Atomic Force Microscopy Study of Tooth Surfaces M. Farina,* A. Schemmel,² G. Weissmu¨ ller,‡ R. Cruz,‡ ,1 B. Kachar,§ and P. M. Bisch‡ *Departamento de Anatomia, Centro de Cieˆncias da Sau´ de, Universidade Federal do Rio de Janeiro, Rio de Janeiro, R.J., 21941-590, Brazil; ²Angewandte Physik, Universita¨ t Mu¨ nchen, Munich, Germany; ‡Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, R.J., 21949-900, Brazil; and §Section on Structural Biology, NIDCD, NIH, Building 36, Room 5D-15, Bethesda, Maryland 20892 Received July 6, 1998, and in revised form November 24, 1998 Atomic force microscopy (AFM) was used to study tooth surfaces in order to compare the pattern of particle distribution in the outermost layer of the tooth surfaces. Human teeth and teeth from a ro- dent (Golden hamster), from a fish (piranha), and from a grazing mollusk (chiton) with distinct feed- ing habits were analyzed in terms of particle ar- rangement, packing, and size distribution. Scan- ning electron microscopy and transmission electron microscopy were used for comparison. It was found that AFM gives high-contrast, high-resolution im- ages and is an important tool as a source of comple- mentary and/or new structural information. All teeth were cleaned and some were etched with acidic solutions before analysis. It was observed that hu- man enamel (permanent teeth) presents particles tightly packed in the outer surface, whereas enamel from the hamster (continuously growing teeth) shows particles of less dense packing. The piranha teeth have a thin cuticle covering the long apatite crystals of the underlying enameloid. This cuticle has a rough surface of particles that have a globular appearance after the brief acidic treatment. The similar appearance of the in vivo naturally etched tooth surface suggests that the pattern of globule distribution may be due to the presence of an or- ganic material. Elemental analysis of this cuticle indicated that calcium, phosphorus, and iron are the main components of the structure while elec- tron microdiffraction of pulverized cuticle particles showed a pattern consistent with hydroxyapatite. The chiton mineralized tooth cusp had a smooth surface in an unabraded region and a very rough structure with the magnetite crystals (already known to make part of the structure) protruding from the surface. It was concluded that the struc- tures analyzed are optimized for efficiency in feed- ing mechanism and life span of the teeth. r 1999 Academic Press Key Words: tooth surface; atomic force micros- copy; analytical microscopy; biomineralization INTRODUCTION Enamel is the hardest substance of the body because of its high mineral content (92 to 96%). However, it has a relatively low resistance to frac- ture, which is attenuated by the particular arrange- ment of the inorganic components distributed in the form of rods or prisms (Fawcet, 1986). The rods stand upright on the surface of the dentine and run through the whole thickness of the enamel layer. Electron microscopy studies show that the prisms and the interprismatic substance consist of long carbonated apatite crystals (Warshawsky, 1989; Lo- wenstam and Weiner, 1989; Mann, 1997) and small amounts of organic material. The most superficial region of mammalian enamel is composed of a very thin layer of crystals oriented perpendicular to the surface (Boyde, 1971; Costa et al., 1996; Kodaka et al., 1991). Each tooth has a form adapted to its specific function. The organization of the enamel with ‘‘spa- ghetti-like’’ apatite crystals compacted inside the enamel prisms is complicated, but seems to be perfectly adapted to the mechanical requirements for the grinding and crushing of food. The outermost surface of the enamel is covered by the enamel cuticle, which is likely produced by the ameloblasts, and an outer acellular layer, probably derived from the keratinized remnants of the dental sac of the developing tooth (Fawcet, 1986). The organic layer that remains covering the tooth after eruption suffers abrasion with time and is replaced by a thin film of precipitated glycoproteins from the saliva. There are differences between human and rodent teeth—the most evident is the continuous growth of the rodent teeth. Rodent teeth have been used as good biomineralization models (Boulton et al., 1997). 1 Present address: Universidade Santa U ´ rsula, Rua Jornalista Orlando Dantas 59, Rio de Janeiro, RJ., 22231-010, Brazil. Journal of Structural Biology 125, 39–49 (1999) Article ID jsbi.1998.4069, available online at http://www.idealibrary.com on 39 1047-8477/99 $30.00 Copyright r 1999 by Academic Press All rights of reproduction in any form reserved.