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Y Michaeli

Publications and source records attributed to Y Michaeli.

At least 19 recordsLinked to original sources
PubMed1992

Histomorphometric study of the periodontal vasculature of the rat incisor.

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_

Alveolar Process↗
PubMed1991

EDTA-dependent pseudothrombocytopenia: a clinical study of 18 patients and a review of the literature.

EDTA-dependent pseudothrombocytopenia (EDTA-PTCP) is the phenomenon of a spurious low platelet count due to the appearance of antibodies that cause platelet agglutination in blood anticoagulated with EDTA. We review here the clinical features of 18 patients with EDTA-PTCP treated in our hospital from 1984 to 1987 as well as those of 34 patients reported in the literature. This phenomenon appears more frequently in severely ill patients, in association with autoimmune, neoplastic, atherosclerosis-related, and liver diseases. In the majority of our patients, EDTA-PTCP appeared during hospitalization, indicating that the antibody is an acquired one. Neither splenomegaly nor the presence of autoimmune markers were features of this entity. Unlike true thrombocytopenias, EDTA-PTCP is associated with a normal mean platelet volume. Awareness of this entity is essential since EDTA-PTCP is frequently misdiagnosed and therefore incorrectly treated.

Adult↗
PubMed1991

Dynamics of tissue changes found after mechanical loading of the rat incisor. I. A three-dimensional longitudinal study of the morphologic aspects.

A three-dimensional morphometric method was used to evaluate progressive changes in shape and size of recovering dental and periodontal tissues after orthodontic loading. In 35 female rats weighing 212 +/- 4 gm, loads of 19.7 +/- 1.6 gm generated by closed-coil springs were applied for 2 weeks to the shortened lower left incisor. The rats were killed in groups of five at 0, 1, 3, 5, 7, 9, and 10 weeks (groups 0-w to 10-w) after the springs were removed. A group of rats with normal incisors (group C-1) and one with five incisors that had been continually shortened for 10 weeks (group C-2) served as controls for groups 0-w and 10-w, respectively. Width, area, and volume of the tooth and enamel-bordering periodontal ligament (e-PDL) and cementum-bordering PDL (c-PDL) were measured. After 2 weeks of loading (group 0-w), the volume of the compressed e-PDL had decreased by 22%, and the volume of the stretched c-PDL had increased by 72%, suggesting that bone apposition lags behind the rate of tooth movement. During the recovery period, the dental and periodontal parameters tended toward a gradual return to control (C-2) values, although at the end of 10 weeks many still lagged significantly behind the controls. Recovery was slowed by repeated reversals at different sites in the various groups. The ability of the preloaded incisor to adjust to changes in occlusal function was lastingly impaired.

Animals↗
PubMed1991

Compensatory hyperplasia of the rat submandibular gland following unilateral extirpation.

This study investigated the morphological changes in rat submandibular glands undergoing compensatory hyperplasia. Fifteen adult male rats underwent left submandibulectomy, after which they were killed in groups of five (at days 3, 7, and 14), and their right submandibular glands (SMG) were excised. Fifteen control rats were killed in groups of five (at days 0, 7, and 14), and their right SMG were removed. Sections of 3 microns were cut, and the parenchymal and stromal cells were counted in 50 microscopic fields and sorted according to their morphological features and "class". Class is equivalent to the number of nuclei in an acinar or tubular cross-section. No change in glandular weight was noted post-surgery. Total cell count/field rose to 138.5 +/- 7.1% of control values on day 3 after gland extirpation, remaining almost constant thereafter until the end of the experiment. Acinar cell count and class showed a 154.1% peak on day 3, followed by a 30% drop in cell count by day 7 and an equivalent decline in class by day 14. Tubular cell count increased gradually to 146.5% by day 14, without a change in class. In the first week, the increase in tubular cells was mainly due to intercalated duct (ID) cells, while in the second week, there was a sharp rise in granular duct (GD) cells. This diverging cellular behavior indicates that the GD cell stems from the ID cell. The cellular changes in the hyperplastic SMG indicate death of newly generated acinar cells and expansion of the glandular progenitor compartment, as expressed in elongation of the ID.

Adaptation, Physiological↗
PubMed1990

Effect of occlusal functional forces on incisor socket morphology and location in the rat mandible.

The effect of functional occlusal stress on dimensional alterations of the rat incisor socket and mandible were studied from roentgenograms. In 12 rats, the lower left incisor was shortened twice weekly, whereas the lower right incisor was allowed to remain in contact with both upper incisors. Thus, the right incisors were subjected to hyperfunction, and the left ones, to hypofunction. The lower incisors of 16 rats with normal occlusal contact served as control. Following an experimental period of 3 months, the animals were killed and standardized radiographs were taken of the cleaned mandibles. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Socket area, its posterior length, posterior mandibular length, and gonial angle changed in the same direction under both hyper- and hypofunction. The anterior socket was relocated in opposite directions: under hyperfunction, it assumed a more inferior position, whereas in hypofunction, it moved superiorly. The angulation of the socket became significantly more acute under hyperfunction, whereas in hypofunction, this parameter remained unchanged. It is concluded that altered functional demands affect the morphology of the incisor socket and its location within the mandibular borders.

Animals↗
PubMed1990

Long-term effects of orthodontic forces on the morphology of the rat-incisor socket and its location in the mandible.

The effect of orthodontic force application on the rat-incisor socket and mandible was studied on roentgenograms. A mean linguo-intrusive force of 19 +/- 0.6 g was applied continuously to the shortened left lower incisor for a period of two (group A) and four weeks (group B). A third group of rats, subjected to shortening of the left mandibular incisor only, served as a hypofunctional control (group C). A fourth group of normal rats constituted the intact control (group D). After a recovery period of three months, the animals were killed, and standardized roentgenograms of the cleaned mandibles were taken. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Comparison of groups A and B with the control groups, on the one hand, and of group C with group D, on the other, facilitated isolation of the hypofunctional factor. In groups A and B, the orthodontic forces caused changes in the parameters affected (i.e., socket area, alveolar bone thickness, mandibular dimensions) and not affected by hypofunction (i.e., socket angulation and location, anterior-socket length). The former findings implies modification of the adaptive capability of dental structures to functional demands. It is concluded that mechanical loading of the incisor for two to four weeks causes long-lasting changes in the socket and its surrounding bone.

Adaptation, Physiological↗
PubMed1989

The streaming of the submandibular gland. II: Parenchyma and stroma advance at the same velocity.

Thirty young male rats aged 7 weeks, weighing 200 g, were injected with 18.5 kBq g-1 (0.5 microCi g-1) body weight tritiated thymidine [3H]TdR (specific activity 185 GBq). The rats were then killed in groups of five, at the following times: 1 hour, and 14, 30, 60, 90, and 120 days. Autoradiograms of sections through the submandibular gland were prepared, and the location of labelled cells in tubular and acinar cross sections was recorded. The nuclear content of each cross section was defined as its 'class'. In this numbering system, narrow tubuli, e.g. intercalated ducts are of low class, and wider tubuli, e.g. striated ducts, of high class. One hour after labelling most labelled tubular cells were found in low class cross sections, i.e. intercalated ducts and narrow granular ducts. Striated ducts were not labelled. From then onward labelled cells entered wider tubuli, e.g. striated ducts. The advancing labelled epithelium was accompanied by labelled stroma. Both cell types traversed 0.089 classes per day. In acini, labelled cells advanced in the opposite direction, starting from acinar cross sections of high class and ending in class-1 cross sections.

Animals↗
PubMed1989

A three-dimensional evaluation of the effects of functional occlusal forces on the morphology of dental and periodontal tissues of the rat incisor.

We examined the effect of function on tooth and periodontal ligament (PDL) morphology in 40 lower incisors of adult female rats. Ten teeth were exposed to occlusal hyperfunction for three months, ten to hypofunction for three weeks, ten to hypofunction for three months, while ten teeth in normal occlusion served as control. Transverse ground sections were cut at various levels perpendicular to the tooth long axis, and their distances from the apex were calculated. The outlines of the tissues were traced and fed into a computer. We plotted the measurements according to their location and fitted them by second-order polynomials. We calculated tissue volume for the proximal 18 mm of bone-embedded tooth. Hyperfunction affected tooth shape, in that it became more rounded. The volumes of the dental tissues remained unchanged, while width and volume of the cementum-bordering PDL increased. Hypofunction did not alter tooth shape, but influenced its size: After three weeks, tooth circumference decreased, and after three months, it expanded. Dentin width was reduced, with concomitant increase of pulp size. The amount of enamel diminished initially, but after three months returned to normal values. The PDL bordering enamel expanded proportionally to the duration of hypofunction. The changes in socket size reflected the total dimensional variations in the tooth and its PDL. The results demonstrate that the shape and size of growing teeth and their periodontium are influenced by functional occlusal forces.

Alveolar Process↗
PubMed1985

Compensatory proliferative response of the rat submandibular salivary gland to unilateral extirpation.

The present experiment was conducted in order to identify the progenitor compartment of the submandibular salivary gland (SSG) and to explore the proliferative activity of this gland in response to unilateral extirpation. Left submandibular and retrolingual glands were extirpated in 30 rats (B.W. 200 +/- 12 g). The rats were killed 0, 1, 2, 3, 5 and 7 days after surgery. Five intact rats served as controls. The animals were given intraperitoneal injections of 3HTdR (0.5 microCi/grB. W) 1 h before they were killed. The contralateral SSG's were subjected to routine histological procedures and embedded in glycol methacrylate. Selected sections (2 micron thickness) were processed for autoradiography. In each gland, labelled and unlabelled nuclei were counted in 50 random microscopic fields and sorted according to their parenchymal histomorphological features and "nuclear class" (number of nuclei/cross section/feature). In the control glands the total labelling index (LI) was 0.18%; during acute compensatory stimulation, however, the total LI reached a maximum of 0.86% on day 3 after surgery. suggesting that the SSG, which normally undergoes a slow turnover, is capable of elevated proliferation in response to a stimulus. In both normal and stimulated glands, the LI was higher in the intercalated ducts (1.1%-5.85%) than in the granular ducts (0.17%-0.93%) and acini (0.05%-0.36%). This consistency of LI ratio between the various histomorphological features in the normal and experimental glands indicates that the glandular progenitor compartment is located in the intercalated ducts, which supply cells to both the ductal system and acini.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

A new method for the estimation of cell cycle phases.

A method is described, which is applicable to cell renewal systems with an anatomical structure in which all cell locations may be uniquely mapped. Its use is demonstrated on the rat incisor inner enamel epithelium, which forms a one cell thick column in the sagittally sectioned tooth. Cells born in the apical part of the column migrate toward the distal end of the tooth, where they mature. As the cells migrate along the column, they traverse the various cell cycle phases. The present study has been designed to estimate the probability of a cell being in a given phase; all cells touching the basement membrane were numbered, and the number of cells separating any two cells was taken as a measure of distance. Since generally all cells move in one direction (lateral cell migration may occur), it is possible to solve the problem with the aid of functions describing the renewal counting stochastic process in which cell distance serves as an independent variable. The method predicts labelled cell and mitotic rates which agree with those estimated in the usual way. It was then utilized to estimate the fraction of cells in G2.

Animals↗
PubMed1979

On the progenitor cell migration velocity.

An attempt is presented to extract cell kinetic information from histomorphological features. It is applicable to rapidly proliferating tissues like the intestinal epithelium. Each replicating tissue has an origin where cells are formed and a periphery toward which cells migrate. The migration path along which they move is denominated as tissue radius on which all cell positions are mapped. Cell migration on the radius is associated with cell proliferation at tissue origin. Each mitosis there is associated with the displacement of all cells distal to it by one cell position. The more mitoses positioned between a cell and tissue origin, the greater its migration velocity. It is possible therefore to derive the cell migration velocity v(x) from the cumulative mitotic distribution on the radius, N(x). v(x) = N(x)/tm (tm = mitotic time). In this form v(x) represents also cell production at any point on the radius and may serve for the computation of other cell kinetic parameters like generation time. These arguments are illustrated on the rat incisor tooth inner enamel epithelium which has been studied in the normal and rapidly erupting tooth.

Ameloblasts↗
PubMed1979

Cell production in the normal and lathyrogenic rat periodontal ligament (PDL).

Thirty male albino rats weighing 200 g. each were separated into two groups. 15 rats received 0.2% 3-amino propionitrile fumarate (BAPN) in drinking water. 15 rats served as controls. Within three weeks eruption rate diminished by 50%. On the 22nd experimental day each rat received one dose of 1 microCi/g. body weight tritiated thymidine (1.9 Ci/mM). 5 rats of each group were then killed after 1 hour; 1 week and 2 weeks. The PDL cell migration rate was evaluated autoradiographically. It diminishes proportionally with the eruption rate. In the BAPN treated animals, the mean total periodontal ligament (PDL) cell count is 55.5% higher than that of the control.

Aminopropionitrile↗
PubMed1979

The growth of the autotransplanted rat incisor tooth odontogenic organ.

74 rat incisor odontogenic organs were autotransplanted intradermally into the auricle. The animals were killed in groups of four up to eight months after grafting. Out of 61 grafts examined from the third week onward, 46% exhibited a typical odontogenic organ or a well differentiated tooth with pulp, vessels and nerve fibers. In 33% only scattered epithelial islands were formed. 21% of the grafts ended as osteodentin. Following the initial trauma leading to aseptic necrosis, the most primitive odontogenic organ cells survive to generate a new tooth. The grafted odontogenic organ resumes its existence as a complex structure which mobilizes its own vascular and nervous supply from the host dermis as evident from nerve fibers which penetrated the tooth pulp. Since all original nerve fibers of the graft had to be disconnected from their cell bodies, they obviously degenerated. Thus any nerve fiber observed in the regenerating tooth pulp had to be of dermal origin.

Animals↗
PubMed1978

The adaptation of a two-compartment cell renewal system to external demands. A study of the rat incisor inner enamel epithelium.

The inner enamel epithelium (IEE) covers the labial tooth aspect as a one cell layer which, when cut sagittally, appears as a longitudinal cell column extending from the tooth origin toward the periphery. Following sudden tooth shortening, the IEE responds by an increased cell production which later declines below normal values. The perturbation affects all cell kinetic parameters; the progenitor compartment, which initially increases, diminishes in size toward end of the experiment. The cell cycle transition times, which initially decline, rise toward the end of the experiment. The mean normal daily cell production rate of 70 cell % (i.e. 70 cells are produced by 100 progenitors) increases to 111 cell % and then declines to a low of 51 cell %. The IEE response typifies the behavior of other cell renewal systems such as intestinal epithelium and epidermis.

Animals↗
PubMed1978

On the potential of the adult rat incisor odontogenic organ to differentiate into two intact teeth.

The odontogenic organ of 10 male albino rats weighing 200 g has been exposed by a longitudinal incision through the masseter muscle. Its site could be identified as a bluish elevation of the mandible. Into this region through the bone, a 2 X 2 mm. tinfoil has been inserted, deep into the odontogenic organ. The tinfoil direction was generally parallel or slightly oblique to the tooth longitudinal axis. The animals were killed after 1 month. Their lower incisors in the bony sockets were fixed and decalcified, cut sagittally and processed histologically. In 3 sockets two separate teeth could be identified, a labial and a lingual tooth. Generally only the labial tooth was covered by enamel, in one case however both teeth exhibited a regular enamel layer. Both teeth were separated by a periodontal ligament and exhibited separate tooth cavities. This experiment demonstrates the capability of the odontogenic organ to reproduce a whole new complex organ, the tooth. A phenomenon hitherto observed only in Urodela in which a severed limb regenerates from primitive pluripotential stem cells known as blastema. Contrary to the newt however, the incisor blastema reproduces continuously throughout the life of the individual and responds to the tinfoil stimulus by a production of an extra tooth.

Animals↗
PubMed1977

Aging of tissues of the roots of nonfunctional human teeth (impacted canines).

In order to examine the aging of dentin and cementum, seventy-two impacted human canines, nonfunctional and not affected by external factors, such as attrition, abrasion, caries, etc., were surgically extracted. Ground sections were prepared and the areas of sclerotic dentin and cementum were measured with the aid of a planimeter and expressed as a percentage of the total root area. It was found that there is a significant increase in sclerotic dentin and apposition of cementum with an increase in age.

Aging↗