resin-to-enamel bonding despite the less distinct enamel etching pattern observed in scanning electron microscopy investigations.     

Absence of enamel kmatrix on root-analogue surfaces of rabbit permanent incisors

Abstract – Permanent incisors from fetal New Zealand white rabbits aged 27–29 d in utero and fromoffspring of New Zealand white rabbits until the 4t d after parturition were processed for scanning electron microscopy. Macroscopic examination and measurements on standardized scanning electron micrographs revealed that the lingual surface of unerupted teeth was covered with developing enamel extending about 2.1 mm from the incisal end as evidenced by the presence of typical Tomes' pits. Such structures were not observed more apically where the lingual tooth surface appeared to be covered by cementum. The permanent incisors erupted into the oral cavity at birth and attrition was initiated within a few hours after parturition, jleading to an inverse correlation between attritional loss of tooth substance and extension of lingual enamel. The findings indicate that the enamel-covered, linguoincisal part of the rabbit permanent incisors is not a root-analogue surface. The results are discussed in te light of recent studies on rabbits and rodents.     

Aspects of the final phase of enamel formation as evidenced by observations of superficial enamel of human third molars using scanning electron microscopy

ObjectiveEnamel structure reflects ameloblast function. By studying the structure of the superficial enamel, information about ameloblast function toward the end of the secretory stage may be obtained.DesignThe superficial enamel in midcoronal areas of acid-etched facio-lingual sections from human third molars was studied in the scanning electron microscope (SEM).ResultsA great variation was observed in occurrence of prism-free enamel. Prism-free enamel dominated in 40% (mandibular) and 47% (maxillary) of observed areas and had a mean thickness of about 30 μm. Striations in the prism-free enamel had an interstriae distance of about 3.3–3.8 μm. The angle between prisms and enamel surface was about 60°, between prisms and Retzius lines about 45° and between Retzius lines and enamel surface about 15°. The distances between regularly occurring Retzius lines and between striations in the prism-free enamel both tended to decrease toward the enamel surface. Prisms could change direction as they approached the enamel surface, mostly in cervical direction. Where Retzius lines curved and converged occlusally, prisms tended to deviate in an occlusal direction.ConclusionsJudged from the incremental lines and occurrence of prism-free enamel, ameloblasts slow down and tend to lose their Tomes’ process as they approach the end of secretion. The crystals of prism-free enamel belong to the same system as the interprism crystals of prismatic enamel. A method, based on the disposition of fine incremental lines, is suggested for evaluation of ameloblast dynamics in the last stage of enamel secretion.     

Transmission electron microscopy of early microbial colonization of human enamel and root surfaces in vivo

Abstract – This study describes the early microbial colomization of teeth by the use of light-and transmission electron microscopy. Six dental students carried a total of 60 test pieces of unerupted enamel and root surface in intraoral acrylic appliances for 4, 8, 12, 24 and 48 h, during which periods oral hygiene was abandoned. Pronounced variations were recorded in structure and thickness of the pellicle across the individual surfaces of both dental tissues. Bacterial single-cell colonization increased the electron density of the adjoining pellicle. Micro-colonies of bacteria were observed in relation to enamel surface irregularities such as perikymata, while the distribution on root surfaces appeared incidental. Root surfaces were generally colonized by thicker deposits than homologous enamel surfaces although the structural composition of the microbiota was similar. Gram-positive bacteria with thick cell walls appeared in coccoid or rod-shaped configurations depending on the age of the bacterial deposit. These bacteria were further characterized by selective invasion between collagen fibers. After 48 h the complexity of the microbiota was increased by the establishment of new bacterial species in the superficial layer. It is concluded that the pattern and composition of the early microbiota on teeth is more complex and variable than hitherto assumed.     

Multiangular viewing of dental enamel in the SEM: an apparatus for controlled mechanical specimen preparation

An apparatus is described which can be used for controlled sectioning and grinding of tooth specimens to be studied in the SEM. Each specimen can be sectioned and ground along several planes. During the procedures the specimen remains fixed to a stub which after the final processing can be inserted directly into the scanning electron microscope.     

Scanning electron microscope observations on collagen fibers in human dentin and pulp

Abstract – Human permanent teeth were examined in the scanning electron microscope after demineralization and exposure to preparative procedures based on hydrogen peroxide, trypsin, and EDTA. These substances removed the inorganic material, the cellular structures, the homogeneous connective tissue ground substance, and interfibrillar matrix. The remaining tissue components comprised a network of distinct collagen fibers whose organization was related to the type of tissue in which these were incorporated. A similar or identical method has not been developed or applied to teeth previously. Dentin and predentin comprised a compact mass of fibers which basically were parallel to the continuously growing interior surface of the predentin, or arranged at an acute angle to this plane. Collagen fibers in the pulp were numerous, but lacked any particular orientation in most areas. Interodontoblastic fibers crossed the odontoblastic zone at a right angle to the pulp chamber wall and mingled with collagen fibers in predentin. When previously published findings of ours are taken into account, it is possible to conclude that other factors than the organization of the collagen fibers are responsible for the stainability of these fibers in predentin and in interglobular dentin with silver methenamine, and that aldehyde groups on collagen fibers in predentin may be actively and directly involved in the mineralization of the dentin.     

Scanning electron microscope and electron microprobe study of reactions of stannous fluoride and stannous chloride with dental enamel

Abstract — Stannous fluoride but not stannous chloride has shown a caries inhibiting effect in animal studies. The effect of aqueous solutions of stannous fluoride and stannous chloride on dental enamel surfaces was investigated by scanning electron microscope and analytical electron microprobe. Some large globules and a continuous layer of small globules were observed after stannous fluoride treatment. The large globules were soluble in both water and alkali, whereas the small ones were only soluble in alkali. Both fluoride and tin were found to be present on the enamel surfaces by the electron microprobe after stannous fluoride treatment. The fluoride could not be detected after immersion in distilled water whereas alkali treatment removed the tin. The large fluoride-containing globules may consist of calcium fluoride as this substance is known to be slightly soluble in water and soluble in alkali. Stannous chloride treatment gave a layer of small tin-containing globules with properties similar to the layer formed on enamel treated with stannous fluoride. It is therefore suggested that the tin-containing layer is not associated with caries protection whereas calcium fluoride-like deposition on the enamel probably is a factor in the caries inhibition caused by stannous fluoride.     

Resin-enamel bonds made with self-etching primers on ground enamel

Self-etching primer adhesives have recently been introduced to simplify bonding. However, the fundamental bonding mechanism of self-etching primers to enamel is not yet fully understood. This study aimed to investigate resin-enamel bonds of self-etching primer adhesives on ground enamel. Two self-etching primer adhesives (Clearfil Liner Bond 2 V and Clearfil SE Bond) were used in this study. A total-etch adhesive (One-Step) was used as a control. Resin-enamel beams were subjected to the microtensile bond test. Subsequently, the failure modes of all specimens were quantified using image analysis. Undemineralized and demineralized ultrathin sections of the resin-enamel bonded specimens were examined using transmission electron microscopy. The bond strengths of Clearfil SE Bond (39.8 +/- 11.9 MPa) and One-Step (46.2 +/- 12.7 MPa) were significantly greater than that of Clearfil Liner Bond 2V (30.4 +/- 6.2 MPa). Scanning electron microscopy of the fractured surfaces revealed the failure direction and weakest portion within each bond. Transmission electron microscopy showed a thin hybridized complex of resin in enamel produced by the self-etching primers without the usual micrometer-sized resin tags seen in resin-enamel bonds produced using the total-etch adhesive. The morphological features of the resin-enamel bonds produced by two self-etching primers tested were different from that created with the total-etch adhesive.     

正畸多次酸处理后牙釉质表面的扫描电镜观察

目的：通过扫描电镜观察正畸多次酸处理后牙釉质表面的结构变化。方法：以正畸临床即将拔除的正常第一双尖牙为实验样本,分为实验组和对照组。应用５０％ 的磷酸处理牙齿的颊面,时间为６０ｓ。对实验组样本分１、２、３ 次粘结托槽。按所设计的酸处理与粘结托槽的次数拔除该牙并固定,扫描电镜下进行观察。结果：镜下的观察显示,第一次酸处理后只是部分釉柱的轻度脱钙,蜂窝样结构少而不均匀。第二次酸处理后牙釉质表面蜂窝样结构密集而规则。经一、二次粘结后牙釉质表面残留的树脂均比较少,第三次粘结后牙釉质表面相对有较多的树脂残留。结论：第二、三次粘结托槽,仍会获得较好的机械性粘合。     

Amelogenesis imperfecta: a scanning electron microscopic and microradiographic study

The aim of the present study was to use scanning electron microscopy (SEM) to visualize the morphology of the enamel surface in 12 primary teeth from children with amelogenesis imperfecta (AI). The observations were correlated to genetic, clinical and microradiographic data from the same teeth and to non-affected control teeth. SEM showed similar disturbances in teeth with a clinical predominance of hypoplasias and in teeth with a predominance of hypomineralization. In the microradiographs the enamel of most teeth showed both hypoplasias and areas of hypomineralization, independently of the predominant clinical manifestation. In the one boy with an X-linked inheritance pattern, both SEM and microradiography showed the morphology of the enamel to be unique in the present study. In the other teeth, similar manifestations were found in cases with AI as an AD trait and in the sporadic cases.     

The ultrastructural localization of iron in rat incisor enamel

abstract — Previous studies have shown that the pigmented surface layer of rat incisor enamel contains up to 30% iron but have left the question open as to whether iron is bound to the hydroxyapatite crystals or is present as a separate crystalline phase. Maxillary incisors from adult rats were demineralized for an extended period of time in EDTA. An insoluble membranous structure representing the remaining superficial portion of the enamel was collected and analyzed in the electron microprobe. The analyses showed that the demineralization procedure had removed calcium and phosphorus nearly completely, whereas the iron content of the surface layer had not been appreciably reduced. Electron microscopic examination of these specimens showed that the residual material contained electron-dense particles whose size, form and orientation indicated that they were remnants of the original crystal population. Several other demineralized and undemineralized specimens were also examined electron microscopically. The results indicate that iron is not present as a separate particulate phase but is, probably, bound to the surface of hydroxyapatite crystals.