Dental Hypotheses

ORIGINAL HYPOTHESIS
Year
: 2017  |  Volume : 8  |  Issue : 1  |  Page : 23--26

A possible explanation for tissue separation observed in histological sections after regenerative periodontal therapy


Firas Kabartai, Alyaa Al Homsi, Thomas Hoffmann 
 Department of Periodontology, Medical Faculty Carl Gustav Carus, TU Dresden, Dresden, Germany

Correspondence Address:
Firas Kabartai
Department of Periodontology, Medical Faculty Carl Gustav Carus, TU Dresden, Fetscherstr. 74 / 01307 Dresden
Germany

Abstract

Introduction: Tissue separation after regenerative periodontal therapy is a common histological observation which is thought to be an artifact. However, several articles have indicated that it can be a serious problem directly related to the weak attachment of the newly formed cementum. The Hypothesis: Tissue separation after periodontal regeneration can be the consequence of losing the fibrous attachment from the cement line between new cementum and the root surface. Evaluation of the Hypothesis: A comparison was made between the cementum–dentin junction, the cement line after root resorption and the cement line after periodontal regeneration because they represent the only means by which the body binds the cementum to root surface. After losing the fibrous attachment from the cement line, the stresses may concentrate at the coronal part of the regenerated tissue leading to the development of tissue separation at that level.



How to cite this article:
Kabartai F, Al Homsi A, Hoffmann T. A possible explanation for tissue separation observed in histological sections after regenerative periodontal therapy .Dent Hypotheses 2017;8:23-26


How to cite this URL:
Kabartai F, Al Homsi A, Hoffmann T. A possible explanation for tissue separation observed in histological sections after regenerative periodontal therapy . Dent Hypotheses [serial online] 2017 [cited 2017 Mar 23 ];8:23-26
Available from: http://www.dentalhypotheses.com/text.asp?2017/8/1/23/202027


Full Text

 Introduction



The current research efforts are devoted mostly to develop new materials that help the human body regenerate the lost periodontal tissues rather than to study the nature of the attachment, by which the newly formed periodontal tissues bind to the treated root surface. Therefore, periodontal regeneration still represents a major problem; the newly formed cementum is often separated from the treated root surface. This tissue separation has been almost always interpreted as an artifact, mainly due to tissue processing for paraffin embedding which can lead to shrinkage alternations. However, Bosshardt et al. concluded that this tissue separation is not an artifact because it has also been observed in resin-embedded specimens, always in the most coronal portion of the regenerated tissues. Moreover, tissue separation after regenerative periodontal therapy develops regardless which material is used (e.g., membrane, bone graft, Emdogain) and does not depend on whether the root surfaces have been exposed surgically or because of periodontitis.[1],[2],[3],[4],[5],[6],[7],[8]

To find the reason behind the development of tissue separation after regenerative periodontal therapy, the following adhesive interfaces between cementum and root surface were compared:

The cement line which is formed after regenerative periodontal therapy.

The cement line which is formed due to the reparative process after root resorption.

The cementum–dentin junction.

The cement line after periodontal regeneration, where tissue separation develops, has the following properties:[2],[5],[7]

It contains an interfacial, electron-dense, slightly mineralized material which is thought to be made up of non-collagenous proteins.

It does not have a collagenous content.

On the other hand, the cement line after root resorption has a similar structure to the cementum–dentin junction. Both represent a slightly mineralized linkage zone that contains high concentrations of non-collagenous proteins and a fibrous attachment between the mineralized tissues.[9],[10],[11],[12],[13]

The non-collagenous proteins

Proteoglycans

They are negatively charged molecules that get trapped and crowded between collagen fibers. Because they occupy only a fraction of their possible hydrodynamic domain, they gain the ability to attract water and generate an osmotic swelling pressure which is restrained by the stiffness and tensile forces of the collagen fibers. Therefore, the proteoglycans together with collagen fibers can act as a hydrogel in reducing the stresses.[14],[15],[16]

Small integrin-binding ligand, N-linked glycoproteins

Bone sialoprotein and osteopontin are the most abundant small integrin-binding ligand, N-linked glycoproteins (SIBLINGs). They play a major role in mineralization because bone sialoprotein can induce mineralization and osteopontin can inhibit it. The existence of bone sialoprotein and osteopontin at the same time may help to control the process of mineralization and the size of the formed crystals.[17],[18] Moreover, both bone sialoprotein and osteopontin are directly involved in the adhesion because they can bind not only to collagen fibrils but also to hydroxyapatite crystals.[8] This is also supported by the fact that the selective removal of the non-collagenous proteins from the cementum–dentin junction results in the separation of cementum from dentin.[9]

The fibrous attachment

Although many studies found that the fibrous attachment in both the cement line and the cementum–dentin junction is confined to limited areas,[12],[13],[19] they were using the polished sections whose technique of preparation could damage the collagen fibrils. However, the recent studies on the cementum–dentin junction have used the ultrasections observed under wet condition and found a true fibrous attachment (i.e., bundles of collagen fibrils) between cementum and dentin.[20] Therefore, both the cement line and the cementum–dentin junction can act as a fibrous joint between the mineralized tissues just the same as the periodontal ligament [Figure 1],[21] but they additionally show a degree of mineralization which may aim to support the collagen fibrils in their function because they cannot be regenerated or even repaired compared to those in the periodontal ligament.{Figure 1}

 The Hypothesis



Tissue separation, which is observed in the histological sections after regenerative periodontal therapy, can be the consequence of losing the fibrous attachment form the cement line between the newly formed cementum and the treated root surface.

 Evaluation of the Hypothesis



The absence of the fibrous attachment from the cement line after periodontal regeneration indicates that the collagen fibers were degraded after they had suffered from tearing:

Either under stress concentration due to a deficiency in hydrogel function but with normal attachment strength of collagen fibers.

Or under physiological stresses due to a weak attachment of collagen fibers.

In both the cases, the collagen fibers will not be seen anymore at the histological examination because they can be regenerated neither in the cement line nor in the cementum–dentin junction, but how can the reason be defined more accurately?

Stresses that collagen fibers experience in the cement line or in the cementum–dentin junction can be the same as the stresses in the periodontal ligament. They are tensile stresses at the coronal part of the root and compressive stresses at the level of root apex.[22],[23] If there were a failure in the hydrogel function due to a defect either in the quality or in the quantity of the non-collagenous proteins, collagen fibers would have been degraded under stress concentration first at the level of root apex because they can tolerate tension but not compression.[24] Moreover, being designed to accommodate tension, collagen fibers at the coronal part of the root may have still been in function even under stress concentration. These results contradict the facts that tissue separation always develops at the coronal part of the regenerated tissues and has no collagen fibers within [[Figure 2]a-[Figure 2]c].{Figure 2}

Therefore, it is most likely that there was a weak fibrous attachment in the cement line so the collagen fibers tore along the whole length of cement line even under physiological stresses and degraded later to leave the noncollagenous proteins alone in the cement line.[2],[5] After the degradation of collagen fibers, the function of proteoglycans as a hydrogel will be considerably affected because the collagen fibers obtain the network that entraps proteoglycans in a hydrodynamic domain smaller than that they need, which helps the proteoglycans to attract water and generate an osmotic swelling pressure. In other words, the absence of the fibrous attachment from the cement line after periodontal regeneration will not only affect its function as a fibrous joint but also its function as a hydrogel so that this cement line has no more function, but how can this lead to tissue separation at the coronal part of the cement line?

The absence of the cementum–dentin junction (which means the absence of its functions) results in stress concentration at the coronal part of the periodontal tissues.[25] Similarly, the absence of a functional cement line after periodontal regeneration can result in stress concentration at the coronal part of the regenerated tissues, which may then lead to tissue separation at that level, especially that this cement line depends in its cohesion only on the adhesion obtained by the remaining non-collagenous proteins [[Figure 2]a-[Figure 2]e]. However, the role of non-collagenous proteins in the adhesion should not be underestimated because tissue separation occurs only at the coronal part of the regenerated tissues where the stresses concentrate while the remaining part stays intact depending only on the adhesion obtained by the non- collagenous proteins (mainly bone sialoprotein and osteopontin).

A possible solution to inhibit the development of tissue separation

Root debridement using hand, sonic, or ultrasonic instruments will result in the accumulation of a smear layer on the treated root surface. Smear layer was considered a potential cause for tissue separation and the main reason behind the formation of a bacteria-containing gab between the new cementum and root surface.[1],[4],[26] Moreover, complicated intermingling will not occur between the already calcified collagen fibrils at the root surface and the newly formed ones. This suggests the need for demineralization of the superficial layer at root surface.[1],[9] To remove the smear layer and expose the collagen matrix at the treated root surface, the concept of root conditioning was developed. Nevertheless, it also resulted in tissue separation, implicating a poor attachment quality and suggesting the need for an improvement.[6]

As postulated above, the fibrous attachment in the cement line after regenerative periodontal therapy can be weak. It may, therefore, tear and degrade even under physiological stresses. A weak fibrous attachment can develop if the collagen fibrils at the treated root surface are damaged so that they cannot afford a strong attachment with the newly formed ones. It is true that the collagen matrix at a periodontally-involved root surface can be damaged due to periodontitis. However, in the experimental studies where the periodontal defects were surgically created without the presence of a periodontitis, a negative role of root conditioning can be suspected as it may still damage the structural integrity of collagen.[27]

Using a collagen cross-linker after root conditioning in regenerative periodontal therapy may help not only to restore the structural integrity of the exposed collagen but also to reinforce the fibrous attachment between the newly formed cementum and the treated root surface, thus inhibiting the development of tissue separation. A study that uses nanoindentation techniques to compare the mechanical properties of the fibrous attachment in the following adhesive interfaces (the cementum–dentin junction, the cement line after root resorption, and the cement line after periodontal regeneration with and without the use of collagen cross-linker) is highly recommended.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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