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PubMed1999

A comparative study of the removal of smear layer by three endodontic irrigants and two types of laser.

AIM: The effects of three endodontic irrigants and two types of laser on a smear layer created by hand instrumentation were evaluated in vitro in the middle and apical thirds of root canals. METHODOLOGY: Sixty human mature extracted mandibular premolar teeth with a single root canal and a closed apex were distributed randomly into five groups of 12 teeth each. Whilst cleaning and shaping up to a size 60 master apical file with a step-back technique, the root canals were irrigated with 3 mL of 5.25% NaOCL and 3% H2O2, alternately, between each file size. Group 1 (G1) were control specimens that were irrigated with a final flush of 17% EDTA. The teeth in group 2 (G2) were irrigated with a final flush of 6% phosphoric acid, and group 3 (G3) with 6% citric acid. In the specimens of group 4 (G4) the root canals were irradiated with a carbon dioxide (CO2) laser, and specimens of group 5 (G5) were irradiated using an Er:YAG laser. The teeth were split longitudinally and prepared for examination by scanning electron microscopy. RESULTS: Control specimens (G1) showed clean root-canal walls with open dentinal tubules in the middle one-third, but in some specimens thick smear layer was observed in the apical one-third. Specimens irrigated with a final flush of 6% phosphoric acid (G2) or 6% citric acid (G3) were cleaner than with 17% EDTA, showing very clean root canal surfaces in the middle one-third but in the apical one-third the smear layer was not completely removed, especially at the openings of the dentinal tubules. The specimens irradiated with the CO2 laser (G4) showed clean root-canal walls with the smear layer absent, charred, melted, recrystallized and glazed in both middle and apical thirds. The root-canal walls of the specimens irradiated with the Er:YAG laser (G5) revealed an absent smear layer with open dentinal tubules in the middle and apical thirds. Statistical analysis showed no significant difference in the cleanliness of root-canal wall between G1 and G2, and G1 and G3. However, there were statistically significant differences (P < 0.01) between G1 and G4, and G1 and G5 in the cleanliness of the middle and apical one-thirds of the root canals. CONCLUSIONS: Irrigation with 17% EDTA, 6% phosphoric acid and 6% citric acid did not remove all the smear layer from the root-canal system. In addition, these acidic solutions demineralized the interbular dentine around tabular openings, which became enlarged. The CO2 laser was useful in removing and melting the smear layer on the instrumented root-canal walls and the Er:YAG laser was the most effective in removing the smear layer from the root-canal wall.

Carbon Dioxide↗
PubMed2000

Effect of smear layers on the bonding of a self-etching primer to dentin.

PURPOSE: The objective of this work was to evaluate the effect of the absence and presence of smear layers on bonds made to dentin using a self-etching primer system, Clearfil SE Bond. MATERIALS AND METHODS: Dentin surfaces with different smear layer thickness were created from mid-coronal sound dentin in extracted, human third molars. The control group was cryofractured to create a bonding surface that was devoid of a smear layer. The experimental teeth were ground with wet 60-, 180- or 600-grit SiC paper. They were bonded using SE Bond, followed by resin composite buildups. After 1 day, bonded specimens were sectioned into multiple 1- x 1-mm beams. Microtensile bond strengths were determined and the results analyzed with ANOVA and the Student Neuman Keuls test. Fractographic study of cross sections of failed interfaces from the dentin side of representative beams was performed using both SEM and TEM. RESULTS: SE Bond produced high bond strengths (ca 50 MPa) to both smear layer-free and smear layer-covered dentin. SEM examination was inadequate to define the exact nature of interfacial failures. TEM observations demonstrated a thin (ca 400 to 500 nm) hybrid layer in the fractured dentin and thicker (ca 1 to 4 microns) hybrid layers on smear layer-covered dentin. This included a thick, hybridized smear layer and a thin, underlying true hybrid layer in the intact dentin. Separation of the two hybrid layers was not evident in interfacial failures. CONCLUSION: Self-etching primers create thin hybrid layers that incorporate the smear layer. This study shows that formation of true hybrid layers occurs irrespective of smear layer thickness and that both hybrid layers may function as a unit during loading without separation. identification of secondary cracks from TEM fractographic analysis exemplifies the complex reaction to tensile stresses in multilayered joint systems that comprise materials of variable compliance.

Acid Etching, Dental↗
PubMed2004

Influence of natural fruit juices in removing the smear layer from root surfaces--an in vitro study.

Certain elements of a patient's diet may be associated with dentin hypersensitivity. The intent of this study was to evaluate the degree of removal of the smear layer from dentin surfaces by various fruit juices. A smear layer was created on extracted human teeth by manual scaling. The roots were reduced and distributed into 8 experimental groups. Distilled water was the negative control. The juices were applied by 2 methods: topical application and topical application with friction. Specimens were photomicrographed and graded according to an index of smear layer removal. With topical application, all but 2 of the tested substances resulted in significantly greater removal of the smear layer and opening of dentinal tubules than was the case with the negative control (p = 0.05); the exceptions were Gala apple and Italian grape juices, which were no different from the control. For the active application (with friction), most substances removed more smear layer than the control (p < 0.05); Gala apple, Italian grape and orange juices were similar to the control. For each of the tested substances, removal of the smear layer did not differ with the method of application (topical vs. friction; p > 0.05). It is concluded that natural fruit juices can remove the smear layer from dentin surfaces, and the efficacy of this removal varies with the type of juice.

Analysis of Variance↗
PubMed2005

The influence of smear layer on coronal leakage of Roth 801 and AH26 root canal sealers.

The aim of this in vitro study was to examine the effect of removal of smear layer on the coronal seal of two commonly used root canal sealers: Roth 801, a zinc oxide-eugenol-based sealer and AH26, an epoxy resin-based sealer. Ninety-six single-rooted human teeth were used. The teeth were instrumented and assigned to four experimental groups of 20 teeth each, with 10 teeth as controls and the remaining six teeth examined under a scanning electron microscope. The teeth in the experimental groups (80 teeth) were divided into four sub-groups and were obturated by laterally condensed gutta-percha with the two sealer cements as follows: Group A1: smear layer left intact and AH26 cement used as sealer; Group A2: smear layer left intact and Roth 801 cement used as sealer; Group B1: smear layer removed and AH26 cement used as sealer; and Group B2: smear layer removed and Roth 801 cement used as sealer. Coronal microleakage was evaluated by measuring the distance of dye penetration. The data was statistically evaluated using a two-way ANOVA test. The results showed that removal of the smear layer resulted in a statistically significant reduction of microleakage values in the groups obturated with AH26 compared with the groups obturated with Roth 801 sealer. It was concluded that the removal of smear layer has a significant influence on the degree of microleakage in obturated root canals.

Adhesiveness↗
PubMed2002

Dentin morphology and permeability after brushing with different toothpastes in the presence and absence of smear layer.

BACKGROUND: The purpose of this study was to evaluate the morphology and permeability of dentin after brushing with different toothpastes in the presence and absence of smear layers. METHODS: Dentin discs were prepared from extracted third molars. Dentin permeability was measured using a hydraulic pressure apparatus working at 70 cm H2O pressure. Dentin was treated with 0.5 M EDTA for 5 minutes and washed to remove a smear layer and to establish the maximum permeability of each dentin disc, which was expressed as 100%. A new smear layer was then created on the upper surface using a #400 carbide paper under water for 30 seconds. Dentin permeability of the smear layer-covered dentin was measured and expressed as a percentage of the maximum permeability of that specimen, permitting each specimen to serve as its own control. Each sample was then brushed by a mechanical device under water for 3 minutes with constant pressure of 250 g using a medium toothbrush and permeability remeasured. Finally, 1 of 5 different toothpastes was applied on the dentin and brushed for 3 minutes. In another group, the same procedures were performed with the exception of the smear layer production, so it was possible to calculate changes in the permeability of dentin with open tubules following brushing. Scanning electron microscopic (SEM) examination of dentin was obtained before and after treatments with brushing and toothpastes. RESULTS: Dentin permeability was reduced by brushing procedures when the smear layer was absent, but it was increased when the smear layer was present. Toothpaste application reduced dentin permeability when no smear layer was present on the top of the surface, but modified and increased permeability of samples with smear layers. SEM observations demonstrated the presence of dentifrice particles on dentin surfaces and inside dentinal tubules, and this may be responsible for the observed reductions in permeability. Smear plugs produced during dentin brushing were not removed by the dentifrices. CONCLUSIONS: Dentin permeability and morphology are significantly affected by toothbrushing and by the type of dentifrice used. The presence of smear plugs in the dentin may decrease severity.

Adult↗
PubMed2002

Clinical implications of the smear layer in endodontics: a review.

It has been recognized for many years that root canal instrumentation produces a smear layer that covers the surfaces of prepared canal walls. This layer contains inorganic and organic substances such as fragments of odontoblastic processes and necrotic debris. There is a lack of agreement regarding the effect of the smear layer on the quality of instrumentation and obturation, but the smear layer itself may be infected and may protect the bacteria within the dentinal tubules. Various methods have been used to remove the smear layer. Conflicting results have been obtained from numerous in vitro studies regarding the significance of the presence or the removal of the smear layer.

Dental Leakage↗
PubMed2004

The smear layer in the root canal and its removal.

Instrumentation of the root canal during endodontic treatment produces a smear layer which is not uniformly attached to the canal wall. Its morphological structure comprises dentin particles, organic debris, odontoblast processes, microorganisms and their metabolic products. The view that has currently gained wide popularity holds that leaving the smear layer in the root canal contradicts the principles of efficient treatment as this might compromise the optimal progression of the healing process. The proven unfavorable effects of the smear layer on treatment outcome bring forward the necessity for additional application of agents aimed at its complete removal. As the smear layer has a complex structure, these agents should possess a potential for dealing with both its organic and inorganic components. The wide range of used medications includes different concentrations of sodium hypochlorite as a major irrigant of the root canal, chlorhexidine gluconate, chelating agents (EDTA), organic acids, combined preparations (MTAD), combined use of agents that can tackle both the organic and inorganic components. Lasers find manifold applications in various medical fields and can be regarded as a future solution to the problem of total smear layer removal. In the present review we have made a critical analysis of currently used agents placing the emphasis on the potential use of new medications, capable of attacking the smear layer.

Dental Pulp Cavity↗
PubMed2003

[A comparative study of root smear layer removal using different pH EDTA salts].

OBJECTIVE: To evaluate the effect of different pH EDTA salts on removing root canal smear layers. METHODS: Sixty human teeth with single root were instrumented using step-back technique, then were irrigated with several irrigating solutions including A: 0.9% saline; B: 5.25% NaOCl +3% H2O2; C: 15% EDTA (pH = 6.5); D: 15% EDTA (pH = 13); E: 15% EDTA (pH = 6.5) 25% NaOCl +3% H2O2; F: 15% EDTA (pH = 13) 25% NaOCl +3% H2O2. After the teeth were split, the root canal walls were examined with scanning electron microscopy at the coronal, middle and apical thirds for smear layer removal. RESULTS: Except A and B group, all the groups were effective on removing smear layer at the coronal, middle thirds of the root canal, group C had a stronger effect to remove smear layer than group D (P < 0.05), group E was the most effective among these groups. However, these groups were all ineffective on removing smear layer at the apical thirds of root canal. CONCLUSIONS: 15% EDTA (pH = 6.5) 25% NaOCl +3% H2O2 was the most effective irrigation on removing smear layer.

Edetic Acid↗
PubMed1990

The smear layer in endodontics.

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.

Chelating Agents↗
PubMed2000

An ultrastructural study of the influence of acidity of self-etching primers and smear layer thickness on bonding to intact dentin.

PURPOSE: The objectives of this study were (1) to determine the depth of demineralization into intact dentin using several self-etching primer systems with different pH values, and (2) to evaluate whether hybridization of intact dentin in Clearfil SE Bond may be affected by variation in the thickness of the smear layers. MATERIALS AND METHODS: Dentin disks were created from mid-coronal dentin in extracted, human third molars. Three self-etching primer systems (Clearfil Liner Bond II, Liner Bond 2V, and SE Bond) were applied separately to these disks to evaluate how deep self-etching systems penetrate through smear layers into intact dentin. Dentin treated with All-Bond 2 using the "no-etch" technique was used as a control group. In the second part of the study, dentin disks with different smear-layer thicknesses were produced. The cryofractured control group was devoid of a smear layer. The experimental teeth were ground with 60-, 180-, or 600-grit SiC paper and bonded using SE Bond. Dentin disks were bonded together and examined with TEM. RESULTS: All-Bond 2 did not etch beyond the smear layer. The three self-etching primers etched beyond the smear layer to form true hybrid layers within intact dentin. This layer was thickest with Liner Bond 2 (ca 1.2 to 1.4 microns), but very thin (0.5 micron) using both Liner Bond 2V and SE Bond. Application of SE Bond to dentin of different surface roughness produced hybridized smear layers of variable thickness. However, the thickness of the underlying true hybrid remained consistent for the four groups (ca 0.4 to 0.5 micron). CONCLUSION: Self-etching primers create thin hybrid layers that incorporate the smear layer. The suspicion that thick smear layers may interfere with the diffusion of self-etching primers into the underlying intact dentin was not confirmed.

Acid Etching, Dental↗
PubMed2006

Conditioning effect on dentin, resin tags and hybrid layer of different acidity self-etch adhesives applied to thick and thin smear layer.

OBJECTIVES: to assess the conditioning effect (CE) of self-etch adhesives of different acidity applied to thick and thin smear layer (SL), the corresponding resin tags (RT) and hybrid layer (HL). METHODS: Twenty-seven molars had their occlusal dentin exposed and were sectioned into two halves. Each of them was ground with a 60 or 600-grit SiC paper, respectively for thick and thin SL production. Three self-etch adhesives: a mild (Clearfil SE Bond), an intermediary (Optibond Solo SE and Solo Plus) and a strong (Tyrian Self Priming Etchant+One Step Plus) and an etch-&-rinse system (Scotchbond Multi Purpose Plus) were used. For CE evaluation, the self-etch primers were applied and rinsed off with acetone and alcohol prior to SEM preparation. For RT and HL specimens self-etch adhesives were applied and restored with Z-250. For RT specimens, dentin was removed with HCl (6N) and NaClO (1%) baths. The HL specimens were fixed, dehydrated, dried with HMDS, embedded, polished and slightly demineralized (6N HCl) and deproteinized (1% NaClO). After gold sputtering they were observed by SEM. RESULTS: The thick smear layer was clearly not totally removed by the mild self-etch primer. RT varied in density and shape among the self-etch adhesives. Thicker HL was observed for the strong self-etch and etch-&-rinse adhesives. CONCLUSIONS: The etch-&-rinse adhesive presented the thickest HL and was the only adhesive to produce RT in high density and uniform distribution along the whole dentin surface, independently of the SL thickness.

Acid Etching, Dental↗
PubMed2000

Effects of irrigation on debris and smear layer on canal walls prepared by two rotary techniques: a scanning electron microscopic study.

Debris and smear layer were evaluated in canals prepared with either Lightspeed (LS) or ProFile (PF) rotary instruments. Irrigants used were tap water (group A) or alternating 5.25% NaOCl and 17% EDTA (group B). Apical stops were prepared to size 52.5 in the LS and to size 6 (approximately ISO size 36) in the PF techniques. The roots were split longitudinally and examined at apical, middle and coronal levels for debris and the smear layer using a 5-step scale. Using only water, mean debris scores were similar for LS and PF. In contrast, with EDTA/NaOCl, LS- and PF-prepared canals had similar debris scores at the apical and coronal levels, but there was a significant difference at the middle level. Mean smear layer scores were similar in LS- and PF-shaped canals when water was the sole irrigant. In contrast, with NaOCl and EDTA, mean smear layer scores were significantly different at the apical and middle levels, but not at the coronal level. Neither technique was superior in removing debris, but larger canal preparations obtained in this study with LS instruments enabled a more effective removal of the smear layer in the EDTA-NaOCl group.

Dental High-Speed Equipment↗
PubMed1989

Interaction between the dentinal smear layer and composite bond strength.

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.

Adhesives↗
PubMed1996

An in-vitro study of smear layer removal and microbial leakage along root-canal fillings.

The objective of this study was to determine the effect of removal of the smear layer on canal obturation as measured by penetration of bacteria from a coronal direction. Fifty-four extracted human teeth were decoronated and instrumented in a uniform manner. Following instrumentation the root canals of 20 teeth were rinsed with 17% EDTA and 5.25% NaOCl to remove the smear layer before obturation. A second group of 20 teeth were flushed with NaOCl alone. The teeth of both groups were obturated with Thermafil plastic carriers and Roth's sealer. The root canals of another 10 teeth, five rinsed with EDTA and five without, were obturated with Thermafil without sealer. Two teeth serving as positive controls were instrumented but not obturated, while another set of two were sealed coronally and apically to serve as negative controls. The root surface of each tooth was sealed with nail varnish. A small chamber was thoroughly sealed around the coronal aspect of each tooth so that bacteria placed therein could move only through the obturated canal space. Each tooth was placed in a test tube containing sterile trypticase soy broth (TSB). An inoculum of Proteus vulgaris in TSB was placed in each coronal chamber at five day intervals and daily observations were made for bacterial growth in the apical reservoir for 21 days. Both positive control teeth showed bacterial penetration after 24 h. Neither of the two negative control teeth demonstrated penetration for the duration of the study. The frequency of bacterial penetration through teeth obturated with intact smear layer (70%) was-significantly greater than that of teeth from which the smear layer had been removed (30%) P < 0.05. All but one tooth obturated without sealer exhibited bacterial penetration, irrespective of the presence or absence of smear layer. Removal of the smear layer enhanced sealability as evidenced by increased resistance to bacterial penetration.

Chi-Square Distribution↗
PubMed1994

Smear layer removal by root canal irrigants. A comparative scanning electron microscopic study.

The effect of six endodontic irrigants on smear layers created by hand instrumentation was evaluated in vitro in the middle and apical sections of 53 root canals. The irrigants evaluated were: 1% and 5% sodium hypochlorite, a combination of 24% phosphoric acid and 10% citric acid, 0.2%, 17%, and 3% ethylenediaminetetraacetic acid. After instrumentation and treatment with the respective irrigants, the root canal specimens were examined by scanning electron microscopy to determine the presence or absence of smear layer. The two sodium hypochlorite solutions did not remove the smear layer, even when 5% sodium hypochlorite was scrubbed on the dentinal walls. The 0.2% ethylenediaminetetraacetic acid solution was more effective than sodium hypochlorite, but it did not completely remove the smear layer, especially at the orifices of the dentinal tubules. The other three solutions effectively removed the smear layer, but no significant difference was found between them (p > 0.05). The solution of 3% ethylenediaminetetraacetic acid was as effective as phosphoric-citric acid and 17% ethylenediaminetetraacetic acid. Ethylenediaminetetraacetic acid, however, did not show the marked demineralizing effect on the dentinal walls and tubules as the acidic solution.

Adult↗
PubMed1998

Apical sealing ability of glass ionomer sealer with and without smear layer.

The effect of two different root canal cements and removal of the smear layer on the apical seal in roots obturated with Thermafil obturators was tested. Thirty extracted human mandibular first molars with 60 canals (mesial roots) were instrumented with the use of a step-back technique. Teeth were placed into 6 groups of 10 canals each. The first three groups had the smear layer removed with EDTA and NaOCl, and the other three groups were irrigated with NaOCl only. Canals were obturated using Thermafil without sealer cement or Thermafil with Ketac-Endo or Thermafil with zinc oxide-eugenol cement. All roots were placed in India ink for 4 days. The roots were cleared, and the degree of linear dye penetration was measured. The study showed that root canal cement significantly improved the apical seal of the Thermafil obturation technique (p < 0.05), whether the smear layer was removed or not. The apical seal exhibited by Ketac-Endo was not significantly different from that provided by zinc oxide-eugenol cement (p > 0.05), regardless of the presence or absence of a smear layer.

Analysis of Variance↗
PubMed2000

An evaluation of the effectiveness of two canal lubricants in removing smear layer.

This study used scanning electron microscopy to compare the effectiveness of two new canal lubricants in conjunction with sodium hypochlorite irrigation in removing smear layer. Both lubricants completely removed the smear layer in the coronal and middle thirds of the root canals, but only partially removed the smear layer in the apical thirds. An explanation of the findings is presented and the clinical significance of smear layer is discussed.

Chelating Agents↗
PubMed2004

Effectiveness of EDTA and EDTA-T brushing on the removal of root surface smear layer.

The purpose of this study was to compare the removal of root surface smear layer following active application of EDTA gel and EDTA-T (texapon) gel in different concentrations (5%, 10%, 15%, 20% and 24%), using scanning electron microscopy. A total of 220 dentin blocks obtained from the root surfaces of extracted teeth were divided into 3 groups: Group I - (control) application of saline solution (n = 20); Group II - EDTA gel (pH 7.0) was applied in the following concentrations: 5%, 10%, 15%, 20% and 24% (n = 100); Group III - EDTA-T gel (pH 7.0) applied in the same concentrations described above (n = 100). The photomicrographs were evaluated by one calibrated examiner using a smear layer removal index and following statistical analysis (Kruskal-Wallis test). The results demonstrated that the specimens treated with EDTA and EDTA-T gel presented a better smear layer removal than the control group (p < 0.01); no statistically significant differences were observed between the EDTA and EDTA-T groups and between the concentrations tested (Mann-Whitney, p > 0.05). Within the limits of this study, it can be concluded that all treatment modalities effectively removed the smear layer from the root surface. The addition of texapon into the EDTA gel formulation did not increase its effectiveness.

Bicuspid↗