title: Axonal Degeneration in Dental Pulp Precedes Human Primary Teeth Exfoliation.
abstract: The dental pulp in human primary teeth is densely innervated by a plethora of nerve endings at the coronal pulp-dentin interface. This study analyzed how the physiological root resorption (PRR) process affects dental pulp innervation before exfoliation of primary teeth. Forty-four primary canine teeth, classified into 3 defined PRR stages (early, middle, and advanced) were fixed and demineralized. Longitudinal cryosections of each tooth were stained for immunohistochemical and quantitative analysis of dental pulp nerve fibers and associated components with confocal and electron microscopy. During PRR, axonal degeneration was prominent and progressive in a Wallerian-like scheme, comprising nerve fiber bundles and nerve endings within the coronal and root pulp. Neurofilament fragmentation increased significantly during PRR progression and was accompanied by myelin degradation and a progressive loss of myelinated axons. Myelin sheath degradation involved activation of autophagic activity by Schwann cells to remove myelin debris. These cells expressed a sequence of responses comprising dedifferentiation, proliferative activity, GAP-43 overexpression, and Büngner band formation. During the advanced PRR stage, increased immune cell recruitment within the dental pulp and major histocompatibility complex (MHC) class II upregulation by Schwann cells characterized an inflammatory condition associated with the denervation process in preexfoliative primary teeth. The ensuing loss of dental pulp axons is likely to be responsible for the progressive reduction of sensory function of the dental pulp during preexfoliative stages.
authors.affiliation: Clínica de Odontología Pediátrica y del Adolescente, Universidad de Valparaíso, Valparaíso, Chile Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile.
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile.
authors.forename: M
authors.initials: M
authors.lastname: Lovera
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Universidad de Valparaíso, Valparaíso, Chile Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
authors.forename: O
authors.initials: O
authors.lastname: Schmachtenberg
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Universidad de Valparaíso, Valparaíso, Chile Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile Instituto de Biología, Laboratorio de Microscopía Electrónica, Universidad de Valparaíso, Valparaíso, Chile eduardo.couve@uv.cl.
authors.forename: E
authors.initials: E
authors.lastname: Couve
mesh_terms: D002648:Child; D003481:Cuspid / Q000473:pathology / Q000503:physiopathology; D003782:Dental Pulp / Q000294:innervation* / Q000473:pathology / Q000502:physiology; D006801:Humans; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009186:Myelin Sheath / Q000648:ultrastructure; D009410:Nerve Degeneration; D009412:Nerve Fibers / Q000648:ultrastructure; D012391:Root Resorption / Q000473:pathology / Q000503:physiopathology; D012583:Schwann Cells / Q000502:physiology; D014080:Tooth Exfoliation / Q000473:pathology / Q000503:physiopathology*; D014094:Tooth, Deciduous / Q000294:innervation* / Q000473:pathology / Q000502:physiology
keywords: Schwann cell; Wallerian degeneration; immune system; myelin; neuroplasticity; pain