Dental Sac Research Articles

特異な石灰化物を伴った歯原性粘液線維しゅの１例

In this paper, a 16 year old male case of odontogenic myxofibroma with peculiar calcareous substances in the lower left molar region and mandibular ramus was reported. He had suffered from a swelling without pain in this region. Radiographic examination revealed a multilocular and radiolucent lesion containing a mandibular third molar and uncertain cloudy radiopaque shadows. Boundary of the lesion was radiographically comparatively clear. Extraction of the second molar and removal of the tumor were performed under general anesthesia. The tumor was 6.5×3. 5×4.0cm in size, trancelucent and light brown color, smooth surfaced with soft consistency and cystic lumens containing viscoid fluid.Thin calcareous substances were scattered in the tumor.Microscopically, the tumor consisted of dense fibrous connective and myxomatous tissues. Tumor cells were stellate or spindle shaped, but mitotic figure was not seen. The tumor contained numerous peculiar calcareous substances which varied in size and were of unknown origin. The tumor was diagnosed odontogenic myxofibroma because of the existence of epithelial islands of odontogenic origin and continuation between dental sac of the embedded third molar and tumor tissue. No recurring after treatment.

The use of cranial bone grafts in the closure of alveolar and anterior palatal clefts.

A method is described for harvesting cancellous bone from the diploic space. In our opinion, this is the material of choice for bone grafting alveolar clefts in the 7- to 11-year age group. The procedure could be performed at an earlier age if the maxillary segments are under orthopedic control and in proper alignment. Success of the procedure depends on proper orthodontic preparation of the maxillary segments and careful, complete closure of the soft tissues across the anterior palatal cleft, the nasal lining defect, and the anterior alveolus. Results have been encouraging in terms of bone formation, and tooth migration into the bone graft can be expected if there has been no damage to the dental sac. Closure of the alveolar defect at the time of the primary lip closure would preclude the eventual need for a bone graft, but it cannot be accomplished without early, precise alignment of the maxillary segments if extensive periosteal denudation is to be avoided. The age beyond which periosteal closure alone will be inadequate to provide sufficient bone formation and should be supplemented by a bone graft remains to be established.

Aberrations involving the enamel epithelium in transplanted developing teeth

Structural changes that occurred when unerupted developing permanent teeth in dogs were transferred to other bony crypts or surgically prepared sockets were assessed histologically. The enamel epithelium and pieces of enamel matrix were often displaced from the developing teeth and contained within the dental sac. The epithelium underwent metaplasia, cysts frequently developed, and cementum was formed in moderate quantities when enamel matrix was directly in contact with connective tissues. Development of the crowns did not continue normally, and the teeth did not erupt.

ラット臼歯の多根形成と髄室床の発生に関する研究

A histomorphological and histochemical study was undertaken to clear the first stage development of the root bifurcation and to observe the enzymatic histochemical detections of alkaline phosphatase, acid phosphatase, adenosine triphosphatase and lactate dehydrogenase activity in the multirooted formation and the floor development of the pulp chamber in the upper first molars of rats. The following results were obtained. 1. In rat, the epithelial thickening for the multirooted bifurcation occuring from epithelial diaphragm started to be formed immediately after birth at the three spots on the palatal side and two spots on the buccal side. They gradually grew up into the epithelial interradical process and formed the original type of orifice of root canal after joining. The original type of five orifices of the root canal was completed with the epithelial interradical process at ten days after birth. 2. It was appered that each of the tips of the above-mentioned epithelial interradical processes was fused not with the one directly opposite but with one in interlacing position. 3. In the neighborhood of the center of the basal area of the dental papilla, namely in the places where the floor of the pulp chamber will be formed in the future, the accumulation of the cells in the dental papilla adjacent to the epithelial diaphragm and the epithelial interradical process was seen from about eight days after birth. At about ten days after birth, the odontoblasts differentiated from those cells formed a thin layer of dentin, and the first stage of floor development of the pulp chamber was observed. 4. It appeared that the significant factor of the collateral branch formation of the pulp floor was the surrounding of the blood vessel connecting between the dental sac and dental papilla in the growth process of the epithelial interradical processes. 5. In alkaline phosphatase, the epithelial diaphragm and the epithelial interradical process did not show the enzymatic activity, but the island-like areas with activity in the dental papilla adjacent to the epithelial interradical process in the neighborhood of the center of basal area of dental papilla at six days after birth. 6. From the beginning stage of the formation of the enamel matrix the epithelial diaphragm and the epithelial interradical process showed acid phosphatase activity, but did not show polarity. In the coincidence with the time when the activity appeared in this epithelial diaphragm and the epithelial interradical process, the accumulation of the cells with activity was seen in the dental papilla adjacent to a part of the epithelial interradical process. When the dentin was formed on the epithelial diaphragm and the epithelial interradical process, the activity in the coincident area showed a tendency to decrease and disappear. 7. In adenosine triphosphatase, the activity was seen in the epithelial diaphragm and the epithelial interradical process together with in the stratum intermedium cells predominantly with the intense activity at the tip. When the dentin was formed, the epithelial diaphragm lost the continuity and a band of the activity area disappeared. 8. In lactate dehydrogenase, the epithelial diaphragm and epithelial interradical process showed the intense activity, but did not show polariity. From about seven days after birth, the accumulation of the cells with the activity was seen in the dental papilla adjacent to the epithelial interradical process in the center of the basal area of the dental papilla.

Recombination experiments on the odontogenic roles of mouse dental papilla and dental sac tissues in ocular grafts

First molar tooth germs were dissected from mandibles of mouse embryos 16, 17, 18 and 19 days of gestational age. The tooth rudiments were separated into dental papilla, dental sac and enamel organ after enzymic digestion. These embryonic dental tissues were recombined and grown for 4 weeks in anterior chambers of eyes of homologous adult mice. The removal of the dental sac from recombinations of only dental papillae and enamel organs did not significantly alter the proportion of grafts which formed teeth when compared with those grafts which consisted of all 3 dental tissues. Both groups of recombinants formed teeth in 50–80 per cent of the grafts cultured. The dental papilla and dental sac tissues showed the same inductive activity with the enamel organ with the 16-day-old tissues. However, the dental papilla cells maintained their inductive capacity for a longer period. Whereas 70 per cent of the 16-day-old tissue recombinations of dental sac and enamel organ formed teeth, only 15 per cent of the recombinations of older ages of the same tissues formed teeth.

Hyperkalemia following exchange transfusion

side. Nursing bottle caries classically affects the maxillary incisors and first molars? 2 Since nearly all the infants left the hospital being bottle-fed, caries may have influenced the appearance of the teeth but would not explain the lateralization and the total failure of some teeth to develop. Enamel defects have been related to prenatal and postnatal hypoxic insults? 4 Though this might explain Some of the enamel hypoplasia seen in a number of the children, there should have been a more symmetrical involvement of the teeth. Neonatal hypocalcemic tetany) hyperbilirubinemia, and drug ingestion have been associated with enamel hypoplasia and discoloration, but none of these would result in the localized distribution of the dental defects described. At birth the maxillary central incisors are, on the average~ .the most developed but the enamel is as yet incompletely formed and the root is very rudimentary. The crown of the tooth and its surrounding dental sac are in close proximity to the alveolar mucosa. The follicles of the incisor teeth are quite vulnerable to mechanical trauma to the alveolar process. Any injury to the follicle is likely to disrupt the final development and eruption of the associated tooth. The deciduous canine and molar teeth are less fully developed, further from the mucosal surface, and thus less susceptible to trauma, which is consistent with the findings in this report. Because laryngoscopy is performed from the right side of the mouth and is frequently associated with trauma to the maxillary alveolar ridge from the right-angle flange of the laryngoscope blade, it is likely that such trauma is related to the defective dentition seen in these children. The presence of an oral endotracheal tube may be an additional aggravating factor. Better technique, the development of a laryngoscope blade with a broad, soft flange, and the use of nasal endotracheal tubes may circumvent much of the maxillary alveolar trauma seen following endotracheal intubation.

Dental Sac Collagenase: Demonstration and Initial Characterization

Dental Sac Collagenase: Demonstration and Initial Characterization

モルモット下顎臼歯の組織構造とその発生に関する研究

The structures and developmental process of guinea pig's lower molar teeth were studied histologically using varying developmental stages from 30 fetal days to postnatal 7 days, new-born and adulthood. The results obtained were summarized as follows. 1. The cheek teeth, which were rootless and continued to grow as their occlusal surfaces were worn down, were compound teeth composing of three plates, mesial, distal and central plates. Each plate were covered with the enamel circumference of the dentin from occlusal to basal side, except only the lingual of them which was covered with the primary cement. There were stood between each plate the cartilage cement with which they were fixed strongly. 2. The periodontal membrane between the lingual cement and the alveolar bone showed structure similar to those of the rooted teeth. However, those between neighboring teeth showed characteristic construction to the present animals ; on the surfaces of the enamel there were distributed at almost regular intervals the cement pearls, from which the bundles of Sharpey's fibers were radiated and intersected with those of the opposite side from the lamina propria mucosae of the gingiva to the tip of the alveolar septum. On the surfaces of the enamel among the cement pearls there were arranged distinct layers of epithelial cells from the enamel organ of the basal portion to the oral mucosae, but their appearance varied depending on their location. 3. The Sharpey fiber bundles disappeared after the lapse of sudden loosing and resolving below the lamina propria mucosae of the gingiva. 4. The majority of germinal tissues in the basal end composed of large enamel organ occupied buccal and bilateral side, the dental papilla and dental sac surrounding them. As following toward the upper end, however, another small enamel organ was occurred within the lingual side of the distal dental papilla. Thereby, the distal dental papilla was divided into two parts. Large and small enamel organ were connected with only outer and inner enamel epithelium at the lingual side of the dental papilla. This connection portion were disappeared presently, and then replaced with dental sac, instead of them. 5. The mesial plate was made of the mesial portion of large enamel organ and the mesial dental papilla, the central and distal plates were made of the distal portion of large enamel organ, small enamel organ and two divided distal dental papilla, respectively. As following toward the upper end, the central portion of large enamel organ and small enamel organ were replaced with the dental sac from which the cartilage cement were formed. 6. The cartilage cement was derived from the growth of the cartilage cement pearls, and the cartilage cement pearls were based on the cement pearls. The cell nucleus of the cartilage cement showed almost necrotic degeneration. 7. Each molar teeth were developed with conical two cusps, but at the tip of the cones enamel formation did not take place. By reason of occlusion movement based on some physiological irritation, the conical cusps flattend at birth. Through thus attrition, the central plate became to appeared gradually between the mesial and distal plates. 8. The deciduous premolar showed crown shaped appearance with three cusps. There were seen at the tips of the cusps as free enamel area as the cusps of the molars. Conspicuous absorpting phenomenon was observed in the cervical dentin after 45 fetal days, without nearly forming their roots. 9. Order of these rooted and rootless teeth to erupt was as follows ; pm and M_1 (fetal 50 days), PM and M_2 (fetal 55 days) and M_3 (within a week after birth). By fetal 55 days, deciduous premolar came into shedding.

永久歯歯胚を含む下顎骨有形片の近遠心転換移植に関する実験的研究

As regards to the study on the transplantation of the tooth germ have been made and reported by Kostecka (1968), Lapchinsky & malinovsky (1941), Ijiri & Suganuma (1943), Shapiro & Maclean (1945), Masuda (1959), Kirino (1960), and others. However, study on the transplantation of the mandibular bone block with tooth germ, except for Ijiri & Yamakawa (1959), Toyoshima (1972), as far as the author has read, could hardly be found. Clinically, some cases of fracture of the jaw and face in young patient, we often meet with involved free bone fragment with permanent tooth germ. In such cases, when free bone fragment with tooth germ made combined transplantation, that was interested in odontologically how about healing process may be traced. The author proved to determine and recongnize the attitude of permanent tooth germ and the healing process of mandibular bone block that was immediately transplanted mandibular bone with changing mesial for distal after resection of complete separation of continuity in infant dogs. The study was made by macroscopical, roentgenological and patho-histological courses. The result on this article are summarized as follows. 1. From 3 to 5 days postoperatively, the reactive cells infiltration was appeared in basal part of the dental papilla, and disordered arrangement of the odontoblasts was observed. The blood clots filled the space between the transplanted mandibular bone and the recipient bone edges. 2. From 10 to 14 days postoperatively, the basal part of the dental papilla and dental sac of the tooth germs was melted and disappeared to become cavityzation. The blood clots showed the tendency of organization, and it replaced, more and more, by the fibrous connective tissue. The new bone began to develop along inferior border of the recipient bone. 3. From 21 to 45 days postoperatively, the tooth germ was melted, in the dental papilla, except enamel and dentin and immature bone appeared along surrounding bone tissue following dental sac had been almost disappeared. The new bone began to develop along the inferior border of the recipient bone remarkably, about 30 days postoperatively, new bone trabeculae was shown union with each other in a greater or less degree. 4. About 60 days postoperatively, the dental papilla and dental sac were filled with fibrous connective tissue, but enamel and dentin partially remaind, and there had been replaced by new bone. Also both transplanted bone and recipient bone was shown complete union with new bone, the part of it has been formatived lamellated bone. 5. The last day of experimental about 120 days, the tooth germ was completely disappeared, and transplanted bone was completely replaced by new bone. The new bone which was recipient bone and transplanted bone, was developed into the bone with neary normal structure histologically and roentgenological. Morphologically, experimental side nearly resembled structure comparing to control side except fourth premolar defected. The findings and facts described above, both transplanted bone and recipient bone was shown complete union with the formation of new bone, more and more, they was replaced by normal bone, finally it has been resembled to jaw bone of control side, morphologically and histologically. But to my regret the permanent tooth did not show eruption itself.

Collagen breakdown in relation to tooth eruption and resorption in the dog

Evidence for collagen breakdown was sought in the dental sac and gubernaculum of the second, third and fourth permanent premolars and in the roots and pulp of the second deciduous premolar of 18 to 21-week-old beagle puppies. At this time, processes of tooth shedding and eruption are most rapid. All structures contained enzyme activity which digested collagen in the presence of calcium ions. This activity is believed to be due to collagenase. The activity was negligible in pulp, high in resorbing roots, moderate in all regions of the dental sac and gubernaculum at 20 weeks, and high in these latter structures at 21 weeks. A second proteolytic activity released collagen breakdown products in the absence of calcium ions; this is thought to be a nonspecific action on denatured or partly-degraded collagen. The dental sac and gubernaculum contained large amounts (25 per cent) of collagen susceptible to trypsin. This is believed to represent collagen which has been partly degraded but not yet released from the collagen fibres. These same structures contained 6–9 per cent of salt-soluble collagen and the resorbing roots contained 25 per cent soluble collagen. These soluble forms are believed to reflect extensive and rapid breakdown of collagen.

カイウサギ下顎臼歯の組織構造とその発生に関する研究

The developmental process of mandibular molar teeth was studies histologically using rabbits at its varying developmental stages from 15 fetal days to 30 postnatal days and adulthood. Results were summarized as follows. Histology 1. Each molar tooth was characterized by the presence of a large indentation beginning from the buccal surface and dividing the tooth body into mesial and distal halves which were connected at the middle of the lingual surface. Both halves of the tooth were consisted of greater part of dentin which was filled with an osseous cementum substance which fused itself with the enamel layers of both halves of the tooth. 2. Of the molar teeth examined, the 1st premolar was the largest in size and most complex in structure with two indentations of small size, one incised on the buccal side of the mesial half of tooth and other on the middle of the mesial side of tooth. These indentations were also filled with an osseous cementum substance. 3. In the 1st premolar, the distal half of the crown lacked the enamel layer at distolingual side, but the rest of molars lacked the enamel layer even wider so that the lacked area extended from the middle of the lingual side toward the mesial side of the mesial half of the crown. The cementum substance directly covered the dentin layer in such regions. 4. The structure of the basal end of individual molars except the 1st premolar showed an incorporation of two tooth anlages. This means that, located in the middle of the basal end mesio-distally, there was present the compound enamel organ that is responsible for the formation of early phages of enamel in both distal side of the mesial half and mesial side of the distal half of the individual teeth. The tooth anlage of the mesial half of the 1st premolar was further divided into two parts, representing future cusps. The basal end was devoid of enamel and osseous cementum substances, and instead there was seen the cementblastic tissue, the dental sac. Genesis 1. By 15 fetal days the dental lamellae of deciduous molars (Pm_1, Pm_2) came into existence, and by 25 fetal days hard tissues were seen to be formed in these lamellae. Eruption of the newly formed teeth started by 3 postnatal days. On the other hand, there were seen signs of resorption in the roots of the teeth that were just being formed. 2. By 5 postnatal days, a greater part of the tooth crown came into eruption, but the root that had been well grown was largely resorbed, except its apical part which was yet to be fully completed. As mechanisms of the root resorption, two kinds of process were observed, of which the one acting through the osteoclasts that attacked from outside and the other from inside the root through spontaneous decalcification of the pulpal wall. 3. Over 20 days after birth the deciduous molars began to be shed and these were replaced by the rootless successors (PM_1, PM_2). 4. Order of these rootless teeth to erupt was as follows : M_1 (15 postnatal days), M_2 (20 postnatal days), PM_2, PM_1 and M_3. 5. Through entire process of development as above described, it was observed that no enamel was formed at every cuspal tips for both rooted and rootless teeth.

Histochemical demonstration of succinic dehydrogenase activity during sequential molar development in the Swiss albino mouse.

Applying the ditetrazolium salt (Nitro-BT) method for succinic dehydrogenase, murine molar teeth were studied sequentially from the cap stage of development through the appositional stages of odontogenesis. Reaction-distribution and intensity varied relative to the developmental stage as well as the zone of maturation within a given stage. The peripheral cells of the parent dental lamina exhibited some activity, as did the outer enamel epithelium of the bell stage. During the period of matrix apposition, components of the stratum intermedium, ameloblastic zone and odontoblastic layer region of the dental papilla demonstrated intense enzymatic activity. Cells actively engaged in enamel matrix production demonstrated activity in the basal and distal cell segments. High activity continued in the papillary layer of the enamel organ, as well as in the cells of the dental sac during the postamelogenic period.

The development of the mouse molar periodontium.

The normal development of the tissues of attachment of mouse molar teeth was studied using standard histological techniques. Jaws were taken from mice on the day of birth and each subsequent day, up to and including thirty days after birth, and examined. At birth, the molar teeth were in the late shell stage of development and were enclosed in the dental sac. Subsequent growth of the crown was accompanied by minor changes in the dental sac and alveolar bone. The periodontal ligament began to develop when root formation began. Fibres were laid down in a superior‐oblique orientation which was maintained throughout the prefunctional and functional phases of eruption although changes which gave rise to the cervical fibre groups took place in the latter part of the prefunctional phase. Changes in the alveolar bone and cementum were observed as the tooth became functional. It was concluded that the periodontal ligament was preadapted to function and changes in other tissues of attachment, occurring as the teeth attained functional occlusion, were designed to strengthen the attachment of the fibres to bone and tooth.

乳歯および永久歯歯胚を含む下顎骨有形片の即時再移植に関する実験的研究

As regards to the study on the transplantation of the developing teeth was made and reported by Apfel (1950), Langdon and Young (1953), Fong (1953), Hirakawa (1955), Yamaguchi (1964) and others. On the other hand, a new concept of immediate reconstruction of the mandibule following the surgical resection of the mandibular block was discovered by Marino, Turco and Craviotto (1949). Since exploitation of this article, the supplementary study was made and described by Stuteville (1950), Huebsch and Wickstrom (1951), Nagai (1952), Hirakawa (1952) and others. However, the detailed report as regards to the healing process and fate of the tooth germs that was involved in the replanted mandibular block was not yet published. At this time, the author proved to determine and recognize the attitude of tooth germs, the changes of deciduous teeth and the healing process of mandibular bone block that was immediately replanted mandibular bone after resection of complete solution of continuity in infant dogs. The study was made by patho-histological and roentogenological courses. The results on this article are summarized as follows. 1. Untill about 10 postoperative days, I observed the blood clots filling the space between the replanted mandibular bone block and the recipient bone edges. Reactive cells infiltration were appeared in the dental papilla, the dental sac, the deciduous tooth pulp and the periodontal membrane, added to this findings, I recognized disordered arrangement of the odontoblasts and the inner-outer enamel cells. 2. From 10 to 14 days after the operation, the blood clots showed the tendency of organization. Following this, there was a decrease of the inflammatory reaction in the dental papilla, the pulp and the periodontal membrane. 3. About 21 days after the operation, they showed remarkable regeneration and growing development of Hertwig's epithelial sheath. Inner-outer enamel cells was shown arrangement alike the normal structures. Also, both replanted bone and recipient bone was shown complete union with the formation of new bone. Still more, the replanted mandibular bone block was reconstructed both functionary and morphologically day and days. 4. Thereafter, the tooth germs was growed into the developing teeth accompanied with growth of infant dogs. At the period of 120 days after the operation, the germs were developed into the tooth with a nearly normal structure histologically and roentogenologically and showed the tendency of eruption itself. The findings and facts described above, I believe the new knowledge in this field. The results of this article were beliebed to give the important suggestions on the treatment of jaw bone injury of the children and infants.

The reaction of permanent tooth buds to injury

A study in miniature pigs has shown the histologic features of many of the lesions occurring in permanent teeth as a result of trauma and/or infection, including (1) enamel hypocalcification, (2) enamel hypoplasia, (3) reparative dentine, (4) epithelial proliferation, (5) cyst formation, (6) pulp stones, (7) cementum, bone, and cartilage formation, (8) dilaceration and deformity, (9) root resorption. The reparative ability of the pulp and dental sac are discussed, and the possible surgical consequences are emphasized.

Morphodifferentiation and structure of Hertwig's root sheath in the cat.

The epithelial root sheath in the cat is a multilayered structure that consists of confluent outer and inner epithelial strata enclosing a central layer of cells, which are morphologically like those of the stratum intermedium. A continuous PAS-positive membrane separates the epithelial structure from the developing pulp. On the dental sac surface, the basement membrane is discontinuous, and even absent in some regions. This situation remains until the root and cementum are completely formed.

Similarities Between Dental Microstructures of Scutellid Echinoids and Primitive Vertebrates: ABSTRACT

Studies of scutellid echinoid teeth in living specimens reveal calcite-impregnated dental tissues which closely resemble the hydroxyapatite-impregnated dentin, cementum, and characteristic of primitive vertebrate teeth and scales. In the echinoids, flexible, scalelike plates are added continuously to the aboral base of each tooth, and fuse to form an imbricate series on emergence from the dental sac. A tubular, dentinlike packing develops between the plates, forming most of the keel. At mid-tooth, cementum encloses the dentin and plates, producing a thin surficial zone with distinctive lacunae and canaliculi. Cementum grades into a protective enamel coating (over a consolidated dentin core) where the tooth passes through the epidermis. Among extant invertebrates, only echinoids possess such cellular dental tissue. Although teeth have been reported in Ordovician echinoids, and all modern lantern elements appeared by Late Silurian time, the microstructure of fossil echinoid teeth is unknown. In contrast, the microstructure of Ordovician vertebrate scales and teeth has been studied in detail. The highly evolved state of vertebrate dental tissue in the Ordovician has remained unexplained because of a lack of feasible ancestral forms. Despite chemical differences, the tissue-type structural similarities between modern scutellids and lower vertebrates are remarkable. Microstructures of early Paleozoic echinoid dental tissues may yield some clues to Precambrian ancestral relations between the echinoid and vertebrate evolut onary lines. End_of_Article - Last_Page 833------------

The unusual nature of root formation in molar teeth of the laboratory rat

The cellular cementum phase of root formation in molar teeth of Sprague-Dawley rats was studied in thin sections for transmission electron microscopy. Once cellular cementum formation is established, cells of Hertwig's epithelial root sheath are embedded en masse between cementum and dentine at the advancing root edge. This developmental event is coincident with an alteration in the rates of formation of cementum and dentine; cellular cementum coming both to precede and to be of greater bulk than dentine at the advancing root edge. This mode of root formation does not seem to have been described for other mammals and should be taken into account in studies utilizing rat molar periodontium. Despite the unusual fate of Hertwig's epithelial root sheath, there is evidence of morphological continuity between epithelial sheath and dental sac compartments prior to cementogenesis. The possible roles of epithelial root sheath and of occlusal function in cellular cementum formation are discussed.

Deciduous central incisor tooth development and coronal cementogenesis in cattle

This study documents chronologically, growth and development of the bovine deciduous central incisor tooth from the earliest available stages of odontogenesis to exfoliation. Gross morphologic and histologic studies were carried out on 48 bovine mandibles. Three specimens were obtained at each monthly interval for 8 months of prenatal life and two specimens were obtained at several representative periods of postnatal life until 2 years of age. The following periods of deciduous central incisor tooth formation were defined: histoand morphodifferentiation, 3 months in utero; beginning of apposition and calcification, 4 months in utero; intra-oral eruption, 9 months in utero-birth; root formation complete, 6 months of age; and exfoliation, 2 years of age. Coronal cementum was found on the lingual surface of the deciduous incisor just prior to oral emergence while the tooth was still covered by a layer of tissue called the gingival sheath. Cementum was also first identified on the permanent incisor tooth crown at about 13 months of age. Coronal cementum was never observed overlying the reduced enamel epithelium, but was only seen in areas where the enamel surface of the crowns were exposed to the connective tissue of the surrounding dental sac. Continuity of root and coronal cementum was observed on the lingual surface of the developing permanent incisor tooth, thus suggesting similar cellular precursors for both structures.

Pulpal vasculature as demonstrated by a new method

The present report deals with the use of a new method of demonstrating the vascular architecture of the dental pulp in developing and mature monkey teeth. It has revealed the following: 1. 1. The first blood vessels for the teeth arise as a plexus of vessels encircling the primitive tooth germ in the area of the dental sac. 2. 2. In the developing tooth germ, the vascular plexus of the dental follicle and dental papilla have a common origin and are intimately related. This relationship persists throughout the life of the tooth. 3. 3. The apical foramina carry numerous small and large vessels. The individual vessel increases in size after entering the root canal proper. 4. 4. The veins are located centrally, while arteries are placed peripherally in the root canal. 5. 5. Blood vessels from the periodontal ligament area often curve around the apices and enter the apical foramina. It is probable that this relationship is the primary cause of accessory canals. 6. 6. It is also probable that fusion of the parts of the diaphragm entraps blood vessels and forms accessory canals in the area of the bifurcation. 7. 7. In multirooted teeth the diaphragm divides the many vessels of the dental papilla into pulp canals, thus establishing a double interradicular vascular flow. 8. 8. It is postulated that the anastomoses between the pulpal and the periodontal vascular plexuses is responsible for the extension of disease from one area to another. This factor further explains how inflammatory diseases of the periodontal tissue and gingiva may extend to the pulp and how diseases of the pulp may extend to the periodontal tissues, even without the presence of accessory canals.