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雄ラット20匹を4群に分け,1群は対照群とし,実験群に0.1, 0.5, 2.5 μg/kgの1 α-OH-D3を30日間連続経口投与した.上顎切歯を材料とし,ビタミンD3の象牙質形成に及ぼす影響,特にOsteodentin形成を光顕と電顕で観察した.1)ビタミンD3低投与群では変化はみず,高投与群で著明な形態的変化を認めた.2)象牙質と象牙芽細胞の配列の乱れは最初に基底側1/3にみ,切端に向い周期的に生じる.3)象牙質と象牙芽細胞の配列が乱れる部位では,象牙前質が消失し,退行性の象牙芽細胞が多数出現し一部は不規則な象牙質中に埋入される.4)象牙芽細胞の配列が乱れる部位では象牙芽細胞直下の歯髄側に前象牙質様の構造物が出現し,これはコラーゲン基質から成る.5)上記の前象牙質様構造物に接する象牙芽細胞の近位端には象牙芽細胞の突起が出現し,基質小胞様の構造物が出現する.以上はビタミンD3の過剰投与により,周期的に象牙芽細胞に退行性変化が生じ象牙芽細胞は自ら分泌した基質中に埋入しOsteodentinを形成する可能性を示唆した

The phosphophoryns show anomalous behavior in solution, and are easily degraded during extraction. They appear in varied forms in the teeth of different species and differ in the teeth of the same species in a developmental and age dependent fashion. This set of properties has made the characterization of the phosphophoryns by biochemical means a difficult and controversial subject. Bovine molar phosphophoryn, bPP, has been characterized in detail by a variety of physical methods, and then compared with the PP from other species by DEAE-HPLC, gel electrophoresis, and immunological cross reactivity. The possible existence of a proPP biosynthetic precursor has been investigated by rat incisor organ culture and examination of the 32P and 14C labeled products. These studies all show marked differences in the Mr values for the PP from teeth of different species, even when they are antigenically cross-reactive.

Rats were maintained on drinking water containing different amounts of fluoride (0, 9, 23 45, 68, and 113 ppm) for 70 days. Physico-chemical properties of the incisor enamel were examined after fluoride administration, using contact microradiography, histochemistry, and microhardness tests. The tooth enamel formed during high fluoride exposure showed marked hypocalcification. Much of organic substance in the enamel seemed to have been retained. In addition, the microhardness of enamel showed a marked decrease. These changes were most prominent in the outer region of enamel and were proportional to the concentration of fluoride administered. Such changes following fluoride administration indicated inhibition of enamel maturation, i.e., an inhibition of the progressive depposition of minerals and/or in inhibition of organic matrix withdrawal by ameloblasts. Enamel seemed more affected by fluoride than dentine.

A three-dimensional reconstruction of undemineralized and paraffin wax- or or glycol methacrylate-embedded demineralized rat incisors was made using a computerized histomorphometry. Compared to the undemineralized ground sections, the two demineralizing and embedding procedures grossly distorted the tooth sections. In general, embedding in wax caused shrinkage and in methacrylate caused swelling. Direction and magnitude of the deformation varied in the different tissues of the tooth and its surrounding structures. The distortion was influenced by the ratio between the soft and hard tissues at different cross-sectional levels of the tooth.

— Thirty male rats in groups of ten were given intraperitoneal injections of oxytetracycline and purified calcein (DCAF) every day for 10 d in order to determine whether these fluorescent hard tissue markers per se had any adverse effects on weight development and dentin apposition and mineralization. It was found that oxytetracycline and DCAF in doses of 15 mg/kg, which are the routine doses used by the author in hard tissue studies, do not seem to have any measurable influence on these parameters, while their ability to cause fluorescence is fully satisfying in dentin as well as in bone.

An electron microscopic study of the periodontal ligament of the rat lower incisor revealed the presence of unmyelinated nerve fibres containing high concentrations of mitochondria. The diameter of such fibres varied from 4 to 0.5 μm. The fibres were probably sensory and occurred singly. The cytoplasm of the cells ensheathing the fibres contained rough endoplasmic reticulum which appeared to be dilated whilst the processes showed large numbers of vesicles and occasional desmosomes. Leptomeric type organelles were also present in the ensheathing cells. The significance of the high mitochondrial density is discussed.

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.

ラット切歯歯髄周辺部毛細血管の部位における変化を脱灰操作を行わずに透過型電顕を用いて観察した。切歯基底部の毛細血管は象牙芽細胞層直下に存在しすべて連続型であった。切歯中部の毛細血管は象牙芽細胞層中に進入した後, terminal webの近傍で網目状に分布し, この血管には連続型と有窓型の両型の内皮が見られた。切歯切縁側部の毛細血管は多くが有窓型であり, その窓は象牙質側を向いたものが多かった。切歯歯髄毛細血管は象牙質の石灰化の進行度とか象牙芽細胞の成長にともない連続型から有窓型へ形態変化を起こすことが推測された。この形態変化の移行部には内皮細胞の著しく肥厚した領域が何らかの働きをしているように思われた。

Maxillary incisor pulp cells from male Wistar rats (7 weeks old) were cultured. After the 52nd subculture, cloning was performed twice and a clonal cell line (RPC-C2A) with high alkaline phosphatase (ALP) activity was established. The population doubling time of RPC-C2A cells was 13.7 h, and the mode of the chromosome number was 42. The heat stability of ALP, the effect of the ALP inhibitors, and the ALP polyacrylamide gel electrophoresis pattern in RPC-C2A cells was the same as for the ALP of the isolated dental pulp.

– Vincristine was administered to 60 rats in four groups in doses of 0,1, 0,3, 0,5 and 0.7mg/kg. Histomorphologic investigation of the dentin and odontoblasts in the maxillary incisors after 1, 2 and 3 weeks revealed a moderate to severe disturbance of dentin production in some parts of the incisors. In some of the affected areas the effect seemed to be reversible in that normal-appearing dentin was found pulpal to the dentinal derangements after 2 and 3 weeks. The distribution and severity of the lesions were similar to those previously observed 3 days after injection of the same doses of vincristine.

The effect of adriamycin on rat incisor was investigated 1 day after administration. Rats were injected intravenously with adriamycin at a dose of 5 mg/kg body weight and sacrificed by perfusion with a 2.5% phosphate buffered glutaraldehyde solution. The principal effect of the drug on the incisor was the production of cell degeneration. This was extensive in the apical region, being present along the entire periphery of the dental papilla. In sections examined more incisally, cell degeneration gradually disappeared from the labial portion of the incisor but was present in the lingual portion. This degeneration of cells was not present at the site where mature odontoblasts had differentiated on the lingual surface of the pulp chamber. It appears that the affected cells were early preodontoblasts and the precursors of preodontoblasts. However, as these cells became more differentiated they apparently became more resistant to the drug's effect.

Rat incisors were evaluated radioautographically for metabolic changes induced by high-speed cavity preparation. Label uptake was reduced substantially in those odontoblasts whose processes had been cut; labeling also was diminished in all other areas of the pulp, especially in that area immediately adjacent to the cavity preparation.

The localization of alpha-actinin, tropomyosin, myosin and actin in odontoblasts was examined by fluorescence microscopy using well characterized antibodies and rhodamine-phalloidin. All the reagents labeled the distal end of the cell body in the form of an oval ring with a preferential axis along the tooth axis. This ring was often interrupted. In conventional electron microscopy, microfilament bundles with periodical dense spots were running along the tooth axis at the level of the distal end of the cell body. The periodicity was about 0.6-1.0 microns. It may be possible that this dynamic structure functions to keep odontoblasts in a layer by contracting in an isometric form.

Cuprolinic blue in a MgCl2-critical electrolyte concentration solution allows a larger surface representation of proteoglycans than other methods. Glycoaminoglycans in predentine were ribbon-like structures 14 nm thick and 60 nm long, with radiating filaments (3-4 nm) located in spaces between collagen fibres. Glycoaminoglycans and collagen together displayed longitudinal and orthogonal relationships. The ground substance was slightly electron dense. In dentine, the precipitate was less in quantity and consisted of rounded granules (15 nm in diameter, and filaments/3 nm in width) closely associated with the surfaces of collagen fibres.

The vascular tissue supplying the pulp of the continuously growing and developing rat incisor was quantitatively analyzed in six female rats, weighing approximately 200 gm each. One hour after a single administration of 3H-TdR, 1 μCi/gm body weight, the rats were sacrificed and the lower left jaws excised and processed histologically. Every 20th section was evaluated for venular and arterial count, endothelial cell count, and percentage of labeled endothelial cells. It was found that the proliferative capacity of the vascular tissue of the rat incisor is confined to its most apical 3.0 mm-a zone defined as the vascular progenitor compartment. Daily production of endothelial vein cells and of veins within the progenitor compartment were calculated to be 7,392 cells/day and two veins/day, respectively. Generation time of these cells was found to be 3.56 days. Endothelial cell production within the progenitor compartment provides for the formation of new vessels and for the enlargement and elongation of existing ones. The vessels originating within the progenitor compartment move in an incisal and centripetal direction, while simultaneously undergoing a continuous process of aging, until their ultimate disintegration.

ラットにストロンチウムを経口投与し, 切歯の形成期エナメル質の石灰化進行像の変化を観察した。体重約100gのラットにSrCl2水溶液 (1.25%, 2%, 3%) を3～35日間飲ませ, 屠殺4時間前にテトラサイクリンを注射した。上顎切歯の縦断研磨片からマイクロラジオグラムと螢光顕微鏡法によるテトラサイクリンラベリング像を得, 一部の試料をエレクトロンマイクロプルーブで分析した。 (1) 石灰化度上昇の勾配は基質形成期と成熟期で, また後者では層によって異なる。 (2) 本実験条件では変化は主に成熟期に現われ, 外層, 中層での石灰化度上昇が抑制される。それに対し, 内層でのそれは正常に近く進行する。 (3) テトラサイクリンによるラベリングは, 最内層と内層では正常動物より基底側で, 中層では切端側で消失するが, 外層では低石灰化のままほとんど正常動物と同じ位置で消失する。 (4) 鉄の沈着は正常ではごく幅狭い最表層に限られるが, 実験動物では低石灰化に伴い深層にまで及ぶ。

This study was undertaken to reveal the changes in the fluoride distribution in the developing enamel of rat upper incisors with varying fluoride administration. The work was carried out on four groups of Wistar rats, which received water containing 0, 25, 50 and 100 ppm fluoride, respectively, for 10 weeks. Six sites were selected in the developing enamel, corresponding to the stages of (A) matrix formation, (B) early maturation, (C) late maturation, (D) pigmented enamel in contact with alveolar bone, (E) enamel attached to gingivae and (F) erupted enamel. Five different enamel specimens were removed from each site except site A. The fluoride distribution in each specimen was analyzed from the enamel surface to the EDJ.The following results were obtained;1) The fluoride concentration was invariably highest at the surface and decreased sharply towards the interior of the enamel at every site in both control and experimental groups. The rat incisor enamel had a clear fluoride-gradient from surface to interior.2) The fluoride concentration increased with fluoride intake throughout the tissue and at each stage of development.3) The fluoride-gradient curves resembled each other at the different sites of tooth development. However, the fluoride concentration of the enamel interior was significantly higher at site B than it was at the other four sites.

We studied the distribution of the phosphophoryn present in rat incisors by immunolocalization and histochemical techniques. The polyclonal antibody used reacts with both phosphorylated and de-phosphorylated phosphophoryn. Technical problems encountered in immunostaining and in preparing sections from mineralized dentin were resolved by use of peroxidase-conjugated protein A as the "second antibody" in indirect immunostaining reactions and by surface etching of partially demineralized sections. Staining with anti-rat incisor alpha-phosphophoryn antibody showed light staining over the odontoblasts and proximal odontoblastic processes, no stain over the predentin, dense staining over the intertubular dentin, and no stain over the mantle dentin. In the intertubular dentin the stain intensity was directly related to the distribution of mineral. These findings were directly corroborated by staining with Stains All. The mineralization of dentin and the distribution of phosphophoryn within the dentin may be much less uniform than previously supposed.

The prism pattern in the inner enamel of adult rat incisors was studied with the SEM in unfixed tissues that had been sectioned, ground, polished, and etched. Six different types of aberrations in the prism pattern were encountered: 1. Prism lamellae may be shorter than the mesio-lateral width of enamel. 2. Prism lamellae may deviate from a transverse orientation. 3. Prism lamellae may “fuse” or “bifurcate.” 4. Prisms of two adjacent lamellae may pursue a common course. 5. Prisms may change direction. 6. Variations exist in the outline of transversely cut prism profiles. Aberrations were observed at any distance from the dentino-enamel junction. These observations were used as a basis for an analysis of the movement of ameloblasts during rat incisor amelogenesis. It was concluded that it is physically possible for the ameloblasts to create the observed aberrations as they move along the path of the prisms. However, the aberrations seem to make it more difficult to understand the factors controlling ameloblast movement. Occasionally crystallite bridges connecting adjacent prisms were observed. A configuration resembling a bifurcating prism is presented.

The distribution of systemically introduced 85Sr-labeled tracer microspheres to unexposed and previously exposed rat lower incisor tooth pulps was investigated. Fewer tracer microspheres entered the microcirculation of pulps that had been previously exposed as compared to control unexposed pulps. The presence of large numbers of dilated blood vessels in the apical tissues of teeth with exposed pulps was observed, and it is postulated that these vessels may be operating as arteriovenous anastomoses so that the pulpal microcirculation of teeth with inflamed pulps is bypassed by the tracer microspheres. The possible clinical significance of these findings is discussed.

Using electron microprobe analysis, the surface layer of enamel of rat maxillary incisors was found to contain 10–30% Fe. The Ca and P concentrations in different areas of the enamel surface varied inversely with the Fe concentration. The Ca/P weight ratio was 1.8 in areas containing 10% Fe, but decreased to 1.0 in the most Fe-rich areas. The Fe concentration was highest at the prism boundaries, whereas the maximum concentrations of Ca and P were found within the enamel prisms. The concentrations of Fe in rat incisor enamel are among the highest values reported for any mineralized tissue.

エナメル質形成がおこらないラット切歯舌側象牙質において基質小胞の形態, 由来等を明らかにするために, 微細構造学的, 酸素細胞化学的に検索し, 唇側象牙質と比較検討した。材料は雄ラットの上顎切歯舌側を用い微細構造観察にはゲルタールァルデヒド, オスミウム酸の二重固定を施し非脱灰切片を透過電顕で観察した。酵素細胞化学にはSundstrom and Momstadの変法でCa2+-Mg2+-ATPase活性を, Mayaharaらの方法でALPase活性を検出した。象牙基質の特徴と象牙芽細胞の分化の状態に基づき, 未分化な状態から一層の石灰化象牙質の出現まで便宜的にStage IからVまでを区分した。その結果, 内・外エナメル上皮細胞は象牙基質形成とともに退化しStageVでは周囲結合組織中に埋めこまれ, その多くは消失した。一方, 歯乳頭細胞から分化した象牙芽細胞は遠心端の突起の形態を除けば唇側とほぼ同様であった。象牙基質は膠原原線維の増加とともに, その厚さが増加したが, 線維の配列は基底板と平行であり, 唇側での基底板に垂直に配列する膠原原線維とは異なっていた。基底板には垂直方向に配列する微細線維がみられたが細胞分化に伴いその配列は急速に乱れ, 石灰化開始時にはほとんど消失していた。基質小胞はStage IIから出現し, しだいに数を増すとともに内部の電子密度が高まりStageIIIでは結晶構造を含むものが多くなった。Stage IIIからStage IVにかけては多数の結晶塊が象牙質の基底板側に偏って集積するようになった。これは互いに癒合し, StageVで一層の石灰化象牙質を形成した。以上の過程は唇側とほぼ同様であるが, 基質小胞の形態は唇側ほど多様でない点, また唇側象牙質に出現するいわゆるCTMあるいはstippled materialsに相当する構造はみとめられなかった。Ca2+-Mg2+-ATPase活性の局在は未分化な時期には主として内エナメル上皮細胞にみられたが, これらの反応は象牙芽細胞の分化とともに急速に弱まり, 消失し, かわって象牙芽細胞に活性局在がみられるようになった。基質小胞にも同酵素活性が早期からみられ, その酵素の由来は主として象牙芽細胞に求められるものの一部は内エナメル上皮細胞由来が示唆された。なお唇側においては本酵素の局在はエナメル芽細胞のみにみられ, 細胞分化に伴い酵素活性の局在性が著しく異なることを明らかにし示ていた。一方, ALPaseは唇側とほぼ同様で主として象牙芽細胞に局在しCa2+-Mg2+-ATPase活性とともに基質小胞の象牙芽細胞の細胞膜由来を強く示唆していた。以上の結果から基質小胞の由来とその機能的役割, 特に初期石灰化機構との関連性を論じた。

A Markov random field model is proposed to quantitate and predict the formation of biological patterns. A tissue is viewed in two dimensions as an equally spaced lattice, the sites of which correspond to the centres of the cells. Each cell can be in either of two states: 0 or 1. In the case of a one cell-type tissue, the states represent different characteristics of the cell, e.g. healthy versus malignant. By estimating local interactions, we are able to quantitate the mechanisms inducing pattern formation and even predict the likelihood of specific patterns. Three examples are discussed: (1) alignment of enamel cells in the rat incisor, (2) quantitation of invasive capacity of one cell-type with oespect to another, and (3) sorting-out of two cell-types.

ラット上顎切歯を舌唇方向に圧刺激すると, 咬筋に緊張性興奮反射だけでなく, 同じ方向の圧刺激により抑制反射もまた起こり得ることを明らかにした。この反射効果の逆転は, 咬筋background activityの程度の違いによって生じる。切歯圧刺激により咬筋興奮反射が生じるのは, 咬筋background activityが弱いときであり, 咬筋background activityが強いときは持続性の抑制反射が生じた。また咬筋の反射反応は圧刺激の強さによっても変化した。弱圧刺激では, 咬筋background activityが弱いと興奮反射が起こり, 抑制反射が生じるのは咬筋background activityが強いときであった。強圧刺激では咬筋backgroundが弱くとも興奮反射出現前に持続の長い抑制反射が起こり, 咬筋backgroundの亢進につれて抑制の持続時間が延長した。これらのことから, 咬筋backgroundと圧刺激の強さが変わると, 興奮相と抑制相の現われ方が変化し, 種々の歯根膜顎反射の反応パターンが咬筋に現われることが考察された。

The effect of a diabetogenic dose of streptozotocin on the secretory activity of ameloblasts was investigated in the rat incisor by radioautography. One group of male Sprague-Dawley rats was injected intravenously with streptozotocin in citrate buffer (pH 4.5). One hour later, this group was again injected intravenously with 3H-proline (2 mCi/kg). A control group of animals was injected with 3H-proline only. All the animals were sacrificed in groups of three at 5 min, 1 h, 2 h, 4 h and 8 h after 3H-proline injection by perfusion with 3% phosphate-buffered formaldehyde followed by an additional perfusion with 2.5% phosphate-buffered glutaraldehyde. The incisors were extracted with the jaws, demineralized, and prepared for radioautographic observations and analysis. The principal effects of streptozotocin were as follows: There was an inhibition of 3H-proline incorporation into the secretory ameloblasts at 5 min after injection. This was followed by a larger uptake and a slower passage of the label out of the cells into the enamel matrix than that seen in the control sample. Finally, there was a slower secretion of labeled proteins out of Tomes' processes between 1 and 4 h after injection. Therefore, streptozotocin had a temporary inhibitory effect on the incorporation and secretion of 3H-proline by the secretory ameloblasts of the rat incisor. This effect was present for about 4 h and was completely reversed 9 h after streptozotocin injection.

This paper describes a stage in the development of deciduous bovine incisor enamel in which the tissue becomes extremely porous. This porosity, due apparently to a loss of matrix protein, is subsequently occluded by the acquisition of mineral in a secondary mineralisation phase. The porous zone has been demonstrated by a difference observed in the location of secondary mineral uptake per dry weight of tissue and secondary mineral uptake per volume of tissue. It appears to represent a stage of development analogous to that previously described in the continuously growing rat incisor.

The phosphoprotein of continually erupting rabbit incisors was extracted from decalcified teeth and purified by gel filtration and ionexchange chromatography. Chemical characterization revealed that its composition was very similar to that of rat incisor and bovine molar phosphoproteins. The presence of similar acidic proteins in the dentin of various mammals is consistent with the suggestion that they are involved in the mineralization process.

The immunoreactivity of procollagen types I and III and of collagen type IV was detected in frozen sections of the growing apical end of rat incisor teeth by an indirect method making use of protein A. The sections were exposed to affinity-purified antibodies against these substances. The bound antibodies were then detected by incubation with radioiodinated protein A, followed by radioautography. This immunoradioautographic approach yielded preparations with low background, in which the reactions could be quantitated by counts of silver grains. The distribution of the radioautographic reactions was essentially the same as that previously observed with direct and indirect peroxidase methods, that is, procollagen I antigenicity predominated in odontoblasts and predentin, with minor amounts in periodontal tissue and pulp; procollagen III antigenicity was present in periodontal tissue and, to a lesser extent, in the pulp; and collagen IV antigenicity was restricted to basement membranes. Moreover, grain counts provided quantitative support for the conclusions on the distribution of procollagen I and III antigenicity.

Adult rats were injected intraperitoneally with radioactive calcium and allowed to survive for periods up to 60 min. Animals were then killed and the upper incisors were removed. Soft tissue was removed from the teeth by dissection and with Clorox. Teeth were then coated with photographic emulsion and, after 17 days, the emulsion on the specimens was developed. Black bands of reduced silver indicated areas of radioactivity where calcium had entered the enamel. These bands were separated by narrower bands of non-radioactive enamel. It was judged that calcium did not gain entry into the enamel in these areas of enamel at this particular time. The patterns made by the bands of calcium entry and restriction were similar to patterns which show where striated border and non-striated border maturation ameloblasts cover the maturing enamel. Maturation ameloblasts with a striated border cover a larger area of the maturing enamel than do maturation ameloblasts without a striated border. It is considered that the maturation ameloblasts with a striated border are engaged in calcium entry into the maturing enamel.

Rats were injected subcutaneously with 75 mg or 125mg/100g body weight of strontium chloride and some with tetracycline at the same time. They were killed 4 days later and the maxillary incisors prepared. Two hypomineralized layers were consistently identified in the labial dentine by microradiography. The tetracycline injection labelled the outer edge of the external hypomineralized layer, indicating that this layer represented the dentine-predentine junction at the time of injection. Because of the interval between the external and the internal hypomineralized layers, the internal one seemed to correspond to the base of the odontoblast process at the time of injection. With electron microscopy, the external hypomineralized layer was less electron-dense than normal dentine, but there were no differences between the external hypomineralized and the normal matrices. On the other hand, the internal hypomineralized layer showed a different texture from the external: sparse collagen fibrils seemed to contain substantial mineral; granules stained with ruthenium red among collagen fibrils seemed to represent glycosaminoglycans or proteoglycans.

Thin ground sections (4–10 μ) of rat incisor enamel were prepared in appropriate planes using a modified hand grinding technique. Phase microscopic observations of these sections confirmed the previously defined rod arrangement in the inner layer of enamel, and also demonstrated a high degree of structural orientation in the outer layer of enamel. The initial layer of enamel formed was found to present a morphologic picture which has not been previously defined: a series of inter-connected pillars of enamel on an elevated base which has a “fish net” appearance in tangential section.

SummaryA single injection of cortisone in adrenalectomized rats resulted in a significant increase in number of 3H-thymidine labeled cells in the cervical loop of maxillary incisors at 7 am, 1 pm, 7 pm, and 1 am when compared to untreated adrenalectomized animals. The increase was most pronounced at 1 pm and least significant at 7 pm. Controls showed consistently and significantly fewer labeled nuclei than cortisone-treated adrenalectomized rats at all periods except 7 pm. Again, the most significant increase occurred at 1 pm. In addition, control values were consistently and significantly higher than those of untreated adrenalectomized rats for all periods except those of the 1 pm period. A circadian rhythm in uptake of 3H-thymidine was noted in all groups. Both treated and untreated adrenalectomized animals revealed significantly more labeled cells at 7 am and 1 pm. Control rats showed a cyclic activity which varied between individual cell layers and was less pronounced than in adrenalectomized rats. Th...

Tracheotomy is performed on the experimental animal under intraperitoneally induced pentothal anesthesia. The ligament connecting the two halves of the mandible is cut and one half is exposed. The alveolar bone covering the incisor is partially removed and the tooth is thinned both from the labial and from the lingual side. Preparation of the lingual side is continued so that observations can be made either on unexposed or on exposed pulp. In the former case the circulation, even capillary activity, can be followed through a dentin layer, 15–20 μ in thickness. In the latter case a dentin window is removed to permit visualization of a small area of the exposed pulp. To prevent drying, the pulp is kept moist with Ringer's solution containing 1/2% gelatin. The instruments used are described, especially in so far as they differ from standard instruments. Using the above method, the authors have produced a film “Microcinematography of the Living Dental Pulp”.

Durch regelmasig wiederholtes mechanisches Kurzen des rechten unteren Rattenschneidezahnes wurde eine beschleunigte Eruption hervorgerufen. Nach 15–17 Tagen trat eine Storung der Schmelzentwicklung in Form einer Produktion von kreideweisem statt normal pigmentiertem Schmelz und ein rotbraunliches Hautchen im Bereich des gingivalen Epithelverschlusses in Erscheinung. Dieses Hautchen wurde nach intravitaler Fixierung mit Glutaraldehyd abprapariert und licht- und elektronenmikroskopisch untersucht. Das Hautchen besteht aus mehreren ubereinander gelagerten Zellschichten: aus Ameloblasten, einem typischen Papillarorgan, einer Bindegewebsschicht und aus flachen Deckzellen. Die Ameloblasten im Bereich des Epithelverschlusses befinden sich im Stadium der fruhen, die Ameloblasten des aus dem Epithelverschlus hervorwachsenden Hautchens dagegen im Stadium der spaten Maturation. Die Ultrastruktur des gesamten Papillarorgans last auf eine intensive metabolische Funktion und auf Ionentransport schliesen. Pigmentgranula, die bei normaler Eruption im Maturationsstadium sowohl im Papillarorgan als auch in den Ameloblasten vorkommen, wurden nur im Bereiche des Epithelverschlusses in vaskularen Elementen und in perivaskularen Bindegewebszellen gefunden. Die Oberflache des Hautchens wird von einer schmalen Schicht flacher, organellenarmer Zellen gebildet. Das bei beschleunigter Eruption aus dem Epithelansatz hervorwachsende Hautchen ist ein ektopisches Schmelzorgan, dessen rotbraunliche Farbung von der reichen Gefasversorgung herruhrt.

Data accumulated with the electron microprobe has shown that strontium produces decreased mineralization and that an inverse relationship exists between strontium and calcium contents in the rat incisor tooth. Semi-quantitative data on the strontium, calcium and phosphorus contents of enamel and dentine are presented. Sagittal sections of the high-strontium teeth revealed gradients of increasing strontium contents from the incisal to apical areas with phosphorus contents that were relatively constant.

Thin sections of rat incisor enamel were studied with the electron microscope. Repeating patterns of minute striations, representing the resolution of sets of lattice planes, were observed in images of individual enamel crystals. In cross-sectioned crystals, fringe patterns with 8.2 repeat period representing the 100 planes of the hydroxyapatite lattice occurred. The hexagonal packing of the unit cells in this projection could be demonstrated. Crystals oriented with their c axis in the plane of the section showed, in addition to the 100 planes, a transverse striation pattern with a periodicity of 3.4 , which was considered to represent the 002 planes. Additional spacings were observed, confirming the interpretation of the orientation of the crystals. With this, the molecular arrangement of hydroxyapatite in dental enamel has been demonstrated visually not only in a projection normal to, but also parallel to, the long axis of the crystals.

Using a modification of the flying spot method for estimation of flow velocity in micro vessels, comparative observations were made on arterioles, venules and capillaries in the pulp of the rat incisor by vital microscopy. It was found that stimulation of the sympathetic nerves to the tooth, either at its apex or in the cervical sympathetic trunk, produced marked reduction of flow which was followed by a return to normal velocities at the cessation of stimulation. Direct stimulation of the sympathetic trunk produced very rapid reduction of flow velocity. Changes were also observed in response to administration of anesthetics and other procedures.

– Images formed in the electron microprobe by the current induced in the sample by absorbed electrons illustrated the prism structure and mineral distribution in the enamel of rat incisors. Close to the dentino-enamel junction a 2 micron wide zone of high electron density was found, bordered on the peripheral side by a 2–3 micron wide zone of low density. Chemical concentration profiles indicated that the content of calcium and phosphorus in this zone was lower than in the underlying dentin.

Eruption, attrition, and crown length were measured in impeded and unimpeded rat incisors in hypophysectomized and magnesium-deficient rats. The rate of unimpeded eruption was twice the rate of impeded eruption; this proves that the rates of eruption and attrition are determined by the amount of occlusal contact and the condition of the periodontal ligament.

Rats were injected with 5 mg NaF/100 g or 125 mg SrCl2/100 g. Animals injected once were killed at intervals of 4, 6, 12 and 24 days after injection. Other animals received pairs of injections, separated by intervals of four or nine days. One maxillary incisor from each animal was embedded in methacrylate, sectioned transversely, and microradiographs prepared. The other incisor was demineralized, sectioned, and the sections stained with histochemical methods for polysac-charide-protein complexes. In the microradiographs, the abnormally mineralized layers of dentin produced by the injections became less distinct as they aged. This recovery was detectable in all animals within two weeks after injection. The histochemical changes were less marked, but the weakly stained (hypomineralized) layers of matrix became more nearly normal as recovery occurred. Apparently, fluoride accelerates the maturation (secondary mineralization) of a thin layer of dentin, while both fluoride and strontium inhibit primary mineralization of predentin. In time, mineralization in the hypomineralized layers overtakes the normally mineralized dentin, and the normally mineralized dentin overtakes the hypermineralized layers.

Five Ci /sup 3/H-glycine/g body weight were administered to six rats 30 min prior to, and to six rats 24 h after, exposure to a single head roentgen dose of 500 R. Autoradiographic investigations of the incisors demonstrated that the most radiosensitive cells, the preodontoblasts just prior to dentin production, proceeded to mantle dentin deposition while the cells were partially deprived of their capacity of circumpulpal dentin production. Slightly less sensitive were mantle dentin-producing cells, the injury to which was also reflected as a partial lack of circumpulpal dentin production. The radiosensitive period (500 R) was approximately equivalent to a maximum of 48 h, and a minimum of 24 h. (auth)