Ultrastructure of Dental Enamel afflicted with Hypoplasia: An Atomic Force Microscopic Study N. Batina, 1 V. Renugopalakrishnan, 2,3 P. N. Casillas Lavı´n, 4 J. C. H. Guerrero, 4 M. Morales, 1 R. Gardun˜ o-Jua´ rez, 5 S. L. Lakka 3 1 Departamento de Quı´mica, Universidad Auto´noma Metropolitana-Iztapalapa, 09340 Me´xico DF, Mexico 2 Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA 3 Department of Biomedical Engineering, Florida International University, Miami, FL 33174, USA 4 Facultad de Odontologı´a, Universidad Nacional Autonoma de Me´xico, 04510 Me´xico DF, Mexico 5 Centre de Ciencias Fı´sicas, Universidad Nacional Auto´noma de Me´xico, 62210 Cuernavaca, Morelos, Mexico Received: 10 May 2003 / Accepted: 16 June 2003 / Online publication: 3 November 2003 Abstract. The ultrastructure of the human tooth enamel from a patient diagnosed with hypoplasia (HYP) was investigated using atomic force microscopy (AFM) and compared with the surface of normal human tooth enamel. Hypoplasia is a hereditary defect of dental enamel in which the enamel is deficient in either quality or quantity. AFM results presented for the HYP tooth enamel clearly demonstrate that the apatite crystal morphology in hypoplasia tooth enamel is perturbed in the diseased state which could result from a defective synthesis of the extracellular matrix proteins, e.g., amelogenin, by the ameloblasts. HYP enamel consisting of loosely packed, very small grains does not present a tendency for association, as in the case of the normal healthy tooth. Indeed, the enamel surface affected by HYP is porous and is made of much smaller grains. In some samples, the HYP part of enamel surface appeared in the form of a point-defect, which we believe may be associated with the early stages of the HYP deforma- tion. Key words: Hypoplasia — Atomic force microscopy — Tooth enamel surface — Surface morphology of tooth enamel — Ultrastructure Hypoplastic type amelogenesis imperfecta (AI) repre- sents a group of hereditary disorders that result in de- fective enamel. The enamel disorders are apparently heterogeneous in their basic structural and chemical defects with a prevalence rate of 1 in 14,000–16,000 re- ported in the literature [1], depending on the specific type of population. There has been at least one report on the prevalence of enamel hypoplasia in Mexican chil- dren [2]. Three major groups of enamel disorders have been classified as hypoplastic (thin enamel), hypocalcified (primary mineralization defect), and hypomaturation (defect in enamel maturation) [3, 4]. The inheritance patterns such as autosomal dominant and recessive, as well as X-linked dominant and recessive, have been re- ported in the literature [5, 6]. The mineral phase in healthy tooth enamel is com- prised of high ordered packing of calcium hydroxyapa- tite (HA) crystallites, more than ten times larger than those of bones, organized into discrete substructure ‘‘prisms’’ in which the individual crystallites are collec- tively oriented with their c-axes essentially normal to the plane of the dentino-enamel junction [7]. It is widely accepted that the tissue-specific proteins of the developing dental enamel, amelogenins, provide the extracellular matrix essential for the formation of the unique enamel mineral phase. Amelogenins [8, 9] form a number of protein species that have been iso- lated, characterized, purified, cloned, and expressed in E. coli. The secondary structure of amelogenin has been postulated to orchestrate the mineralization process in enamel. The precise mechanisms underlying the miner- alization process are not well understood at the present time. However, it is clear that these unique tissue-spe- cific proteins play a central role in amelogenesis. The secondary structure of bovine amelogenin containing a unique b-spiral structure in the core was derived from circular dichroism (CD) [10], Fourier transform infrared (FT-IR) spectroscopic studies, [11], Raman spectro- scopic studies [12] from our laboratory and from mo- lecular mechanics-dynamics refinement from Nuclear Over Hauser (NOE) contacts from 3D NMR studies [13–15]. The 3D structure of bovine amelogenin from multi-nuclear 3D NMR has now been refined (Re- nugopalakrishnan et al., unpublished data). Recently we have also derived the tentative secondary structure of a more soluble mouse amelogenin, M179, from FT-IR studies (Renugopalakrishnan et al., unpublished data) and its thermal unfolding was investigated using CD Correspondence to: V. Renugopalakrishnan; E-mail: renu@ fiu.edu Calcif Tissue Int (2004) 74:294–301 DOI: 10.1007/s00223-002-1045-2 Calcified Tissue International Ó 2003 Springer-Verlag New York Inc.