title: Is hard tissue formation in the dental pulp after the death of the primary odontoblasts a regenerative or a reparative process?
abstract: OBJECTIVE
  Conceptually, two types of tertiary dentine may be produced in response to caries and environmental irritations: "reactionary dentine" that is secreted by existing primary odontoblasts and "reparative dentine", formed after the death of the odontoblasts by proliferation and differentiation of progenitor cells into odontoblast-like cells. Because histologic evidence for tubular dentine generated by newly differentiated odontoblast-like cells is lacking in human teeth, the present study examined pulpal cellular changes associated with caries/restorations, in the presence or absence of pulpal exposures.
  
  
  METHODS
  Ninety-six extracted human teeth were histologically processed and serial sectioned for light microscopy: 65 contained untreated enamel/dentine caries; 20 were heavily restored and 11 had carious exposures managed by direct pulp-capping.
  
  
  RESULTS
  Sparsely distributed, irregularly arranged dentinal tubules were identified from the tertiary dentine formed in teeth with unexposed medium/deep caries and in restored teeth; those tubules were continuous with the tubules of secondary dentine; in some cases, tubules were absent. The palisade odontoblast layer was reduced to a single layer of flattened cells. In direct pulp-capping of pulp exposures, the defects were repaired by the deposition of an amorphous dystrophic calcified tissue that resembled pulp stones more than dentine, sometimes entrapping pulpal remnants. This atubular hard tissue was lined by fibroblasts and collagen fibrils.
  
  
  CONCLUSIONS
  Histological evidence from the present study indicates that reparative dentinogenesis cannot be considered as a regenerative process since the so-formed hard tissue lacks tubular features characteristic of genuine dentine. Rather, this process represents a repair response that produces calcified scar tissues by pulpal fibroblasts.
  
  
  CONCLUSIONS
  Formation of hard tissue in the dental pulp after the death of the primary odontoblasts has often been regarded by clinicians as regeneration of dentine. If the objective of the clinical procedures involved is to induce healing, reduce dentine hypersensitivity, or minimise future bacteria exposure, such procedures may be regarded as clinical success. However, current clinical treatment procedures are not adept at regenerating physiological dentne because the tissues formed in the dental pulp are more likely the result of repair responses via the formation of calcified scar tissues.
authors.affiliation: Private Practice, Cetraro, Italy. Electronic address: dricucci@libero.it.
authors.forename: Domenico
authors.initials: D
authors.lastname: Ricucci
authors.affiliation: Private Practice, Cetraro, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Loghin
authors.affiliation: Department of Endodontics, New York University, New York, USA.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Lin
authors.affiliation: Division of Endodontology, University of Connecticut School of Dental Medicine, Farmington, CT, USA.
authors.forename: Larz S W
authors.initials: LS
authors.lastname: Spångberg
authors.affiliation: Department of Endodontics, College of Dental Medicine, Georgia Regents University, Augusta, GA, USA. Electronic address: tayfranklin7@gmail.com.
authors.forename: Franklin R
authors.initials: FR
authors.lastname: Tay
mesh_terms: D016923:Cell Death / Q000502:physiology; D003094:Collagen / Q000648:ultrastructure; D003731:Dental Caries / Q000473:pathology; D003782:Dental Pulp / Q000166:cytology / Q000502:physiology; D003784:Dental Pulp Calcification / Q000473:pathology; D003785:Dental Pulp Capping / Q000379:methods; D003789:Dental Pulp Exposure / Q000473:pathology; D003793:Dental Restoration, Permanent / Q000379:methods; D003809:Dentin, Secondary / Q000502:physiology* / Q000648:ultrastructure; D005347:Fibroblasts / Q000473:pathology; D006801:Humans; D009804:Odontoblasts / Q000473:pathology*; D011671:Pulpitis / Q000473:pathology; D012038:Regeneration / Q000502:physiology; D014945:Wound Healing / Q000502:physiology
chemical_list: D003094:Collagen
keywords: Dental caries; Odontoblast; Pulp capping; Reactionary dentine; Regenerative dentinogenesis; Reparative dentine; Tertiary dentine