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In these two papers the nature of the smear layer will be considered first. The clinical management will then be discussed, and finally, preparation of the dentine surface to receive the new bonding systems will be considered. A subsequent paper will discuss bonding agents.
The smear layer was first described as a debris layer which is left on all cavity walls following tooth preparation. It is composed of an outer contiguous layer of amorphous instrumentation matrix which covers all cavity walls, and a deeper zone of matrix plugs which obturate the cut tubules. Recent scanning electron microscopic (SEM) studies have characterized the smear layer as mineralized collagen fibers appearing as globules dispersed within an amorphous cutting matrix. Removal of smear plugs increases the outward hydraulic conductance (Lp) of dentinal fluid flow which may lead to dentinal hyperalgesia, bacterial infection and pulp pathosis if left untreated.
The smear layer is a debris-ladden layer, adhering firmly to the hard tissues of the tooth. It plays a major role in the different adhesive systems. An update of the recent knowledge on smear layer will be done in this article. When the carious lesion is removed, a microscopic debris-ladden layer forms at the level on the enamel and the dentine. This layer of materials is extremely adherent to the dental structure, and will come in between the hard dental tissues and the filling materials. In this article different studies were reviewed on the formation, structure and physiology of the smear layer. Consequences of this smear layer's removal on the pulp are discussed. A small study of different adhesive systems is conducted.
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The influence of a smear layer on the adhesion of sealer cements to dentin was assessed in recently extracted human anterior teeth. A total of 120 samples was tested, 40 per sealer; 20 each with and without the smear layer. The teeth were split longitudinally, and the internal surfaces were ground flat. One-half of each tooth was left with the smear layer intact, while the other half had the smear removed by washing for 3 min with 17% EDTA followed by 5.25% NaOCl. Evidence of the ability to remove the smear layer was verified by scanning electron microscopy. Using a specially designed jig, the sealer was placed into a 4-mm wide x 4-mm deep well which was then set onto the tooth at a 90-degree angle and allowed to set for 7 days in 100% humidity at 37 degrees C. This set-up was then placed into a mounting jig which was designed for the Instron Universal Testing Machine so that only a tensile load was applied without shearing or applying preloading forces. The set-up was subjected to a tensile load at a crosshead speed of 1 mm per min. The results show significant differences (p less than 0.001) among AH26, Sultan, and Sealapex, with AH26 being the strongest and Sealapex being the weakest. The only significant difference with regard to the presence or absence of the smear layer was found with AH26, which had a stronger bond when the smear layer was removed.
Smear layers are created on hard tissues whenever they are cut with hand or rotary instruments. This thin (1-2 microns) layer of denatured cutting debris is very tenacious and, in fact, is often the surface to which restorative materials are luted. The solubility characteristics, chemical reactivity and the structure-function relationships of this layer have not yet been well-defined. During creation of the smear layer, cutting debris is forced variable distances into dentinal tubules. These so-called smear plugs, together with the smear layer decrease dentin permeability, dentin sensitivity and surface wetness. Bonding adhesive resins to smear layers appears to limit the theoretical bond strength unless the smear layers are loosened or partially removed. Future research in this area will include the use of surface analytical techniques such as Auger electron spectroscopy and ESCA. These techniques are required because of the thinness of the smear layer. It is clear that the nature of this critical interface between dental materials and cut hard tissues remains largely unknown. This field will provide fertile ground for future research.
The influence of a smear layer on the adhesion of sealer cements to dentin was assessed in recently extracted human anterior teeth. A total of 120 samples was tested, 40 per sealer; 20 each with and without the smear layer. The teeth were split longitudinally, and the internal surfaces were ground flat. One-half of each tooth was left with the smear layer intact, while the other half had the smear removed by washing for 3 min with 17% EDTA followed by 5.25% NaOCI. Evidence of the ability to remove the smear layer was verified by scanning electron microscopy. Using a specially designed jig, the sealer was placed into a 4-mm wide x 4 mm deep well which was then set onto the tooth.
Smear-layer debris was sonicated from dentine surfaces and trapped on microfilters for microscopy, which showed that the layers are composed, in part, of aggregates of globular subunits approx. 0.05-0.1 micron in diameter. Such globules were also seen in smear layers in situ and on fractured dentine surfaces. The composition of smear layers may reflect the substructure of dentine matrix.
The effect on bond strength of smear layer removal (40% polyacrylic acid or 10% phosphoric acid) versus smear layer conditioning for dentin bonding agents requiring conditioning was compared. Results indicated no difference in shear bond strength for groups in which the smear layer was conditioned or removed with phosphoric acid. Smear layer removal with polyacrylic acid resulted in lower bond strengths between DBAs and dentin than either phosphoric acid removal or conditioning (P less than 0.01). Scanning electron photomicrographs of dentin treated with each dentin bonding agent revealed various surface morphologies.
A smear layer is formed after cavity or root canal preparation. The aim of the present study was to reinforce the dental surface in order to prevent the invasion of foreign irritants, by treating the smear layer with fluoride. Dentinal samples whose surfaces had been washed with water after the formation of a smear layer, and corresponding samples without washing, were examined by the dye penetration test, and the results were compared. Although there was no significant difference between the two groups of samples, dye penetration was suppressed by about 30% in washed samples, whereas the suppression was 20% in unwashed samples. When washed samples were treated with 1.0% SnF2, 10.0% SnF2, 7.5% Na2PO2F, 15% Na2PO2F, APF, 10 mM In(NO3)3, 100 mM TiF3, 50 mM TiF3, or 10 mM TiF3, samples washed after treatment with 1.0% SnF2 showed a dye penetration suppression of about 60% as a whole, in comparison with samples having no smear layer. Hardly any suppression of dye penetration was observed after treatment with other fluorides.
Despite concerns and claims that the smear layer on dentin is undesirable for bonding, supportive evidence is lacking. The clinical efficacy of various agents for smear layer removal and the effect of smear layer removal on the bond strengths of a glass-ionomer cement and three representative dentin bonding agents were examined. For all but one dentin bonding agent (Gluma), a 15-second treatment with 17% EDTA caused a reduction in bond strength. For Gluma, no significant bond was obtained without EDTA treatment. While Gluma probably bonds via dentinal collagen, the other materials interact primarily with dentinal calcium. Removal of the smear layer for adhesives reliant on the presence of calcium is therefore undesirable. The clinical effects of some agents proposed for smear layer removal were examined by SEM of replicas.
The "smear layer" is composed of debris that cover and insert into dentinal tubules. It is not really known if this form of debris may harbon viable bacterias or does form a barrier that enhances endodontic fillings by lining or plugging the tubules. The purpose of this study is to determine the role of the smear layer in leakage by using two groups of teeth in which the smear layer was removed of the root canals, in the first group and left into the roots in the second group. Some samples were beveled and all teeth were retrofilled after Root Canal Preparation, and then filled with India Ink. After examination of leakage under various conditions, it has been found a correlation between leakage and removal of smear layer.
A layer, which is readily detectable at higher magnifications with scanning electron microscope (sem) is consistently seen on canal walls that have been endodontically instrumented. This layer in the international bibliography reported as smeared layer. The surface of this layer is amorphous, irregular and granular. Although the composition of this layer has not been completely determined, it probably contains fine inorganic particles of dentin produced by mechanical preparation of root canal walls. As well as some organic material from necrotic or vital pulp tissue, bacteria and blood cells. The clinical importance of the smeared layer is still not fully understood. It may be beneficial since it is known to plug the orifices of the dentinal tubules and to reduce the permeability of dentin. In addition, the Smeared layer covering prepared areas of root canal prevents medicaments and filling materials from penetrating the dentinal tubules on even contacting the canal wall. The formation of this layer, the composition, the clinical importance and various methods for removing the smeared layer from the system of root canals, is the object of this paper.
The effect of the removal of the smear layer on coronal leakage of root fillings was studied using two sealer cements. Sixty single-rooted teeth with mature apices were prepared chemomechanically using a modified double-flared technique with non-cutting tipped files and copious irrigation with 2% sodium hypochlorite. The teeth were randomly allocated to four groups of 15 teeth each. Two groups were treated with 40% citric acid to remove the smear layer. Two groups of teeth, one with and one without smear layer, were filled by lateral condensation of gutta-percha with either Tubliseal or a resin-based glass ionomer, Vitrebond. The teeth were stored for 1 week, thermocycled, and the extent of coronal leakage determined for each group after immersion in Indian ink for 90 h. The teeth were demineralized, dehydrated and immersed in methyl salicylate which rendered them transparent. Linear measurement of dye penetration was recorded. The mean depth (+/- SD) of leakage for the groups in which the smear layer was left intact was 4.26 +/- 1.53 mm and 6.83 +/- 1.65 mm for the Vitrebond and Tubliseal, respectively. When the smear layer had been removed, the mean depth of leakage for the Vitrebond group was 1.13 +/- 0.29 mm, and 3.72 +/- 1.23 mm for the Tubliseal group. There was a statistically significant difference in leakage between the groups (P < 0.001). With both sealers, those teeth in which the smear layer had been removed showed less leakage than the specimens in which the smear layer was left intact (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
With the cascade of new restorative products being unveiled almost monthly, dentists incorporating endodontics into their practices must be able to evaluate the potential of these products for successful integration into their procedures. This evaluation should be based on a knowledge of how the new products relate to the smear layer formed along the root canal walls. Rather than relying on information supplied by the dental manufacturers, the aware dentist should regularly resort to the most current research reports available in journal or abstract form. With the use of certain products in some clinical situations, other branches of restorative dentistry may suggest retention of the smear layer. Although pulpally infected teeth have been successfully treated for generations in the presence of the smear layer, it has become accepted practice now in endodontics to remove the smear layer. Different quantities and qualities of smear layer can be produced by various techniques of instrumentation. However, they all present a barrier to intimate contact between obturating materials and the canal wall. Various types of solvents will produce different results in smear layer removal. One ideal endodontic irrigant follows the use of the antimicrobial 5.25 per cent sodium hypochlorite solution with the equally antimicrobial 6 per cent citric acid solution or 17 per cent EDTA. Chelating agents are effective in that they remove the smear layer, open the dentinal tubules, and produce a clean surface for closer obturation. Removal of the smear layer encourages the creation of a good apical plug to prevent over filling, post-filling sensitivity, and possible microleakage. The use of glass ionomer cements and unfilled resin as a cementing medium following smear layer removal shows promising results in both strength of cementation and the possibility of reducing post lengths. Controversies will always arise in dentistry with the advent of new information and the discovery of new clinical techniques. But a total awareness of both sides of a controversy will enable the practitioner to find a way through the confusion.
Freshly extracted human molars were used to study the interaction between dentinal smear layer removal with various agents, a dentinal adhesive, and the shear bond strength of a posterior composite resin to dentin. The use of Scotchbond dentinal adhesive in conjunction with the composite P-30, with the smear layer intact, produced the highest shear bond strengths. Removal of the smear layer produced bond strengths similar to those obtained with the smear layer intact. Application of ferric oxalate, and to a lesser degree 17% EDTA, resulted in diminished bond strengths. It was concluded that optimal bond strengths with the adhesive-composite resin systems tested may be obtained with an intact smear layer.
Whenever dental tissues cut with a rotary instrument, a layer of grinding debris and organic film left of their surfaces, which is described by the term "smear layer". In this paper, we present the morphology and views for the formation of the smear layer. Additionally, we examine the influence of smear layer, on dentin permeability, infection by bacteria beneath dental restorations and on bonding capacity of adhesive dental materials. Following, detailed description of cleaning and chemical agents, used for smear layer removal from prepared dentin surfaces.
In this study, the effect of citric acid and LIV CENERA Liquid (40% poly-acrylic acid) on the smear layer of the dentine surface was investigated. Twelve freshly extracted, non-carious human molar teeth were used and approximately 25 mm2 flat occlusal dentine surfaces were prepared. Citric acid and LIV CENERA Liquid were applied for 10 and 30 seconds to the dentine surfaces. The results of our study indicated that: 1. Conditioning with LIV CENERA Liquid for 10 seconds was not effective in removing the smear layer on the dentinal tubules but application for 30 seconds was partially effective. 2. Although 10 seconds application of citric acid was not effective in removing the smear layer, 30 seconds application removed it completely, but harmful effects were observed on the dentinal tubules. 3. Conditioning with citric acid is more effective than the application of LIV CENERA Liquid in removing the smear layer, but LIV CENERA Liquid in contrast to citric acid application, did not enlarge the dentinal tubules.