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Biomedical subjects

R M Frank

Publications and source records attributed to R M Frank.

At least 19 recordsLinked to original sources
PubMed1992

Human amelogenesis. I: High resolution electron microscopy study of ribbon-like crystals.

Ribbon-like crystals, from developing enamel of human fetuses, were studied by high resolution electron microscopy. These crystals were classically described as the first organized mineral formed during amelogenesis. They were characterized by a mean width-to-thickness ratio (W.T-1) of 9.5, and 40% were bent. On lattice images we noted the presence of the central dark line (CDL) associated with white spots. Both structures were found in crystals with a minimum thickness of 8-10 nm. CDLs were localized in the center of the crystals and seemed to be linked to the initial growth process, but their exact structure and function were not fully determined. We were able to study the structure of the ribbon-like crystals with a Scherzer resolution close to 0.2 nm. The good correspondence between experimental and computed images showed that their structure was related to hydroxyapatite (HA). In addition, the presence of ionic substitutions and deficiencies were also compatible with HA. In this study, about 50% of the crystals showed structural defects. Screw dislocations were the most often noted defects and were observed within crystals aligned along five different zone axes. Low- and high-angle boundaries were also detected. Low-angle boundaries, found in the center of the crystals, could thus be related to CDLs and be implicated in the nucleation step of crystal formation, whereas high-angle boundaries could result from the fusion of ribbon-like crystals. Such mechanisms could induce an acceleration of the growth in thickness of the crystal observed during the maturation stage of amelogenesis.

Amelogenesis↗
PubMed1992

Effects of carbon dioxide, Nd:YAG and carbon dioxide-Nd:YAG combination lasers at high energy densities on synthetic hydroxyaptite.

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J.cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 A and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. alpha-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of TCP.

Aluminum Silicates↗
PubMed1992

Urinary fluoride excretion in children using potassium fluoride containing salt or sodium fluoride supplements.

With the introduction of fluoridated domestic salt in France in 1986, questions have arisen with respect to its efficacy in caries prevention. It has been of interest to compare the urinary excretion of fluoride in children who consume fluoridated salt to that in children who take fluoride tablets. Ninety-three schoolchildren, 10-14 years of age, participated in the study and were divided into four groups: group I consumed fluoridated salt with every meal; group II ate at a school restaurant once a day and consequently consumed fluoridated salt at only their evening meal, as fluoridated salt is not authorized for use in collective restaurants; group III consisted of children taking fluoride tablets (1.0 mg F/day) exclusively, and group IV did not receive any systemic administration of fluoride for prevention and constituted a low-fluoride control group. Total 24-hour urine samples were collected from all subjects. The average daily urinary flow rates varied from 0.51 to 0.68 ml/min, but showed no statistically significant differences among the groups. The average urinary fluoride concentrations were 0.60, 0.30, 0.99, and 0.28 mg/l, respectively, for groups I-IV. The mean 24-hour urinary fluoride concentrations and excretion rates for children who consumed fluoridated salt at all meals (group I) were not statistically different from those using tables (group III). There were also no statistically significant differences between groups II and IV. The differences between urinary fluoride concentrations and excretion rates of groups I and III, as compared with group IV, were statistically significant.

Administration, Oral↗
PubMed1991

Effects of complete denture wearing on temporomandibular joints: a histomorphometric study.

At autopsy, 54 human temporomandibular joints were distributed in three groups. The first group was made up of 14 joints of dentate subjects (mean age = 51 years). The second group was composed of 12 temporomandibular joints of totally edentulous patients who had lost their teeth for at least 10 years (mean age = 82 years). The third group was composed of 28 joints of edentulous patients who had been wearing complete dentures for at least 20 years (mean age = 66 years). Sagittal serial decalcified sections were studied by light microscopy and was submitted to histomorphometry. Group 1 was characterized by a deep mandibular fossa with well-marked cortical layers of the temporal bones and the condyles. The fibrocartilages were multilayered and the articular disks had biconcave outlines. In group 2 a flattening of the mandibular fossa was observed, with a thinning of the cortical and spongy bones. The fibrocartilages were thin and not multilayered. In group 3, the structure of joints was similar to that of group 1. The mean values of the surfaces, thicknesses, and lengths of the measured parameters were systematically highest in group 1, whereas these mean values in group 3 were similar to or had a tendency to be close to the means of group 1. In contrast, the mean values of group 2 were always the lowest. It can be concluded that complete dentures had a favorable protective effect on temporomandibular joint structures.

Adult↗
PubMed1991

HREM study of irradiation damage in human dental enamel crystals.

Several phenomena have been observed during the examination of human dental enamel crystals (mainly constituted by hydroxyapatite (OHAP] by high-resolution electron microscopy (HREM) at 300 and 400 keV: orientation-dependent damage in the form of mass loss from voids or uniform destruction of crystal structure, beam-induced diffusion creating outgrowths at the crystal surfaces, recrystallization of the bulk crystal and crystallization of the inorganic components of the matrix surrounding the crystals. These beam-induced crystals have the CaO structure. The phenomena observed are most likely due to various electron-crystal interaction mechanisms (ballistic knock-on damage, electronic excitations, temperature rise, etc.). In this paper, the contribution of the ballistic process to the phenomena observed is discussed. The quantitative description of the knock-on collisions rests on the McKinley-Feshbach cross-section formula. The minimum ion displacement energies which appear in this expression have been estimated on the basis of the electrostatic ion binding energies, and the covalent bond energies if required. It is shown that hydroxyl, calcium and oxygen ions can effectively be displaced by the incident 300 and 400 keV electrons. Thus, the formation of CaO crystals by the combination of calcium and oxygen ions diffusing from their initial sites inside the OHAP lattice can tentatively be explained.

Adult↗
PubMed1991

Compositional variations in apatites with respect to preferential ionic extraction.

Detection of ionic losses from the apatitic structure (Ca10(PO4)6(OH)2) by high-resolution electron microscopy was investigated theoretically. Linear image analysis showed the need for an objective aperture of at least 3.7 nm-1 to visualize four different coordinates (CaII, OH-, P and mid-point between CaII-P bond). High-resolution image analysis and plotting of OH- column intensity against specimen thickness showed an inverse proportionality between composition and OH- image intensities for very thin specimens (less than 2 nm). Image intensity variation would be detectable experimentally, but the preparation of such thin specimens by ultramicrotomy is impossible.

Apatites↗
PubMed1991

Ultrastructural demonstration of the importance of crystal size of bioceramic powders implanted into human periodontal lesions.

Stages in bone formation were studied ultrastructurally after the implantation of the following 3 bioceramic powders into human periodontal lesions: (1) beta-tricalcium phosphate whitlockite (Synthograft) consisting of particles with a mean length of 229 +/- 87 microns in SEM and appearing in TEM as crystals with a mean diameter 488 +/- 192 nm; (2) an hydroxyapatite (Bioapatite) which consisted of particles with a mean length of 283 +/- 87 microns in SEM and of crystals with a mean diameter of 146 +/- 47 nm in TEM; and finally (3), a microsized hydroxyapatite consisting of elongated platelets with a mean length of 32 +/- 4 microns in SEM, composed of small crystals with a mean diameter of 38 +/- 16 nm in TEM. In a preliminary experiment in rats, it appeared that the microsized hydroxyapatite implanted into the alveolar region after first molar extraction exhibited biocompatibility. In 6- and 12-month biopsies, it appeared that bone formation in association with the 3 bioceramics tested in human periodontal lesions occurred through similar mechanisms at the ultrastructural level. After the appearance of peripheral fibroblast-like or osteoblast-like cells with an interposed layer reminiscent of an osteoid tissue, collagen fibrils were observed in the intercrystalline spaces. These spaces subsequently underwent mineralization, with deposition of bone apatite crystals followed by the peripheral deposition of a thin inner bone layer with a granular appearance and an outer normal bone layer of either woven bone, lamellar bone or bone with parallel calcified collagen fibrils. These bone nodules, however, formed around the bioceramic particles at highly variable time intervals. Bone formation was observed around Synthograft and Bioapatite implants only in 12-month biopsies, and thicker layers of peripheral bone were observed with the latter hydroxyapatite implant. With microsized hydroxyapatite, a significant amount of peripheral bone formation had already occurred by 6 months, strongly suggesting an important effect of crystal size on bone formation.

Adult↗
PubMed1991

Experimental erosion of dentin.

Experimental erosion in human dentin was investigated with scanning electron microscopy. Erosion was caused by solutions containing either 0.030 mekV/g malic acid (pH 3.4), 0.034 mekV/g phosphoric acid (pH 2.6), or 0.038 mekV/g citric acid (pH 2.8). Test specimens prepared from the coronal parts of erupted third molars were immersed in the solutions from 30 s to 60 min. When compared with controls, exposure of dentin tubules was observed in all the specimens already after 30 s immersion, irrespective of the acid used. Mineral loss was seen to progress at the interface between peritubular and intertubular dentin in specimens immersed for 60 s in the acidic solutions. Longer times of immersion resulted in hollowing of the tubular openings by complete destruction of the peritubular dentin. Surface roughness and porosities were seen also at the intertubular areas. Although based on a simplified study model, our results may explain why so many patients with erosions suffer from painful sensitivity of their teeth: the acids causing erosion can expose inner dentin structures to outer stimuli by significant enlargement of the dentinal tubules.

Acid Etching, Dental↗
PubMed1991

Scanning electron microscopic study of the effect of salivary pellicle on enamel erosion.

A bovine tooth model system was used to study the effect of experimental salivary pellicle on enamel erosion. Test blocks with varnish-covered control surfaces in each specimen were immersed into an acidic cola beverage (pH 2.6) for 120 min, either with or without the pellicle which was grown for 7 days by using clarified human saliva. After immersion, the pellicle was removed from some specimens with 10% sodium hypochlorite (20 h at 20 degrees C) and ultrasonic bath (60 s) to study its effect on erosion. All specimens were then studied in the scanning electron microscope. The specimens without pellicle (positive controls) showed gross erosion with prism core dissolution in all study blocks. The specimens with pellicle showed occasionally a film-like integument covering the apparently intact test surfaces with adjacent enamel surfaces slightly eroded. The erosion, however, was not of the same magnitude as in the positive controls. After removing the pellicle, the enamel surfaces showed pitted appearance of the prism heads; the demineralization seemed to attack more the prism sheath areas. Thus, salivary pellicle was found to protect the underlining enamel from erosion in vitro.

Animals↗
PubMed1991

Progression and surface ultrastructure of in vitro caused erosive lesions in human and bovine enamel.

Surface prismatic and aprismatic human enamel and unpolished or diamond-polished specimens of bovine enamel, with test and control surfaces on each studied block, were immersed in phosphoric acid containing cola beverage (pH 2.6) and citric or malic acid containing sports drinks (pH 2.8 and 3.4, respectively) for 15-180 min. The specimens were then prepared and studied in a JEOL 35C scanning electron microscope. In human aprismatic surface enamel an irregular type of dissolution was observed, with severely affected areas adjacent to less affected ones. Prismatic human and bovine specimens showed a characteristic dissolution where initial erosion after 15 min immersion was seen to affect specifically the prism sheath areas. Longer immersion caused dissolution of enamel prism cores followed by interprismatic areas. In bovine enamel malic acid affected least the surface ultrastructure when compared with citric and phosphoric acids after 15-30 min of immersion, but thereafter no difference was observed between the acids in causing erosion. Diamond-polished enamel was found more liable to erosion than non-polished enamel. Thus, the structure of enamel greatly modified the progression of in vitro caused erosion, in particular in human tooth specimens.

Animals↗
PubMed1991

Bacterial invasion of periodontal tissues after experimental immunosuppression in rats.

A moderate gingivitis was produced in 3 groups of 10 adult Wistar rats with diet 2000 of Keyes and Jordan (1964) delivered for 30 days with a controlled feeding unit. The first group served as untreated control. The second group received 5 intraperitoneal injections of cyclosporine A (15 mg/kg body weight) from day 20 to 30 to interfere with the activation of T lymphocytes and interleukin synthesis. The third group received 2 intraperitoneal injections of cyclophosphamide (100 mg/kg on day 20 and 25) which induced a severe neutropenia. The gingival areas between the upper molar regions were prepared for light and transmission electron microscopy. In the untreated control group, a layer of polymorphonuclear neutrophils (PMN) was observed between the dental plaque and the junctional epithelium with a round cell infiltration in the superficial connective tissue. No bacterial invasion was observed. In the cyclosporine group, despite the action on T lymphocytes, no bacterial invasion occurred, but a differentiated PMN layer was present between the apical dental plaque and the junctional epithelium. In the cyclophosphamide group an important bacterial invasion was observed in the interdental epithelium as well as in the underlying connective tissue. In the local absence of PMNs, a mixed flora of Gram positive and negative bacteria of various shapes invaded epithelial as well as connective tissue cells and came in contact with the alveolar crestal bone. Resorption of the alveolar crestal bone scored according to the Keyes and Gold method (1955) was significantly more important in the cyclosporine and the cyclophosphamide group when compared to the controls (p less than 0.05). No statistical difference in bone resorption was noted between the cyclosporine and the cyclophosphamide groups. It can be concluded that the PMN layer constitutes the first line of defense opposed to bacterial invasion of the periodontal tissues.

Alveolar Bone Loss↗
PubMed1991

[Histological comparison of the effect of different implanted hydroxyapatites in the animal periodontium].

The effect of various types of synthetic hydroxyapatites (HA), coated or not with collagen or human plasmatic fibrin, has been studied after 3 month implantation either in freshly extracted alveoli in miniature pigs or in experimentally induced periodontal lesions in beagle dogs. The best histological results were observed in HA without organic coating. The Bioapatite consisting in crystals with a mean size of 146 nm +/- 47 nm were well integrated in the alveolar bone. Similar results were obtained with micro-sized hydroxyapatite, with a mean crystal size of 38 nm +/- 16 nm. But at 3 months, this HA type was still actively integrated in bone with osteogenesis. When these 2 types of HA were coated with collagen or plasmatic fibrin, they were less well incorporated in alveolar bone and were even able to develop localized and moderate inflammatory reactions. The main purpose of synthetic HA is to promote alveolar bone formation in periodontal lesions. For an improved tissular regeneration, it is recommended to use simultaneously in the future synthetic HA together with resorbable biocompatible synthetic membranes.

Alveolar Bone Loss↗
PubMed1990

Immunolabelling of SR protein and serotype polysaccharide in Streptococcus mutans.

Immunoelectron microscopy was used to determine the accessibility of gold-labelled monoclonal antibodies, specific for the SR protein and serotype polysaccharide, to the surface of viable cells of Streptococcus mutans. The results indicate that both antigens are simultaneously accessible to their respective antibodies.

Antibodies, Monoclonal↗
PubMed1990

High-resolution electron microscopy of human enamel crystals.

The structure of enamel crystals obtained from four human premolars has been studied by high-resolution electron microscopy (HREM) in the [0001], [2110], [1540], [0110] and [1213] crystallographic directions at various microscope defocus and crystal thickness values. The resolution obtained has not previously been reported for human enamel crystals. In all cases, it was possible to match the experimental images to images calculated using the atomic positions of mineral hydroxyapatite. However, a deviation from hexagonal symmetry characterized by marked (1010) planes of intensity different from the one of the (3030) and (1010)-type planes was observed. In this work, we present an improvement of Scherzer resolution of 0.25-0.20 nm over previous work on biological enamel crystals. This improvement of resolution has permitted the incorporation of crystallographic reflections of higher spatial frequencies into the imaging process of the microscope and has led to a more precise structure determination of the crystals studied.

Adult↗
PubMed1990

Comparison of lead levels in human permanent teeth from Strasbourg, Mexico City, and rural zones of Alsace.

A comparative study of the mean lead concentrations in enamel and dentin of human premolars and permanent molars was conducted by means of a systematic sampling procedure with energy-dispersive x-ray fluorescence analysis. In a first series of analyses, no significant statistical differences in mean lead concentrations at various levels of enamel and dentin were noted between young patients of Strasbourg and those of small villages of Alsace, nor between elderly patients living in these two locations, despite the fact that motor traffic was significantly lower in the rural zones. However, in both locations, a significantly higher concentration of lead was observed in enamel and dentin in relation to age. In a second series of analyses, the mean lead concentrations of both dental hard tissues of premolars and permanent molars of young individuals from Strasbourg, rural Alsace, and Mexico City were compared. Significantly higher mean lead concentrations were found in enamel and dentin samples from Mexico City. This was most evident for inner coronal dentin (5.7 and 6.1 times greater than in teeth of Strasbourg and rural zones of Alsace, respectively) and for pulpal root dentin (6.9 and 8.9 times greater than in teeth of Strasbourg and rural zones of Alsace). It is proposed that the higher lead concentrations are related to the higher lead content of motor gasoline and to more intense traffic conditions. The dental hard tissues appear to be of value for the study of environmental lead pollution.

Adolescent↗
PubMed1990

Structural events in the caries process in enamel, cementum, and dentin.

The structural events observed in enamel, cementum, and dentin during the caries process have been reviewed. In incipient enamel lesions, the prevailing concept of an almost intact surface layer has been seriously challenged by SEM and TEM observations demonstrating structural pathways (such as enlarged prism junctions or sheaths) from the enamel surface to the sub-surface lesion. The destruction in this latter location consisted of (1) enlarged prism junctions, (2) diffuse mineral destruction in the prism cores, and (3) destruction of the interprismatic substance. In root caries, the destruction of cementum started along junctions between calcified layers of extrinsic (Sharpey) and intrinsic collagen fibers as well as along incremental lines. Invasion of Gram-positive micro-organisms followed these enlarged junctions. Dentin caries was similar in coronal and root caries. It consisted of sclerosis of the lumens of the dentinal tubules, followed by an important gradient of demineralization of intertubular dentin and destruction of occluded tubular lumens and peritubular dentin. Bacterial penetration occurred initially in the dentinal tubules and was followed by bacterial invasion and destruction of the intertubular dentin. Various phenomena of crystalline remineralization were described in enamel and dentin. Whereas in enamel and dentin caries, an important gradient of demineralization was observed before bacterial invasion, a simultaneous destruction of the mineral and organic components seemed to occur in cementum.

Dental Caries↗
PubMed1990

[Preventive dentistry in France].

In France, oral prevention has recently progressed in various aspects of dental caries prophylaxis which is reviewed in this paper. A better knowledge of dental caries prevalence has been obtained at a national level and the French Government authorized in October 1985 salt fluoridation for a period of 5 years which in addition to other means of caries prevention such as fluoridated toothpastes and various local and topical procedures has increased the potentials of fluoride use in France. In addition a larger use of fissure sealants has been encouraged. It is hoped that the introduction of salt fluoridation in France will reduce the caries incidence to a DMFT not more than 3 for the 12 year old children thus fulfilling the WHO goals for oral health in the year 2000.

Adolescent↗