Scanning Microscopy Volume 4 Number 4 Article 12 9-16-1990 Fine Structure of the Inner Enamel in Human Permanent Teeth T. Kodaka Showa University M. Kuroiwa Showa University M. Abe Showa University Follow this and additional works at: https://digitalcommons.usu.edu/microscopy Part of the Biology Commons Recommended Citation Kodaka, T.; Kuroiwa, M.; and Abe, M. (1990) "Fine Structure of the Inner Enamel in Human Permanent Teeth," Scanning Microscopy: Vol. 4 : No. 4 , Article 12. Available at: https://digitalcommons.usu.edu/microscopy/vol4/iss4/12 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Scanning Microscopy, Vol. 4, No. 4, 1990 (Pages 975-985) 0891-7035/90$3.00+.00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA FINE STRUCTURE OF THE INNER ENAMEL IN HUMAN PERMANENT TEETH T. Kodaka*, M. Kuroiwa and M. Abe The Second Department of Oral Anatomy, School of Dentistry, Showa University, Tokyo 142, Japan (Received for publication June 24, 1990, and in revised form September 16, 1990) Introduction Abstract In human permanent teeth, Gustafson Using SEM after EDTA etching, the and Gustafson [1967] reported that it mid-corona 1 inner ename 1 of human was often impossible to distinguish permanent teeth was classified into individual prisms in the innermost three regions of the 1st, 2nd, and 3rd enamel which had therefore a more or zones. The 1st zone showing a highly less homogeneous structure by polarized negative birefringence was the innermost light. 10 - 15 µm enamel. This zone consisted By means of ground sections which of arcade and circular initial prisms, were roughly tangential to the surface and the succeeding arcade prisms only. of a human tooth with serial focussing These initial prisms arising transmitted light, Osborn [1968, 1973] perpendicularly to the dentine surface divided the mid-coronal inner enamel resembled pseudoprisms because these into three Zones: I, II, and Ill. Zone I prisms showed a somewhat centripetal was very close to the dentine-enamel arrangement of crystal lites and junction (DEJ), and was a structure less indistinct prism boundaries. The layer of variable thickness up to about succeeding prisms were frequently bent 5 µm from the DEJ; Zone II adjacent to following a faint slit within the prism. Zone I, measuring about 20 µm in The 2nd zone adjacent to the 1st zone thickness, showed variable shapes of measured 20 - 40 µmin thickness. This prisms such as U-shaped, circular, and zone was mainly composed of horseshoe­ spiral or double borders, that is one shaped prisms with EDTA-insoluble prism sheath inside another; and Zone III sheaths in the deep-etched prism measuring up to 50 or 60 µmin thickness boundaries, but the inner-half layer had showed Pattern 2 prisms. In addition, dotted irregular prisms including Boyde [1965, 1976] classified enamel circular, double marginal, and spiral prisms into Patterns 1, 2, and 3 based shapes with the prism sheaths. Prismless on prism shapes and arrangements. structures were rarely seen in the 2nd Osborn [1968, 1970, 1973] believed zone. The 3rd zone was mainly occupied that there were no prism boundaries or by horseshoe-shaped prisms without EDTA­ poorly defined structures in Zone I. irisoluble prism sheaths in the deep­ However, Hinrichsen and Engel [1966] etched pr ism boundaries, a 1 though tuft showed prism boundaries in the innermost prisms in the 3rd zone contained a large human ename 1 adjacent to the DEJ by amount of EDTA-insoluble substances in transmission electron microscopy (TEM) the prisms, interprismatic regions, and of decalcified sections. Swancar et al. the boundaries. [1970] reported by using TEM on the replicas that irregular prism boundaries KEY WORDS. inner enamel, EDTA etching, including circles, concentric circles, scanning electron microscopy, prism and spirals were most frequently arrangement, prism structure, initial observed in the area near the DEJ. prism, irregular prism, EDTA-insoluble Whittaker [1978] used scanning electron substance, prism sheath, enamel tuft, microscopy (SEM) after acid etching and prismless enamel. observed enamel prisms to be closely *Address for correspondence: T. Kodaka associated with the dentine in human The Second Department of Oral Anatomy, teeth, but there was a zone of a 1 tered Showa University, School of Dentistry, enamel about 20 µmin width in contact 1-5-8 Hatanodai, Shinagawa-ku, with the DEJ. Similar images were reported by Kodaka [1978] using SEM Tokyo 142, Japan Phone No. 03-784-8157 after EDTA etching. 975 T. Kodaka et al. Recently, Boyde and Jones [1983], ethanol. The mid-coronal enamel of the Boyde et al. [1988] and Boyde [1989] remaining five teeth were fractured showed prism-free layers close to the transversely. They were ultrasonically dentine in human enamel using cleaned in distilled water and backscattered electrons of SEM. dehydrated with ethanol. Al 1 specimens Fejerskov and Thylstrup [1986] reported (in the inner enamel of a buccal side) that there was an aprismatic layer in were observed under a Hitachi S-430 the innermost ename 1 of a human tooth in scanning electron miucroscope (SEM) SEM of the fractured surface. operated at 20 kV after critical point drying with CO in a Hitachi HCP-2 Nevertheless, Fejerskov and Thylstrup 2 [1986] and Boyde [1989] also showed critical point dryer and coating with a prism-like structures on the dentine 10 - 15 nm thick Pt-Pd layer. surfaces in developing human teeth with SEM. It is generally accepted that EDTA Results etching se 1 ecti ve 1 y d isso 1 ved pr ism boundaries [Hoffman et al., 1969; Using polarized-light microscopy Johnson et al., 1971; Simmelink et al., with the longitudinal ground section of 1974; Kodaka et al. 1989a, 1990b]. On a human permanent tooth, a highly the other hand, the i nner enamel negatively birefringent layer measuring associated with enamel tufts were apt to about 10 - 15 µm in thickness was be insoluble in EDTA [Weatherell et al., observed in the innermost enamel 1968; Weidemann and Eyre, 1971; Kodaka, covering the DEJ (Fig. 1). Prism 1978; Kodaka and Debari, 1982] or the structures were not found in the inner­ tufts only [Amizuka and Ozawa, 1989; half layer adjacent to the DEJ, but Robinson et al., 1989]. In the present frequently seen in the outer-half layer. study, the mid-corona 1 inner human By reflected light through the DIC (Fig. enamel was investigated with SEM after 2), however, prism shapes were faintly EDTA etching. observed in the inner-half layer of the transverse ground plane. When transverse ground planes of Materials and Methods the mid-coronal enamel were observed under the SEM following EDTA etching, Tw enty -two human caries-free the i nner enamel layer (other than permanent premolars extracted from ename l tufts) was roughly classified orthodontic patients aged 9 to 12 years into three regions of the 1st, 2nd, and were fixed in 10 % neutral formaldehyde 3rd zones (Fig. 3). The 3rd zone over for about one week and then were rinsed about 30 - 50 µm distance from the DEJ in running tap water. Three teeth were was occupied by horseshoe-shaped prisms longitudinally sliced and 80 - 120 µm selectively dissolved in the peripheries thick ground sections were prepared and with EDTA etching (Figs. 3 and 4). This observed under an Olympus polarized zone basically showed Pattern 2 prisms. light microscope. Mid-coronal enamel of The 1st zone was the innermost 10 - fourteen teeth was sliced about 1 mm 15 µm enamel covering the DEJ and almost thick at about 10 - 20° angle to the agreed with the highly negatively transverse plane of a tooth with a birefrinqent layer (Fig. 1). In the diamond whee 1, for the purpose of inner-half 5 - 10 µm layer, initial obtaining transverse prism planes in the prisms were found (Figs. 5 and 6). The inner enamel of a buccal side [Swancar interprismatic regions showed a stronger et al., 1970]. The cuspal-side planes resistance to EDTA than the prism bodies were polished with 0.3 µm alumina on although these peripheral regions were polishing cloth and treated with selectively dissolved, so that the ultrasonic cleaning in distilled water. boundaries of the initial and the Three specimens were observed with succeeding prisms indistinctly appeared reflected light through a differential in the 1st zone. These prisms basically interference contrast (DIC) in a Zeiss showed an arcade shape (Figs. 5 and 13 - photomicroscope III after coating with 15), although the prisms were more or 10 - 15 nm thick platinum-palladium (Pt­ less enclosed by the interprismatic Pd) in an Eiko IB-3 ion-sputtering regions. An indistinct circular shape, apparatus in order to increase the arising perpendicularly to the dentine reflected light values. surface, frequently appeared in the area The ground enamel planes of the closely surrounded by a smaller and remaining eleven slices were etched with deeper dome-shaped excavation of the DEJ 2 % ethylene diamine tetraacetic acid (Fig. 6). (EDTA) at pH 7.2 for 15 minutes [Kodaka, The 1st zone showed Pattern 3 1978; Kodaka and Debari, 1982]. This was prisms in the arcade prisms (Figs. 5, followed by rinsing in running tap water and 13 - 15) or Pattern 1 prisms in the for one hour then dehydrating with circular prisms (Fig. 6). Crystallites in the initial prisms tended to show a 976 Structure of human inner enamel Figs. 1 and 2. Light-microscopic photographs of the inner enamel of human teeth. Fig. 1: Polarized-light image in a longitudinal ground section.