Biomedical subjects

S Risnes

Publications and source records attributed to S Risnes.

At least 19 recordsLinked to original sources

PubMed2002

Development of enamel defects in rat mandibular incisor after thyro-parathyroidectomy.

Previous studies with scanning electron microscopy (SEM) demonstrated the presence of small hypoplastic defects in the incisal third of incisors and deep hypoplasia in the apical third of the incisors after thyro-parathyroidectomy in the rat. These studies provided a morphological description of the defects, but uncertainty remained concerning their development throughout amelogenesis. The aim of the present investigation was to study, with SEM operated in the backscattered mode, the development of the hypoplastic defects, from the beginning of the secretion to the end of the maturation zone of the enamel, in the lower incisor of thyroparathyroidectomized rats. The results of the present study showed that the large and small defects developed are separate entities that do not develop into the other. The distribution of large defects might be linked to a reduction of the eruption rate in these rats. The pathogenesis of these defects needs further investigation.

Animals↗

PubMed2002

TEM observations on the ameloblast/enamel interface in the rat incisor.

The structure of rat incisor enamel is established at the topographically complex interface between secretory ameloblasts and forming enamel. The aim of this study was to gain additional information on this interface by sectioning parallel with the rows and the long axis of Tomes' processes and prisms. Rats were sacrificed and fixed by glutaraldehyde/paraformaldehyde perfusion. After dissection, demineralization and embedding transverse jaw/incisor segments were cut, reembedded, and reoriented. Sections were prepared for and observed in the transmission electron microscopy (TEM). The intraenamel part of Tomes' process was about 18 microns long. The forming prism occupied a longitudinally grooved invagination on its apical aspect. The parts of Tomes' process forming the side walls of the groove were attenuated and showed variation in extent and outline. Prism growth occurred over the whole grooved area. An estimation of Tomes' process secretory area in rat compared with data from humans suggests that there may be a relationship between secretory area and rate of prism formation. Prism crystals were oriented obliquely or parallel to the secretory surface of Tomes' process. At interprism growth sites matrix deposition was irregular and required some redistribution to conform to the pattern of interprism sheets.

Ameloblasts↗

PubMed2000

Enamel pearls and cervical enamel projections on 2 maxillary molars with localized periodontal disease: case report and histologic study.

Presented here is an unusual case of teeth with aberrant enamel. One small and 3 large enamel pearls were identified in 2 maxillary third molars of a patient. One long enamel projection was connected to one of the large enamel pearls, along with 2 short cervical enamel projections. The ectopic enamel was associated with advanced localized periodontal destruction. After extraction, the molars were investigated radiographically and under the scanning electron microscope. The 3 large pearls contained distinct dentinal cones. The enamel of the pearls and the long cervical projection exhibited most of the structural attributes of crown enamel but were somewhat irregular, with variable shape and course of the prisms. Morphologic considerations suggest that these enamel pearls were aberrations and should not be regarded as attempts at new cusp or new tooth formation.

Dental Enamel↗

PubMed1999

A comparative infrared spectroscopic study of hydroxide and carbonate absorption bands in spectra of shark enameloid, shark dentin, and a geological apatite.

The purpose of the present work was to investigate the infrared (IR) spectrum of shark enameloid, especially with regard to hydroxide and carbonate bands. With thin sections placed directly in the IR beam it was possible to get high concentrations of ions without interfering effects from a dispersion medium (e.g., alkali halides). For comparison, spectra of shark dentin and a geo-apatite were also recorded. In spectra of shark enameloid and geo-apatite medium strong hydroxide absorption bands were found around 3535 cm(-1), and in shark dentin and geo-apatite spectra weak shoulders were observed at about 3570 cm(-1). Hydroxide libration bands at about 740 cm(-1) were found in shark enameloid and geo-apatite spectra; in the latter, also a band at 680 cm(-1). Carbonate bands were found in shark enameloid spectra at 1480 (weak shoulder), 1453, 1423, and 868 cm(-1). In shark dentin spectra there were carbonate bands at 1452, 1417, and 875 cm(-1), and probably also a carbonate band at about 1530 cm(-1) overlapped by an amide II band. Weak carbonate bands were also found in the spectra of the geo-apatite at 1452 cm(-1), and at about 1425 and 880 cm(-1). The relative intensities of the bands at 1453 cm(-1) (contributed from A and B sites) and around 1420 cm(-1) (B sites) changed from shark enameloid to shark dentin, and also from shark enameloid to the geo-apatite. More A sites seem to be occupied by carbonate in shark dentin than in shark enameloid, supposedly owing to fluoride occupation of A sites in shark enameloid. In geo-apatite and shark enameloid there are hydroxide ions hydrogen bonded to fluoride. Both shark enameloid and the geo-apatite are fluoride rich, and geo-apatite seems to have the highest fluoride concentration. There are, however, indications that the hydroxide concentration is also higher in the geo-apatite than in shark enameloid. This can be explained by the much higher carbonate content, and partly also by the higher water content in shark enameloid. There are A sites in geo-apatite and probably also in shark enameloid which are occupied by carbonate, but the proportion of occupied A sites relative to occupied B sites is greater in geo-apatite than in shark enameloid. This difference can be explained by the preference of A sites when the carbonate concentration is very low. On the other hand, for greater amounts of carbonate such as we have in shark enameloid, B sites are preferred.

Animals↗

PubMed1998

Crown morphology, enamel distribution, and enamel structure in mouse molars.

BACKGROUND: Biomolecular research and genetic manipulations have stressed the importance of thorough knowledge of normal organ morphology. Mouse molar teeth are convenient models for studying basic interactions in organ development and morphogenesis. The aim of the present study was to provide basic information on their morphology. METHODS: Intact and sectioned/ground molars of mice of various ages were observed with SEM. RESULTS: Enamel-free areas (EFA) were present on cusp tips at time of eruption. The dominating structural configuration in enamel was prism decussation in inner enamel and parallel prisms in outer enamel. Prism decussation tended to be absent at cusp ridges and in the bottom of grooves. In the former location, the distinction between prisms and interprism was often obscured in the middle enamel zone due to decreased difference in orientation of their crystals. A thin layer of enamel, often aprismatic, covered the distal aspect of cusps in maxillary molars and the mesial aspect of cusps in mandibular molars. The enamel abutting on EFA was often aprismatic. Aprismatic enamel exhibited incremental lines with a periodicity of about 1 microm and was often traversed by cracks. The enamel surface was porous in the bottom of grooves. Parts of mouse molar enamel were incompletely mineralized at the time of eruption. CONCLUSIONS: SEM is a convenient method for combined studies of crown morphology and enamel structure. Based on morphological criteria, a modification of the cusp nomenclature is proposed. Enamel thickness and structure in mouse molars show regional variations. Fundamental similarities exist between mouse molar cusps and mouse incisors. Mouse molar enamel undergoes posteruptive maturation.

Animals↗

PubMed1998

A scanning electron-microscopic study of developing human deciduous enamel on the dependence of the outline of surface pits on the angle of observation.

On the developing enamel surfaces of fetal human deciduous teeth, many of the surface pits were arcade-shaped with the arcade preferentially pointing in a cervical direction. The configuration of the interprism ridges between the pits contributed to this appearance. Surface cracks allowed verification of an incisal inclination of the subsurface prisms. This apparent paradox was solved when the specimens were tilted so that the pits were viewed in the directions of the prisms, giving the pits a compressed arcade-shape with the arcades pointing incisally. It is recommended that care should be exercised and due attention paid to the angle of observation when determining the orientation of pit arcades. Pit entry direction seems to be a more reliable feature for inferring the direction of tangential ameloblast movement.

Ameloblasts↗

PubMed1998

Scanning electron microscopy and energy-dispersive X-ray analysis of defects in mature rat incisor enamel after thyroparathyroidectomy.

The surface and the structure of the erupted enamel of the continuously growing rat incisor were studied by scanning electron microscopy (SEM) to analyse the effect of thyroparathyroidectomy on enamel formation. Ten male 21-day-old Wistar rats were thyroparathyroidectomized and five sham-operated rats were used as controls. Two months after surgery the rats were perfused with 1% glutaraldehyde and their mandibles dissected. The erupted ends of the incisors were cut off and routinely processed for SEM. An energy-dispersive analysis of X-rays (EDX analysis) was performed for the calcium:iron ratio of the enamel surface defects. Thyroparathyroidectomy induced surface defects and structural abnormalities in the outer layer of the mature erupted enamel. It was established that the surface and structural defects were related. The EDX analysis of the outer enamel showed that the enamel defects were associated with an abnormal elevation of the iron content. The SEM appearance and the EDX analyses indicated that these defects were hypomineralized and rich in iron. The reddish colour of the enamel is due to the high concentrations of iron.

Animals↗

PubMed1998

SEM study of the development of rat incisor enamel hypoplasia under hypocalcemia induced by thyro-parathyroidectomy.

Several clinical studies have reported the presence of enamel hypoplasia in congenital hypoparathyroidism or hypocalcemia. In previous studies we showed that thyroparathyroidectomy (TPTX) induced perturbations of the ameloblast morphology and secretion, of the rod pattern and of the enamel surface at late secretory stage and beginning of maturation, and limited hypoplasia in the erupted enamel of rat incisor. The aim of the present study was to evaluate by SEM, the extent and evolution of the enamel alterations of thyro-parathyroidectomized rats during the maturation stage. Wistar rats were thyro-parathyroidectomized and sacrificed 57 days later. The incisors were dissected out and processed for SEM. The surface of the incisor was observed from the end of secretion/beginning of maturation to its incisal erupted end. Transverse sections were prepared to study the structural defects and the prism pattern at different stages. The results showed that the surface of the TPTX incisors presented large hypoplastic defects at the end of secretion/beginning of maturation and only small defects in the erupted part. Transverse sections showed that, at the transition from secretion to maturation, the enamel defects extended to the mid-thickness of the tissue. At the incisal end the defects were limited to the outer enamel. As it is difficult to understand how the large apical defects could recover to appear as small hypoplasia at the incisal end, these results raise new questions concerning: (1) the effect of a long term calcium deficiency upon the cellular activity of the ameloblasts, and (2) the capacity of the enamel organ to compensate structural abnormalities.

Animals↗

PubMed1996

Intraoral storage phosphor radiography for approximal caries detection and effect of image magnification: comparison with conventional radiography.

OBJECTIVES: The aim of this study was first to test the newly developed storage phosphor (SP) system Digora for diagnostic accuracy of approximal caries detection with special emphasis on image magnification compared with conventional radiography, and second, to test whether the image surroundings could have an influence on observer performance. DESIGN: SP plates and Ektaspeed films were exposed simultaneously to 50 extracted premolars/molars, and the SP image files were transported to a different platform for processing. Ten observers rated 95 approximal surfaces for caries with four imaging modalities: (1) SP images at dental film size viewed with black surroundings, (2) magnified (x4) images viewed in the same manner, (3) magnified (x4) images viewed with text and graphics framing, and (4) films viewed on a light box. The observations were validated with microscopy. Diagnostic accuracy was calculated as the area beneath the receiver operating characteristic curve (AZ). RESULTS: No significant differences were found between SP images and films. Magnified SP images with text and graphics demonstrated significantly higher AZ values than nonmagnified images both for enamel and dentin, and magnified images with black surroundings demonstrated similar results for dentin. CONCLUSIONS: In this in vitro material the observer performance for approximal caries detection with SP images was comparable to that with Ektaspeed films. The magnified SP images generally showed a significantly higher diagnostic accuracy than the nonmagnified SP images.

Adult↗

PubMed1996

Trace element analysis of blackish staining on the crowns of human archaeological teeth.

A blackish staining found on the crowns of teeth of 51 skulls from the excavation of the medieval St. Olav's church in Trondheim was analyzed using secondary ion mass spectrometry (SIMS) and atomic absorption spectrometry (AAS). In four teeth, mass spectra and step scan concentration profiles of SIMS were performed and compared with the grey scale pattern in photographs of the analyzed paths. The manganese curve showed the highest degree of conformity with the grey scale pattern. The AAS analysis confirmed the increased content of manganese in blackish stained enamel. It was concluded that manganese, probably in the form of an oxide deposited from the soil, was the cause of the blackish staining.

Dental Enamel↗

PubMed1996

Effects of accelerated eruption on the enamel of the rat lower incisor.

The effect of accelerated eruption of the rat lower incisor on enamel was studied in a series of segments obtained when the incisor was cut repeatedly out of occlusion over a five-week period. The segments were ground, cleaned, acid-etched, observed with SEM, and analyzed with EDX. Pigmentation was lost within 11 days. Pigmented superficial enamel was more acid-resistant than the rest of the enamel, but this quality decreased with decreasing iron content. Hypomineralized enamel first appeared in a restricted area at the mesio-labial angle of the tooth in the 6th-7th segment obtained after 11-14 days. Later, hypomineralization became more generalized. All enamel zones were retained throughout the experiment. The geometry of the prism pattern was affected. The angle between prism rows and the enamel-dentin junction increased from 44 degrees to 48 degrees, while the angle of decussation increased from 60 degrees to 70 degrees. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25 degrees to 29 degrees. However, the prisms retained their incisal direction. The connection between enamel and dentin was partly disrupted from about the 9th segment onward. The depth of the mesial concavity of the enamel-dentin junction decreased from about the 10th segment onward. Accelerated eruption affects all stages of enamel formation and is a suitable and predictable model for studying regulatory mechanisms in amelogenesis.

Ameloblasts↗

PubMed1996

Detection of approximal caries with a storage phosphor system. A comparison of enhanced digital images with dental X-ray film.

OBJECTIVES: To compare the accuracy of approximal caries detection using enhanced and unenhanced storage phosphor images and dental X-ray film. METHODS: Fifty premolar/molar teeth were exposed simultaneously under standardized conditions on storage phosphor (SP) image plates (Digora) and Ektaspeed film. The image files were transferred to a different platform for image processing. Using a five-point confidence scale, ten observers rated 95 approximal surfaces for caries in enamel and dentin with three image modalities: enhanced and unenhanced SP images and film. The observations were validated microscopically. Diagnostic accuracy was measured as the area beneath the ROC curve (Az). RESULTS: Enhanced SP images had significantly higher Az values in both enamel (Az = 0.819) and dentin (Az = 0.845) than unenhanced images and film. No significant differences were found in either enamel or dentin between unenhanced SP images (Az = 0.780 and Az = 0.789) and film (Az = 0.688 and Az = 0.793). CONCLUSION: Enhancement of storage phosphor images improved detection of approximal caries in this in vitro study compared with unenhanced images and Ektaspeed film.

Adult↗

PubMed1996

Morphological characteristics of mouse incisor enamel.

Maxillary and mandibular incisors of mice aged 5 wk were sectioned and ground along various planes, acidetched and observed by scanning electron microscopy (SEM). The general design of the enamel structure resembled rat incisor enamel with an uniserial lamellar pattern of prisms in the inner enamel and incisally directed parallel prisms in the outer enamel. The centrolabial thickness of the enamel was about 60 microns in the maxillary and about 95 microns in the mandibular incisor. The angle between prism rows and enamel-dentine junction was about 70 degrees in the maxillary and about 45 degrees in the mandibular incisor, while the angle of decussation, which increased from the enamel-dentine junction towards the outer enamel, was 50-95 degrees and 30-80 degrees respectively. The angle between outer enamel prisms and enamel surface was about 12 degrees in the maxillary and 5-15 degrees in the mandibular incisor. The outer 1/2-1/3 of the outer enamel contained iron and was more acid-resistant than the rest of the enamel. The superficial 3-5 microns was prismless with a Fe/Ca ratio of about 25/75 in the maxillary and about 10/90 in the mandibular incisor. The latter concentration of iron was insufficient to give visible pigmentation to the enamel. The extreme mesial and lateral enamel was neither typical of inner nor of outer enamel. Assuming that the length of the zone of enamel secretion is half the corresponding length in the rat, it could be calculated that ameloblasts in mouse mandibular incisors produce enamel at a rate of about 6 microns per day, about half the corresponding rate in the rat. In spite of this, the mouse mandibular incisor has a relatively thick layer of enamel, since the ameloblasts spend a relatively long time in the zone of enamel secretion due to a fairly slow eruption rate.

Animals↗

PubMed1995

A synthetic, chemically modified ribozyme eliminates amelogenin, the major translation product in developing mouse enamel in vivo.

Ribozymes are small RNA structures capable of cleaving RNA target molecules in a catalytic fashion. Designed ribozymes can be targeted to specific mRNAs, blocking their expression without affecting normal functions of other genes. Because of their specific and catalytic mode of action ribozymes are ideal agents for therapeutic interventions against malfunctioning or foreign gene products. Here we report successful experiments to 'knock out' a major translation product in vivo using synthesized, chemically modified ribozymes. The ribozymes, designed to cleave amelogenin mRNA, were injected close to developing mandibular molar teeth in newborn mice, resulting in a prolonged and specific arrest of amelogenin synthesis not caused by general toxicity. No carriers were required to assist cellular uptake. Amelogenins are highly conserved tissue-specific proteins that play a central role in mammalian enamel biomineralization. Ultrastructural analyses of in vivo ribozyme-treated teeth demonstrated their failure to develop normally mineralized enamel. These results demonstrate that synthesized ribozymes can be highly effective in achieving both timed and localized 'knock-out' of important gene products in vivo, and suggest new possibilities for suppression of gene expression for research and therapeutic purposes.

Amelogenin↗

PubMed1995

Accelerated eruption of rat lower incisor. Relationship between impeded and unimpeded eruption rates, rate of attrition, tooth length, and production of dentin and enamel.

The present investigation studies the effects of persistently cutting one lower rat incisor out of occlusion. Within four days, the rate of eruption of the cut (unimpeded) incisor increased to 216% and that of the uncut (impeded) contralateral to 136% of the baseline rate. While the former remained high, the latter decreased gradually to about 90% within three weeks. The rate of attrition of the impeded incisor increased to 233% of the baseline rate within two days, then fell abruptly, and remained at a slightly lower level than the rate of eruption. Accordingly, the length of the erupted part of the impeded incisor decreased initially, but increased gradually after about four days. Measurements made on SEM micrographs of the series of transverse tooth segments obtained when cutting the incisor out of occlusion, showed that growth-related increase in mesiodistal tooth width was arrested from the 10th segment, dentin thickness decreased gradually to about 50% in the 12th segment, and enamel thickness, after an initial increase, decreased to about 80% in the 11th segment. The present study provides experimental evidence that accelerated eruption affects morphogenesis and histogenesis of the rat lower incisor. An impeded incisor, especially the contralateral, may not serve as an ideal control.

Animals↗

PubMed1993

Occurrence and distribution of blackish staining on the crowns of human teeth obtained from an archeological excavation of a medieval site in Norway.

An excavation in Trondheim, Norway, in 1984-85, uncovered a part of the medieval (1100-1600) cemetery of St Olav's Church. Of 388 excavated skeletons, 248 had skulls where the condition of the jaws and teeth allowed examination. In 51 of these skulls the teeth exhibited a characteristic blackish staining. A higher percentage of affected skulls was found in areas with organic, woodchip layers than in areas with gravelly sand. Affected skulls tended to have a high percentage of their teeth stained, but the staining tended to be restricted to only one or two of the three tooth surfaces scored. Posterior teeth were more often affected than anterior teeth, the occlusal/incisal part more often than the cervical part, and the buccal/labial part more often than the lingual part. Nonerupted third molars could also be stained. Staining seemed to be hampered by calculus. Occurrence of staining was independent of the presence or absence of a coffin and of coffin type. The extent of staining (% of stained surfaces within a dentition) was independent of sex and age. High correlation was found between all four jaw quadrants. There was no independence between color of the jawbone and occurrence of stained teeth. It was concluded that the staining phenomenon probably can be ascribed to factors in the soil. In vivo predisposing influences cannot be excluded.

History, Medieval↗

PubMed1990

Structural characteristics of staircase-type Retzius lines in human dental enamel analyzed by scanning electron microscopy.

Based on a scanning electron microscopic (SEM) analysis of adjoining, acid-etched planes cut through human cervical enamel, the structural characteristics of staircase-type Retzius lines have been clarified. Structural features associated with this type of Retzius lines--such as cleftlike defects, decreased dimension of prisms, increased interprism, club-shaped appearance of prisms, oblique ridges, and triangular regions--have been incorporated into a unifying, three-dimensional model. A continuous discontinuity defect, involving both prisms and interprism, is a prominent feature of this type of Retzius lines. Prisms and interprism facing the deep aspect of the cleftlike defect show an enlarged, flat surface that encroaches on the cervically situated prisms being rebuilt from the same cleft. The initial part of a prism taking off from the cleft is of distorted shape. As the prism reaches the level of the interprism cleft, it abruptly regains its normal size and shape. The relationship between this type of Retzius lines and the carious process is discussed, and it is suggested that the discontinuity defect may retard the carious lesion due to a protective effect of its supposed organic content. The developmental events creating staircase-type Retzius lines are discussed, and it is suggested that Tomes' processes are constricted near their bases with a corresponding increase in interprismatic growth region. Tomes' processes will have to reshape plastically as they move out of the constricted pits, trailing the parent ameloblasts as they resume enamel production and move in the direction of the prisms.

Amelogenesis↗

PubMed1990

Amelogenin gene similarity in vertebrates: DNA sequences encoding amelogenin seem to be conserved during evolution.

Mouse amelogenin cDNA was used in hybridization assays with genomic DNA, cut with the restriction enzyme Eco RI, from the edentulous chicken (Gallus domesticus), the monophyodont mouse (as control), diphyodont man, and the polyphyodont fishes Atlantic salmon (Salmo salar) and seawolf (Anarrhichas lupus). The hybridization assay was performed under stringent conditions with non-radioactive probes. Hybridization was obtained with mouse (6.4-kb band), man (9-kb and 13-kb bands), and seawolf (18-kb band) genomic DNA. This demonstrates DNA sequence similarities between these species, and supports the theory that DNA sequences encoding enamel proteins appear to be highly conserved during the evolution of vertebrates. Lack of hybridization in salmon and chicken may be due to sequence divergences or structural differences in an amelogenin gene analog, or it may be that no amelogenin gene is present in these animals.

Amelogenin↗