Hubert E. Schroeder

Types and incidence of human periapical lesions obtained with extracted teeth

OBJECTIVES To determine (1) the frequency of the incidence of abscess, granuloma, and radicular cyst among human periapical lesions obtained with extracted teeth; and (2) whether periapical cysts occur in two categories when histologically analyzed in relation to the root canals. STUDY DESIGN A total of 256 lesions were analyzed. The specimens were decalcified and embedded in plastic. Serial sections or step-serial sections were prepared, and the sections were evaluated on the basis of predefined histopathologic criteria. RESULTS The 256 specimens consisted of 35% periapical abscess, 50% granuloma, and 15% cysts. The latter occurred in two categories, the apical true cysts and the apical pocket cysts. CONCLUSIONS These results show (1) the low incidence of radicular cysts among periapical lesions as against the widely held view that almost half of all periapical lesions are cysts; and (2) the occurrence of two classes of radicular cysts. We are of opinion that the pocket cysts may heal after root canal therapy but the true cysts are less likely to be resolved by conventional root canal treatment.

Tooth eruption: Theories and facts

The mechanisms of tooth eruption (i.e., the answer to the question of how and why teeth erupt) has been a matter of long historical debate. This review focuses on human and other mammalian teeth with a time‐ and spacewise limited period of eruption and analyzes recent observations and experimental data on dogs, rats, primates, and humans in a framework of basic biological parameters to formulate a guiding theory of tooth eruption. Acknowledging basic parameters (i.e., that teeth move in three‐dimensional space, erupt with varying speed, and arrive at a functional position that in inheritable) eliminates a number of previously held theories and favors those that accommodate basic parameters, such as alveolar bone remodeling in association with root elongation, with possible correction factors in the form of cementum apposition and periodontal ligament formation. We have critically analyzed, summarized, and integrated recent findings associated with preeruptive movements of developing teeth, the intraosseous stage of premolar eruption in dogs, molar eruption in rodents, and premolar and molar eruption in primates. The variable speeds of eruption are particularly important. We conclude with basic principles of tooth eruption—that is, the type of signals generated by the dental follicle proper, the conditions under which teeth are moved and the clinical understanding to be derived from this knowledge.

Cementogenesis reviewed: a comparison between human premolars and rodent molars.

Cementum continues to be the least‐known mineralized tissue. Although recent advances in the field of molecular biology have contributed to an understanding of the involvement of molecular factors in cementum formation during development and regeneration, cementogenesis on a cell biological basis is still poorly understood. Virtually nothing is known about cementoblast origin, differentiation, and the cell dynamics during normal development, repair, and regeneration. This review describes the recent findings of cementogenesis on roots of human premolars and opposes them to those of teeth from other mammals, particularly the rodent molar.

Morphometric model, tissue sampling and test of stereologic procedures

Stereologic point counting procedures were applied to estimate volumetric and numerical densities of tissue components residing in and forming a defined, simplified model of human marginal gingiva. This included the quantitative characterization of inflammatory cell infiltrates occurring in the epithelial as well as the connective tissue fractions of this model. The gingival tissue was harvested from defined intraoral sites of 9–15 year‐old children and processed under standardized conditions for light and electron microscopic observation. Random cross‐sections of this tissue were subjected to morphometric analysis based on a multistage sampling technique. At each sampling level, tests were performed to study (1) the suitability of different test systems, (2) the parameter variation within one and between different biopsies and (3) the comparability and reliability of the data obtained. Based on these tests, a morphometric technique was designed which resulted in an accurate estimation of the various parameters characterizing the model tissue. These parameters were the volumetric densities of the following constituents: oral epithelium, junctional epithelium and its leucocyte content, infiltrated and non‐infiltrated connective tissue, and its respective collagen fibre content. Infiltrated and non‐infiltrated connective tissue fractions were analysed for their respective volumetric and numerical densities of fibroblasts, neutrophilic granulocytes, monocytes, macrophages, small and medium‐sized lymphocytes, immunoblasts, plasma cells and mast cells. Sampling technique, test procedures and the design and results of the morphometric system are discussed.

Biological Problems of Regenerative Cementogenesis: Synthesis and Attachment of Collagenous Matrices on Growing and Established Root Surfaces

Publisher Summary This chapter highlights the biological problems of regenerative cementogenesis. It describes the synthesis and attachment of collagenous matrices on growing and established root surfaces, with emphasis on cementogenesis in human teeth. Root cementum represents the most cardinal periodontal tissue component that is primary and indispensible for regenerating the tooth–bone connection, i.e., for reconstituting tooth anchorage. A new and increasingly accepted classification of root cementum on human teeth differentiates among four varieties according to the absence or presence of cells and to the source of collagen fibers, i.e., the major matrix component contained within. These varieties include (1) acellular, afibrillar cementum (AAC), (2) acellular, extrinsic-fiber cementum (AEFC), (3) cellular, intrinsic-fiber cementum (CIFC), and (4) cellular, mixed-stratified cementum (CMSC). Attachment of the early, first-formed cementum matrix to root dentine is one of the cardinal aspects of root development. In both humans and rats, cementum-matrix attachment occurs on a previously formed dentine surface while the respective tooth erupts, i.e., the dentine surface serving as an attachment site moves in the coronal direction while attachment is secured.

A quantitative electron microscopic analysis of the keratinizing epithelium of normal human hard palate

SummaryThe epithelium of normal human hard palate was subjected to stereologic analysis. Ten biopsies were selected from a total of twenty specimens collected from 9 to 16 year old females, and processed for light- and electron microscopy. At two levels of magnification, electron micrographs were sampled from three strata (basale, spinosum, granulosum) in two locations (epithelial ridges and portions over connective tissue papillae). Stereologic point counting procedures were employed to analyse a total 1560 electron micrographs. In general, the thickness of the palate epithelium was 0.12 mm (over papillae) and 0.31 mm (in ridges), the epithelium is distinctly stratified, and homogeneously ortho-keratinized. From basal to granular layers, the composition of strata revealed decreasing densities of nuclei, mitochondria, membrane-bound organelles and aggregates of free ribosomes. Keratohyalin bodies and membrane coating granules increased, and cytoplasmic filaments with a constant diameter of about 85 Å increased from 14 to 30% of cytoplasmic unit volume. The cytoplasmic ground substance occupied a stable 50% of the epithelial cytoplasm in all strata. The composition of basal layers in ridges differed from that over connective tissue papillae. The data are discussed in relation to the observations that (1) an increasing gradient of filament density is not the most characteristic feature of ortho-keratinizing oral epithelium and (2) differences in the degree of differentiation in cells of the stratum basale coincided with the comparable frequency distribution pattern of dividing cells.ZusammenfassungDas Epithel des normalen menschlichen harten Gaumens wurde einer stereologischen Analyse unterworfen. Insgesamt wurden 20 Biopsien aus 9–16 Jahre alten, gesunden Mädchen gewonnen und für licht- und elektronenmikroskopische Studien verarbeitet. Aus 10, zufällig ausgewählten Biopsien wurden Stichproben elektronenmikroskopischer Bilder aus 3 Straten (basale, spinosum, granulosum) und in 2 verschiedenen Bereichen (in epithelialen Leisten und im Epithel über Bindegewebspapillen) entnommen. Ein Total von 1560 elektronenmikroskopischen Bildern wurde mit Hilfe stereologischer Punktzählverfahren analysiert. Die Dicke des Gaumenepithels schwankte zwischen durchschnittlich 0,12 (über Papillen) und 0,31 mm (in Leistenbereich). Das Epithel ist deutlich geschichtet und gleichmäßig orthokeratinisiert. Vom Stratum basale gegen das Stratum granulosum fiel die volumetrische Dichte für Kerne und Mitochondrien, für membrangebundene, synthetisierende Organellen und für Aggregate freier Ribosomen ab, während Keratohyalinkörper und membran-ver-steifende Granula dichtemäßig zunahmen. Der zytoplasmatische Gehalt an Tonofilamenten, die einen konstanten Durchmesser von 85 Å aufwiesen, stieg von 14 auf 30% an, während die strukturlose, zytoplasmatische Grundsubstanz in allen Straten etwa 50% des Zytoplasmavolumens einnahm. Die strukturelle Zusammensetzung des Stratum basale war je nach Lokalisation (Leisten- und Papillenbereich) verschieden. Die Ergebnisse werden insbesondere im Hinblick auf die Beobachtungen diskutiert, daß 1. ein Ansteigen des Gradienten der Tonofilamentdichte nicht als das besonders charakteristische Kennzeichen für orthokeratinisierendes orales Epithel gelten kann, und 2. die Unterschiede im Differentiationsgrad zwischen Basalzellen verschiedener Lokalisation mit der vergleichbaren Häufigkeitsverteilung von sich teilenden Zellen gut übereinstimmte.

Application of stereologic methods to stratified gingival epithelia

Stereologic point‐counting procedures were applied to estimate quantitative tissue and cytoplasm parameters of the oral and the junctional epithelium of the human gingiva. Three gingival biopsies of female children, obtained and processed under standardized conditions, served (1) to determine the minimal sample size of cytoplasmic area required for estimating representative volumetric parameters in different strata of both epithelia, and (2) to compare average volume and surface density data derived from standardized samples in epithelial cross sections cut at two planes orientated perpendicular to each other. Sampling of electron micrographs, performed at two levels of magnifications according to a systematic stratified random sampling procedure consisted of recording field strips parallel to the epithelial or tooth surface within each of the various strata. The optimal sample size required varied for different organelles and epithelial strata. Minimal sample size of cytoplasmic area per biopsy were 300–440 μm2 for basal, and 450 μm2 for stratum spinosum cells of oral epithelium, and 130–185 μm2 for basal cells of the junctional epithelium. Average morphometric parameters for gross tissue components (cells, nuclei, cytoplasm, intercellular space) which resulted from analysing 4900 μm2 tissue area in each of the epithelia in each biopsy, were almost identical when determined in two different section planes. Volume and surface density data of cytoplasmic organelles (mitochondria, rough and smooth endoplasmic reticulum, cytoplasmic filaments) resulting from a sample of 280 μm2 cytoplasmic area per stratum and biopsy, revealed differences of varying magnitude, when determined in the two section planes. These differences were markedly smaller than those between comparable strata of both epithelia. Discussion of sampling procedures concluded that the type of sampling used for the present study is suitable for comparative morphometric studies.

Quantitative electron microscopic analysis of the stratified epithelium of normal human buccal mucosa

SummaryThe epithelium of normal human buccal mucosa was subjected to stereologic analysis. Ten biopsies were selected from a total of 20 specimens collected from 10 to 15 year old females, and processed for lightand electron microscopy. At two levels of magnification, electron micrographs were sampled from four strata in epithelial ridges and from three strata in regions over connective tissue papillae. Stereologic point counting based on a recently improved system for analyzing stratified epithelia was employed to analyze a total of 1820 electron micrographs. Buccal epithelium was found to be 0.48 mm thick, interdigitated by long, slender connective tissue papillae, and comprised of a narrow basal and suprabasal, and a broad, homogeneously structured spinous and surface compartment. From basal to surface layers, the epithelium displayed a differentiation pattern different from that of keratinizing epithelia. This pattern was a function mainly of a drastic density increase of cytoplasmic filaments of a constant 80 Å diameter, a corresponding decrease of the cytoplasmic ground substance, the appearance of dark-cored membrane coating granules and individually varying amounts of glycogen deposition. It is suggested that the dense meshwork of filaments which fill 70% of the epithelial cytoplasm in a broad subsurface and surface layer, serves as the functional matrix for epithelial distensibility.ZusammenfassungDas Epithel der normalen menschlichen Wangenschleimhaut wurde einer stereologischen Analyse unterworfen. 20 Biopsien aus 10–15 Jahre alten, gesunden Mädchen wurden für lichtund elektronenmikroskopische Studien verarbeitet. Aus 10 zufällig gewählten Biopsien wurden auf zwei Vergrößerungsstufen Stichproben elektronenmikroskopischer Bilder a) aus 4 Schichten im Bereich epithelialer Leisten und b) aus 3 Schichten im Epithel über Bindegewebspapillen entnommen. Insgesamt wurden 1820 Bilder mit Hilfe stereologischer Punktzählverfahren analysiert. Das Wangenepithel war im Durchschnitt 0,48 mm dick; es wurde von langen, schmalen Bindegewebspapillen durchzogen und umfaßte ein schmales, basales und suprabasales, sowie ein breites, homogen strukturiertes Oberflächenkompartment, gebildet aus dem Stratum spinosum und den Oberflächenschichten. Die vom Stratum basale gegen die Oberfläche fallenden oder steigenden Strukturgradienten ergaben ein epitheliales Differenzierungsmuster, das völlig verschieden von dem keratinisierender Epithelien ist. Dieses Muster wurde zur Hauptsache durch einen sehr starken Anstieg der Dichte der Filamente, die einen konstanten Durchmesser von 80 Å aufwiesen, durch einen entsprechenden Abfall der Volumendichte der zytoplasmatischen Grundsubstanz, durch das Auftreten von membranversteifenden Granula und durch individuell verschieden starke Glykogenablagerungen hervorgerufen. Es ist möglich, daß das dichte, filamentöse Maschenwerk, welches 70% des epithelialen Zytoplasma innerhalb einer breiten, oberflächlichen Epithelschicht füllt, als funktionelle Matrix für die Dehnbarkeit des Wangenepithels dient.

Initiation of acellular extrinsic fiber cementum on human teeth

SummaryThe 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 Karnovskys 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 μm 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 μm 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.

Establishment of acellular extrinsic fiber cementum on human teeth

SummaryThe 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 Karnovskys 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 μm 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.