Smear layer removal with 8% EDTA root conditioning:

Nadir Babay, DDS, MS, DESM
Department of Preventive Dental  SciencesKing Saud University, College of DentistryRiyadh, KSA
 

Root surfaces affected by periodontitis become hypermineralized1,2 and contaminated with endotoxins3 as well as other toxic bacterial products.4 Such surface does not encourage cell attachment or migration which are necessary events for optimal spontaneous periodontal healing.5 It is not possible to decontaminate the periodontitis affected root mechanically using bur or hand instruments,6 since these methods always produce a smear layer covering the healed root surface.7 Lately however, a supersaturated pH neutral etching solution of EDTA has been found to be as effective as low pH etchants with respect to smear layer removal8 and superior in exposing root surface associated collagen9 in both experimental in vitro and in vivo studies.

Cell attachment8 and periodontal healing10 have been shown to be promoted by EDTA etching compared to etching with low pH agents. Of etchants in clinical use, EDTA is the only one which exclusively exerts its demineralizing effect through chelating divalent cations at neutral pH, while phosphoric acid acts through its low pH and dissolves or erodes a mineralized surface.8 Citric acid (pH 1) functions by a combination of these two mechanisms.11

Dentin block preparation

Dentin blocks were prepared from 12 extracted  periodontally involved human teeth. After extraction, the teeth were immediately cleaned and rinsed in distilled water and then stored for 36h at 4oC in distilled water until ready to be used. The dentin specimens were prepared as described by Demirel et al.13  The crown and root coronal to the mid root region were sectioned through the root canal in a plane parallel to the root surface using a diamond disc under water irrigation. The pulpal tissue was removed using a round carbide bur, and the pulpal dentin was disked until smooth and hard. An identification notch was placed on the pulpal root surface. The cementum was removed by water-cooled diamond burs to a depth of at least 0.25 mm, a depth which exceeds the average thickness of human cementum at the midportion of the root.14 Mesiodistal vertical separation cuts, 1 mm apart, and a horizontal cut, released the specimens from the root. Each dentin specimen was about 4x7x2 mm in size. This yielded a total of 48 dentin specimens; 36 experimental and 12 control. 48 blocks were randomly divided into 4 groups and each tooth contributed one block to each treatment group.

The treatment groups were as follows:

Group I: Immersion in 8% EDTA solution for 1 min

Group II: Immersion in 8% EDTA solution for 3 min

Group III: Immersion in 8% EDTA solution for 5 min

Group IV: Control

The control specimens were obtained from the non-chelated (EDTA) treated part of the root  and were soaked in saline.

The following solutions were used for treatment of the root dentin:

1.         Saline (pH 5.1) for control group

2.         8% EDTA dissolved in phosphate buffer                               solution (pH 7.3) for the experimental                                    group

Following conditioning, each specimen was rinsed in distilled water and placed into a well of a 96-well microtiter plate (Honeycombplates, Labsystem) containing glutaraldehyde in cacodylate buffer at pH 7.3.15

Preparation for SEM

All specimens were prepared for scanning electron microscopy (SEM). After fixation dehydration was done in a graded series of ethanol and with 100% acetone as a final step. Each of the sectioned pieces was mounted on aluminum stub, coated in gold with a sputter technique.16 The specimens were examined in the scanning electron microscope (Jeol, Japan) operated at 20 to 25 Kv and with a tilt angle of between 0 and 30 degrees.

Control teeth

SEM examination of control, untreated specimens exhibited a significant amount of grinding debris. It also revealed a thin, mineralized smear layer. Nowhere were the dentin surfaces or any patent dentinal tubules visible (Fig. 1).

 8% EDTA for 1 minute

The surfaces of samples soaked with 8% EDTA for 1min showed partial removal of the smear layer. Remnants of debris were seen in most of the dentinal tubule. However, nowhere were patent dentinal tubules visible (Fig. 2).

8% EDTA for 3 minutes

There were no traces of smear layer on any of the dentin surfaces in any of the test  group. About half of the tubules were plugged  but  the total number of visible tubules opening were higher than in group II (Fig. 3)

8% EDTA for 5 minutes

The smear layer has been described as a layer composed of very small particles of mineralized collagen matrix.17 Studies have suggested that the presence of this smear layer interposed between the root surface and adjacent connective tissue may serve as a physical barrier to the development of a connective tissue attachment to the root surface.18 It has been shown that EDTA treatment of root dentin by the burnishing action results in removal of the smear layer.9

In the current study, surfaces that received only root planing presented an amorphous, irregular coating with little evidence of patent dentinal tubules. This characteristic appearance was probably due to the presence of a surface smear layer . Treatment of dentin specimens with 8% EDTA in three different timings (1, 3 and 5 minutes) resulted in partial or total disappearance of the above mentioned amorphous surface. The dentinal tubules and the dentin between the tubules were affected differently according to the time used.  Application time of 5 minutes showed dentinal tubule orifices more widely exposed than 3 and 1-minute applications suggesting that the smear layer removal is time dependent.

In clinical dentistry, etching of the teeth is performed for different purposes, consequently different etchants are in use. In surgical periodontal procedures, citric acid has been recommended for removing smear layer from root planed surface in order to delay downgrowth of gingival epithelium19 and enhance clinical attachment gain.20 In periodontal therapy, citric acid has been the most commonly used etchant but a recent experimental study has indicated that EDTA may be the etchant of choice.9 According to these authors, etching at neutral  pH (EDTA) for 20 seconds preserved adjacent tissue vitality  while etching at low pH (citric acid) necrotized the flap and adjacent periodontium after 20 seconds of exposure in an in vivo animal study.

A recent in vitro study demonstrated that EDTA applied for 3 minutes and citric acid applied for 20 seconds by the rubbing technique were able to remove mineral from the dentin surfaces exposing a matrix structurally resembling collagen fibers of the unmineralized predentin.8

The purpose of this study was to explore the possibility of obtaining an acceptable smear removing effect using three different timings of 8% EDTA applied by the soaking technique to the root dentin.

The 5 minutes passive application completely removed the smear layer and exposed the dentinal tubul while the 3 minutes application was significantly more effective than the 1 minute application with regard to smear layer removing capacity. However, the 3 minutes application partially exposed the dentinal tubules while the 1 minute application showed occluded dentinal tubules.

The present result regarding the EDTA use are in contrast with recently produced results.8 The authors claimed that 20 seconds of rubbing the root dentin with EDTA was enough to remove the smear layer. The present findings suggest that 5 minutes passive application of 8% EDTA on the root dentin is adequate.

The differences are mainly due to the different modes of application used in this study. As it is difficult to standardize the rubbing technique used in the BlomlÖf study, the passive method by soaking the dentin specimen into the 8% EDTA solution was used in this study. Wen et al 21 in an in vitro study, evaluated the effects of citric acid (pH 1.0) application techniques on freshly extracted teeth and concluded that "it may be undesirable to apply citric using excessive pressure by the rubbing technique". Also, they found that with the rubbing technique, the exposed dentin may often be masked creating a "smear" layer with obliterated tubules. These observations are further supported by another study.22 In this respect, it appears reasonable to assume that the longer exposure times would enhance the smear removing effect. A longer etching may thus be of value only if a more profound effect on the dentin surface is desired, thus assuring the complete removal of smear layer as shown by Trombelli et al.23  While it has been suggested that EDTA application for 3 minutes may necrotize surrounding cells thus having a negative influence on periodontal wound healing,24 a recent experimental in vivo study did not show any harmful effects on the vitality or healing capacity of the periodontium.11

According to Sterrett,25 a longer application of a conditioning agent on root dentin will result in a chemical and mechanical action enhancing the removal of chemically loosened organic material and surface debris exposing underlying dentin to the demineralized action of the root conditioning. The present findings are in accord with this concept. The 5 minutes application of 8% EDTA was necessary to completely remove the smear layer. EDTA operating at neutral pH appeared to be able to selectively remove mineral from a dentin surface. This type of dentin surface appeared to produce a more biocompatible surface. EDTA may be needed to achieve smear layer removal within a clinically acceptable time period. However, there may be a risk in etching a root planed surface consisting of dentin. The resultant opening of dentinal tubules between the pulp chamber and the periodontium may cause tooth sensitivity or interaction between the pulp tissue and the periodontium according to Ehnevid.26

Based on the findings of this in vitro study, the following conclusions can be drawn:

1.         Saline application on root dentin did not result in the disappearance of the smear layer.

2.         1 minute application of 8% EDTA on root dentin removed the smear layer partially.

The author wishes to express his appreciation to the College of Dentistry Research Center

E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

(CDRC) for the use of the scanning electron microscope and to Mr. Arturo Palustre for his technical assistance.

Address reprint requests to:

Dr. Nadir Babay

PO Box 60169