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PubMed1996

A scanning electron microscopic evaluation of the debridement capability of sodium hypochlorite at different temperatures.

The effect of raising the temperature of the irrigant solution on the smear layer was evaluated in the middle and apical third of 22 human upper incisors. A 5% sodium hypochlorite (NaOCl) solution was used at 21 degrees C and at 50 degrees C. After hand instrumentation and treatment with the irrigant, teeth were fractured into halves and examined by scanning electron microscopy. Characteristics of the smear layer in the two groups of specimens were compared. In the middle third, where NaOCl had been used at 50 degrees C, the smear layer was thinner and made of finer, less well-organized particles than where it had been used at 21 degrees C. In the apical third, the smear layer was of almost the same thickness in the two groups of specimens, although the particles were finer where the NaOCl had been used at 50 degrees C.

Dental Pulp Cavity↗
PubMed1991

Epinephrine permeation across dentin in vitro.

The permeation of epinephrine across human dentin discs was studied in vitro. Permeation was measured across dentin of two different thicknesses, with and without the presence of smear layers. Epinephrine was readily detected at the earliest measured time (10 min) and reached peak concentrations between 30 and 50 min. Epinephrine flux (concentration multiplied by the volume of the effluent per min) increased with decreasing thickness of the discs and increased significantly with the removal of the smear layer. The T 1/2 (half-time in min necessary to reach steady-state diffusion of epinephrine) decreased as dentin thickness was reduced and fell further in the absence of the smear layer. This study suggests that the permeation of epinephrine across dentin is inversely related to dentin thickness and retarded by the presence of a smear layer. Also, the topical use of 1 mg/ml epinephrine produced therapeutically useful drug concentrations, but the rate of permeation was relatively slow.

Dental Pulp↗
PubMed1992

A confocal microscopic evaluation of the interface between Syntac adhesive and tooth tissue.

The aim of this study was to microscopically evaluate the effect of dentine smear layer thickness, tubular orientation and immediate stress application on a modern dentine bonding agent. Eighty mesial and distal wedge-shaped cavities were cut into dentine/cementum cervically in 40 extracted human lower third molars. The thickness of the dentine smear layer was reduced by polishing the cavity surface in half the samples. Each component of the bonding agent (Syntac: Ivoclar Vivadent) was labelled with a fluorescent dye, the unfilled resin being light cured for 30 s with the composite restoration placed in one increment and light cured for 40 s. The samples were longitudinally sectioned using a slow speed diamond saw underwater, either immediately or 24 h post placement. The sectioned surfaces were then viewed using a confocal optical microscope. The thickness of the smeared layer only effected the penetration of adhesive in dentine tubules which were separated from the pulp chamber by the cavity design. These areas were well filled with adhesive; however, areas communicating with the pulp chamber showed no penetration differences due to smear layer reduction by polishing. The interdependence of the adhesive components was illustrated by failure to achieve a well-impregnated tooth/adhesive hybrid layer when the materials were incorrectly handled. The Syntac/dentine interface was generally able to withstand the stress of sectioning immediately post placement, but showed signs of failure in the cavity line angle when the applied stresses were greatly increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1990

Effect of a new conditioning agent on dentin.

The effect of varying the duration of application of the conditioner for light-cured Zionomer was studied. The conditioner is a solution of oxalic acid and aluminum nitrate in a weak mineral acid and has a pH of 2.06. Recently extracted non-carious human premolars were sectioned horizontally 300 microns below the amelodentinal junction and then lightly ground with a high-speed diamond bur under copious water-spray to produce a smear layer. Each was then sectioned vertically into three and all the specimens were either treated with the Zionomer Conditioner for 5, 10, 20 or 30 seconds, or with distilled water as a control. All the specimens were examined in a scanning electron microscope at x1000 and photomicrographs taken which were then assessed, independently, by the authors. The results revealed that application of Zionomer Conditioner for as little as 5 seconds was sufficient to remove most of the smear layer. There was complete removal of the surface smear layer in specimens treated for 10 seconds or more. Either a 20 second or a 30 second application removed the smear layer completely and could also widen the exposed tubule orifices.

Acid Etching, Dental↗
PubMed1994

Scanning electron microscopic evaluation of different endodontic procedures on dentin morphology of human teeth.

Four manual endodontic instruments, an ultrasonic and an endosonic system were studied with a view to evaluating the morphology of the smear layer and the amount of debris and pulpal residues in the apical third of human extracted straight teeth from 55- to 75-yr-old patients. The manual instruments were K files, Ergoflex files used with the step-back technique, Canal Master with its own technique, and Flex-R with the Roane technique. The ultrasonic system was Suprasson Piezo and the endosonic was Excalibur. Human extracted teeth with straight canals were used and examined under a scanning electron microscope. All manual instrumentations showed a homogeneous compact smear layer and no pulp residues. No statistical differences were observed among the four manual techniques. Ultrasonic technique showed the complete removal of the smear layer, leaving small amounts of pulp debris at the apical third, while the Excalibur showed an almost complete elimination of the smear layer, leaving a homogeneous layer of pulpal residues along the canal.

Aged↗
PubMed1996

Effect of dentin treatment on in vitro root tubule bacterial invasion.

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 samples were randomly 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.

Animals↗
PubMed1991

Permeability of normal versus carious dentin.

Although a number of reports have been published demonstrating that carious dentin is less permeable than normal dentin, these reports have been qualitative rather than quantitative. The purpose of this in vitro study was to apply a quantitative technique to the study of the permeability of carious human teeth before and after excavation, before and after removal of the smear layer and before and after preparation of a control cavity of similar size and depth in normal dentin subjected to the same measurements, for comparative purposes. Dentin permeability was measured as a hydraulic conductance. The permeability values measured at each step in the protocol were expressed as a percent of the maximum permeability of both cavities, permitting each tooth the serve as its own control. Carious lesions exhibited a slight degree of permeability (2.3 +/- 0.6% of controls) which remained unchanged after excavation of the lesions. Removal of the smear layer in the excavated carious lesions increased the permeability significantly to 6.9 +/- 3.2%. Preparation of a control cavity of the same area and depth increased the permeability slightly. Removal of its smear layer increased the permeability of the dentin 91%. These results confirm previous qualitative studies that carious dentin, even after excavation and removal of the smear layer has a very low permeability.

Acid Etching, Dental↗
PubMed2001

Adhesion of a glass-ionomer root canal sealer to the root canal wall.

Glass-ionomer root canal sealer is commonly used because of its chemical bonding and favorable physical characteristics when bonding to dentin. This study was designed to determine the tensile bond strength of a glass-ionomer sealer (Ketac Endo, Espe, Seefeld, Germany) on root canal walls after pretreatment with different conditioners. Flat inner surfaces of root canal specimens were prepared. The specimens were divided into five groups of 10 teeth, and the groups were conditioned with one of the following smear layer removal solutions: 15% EDTA/NaOCl, 10% polyacrylic acid, 35% phosphoric acid, 6% citric acid, and 5.25% NaOCl as a control. Then the exposed root canal areas were coated with Ketac-Endo. Tensile bonding was measured using a universal testing machine until ultimate failure was obtained. The groups that were treated with phosphoric acid and citric acid showed significantly higher bond strengths than the groups that were treated with 15% EDTA and polyacrylic acid (p < 0.05). Bonding to dentin without smear layer removal (NaOCl group) was too low to be measured in the testing apparatus. Scanning electron microscopy confirmed that phosphoric and citric acids were more effective in removing smear layer than EDTA or polyacrylic acid. The result supported the view that pretreatment with phosphoric acid or citric acid should be used in association with glass-ionomer root canal sealer to achieve the most effective removal of the smear layer and to provide better adhesion.

Acid Etching, Dental↗
PubMed1999

Effects of Nd:YAG lasers on root canal walls: a light and scanning electron microscopic study.

OBJECTIVE: This study evaluated amounts of debris, smear layer, and recrystallized dentin on root canal walls treated with an Nd:YAG laser. The presence of carbonized material was also assessed. METHOD AND MATERIALS: The root canals of 36 extracted incisors were prepared by stepdown and stepback techniques and divided into 4 groups. One group was not treated further, while 3 others were exposed to the laser beam at an energy density of 159, 239, or 318 J/cm2. The roots were split longitudinally, photographed, and examined using a scanning electron microscope. The amounts of debris, smear layer, and recrystallized dentin were recorded from horizontal bands around the root, 2, 6, and 10 mm from the apices. RESULTS: Mean smear layer scores were similar for all groups at the 3 levels examined, ranging from 2.157 to 2.851 on a scale of 0.0 to 3.0. Mean debris scores were similar for all groups at the 3 levels examined, ranging from 0.774 to 1.408 on a scale of 0.0 to 3.0. Recrystallized dentin was recorded in all 3 irradiated groups at the 2-mm level, but only in the group irradiated with 318 J/cm2 at the 6- and 10-mm levels. Severe carbonization was recorded at the 2-mm level. CONCLUSION: Use of the Nd:YAG laser did not reduce the mean amounts of debris and smear layer compared to a nonirradiated group. Carbonization was recorded in the apical part of the canal, but this is not obvious when only scanning electron photomicrographs are examined.

Dental Pulp Cavity↗
PubMed1993

Cleaning of oval canals using ultrasonic or sonic instrumentation.

This study investigated the effect of direction of file oscillation on the amount of debris and smear remaining within oval canals. Sixty-five lower premolars were allocated to six experimental groups (n = 10) and one control group (n = 5). Canals were prepared using Gates Glidden burs and hand instruments. Preparations were completed using either an ultrasonic size 15 K file or a sonic size 15 shaper file. Three preparation techniques were used: (a) file oscillation toward oval recesses within the canal, (b) file oscillation at right angles to the recesses, and (c) rotational movement of handpiece. Canals were examined under the scanning electron microscope and blindly scored for debris and smear layer. Log linear analysis revealed no significant difference (p > 0.05) between sonic or ultrasonic instrumentation as to debris or smear layer remaining. File oscillation directed toward oval recesses left the least amount of debris (p < 0.05). Smear layer remained unaffected by all techniques.

Chi-Square Distribution↗
PubMed2000

The effect of root canal preparation on microleakage within endodontically treated teeth: an in vitro study.

AIM: The purpose of this study was to evaluate the effects of smear layer and canal instrumentation on leakage in root-filled teeth. METHODOLOGY: Six groups (n = 12) of freshly extracted human canines and premolars with closed apices and single roots were used. Groups A, B, C, and D were instrumented with engine-driven rotary nickel-titanium MCXIM files and Groups E and F were instrumented with conventional stainless steel hand files. Groups A, C, and E were flushed with 3.0 mL of 17.0% REDTA to remove the smear layer prior to obturation. All teeth were flushed with 5.25% NaOCl, then obturated with AH-26 sealer and either the lateral condensation (Groups C-E) or thermomechanical compaction technique (Groups A and B). Copper wire was placed coronally in contact with the gutta-percha in each tooth and, after immersion in 0.9% NaCl solution, a 10 volt dc voltage was connected between each tooth and a stainless steel electrode. The current flow in the circuit was observed for 45 days. One way ANOVA and Duncan's Multiple Range Test were used to compare Groups A-F at time intervals of 10, 20, 30 and 45 days and identify statistically significant differences. RESULTS: Significantly less microleakage occurred when the smear layer was removed and when the canals were obturated with thermoplasticized gutta-percha. Canals instrumented with engine-driven NiTi files exhibited less leakage than hand-instrumented canals irrespective of obturation method. CONCLUSIONS: Smear layer removal is beneficial to root canal sealing. Obturation with thermoplasticized gutta-percha provides a superior seal whilst canal instrumentation with engine-driven NiTi files reduces the extent of microleakage in root canals.

Analysis of Variance↗
PubMed2003

The effect of three types of rasps on the occlusal surface of equine cheek teeth: a scanning electron microscopic study.

Two hand rasps (tungsten chip blade, solid carbide blade) and an electrically-driven solid carbide axial bur were used to treat the cheek teeth of 2 horses immediately postmortem. All teeth were normal and were rasped to a standard considered satisfactory in practice. Six teeth from each horse served as untreated controls. Following treatment, the teeth were extracted and the clinical crown removed and prepared for scanning electron microscopy. Teeth were also extracted and examined from a horse that had excessive dental treatment previously. Dental debris created by the procedures was collected and examined. All three rasp techniques resulted in amputation of odontoblast processes. The solid carbide blade cut deep gouges and grooves into the surface of the dentin, chipping the enamel and peripheral cement. No smear layer was created. Rasping with a tungsten chip blade created a partial smear layer and a smoother surface than the solid carbide blade. The electrically-driven bur produced a complete smear layer and removed all dental tissues to a smooth layer. The enamel had also been damaged by the electric bur. Crown particles collected after the procedures were larger following hand rasping compared with particles produced by the electric bur. The extent of damage to sensitive and vital dentin tissue was of concern. Further studies are required to establish the optimum technique for rasping equine cheek teeth.

Animals↗
PubMed2001

Anti microbial activity of dimercaptosuccinic acid (DMSA): a new chelating agent.

Successful outcome of endodontic treatment depends on elimination of bacteria and their products present in the root canal. It has been reported that after careful chemicomechanical preparation, smear layer is formed on the walls of canal, which contains bacteria and their products. Chelating agents, when used during chemicomechanical preparation, remove the smear layer. DMSA--a new chelating agent, when used in root canals, removes the smear layer more than EDTA when used as irrigant in root canals. This study was conducted to determine whether DMSA has anti microbial activity and compare it with EDTA. The results show that EDTA (10% & 15%) had marked anti microbial activity, both on culture plates and in broth. DMSA (10% & 15%) did not show anti microbial activity on culture plates while in broth it had marked activity.

Anti-Infective Agents, Local↗
PubMed1996

Relationship between endodontic preparations and human dentin permeability measured in situ.

Endodontic preparations may induce changes in the permeability of radicular dentin. The aim of this study was to analyze the variation of hydraulic conductance measured in situ after three endodontic preparations (manual K+H files, ultrasonic preparation, and manual with NaOCI and EDTA). Scanning electron microscopic analysis of the canal walls was made to permit correlations between variations of permeability and the amount of surface covered with smear layer or organic debris. There was an inverse relationship between the variations in dentin permeability and the presence of smear layer. The significance of this correlation was variable according to the techniques used. Dentin thickness was as significant a factor in influencing radicular permeability as was the smear layer. The use of EDTA induced a considerable increase in radicular permeability. The use of ultrasonics produced a similar but weaker effect.

Analysis of Variance↗
PubMed1997

The effectiveness of three irrigating solutions on root canal cleaning after hand and mechanical preparation.

The purpose of this in vitro study was to evaluate and compare the efficacy of three irrigating solutions after hand and mechanical instrumentation. Sixty intact, single, straight-rooted, human teeth were used in this study. They were instrumented using K-files sizes 15 to 50 with hand or mechanical instrumentation. Mechanical instrumentation was with one of two handpieces, the Endocursor or Endolift. Instrumentation time for each file was 1 min. Each change of file was followed by irrigation with 1 mL 1% NaOCl. A flush of 2 mL of one of three irrigating solutions Largal Ultra, Tubulicid Plus or 50% citric acid, was administered at the end of the instrumentation and a final flush of 5 mL distilled water completed the treatment. The specimens were prepared and viewed under the scanning electron microscope. There were no significant differences in the smear layers produced by the three methods of instrumentation. The use of Largal Ultra and Tubulicid Plus removed considerable amounts of the smear layer regardless of the method of instrumentation. The use of 50% citric acid, on the other hand, removed the smear layer only partially whilst producing rather diverse findings.

Adult↗
PubMed1990

[Bacterial penetration of bovine dentinal tubules. 1].

The penetration by bacteria through dentinal tubules was studied using a device that included portion of bovine anterior teeth. Strains of 4 genera, Streptococcus mutans, Lactobacillus casei, Staphylococcus aureus and Escherichia coli, were used for the experiment, and the effects of acid etching of dentin on the penetration of bacteria through the dentin was examined. The time required for penetration through dentinal tubules of acid-etched samples was shorter than that of unetched samples. The minimum time required for half the samples to become positive for bacterial penetration through dentin MPT50 was 4 hours for all strains chosen when the acid-etched dentin was the target. In non-acid etched samples, the MPT50 varied among the genera and ranged from 20 hours to 48 hours; the speed of penetration was Sta. aureus = L. casei greater than Str. mutans greater than E. coli. Observation under the scanning electron microscope indicated that the smeared layer was completely coated on the surface of the prepared cavity, and when bacterial penetration occurred, a portion of the smear layer on the dentin disappeared. In longitudinal sections, the penetration by the bacteria into the tubules was visible. From these results, it is suggested that the smeared layer have an important effects on bacterial penetration through these tubules.

Acid Etching, Dental↗
PubMed1994

The effects of current dentinal adhesives on the dentinal surface.

The effects of the dentinal surface treatments from six currently available commercial dentinal adhesives are presented. The adhesives are All-Bond 2, etched and unetched, Syntac, Prisma Universal Bond 3, Scotchbond Multipurpose, Tenure Solution, and Adhesive By Choice. Unerupted third molar human teeth were sectioned and treated with the appropriate adhesive according to the manufacturer's directions. After the teeth were treated, they were processed for observation by scanning electron microscopy. Scanning-electron microscopic photomicrographs were made of each step in the process to show the effects of the constituents, including the adhesives, on the dentinal surface. For All-Bond 2, unetched, the smear layer was not removed before the primer and the adhesive were applied. The primer for Prisma Universal Bond 3 altered the smear layer by reacting with it but did not produce a large demineralized zone in the dentin. All the other adhesives did remove the smear layer before the tooth was treated with the primer and adhesive.

Acid Etching, Dental↗
PubMed2004

Dentine hypersensitivity: development and evaluation ofamodel in situ to study tubulepatency.

BACKGROUND AND AIMS: Lesions of dentine hypersensitivity have numerous tubules open at the dentine surface as opposed to non-sensitive dentine where tubules are mostly covered by a smear layer. The present two studies were designed to model both states in situ and evaluate the effects of agents on the model. METHOD: Etched (sensitive) and smeared (non-sensitive) dentine specimens prepared from human third molar teeth were retained in lower buccal acrylic appliances. The results of Study 1 led to the development of a method to ensure tubules were sectioned at right angles. Study 1 was a 5-day period, seven treatment regimens randomised, part blind cross over design involving five subjects. Treatments were 2x day application of a desensitising (SA) or non-desensitising toothpastes (F) or chlorhexidine (CHX) mouthwash with or without drinking orange juice (OJ)(1 l/day). A no treatment group (P) allowed plaque to accumulate. The evaluation of effects was observational by scanning electron microscopy (SEM). Study 2 involved 1 subject, 4 treatments applied once and studied after 0, 6, and 12 h by SEM with image analysis. The 12 h groups were studied with and without imbibing water or OJ. Treatments were two desensitising (SA & SC) and one non-desensitising (F) toothpastes and an in office product (DS). RESULTS: Study 1: Treatment SA resulted in occlusion of tubules an outcome little changed by OJ. Treatment P produced a bio-film, which covered the dentine surface. CHX produced some tubule occlusion in three of the five subjects. F+/-OJ and CHX+OJ had little effect and tubules remained open. For smeared specimens toothpastes and OJ removed the smear layer but SA+/-OJ blocked tubules. P and CHX had no effect on the smear layer. Study 2: At 0 h, tubule occlusion was in order of magnitude DS>or=SA>SC>F. After 6 and 12 h with SA, SC and F some loss of occlusion occurred but not DS. Water and OJ by 12 h decreased occlusion for SA, SC and particularly F. Water and OJ removed virtually all of DS. CONCLUSIONS: The aims of Study 1 were achieved and effect of treatments was not inconsistent with data in vitro. The need for more standardisation of specimens was appreciated and applied in Study 2 to allow image analysis to quantitatively record data. Further use of the model in randomised controlled clinical trials is envisaged.

Acid Etching, Dental↗