A light and transmission microscopic study of mechanically exposed monkey pulps: dynamics of fiber elements during early dentin bridge formation

Tertiary dentinogenesis with calcium hydroxide: a review of proposed mechanisms

Calcium hydroxide has been used extensively in dentistry for a century. Despite its widespread use as a pulp-capping agent, its mechanisms of action still remain ambiguous. Understanding its modes of action will lead to a broader understanding of the mechanisms associated with induced dentinogenesis and help in optimizing the currently available agents to target specific regenerative processes to obtain the best possible clinical outcomes. A literature search relating to mechanisms of dentinogenesis of calcium hydroxide up to December 2011 was carried out using pubmed and MEDLINE database searches as well as manual searching of cross-references from identified studies. Resulting suggestions regarding dentinogenic mechanisms of calcium hydroxide range from direct irritating action of the material to induction of release of biologically active molecules. The purpose of this article is to discuss various mechanisms through which calcium hydroxide may induce tertiary dentinogenesis in the light of observations made in included studies.

Immunohistochemical identification of type I and type III collagen and chondroitin sulphate in human pre-dentine: a correlative FEI-SEM/TEM study

AIM

To identify type I- (I-CF) and type III-collagen fibrils (III-CF) and chondroitin 4/6 sulphate (CS) within human pre-dentine by means of a correlative analysis under field emission in-lens-scanning electron microscopy (FEI-SEM) and transmission electron microscopy (TEM).

METHODOLOGY

Human-extracted teeth were obtained and submitted to either a pre-embedding or a post-embedding immunolabelling procedure using monoclonal primary antibodies anti-I-CF, anti-III-CF and anti-CS. Gold-conjugated secondary antibodies were coupled to primary antibodies to visualize labelling under the electron beam. Correlative labelling patterns were obtained for I-CF and CS under both FEI-SEM and TEM.

RESULTS

Field emission in lens-SEM analysis revealed an intricate three-dimensional network of I-CF and CS clarifying the intimate relationship between the two main components of the pre-dentine organic matrix. TEM analysis revealed odontoblasts exhibiting intracellular labelling for CS, which became more intense and diffuse over the pre-dentine organic matrix. The same diffuse immunoreaction was revealed for I-CF, whereas a weak immunolocalization of III-CF was found scattered throughout the pre-dentine layer and over the collagen fibrils.

CONCLUSIONS

Both the pre- and post-embedding immunohistochemical approaches have led to the visualization of CF- and CS-labelling distribution within the pre-dentine layer, adding further knowledge on the elucidation of collagen-proteoglycans interaction in the organic matrix of human dental roots.

Location, arrangement and possible function of interodontoblastic collagen fibres in association with calcium hydroxide-induced hard tissue bridges

AIM

To assess the location, arrangement and possible function of interodontoblastic collagen fibres in association with calcium hydroxide-induced hard tissue bridges by using light and transmission electron microscopy techniques and immunohistochemical staining localization.

METHODOLOGY

Prior to the study, an animal use protocol form was reviewed and approved by the Screening Committee for Animal Research of the Tokyo Medical and Dental University. Exposed monkey pulps were capped with a hard-set calcium hydroxide and histopathologically evaluated at 3, 14, 21, 30 and 90 days, using light microscopy with silver staining and transmission electron microscopy to differentiate structural features of interodontoblastic collagen fibres. In addition, an attempt was made to identify and to differentiate between several types of collagen and fibronectin using immunohistochemical localization techniques.

RESULTS

At 14 days, interodontoblastic collagen fibres were observed extending from the original dentine, passing through the odontoblasts, and consisted of two portions: a thick fibril and a thin fibril. At 21 days, interodontoblastic collagen fibres were seen penetrating into the predentine and becoming incorporated into the mineralized dentine. At 30 days, interodontoblastic collagen fibres reached the cell process. Although interodontoblastic collagen fibres were no longer observed near the odontoblastoid cells at the area of the newly formed tubular dentine, interodontoblastic collagen fibres were observed embedded within the primary formed dentine bridge. Immunohistochemical staining demonstrated type I collagen and fibronectin within the interodontoblastic collagen fibres.

CONCLUSIONS

Interodontoblastic collagen fibres were routinely detected throughout early dentine bridges. Interodontoblastic collagen fibres are thought to be important for initial dentine bridging to induce and support a dentinogenesis framework.

Hierarchy of variables correlated to odontoblast-like cell numbers following pulp capping

OBJECTIVES

Following tooth pulp exposure, pulpal repair is accomplished by dentine bridge secretion by odontoblast-like cells. However, little information is available about the hierarchy of variables, which influence odontoblast-like cell numbers. The purpose of this study was to examine correlations between pulp capping events and odontoblast-like cell numbers.

METHODS

Two hundred and fifty standardised pulp exposed cavities were prepared in non-human primate teeth according to ISO usage guidelines. Exposed pulps were capped with Calcium hydroxide [Ca(OH)(2)], and multi-step and self-etching primer composite resins. Teeth were collected from 3 to 60-days to observe pulp reactions. Statistical analysis was evaluated using analysis of variance.

RESULTS

The hierarchy of variables correlated to odontoblast-like cells were the dentine bridge area (P = 0.0001), time since pulp exposure (P = 0.0001), odontoblast numbers opposite the exposure site (P = 0.0002), and pulp capping materials (P = 0.0313). Other pulp capping variables were found to be less likely to be correlated with odontoblast-like cell numbers.

CONCLUSIONS

The area of dentine bridge formation is directly related to the numbers of odontoblast-like cells, cell activity is time dependent, and the cell numbers are much lower than original odontoblast cells. The time-lag between the appearance of odontoblast-like cells at the site of pulp exposure, and the limited numbers of these cells, explain why pulpal repair is difficult to achieve successfully following pulp exposure.