Prismless Enamel Research Articles

Ultrastructure of quick-frozen secretory ameloblasts of the rat molar tooth

Ameloblasts in molar tooth germs from 4 to 12-day-old neonatal rats were quick-frozen and then freeze-substituted in acetone-tannic acid and acetone-osmium tetroxide. Following quick freezing and freeze-substitution, the preservation of ameloblasts was principally the same as seen in conventionally-fixed ones. Several differences, however, became apparent between two methods. Concerning enamel formation, the quick-freezing procedure greatly improved the preservation including that of the extrusion of secretory granules into the extracellular space. This exocytosis is a type of merocrine secretion. The precursor stippled material was demonstrated at the front of Tomes' processes and in the intercellular space of the distal terminal junction. In the more advanced stage, the stippled material tended to decrease gradually in amount. Prior to the formation of the typical Tomes' process, large secretory granules fused directly with the distal plasma membrane, which plays a role in the formation of prismless enamel. After the typical Tomes' process had formed, secretory granules containing electron-dense material instead of the large secretory granules accumulated in the distal portion of the Tomes' process. These latter secretory granules had two different destinations; i.e. the granules discharged their contents into the infoldings of the distal part of Tomes' process and into the infoldings of the lateral cell membrane. These types of secretion seem to have a functional role in the rod or inter-rod enamel formation. The ultrastructure of the stippled material consisted of 3-dimensionally interconnected strands after quick freezing, which is different from the appearance of granules embedded in amorphous material after conventional fixation. The stippled material was seen in the intercrystal space among the newly formed crystals. Also, an extensive tubulo-vesicular structure was preserved in both the cell body and Tomes' process. The present data suggest that the membrane of this structure showed a smooth contour opening to the extracellular space, and also an intimate relationship with the secretory granules.

Sequential observations followed by acid etching on the enamel surfaces of human teeth under scanning electron microscopy at low vacuum.

A scanning electron microscope equipped with a low vacuum specimen chamber and a Robinson's backscattered electron detector was employed to observe the natural surfaces of human buccal enamel before and after 30 percent phosphoric acid etching sequentially up to 90 sec at the same sites with no coatings. Furthermore, successive etching patterns were compared between deciduous and permanent teeth. On the imbrication lines of young permanent teeth, prism-end pits surrounded with a "prismless" structure occasionally disappeared after acid etching and became a prismless enamel. Sequential etching caused the prismless areas and the areas of a type 1 etching pattern to decrease, and a cone-shaped prism structure and a complex type of the type 1 and type 2 etching pattern (type 1-2) to appear. The former was a transitional type between the prismless enamel and type 2 prisms. These etched surfaces show type 2 prisms after deeper etching. Small dome-shaped structures, slightly elevated on the attrited enamel surfaces, were found only in deciduous teeth. After acid etching, such areas which retained the prismless enamel rose to the underlying surfaces of cone-shaped prisms.

Structure of the so-called 'prismless' enamel in human deciduous teeth.

The surface enamel of human deciduous teeth showing a more negative birefringence by polarized light was investigated by differential interference contrast microscopy and by scanning electron microscopy (SEM) following EDTA etching. Though this surface enamel has been generally called the 'prismless' enamel, in this study, the so-called 'prismless' enamel was categorized into 'false', 'moderate', 'essential' and 'complex' types according to whether they took the form of distinct prisms which bended at the subsurface, indistinct circularly based prisms or not. Based on the SEM observations some types of the 'prismless' enamel showed parallel crystallites and no prism boundaries. However, if indistinct prisms showing centripetal crystallites within the circular boundaries are admitted into the prismless enamel, other types except the 'false' one will generally belong to it.

The absence of an age effect on enamel solubility in phosphoric acid

The growing proportion of older Americans and the projections in declining edentulousness in future cohorts of elderly necessitate elucidation of the responses of the aging human dentition to existing restorative techniques. This study investigated the results of the acid etch process as a function of age of specimen donors as well as a function of race, tooth type, and time between extraction and etch. Statistical analysis of data showed no significant effect on solubility by age, race, or length of time from extraction until etch. Molars were significantly less soluble than other teeth. The most frequently observed microscopic texture was an irregular, granular configuration termed 3g. Widely textural variation was observed in each specimen. A possible explanation for the observations is the distribution of prismless enamel. The widespread belief that older teeth are less efficaciously etched may be based on the greater frequency of composite restoration failures in the elderly, which in turn is more likely a factor of restoration size and changes in intraoral environment than of age.

Structure of Sorex (Insectivora) enamel.

The enamel pigmentation of Sorex (Insectivora) is distributed over the whole of the tooth from the enamel surface to the zone of the middle enamel layer, except for some unpigmented micro-areas. With respect to the structure of the enamel, Sorex has two types of organization in the unpigmented enamel (UE) and pigmented enamel (PE); prismatic and prismless enamel or tubular and atubular enamel types. In the UE areas, the enamel prisms run in a relatively complex but systematic way. However, on the PE, the enamel prisms run almost parallel to the enamel surface.The enamel pigmentation is caused by iron. The X-ray micro-diffraction pattern suggests that the apatite of the PE is similar to that of the UE. The electron-diffraction pattern shows that the length of the axis of PE apatite is slightly different from that of natural apatite crystallites, and many dislocations were observed in PE crystals in high-resolution electron micrographs. These results suggest that some iron atoms may be distributed not only between but also inside the crystallites. The iron content is about 8% (by weight) of the enamel, as shown by SEM electron-probe microanalysis.

In vivo adaptation of restorative materials to dentin

lhe enamel acid-etch technique is an integral restorative procedure for composites. It improves marginal adaptation and retention and reduces marginal leakage.’ However, bacterial invasion from the oral environment can still occur at the cavity margins.‘,’ In clinical practice the gingival margin is a weak link. Occurrence of prismless enamel or an exceedingly thin layer of enamel makes the use of the acid-etching technique impossible. Increased marginal leakage can occur. Intensive research on adhesion to dentin started 20 years ago.’ Adhesive bonding to dentin requires removal of the smear layer. The use of cavity cleansers and etching agents has been suggested, although these can enhance the pulpal response.‘,” However, other studies show that acid pretreatment per se did not cause pulpal injury.‘, R Etching the dentin with 37% phosphoric acid for 15 to 60 seconds removes the amorphous smear layer and dissolves the dentin.’ Resin tags penetrating the dentinal tubules have been reported.’ ‘)-‘I These tags can possibly serve as mechanical retention for the restoration. However, dentinal tags do not assure a permanent, serviceable adaptation of the restorative material to the cavity walls in vivo. The tags initially penetrate the dentinal tubules but tend to withdraw because of contraction and stresses. Recently developed commercial dentin bonding agents show reduced leakage and increased bond strength to acid-etched dentin in vitro.‘z”5

Acid‐etching of enamel cavity walls

Abstract— The acid‐etched patterns produced on enamel cavity walls and the enamel tooth surface were investigated and the implications of these patterns on cavity preparation for composite resin restorations are discussed.The predominant pattern on enamel cavity walls is of obliquely and longitudinally sectioned prisms. Less commonly, cross‐sectioned prisms, prismless enamel and a rough, pitted appearance are observed. Excessive etching (for example, for four minutes) should be avoided.

Materials Science

We have developed a vibration etching technique in which occlusal pits and fissures are simultaneously cleansed and acid-etched using a fissure needle mounted on an electromagnetic vibrator. When tested on extracted teeth, the needle completely cleansed the fissures by removing the contents and the prismless enamel layer, and widened them to from 100 to 150 micrometers to the depth reached by the needle. The sealant penetrated readily and adhered to the reduced and etched fissure walls interlocking with resin tags.

A clinical, genetic, and ultrastructural study of snow-capped teeth: Amelogenesis imperfecta, hypomaturation type

Snow-capped teeth (SCT) is a rare form of amelogenesis imperfecta, hypomaturation type. It has been alluded to on numerous occasions but, to our knowledge, no pedigree or clinical-histopathologic data have been published. In this report, two families are described. Scanning electron microscopic (SEM) studies of unetched teeth from affected persons revealed numerous defects of the enamel surface. After etching with 10 percent hydrochloric acid for 2 1 2 minutes to remove the outer prismless layer of enamel, SEM features of the enamel prism were essentially identical to those of normal teeth. These findings suggest that the structural defect in SCT is confined to the outer prismless enamel layer and that the bulk of the enamel is normal. The genetic analysis supports the concept that SCT is inherited in an X-linked recessive fashion and not as an autosomal dominant trait, as previously reported.

Scanning electron microscopic study of the enamel carious lesion in human deciduous front teeth

Scanning electron microscopy of early carious lesions of the labial and proximalsurfaces of deciduous front teeth demonstrated two distinct patterns in the progression of incipientcaries.The variable patterns could be related to the differences of the enamel surface structure between the prismatic enamel and prismlessenamel. The breakdown of the prismatic enamel surface developed continuously through rod end depressions. The prismless enamel showed rough surfaces with channels and cracks extending from the surface to the decalcified subsurface area. Microscopically scattered and dissolved portions of the enamel surface were detected and this may suggest multi-occurrence of carious lesions.Artificially produced carious lesions showed the characteristic demineralization at the prismaticenamel surface of cervical region. This phenomenon revealed an important factor ofthe prismless enamel layer in the resistance to carious progress.

A scanning electron microscopic study on the differences between newly erupted teeth and old teeth with reference to fissure enamel surfaces and contents.

Scanning electron microscopy of the fissure enamel surfaces of newly erupted permanent teeth and old sound teeth long-standing against caries demonstrated two distinct features; prismatic enamel and prismless enamel. Prismatic enamel was commonly found on the walls of fissures of newly erupted teeth and rarely found on both sides of fissures of old teeth. Prismless enamel was usually found on both sides of fissures of old teeth. Various types of calcified contents were almost confined on the prismless enamel surfaces of the occlusal orifice of fissures of old teeth, while organic materials and bacterial contents were found on the prismatic enamel surfaces of newly erupted teeth.

The structure of surface enamel with special reference to occlusal surfaces of primary and permanent teeth.

Clinical studies have shown that fissure sealants are not retained by primary teeth as well as they are by permanent teeth, presumably due to the presence (of a surface layer of prismless enamel in primary teeth. In order to compare the enamel structure and main crystallite orientation on occlusal surfaces, sections from primary molars and permanent premolars were examined by polarized light microscopy. Crystallite orientation to the enamel surface was measured at various distances from the fissure entrance. It was found that the crystallites were arranged almost perpendicular to the enamel periphery whilst the prisms formed an acute angle with the periphery. Only on rare occasions was prismless surface enamel observed. It was concluded that main crystallite orientation and prism arrangement were alike in primary and permanent occlusal enamel, and that the poor retention of sealants on primary teeth cannot be explained by the presence of a prismless surface.

Human prismless enamel and its influence on sealant penetration

A lower incidence of sealant retention has been noted for deciduous compared to permanent human teeth. The presence of prismless enamel, common in deciduous teeth, may significantly influence resin retention due to its limited porosity and penetrability, following acid-conditioning. Prismless enamel allowed very limited resin penetration compared to prismatic enamel, so that mechanical bonding may be impaired.

Scanning electron microscopy of prismless enamel in human teeth

Three permanent incisors and a canine of an unknown patient were sectioned longitudinally and transversely. After polishing, sections were etched with dilute hydrochloric acid. They were coated with carbon and gold in a vacuum evaporator and examined in a scanning electron microscope. In all 4 teeth there were wellmarked striae of Retzius and within these areas there were zones about 130 μm wide in which no prism structure could be seen and in which apatite crystals were orientated perpendicular to the striae of Retzius.