Braz J Oral Sci. January/March 2005 - Vol.4 - Number 12 Dental cementum reviewed: development, structure, composition, regeneration and potential functions Patricia Furtado Gonçalves 1 Enilson Antonio Sallum 1 Abstract Antonio Wilson Sallum 1 This article reviews developmental and structural characteristics of Márcio Zaffalon Casati 1 cementum, a unique avascular mineralized tissue covering the root Sérgio de Toledo 1 surface that forms the interface between root dentin and periodontal Francisco Humberto Nociti Junior 1 ligament. Besides describing the types of cementum and 1 Dept. of Prosthodontics and Periodontics, cementogenesis, attention is given to recent advances in scientific Division of Periodontics, School of Dentistry understanding of the molecular and cellular aspects of the formation at Piracicaba - UNICAMP, Piracicaba, São and regeneration of cementum. The understanding of the mechanisms Paulo, Brazil. involved in the dynamic of this tissue should allow for the development of new treatment strategies concerning the approach of the root surface affected by periodontal disease and periodontal regeneration techniques. Received for publication: October 01, 2004 Key Words: Accepted: December 17, 2004 dental cementum, review Correspondence to: Francisco H. Nociti Jr. Av. Limeira 901 - Caixa Postal: 052 - CEP: 13414-903 - Piracicaba - S.P. - Brazil Tel: ++ 55 19 34125298 Fax: ++ 55 19 3412 5218 E-mail: [email protected] 651 Braz J Oral Sci. 4(12): 651-658 Dental cementum reviewed: development, structure, composition, regeneration and potential functions Introduction junction (Figure 1). The areas and location of acellular Cementum is an avascular mineralized tissue covering the afibrillar cementum vary from tooth to tooth and along the entire root surface. Due to its intermediary position, forming cementoenamel junction of the same tooth6-9. Its major the interface between root dentin and periodontal ligament, structural organic components are glycosaminoglycans6, cementum is a component of the tooth itself, but belongs and its functional significance is unknown. The lack of functionally to the dental attachment apparatus, that is, collagen fibrils indicates that this cementum variety has no the periodontium. One of the main functions of cementum function in tooth attachment. is to anchor the principal collagen fibers of the periodontal ligament to the root surface, but it also has important adaptative and reparative functions, playing a crucial role to maintain occlusal relationship and to protect the integrity of the root surface. Until recently, knowledge of the development and the general structure of the periodontium was limited to morphological information, although, during the last decade, rapid progress has been made in understanding the molecular and cellular biology of periodontal tissue development and regeneration, including cementum. Dental cementum is unique in various aspects: it is avascular and not innervated, does not undergo continuous remodelling like bone, but continues to grow in thickness 1 throughout life . In contrast with these specific histological Fig. 1. Acellular cementum (arrow). Notice that acellular afibrillar characteristics, it appears not to be specific at the cellular cementum overlaps the cervical end of the enamel. This is the most and molecular level2. Unlike dentine and enamel, where there common relationship between the two tissues. Unstained, 100x are clear differences in the proteins present in these tissues and the factors regulating their functions when compared Cellular intrinsic fiber cementum contains cementocytes with bone, cementum has not demonstrated to express embedded in a collagenous matrix of intrinsic collagen specific proteins, appearing to contain factors in common fibers (Figures 3 and 4). These collagen fibers are oriented with bone and to be developmentally controlled by similar mostly parallel to the root surface and course in a circular factors2-3. fashion around the root6. A fast matrix deposition by the There is accumulating histological evidence that cementum cementoblasts, which occurs in the space between is critical for appropriate maturation of the periodontium, deviating epithelial cells of Hertwig´s root sheath and the both during development and as well as that associated dentinal surface appears to be the reason for the with regeneration of periodontal tissues3. Recent studies incorporation of some of the cementoblasts10-11. Cellular have contributed to an understanding of the possible intrinsic fiber cementum is found in the furcation, on the involvement of some of the molecular factors in cementum apical root portion, in old resorption lacunae and in root regeneration4, but cementogenesis, on a cell biological fracture sites, playing an important role as an adaptative basis, continues to be poorly understood. The aim of this tissue that brings and maintains the tooth in its proper chapter is to give a comprehensive review about some position and also participating in the repair process, important aspects of this unique tissue, including its although it has no immediate function in tooth varieties, development, structure, composition, attachment1,6. Only cellular intrinsic fiber cementum can regeneration and potential functions. repair a resorptive defect of the root in a reasonable time, due to its capacity to grow much faster than any other Types of cementum type of cementum10. Traditionally, cementum has been classified as cellular and Acellular extrinsic fiber cementum is mainly found on acellular, depending on the presence or absence of cervical and middle root portions, covering 40% to 70% of cementocytes in its structure. Another classification the root surface. On anterior teeth, it may also cover part of includes intrinsic or extrinsic fiber cementum, depending the apical root portion, since its apical extension increases on the presence of collagen fibers formed by cementoblasts from posterior to anterior teeth. It serves the exclusive or by fibroblasts, respectively5-6. Mainly three cementum function of anchoring the root to periodontal ligament. The types differing in these aspects are distinguished in humans. acellular extrinsic fiber cementum matrix consists of a dense Acellular afibrillar cementum covers minor areas of the fringe of short collagenous fibers that are implanted into enamel, particularly at and along the cementoenamel the dentinal matrix (glycosaminoglycans) and are oriented 652 Braz J Oral Sci. 4(12): 651-658 Dental cementum reviewed: development, structure, composition, regeneration and potential functions about perpendicularly to the root surface6. When they become elongated and eventually continuous with the principal periodontal ligament fibers they are called Sharpey´s fibers. Although acellular extrinsic fiber cementum is a quite constantly growing tissue, appositional lines (Figure 2) represent the periodical deposition of cementum layers in frequent association with an abrupt change in the direction of Sharpey´s fibers12. Moreover, as can be deducted from faster growth rates on distal (4.3mm/year) than on mesial (1.4mm/year) root surfaces13, acellular extrinsic fiber cementum has the potential to adapt to functional alterations such as mesial tooth drift. In humans, the extrinsic fibers traverse and intermingles the intrinsic fiber cementum variety either sporadically or densely arrayed in parallel; this mixed Fig. 3b: Higher magnification of previous image. Notice that the cementum is referred to as cellular mixed stratified canaliculi of cementocytes (*) have a tendency to be polarized and extend toward the periodontal ligament side of the root. Unstained, 400x cementum6. Origin and development of cementum Based on the observation that populations of cementoblasts are phenotipically distinct, some authors defended the possibility that acellular and cellular cementum have different developmental origin14. Some studies15-16 suggested that cementoprogenitor cells arise from the dental follicle proper, which is of ectomesenchymal origin (that is, a derivative of the cranial neural crest). However, as pointed out by Thomas & Kollar17, labeled cementoblasts could also be of epithelial origin, since cells of the enamel organ, which give rise to HERS, also incorporate 3H- thimidine prior to transplantation in mice. More recent ultrastructural and immunohistochemical studies support, Fig. 2: Acellular cementum. At a higher magnification, notice indeed, the hypothesis that cementoblasts originate from that this type of cementum has incremental lines of growth (arrow) which are oriented parallel to the root surface. Tomes’ granular epithelial cells of HERS when they undergo an epithelial- layer (*)and dentinal tubules (thin arrow) are also visible in the mesenchymal transformation18-20. There is increasing field. evidence that Hertwig’s epithelial root sheath is actively involved in the formation of both acellular and cellular cementum. Diekwisch21 (2001), published an extensive literature review on early cementogenesis and performed a detailed morphological and molecular analysis to illustrate and verify key issues in the current debate about epithelial and mesenchymal contributions to root cementum. The author demonstrated that prior to cementogenesis, Hertwig’s epithelial root sheath disintegrates and dental follicle cells penetrate the epithelial layer to invade the root surface. Other studies confirmed that HERS became disrupted or disintegrated prior to cementum deposition, and visualized how mesenchymal