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Differentiation of odontoblasts involves cell-to-cell recognition, contact stabilization involving the formation of attachment specializations, cytoplasmic polarization, development of the protein synthetic and secretory apparatus, and the active transport of mineral ions. The secretory odontoblast is characterized by an extensive rough-surfaced endoplasmic reticulum, a highly developed Golgi complex, and the presence of specific secretion granules. Type I collagen, a major constituent of dentin matrix, appears to be secreted by the odontoblast into predentin at the proximal portion of the odontoblast process, the major cytoplasmic process extending from the odontoblast cell body into the dentin. The odontoblast process contains a rich network of microtubules and microfilaments. The proximal portion of the process is also a site of fluid-phase endocytosis. Adjacent odontoblasts are held together by numerous macula adherens junctions and a well-developed distal junctional complex adjacent to be predentin. Junctional strands of the occludens type have been observed to be a component of this junctional complex. Tracer studies employing horseradish peroxidase indicate that this junctional complex does not form a tight barrier to the diffusion of tissue fluid from the interodontoblast spaces into the predentin. Many well-developed gap junctions are formed between adjacent odontoblasts and between odontoblasts and the fibroblasts that make up the subodontoblastic layer. Ca-ATPase activity is demonstrated in the Golgi complex and mitochondrial cristae and along the distal plasma membranes of odontoblasts. ALPase activity is also intense along the entire odontoblast cell surface. The osmium tetroxide-pyroantimonate technique for calcium localization demonstrates prominent reaction precipitates in mitochondria of odontoblasts. Energy-dispersive x-ray microanalysis of anhydrously fixed and processed odontoblasts detected Ca and P peaks throughout the cytoplasm. A sulfur peak is noted in the distal cytoplasm of odontoblasts and in matrix vesicles. Together, these results demonstrate the complexity and variety of cell functions involved in dentinogenesis.

Two of the most important figures in the development of the dental profession in eighteenth-century France were Pierre Fauchard and Etienne Bourdet. The title, father of modern dentistry, rightly belongs to Fauchard, for his treatise was the first comprehensive description of dental practice. He broke new ground, and in so doing he set high standards for those who would follow. Bourdet, one generation after Fauchard, was equally effective in describing the practice of dentistry in his treatise published in 1757. The fame of Fauchard continues to overshadow the merit of some of Bourdet's original contributions, especially in the area of periodontal disease. Examination of Fauchard's and Bourdet's concepts of gingival and periodontal pathology, and their methods of managing the disease, reveals many similarities as well as significant differences. Bourdet linked gingival inflammation to local alveolar bone loss with much intuition. In his writings we see the origin of the notions of the gingival pocket, and of an ulcerated pocket epithelium. Furthermore, his treatment rationale was based on a clearly defined concept of the local pathology formed from personal observation.

Using 12- to 18-month-old rats, we examined the ultrastructural and cytochemical features of multinucleated fibroblastic cells (MFCs) in the periodontal ligament (PDL) of molars. In aged rats, the MFCs were distributed randomly in the PDL and exhibited cytoplasmic structural variations which were not dependent on the number of nuclei. There was a tendency for the MFCs to cluster in the PDL. The MFCs, rich in cytoplasmic organelles involved with procollagen synthesis such as rough endoplasmic reticulum and the Golgi apparatus, incorporated and secreted 3H-proline-labelled products. The MFCs also possessed many phagosomes containing intact collagen fibrils. These MFCs were apparently involved in phagocytosis and intracellular degradation of incorporated collagen fibrils. Phagosome-rich MFCs contain acid phosphatase activity in primary and secondary lysosomes, similar or stronger in intensity to that which can be demonstrated in mononuclear fibroblasts. However, unlike mononuclear fibroblasts, the MFCs did not exhibit alkaline phosphatase activity along their plasma membranes. These results suggest that MFCs demonstrate a range of fibroblastic cellular activity, including collagen phagocytosis, and that they may lack certain plasma membrane glycoproteins, which might explain the occurrence of multinucleation in these cells.

Occurrence of epidermal growth factor (EGF)-binding sites during differentiation of cementoblasts and periodontal ligament (PDL) fibroblasts was investigated using radioautography after I. V. injection of 125I-EGF to 14-day-old rats. During differentiation of cementoblasts, a very low level of EGF-binding sites was present on the mesenchymal cells in dental follicle proper, precementoblasts, and cementoblasts. On the other hand, during differentiation of PDL fibroblasts, numerous EGF-binding sites were observed on the undifferentiated paravascular cells and on the perifollicular mesenchymes representing the major source of PDL fibroblast precursor cells. Also heavy labeling was observed throughout their differentiation to PDL fibroblasts, as well as during full synthetic activity as mature cells. Quantitative analysis of the light microscopic radioautographs revealed that these cells demonstrated approximately 4 grains per 100 microns 2 of cell area. These results suggest that EGF plays an important role in differentiation of PDL fibroblasts, but not in that of cementoblasts. Furthermore, the well-known in vivo effect of EGF in producing precocious eruption of teeth may be a consequence of a more extensive effect of EGF throughout differentiation of PDL fibroblasts as well as during full synthetic activity as mature cells.

Voltaire, the leading French intellect of the 18th century, was a notorious hypochondriac. His numerous letters contain hundreds of references to his medical and dental disorders, as well as to those of close friends. Voltaire lived to be 84 years old, but not without suffering from several systemic medical disorders and from periodontal disease that left him nearly edentulous by his mid-50s. His dental condition was diagnosed as a scorbutic condition, requiring systemic medication. As a result of neglect and possible mercury intoxication, his condition worsened, and he lost most of his teeth and suffered facial collapse because he did not wear a dental prosthesis. This paper recounts events in Voltaire's life that were connected to his medical and dental history, and in so doing provides a glance at medical and dental practice in 18th-century France.

The School of Dental Medicine was planned and functions as an integral part of the Health Sciences Center at the State University of New York at Stony Brook. It has been in operation for almost 20 years. The mission of the school is multifaceted. It educates new dentists and scientists at the doctoral level. Its research advances the knowledge on which dental care is provided. Through its clinical activities, the school provides care to people in need and to special segments of the population that are underserved. And its faculty serves as a reservoir of expertise to the profession and the community.

Pierre Fauchard possessed the following attributes: Curiosity, intelligence, courage, perseverance, honesty, dexterity, and social responsibility. I suspect that these qualities would have assured him success in whatever career he might have followed. He chose surgery, and through his experience as a ship's doctor in the French navy, he specialized in diseases of the mouth and teeth (common among seamen), qualifying as a surgeon-dentist prior to establishing his highly successful private practice in Paris. In his long career he stood for excellence, the scientific approach, comprehensive care, high ethical standards, and technical innovation. Although we know almost nothing of his private life, his book does reveal a good part of his character. Based solely on this source it is possible to conclude that Fauchard was a true son of the enlightenment, who justifiably holds the title of Father of Modern Dentistry. His treatise contains lessons to be emulated even into the 21st century.

A combined HCl-collagenase digestion technique and scanning electron microscopy were used to isolate the enamel organ and to confirm the presence of maturation ameloblasts of both ruffle-ended (RA) and smooth-ended (SA) types on maturing enamel in kitten permanent tooth germs. EDTA perfusion of animals fixed with aldehyde produced two or three belt-like shallow grooves (from 30 to 100 micron wide) running horizontally through the maturing enamel surface, coinciding closely with the SA distribution pattern. In animals that had been perfusion-fixed with unbuffered osmium tetroxide containing 2.5% potassium pyroantimonate, SEM-EDX analysis detected K in a superficial enamel layer overlaid by the SA layer. Potassium concentration decreased gradually toward the deeper layers. Very little K penetrated the enamel under the RA layer. Energy-dispersive x-ray analysis of Ca and P concentrations in the enamel revealed an even distribution of these elements throughout the superficial layer of maturing enamel. These results suggest that the SA layer forms an access route for K and EDTA and that, in spite of the obvious morphological and functional differences between RA and SA, the maturing enamel surfaces overlaid by these two cell types show similar degrees of mineralization.

The effects of the calmodulin blocker, trifluoperazine (TEP), on membrane-bound Ca++-ATPase, Na+-K+-ATPase (EC 3.6.1.3.) and the ultrastructure of the enamel organ were investigated in the lower incisors of normal and TFP-injected rats. The rats, of about 100 g body weight, were given either 0.2 ml physiological saline or 100 micrograms TFP dissolved in 0.2 ml physiological saline through a jugular vein and fixed by transcardiac perfusion with a formaldehyde-glutaraldehyde mixture at 1 and 2 h after TFP administration. Non-decalcified sections of the enamel organ less than 50 micron in thickness, prepared from dissected lower incisors, were processed for the ultracytochemical demonstration of Ca++-ATPase and Na+-K+-ATPase by the one-step lead method at alkaline pH. In control saline-injected animals the most intense enzymatic reaction of Ca++-ATPase was demonstrated along the plasma membranes of the entire cell surfaces of secretory ameloblasts. Moderate enzymatic reaction was also observed in the plasma membranes of the cells of stratum intermedium and papillary layer. Reaction precipitates of Na+-K+-ATPase activity were localized clearly along the plasma membranes of only the cells of stratum intermedium and papillary layer. The most drastic effect of TFP was a marked disappearance of enzymatic reaction of Ca++-ATPase from the plasma membranes of secretory ameloblasts, except for a weak persistent reaction in the basolateral cell surfaces of the infranuclear region facing the stratum intermedium. The cells of stratum intermedium and papillary layer, however, continued to react for Ca++-ATPase even after TFP treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The post-secretory portion of the rat incisor enamel organ was prepared for routine transmission electron microscopy and freeze-fracture replication in order to define further the structural surface features of the ruffle-ended ameloblasts. Surface views of the distal plasma membrane of the ruffle-ended ameloblasts revealed a well-developed zonula occludens junction with from six to ten rows of tight junctional strands. Gap junctions were also observed just proximal to the tight junctional strands. The membranes of the ruffled border contained a rich supply of intramembrane particles (IMP). The IMPs were approximately 7 to 8 nm in diameter and preferentially located on the P-face profiles of the membrane. The density of IMPs on the membranes of the ruffled border was higher than that on the lateral borders of the cell. It is suggested that the IMPs of the ruffled border may represent enzymatic proteins in the basal cell membrane of absorptive ameloblasts. In addition, the large, highly-developed zonula occludens appeared structurally capable of sealing the intercellular spaces between the ruffle-ended ameloblasts.

The enamel organ of the growing rat incisor was fixed with a mixture of formaldehyde and glutaraldehyde and processed for ultracytochemical demonstration of Ca- and Mg-activated membrane ATPase by a one-step lead technique at alkaline pH. To inhibit nonspecific alkaline phosphatase, 5 mM levamisole was added to the incubation media. Intense Ca- and Mg-ATPase activity was demonstrated in the cell surfaces of the secretory ameloblasts, except at the proximal and distal junctional complexes and the gap junctions in the lateral and basal cell surfaces. Deep plasma membrane invaginations at the proximal and distal parts of Tomes processes facing interrod- and rod-enamel growth regions exhibited the strongest enzymatic reaction. Mg-ATPase activity was also shown to be present in the plasma membranes of secretory ameloblasts but it was less intense than Ca-ATPase. Except for a slight reaction in the Golgi membranes, all other cell organelles of the secretory ameloblasts and the adjacent enamel matrix were free of enzymatic reaction. However, when the tissues were incubated in media lacking levamisole, a prominent enzymatic reaction was observed in the newly secreted enamel matrix of the rod and interrod growth regions as well as on the plasma membranes of the cells. In maturation ameloblasts of both ruffle-ended and smooth-ended types, a weak reaction for Ca- and Mg-ATPase was restricted to basal cell surfaces facing the papillary cell layer. In tissues incubated in media lacking levamisole, a variable deposition of reaction products was observed in the Golgi membranes, mitochondrial membranes, tubular elements of smooth endoplasmic reticulum in the ruffled border zone, and along the plasma membranes of the ruffled border. Throughout the secretory and maturation stages, a moderate and/or weak enzymatic reaction for both Ca- and Mg-ATPase was seen in the plasma membranes of the cells of the stratum intermedium and the papillary layer when incubated in media with levamisole. Omission of substrate ATP and/or the enzyme activator CaCl2 from the incubation media for Ca-ATPase produced a negative reaction in the tissues examined. When the calmodulin blocker trifluoperazine was administered to the rats intravenously, Ca-ATPase activity was almost completely abolished from the plasma membranes of secretory ameloblasts, but not of other cell types.

Periodontal ligament fibroblasts contain numerous intracellular or cytosegragated collagen fibrils. These fibrils appear to be broken down within the lysosomal apparatus of the cells. There is an increase in this activity in fibroblasts associated with osteoclastic bone resorption. Cytoplasmic microfilaments and attachments to substrata indicate that the fibroblasts of the ligament have the potential of migration and cytoplasmic contraction. A theory of collagen fiber maintenance within the periodontal ligament is proposed which takes into account: (1) the motility and contractility of fibroblasts, (2) the phagocytic and degradative potential of fibroblasts, (3) the presence of intracellular collagen and (4) the reported high turnover rate of acid-insoluble collagen within the periodontium.

Sprague-Dawley strain rats of 4-5 weeks old were perfusion-fixed with either a mixture containing 0.1 or 0.25% glutaraldehyde and 2% formaldehyde, or a 2% formaldehyde in 0.1 M sodium cacodylate buffer for 10 minutes. Non-decalcified 30-50-micron sections of the enamel organ taken from lower incisors were then processed for ultracytochemical demonstration of ouabain-sensitive, K+-dependent, p-nitrophenyl phosphatase, by use of the one-step lead method, representing the second dephosphorylative step of Na+-K+-ATPase. Throughout the secretory, transition, and maturation stages of amelogenesis, the enzymatic activity was demonstrated along the cytoplasmic side of the plasma membranes of the stratum intermedium and the papillary layer cells, especially along their numerous microvilli. The plasma membranes forming gap junctions and desmosomes were free of reaction or showed slight focal precipitates of reaction products. The stellate reticulum and the outer enamel epithelium exhibited either a weak reaction or were reaction negative. Secretory ameloblasts showed a weak trace-like reaction along the basal and lateral cell surfaces; however, the latter surfaces were sometimes completely free of reaction. Tomes' processes were usually reaction negative. Ameloblasts in the transition and maturation stages were devoid of enzymatic activity, except for a slight reaction along the plasma membranes of the basal cell surfaces of transition ameloblasts facing the papillary layer. The enzymatic activity described above was completely dependent on the presence of potassium and substrate in the incubation media and was almost completely inhibited by an addition of 10 mM ouabain to the incubation media.

Plasma cells are widely distributed in inflamed periodontal tissues, the adjacent periodontal ligament and nearby alveolar bone spaces, of old rats (20 and 27 months) raised on a conventional diet in a normal laboratory environment. Electron microscopy revealed three morphologic types (or perhaps stages) of these cells based on the arrangement and content of the granular endoplasmic reticulum. Close contact between plasma cells and other cell types, such as lymphocytes, macrophages and fibroblasts, were commonly observed. It is suggested that plasma cell infiltration is a widespread and prominent feature of naturally occurring periodontitis in old rats, resembling the condition known to exist in humans, monkeys and dogs. The occurrence of large numbers of apparently fully differentiated plasma cells in otherwise normal alveolar bone marrow is discussed.

The effect of a proline analog, L-azetidine-2-carboxylic acid (LACA), on protein matrix secretion by odontoblasts and ameloblasts was compared by light and electron microscopic radioautography after injection of 3H-glycine in young mice. LACA inhibited the secretion of dentin matrix with consequent accumulation of 3H-glycine labeled procollagen in the cisternae of the rough endoplasmic reticulum. In contrast, LACA had no apparent effect on ameloblasts as enamel matrix continued to be packaged in the Golgi apparatus and secreted from Tomes' process within 30 min after injection of the radioprecursor. Electron microscopy revealed that LACA did not cause any change in ameloblast ultrastructure but produced a marked alteration of the odontoblast Golgi complex. All odontoblast Golgi saccules and collagen secretion granules disappeared within 2 h after LACA administration. Odontoblast Golgi cisternae, however, appeared not to be affected. These observations confirm previous studies conducted in this laboratory showing that Golgi saccules in collagen-secreting cells are the initial staging areas for the formation of secretory granules. These results also indicate that a close correlation exists between form and function in the Golgi apparatus of collagen-secreting cells.

Permanent canine and molar tooth germs of kittens were processed for thin-sectioning and freeze-fracture replication. Maturation ameloblasts were divided into ruffle-ended (RA), smooth-ended (SA) and intermediate (IA). RA had an extensive distal ruffled border consisting of deep membrane invaginations, forming complicated extracellular channels. Adjacent RA were connected by extensive distal junctional complexes (zonulae occludentes). The SA had flattened distal cell surfaces and few coated and smooth vesicles in the distal cytoplasm. Adjacent SA were connected by proximal zonulae occludentes, but had only maculae occludentes at their distal ends so permitting broad lateral extracellular spaces to communicate directly with the enamel surface. IA near the RA layer had a ruffled border consisting of deep and narrow membrane invaginations and pinosomes filled with granular material. IA next to the SA layer had no ruffled border but had pinosomes that seemed to originate directly from the distal cell surfaces. IA were polarized and connected by proximal and distal junctional complexes consisting of either zonulae or fasciae occludentes and associated gap junctions.

Freeze-dried rat incisors were examined by high-resolution scanning electron microscopy (SEM) combined with energy-dispersive x-ray microanalysis (EDX) for determination of the correlation between the morphology of the enamel organ and the concentrations in the adjacent developing enamel matrix of calcium (Ca), phosphorus (P), and sulfur (S), as well as the Ca/P ratio. In SEM examination of the freeze-dried enamel organ, it was possible to identify the stages of enamel secretion, transition, and maturation, and furthermore to identify ruffle-ended and smooth-ended maturation ameloblasts. EDX analysis of the outer layer of forming and maturing enamel was carried out from the apical to the incisal end at interval points of approximately 50 micron. Ca and P concentrations increased gradually and continuously from the secretion zone to the end of the maturation zone, but never showed a steep rise in any of the zones examined. Maturing enamel overlaid by either ruffle-ended or smooth-ended maturation ameloblasts showed similar Ca and P concentrations. Throughout the outer enamel layer, the Ca/P molar ratio was fairly constant. Sulfur concentration began to decrease in the zone of enamel secretion, and was no longer detected in the middle of the maturation zone.

The administration of colchicine disrupts the normal organization of the Golgi complex and blocks the secretion of collagen precursors in periodontal ligament fibroblasts of the mouse. The fate of the unsecreted collagen precursors contained in Golgi-derived saccules and newly formed dense bodies was followed by electron microscopy. A progressive condensation of saccule content along with phase separation of electron-dense and electron-lucent material was observed. Fusion of saccules with dense secretory bodies gave rise to larger inclusions (zebra bodies; ZB) filled with a combination of electron-dense and electron-lucent material. In some ZB, these materials appeared to polymerize into fibrillar units. The fibrillar units stained with silver methenamine like normal collagenous fibrils. These results suggest that unsecreted collagen precursors accumulate in vesicular compartments within which partial polymerization can occur. This finding may explain some reports of intracellular collagenous fibrils in fibroblasts of pathologically altered connective tissues.

To investigate the mechanisms whereby annular gap junctions in the papillary cells of the enamel organ are degraded intracellularly, continuously growing rat incisors were examined by electron microscopy of routine thin sections as well as for the cytochemical localization of inorganic trimetaphosphatase activity. Routine thin-section analysis revealed small flat or undulated gap junctions, hemi-annular gap junctions between an invaginated cell process and a cell body, and fully internalized cytoplasmic annular gap junctions. Both hemi-annular and annular gap junctions usually contain various organelles and/or inclusions, such as mitochondria, endoplasmic reticulum, ribosomes, vesicles, and lysosomes in the cytoplasm confined by the junctional membranes. Annular gap junctions are sometimes fused with vesicular or tubulovesicular structures. Cytochemistry of inorganic trimetaphosphatase activity revealed an intense enzymatic reaction within a system of tubular structures and round or oval dense bodies. Both structures are believed to correspond to primary lysosomes. A part of the Golgi apparatus also shows a weak reaction. Although hemi-annular gap junctions never show enzymatic reaction, annular gap junctions sometimes contain reaction products throughout their interior cytoplasm and inclusions. Fusion of annular gap-junctional membranes with reaction-positive tubular structures is also observed. In one instance, revealed in serial sections, an annular gap junction was encircled entirely by a reaction-positive structure. These results suggest that cytoplasmic annular gap junctions are formed by endocytosis of hemi-annular gap junctional membranes from the cell surface and then degraded intracellularly by lysosomal enzymes.

Affinity purified antibodies to plasma fibronectin were used to localize fibronectin in the connective tissues of inflamed and noninflamed beagle gingiva. In noninfiltrated gingival connective tissue, fibronectin was demonstrated in the basement membrane beneath gingival epithelium and around blood vessels as a uniform and intensely stained band about 3 to 10 micron thick. Fibronectin was also distributed throughout the connective tissue in association with collagen fibrils as a more diffuse, less intensely stained pattern. The inflamed gingiva included in this study was characterized by proliferation of epithelial pegs, heavy infiltration of plasma cells and loss of collagen within the subepithelial connective tissue. In these sites, fibronectin was present as an intensely stained band around blood vessels and at the crest of connective tissue papillae nearest the sulcular space. The fibronectin in the basement membrane beneath the epithelium appeared diminished and less uniformly distributed. A delicate network of fibronectin was present around plasma cells and the remaining collagen fibers.

Mouse iodinated epidermal growth factor (EGF) was localized by light and electron microscopic radioautography in basal cells of oral epithelium, papillary cells of the enamel organ, periodontal ligament fibroblasts, preodontoblast precursor cells, and preosteoblasts of the alveolar bone of 13-day-old Sprague-Dawley rats. The specificity of binding in these cells was suggested by an observed reduction of about 90% in the labeling when excess unlabeled EGF was injected along with the 125I-EGF. In contrast, fully differentiated cells, such as ameloblasts, odontoblasts, and osteoblasts, were only poorly labeled. Quantitative analysis of the light microscopic radioautographs revealed that the papillary cells had the highest level of labeling (5.5 grains per 100 micron 2 of cell area). The significance of the rather high labeling of the preosteoblasts of the alveolar bone and the fibroblasts of the periodontal ligament is unknown. However, the well-known effect of EGF in producing precocious eruption of teeth may be a consequence of an effect on these two cell types.

[3H]-fucose utilization by odontoblasts was studied by light and electron microscopic radioautography. At 10 min after injection, fucose label was concentrated in the Golgi area. By 20-30 min, there was a progressive decline in Golgi labelling with label present at the plasma membrane, terminal web, odontoblast process and predentine matrix. At 4 h, the predentine and the predentine-dentine junction were heavily labelled. At the ultrastructural level, Golgi labelling at 10 min was mostly localized to cisternal elements and at 20 and 30 min secretory granules and dense bodies were also labelled. Most of the silver grains observed in the terminal web were associated with microfilaments near the plasma membrane. In the predentine, the matrix itself accounted for 23.0 per cent of the label at 4 h and the plasma membrane of the odontoblast process accounted for 19 per cent. The results indicate that odontoblasts, in addition to secreting glycoproteins into the dentinal matrix, also continuously manufacture glycoproteins for incorporation into the cell surface, the lysosomal system and the terminal web.

The formation of acellular cementum and the deposition of [3H]mannose-labeled extracellular matrix were studied in 14-day-old Sprague-Dawley rats. The sequential events of cementogenesis and periodontal ligament formation observed by light and electron microscopy were described from the stage of an intact root sheath to postcementogenesis. Ultrastructural examination of cementoblasts and periodontal ligament fibroblasts revealed [3H]mannose labeling of the Golgi apparatus at 10 minutes, collagen secretion granules at 30 minutes, and the extracellular matrix beginning at 30 minutes. The extracellular matrix between cementoblasts and dentin was heavily labeled at 1 and 4 hours. Newly formed principal fibers of the periodontal ligament were also heavily labeled at 4 hours. Fully differentiated cementoblasts exhibited the largest sectional profiles and the highest number of silver grains per unit area of cytoplasm. The morphologic and radioautographic data suggest that during the formation of acellular cementum, the cementoblast phenotype is expressed for a short period of time, after which cementoblasts appear to mix with the fibroblasts of the periodontal ligament.

Ultrastructure and three-dimensional architecture of the papillary layer and associated capillaries in the enamel organ of 2-3-month-old kittens were examined by means of routine thin sections, freeze-fracture, and scanning electron microscopy of the tissues digested by HCl-collagenase and of vascular corrosion casts. Outwardly, the papillary layer formed gently sloping upheavals, but did not show prominent papillary ridges. The papillary cells were characterized by a high concentration of intramembranous particles on the plasma membrane P-face, by numerous hemi-annular gap junctions between the cell process of one papillary cell and the cell body of another host cell, and by annular gap junctional vesicles in the subsurface cytoplasm. Some annular gap junctions appeared partially degenerated. These findings led us to speculate that these annular gap junctions are produced by the endocytosis of gap junctional membranes from the cell surface into the subsurface cytoplasm. Capillaries were distributed on the enamel organ within shallow furrows between the papillary upheavals. A part of these capillaries penetrated deeply into the enamel organ but did not contact the ameloblasts. The endothelial walls of the capillaries were pierced with many endothelial fenestrations, especially when facing the papillary layer. The endothelial cell also contained numerous micropinocytotic vesicles throughout its entire cytoplasm. These findings suggest that the papillary cells and associated capillaries are highly specialized for transport of solutes and molecules between the vascular region and the enamel organ during the phase of enamel maturation.

Migration of mitochondria and modulation of Ca-ATPase activity in secretory ameloblasts were investigated ultrastructurally and ultracytochemically by using lower incisors taken from normally fed, 30-hr-fasted, and calcium (Ca)-loaded rats. In normally fed rats, almost all mitochondria were localized in a narrow infranuclear compartment between the nucleus and proximal cell webs of secretory ameloblasts. In 30-hr-fasted rats, a prominent migration of many mitochondria into the supranuclear region of the cells was noted. Mitochondria returned to the infranuclear compartment and seldom appeared in the supranuclear region when fasted rats were Ca-loaded by transcardiac perfusion with physiological Ca solution. Normally, the mitochondria of secretory ameloblast exhibited moderate Ca-ATPase activity along their inner membranes. This mitochondrial Ca-ATPase was decreased by a 30-hr fast and became prominent again after Ca loading. Plasma-membrane Ca-ATPase was demonstrated in the entire cell surface of secretory ameloblasts. An especially abundant reaction was found along the invaginated cell surface of the Tomes process. This Ca-ATPase also became very weak and was almost abolished from the Tomes process after fasting, but Ca loading caused reappearance of an intense Ca-ATPase activity on the entire cell surface, including along Tomes's processes. These results suggest that 1) mitochondrial localization in secretory ameloblasts is influenced by the Ca concentration of the extracellular milieu, and 2) the level of mitochondrial and cell-membrane ATPase activity is responsive to the concentration of extracellular calcium.

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.