Optical Microscopic, Microradiographic and Scanning Electron Microscopic Observations of Some Dens Invaginatus

Original J. Showa Univ. Dent. Soc. 15: 7-16, 1995 Optical Microscopic, Microradiographic and Scanning Electron Microscopic Observations of Some Dens Invaginatus Tetsuo KODAKAand Shohei HIGASHI SecondDepartment of Oral Anatomy,Showa University School of Dentistry 1-5-8 Hatanodai,Shinagawa-ku, Tokyo, 142 Japan (Chief:Prof. ShoheiHigashi) Abstract: The simple or branched invaginations of dens invaginatus were histologically observed by using 6 ground sections (2 molars and 4 incisors). In all the teeth, the invaginations have hypoplastic enamel showing a variable thickness and an irregular outline. The relatively thick enamel irregularly arranged the Retzius lines and prismless structures were present in the innermost layers besides the surface layers. In 4 teeth, enamel-free areas were partially found on the dentin surfaces, and afibrillar cementum occasionally covered the enamel-free areas as well as the enamel surfaces. The dentin of a molar tooth had giant tubules between the dichotomously branched invaginations and other giant tubules opened into the invagination floor. Some dentinal tubules in the terminal regions had abnormal structures similar to the Tomes' granules adjacent to the invaginations of the 2 molar teeth. In all the incisor teeth, a seam line of dentin fusion or a slit line succeeding to the dental pulp cavity was present in the dentin under the linguogingival ridge. Thus, the gross formation of dens invaginatus also causes the invagination to form locally abnormal structures, especially in the enamel regions; although some findings have been previously reported. Key words: dens in dente, invagination, prismless enamel, afibrillar cementum, enamel-free area It is strongly suggested that most of the dens lar cementum25) including cementicle-like globular in dente, recently named dens invaginatus, are structures26) on the floors, although the dentin formed by the abnormal infolding of an enamel under the fissures generally shows a normal organ towards the dental papilla during a tooth structure. In human teeth, prismless structures germ stage'-8). The gross morphology of dens often occupy the thin cervical ename123,27), and invaginatus has been reported with intra-oral afibrillar cementum showing a periodic lamina- radiographs1-3,5-18), radiographs of thick-section frequently attaches to the cervical region26,28). tioned') or intact extracted teeth3,5-8,12,15,16,19), The cervical enamel is formed by ameloblasts decalcified sections3,4,6,7,11,13,20), ground sec- differentiated in the last stage of amelogenesis21). tions1-3,5,7,8,11,18,19), and contact microradiographs In this preliminary report of the invaginations of ground sections?). On the other hand, there of some dens invaginatus, the fine structures were are only a few histological observations of the observed by microradiography and several micro- invaginations',5-7). scopies. As is well known, the deep fissures of human molar teeth, somewhat similar to the invagina- Materials and Methods tions, are the native structures formed by ameloblasts differentiated in the later to the last stage Six human teeth possessing a simple or of amelogenesis21). The fissure enamel has usu- branched invaginations, namely dens invaginatus, ally prismless structures in the surface layer22-24) were collected from the ground sections of 440 and the deep fissures occasionally deposit afibril- teeth with a transmitted-light microscope (Nikon, 8 昭和歯学会雑誌第15巻第1号 20 kV after coating with an about 15-nm-thick platinum-palladium layer in an ion sputtering apparatus (IB-S, Eiko, Japan). Results Figure 1 shows the ground section of a small invagination of a tooth, probably the third molar. The invaginated enamel was very thin and partially free on the dentine surface. Several cementicle-like globular structures (AFC) were seen on the enamel surface. No caries areas were seen in the invagination, In the dentin surrounding the floor of the invagination, some dentinal tubules in the terminal regions had abnormal structures similar to the Tomes' granules in the root surface dentin. Figure 2a shows the ground section of a molar tooth possessing dichotomously branched invaginations. Both the branches showed an irregular 1 outline and enamel-free areas were partially observed on the dentin surfaces (Figs. 2b, c). No Fig. 1 A small invagination of a molar tooth. caries areas were seen in the invaginations. The Transmitted-light micrograph. V: invagina- relatively thick enamel occasionally showed prism- tion. E: enamel. D: dentin. EFA: less structures in the innermost layers as well as enamel-free area. AFC: cementicle-like in the surface layers. In Fig. 2b, these prismless globular structure (afibrillar cementum in layers gradually proceeded to the thinner enamel Fig. 2f). AT: abnormal structures of itself. In some parts of the periperal regions of dentinal tubules. the invaginations, unidentified material and cementicle-like globular structures were seen (AFC in Japan), which had been made out in the routine Figs. 2b, c). The dentin between the branched dissection course at the School of Dentistry, invaginations had giant tubules, and other giant Showa University, Tokyo. These 6 teeth (2 tubules opened into the enamel-free floor of molars and 4 incisors) were ground again with the left invagination (Figs. 2d, e). Some dentinal grindstones up to about 100 pm in thickness, The tubules in the terminal regions had abnormal ground sections were observed with several structures similar to the Tomes' granules under optical microscopes including transmitted light the left invagination (Fig. 2d). (Nikon), polarized light (Olympus, Japan), and Figures 2e and 2f show the SEM images of the differential interference contrast (Nikon). After left invagination shown in Fig. 2a after EDTA the contact microradiographs of the ground etching. The SEM image (Fig. 2e) revealed the sections were prepared with a soft X-ray irradia- complex area of the enamel and dentin as com- tion apparatus (Softex, Japan), the ground planes pared with the transmitted-light micrograph (Fig. were polished with 5- and 0.3-pm alumina on 2c). The unidentified material and cementicle- polishing cloths and then cleaned ultrasonically like globular structures as shown in Figs. 1, 2b, in distilled water. This was followed by etching and 2c were clearly distinguishable from the with 2 % EDTA at pH 7.2 for 15 to 30 min, rinsing enamel by SEM (Fig. 2f). The material showing in running water, dehydrating with ethanol, and a periodic lamination on the ground plane etched drying with a critical point of CO, in a critical with EDTA, evaluated as afibrillar cementum, point dryer (HCP; Hitachi, Japan). The EDTA- covered the enamel-free dentin as well as the etched planes were observed with a Hitachi S-430 enamel surface (Fig. 2f). scanning electron microscope (SEM) operated at Figure 3a shows the microradiograph of a main 92acbd 平成7年 3月 Fig. 2 a-d Dichotomously branched invaginations of a molar tooth. Transmitted-light micrographs. LV and RV: left and right invaginations. E: enamel. D: dentin. EFA: enamel-free area. PLE: prismless enamel. AFC: unidentified material or cementicle-like globular structure (afibrillar cementum in Fig. 2f). AT: abnormal structures of dentinal tubules. GT: giant tubule of the dentin. 10 昭和歯学会雑誌第15巻第1号 Fig. 2 e, f The SEM images after EDTA etching in part of Fig. 2a. The region of Fig . 2f is shown with the arrow f in Fig. 2e. LV: left invagination. E: enamel. D: dentin. GT: giant tubule . AFC: afibrillar cementum. invagination with a small branch in an incisor had a seam line under the linguogingival ridge. tooth. These surfaces were attached with dental The innermost enamel besides the surface enamel calculus showing a poreous structure compared occasionally showed prismless structures (Fig. 4b). with the enamel, whereas no caries areas were A similar simple invagination was observed in seen. The dentin under the linguogingival ridge another incisor tooth, although the enamel was had a low mineralized line. Figures 3b—d show partially free on the dentin surface. the SEM images of the invaginations after EDTA Figures 5a and 5b, respectively, show the ground etching. The enamel was partially interrupted on section and the microradiograph of a typical dens the dentin surface of the main invagination when invaginatus in an incisor tooth. In the invagi- dental calculus was removed (Figs. 3b, c). In nation, the dentin-enamel junction, especially the the left side of the main invagination (Fig. 3c), lingual region, showed an irregular line and the afibrillar cementum covered the enamel-free dentin caries-free enamel showed variable thickness. A as well as the enamel surface. Prismless struc- linear small gap was seen in the enamel. In the tures were observed in the innermost enamel. dentin under the linguogingival ridge, a slit line Figure 3d shows the floor of the small branched succeeding to the dental pulp cavity was clearly invagination attached with dental calculus. The seen (Fig. 5b). Figure 5c shows the polarized- abnormal Retzius line was embedded with the both- light micrograph of part of the left-side invaginated side prisms arranged almost at right angles to the enamel. The orientation of the Retzius lines prism directions from each other. The prismless was distinguishable between the enamel regions layer with a fine lamination was seen in the surface divided with the linear gap. Figure 5d shows enamel. the differential-interference-contrast micrograph Figure 4a shows the SEM image of a simple of part of the right-side invaginated enamel. The invagination in an incisor tooth. The caries-free innermost and surface prismless layers were invagination was entirely covered with the enamel observed. Such prismless layers are also seen in although the thickness was irregular. The dentin the SEM image (Fig. 5e). The prismless enamel 2ef 平成7年 3月 11 Fig. 3 a-d An invagination with a small branch of an incisor tooth. a: microradiograph. b-d: SEM images after EDTA etching.

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