Calcified Tissue Research

Calcif. Tiss. Res. 24, 239-242 (1977)

9 by Springer-Verlag 1977

Further Observations on the Fine Structure of Cellular Cementum from Deciduous Teeth of Pigs Randi Furseth Department of Anatomy, Dental Faculty, University of Oslo, P.b. 1052 Blindern, Oslo 3, Norway

S u m m a r y . Examination o f microradiographs from the deciduous teeth o f pigs revealed large lacunae or radiolucent zones close to the c e m e n t o - d e n t i n a l junction. Electron microscopic studies of the ground sections showed areas or irregularly shaped zones devoid of mineral and filled with collagen fibers. In the wide unmineralized zones, spherical clusters of crystallites were noted. Several cementum lacunae bordered by a b r o a d rim o f unmineralized collagen fibers were noted and some lacunae also contained zones of a moderately electron dense material. This material did not yield a diffraction pattern, while the mineralized part of the cementum gave the diffraction pattern typical of hydroxyapatite. Key

words:

Cementum

--

Lysis

--

Electron

microscopy.

purpose of the present investigation was to study the radiolucent zones using electron microscopy.

Material and Methods

Microradiographs of ground sections from 47 deciduous teeth from five pigs of the Norwegian land race in the age group 9-15 weeks were examined (Furseth, 1970). The teeth were fixed in 2.5% cacodylate buffered glutaraldehyde, rinsed in the buffer and then placed in 1% cacodylate-buffered osmium tetroxide at pH 7.2 for 2 h. Thereafter, the teeth were dehydrated in a graded series of acetone solutions and embedded in Vestopal W. Based on microradiographic findings, ground sections of ten teeth from five pigs which demonstrated radiolucent areas or zones close to the cemento-dentinal junction were selected and ultrathin sections were cut with a diamond knife on an LKB Ultrotome III and floated on 2% acetone adjusted to pH 7.5 with NaOH. The time which the sections were in contact with water was reduced as much as possible to avoid dissolution of mineral (Boothroyd, 1964). Some sections were stained with uranyl acetate and lead citrate. Stained as well as unstained sections were examined in a Siemens Elmiskop la electron microscope. Selected area electron diffraction was performed on the unstained sections.

Introduction

M a n y investigators have described osteolysis, and it appears established that osteocytes can resorb both the inorganic and organic components of bone, particularly if they are stimulated (Belanger et al., 1963; Baylink et al., 1972). It is claimed that a similar process (cementolysis) m a y take place in cellular dental cementum (Belanger, 1968; Henrikson, 1968; Jande and Belanger, 1970). Examination of microradiographs from the deciduous teeth o f pigs revealed large lacunae or radiolucent zones close to the cemento-dentinal junction. Similar findings in the teeth o f rats, mice, and dogs were interpreted as cementolysis (Belanger, 1968; Henrikson, 1968). The

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Results

The microradiographs of ground sections of the deciduous teeth showed cellular cementum with large lacunae or radiolucent zones close to the c e m e n t o dentinal junction (Fig. 1). The corresponding electron mierographs showed areas or irregularly shaped zones devoid o f mineral (Figs. 2, 3). The zones varied in size from n a r r o w (Fig. 2) to wide (Fig. 3) and were usually filled with collagen fibers (Fig. 4), but small areas devoid of fibers were also noted. In the wide unmineralized zones, spherical clusters of crystaUites were noted (Figs. 3, 4). Several cementum lacunae bordered b y a b r o a d rim of unmineralized collagen fibers were observed. Some lacunae also contained zones of a m o d e r a t e l y electron

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R. Furseth: The Fine Structure of Cellular Cementum

Fig. 1. Microradiograph of ground section from the deciduous teeth of pigs showing cellular cementum (C) and dentine (D). Close to the cemento-dentinal junction (CDJ) large lacunae or radiolucent zones (arrows) can be noted, x85 Fig. 2. Electron micrograph showing stained section of the inner layer of the cementum. Close to the cementodentinai junction (CDJ) two lacunae (L) containing zones of a moderately electron dense material can be noted. Further peripherally a narrow unmineraiized zone (arrows) with an irregular course is seen. Numerous small unmineralized areas can also be noted, x 2800 Fig. 3. Electron micrograph of stained section showing cellular cementum. Close to the cemento-dentinal junction three lacunae (L) are seen. Further peripherally unmineralized areas as well as a wide unmineralized zone containing spherical clusters of crystallites can be noted. Higher magnification of outlined areas is shown in Figures 4 and 5, x 2000

dense material (Figs. 2, 3, 5), and small areas of electron dense material were also observed in connection with unmineralized collagen fibers (Fig. 5). The electron dense material was observed both in unstained and stained sections. Electron diffraction carried out on unstained sections showed that the mineralized part o f the cementum gave the diffracton pattern typical o f hydroxyapatite, while the electron dense material did not give a diffraction pattern.

Discussion Cementolysis was first described by Belanger (1968). He examined the cementum in rats and mice and

found large cementocytes and large or confluent lacunae, particularly close to the c e m e n t o - d e n t i n a l junction. Bordering the dentin, he also observed empty lacunae. Administration of p a r a t h y r o i d extract gave an increase in the size of the lacunae, particularly those at the c e m e n t o - d e n t i n a l junction, and this was thought to be due t o resorption by the cementocytes. Belanger (1968) did not c o m m e n t on the fact that the most pronounced effect of p a r a t h y r o i d administration was observed in the area where empty lacunae were found. In a later electron microscopic study, Jande and Belanger (1970) also describe incorporated epithelial cells in large irregular lacunae at the cemento-dentinal junction. The authors did not observe cementolytic activity by the epithelial cells, but

R. Furseth: The Fine Structure of Cellular Cementum

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Fig. 4. Higher mangification of area outlined in Figure 3. Spherical clusters of crystallites (SC) and bundles of unmineralized collagen fibers (CF) with varying orientation can be noted, x 19,000 Fig. 5. Higher magnification of area outlined in Figure 3. The peripheral part of the lacuna contains numerous unmineralized collagen fibers (CF). Between the collagen fibers spots of electron dense material (arrows) can be seen. A zone of electron dense material (ED) can also be noted. The electron dense material was also observed in unstained sections, x 19,000

offered no explanation as to how the large irregular lacunae originated. Henrikson (1968) observed radiolucent areas close to the cemento-dentinal junction in dogs with secondary hyperparathyroidism, and interpreted this observation as cementolysis. The unmineralized areas and zones observed in the present study contained typical unmineralized collagen fibers and, thus, the images observed do not conform to those described for cementolysis and may, in fact, represent regions which failed to mineralize during cementogenesis. This shows that large unmineralized areas close to the c e m e n t o dentinal junction are not necessarily signs of cementolysis. Lester (1969a, b) studied the formation of rat molar cementum and found that, particularly in the

apical areas, large parts of Hertwig's root epithelium were incorporated in the cementum close to the cemento-dentinal junction. This observation also indicates that caution should be exercised when radiolucent areas close to the cemento-dentinal junction are interpreted. The nature of the electron dense material observed in some of the cementum lacunae is difficult to assess. The fact that it was observed in the unstained sections and was of high electron density indicates that it m a y be of an inorganic nature, and the fact that it did not give a diffraction pattern indicates that, if mineral, it is in an amorphous phase. Depending on the preparative procedures used during the processing of tissues for electron microscopy, there is always a chance of gain or loss of mineral (Boothroyd, 1964; 1968;

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Bonucci, 1967; Furseth, 1969). It may be, therefore, that the electron dense material observed in the lacunae is an artifact and does not represent the situation in vivo.

References Baylink, D., Wergedal, J.E., Sipe, J.: Increased osteocytic bone resorption in vitamin D-treated rats determined by means of mercury porosimetry. Clin. Res. 20, 540 (1972) Belanger, L.F.: Resorption of cementum by cementocyte activity ("Cementolysis"). Calcif. Tissue Res. 2, 229-236 (1968) Belanger, L.F., Robichon, J., Migicovsky, B.B., Copp, H., Vincent, J.: Resorption without osteoclasts (osteolysis). In: Mechanisms of hard tissue destruction (R.F. Sognnaes, ed.), pp. 531-556. Washington D.C.: Am. Ass. Advanc. Sci. 1963 Bonucci, E.: Fine structure of early cartilage calcification. J. Ultrastruct. Res. 20, 33-50 (1967) Boothroyd, B.: The problem of demineralisation in thin sections of fully calcified bone. J. Cell Biol. 20, 165-173 (1964)

R. Furseth: The Fine Structure of Cellular Cementum Boothroyd, B.: Sources of artefact in preparations of bone for electron microscopy. In: Electron microscopy 1968. (S.D. Bocciarelli, ed.) Pre-congress abstracts 4th Europ. reg. Conf. Vol. II. pp. 429-430. Rome: Tipografia Poliglotta Vaticana, 1968 Furseth, R.: The occurrence of atypical crystals in human cellular cementum fixed in phosphate-buffered fixatives. Archs. Oral Biol. 14, 1419-1427 (1969) Ftirseth, R.: A microradiographic, light microscopic and electron microscopic study of the cementum from deciduous teeth of pigs. Acta Odontol Scand. 28, 811-831 (1970) Henrikson, P.A.: Periodontal disease and calcium deficiency. Acta Odontol Stand. 26, Suppl. 50, 1-132 (1968) Jande, S.S., Belanger, L.F.: Fine structural study of rat molar cementum. Anat. Rec. 167, 439-464 (1970) Lester, K.S.: The incorporation of epithelial cells by cementum. J. Ultrastruct. Res. 27, 63-87 (1969a) Lester, K.S.: The unusual nature of root formation in molar teeth of the laboratory rat. J. Ultrastruct. Res. 28, 481-506 (1969b)

Received June 30, 1976 / Accepted February 17, 1977

Further observations on the fine structure of cellular cementum from deciduous teeth of pigs.

Calcified Tissue Research Calcif. Tiss. Res. 24, 239-242 (1977) 9 by Springer-Verlag 1977 Further Observations on the Fine Structure of Cellular Ce...
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