title: Structural analysis of reactionary dentin formed in response to polymicrobial invasion.
abstract: In response to microbial invasion of dentin odontoblasts secrete an altered calcified matrix termed reactionary dentin (Rd). 3D reconstruction of focused-ion-beam scanning electron microscopy (FIB-SEM) image slices revealed helical tubular structures in Rd that contrasted with regular cylindrical tubules characteristic of dentin from healthy teeth and affected so-called physiological dentin (Pd) lying exterior to Rd. This helical structure in Rd provided effective constriction of tubule lumen diameter that formed a barrier to bacterial advance towards the dental pulp. SEM of resin cast preparations revealed altered extension of odontoblast processes through Rd. The distribution of key mineral elements was studied by combination of 3D reconstruction of focused-ion-beam based X-ray microanalysis (FIB-EDS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). There was a marked redistribution of calcium and phosphorous in Rd together with an increase of diffusely deposited magnesium compatible with the mineral deposition phase of synthesis of this altered matrix. Changes in tubule structure and mineral content characteristic of Rd are consistent with reduced hardness and lower elastic modulus reported for this matrix. Findings provide insight into the unique structure of Rd synthesised as a primary response to infection.
authors.affiliation: Institute of Dental Research, Westmead Millennium Institute and Westmead Centre for Oral Health, Westmead, Sydney, New South Wales, Australia. ncha1431@uni.sydney.edu.au
authors.forename: Nattida
authors.initials: N
authors.lastname: Charadram
authors.forename: Christine
authors.initials: C
authors.lastname: Austin
authors.forename: Patrick
authors.initials: P
authors.lastname: Trimby
authors.forename: Mary
authors.initials: M
authors.lastname: Simonian
authors.forename: Michael V
authors.initials: MV
authors.lastname: Swain
authors.forename: Neil
authors.initials: N
authors.lastname: Hunter
mesh_terms: D000328:Adult; D003804:Dentin / Q000648:ultrastructure*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D009804:Odontoblasts / Q000382:microbiology* / Q000648:ultrastructure; D017550:Spectroscopy, Fourier Transform Infrared; D055815:Young Adult