PubMed Health⌕ Search

Biomedical subjects

H E Schroeder

Publications and source records attributed to H E Schroeder.

At least 19 recordsLinked to original sources
PubMed1992

Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar calcified cartilage.

In an attempt to show maturational alterations in the calcified cartilage, mandibular condyles of four growing and four adult male monkeys (Macaca fascicularis) were studied using light microscopy as well as transmission and scanning electron microscopy. All specimens were initially fixed by perfusion in the presence of ruthenium red. For examination of the hard tissue surfaces in the scanning electron microscope, uncalcified tissues were removed with sodium hypochlorite. In growing animals, almost the entire hard tissue surface in the joint region of the condyle was formed by calcified cartilage, while in adult animals, calcified cartilage was confined to load-bearing regions. In growing animals, the appearance of the calcified cartilage surface suggested a continuously advancing mineralizing front similar to that seen in the epiphyseal plate. Chondrocytes mostly exhibited a terminal stage of hypertrophy, and seemed to die and get lost through vascular invasion and subsequent endochondral ossification. In adult animals, most of the calcified cartilage surface appeared comparatively stable, and resembled the tidemark of articular cartilage. Chondrocytes were usually small and appeared viable. However, on the adult condyles, there were always circumscribed islands where chondrocytes and the pattern of mineralization resembled those seen in growing animals. In these regions, prominent chondroclastic activity indicated extensive articular remodelling. These observations suggest that at the end of somatic growth, condylar calcified cartilage undergoes considerable maturation from a type reminiscent of hyaline growth cartilage to a type resembling articular cartilage. Concomitantly, chondrocytes appear to change their developmental program, in that they stop enlarging and lose their commitment to death. However, they may be able to retain, or switch back to, a more immature stage, in case there is need for extensive articular remodelling.

Animals↗
PubMed1992

Number and size-spectra of myelinated nerve fibers of human premolars.

The primary objective of this study was to determine the number and size of myelinated nerve fibers at the subcervical, midroot and juxta-apical levels of human premolars. Sixty-seven healthy premolars extracted from adolescents were utilized. Root-discs were prepared from the three sites and processed for light and electron microscopy. The myelinated nerve fibers were counted from semithin sections using a sampling microscope. The measurements were taken from composite electron micrographs using an electronic image processing unit. A total of 1883 myelinated axons from seven mandibular second premolars was gauged. The 67 teeth had an average of 312 +/- 149 myelinated nerve fibers at the juxta-apical level (range 18 to 728). The contra- and ipsilateral differences in means among the four groups of premolars were not significant (P > 0.05). The number of nerves increased significantly (P < 0.05) toward midroot and subcervical (P < 0.001) levels in all groups. The average neural diameter was 3.5 + 1.0 microns at the juxta-apical level, and the between-teeth difference in mean was found to be significant (P < 0.01). There was no decline (P > 0.05) in the diameter of myelinated nerve fibers toward midroot and subcervical levels.

Adolescent↗
PubMed1992

Palatal taste buds in man: topographical arrangement in islands of keratinized epithelium.

In an attempt to find and reconstruct the exact anatomical correlate of taste sensitivity in the human soft palate, a novel approach was used to examine the mucosal surface in conjunction with serial tissue sectioning. Six human subjects, 15 to 29 years of age, 3 females and 3 males, served to take precision impressions of the hard and the anterior soft palate, using non-commercial trays and a self-curing resin. From these impressions, replicas were cast in Epon and subsequently sputter-coated with gold and examined in a scanning electron microscope. In addition, one biopsy was taken from one of the volunteers, in an area including taste bud-suspicious elements. It was found that the anterior soft palate mucosa included 10 to 30, oval to round, site-exotic islands, about 0.2-0.6 mm in diameter, which were covered by a thin, keratinizing stratified squamous epithelium. These islands occurred mainly in an area located in the central part of the soft palate, immediately posterior to the hard/soft palate boundary. The keratinizing epithelium of such islands carried four to seven taste buds which were lacking elsewhere. These islands were formed by a large, mushroom-like connective tissue papilla penetrating most of the site-specific mucosal epithelium, with its cover of keratinizing epithelium, forming sharp external and internal cell-to-cell borderlines with the surrounding, non-keratinizing stratified squamous epithelium. These findings are discussed in relation to induction phenomena necessary to form such islands, and to the variable taste sensitivity detected clinically in this region.

Adolescent↗
PubMed1992

Initial formation of cellular intrinsic fiber cementum in developing human teeth. A light- and electron-microscopic study.

The present study describes the formative process of the initiation of cellular intrinsic fiber cementum (CIFC) in still growing human teeth. From 29 premolars and molars with incomplete roots developed to 60-90% of their final length, 8 premolars (with roots formed to three quarters of their final length) were selected for electron-microscopic investigation. All teeth were clinically intact and prefixed in Karnovsky's fixative immediately after extraction. Most of them were decalcified in ethylene diaminetetraacetic acid (EDTA), and the apical part of the roots was divided axially into mesial and distal portions that were subdivided in about 5 slices each. Following osmication and embedding in Epon, these blocks were cut for light- and electron-microscopic examination. In addition, 5 teeth with incomplete roots were freed from organic material and processed for scanning electron microscopy. It was found that CIFC-initiation commenced very close to the advancing root edge and resulted in a rapid cementum thickening. Thereafter, appositional growth continued on the already established cementum surface. Large, basophilic and rough endoplasmic reticulum-rich cementoblasts, some of which became cementocytes, were responsible for both fast and slow CIFC-formation. The CIFC-matrix was free of Sharpey's fibers and composed of more or less organized intrinsic collagen fibrils, in part fibril bundles, that ran roughly parallel to the root surface. Initially, the cementum fibrils intermingled with those of the dentinal collagen fibrils, which were not yet mineralized. This boundary subsequently underwent calcification. The development of collagen fibril bundles and their extracellular arrangement were associated with cytoplasmic processes probably involved in fibril formation and fibril assembly. Many cementoblasts contained intracytoplasmic, membrane-bounded collagen fibrils, which probably were related to fibril formation rather than degradation.

Adolescent↗
PubMed1992

Vicilin with carboxy-terminal KDEL is retained in the endoplasmic reticulum and accumulates to high levels in the leaves of transgenic plants.

Gene constructs were designed to test the effect of the endoplasmic reticulum (ER)-targeting signal, KDEL, on the level of accumulation of a foreign protein in transgenic plants. The gene for the pea seed protein vicilin was modified by the addition of a sequence coding for this tetrapeptide at its carboxyl terminus. The altered gene was placed under the control of a CaMV 35S promoter and its expression in the leaves of both tobacco and lucerne (alfalfa) was compared with that of an equivalent vicilin construct lacking the KDEL-coding sequence. The presence of the ER-targeting signal led to a greatly enhanced accumulation of the heterologous protein. In lucerne and tobacco leaves, the level of vicilin-KDEL protein was 20 and 100 times greater than that of the unmodified vicilin, respectively. These differences in expression level could not be explained by corresponding differences in the steady-state levels or the translatability of the mRNAs. However, when the stability of vicilin and vicilin-KDEL proteins was compared in their respective transgenic hosts, unmodified vicilin was found to be degraded with a half-life of 4.5 h while vicilin-KDEL was much more stable with a half-life of more than 48 h. Immunogold labelling of leaf tissues from transgenic lucerne and tobacco showed the presence of vicilin associated with large aggregates within the ER lumen of vicilin-KDEL plants. No such aggregates were detected in transgenic plants expressing wild-type vicilin. It is concluded that the carboxy-terminal KDEL caused the retention of the modified vicilin in the ER, and that this retention led to the increased stability and higher level of accumulation of vicilin-KDEL in leaves of transgenic plants.

Amino Acid Sequence↗
PubMed1992

Growth of acellular extrinsic fiber cementum (AEFC) and density of inserting fibers in human premolars of adolescents.

The present study describes for the first time the changes of both AEFC thickness and the numerical density of collagen fibers inserting into AEFC at specified levels and sites of human premolars at different stages of development. The investigation was based on 45 premolars (25 maxillary, 20 mandibular; 25 first and 20 second), extracted from adolescents and young adults. All teeth were free of disease and presented with roots developed from 30-100% of their final length. They were prefixed in Karnovsky's fixative, decalcified in EDTA and subdivided into about 14 slices each, cut from mesial and distal root surfaces, vertical to and along the root axis. The slices were postfixed in OsO4, embedded in Epon and cut for light-microscopic study. AEFC thickness (4086 measurements) and the density of the collagenous fiber fringe (454 counts) inserting in AEFC were measured at 1, 3, 5 and 7 mm apical to the cementoenamel junction. The data obtained showed: AEFC thickness increased with age and varied between 0 and 57.5 microns. Between 9 and 17 years, cervical AEFC thickness increased in maxillary first premolars from an average of 5 to 30 microns, and in mandibular second premolars from 6 to 20 microns, i.e., AEFC grew at approximately the same rate as later in life. Depending on the differences in tooth development, AEFC on maxillary first premolars became thicker than that on mandibular second premolars. Due to the corono-apically decreasing gradient of AEFC development, its increase in mid-root regions lagged behind that in cervical regions of all teeth in people younger than about 14 yr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Morphological and labeling evidence supporting and extending a modern theory of tooth eruption.

As the interest in biological mechanisms of tooth eruption has recently been revived by a new eruption theory, the present study was an attempt to contribute new data to this problem. Four male Macaca fascicularis monkeys, two infant (about 13 months old) and two juvenile (about 44 months old), were labeled either by sequential fluorochrome or by single 3H-proline injections and then served for studying the bone apposition patterns around erupting premolars and molars. About 100 microns thick ground sections cut either in the mesiodistal or bucco-oral direction and the corresponding micrographs, microradiographs and autoradiographs, as well as fluorescence micrographs were used. In the multirooted teeth studied, bone apposition was most prominent and fast in the inter-radicular region, while at the fundus of the alveoli, bone apposition was slight or negligible. Around maxillary premolars and molars, bone apposition pointed in the mesial as well as in the axial direction. This was true for the intraosseous and the supraosseous phase of tooth eruption. Using these observations in addition to preliminary data calculated for the rates of bone apposition in the inter-radicular, apical and crestal regions, and for the rate of root elongation, the new eruption hypothesis could be extended. It is suggested that eruption of multirooted teeth, in the presence of corresponding coronal resorption, is entirely explained by forces generated through inter-radicular bone apposition and that their dental follicle is in a stimulating mode inter-radicularly but neutral apically at the bottom of the alveolar fundus.

Animals↗
PubMed1991

Initiation of acellular extrinsic fiber cementum on human teeth. A light- and electron-microscopic study.

The development of acellular extrinsic fiber cementum (AEFC) has never before been studied in human teeth. We have therefore examined the initiation of AEFC in the form of a collagenous fiber fringe and its attachment to the underlying dentinal matrix, in precisely selected, erupting human premolars with roots developed to 50%-60% of their final length. Freshly extracted teeth were prefixed in Karnovsky's fixative, decalcified in EDTA and subdivided into about 10 blocks each, cut from the mesial and distal root surfaces, vertical to and along the root axis. The blocks were postfixed in osmium tetroxide, embedded in Epon and cut for light- and electron-microscopic investigation. Starting at the advancing edge of the root, within a region extending about 1 mm coronal to this edge, fibroblast-like cells were seen closely covering the external root surface. Along the first 100 microns from the root edge, these cells extended cytoplasmic processes and contacted the dentinal collagen fibrils. Between these cells and the dentinal matrix, new collagen fibrils and very short collagen fibers gradually developed. Within the second 100 microns from the root edge, this resulted in the formation of a cell-fiber fringe network. Newly formed fibers of the fringe were directly attached to the non-mineralized matrix containing dentinal collagen fibrils and could be distinguished from the latter by differences in fibril orientation. During the process of dentin mineralization, the transitional zone between the fiber-fringe base and the dentinal matrix, i.e., the future dentino-cemental junction, also mineralized. It is suggested that this fiber fringe is the base of AEFC, which later increases in thickness by fiber extension and subsequent mineralization.

Bicuspid↗
PubMed1991

Establishment of acellular extrinsic fiber cementum on human teeth. A light- and electron-microscopic study.

The present study describes for the first time the development of early acellular extrinsic fiber cementum (AEFC) until its establishment on human teeth. Precisely selected premolars with roots developed to 50%-100% of their final length were prefixed in Karnovsky's fixative and most of them were decalcified in EDTA. Their roots were subdivided into about 10 blocks each, cut from the mesial and distal root surfaces. Following osmication, these blocks were embedded in Epon and sectioned for light- and transmission electron microscopy. Some blocks were cut non-demineralized. From semithin stained sections, the density of the collagenous fiber fringe protruding from the root surface was measured by using the Videoplan-system. After initiation of this fiber fringe and its attachment to the dentinal root surface followed by mineralization, the fringe gradually increased in length and subsequently became mineralized. Fringe elongation and the advancement of the mineralization front appeared to progress proportionally. Thus, in all stages of AEFC development, a short fiber fringe covered the mineralized AEFC. Its density remained constant, irrespective of AEFC thickness. The latter gradually increased and reached an early maximum of 15-20 microns in the cervical region. At this stage, the AEFC fringe appeared to fuse with the future dentogingival or other collagen fibers of the tooth supporting apparatus. Mineralization of the fringe commenced with isolated, spherical or globular centers, which later fused with the mineralization front and became incorporated in AEFC.

Adolescent↗
PubMed1991

[The effects of furcation morphology on periodontal disease].

Enamel spurs projecting from the cemento-enamel junction into the furcation as well as small islands and droplets of enamel deposited on furcational root surfaces are characteristic morphological features of human maxillary and mandibular molars. The furrows and recesses created by these structures form pathways for bacterial invasion and predispose for local periodontitis. Furthermore, the furcations are often covered by thick central cementum ridges, with steplike or tongue-like deepenings around enamel droplets. In the cementum, there is a variable number of small and large openings, representing either cementum-inherent channels or large open connections between pulp chamber and furcation. These structures offer ample opportunities for uncontrollable bacterial retention and colonisation, and the possibility for pulpal infections to spread into the furcation. The literature covering these issues is summarized.

Dental Cementum↗
PubMed1991

[The rate of the eruption of human teeth. A review].

The speed that a tooth bud or growing tooth attains on its way to the level of occlusion merits biological and clinical interest. In this work, all data available in the literature related to the eruptive movement of the various permanent teeth in man, both prior and after their clinical emergence in the oral cavity, have been gathered and recalculated in rates of movement per day. For comparative purposes, the rates of migration of nonerupted teeth, of bone resorption and bone apposition, as well as the rate of elongation of growing tooth roots were also collected from the literature. The standardized data (rates in micron/day) revealed the intraosseous movements of tooth buds and growing teeth are dependent and limited in speed by the rates of bone resorption and bone apposition. The extra-alveolar movement of clinically visible tooth crowns on their course of prefunctional eruption occurs at a much higher speed which probably results from a combination of the rate of bone apposition in the apical region and the rate of root elongation. These findings are discussed in connection with our present knowledge on the mechanisms of tooth eruption.

Bone Development↗
PubMed1990

In-vitro formation of a collagenous matrix upon previously diseased and experimentally treated cemental root surfaces.

A diseased and mechanically treated surface of root cementum is known, clinically, to favor periodontal regeneration. The present investigation was undertaken to test whether previously diseased and experimentally treated root surfaces can support the in-vitro formation of a new collagenous matrix. Three teeth extracted for advanced periodontitis were treated first with 5% sodium hypochlorite for 2 h to remove all organic material from the root surface. After the healthy, apical one third of the root was cut off, the roots were scaled with moderate pressure to remove visible calculus. Non-demineralized root discs were cut and placed on a co-culture of periodontal ligament- and alveolar bone-derived cells. After 7 weeks in culture, either one of two matrix types was found along the root surface. The most frequent matrix consisted of clusters of cells layered within densely aggregated collagen fibrils. The other, less frequent matrix consisted of loosely arranged collagen fibrils adjacent to the cemental surface. The findings support the notion that, in vitro, a collagenous matrix is formed in contact to diseased and experimentally treated root surfaces. However, the smooth, non-demineralized and scaled cemental surface does not appear to be a suitable substrate for interdigitation with newly produced collagen fibrils.

Alveolar Process↗
PubMed1990

Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar articular layer.

In an attempt to establish maturational alterations in the morphology of the articular tissue layer, mandibular condyles of four immature and four mature male monkeys (Macaca fascicularis) were studied using light microscopy as well as scanning and transmission electron microscopy. Specimens were fixed in situ by perfusion in the presence of ruthenium red to stabilize proteoglycans. Preparations intended for observation in the scanning electron microscope were first dehydrated and sputtered for the examination of articular surfaces, and afterwards treated with trypsin to expose the spatial arrangement of collagen fibrils. Gross anatomical relations between joint components indicated that the anterior and central, but not the posterior region of the condylar articular surface can be subject to compressional load. Load-bearing and non-load-bearing regions differed with respect to the morphology of the articular layer. Load-bearing surfaces were covered by a prominent articular surface lamina similar to that observed on articular cartilage. This lamina seemed to constitute an integral part of the articular layer, distinct from the lining of synovial fluid, and to be composed largely of proteoglycans. It was unaffected by maturation. The subjacent, load-bearing articular layer differed markedly in structure, both from articular cartilage, and between immature and mature animals. Articular cells of immature animals were classified as fibroblastlike, but unlike typical fibroblasts, were surrounded by a thin, often incomplete halo of fibril-free pericellular matrix, presumably consisting of proteoglycans. In mature animals, articular cells closely resembled chondrocytes, but exhibited prominent nuclear fibrous laminae, which usually are found only in fibroblasts. Thus, the load-bearing part of the articular layer seems to undergo a maturation-dependent metaplastic conversion, from a dense connective tissue with some features of fibrocartilage, to a fibrocartilage-like tissue containing chondrocyte-like cells with some features of fibroblasts. This conversion might reflect an adaptation to a maturation-associated increase in articular stress.

Animals↗
PubMed1990

Social skills training with schizophrenics: a meta-analytic evaluation.

A meta-analytic review of 27 studies on social skills training with schizophrenics was conducted to address 3 critical issues in the literature: (a) the magnitude of treatment effects relative to different outcome measures; (b) the extent of the generalization and maintenance of treatment effects; and (c) the impact of 2 methodological issues: diagnostic clarity and training variations. Social skills training has a strong, positive impact on behavioral measures of social skill, self-rated assertiveness, and hospital discharge rate, and a moderate impact on relapse rate. In addition, when behavioral measures are used, the data support generalization and maintenance of skill gains. However, effects are only marginally significant for broader ratings of symptoms and functioning. Diagnostic homogeneity, the number of techniques used, and the amount of training do not appear to be significantly associated with outcome. Specific directions for future research are discussed.

Assertiveness↗
PubMed1990

Evidence for rapid multipolar and slow unipolar production of human cellular and acellular cementum matrix with intrinsic fibers.

The genesis of root cementum has been studied infrequently in animal models, e.g., in mice, rats and dogs, but rarely in the human. The present study was based on 8 premolars (4 maxillary and 4 mandibular, 7 first and 1 second) selected from a large collection of freshly extracted human teeth. All teeth were free of disease and presented with roots developed to about 50-80% of their length. After decalcification in EDTA, the apical half of the roots was divided axially into mesial and distal portions. The latter were subdivided into 4 slices cut in the corono-apical direction. These slices were Epon-embedded and cut for examination in the light- and transmission electron microscope. It was found that 2 basically different modes of cementum matrix production occurred at or near the advancing root edge. These 2 modes, i.e., the multipolar versus unipolar matrix production, resulted in either cellular (CIFC) or acellular intrinsic fibre cementum (AIFC). Both varieties did not contain fibres of Sharpey and were restricted to regions of the root usually covered with cellular mixed stratified cementum (CMSC). By comparison with recently published data on the rate of cementum apposition, it is suggested that the multipolar mode is a rapid form, whereas the unipolar mode is a slow-rate form of producing intrinsic fibre cementum.

Adolescent↗
PubMed1990

[Age-related changes of the pulpal dentin wall in human front teeth].

A total of 55 extracted, vital human teeth (i.e. central and lateral incisors of the maxillary [n = 17] and the mandibular [n = 38]jaws) of patients between 40 and 97 years of age has been used to study the age-related restriction of the pulp chamber, in particular the root canal, and the structure of the inorganic dentinal wall of the pulp chamber by means of X rays and scanning electron microscopy. In addition, the density of the openings of the dentinal tubules was, under standardized conditions, determined at the coronal pulp chamber, in the middle of the root canal and apically on each of the four aspects of the pulp chamber, i.e. vestibular, mesial, oral and distal. The results demonstrated that the pulp chamber, in particular the root canal, with increasing age of the patient becomes restricted in the mesio-distal, but not or much later in the vestibulo-oral direction. This is because a network of tubule-free fibrodentin or more regular secondary dentin with or without tubules is deposited at these pulp chamber walls. The density of the tubules was at vestibular and oral aspects of the dentinal walls and also in upper incisors higher than at mesial and distal walls and in lower incisors. It also decreased mainly from the middle of the root canal towards the apex. However, because of the very heterogeneous structures at the pulp chamber walls, the tubule density was enormously variable.

Adult↗