Smear layer
Encyclopedia
The smear layer is a layer of microcrystalline
and organic particle debris that is found spread on root canal
walls after root canal instrumentation. It was first described in 1975 and much research has been performed since then to evaluate its importance in assisting or preventing the penetration of bacteria into the dentinal tubules.
that was 2 to 5 micrometre
s thick.
In 1975 McComb and Smith first described the smear layer. They observed an amorphous layer of debris, with an irregular and granular surface, on instrumented dentinal walls using a scanning electron microscope
(SEM). This smear layer was composed of dentin
, pulp
and bacteria
l remnants. The authors stated that “most standard instrumentation techniques produced a canal wall that was smeared and packed with debris.”
In 1984 Pashely described the smear layer as being composed of two phases; an organic phase, composed of collagen
residues and glycosaminoglycan
s from extracellular matrix
of pulp cells, which acts as a matrix for an inorganic phase. This organomineral content is composed of two distinct superposed layers. The first layer covers the canal wall and is loosely adherent and easy to remove. The second layer however occludes the dentinal tubule
s and strongly adheres to the canal walls.
In the same year Mader et al. studied the morphological
characteristics of the smear layer in teeth that were endodontically instrumented with k type files and irrigated with 5.25% NaOCl. The smear layer was examined from two aspects; the first “downonto” the smear layer and the second from the side or profile view. Photomicrographs obtained by SEM showed that the smear layer consists of two confluent components. A thin superficial layer 1-2 micrometres thick overlying a densely packed layer that penetrated into the dentinal tubules for distances of up to 40 micrometres. The packed material showed finger like structures projecting into the tubules from the canal wall. There is still controversy
over whether the smear layer should be removed and whether the disadvantages of leaving it in place overcome its benefits.
the penetration of bacteria into tubules of intact dentin exposed by fracture was compared in pairs of teeth, one of which in each pair was mounted with intrapulpal hydrostatic pressure (30mmHg). In vivo
, intra pair comparisons of bacterial invasion into dentinal tubules beneath ground, fractured and acid treated surfaces were made. They observed that an outward flow of fluid
s into the tubules due to intrapulpal pressure mechanically hindered bacterial growth
and that the debris and smear layer produced from grinding obstructed the bacterial invasion into tubules. However this barrier seemed to be removed after a few days which allowed bacterial growth into intact dentin. Olgart came to a conclusion that acid
produced by microorganism
s may dissolve the smear layer allowing bacteria to pass into dentinal tubules.
However when Pashley et al. (1981) studied the scanning electron microscope (SEM) appearance of dentin before and after removing successive layers of the smear layer they came to a different conclusion. Twenty dentin disks were cut from human extracted third molar
s. The dentin surface of the disks was etched with 6% citric acid
for 5, 15, 30, 45 and 60 seconds. SEM examination showed that citric acid was able to remove smear layer in successive layers according to etching time finally exposing the dentinal tubules. Pashley concluded that the maintenance of the smear layer established a protective diffusion barrier
.
Gettleman et al. (1991) assessed the influence of a smear layer on the adhesion
of sealer cements to dentin. A total of 120 teeth was tested, 40 per sealer namely AH26, Sultan, and Sealapex; 20 each with and without the smear layer. The teeth were split longitudinally, and the internal surfaces were ground flat. In the smear layer-free specimens the smear layer was removed by washing for 3 minutes with 17% EDTA
followed by 5.25% NaOCl. Using a specially designed jig, the sealer
was placed into a 4-mm wide × 4-mm deep well which was then set onto the tooth at a 90-degree angle and allowed to set for 7 days. 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. The set-up was subjected to a tensile load at a crosshead speed of 1 mm per min. 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.
around obturating materials. Thirty extracted teeth were classified into two test groups; the first group had the smear layer removed by rinsing with 17% EDTA while in the second group the smear layer was left intact. Canal preparation and obturation using lateral condensation, gutta-percha
, and AH 26 sealer was performed on all of the teeth. The model systems consisted of an upper chamber attached to the cemento-enamel
junction and a lower chamber at the apices of the teeth. Standardized bacterial suspensions containing Fusobacterium nucleatum
, Campylobacter rectus
and Peptostreptococcus micros
were inoculated into the upper chambers. Models were incubated anaerobically at 37 degrees C. Leakage results were as follows: In the first group 6 teeth showed bacterial leakage, the second group and third groups showed no bacterial leakage. This study indicated that removal of the smear layer reduced the leakage of bacteria through the root canal system.
Kokkas et al. (2004) examined the effect of the smear layer on the penetration depth of three different sealers (AH Plus, Apexit, and a Grossman type-Roth 811) into the dentinal tubules. Sixty four extracted human single-rooted teeth were used and divided into two groups. The smear layer remained intact in all the roots of group A. Complete removal of the smear layer in group B was achieved after irrigation
with 3 ml of 17% EDTA for 3 min, followed by 3 ml of 1% NaOCl solution. Ten roots from each group were obturated with AH Plus and laterally condensed gutta-percha points. The same process was repeated for the remaining roots by using sealers Apexit and Roth 811 correspondingly. After complete setting, the maximum penetration depth of the sealers into the dentinal tubules was examined in upper, middle, and lower levels. The smear layer prevented all the sealers from penetrating dentinal tubules. In contrast, in smear layer–free root canals, all the sealers penetrated dentinal tubules, although the depth of penetration varied between the sealers. Furthermore smear layer adversely affected the coronal and apical sealing ability of sealers.
Çobankara et al. (2004) determined the effect of the smear layer on apical and coronal leakage in root canals obturated with AH26 or RoekoSeal sealers. A total of 160 maxillary anterior teeth were used. Eight groups were created by all possible combinations of three factors: smear layer (present/absent), leakage assessment (apical/coronal), and sealer used (AH26/Roeko-Seal). All teeth were obturated using lateral condensation technique of gutta-percha. A fluid filtration method was used to test apical or coronal leakage. According to the results of this study, the smear (+) groups displayed higher apical and coronal leakage than those smear (-) groups for both root canal sealers. Apical leakage was significantly higher than coronal leakage for both root canal sealers used in this study. It was determined that that removal of the smear layer has a positive effect in reducing apical and coronal leakage for both AH26 and RoekoSeal root canal sealers.
However Bertacci et al. (2007) evaluated the ability of a warm gutta-percha obturation system Thermafil to fill lateral channels in the presence or absence of the smear layer. Forty single-rooted extracted human teeth were randomly divided into two groups one of which had the smear layer removed by 5 ml of 5% NaOCl followed by 2.5 ml of 17% EDTA. Obturation was performed using AH Plus sealer and Thermafil. Specimens were cleared in methyl salicylate and analyzed under a stereomicroscope to evaluate the number, length, and diameter of lateral channels. All lateral channels were found to be filled in both groups. No statistically significant differences regarding number, length, and diameter were observed between the two groups. It was concluded that the smear layer did not prevent the sealing of lateral channels.
Yildirim et al. (2008) investigated the effect of the smear layer on apical microleakage in teeth obturated with MTA. Fifty single-rooted central maxillary teeth were used in this study. The selected teeth were instrumented and randomly divided into 2 groups. In the first group (smear [+]), the teeth were irrigated with only 5.25% NaOCl. In the second group (smear [-]), the teeth were irrigated with EDTA (17%) and NaOCl (5.25%) to remove the smear layer. The teeth were then filled with MTA. The computerized fluid filtration method was used for evaluation of apical microleakage. The quantitative apical leakage of each tooth was measured after 2, 30, and 180 days. It was found that there was no difference between the groups after 2 days but removal of the smear layer caused significantly more apical microleakage than when the smear layer was left intact after 30 and 180 days. It was concluded that the apical microleakage of MTA is less when the smear layer is present than when it is absent.
Saleh et al. (2008) studied the effect of the smear layer on the penetration of bacteria along different root canal filling materials. A total of 110 human root segments were instrumented to size 80 under irrigation with 1% sodium hypochlorite. Half of the roots were irrigated with a 5-mL rinse of 17% EDTA to remove the smear layer. Roots were filled with gutta-percha (GP) and AH Plus sealer (AH), GP and Apexit sealer (AP), or RealSeal cones and sealer (RS). Following storage in humid conditions at 37 degrees C for 7 days, the specimens were mounted into a bacterial leakage test model for 135 days. Survival analyses were performed to calculate the median time of leakage and log-rank test was used for pairwise comparisons of groups. Selected specimens were longitudinally sectioned and inspected by scanning electron microscopy for the presence of bacteria at the interfaces. In the presence of the smear layer, RS and AP leaked significantly more slowly than in its absence. In the absence of the smear layer, AH leaked significantly more slowly than RS. It was concluded that removal of the smear layer did not impair bacterial penetration along root canal fillings. A comparison of the sealers revealed no difference except that AH performed better than RS in the absence of the smear layer.
Fachin et al.(2009) evaluated whether smear layer removal has any influence on the filling of the root canal system, by examining the obturation of lateral canals, secondary canals and apical deltas. Eighty canines were randomly divided into two groups, according to their irrigation regimen. Both groups were irrigated with 1% NaOCl during canal shaping, but only the teeth in Group II received a final irrigation with 17% EDTA for smear layer removal. The root canals were obturated with lateral condensation of gutta-percha and the specimens were cleared, allowing for observation under the microscope. The results showed that In Groups I and II, 42.5% and 37.5% of the teeth, respectively, presented at least one filled canal ramification. In conclusion, smear layer removal under the conditions tested in this study did not affect the obturation of root canal ramifications when lateral condensation of gutta-percha was the technique used for root canal filling.
Microcrystalline
A microcrystalline material is a crystallized substance or rock that contains small crystals visible only through microscopic examination.-See also:* Macrocrystalline* Microcrystalline silicon* Protocrystalline* Rock microstructure...
and organic particle debris that is found spread on root canal
Root canal
A root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber , the main canal, and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.-Root canal anatomy:...
walls after root canal instrumentation. It was first described in 1975 and much research has been performed since then to evaluate its importance in assisting or preventing the penetration of bacteria into the dentinal tubules.
First description
Early studies of dentinal walls after cavity preparation performed by Brännström and Johnson (1974) showed the presence of a thin layer of debrisDebris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
that was 2 to 5 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s thick.
In 1975 McComb and Smith first described the smear layer. They observed an amorphous layer of debris, with an irregular and granular surface, on instrumented dentinal walls using a scanning electron microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
(SEM). This smear layer was composed of dentin
Dentin
Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
, pulp
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective tissue and cells called odontoblasts.- Anatomy :Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the primary teeth....
and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l remnants. The authors stated that “most standard instrumentation techniques produced a canal wall that was smeared and packed with debris.”
In 1984 Pashely described the smear layer as being composed of two phases; an organic phase, composed of collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
residues and glycosaminoglycan
Glycosaminoglycan
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...
s from extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
of pulp cells, which acts as a matrix for an inorganic phase. This organomineral content is composed of two distinct superposed layers. The first layer covers the canal wall and is loosely adherent and easy to remove. The second layer however occludes the dentinal tubule
Tubule
A tubule is a very small tube or fistular structure.A system of surface-connected membranes in muscle that enables a nerve impulse to travel to the interior of the muscle fibre.In anatomy, a tubule is a minute tube lined with glandular epithelium....
s and strongly adheres to the canal walls.
In the same year Mader et al. studied the morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
characteristics of the smear layer in teeth that were endodontically instrumented with k type files and irrigated with 5.25% NaOCl. The smear layer was examined from two aspects; the first “downonto” the smear layer and the second from the side or profile view. Photomicrographs obtained by SEM showed that the smear layer consists of two confluent components. A thin superficial layer 1-2 micrometres thick overlying a densely packed layer that penetrated into the dentinal tubules for distances of up to 40 micrometres. The packed material showed finger like structures projecting into the tubules from the canal wall. There is still controversy
Controversy
Controversy is a state of prolonged public dispute or debate, usually concerning a matter of opinion. The word was coined from the Latin controversia, as a composite of controversus – "turned in an opposite direction," from contra – "against" – and vertere – to turn, or versus , hence, "to turn...
over whether the smear layer should be removed and whether the disadvantages of leaving it in place overcome its benefits.
Bacterial penetration
Olgart et al. (1974) examined the penetration of bacteria into dentinal tubules of ground, fractured and acid treated dentin surfaces. In vitroIn vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
the penetration of bacteria into tubules of intact dentin exposed by fracture was compared in pairs of teeth, one of which in each pair was mounted with intrapulpal hydrostatic pressure (30mmHg). In vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
, intra pair comparisons of bacterial invasion into dentinal tubules beneath ground, fractured and acid treated surfaces were made. They observed that an outward flow of fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
s into the tubules due to intrapulpal pressure mechanically hindered bacterial growth
Bacterial growth
250px|right|thumb|Growth is shown as L = log where numbers is the number of colony forming units per ml, versus T Bacterial growth is the division of one bacterium into two daughter cells in a process called binary fission. Providing no mutational event occurs the resulting daughter cells are...
and that the debris and smear layer produced from grinding obstructed the bacterial invasion into tubules. However this barrier seemed to be removed after a few days which allowed bacterial growth into intact dentin. Olgart came to a conclusion that acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
produced by microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s may dissolve the smear layer allowing bacteria to pass into dentinal tubules.
However when Pashley et al. (1981) studied the scanning electron microscope (SEM) appearance of dentin before and after removing successive layers of the smear layer they came to a different conclusion. Twenty dentin disks were cut from human extracted third molar
Third molar
A wisdom tooth, in humans, is any of the usually four third molars. Wisdom teeth usually appear between the ages of 17 and 25. Most adults have four wisdom teeth, but it is possible to have fewer , or more, in which case they are called supernumerary teeth...
s. The dentin surface of the disks was etched with 6% citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
for 5, 15, 30, 45 and 60 seconds. SEM examination showed that citric acid was able to remove smear layer in successive layers according to etching time finally exposing the dentinal tubules. Pashley concluded that the maintenance of the smear layer established a protective diffusion barrier
Diffusion barrier
A diffusion barrier is a thin layer of metal usually placed between two other metals. It is done to act as a barrier to protect either one of the metals from corrupting the other....
.
Gettleman et al. (1991) assessed the influence of a smear layer on the adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
of sealer cements to dentin. A total of 120 teeth was tested, 40 per sealer namely AH26, Sultan, and Sealapex; 20 each with and without the smear layer. The teeth were split longitudinally, and the internal surfaces were ground flat. In the smear layer-free specimens the smear layer was removed by washing for 3 minutes with 17% EDTA
EDTA
Ethylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...
followed by 5.25% NaOCl. Using a specially designed jig, the sealer
Sealer
-See also:*Seal *Sealing...
was placed into a 4-mm wide × 4-mm deep well which was then set onto the tooth at a 90-degree angle and allowed to set for 7 days. This set-up was then placed into a mounting jig which was designed for the Instron
Instron
Instron is a manufacturer of test equipment designed to evaluate the mechanical properties of materials and components.In 1946, Harold Hindman and George Burr, who worked together at Massachusetts Institute of Technology , teamed up to determine the properties of new materials to be used in...
Universal Testing Machine so that only a tensile load was applied without shearing. The set-up was subjected to a tensile load at a crosshead speed of 1 mm per min. 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.
Further research
Clark-Holke et al. (2003) focused on determining the effect of the smear layer on the magnitude of bacterial penetration through the apical foramenApical foramen
In anatomy the apical foramen is the opening at the apex of the root of a tooth, through which the nerve and blood vessels that supply the dental pulp pass...
around obturating materials. Thirty extracted teeth were classified into two test groups; the first group had the smear layer removed by rinsing with 17% EDTA while in the second group the smear layer was left intact. Canal preparation and obturation using lateral condensation, gutta-percha
Gutta-percha
Gutta-percha is a genus of tropical trees native to Southeast Asia and northern Australasia, from Taiwan south to the Malay Peninsula and east to the Solomon Islands. The same term is used to refer to an inelastic natural latex produced from the sap of these trees, particularly from the species...
, and AH 26 sealer was performed on all of the teeth. The model systems consisted of an upper chamber attached to the cemento-enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
junction and a lower chamber at the apices of the teeth. Standardized bacterial suspensions containing Fusobacterium nucleatum
Fusobacterium nucleatum
Fusobacterium nucleatum is an oral bacterium, indigenous to the human oral cavity, that plays a role in periodontal disease. This organism is commonly recovered from different monomicrobial and mixed infections in humans and animals...
, Campylobacter rectus
Campylobacter rectus
Campylobacter rectus is a species of Campylobacter. It is implicated as a pathogen in chronic periodontitis which can induce bone loss. It is a gram negative motile, aerotolerant rod....
and Peptostreptococcus micros
Peptostreptococcus
Peptostreptococcus is a genus of anaerobic, Gram-positive, non-spore forming bacteria. The cells are small, spherical, and can occur in short chains, in pairs or individually. Peptostreptococcus are slow-growing bacteria with increasing resistance to antimicrobial drugs.The most frequently...
were inoculated into the upper chambers. Models were incubated anaerobically at 37 degrees C. Leakage results were as follows: In the first group 6 teeth showed bacterial leakage, the second group and third groups showed no bacterial leakage. This study indicated that removal of the smear layer reduced the leakage of bacteria through the root canal system.
Kokkas et al. (2004) examined the effect of the smear layer on the penetration depth of three different sealers (AH Plus, Apexit, and a Grossman type-Roth 811) into the dentinal tubules. Sixty four extracted human single-rooted teeth were used and divided into two groups. The smear layer remained intact in all the roots of group A. Complete removal of the smear layer in group B was achieved after irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
with 3 ml of 17% EDTA for 3 min, followed by 3 ml of 1% NaOCl solution. Ten roots from each group were obturated with AH Plus and laterally condensed gutta-percha points. The same process was repeated for the remaining roots by using sealers Apexit and Roth 811 correspondingly. After complete setting, the maximum penetration depth of the sealers into the dentinal tubules was examined in upper, middle, and lower levels. The smear layer prevented all the sealers from penetrating dentinal tubules. In contrast, in smear layer–free root canals, all the sealers penetrated dentinal tubules, although the depth of penetration varied between the sealers. Furthermore smear layer adversely affected the coronal and apical sealing ability of sealers.
Çobankara et al. (2004) determined the effect of the smear layer on apical and coronal leakage in root canals obturated with AH26 or RoekoSeal sealers. A total of 160 maxillary anterior teeth were used. Eight groups were created by all possible combinations of three factors: smear layer (present/absent), leakage assessment (apical/coronal), and sealer used (AH26/Roeko-Seal). All teeth were obturated using lateral condensation technique of gutta-percha. A fluid filtration method was used to test apical or coronal leakage. According to the results of this study, the smear (+) groups displayed higher apical and coronal leakage than those smear (-) groups for both root canal sealers. Apical leakage was significantly higher than coronal leakage for both root canal sealers used in this study. It was determined that that removal of the smear layer has a positive effect in reducing apical and coronal leakage for both AH26 and RoekoSeal root canal sealers.
However Bertacci et al. (2007) evaluated the ability of a warm gutta-percha obturation system Thermafil to fill lateral channels in the presence or absence of the smear layer. Forty single-rooted extracted human teeth were randomly divided into two groups one of which had the smear layer removed by 5 ml of 5% NaOCl followed by 2.5 ml of 17% EDTA. Obturation was performed using AH Plus sealer and Thermafil. Specimens were cleared in methyl salicylate and analyzed under a stereomicroscope to evaluate the number, length, and diameter of lateral channels. All lateral channels were found to be filled in both groups. No statistically significant differences regarding number, length, and diameter were observed between the two groups. It was concluded that the smear layer did not prevent the sealing of lateral channels.
Yildirim et al. (2008) investigated the effect of the smear layer on apical microleakage in teeth obturated with MTA. Fifty single-rooted central maxillary teeth were used in this study. The selected teeth were instrumented and randomly divided into 2 groups. In the first group (smear [+]), the teeth were irrigated with only 5.25% NaOCl. In the second group (smear [-]), the teeth were irrigated with EDTA (17%) and NaOCl (5.25%) to remove the smear layer. The teeth were then filled with MTA. The computerized fluid filtration method was used for evaluation of apical microleakage. The quantitative apical leakage of each tooth was measured after 2, 30, and 180 days. It was found that there was no difference between the groups after 2 days but removal of the smear layer caused significantly more apical microleakage than when the smear layer was left intact after 30 and 180 days. It was concluded that the apical microleakage of MTA is less when the smear layer is present than when it is absent.
Saleh et al. (2008) studied the effect of the smear layer on the penetration of bacteria along different root canal filling materials. A total of 110 human root segments were instrumented to size 80 under irrigation with 1% sodium hypochlorite. Half of the roots were irrigated with a 5-mL rinse of 17% EDTA to remove the smear layer. Roots were filled with gutta-percha (GP) and AH Plus sealer (AH), GP and Apexit sealer (AP), or RealSeal cones and sealer (RS). Following storage in humid conditions at 37 degrees C for 7 days, the specimens were mounted into a bacterial leakage test model for 135 days. Survival analyses were performed to calculate the median time of leakage and log-rank test was used for pairwise comparisons of groups. Selected specimens were longitudinally sectioned and inspected by scanning electron microscopy for the presence of bacteria at the interfaces. In the presence of the smear layer, RS and AP leaked significantly more slowly than in its absence. In the absence of the smear layer, AH leaked significantly more slowly than RS. It was concluded that removal of the smear layer did not impair bacterial penetration along root canal fillings. A comparison of the sealers revealed no difference except that AH performed better than RS in the absence of the smear layer.
Fachin et al.(2009) evaluated whether smear layer removal has any influence on the filling of the root canal system, by examining the obturation of lateral canals, secondary canals and apical deltas. Eighty canines were randomly divided into two groups, according to their irrigation regimen. Both groups were irrigated with 1% NaOCl during canal shaping, but only the teeth in Group II received a final irrigation with 17% EDTA for smear layer removal. The root canals were obturated with lateral condensation of gutta-percha and the specimens were cleared, allowing for observation under the microscope. The results showed that In Groups I and II, 42.5% and 37.5% of the teeth, respectively, presented at least one filled canal ramification. In conclusion, smear layer removal under the conditions tested in this study did not affect the obturation of root canal ramifications when lateral condensation of gutta-percha was the technique used for root canal filling.