New Insights on the Composition and the Structure of the Acellular Extrinsic Fiber Cementum by Raman Analysis.

Yann Delannoy,Benoit Bertrand,Stephan Naji,Olivier Devos,Clara Balsack,Thomas Colard,Guillaume Falgayrac,Guillaume Penel

doi:10.1371/journal.pone.0167316

Abstract

Acellular extrinsic fiber cementum is a mineralized tissue that covers the cervical half of the tooth root surface. It contains mainly extrinsic or Sharpey’s fibers that run perpendicular to the root surface to anchor the tooth via the periodontal ligament. Acellular cementum is continuously and slowly produced throughout life and exhibits an alternating bright and dark pattern under light microscopy. However, although a better understanding of the structural background of acellular cementum is relevant to many fields, such as cementochronology, periodontology and tissue engineering, acellular cementum remains rarely studied and poorly understood. In this work, we studied the acellular cementum at the incremental line scale of five human mandibular canines using polarized Raman spectroscopy. We provided Raman imaging analysis and polarized acquisitions as a function of the angular orientation of the sample. The results showed that mineral crystals were always parallel to collagen fibrils, and at a larger scale, we proposed an organizational model in which we found radial collagen fibers, “orthogonal” to the cementum surface, and “non-orthogonal” fibers, which consist of branching and bending radial fibers. Concerning the alternating pattern, we observed that the dark lines corresponded to smaller, more mineralized and probably more organized bands, which is consistent with the zoological assumption that incremental lines are produced during a winter rest period of acellular cementum growth.

Highlights

Cementum is an avascular and not innerved mineralized tissue that covers the tooth root surface and is continuously and slowly produced throughout life
Raman spectra were acquired from the bright and dark lines, and similar spectra between those incremental lines were revealed in all samples
The Mineral/Organic intensity ratio (Fig 2E), the type B carbonatation (Fig 2F) and Raman images of intensity (Fig 2B–2D) exhibit a pattern that perfectly matches the alternation between the bright and dark incremental lines observed under microscopy (Fig 2A)

Summary

Introduction

Cementum is an avascular and not innerved mineralized tissue that covers the tooth root surface and is continuously and slowly produced throughout life. It is not subject to remodeling processes [1]. Cementum is generally classified into five different categories, which are mainly based on the presence/absence of cementocytes and the nature (extrinsic and/or intrinsic) of the collagen fibers [2,3,4]. The three main types are the Cellular Intrinsic Fibers Cementum (CIFC), the Acellular Extrinsic Fibers Cementum (AEFC) and the Mixed Stratified Cementum, which exhibits lines of cellular and acellular cementum.

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