title: Role of hybridization on marginal leakage and bond strength. Effect of removal of the smear layer on apical microleakage. Assessment of apical and coronal root canal seals using contemporary endodontic obturation and restorative materials and techniques. Effect of dentin treatment on in vitro root tubule bacterial invasion. The effect of smear layer removal on marginal contraction gaps. Effect of precurving endosonic files on the amount of debris and smear layer remaining in curved root canals. An in vitro comparison of adhesive systems to seal pulp chamber walls. Coronal leakage following three obturation techniques. Apical sealing ability of a new glass ionomer root canal sealer. Assessment of coronal leakage in teeth root filled with gutta-percha and a glass of ionomer root canal sealer. Sealability of the Trifecta technique in the presence or absence of a smear layer. The effect of smear layer on microbial coronal leakage of gutta-percha root fillings. Microleakage at gingival dentin margins of Class V composite restorations lined with light-cured glass ionomer cement. A study of cavity preparation by Er:YAG laser. Effects on the marginal leakage of composite resin restoration. Adaptation and sealability of two contemporary obturation techniques in the absence of the dentinal smear layer. A comparison of techniques for assessment of coronal dye leakage. Bacterial retention in canal walls in vitro: effect of smear layer. Assessment of morphological changes and permeability of apical dentin surfaces induced by Nd:Yag laser irradiation through retrograde cavity surfaces. Scanning electron microscopic study of the apical dentine surfaces lased with ND:YAG laser following apicectomy and retrofill. Bacterial penetration through canals of endodontically treated teeth in the presence or absence of the smear layer. Effects of dentin age and bonding on microgap formation. Preliminary report of an experimental design for in vivo testing of bonded restorations applied to a new enamel-dentinal bonding agent. The effect of etching on bacterial microleakage of an adhesive composite restoration.
abstract: PURPOSE To evaluate whether the hybrid layer significantly contributes to the seal of adhesive Class V restorations placed in vivo and to the bond strength obtained in vitro . MATERIAL S AND METHODS 20 periodontally severely compromised anterior teeth were selected for the leakage study . In each tooth , one round 3 mm wide V-shaped cavity with a maximum depth of 2 mm was prepared on the labial surface crossing the cementum-enamel junction . The sample teeth were r and omly divided into two groups of ten sample s each : in Group 1 , Scotchbond Multi- Purpose Plus was applied in combination with Z-100 following the manufacturer 's instructions . In Group 2 the bonding procedure was the same as in Group 1 , except that after the phosphoric acid treatment , the cavities were treated with 5 % NaOCl for 2 min . Following a period of clinical service of 60 - 90 days , the teeth were extracted and processed for the leakage test . RESULTS At the enamel site , 30 % of the sample s of Group 1 and 70 % of the sample s of Group 2 showed dye penetration . At the dentin site , 50 % of the sample s of Group 1 showed leakage , while all the sample s of Group 2 were severely infiltrated . Statistically significant differences between the groups both for the enamel sites ( P < 0.05 ) and for dentin-cementum sites ( P < 0.001 ) were found . Bond strength tests were performed on 2 mm thick dentin slides of tapered Class I cavities ( n = 10 in each group ) . The mean bond strength value obtained from cavities treated without NaOCl was 15.23 ( + /-1.40 ) MPa and with NaOCl treatment 20.52 ( + /-1.70 ) MPa . Statistical analysis showed significant differences ( P < 0.05 ) between the two groups . No hybrid layer was detected on the NaOCl-treated sample s by scanning electron microscopy It has been shown previously that the smear layer created during instrumentation of the root canal promotes apical microleakage . The purpose of the present study was to investigate the effect of removal of the smear layer on apical microleakage , using the fluid filtration method . Thirty-six single-rooted human premolar teeth were used . Six of the teeth were selected r and omly as controls , and the remaining 30 teeth were r and omly divided into two groups of 15 teeth each . For the first group ( group 1 ) teeth were irrigated with NaOCl only ( smear layer not removed ) . In the second group ( group 2 ) the teeth were irrigated with 15 % EDTA , followed by NaOCl to remove the smear layer . Both groups were filled with thermoplasticized gutta-percha ( Obtura II ) using glass-ionomer cement as sealer . All teeth were stored at 37 degrees C and 100 % humidity for 2 days . Apical microleakage of the filled root canal was measured by the fluid filtration technique . Hydraulic conductance was measured by the movement of an air bubble in a capillary tube after a pressure of 200 mm Hg was applied to the system . The mean microleakage rate of group 1 and group 2 were 13.0 ( SD + /- 5.1 ) and 16.9 ( SD + /- 15.3 ) nl/s , respectively . Removal of the smear layer caused significantly more apical microleakage ( p < 0.05 , Student 's t test ) than when the smear layer was left intact AIM The purpose of this study was to evaluate the sealing ability of two contemporary  endodontic obturation and restorative techniques and material s. METHODOLOGY Seventy-nine extracted human single-rooted teeth were distributed r and omly in two experimental groups of 36 and 37 specimens ( groups 1 and 2 , respectively ) , one group of three positive controls and one of three negative controls . The teeth were radiographed preoperatively , accessed , and instrumented . After smear layer removal , the teeth in group 1 were obturated using the System B and Obtura and were restored coronally with Core Paste using Tenure as a bonding agent . The teeth in group 2 were obturated using the Microseal technique and were restored coronally with amalgam using Panavia 21 as a bonding agent . All teeth in groups 1 and 2 were coated with three layers of nail varnish on all of their surfaces apart from the apical 4.0 mm and the coronal area above the cemento-enamel junction . The positive control teeth were obturated , restored coronally and completely coated with varnish , whereas the negative control teeth were not obturated , restored coronally , nor coated with varnish . The teeth were radiographed postoperatively and retained in saline solution for 10 days . For the next 10 days they were submerged in India ink . Subsequently all teeth were demineralized , dehydrated and rendered transparent . Dye penetration was measured using a stereomicroscope . RESULTS All material s and techniques provided minimal to zero dye penetration , apart from one specimen in the Core Paste group that showed 4.0 mm of dye penetration . The Wilcoxon rank sum test and t-test showed no statistically significant differences and all material s and techniques tested presented with a high degree of acceptability . CONCLUSIONS It was concluded that these contemporary techniques and material s provide equally good results , but long-term studies are needed for outright inferences to be drawn relative to their clinical performance In light of the in vitro S. sanguis bacterial migration observed deep into root dentin , an in vitro system was developed to determine the viability of these bacteria at the end of migration . Also of interest is whether the smear layer formed during root canal instrumentation modifies migration into root dentinal tubules . Forty-eight bovine root dentin sample s were r and omly split into two groups . Group 1 dentin blocks were not instrumented and were treated with 17 % ethylenediamine tetraacetic acid and 2.5 % sodium hypochlorite for 4 minutes in an ultrasonic bath Group 2 root canals were conventionally instrumented . The smear layer formed was not removed . Dentin blocks were inoculated with a S. sanguis National Collection of Type Culture 7863 suspension . Each sample was immersed in a receiver broth , incubated at 37 degrees C , and checked daily for 14 days . After a 14-day incubation period , group 1 S. sanguis cells remained viable and capable of inoculating the receiver medium after migration through the tubules . Group 2 cells , where the smear layer was intact , revealed an absence of S. sanguis migration in 88 % of the cases . It is therefore plausible that smear layer on canal walls limits S. sanguis penetration of dentinal tubules in vitro The presence of the smear layer prevents direct contact between dentine and a dentine adhesive . The use of agents to remove the smear layer theoretically should improve the bonding of composite resins to dentine . This study examined the effect of smear layer removal on the effectiveness of a dentine bonding agent in reducing marginal contraction gaps . The agent used for smear layer removal in this study was ethylenediamine tetra-acetic acid ( EDTA ) .  Eighty cavities measuring 2 mm in diameter and 1.5 mm in depth were prepared in dentine and r and omly assigned to two equal groups . The control group was restored with Prisma Universal Bond 2 Adhesive and Prisma Fil Resin . The experimental group was similarly restored after pretreatment of dentine with 0.5 % EDTA for 60 s. All specimens were thermocycled and the marginal contraction gaps were assessed using a Nikon Measures cope . The mean contraction gap was expressed as a percentage of the cavity diameter . Results showed that the experimental group registered smaller contraction gaps ( mean : 0.021 % ) than the control group ( mean : 0.027 % ) . No penetration of material into dentine was observed . Pretreatment with EDTA did not significantly improve the effectiveness of the dentine bonding agent used in terms of reduction of marginal contraction gaps Endosonic files are prone to constraint ; this reduces their efficiency , particularly in the apical third and in curved root canals . Precurving the file may reduce constraint , thereby improving the file 's ability to debride . This investigation was undertaken to compare both straight and precurved endosonic files as to debris and smear layer removal .  Thirty-six curved root canals were r and omly allocated into six groups . Each group was prepared using a step-down technique , then instrumented with either a straight or precurved endosonic file of size 15 , 20 , or 25 . The tooth roots were split and examined under the scanning electron microscope . Blind examinations were made for debris and smear layer removal and evaluation scores were analyzed using a log linear approach . The root canals instrumented with the precurved files had a significantly lower debris score than those prepared with straight files . Precurving did not affect smear layer removal . In conclusion , precurving of files decreased the amount of debris but did not affect smear layer removal AIM To compare in vitro the sealing properties of five different dentine adhesive material s ( Prime&Bond NT ( PBNT ) ; Prompt L-Pop ( PLP ) ; Clearfil SE Bond ( CSEB ) ; Scotchbond Multi Purpose Plus ( SMPP ) ; EBS-Multi ( EBSM ) ) inside the pulp chamber . METHODOLOGY Seventy-five recently extracted human molar teeth were used . The roof of the pulp chambers and roots were removed under water cooling . Pulp tissue was removed , and the canal orifices were sealed . The pulp chambers were then treated with 5 % sodium hypochlorite ( NaOCl ) for 1 min . The teeth were r and omly divided into five groups of 15 teeth each . Adhesive systems were applied to the pulp chamber walls according to the manufacturers ' instructions . The sample s were connected to Plexiglass plates , and a fluid filtration method was used for quantitative evaluation of leakage . Measurements of fluid movement were made at 2-min intervals for 8 min . The quality of seal of each specimen was measured immediately , after 24 h , 1 week and 1 month . The data were statistically analysed by repeated- measurements multivariate anova , Friedman test , Wilcoxon signed rank test , Kruskal-Wallis of one-way anova and Mann-Whitney U-tests . The pulp chamber wall with and without NaOCl and resin-dentine interfaces of specimens were observed under a scanning electron microscope ( SEM ) . RESULTS The leakage values of the material s were significantly different at different measurement periods . In all groups , leakage values decreased with time ( P < 0.05 ) . PBNT and PLP had the least leakage during immediate measurements ( P < 0.05 ) . After 1 month , leakage of all adhesive systems was not significantly different ( P < 0.05 ) . SEM observation of pulp chamber walls demonstrated that the irregular dentine surface without smear layer was present in the nontreated group . However , NaOCl application removed the collagen fibrils leaving the dentine surface smooth . At resin-dentine interfaces of specimens , no hybridization zone was observed . CONCLUSIONS None of the material s had created a perfect seal to the pulp chamber walls . PBNT and PLP had better sealing over the short term , but over the long term , there were no differences between the material AIM To compare coronal bacterial and India ink leakage in three different obturation techniques with the smear layer having been removed . METHODOLOGY Seventy extracted single-rooted teeth were instrumented to an apical preparation size 7 Profile Series 29 ( Tulsa Dental Products , Tulsa , OK , USA ) . The smear layer was removed and 20 teeth were r and omly obturated with lateral compaction , 20 teeth with vertical compaction , and 20 teeth with Thermafil ( Tulsa Dental Products , Tulsa OK , USA ) . Ten teeth were used for positive ( five teeth ) and negative ( five teeth ) controls . Teeth were stored for 90 days in 100 % humidity , then subjected coronally to Proteus vulgaris for 21 days to assess bacterial leakage . Following bacterial challenge , India ink was placed coronally for a further 21 days , then scored according to depth of dye leakage . RESULTS  Vertical compaction leaked significantly less than lateral compaction during bacterial challenge . However , when dye was used there were no significant differences . CONCLUSIONS Bacterial leakage and dye leakage demonstrated considerable variability . The use of a dye following bacterial testing may highlight the failure of experimental devices and vertical root fractures , thus avoiding false positive results found with bacterial testing alone This study compared the sealing ability of Ketac Endo with and without smear layer and Tubli Seal .  Thirty upper central incisors and canines with straight canals were instrumented and r and omly divided into three equal groups of 10 . All teeth were obturated with laterally condensed gutta-percha . An additional group of five teeth with unobturated++ root canals served as positive controls . The sealers were Tubli Seal ( group A ) , Ketac Endo ( group B ) , and Ketac Endo preceded by the removal of the smear layer ( group C ) . The teeth were immersed in India ink for 7 days , centrifuged for 5 min at 3000 rpm , cleared , and then examined under a light microscope at X 50 magnification . The mean value of ink penetration for group A was 0.14 mm , for group B 0.24 mm , and for group C 0.48 mm . No statistically significant differences were observed among groups ( p > 0.05 ) The effect on coronal leakage of the use of either a single gutta-percha cone or cold lateral condensation of gutta-percha , with a glass ionomer sealer cement was studied . In addition , the effect of the removal of the smear layer was also determined . Eighty-eight single-rooted teeth were prepared chemomechanically using h and files , with the balanced force technique . Lubrication was provided by either Hibiscrub ( maintaining the smear layer ) or an EDTA-containing paste ( to remove the smear layer ) . Copious irrigation was carried out with 2.2 % sodium hypochlorite . The teeth were allocated r and omly to four groups of 20 teeth each , the remaining eight teeth served as controls . Two groups of teeth , one with and one without smear layer , were obturated with either a single gutta-percha cone or cold laterally condensed gutta-percha , with Ketac Endo as the sealer . The teeth were stored for 6 weeks , thermocycled , and the extent of coronal leakage determined for each group after immersion in India ink for 90 h. The teeth were demineralized , dehydrated and immersed in methyl salicylate , which rendered them transparent . Linear measurement of maximum dye penetration was recorded . The mean depth ( + SD ) of leakage for the groups in which the smear layer was left intact was 1.68 mm ( + 0.38 ) for the single cone ( A1 ) and 2.29 mm ( + 1.58 ) for lateral condensation ( B1 ) . When the smear layer was removed the mean depth of leakage for the single cone group ( A2 ) was 2.04 mm ( + 0.73 ) and 2.37 mm ( + 1.70 ) for the laterally condensed group ( B2 ) . There was no significant difference in coronal leakage between the groups ( P > 0.05 ) The aim of this in vitro study was to assess the sealability of a recently introduced thermoplasticized gutta-percha technique ( Trifecta , Hygenic Corp. , OH , USA ) in the presence or absence of a smear layer . A total of 100 teeth with single straight root canals were included in the study . The teeth were decoronated and the canals prepared with a modified double-flared technique under constant irrigation with 2.5 % sodium hypochlorite solution . The apical matrix was prepared to size 40 and apical patency subsequently confirmed with a size 10 file . Four teeth were discarded for technical reasons and the remaining 96 allocated r and omly into two groups of 44 teeth and a group of eight teeth which acted as controls . Canals in group 1 were obturated r and omly with either cold lateral condensation of gutta-percha or with the Trifecta technique . Canals in Group 2 were rinsed with 17 % REDTA to remove the smear layer and then obturated with lateral condensation or the Trifecta technique . All teeth were suspended in India ink for 9 days , demineralized , and rendered transparent prior to the assessment of apical linear dye penetration . Apical extrusion of sealer and gutta-percha occurred commonly but there was no significant difference between the four obturation groups . However , overall , there was significantly more extrusion of sealer with the Trifecta technique compared with lateral condensation ( P < 0.05 ) . The majority of canals ( 79 out of 88 ) had no evidence of apical leakage and there was no significant difference between the groups . ( ABSTRACT TRUNCATED AT 250 WORDS The aim of this in vitro 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 . One hundred and twenty extracted human teeth with straight , single root canals were decoronated . The canals were prepared using the modified double-flared technique with balanced force under copious irrigation . The apical matrix was prepared to size 40 and apical patency subsequently confirmed with a size 15 file . The teeth were divided r and omly into experimental groups ( 80 teeth ) and control groups ( 40 teeth ) . The root canals of 40 experimental and 20 control teeth were rinsed with 40 % citric acid and 2 % NaOCl to remove the smear layer before obturation . In experimental groups , 20 teeth with smear layer intact and 20 teeth with smear layer removed were obturated with lateral condensation of cold gutta-percha and Apexit sealer . A further 20 teeth with smear layer intact and 20 teeth with smear layer removed were obturated with the Trifecta technique with the same sealer . In control groups , 10 teeth with smear layer intact and 10 teeth with smear layer removed were obturated with lateral condensation of cold gutta-percha and Apexit sealer . These teeth were completely sealed both coronally and apically to serve as negative controls . The remaining 20 teeth with either smear layer intact or smear layer removed were not obturated and served as the positive controls . The root surface of each tooth was sealed with nail varnish . The cut end of a polypropylene tube was sealed around the coronal part of each root canal so that bacteria placed therein could move only through the obturated canal space . Each root was placed in a glass bottle containing sterile Todd-Hewitt Broth ( THB ) and aliquots of 0.5 ml of THB were injected into the polypropylene tube . The model system was centrifuged at 168 g. An innoculum of Streptococcus sanguis in THB was placed in each coronal chamber at 5-day intervals and daily observations were made for bacterial growth in the apical reservoir for 90 days . All positive control teeth showed bacterial penetration within 24 h , while the negative control teeth remained uncontaminated throughout the test period . Leakage through the experimental teeth was variable ranging from 7 to 86 days . There was no statistical significant difference ( P > 0.05 ) in leakage between the obturated canal when the smear layer was either removed or intact This study compared the microleakage of  light-cured and auto-set glass ionomer liners used in Class V composite laminated glass ionomer restorations by determining the amount of microleakage at the gingival cementum/dentin margins . St and ardized nonundercut V-shaped Class V cavities with gingival margins below the cementoenamel junction were prepared on the mesial and distal surfaces of 40 molars , establishing a total of 80 cavities , which were r and omly divided into four groups . Each was lined with glass ionomers : group 1 , Ketac-Bond ( ESPE-Premier ) , which served as the control ; group 2 , XR-Ionomer ( Kerr ) ; group 3 , XR-Ionomer with polyacrylic acid ( PAA ) pretreatment ( Kerr ) ; and group 4 , Vitrabond ( 3 M ) . Specimens were thermocycled for 300 cycles in 0.5 % aqueous solution of basic fuchsin between 4 and 55 C with a 1-minute dwell time , and individually embedded in an epoxy resin . Statistical analysis indicated no differences among groups using the light-cured glass ionomer ( groups 2 to 4 ) , and they showed significantly less leakage than the control ( group 1 ) at P less than 0.00001 ) . Removal of the smear layer using 10 % polyacrylic acid solution did not influence microleakage in restorations with light-cured glass ionomer liners The purpose of this study was to evaluate marginal leakage of composite resin restoration from cavities prepared by Er : YAG laser .  The observation of the dentin surface after the application of laser irradiation was performed by LSM , the cutting surface showed a rough surface similar to scales , and exposed dentinal tubules were observed without striations or a smeared layer formation that were observed when using a rotary cutting device . Leakage tests revealed no significant differences in the marginal seal for both enamel and dentin between cavities prepared by Er : YAG laser irradiation and when using an air-turbine . In this study , the usefulness of cavity preparation by Er : YAG laser irradiation in composite resin restoration was suggested AIM The aim of this study was to evaluate the adaptation and short- and long-term sealability of two different thermoplastic techniques -- a core carrier technique , Thermafil ; and a warm vertical continuous wave of compaction technique , System B. METHODOLOGY Fifty-one mesial roots of m and ibular molars with separate canals , patent canal orifices and curvature greater than 15 degrees were cleaned and shaped with Orifice Shapers and ProFile.04/.06 taper Ni-Ti rotary files using 5.25 % NaOCl and 17 % REDTA to a size 30.04 taper Profile at the apex to create a continuous tapered preparation . Canals were r and omly obturated with Sealapex root canal sealer and either alpha-phase gutta-percha on a plastic Thermafil carrier , or nonst and ardized beta-phase gutta-percha using the System B heat source . Proximal radiographs of roots were evaluated by three examiners based on established criteria for overall material adaptation , apical adaptation and filling material extrusion . Teeth were r and omly separated into three groups of 17 each and placed in black India ink for 10 days , 24 h , or after 67 days storage in Hank 's Balanced Salt Solution . All roots were demineralized and rendered transparent . Three examiners evaluated the apical leakage by the linear measurement of dye penetration under the stereo-microscope . The movement of filling material into canal irregularities was also evaluated . RESULTS Both obturation techniques were not significantly different in the overall canal obturation and in the apical third adaptation ( P > 0.05 ) . Significantly more filling material extrusion beyond the apex was noted with the Thermafil technique ( P < 0.001 ) . No significant difference was found amongst the 67-day , 10-day and 24 h System B groups ( P > 0.05 ) . The 67-day Thermafil group showed significantly more leakage than the 10-day and 24 h Thermafil groups . There was a significant difference in the degree of leakage between the 67-day Thermafil group and the 67-day System B group ( P < 0.05 ) , but not between the 10-day and 24 h groups ( P > 0.05 ) . Both obturation techniques produced substantial filling material movement into canal irregularities . CONCLUSIONS It was concluded that Thermafil demonstrated more filling material extrusion beyond the apex and significantly more long-term apical leakage This study was design ed to compare different techniques for coronal dye leakage testing . One hundred and fifty extracted human anterior teeth were fully instrumented and r and omly divided into two experimental groups of 60 teeth each , plus two groups of 15 teeth each for positive and negative controls . One group was rinsed with 5.25 % NaOCl ( smear layer intact ) , whereas the other group was flushed with 17 % EDTA and 5.25 % NaOCl ( smear layer removed ) . Roots were obturated with gutta-percha using lateral condensation and AH Plus as root canal sealer . Each experimental group was divided into three subgroups of 20 teeth each for three methods of testing coronal dye leakage : passive dye penetration , penetration with vacuum applied , and fluid filtration methods . The teeth were left in 100 % humidity at 37 degrees C for 5 days before being immersed in Indian ink for 2 days and cleared . The linear extent of dye penetration was measured . Mean depth of leakage for the groups with the smear layer intact was 2.5 + /- 1.0 mm for passive dye penetration , 6.7 + /- 2.8 mm for vacuum dye penetration , and 3.0 + /- 1.1 mm for fluid filtration dye penetration . In the group in which the smear layer was removed , the mean depths of leakage were : 3.2 + /- 2.1 mm for passive dye penetration , 5.8 + /- 2.8 mm for vacuum dye penetration , and 3.4 + /- 2.1 mm for fluid filtration . The vacuum method result ed in significantly ( p < 0.05 ) more dye penetration than fluid filtration and passive dye penetration . The presence or absence of smear layer had no statistically significant effect ( p > 0.05 ) on any of the leakage testing techniques When dentin is planed by endodontic instruments , a smear layer forms . Whether this layer should be removed is unknown and controversial . This study was conducted to assess the effect of the smear layer on retention of bacteria using an in vitro root canal bacterial colonization model . Canals of 26 extracted human canines were step-back prepared using 2.5 % NaOCl . Teeth were then r and omly divided into two groups based on the type of high volume final flush : 1 - 20 ml of sterile saline ( 0.85 % wt/vol ) or ( 2 - 10 ml of 17 % EDTA followed by 10 ml of 2.5 % NaOCl which removes smear layer . Streptococcus anginosus ( milleri ) was cultured in trypticase soy broth supplemented with 0.5 % yeast extract at 37 degrees C in 5 % CO2 . Cells were harvested by centrifugation and resuspended in fresh media . Serial dilutions were performed to achieve inocula of 10(6 ) colony-forming units in a 30-microliters volume . Teeth were inoculated and incubated for 2 h in 5 % CO2 at 37 degrees C. Following incubation , teeth were split and processed for microbiological analysis . Numbers of colonizing bacteria were determined by a spiral-plating system . Enumeration of the numbers of bacteria revealed a reproducible , order of magnitude difference ( p = 0.0002 ) between teeth with smear layer ( 10(4 ) colony-forming units ) versus teeth without smear layer ( 10(5 ) colony-forming units ) . This suggests that smear layer produced during root canal therapy may inhibit bacterial colonization of root canals . One suggested mechanism is that smear layer may block bacterial entry into dentinal tubules The purpose of this in vitro study was to observe the morphological changes and apical dye penetration at apical dentin surfaces induced by Nd : YAG laser irradiation at different power setting s with and without a laser initiator . Seventy five single rooted human maxillary anterior teeth were used . Following the establishment of the working lengths , the root canals were enlarged with step-back technique . The apex of each root was resected 3 mm perpendicular to its long axis . St and ard Class I cavities of 2 mm depth and 2 mm width were prepared . The teeth were r and omly divided into five groups with fifteen teeth in each . In Group 1 , the retro grade cavity preparations were lased with Nd : YAG laser at 2 W and those in Group 2 preparations were lased with Nd : YAG laser at 3.2 W. In Group 3 , the retro grade cavity surfaces were lased with Nd : YAG laser at 2 W following the application of India ink . Group 4 was lased with the same setting s of Group 2 after an absorbent cotton point soaked with India ink was inserted into the cut dentinal surfaces and the inner walls of the apical preparations . Group 5 served as control . Five teeth from each group were examined using scanning electron microscopy ( SEM ) . The amounts of smear layer , debris , and recrystalized dentin present were assessed and scored . Retro grade cavities of ten teeth from each group were filled with amalgam to examine apical dye penetration . The teeth were immersed in 2 % basic fuscin and kept for 48 hours . Dye penetration was evaluated by stereomicroscope at a magnification of X10 . The results showed the usage of India ink with Nd : YAG laser enhanced the amount of melting and recrystalization of dentin and the radiation and initiator increased the leakage The purpose of this investigation was to study the effects of a Nd : YAG laser on the cut surface of teeth using scanning electron microscopy ( SEM ) . Eighteen single-rooted teeth were cleaned , shaped , and obturated with gutta-percha and root canal sealer . The apical 3 mm of each tooth were resected with a diamond fissure bur , and the teeth were r and omly divided into two groups of nine teeth each . The resected surface of each root in one group was lased twice . The duration of lasing and the number of pulses were recorded for each tooth . The teeth were air dried , mounted on stubs , sputter-coated with gold-palladium and examined under SEM . Application of the Nd : YAG laser caused melting of apical dentine surfaces . The melted material resembled the appearance of glazed interconnected droplets . Resolidification and recrystalization of the melted areas appeared to be incomplete and discontinuous . Some areas between the glazed regions appeared similar to those of non-lased apical dentine resected root surfaces OBJECTIVES The goal of this study is to determine if the smear layer affects the passage of bacteria through or around obturating material as evidence d by penetration of bacteria through and out the canal . Specifically , this study focused on determining the effect of the smear layer on the magnitude of bacterial penetration through the apical foramen . METHODS Thirty extracted , maxillary central or lateral incisors were collected . Teeth were r and omly assigned ( 10 teeth per group ) to three groups : ( 1 ) smear layer removed , ( 2 ) smear layer present , and ( 3 ) negative control . Canal preparation and obturation using lateral condensation , gutta percha , and AH 26 sealer was performed on all of the teeth . Removal of the smear layer was accomplished by rinsing with 17 % EDTA . The model systems consisted of an upper chamber attached to the cemento-enamel junction and a lower chamber at the apices of the teeth . St and ardized bacterial suspensions containing Fusobacterium nucleatum , Campylobacter rectus , and Peptostreptococcus micros were inoculated into the upper chambers . Models were incubated anaerobically at 37 degrees C. At various times over a 60-day period , sample s were taken from the lower chamber and spiral-plated on selective-differential media to determine numbers and types of bacteria . RESULTS Leakage results were as follows : ( 1 ) smear layer present-6/10 leaked ; ( 2 ) smear layer removed-0/10 leaked ; ( 3 ) negative control-0/10 leaked . Profiles of bacterial leakage were similar among the groups . F. nucleatum was the predominant microorganism . CONCLUSIONS This study indicated that removal of the smear layer reduced the leakage of bacteria through the root canal system This study compared the effectiveness of dentin adhesives  in extracted molars from younger ( 16 - 26 ) and older ( 58 - 87 ) human subjects . Extracted molars were selected to be restored with one of two dentin bonding agents ( n = 22 per group ) . Opposite sides of each molar were ground flat and a 3 mm x 3 mm cylindrical preparation was milled into each surface . The opposing surfaces of each molar were then r and omly restored with either a dentin bonding system that adhered to the dentin smear layer or one which bonded to the dentin after the smear layer was removed . All sample s were examined at x150 to determine both the maximum gap in micrometers and extent of the gap in degrees . There were significantly shorter ( P < 0.05 ) microgaps in older dentin with a bonding system that removed smear layer . This bonding system also produced shorter gaps in older dentin than in younger dentin . However , there was no statistically significant difference in the percentage of gap-free margins between age groups Because of inconsistency often found between in vitro testing and in vivo performance , a new restorative bonding system was evaluated by the placement of  restorations in vivo in teeth to be extracted . The microleakage was determined following extraction after 3 months of clinical service . In each of the sample teeth , two restorations were placed on the labial surface , one in the middle of the enamel portion and the other extending over the cementoenamel portion . The results of this pilot study indicated that bonding to conditioned enamel with the new adhesive material is effective , and bonding to conditioned dentin appears to be clinical ly adequate OBJECTIVES The incidence of bacterial microleakage , pulp inflammation and necrosis associated with dentine etching treatments prior to restoration are not known . Consequently , to resolve some of the controversy surrounding the effects and importance of vital dentine etching , the authors investigated these factors . METHODS 110 st and ardised class V cavities were cut into buccal dentine , without exposing the pulp of teeth scheduled for extraction for orthodontic reasons . Cavities were either left unetched , or etched with the non-equivalent treatments of phosphoric acid gel for 60s or Ethylenediaminetetraacetic acid ( EDTA ) for 30s , prior to placement of composite resin . Teeth were collected and pulp responses were evaluated according to ISO guidelines , using pathohistomorphometric analysis and ANOVA statistics . RESULTS Etching was found to be correlated to bacterial microleakage ( p=0.0001 ) and tertiary dentine formation ( p=0.0023 ) . Bacterial microleakage was correlated to inflammatory activity ( p=0.0001 ) . The frequency of bacterial microleakage was : no etching ( 65 % ) , EDTA ( 51 % ) and phosphoric acid ( PA ) ( 20 % ) . SIGNIFICANCE Vital dentine etching treatment is of extreme importance for the placement of RC to minimise bacterial microleakage .  PA etching proved to be more effective at preventing bacterial microleakage than non-etching , and etching with EDTA
target: Under the conditions of these in vitro leakage studies , it is concluded that smear layer removal improves the fluid-tight seal of the root canal system whereas other factors such as the obturation technique or the sealer , did not produce significant effects
background: The purpose of this systematic review was to determine whether smear layer removal reduces leakage of obturated human teeth in vitro .