Transmission electron microscopy comparison of methods for collecting in situ formed enamel pellicle

The in vivo formed salivary pellicle is composed of an outer globular and a densely structured basal layer. This study developed a method for selective recovering of these pellicle layers from the enamel surface. Two-hour in situ pellicles were formed by intraoral exposure of enamel specimens in two adults. Pellicle-covered enamel specimens were treated either mechanically (scraping with scaler, curette or razor blade, or rubbing with a sponge) or chemically (phosphate buffer, NaCl, NaOCl, CaCl₂, NaSCN, urea, tetrahydrofurane, guanidine, SDS, HCl, or EDTA with or without additional ultrasonication). Specimens were processed for transmission electron microscopic analysis to detect pellicle residues remaining on the enamel surface after the different treatments. Most of the chemical treatments caused partial, incomplete removal of the globular layer. Complete removal of the globular layer without disruption of the basal layer was obtained by sponge rubbing or by CaCl₂ combined with ultrasonication, whereas scraping caused partial disruption of the basal layer. Removal of the basal layer was observed after treatment with HCl, EDTA, or NaOCl combined with ultrasonication. Electrophoretical analysis of recovered pellicle fractions indicate that combination of sponge-rubbing followed by EDTA treatment can be recommended for stepwise removal of the globular and basal pellicle layers.     

Morphological study of lingual papillae in the fetal cat at mid-gestation,as revealed by light and scanning electron microscopy

 Tongues were removed from five cat fetuses, after approximately 1 month of gestation, for examination by light and scanning electron microscopy. Rudiments of filiform papillae were visible over the entire dorsal surface of the tongue. The epithelium of the dorsal surface of the tongue was of the stratified cuboidal type. No evidence of keratinization was detected anywhere in the entire dorsal lingual epithelium. Rudiments of fungiform papillae were recognizable only at the lingual apex; none were recognizable on other parts of the dorsal surface of the tongue at this stage. By contrast, rudiments of circumvallate and foliate papillae were already distinguishable from the filiform papillae. Differences between these results and those obtained previously in rats and mice are discussed. Received: August 29, 2001 / Accepted: May 7, 2002     

Effect of Carisolv™ solution on sound, demineralized and denatured dentin – an ultrastructural investigation

The purpose of this in vitro study was to analyze the micromorphological changes caused by Carisolv^™ gel on sound, demineralized, and denatured dentin. Fractured dentinal surfaces, dentinal surfaces demineralized superficially by phosphoric acid etching and dentinal surfaces denatured due to lactic acid and collagenase pretreatment were exposed to freshly mixed Carisolv^™ gel or 0.25% sodium hypochlorite. No additional mechanical action was exerted during the 20-min exposure of specimens to the Carisolv^™ solution. Specimens were evaluated by transmission electron microscopy. Electron microscopic evaluation did not indicate any ultrastructural changes of the fractured or demineralized dentinal surfaces due to the 20-min Carisolv^™ treatment. Denatured dentin was partially removed within a 20 min period of chemical action of the Carisolv^™ solution leaving only a 1- to 2-μm thick layer of residual denatured dentin on the specimen’s surface. In contrast, 0.25% sodium hypochlorite treatment completely dissolved the demineralized as well as denatured dentin layer within 20 min. It is concluded that Carisolv^™ gel (1) does not affect sound fractured dentin, (2) does not dissolve demineralized dentin, and (3) has a limited potential to chemically dissolve denatured dentin. Received: 30 June 1999 / Accepted: 13 July 1999     

Terminal end of the human odontoblast process: a study using SEM and confocal microscopy

Towards the middle of the eighteenth century, Tomes described the presence of membranous structures of cellular origin inside the dentinal tubules. Subsequent studies have been controversial regarding the terminal end of the odontoblasts. According to Fusayama, this cellular process reaches even the dentinal-enamel junction; others, such as Brännström, believed that this cellular process is present only in the inner third of the dentin. The aim of the present study was to determine the exact area up to which the terminal ends of the odontoblasts extend. With the aid of advanced confocal laser scanning microscopy (CLSM) cylindrical structures were demonstrated inside the tubules even in the absence of odontoblasts. This would confirm that the structures previously described as cellular processes can be identified with the lamina limitans of the peritubular dentin. High resolution field-emission scanning electron microscopy (FE-SEM) provided further evidence that tubular structures are only seen in the inner third of the dentin, towards the pulp.     

Effects of salivary pH on coating durability of two different aesthetic archwire coatings under a simulated intraoral environment

ObjectivesThis study compared the effects of normal salivary pH, and acidic pH found in patients with poor oral hygiene, on the durability of aesthetic archwire coated with epoxy resin and polytetrafluoroethylene (PTFE).MethodsThe posterior parts of the archwires were sectioned into 20 mm segments (N = 102) and divided among six groups. Four groups were treated with different pH levels and two served as controls. The specimens were immersed in individual test tubes containing 10 ml of artificial saliva adjusted to a pH of 6.75 or 3.5. The tubes were sealed and stored in a 37 °C water bath for 28 days. After 28 days, the specimens were ligated to brackets embedded in an acrylic block and subjected to mechanical stress using an electronic toothbrush for 210 s. The specimens were photographed, and images were measured for coating loss using AutoCAD® software. Surface morphology was observed using a scanning electron microscope (SEM).ResultsSignificant coating loss (p < 0.001) was found in the epoxy resin groups, regardless of pH value, but not in the PTFE groups. The acidic pH caused epoxy resin layer coating loss by twice as much as normal pH. SEM revealed existing manufacturing defects on the as-received epoxy resin coating, whereas the retrieved epoxy resin demonstrated rupture, roughness, and coating loss in multiple locations.SignificanceEpoxy resin coatings demonstrate poor durability in acidic environments. This condition is worsened by the existing manufacturing defects found on as-received archwires. Hence, archwires coated with epoxy resin are not recommended in patients with poor oral hygiene.     

An in vitro study of fluoride release from a resin-modified glass ionomer cement after exposure to toothpaste slurries of different pH

. The aim of the study was to evaluate the fluoride release from an aged resin-modified glass ionomer (Vitremer) after exposure to five toothpaste slurries with different pH values. Cylindrical specimens of the material were leached in de-ionized water for 3 months and then exposed for 30 min daily for 10 days to three dentifrice slurries (20 specimens/group) containing 0.05% fluoride with pH values of 2.6, 5.7 and 8.3 and two non-fluoridated slurries with pH values of 2.5 and 5.7. A neutral NaF solution (0.05% F) was used as a control. During the 30 min exposure time, the fluoride concentration was gradually decreased in order to imitate the clinical situation. Thereafter, specimens were immersed individually in de-ionized water and the fluoride release determined. After the first day of exposure, all groups except one without fluoride (pH 5.7) showed significantly (P<0.05) increased fluoride release. After exposure to the fluoridated toothpaste slurry with pH 5.7, significantly (P<0.05) more fluoride was released compared to the toothpaste slurry with pH 8.3. Low pH (2.5 or 2.6) of the slurry resulted in a significantly (P<0.05) higher fluoride release, regardless of whether it was fluoridated or not. The total amount of fluoride released after exposure to the more acidic fluoride toothpaste slurry was greater than that released from the more acidic non-fluoride toothpaste and the less acidic fluoride toothpaste. Our data indicate that the fluoride release from the resin-modified glass ionomer studied may be in-creased after treament with an acidified NaF-toothpaste. Received: 24 January 2000 / Accepted: 20 July 2000