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Biomedical subjects

H J Orams

Publications and source records attributed to H J Orams.

At least 19 recordsLinked to original sources
PubMed1992

The effect on the ultrastructure of dental enamel of excimer-dye, argon-ion and CO2 lasers.

This study aimed to investigate the ultrastructural changes that occur in dental enamel irradiated with pulsed excimer-dye, continuous-wave (CW) argon-ion and CW CO2 lasers. The pulsed excimer-dye laser produced deep craters, rough damaged surfaces with underlying porosity and amorphous vitrified material. The vitrification of the enamel indicated that the temperature in these areas must have been at least in the range 1280 to 1600 degrees C. The CW argon-ion laser irradiation produced a changed non-cratered surface with inter-crystalline porosity and a mixture of small and some large irregularly packed recrystallized enamel crystals. The CW CO2 laser produced shallow craters, surface crazing and lifting off the removal of the surface layer to expose the underlying roughened enamel. The ultrastructure revealed inter- and intra-crystalline porosity, a mixture of small but variable size irregularly packed recrystallized enamel crystals and also well packed large crystals which indicated further grain growth. The porosity in lased enamel was overall very similar to that seen in enamel heated in an electric furnace to a temperature of 600 degrees C. The presence of recrystallized enamel crystals indicated a temperature rise of approximately 1000 degrees C and the grain growth indicated that a temperature > or = 1000 degrees C existed for some time after the laser irradiation. In general the excimer-dye laser produced most surface destruction because of its higher power density and shorter interaction time and the argon-ion laser produced least damage. These results indicated that the lasers used in this study require much more refinement before they can find therapeutic application to dental enamel, and this may well be the case for other lasers being investigated for clinical dental practise.

Argon↗
PubMed1991

The type, origin and function of the odontogenic cells of continuously growing guinea-pig molars.

Little is known about which cell types act as the origin of odontogenic stem cells and how these stem cells differentiate to become functional. In the present study 3-day-old guinea-pigs were injected with tritiated thymidine, killed at intervals and their molars studied. The odontogenic cells were found to originate from the stem cells which by autoradiography were shown to be slow cycling and lightly labelled. As they differentiated they became heavily labelled and were designated transit 'dividing cells'. With further differentiation the cells were unlabelled and were designated 'simple transit cells'. It was concluded from the present study that outer enamel epithelium functioned as the source of all odontogenic epithelium; that primitive mesenchyme around the cervical loop functioned as the source of all odontogenic mesenchyme and that all of the transit cells which differentiated to become functional migrated coronally.

Animals↗
PubMed1990

An estimation of ameloblast generation time and of the ameloblast proliferative compartment of guinea pig teeth.

The generation time of inner enamel epithelial cells has been estimated by many investigators using rodent and lagomorph teeth but the results have varied. In the present study of guinea pig molars, the inner enamel epithelial cell generation time (Tc) and its fractions (Ts, Tg2, Tm and Tg1) were calculated. Previous investigators have attempted to determine the extent of the proliferative compartment of inner enamel epithelial cells using the position of mitotic figures as their guide, but results have been inconsistent. It appears that this has been due to the small percentage of mitotic figures among the cell population and the difficulty of visualising them. In the present study, a novel approach was used to determine the extent of the inner enamel epithelial cell proliferative compartment which was not based on the position of mitotic figures, but on the calculation of other generation time fractions. It was found that the proliferative compartment extended for approximately 47 cells occlusally from the synthetic compartment. The results also showed that there was no evidence of stem cells in the ameloblast columns and hence, ameloblasts depended on their cell supply from the stem cell compartment apical to the ameloblast columns.

Ameloblasts↗
PubMed1989

Effects of continuous-wave CO2 laser on the ultrastructure of human dental enamel.

Laser-induced changes in plano-parallel sections were examined by light microscopy (LM) and scanning electron microscopy (SEM), and correlated with ultrastructural changes as observed by transmission electron microscopy (TEM). LM and SEM revealed two different changes--extensive crazing, and crazing and cratering. Rough exposed enamel was commonly found, resulting from lifting off and removal of the top layer of crazed, or crazed and cratered, enamel. The type of induced change was mainly dependent on the energy density used (range approximately 0.8 to approximately 200 J cm-2) and on enamel prism orientation. Lased enamel was also softer than unlased enamel. TEM of both crazed enamel and rough exposed enamel revealed that most crystals generally resembled those of unlased enamel in size and shape, but that inter- and intra-crystalline voids were present in some areas. The crazed and cratered enamel had significant ultrastructural changes: new homogeneous and inhomogeneous crystals of apatite with a different shape and larger size than those of the original, and a loss of prismatic structure. The lack of uniformity of the laser effect on crazed and cratered enamel was shown by variation in crystal packing (from good to poor), variations in crystal size from area to area, and the presence of pockets of poorly packed homogeneous crystals alongside pockets of well-packed inhomogeneous crystals. The crazing, crazing and cratering, rough exposed enamel and the greater number of voids, as well as the relative softness of lased enamel do not indicate an overall ultrastructural improvement. However, the larger apatite crystal size and loss of prismatic structure in crazed and cratered areas may partly explain previous observations of reduced rates of subsurface demineralization in lased enamel.

Carbon Dioxide↗
PubMed1989

On the pattern of ameloblast migration.

The kinetics of ameloblast cells in continuously growing guinea pig molars were studied using autoradiography. The results showed that there was no direct relationship between ameloblast migration rate and ameloblast production rate, which indicated that ameloblasts actively migrated coronally. It was found that ameloblast migration rate was maximal at the root apex, and then reduced to a minimum value as the ameloblasts left their proliferative compartment and migrated coronally. A multiple regression model was found to be the most suitable one to represent the ameloblast migration pattern.

Ameloblasts↗
PubMed1989

Ultrastructure of spindles and tufts in human dental enamel.

A transmission electron microscope (TEM) study was made of spindles and tufts as identified in the light microscope, from samples prepared by selected-area argon-ion-beam thinning. Spindles in human dental enamel were found to be continuous with dentinal tubules across the dentin-enamel junction (DEJ) and usually appeared at the DEJ as electron-lucent, empty channels nearly circular in cross-section. The spindles were found to cross prism boundaries, branched rarely, and some were occasionally found to be occluded or partially occluded with small needle-like crystals (approximately 5 nm width and approximately 70 nm length), granular material (approximately 1.5 nm diameter) and/or amorphous material. Near the DEJ, the majority of spindles had a diameter less than 2 microns, while in the prismatic enamel away from the DEJ, spindles with a diameter greater than 2 microns were generally found. Spindle varicosity was characterized by an enlargement of their diameter. Tufts started at the DEJ and were not associated with dentinal tubules. Two types of ultrastructure were observed in the TEM: (i) disrupted regions of enamel incorporating large voids (up to approximately 0.1 microns in diameter), or, more commonly, (ii) channels within the enamel occluded or partially occluded, with small needle-like crystals and granular and/or amorphous material similar to that found in the enamel spindles. It was concluded that spindles and tufts represent areas of hypomineralization with increased void volume and partial remineralization.

Child↗
PubMed1987

The ultrastructure of human dental enamel heat-treated in the temperature range 200 degrees C to 600 degrees C.

Heating enamel in the temperature range 200 degrees C to 600 degrees C resulted in poor crystal packing due to void formation, permanent change in the sign of its birefringence (from negative to positive) in some areas, and an altered crystal morphology. Transmission electron microscopy of enamel heated in the temperature range 200 degrees C to 400 degrees C revealed that the distinction between the positively birefringent regions and the negatively birefringent regions (which were present up to 350 degrees C and occasionally up to 400 degrees C) at the tooth's surface was due to the greater volume of intra- and inter-crystalline voids within the positively birefringent regions. There was a significant increase in void volume at 400 degrees C, and above this all of the enamel was positively birefringent and opaque. Large remineralized crystals of beta-tricalcium phosphate (beta-TCP) phase (whitlockite) were initially formed at 400 degrees C, and their size and number increased at 500 degrees C and above. Both the greater solubility of beta-TCP crystals and the increased surface area due to the presence of voids would increase the rate of demineralization of heat-treated enamel.

Crystallography↗
PubMed1986

Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel.

Electron microscopy of the intact surface zone of white spot and brown spot carious lesions showed that in general their ultrastructure was similar. Their outermost crystalline surface consisted of small crystals similar to those in healthy enamel, crystals with central core dissolution, and rounded crystals. Below this, surface demineralization of enamel was observed as the enlargement of micropores, the central core dissolution of crystals, the formation of channels and the enlargement of spaces at prism boundaries. Remineralization of enamel was observed as the partial occlusion of voids, the rounding and enlargement of crystals, and some new needle-shaped crystals. Some other features indicated combined demineralization and remineralization. The occlusion of spaces at prism boundaries was a more common feature in brown spot lesions, whereas the pockets of rounded crystals were more common in white spot lesions. A relatively uniform distribution of needle-shaped crystals throughout the intact surface zone was a feature of some brown spot lesions only.

Adult↗
PubMed1986

Laminated zones in carious human dental enamel.

Laminated zones within the body of carious lesions were studied by polarized light microscopy and transmission electron microscopy. Areas from within and surrounding the laminated zones, precisely selected using light microscopy, were argon-ion-beam thinned and examined by transmission electron microscopy. Laminated zones were present in approximately 7% of the samples studied. Polarized light microscopy showed variation in mineralization from zone to zone and the enamel surrounding the zones in the body of the lesion. Laminated zones whose central region showed approximately 1% of space when examined in air and whose boundaries showed approximately 2-4% of space when imbibed in quinoline were selected for ultrastructural studies. Electron microscopy showed the laminated zone to be less demineralized than the surrounding enamel in the body of the lesion. The ultrastructure of their central regions was similar to healthy enamel but their boundaries showed demineralization which increased into the body of the lesion. Within the central region of lamination there was greater evidence of resistance to demineralization rather than the presence of remineralization.

Dental Caries↗
PubMed1984

On the nature of the opaque and translucent enamel regions of some macropodinae (Macropus giganteus, Wallabia bicolor and Peradorcas concinna).

Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 microns in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.

Animals↗
PubMed1983

Cyclophosphamide-induced changes in rodent odontogenesis. A light- and electron-microscopic study.

Cyclophosphamide-induced changes in rodent odontogenesis were investigated by light and electron microscopy in four-day-old Sprague Dawley rats given one injection of 40 mg/kg of body weight of cyclophosphamide and killed at intervals of one hour, one day, one week and two weeks. Incisor and molar teeth were dissected from the animals, fixed in 2.0% glutaraldehyde in 0.1 M sodium cacodylate with 3.4% sucrose, and subsequently some were incubated for alkaline phosphatase reaction, and embedded in Spurr's medium for sectioning at light- and electron-microscopic levels. From three days a cell-sparse zone was created in the pulp in the growing end of the tooth and progressive cellular changes were observed which became more severe in the one-week and two-week specimens. Subodontoblast and adjacent pulpal cells were the most affected showing nuclear changes, damage to, or loss of, organelles, and inclusion bodies. Odontogenic epithelium was less affected and odontoblasts appeared to be unaffected by the drug. A new irregular matrix was laid down in the defect area and seemed to be the product of depolarized odontoblasts. This new matrix showed alkaline phosphatase activity, as did the cells embedded in it, and later it became mineralized. It is speculated that the polarity of odontoblasts might be maintained by an intact subodontoblastic layer; when this is lost the odontoblasts become depolarized and capable of secreting matrix from both ends.

Aging↗
PubMed1982

Ultrastructural localization and gradient of activity of alkaline phosphatase activity during rodent odontogenesis.

The ultrastructural localization and gradient of activity of alkaline phosphatase were studied with respect to cell differentiation, matrix synthesis, and matrix mineralization in the incisor and molar teeth of 4-day-old Sprague-Dawley rats. The animals were perfused intracardially at room temperature with 2.5% glutaraldehyde in 0.1M sodium cacodylate (pH 7.4) with 3-4% sucrose. The jaws were dissected, immersion-fixed for 24 h, and the incisor and molar tooth germs removed. These were determined in 10% EDTA in NaOH (pH 7.4) with 7% sucrose. After reactivation of the enzyme with 0.1M MgCl in Tris-maleate buffer (pH 7.4) at 4 degrees C, the medium consisting of 6 ml 3% sodium beta-glycerophosphate, 4 ml 0.2M Tris-HCl buffer (pH 9.2), 3 ml 1.6% MgSO4, 12 ml 0.5% lead citrate (pH congruent to 12), and 2.1 g sucrose. The pH was adjusted to 9.2 with 0.2M HCl, the volume made up to 30 ml, and the solution centrifuged for 10 min at 5000 rpm. Control teeth were incubated in medium minus the substrate. Finally, the specimens were routinely post-fixed and embedded for sectioning and examination with a Philips 300 electron microscopy. A gradient of alkaline phosphatase activity was mapped along the developing teeth in the cells of the stratum intermedium, the proximal borders of the ameloblasts, the early dentine matrix, the predentine-dentine border, matrix vesicles, and the plasma membranes of odontoblasts and subodontoblast cells. The gradient of alkaline phosphatase activity was evident in the forming tooth from the cervical loop to the crown apex and was related to the cellular events, matrix synthesis, and matrix mineralization occurring during odontogenesis.

Alkaline Phosphatase↗
PubMed1981

Electron-microscope study of the dentine-enamel junction of kangaroo (Macropus giganteus) teeth using selected-area argon-ion-beam thinning.

Transmission electron microscopy of selected-area argon-ion-beam thinned kangaroo (Macropus giganteus) enamel revealed a complex ultrastructure in the region of the dentine-enamel junction (DEJ). Characteristic features were multiple branching of dentinal tubules, rejoining of enamel tubules, elongated defects, extended protrusions of dentine into enamel, two types (A and B) of hypomineralized enamel and a continuity between dentinal and enamel tubules. In the intertubular regions of the DEJ a complex intermingling of finer enamel and dentine crystals, similar to that found in human enamel, was observed. The varicosities observed in the light microscope were a combined optical effect caused by the hypomineralized (type A) enamel and the branching and rejoining of the enamel tubules.

Animals↗
PubMed1980

Ultrastructural changes in the translucent and dark zones of early enamel caries.

Selected areas of early enamel caries ('White spot' lesion) in human teeth were argon-ion-beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter-rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter-rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.

Adolescent↗