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PubMed1996

Postnatal development of membrane properties of layer I neurons in rat neocortex.

Using whole-cell patch-clamp techniques in brain slices, we studied the postnatal development of electrophysiological properties of rat neocortical layer I neurons during the first three weeks of postnatal life. Neurons, including Cajal-Retzius cells, were visualized under Nomarski optics before recording. In the first postnatal week, all layer I neurons, including Cajal-Retzius cells, had low resting membrane potentials (-40 to -55 mV), high input resistances (1-5 G omega), and long membrane time constants (80-130 msec). Action potentials (APs) of layer I neurons early in postnatal development were lower in amplitude and longer in duration. The threshold for APs also was more depolarized than in older neurons. A medium after-hyperpolarization already was present at postnatal day 0 (PN0), but fast afterhyperpolarizations were not seen until PN10. At all postnatal ages, layer I neurons were capable of repetitive firing, displayed little or no frequency adaptation, and did not display slow afterhyperpolarizations. Early in development, layer I neurons had a prominent hyperpolarization-activation depolarizing sag that decreased with age. These results suggest that the membrane properties of rat neocortical layer I neurons mature rapidly during the first two postnatal weeks. Cajal-Retzius cells had electrical properties similar to other layer I neurons and did not show an earlier maturation of membrane properties.

Action Potentials↗
PubMedDate not supplied

Comparative SEM and TEM observations of nanoleakage within the hybrid layer.

Most adhesive interface studies have involved SEM demonstration of the penetration of adhesive resins into demineralized dentin surfaces with subsequent creation of hybrid layers. Nanoleakage is a term that describes the diffusion of small ions or molecules within the hybrid layer in the absence of gap formation. The present microscopic study examined the nanoleakage of the hybrid layer using a silver nitrate staining technique. Adhesive dentin sandwiches, which were immersed in a silver nitrate solution, were prepared for both SEM and TEM examination using both the Clearfil Liner Bond and All-Bond 2 adhesive systems. Both systems demonstrated silver accumulation within the hybrid layers. Clearfil Liner Bond System showed scattered silver particles at the bottom two-thirds of the hybrid layer by both SEM and TEM observation, whereas All-Bond 2 revealed stained fiber-like structures within the full thickness of the hybrid layer. To evaluate the quality of the hybrid layer, the utilization of tracer molecules such as silver nitrate that are detectable by both SEM and TEM is proposed. It is important to determine the location and morphology of these nanometer-sized porosities that may permit the hydrolysis of collagen fibers and degradation of adhesive monomers.

Collagen↗
PubMed1996

Contributions of individual layer 6 pyramidal neurons to local circuitry in macaque primary visual cortex.

We have studied the contributions of individual layer 6 pyramidal neurons in macaque primary visual cortex to local cortical circuitry by intracellular labeling and analysis of the morphologies of 58 neurons. These neurons are separated based on the laminar specificity of axonal and dendritic arbors into two classes, class I and class II, and into several types within these classes. Class I neurons project axons heavily and predominantly to layer 4C, whereas class II neurons have axonal projections primarily to layers other than 4C. Only 16 of the 58 neurons in our sample (28 percent) project to the white matter. Class I projection neurons are found at the top and bottom of layer 6, suggesting that they project to the lateral geniculate nucleus, whereas class II projection neurons are located in the middle of layer 6, suggesting that they project to the claustrum. The different types of class I neurons are distinguished from one another based on the sublaminar specificity of their axonal and dendritic arbors within layer 4, where they are biased toward compartments dominated by input from different functional streams. They are also distinct in their distributions within the depth of layer 6. The distinctive characteristics of the neuronal types we have identified suggest that each receives input from different sources and projects to a set of targets that is functionally appropriate. Thus, each type is likely to contribute uniquely to computations within V1 and extrinsically.

Animals↗
PubMed1997

[Thickness of the muscle layer of the gastroepiploic artery and the internal mammary artery--a presumable factor of flow instability in GEA during the perioperative period].

UNLABELLED: Recently the right gastroepiploic artery (RGEA) is often used for coronary bypass grafting. Although patency rate of the RGEA is as high as that of the IMA, instability of blood flow through the RGEA during the perioperative period is reported. We assumed that the RGEA is more predisposed to spasm than the internal mammary artery (IMA). This study was carried out to verify the following two points. 1. The GEA has a smaller internal diameter and thicker muscle layer than the IMA. 2. The contractile force of the muscle layer of the GEA are stronger than those of the IMA under the same transmural pressure due to the greater thickness o the muscle layer of the GEA. METHODS: The RGEA was obtained at its full length from gastorectomy cases due to gastric cancer (n = 25). The distal section of the IMA was obtained from the left IMA during bypass grafting (n = 23). All specimens were stained by the Masson-trichrome method and examined microscopically. The thickness of the smooth muscle layer of the media and the internal radius were compared between the RGEA and the IMA. RESULTS: The thickness of the muscle layer was 274.0 +/- 13 microns in the RGEA, and 169.1 +/- 8 microns in the IMA (p < 0.01) that is the thickness in the GEA was 1.62 times greater in the IMA. Although a significant difference was not obtained, the internal radius of GEA (563.7 +/- 21.8 microns) was smaller than that of IMA (583.1 +/- 12.0 microns). Based on the internal diameter-elastic wall tension relationship and the Laplace law, internal diameter and elastic tension in both arteries were obtained at the same blood pressure. Mean elastic tension and internal diameter in the GEA were considered to be smaller than than those in the IMA. The values of the internal diameter of the arteries obtained from the theoretical view point were correlated well with those obtained by the histometoric methods. As the muscle layer of the arterial wall of the GEA is thicker than that o the IMA, and the internal diameter of the GEA tends to be smaller than that of the IMA, the stronger contraction o the muscle layer, when induced, would reduce the blood flow in much greater extent in the GEA than the IMA. CONCLUSION: These results support the assumption that the RGEA reacts strongly than the IMA to constructor agents and physical stimuli, thereby inducing a greater instability of blood flow. Therefore, RGEA grafts should be carefully handled during bypass grafting.

Arteries↗
PubMed1998

The development of local, layer-specific visual cortical axons in the absence of extrinsic influences and intrinsic activity.

The laminar specificity of vertical connections in the primary visual cortex (area 17) develops precisely from the outset, leading to the hypothesis that layer-specific axonal targeting is attributable to molecular cues intrinsic to the cortex (Lund et al., 1977; Katz and Callaway, 1992). However, alternative factors that could influence axonal development have not been investigated. This study examines the roles of intrinsic cortical activity and extrinsic influences that could arise from earlier-formed connections with outside cortical and subcortical areas. Organotypic slice cultures were prepared from ferret area 17 before the formation of local axonal connections and were incubated for 5-7 d to allow initial, local axonal arbors to form in the absence of extrinsic influences. Additionally, some slices were cultured in the presence of the Na+ channel blocker tetrodotoxin to block spontaneous action potentials within the slice. Individual neurons were labeled intracellularly with biocytin, and their patterns of local axonal arborizations were reconstructed. This study focuses on the development of layer 6 pyramidal neurons, the axons of which in vivo bypass an incorrect target, layer 5, before specifically arborizing in their local target, layer 4. We found that axonal arbors developing in vitro preferentially arborized in layer 4 versus layer 5. However, inhibition of spontaneous activity within the cortical slice decreased this specificity, resulting in similar numbers of axonal branches in layers 4 and 5. Thus, although cortical axons do not require influences from outside areas, intrinsic spontaneous activity is required for specific axonal arborization in correct laminar targets.

Animals↗
PubMed2005

Smear layer production of K3 and ProFile Ni-Ti rotary instruments in curved root canals: a comparative SEM study.

OBJECTIVE: The aim of this scanning electron microscopic study was to compare the quality and amounts of smear layer generated by 2 brands of nickel-titanium rotary instruments during canal preparation in the apical thirds of curved root canals. STUDY DESIGN: Forty mandibular mesial root canals with intact apex and mean curvature between 30 and 35 degrees were selected for this study. The root canals were randomly divided into 2 instrumentation groups of 15 each. Automated preparation was performed with ProFile (Dentsply Maillefer, Ballaigues, Switzerland; n = 15) and K3 (SybronEndo, Orange, Calif; n = 15) instrumentss using a crown-down technique. As a control group, barbed broaches (Mani; Matsutani Seisakusho, Takanezawa-Machi Tochibi-Ken, Japan; n = 10) were used to extirpate the necrotic pulp tissue from the root canals. All root canals were prepared to size #35. Glyde (File Prep, Dentsply Maillefer) was used as lubricant and 1% sodium hypochlorite solution as irrigant. At the conclusion of the experiments, all roots were split longitudinally and the root canal walls were examined at the apical third from 2 different perspectives using a scanning electron microscope. A 4-category scoring system for assessing the smear layer accumulation was used, and the resulting scores were statistically analyzed. RESULTS: Less smear layer was obtained in the K3 group at the selected apical third of curved root canals (P < .05). However, all instruments left a smear layer. The surface texture of the smear layer, in addition to the depth and the frequency of packed materials into the dentinal tubules, varied with instrument type. CONCLUSIONS: This finding may imply that, compared to ProFile, compression of the remaining smear layer is minimized when using the K3 rotary nickel-titanium system.

Dental Alloys↗
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↗
PubMed1998

Comparative study about the removal of smear layer by three types of laser devices.

OBJECTIVE: The aim of this study was to analyze the effectiveness of three types of laser, argon, Nd:YAG, and Er:YAG, to remove the smear layer from the prepared root canal walls in vitro. METHODS: After cleaning and shaping by step-back preparation, 32 human extracted maxillary molar teeth were divided randomly into four groups. Root canals in group 1 (G1) were unlased and were irrigated by 17% EDTA. In group (G2), root canals were irradiated by argon laser at the parameters of 1 W, 50 mJ, and 5 Hz. In group 3 (G3) root canals received Nd:YAG laser irradiation at 2 W, 200 mJ and 20 Hz. Teeth in group 4 (G4) were irradiated by Er:YAG laser at the following parameters: 1 W, 100 mJ and 10 Hz. Then these teeth were bisected longitudinally, observed using SEM, and evaluated. RESULTS: The middle third of the teeth from G1 showed clean wall surfaces with open dentinal tubules. In G2, at the middle third, the smear layer was free and vaporized pulpal tissue remnants were observed. In G3, most of the specimens showed very clean walls with the smear layer evaporated, melted, fused, and recrystallized in both the middle and apical thirds. The walls of G4 revealed the evaporated smear layer and open dentinal tubules in the middle and apical thirds. Statistical analysis showed significant differences between G1 and G2, G1 and G3, and G1 and G4. CONCLUSIONS: These results show that the argon laser and Nd:YAG laser are useful to remove the smear layer and that the Er:YAG laser irradiation is the most effective to remove the smear layer on root canal walls.

Argon↗
PubMed2000

Smear layer influence on the apical seal of four different obturation techniques.

The purpose of this study was the in vitro evaluation of four techniques for the obturation of the root canal system in the presence or absence of a smear layer. Ninety-six human upper central incisors were instrumented using the pressureless crown-down technique and irrigated with 5.25% NaOCl. The teeth that had the smear layer removed were irrigated with this solution in combination with 17% EDTA. The teeth were obturated with lateral condensation with an accessory or standardized cone as the main cone, with vertical condensation of warm gutta-percha or with thermoplasticized injectable gutta-percha. Apical leakage was assessed by measuring the linear penetration of methylene blue dye with a stereomicroscope. The results showed no significant differences in the degree of leakage with and without the smear layer when the samples were considered as a whole. However, when the groups were assessed separately, teeth in the lateral condensation with an accessory main cone group and teeth in the thermoplasticized group leaked less with a smear layer present. In contrast teeth with lateral condensation and a standardized main cone leaked more with a smear layer present. In the vertical condensation groups there was no difference attributable to the smear layer.

Chelating Agents↗
PubMed2001

Effect of removal of the smear layer on apical microleakage.

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 randomly as controls, and the remaining 30 teeth were randomly 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.

Bicuspid↗
PubMed2003

The effect of various concentrations of sodium hypochlorite on the ability of MTAD to remove the smear layer.

Various organic acids, ultrasonic instruments, and lasers have been used to remove the smear layer from the surface of instrumented root canals. The purpose of this study was to investigate the effect of various concentrations of sodium hypochlorite (NaOCl) as an intracanal irrigant before the use of MTAD (a mixture of a tetracycline isomer, an acid, and a detergent) as a final rise to remove the smear layer. Ten operators, using a combination of passive step-back and rotary 0.04 taper, nickel-titanium files, prepared 80 single- and multirooted human teeth. Distilled water, four different concentrations of NaOCl, or MTAD was used as intracanal irrigant. The canals were then treated for 2 min with 5 ml of one of the following solutions as a final rinse: 5.25% NaOCl, sterile distilled water, 17% EDTA, or MTAD. The presence or absence of smear layer and the amount of erosion on the surface of the root canal walls at the coronal, middle, and apical portion of each canal were examined under a scanning electron microscope. The results show that although MTAD removes most of the smear layer when used as an intracanal irrigant, some remnants of the organic component of the smear layer remain scattered on the surface of the root canal walls. The effectiveness of MTAD to completely remove the smear layer is enhanced when low concentrations of NaOCl are used as an intracanal irrigant before the use of MTAD as a final rinse. This regimen does not seem to significantly change the structure of the dentinal tubules.

Anti-Bacterial Agents↗
PubMed2004

The influence of the smear layer on dentinal tubule penetration depth by three different root canal sealers: an in vitro study.

The effect of the smear layer on the penetration depth of three different root canal sealers into the dentinal tubules was examined in 64 recently extracted single-rooted teeth. After chemomechanical preparation, the samples were randomly divided in two equal groups. The smear layer remained intact in group A, whereas complete removal of the smear layer was performed in group B. Two roots from each group were used as controls. Ten roots from each group were obturated with laterally condensed gutta-percha points and sealers AH Plus, Apexit, and Roth 811, respectively. Examination in scanning electron microscope revealed that the smear layer obstructed all the sealers from penetrating dentinal tubules. In contrast, smear layer removal allowed the penetration of all sealers to occur to a varying depth. These findings suggest that smear layer plays an important role in sealer penetration into the dentinal tubules, as well as in the potential clinical implications.

Analysis of Variance↗
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↗
PubMed1997

Dentin bonding: effect of tubule orientation on hybrid-layer formation.

In an attempt to compare the morphology of the resin-dentin interface in areas where the dentinal tubules run perpendicularly or at an angle to the cavity surface with that of areas where they run parallel to it, we studied a dentin adhesive system using transmission electron microscopy and fluorescence confocal laser scanning microscopy. The design of the study included the simulation of the normal hydrostatic pressure within the pulp and the dentinal tubules. Following acid etching of the dentinal surface with maleic acid/HEMA, the smear layer was removed, and a superficial zone was demineralized in such a way that the exposed collagenous dentin matrix retained its integrity. Confocal laser scanning microscopal investigations using primer labeled with rhodamine B showed that the penetration of the primer occurred not only vertically via surface porosities, but mainly laterally, via the dentinal tubules. The adhesive resin labeled with fluorescein completely infiltrated the demineralized layer, thereby forming a hybrid layer. The orientation of the dentinal tubules had a profound effect on the formation of the hybrid layer. In areas with perpendicular tubule orientation, the layer was 3.2 +/- 0.8 microns thick, showing solid 27.2 +/- 0.8 microns long resin tags in the dentinal tubules, and a network of tiny tags in their side-branches. In areas with parallel tubule orientation the layer was significantly thinner (1.3 +/- 0.6 microns) and resin tags were absent.

Acid Etching, Dental↗
PubMed2001

Molecular structure of acid-etched dentin smear layers--in situ study.

It is commonly reported that acid etchants remove the smear layer, but to date, there has been no chemical evidence to support these observations. The purpose of this study was to determine the molecular structure of acid-etched carbide- and diamond-bur-created smear layers. This project tested the null hypothesis that such smear layers are totally removed with current etchants. Smear layer/demineralized/mineralized dentin interfaces were analyzed at 1- m intervals by micro-Raman spectroscopy. Features associated with the organic component were substantially broadened with loss of fine structure, and mineral peaks were clearly evident in the spectra of acid-etched smear layers. The organic features in the spectra of the EDTA-treated smear layer showed relative intensity ratios similar to demineralized dentin without contribution from the mineral phase. The disorganized collagen within the smear layer was not removed but was denatured by the acid treatment; the mineral was trapped in this gelatinous matrix and shielded from complete reaction.

Acid Etching, Dental↗
PubMed2003

The removal of the smear layer using EGTA: a scanning electron microscopic study.

The smear layer associated with endodontic instrumentation is currently thought to be a thin layer that occludes the orifices of the dentinal tubules and covers the intertubular dentin of the prepared canal wall. The purpose of this study was to compare the effect of ethylene glycol bis (beta-amino ethyl ether)-N, N, N', N'-tetra acetic acid (EGTA) and ethylene diamine tetra acetic acid (EDTA) on removal of the smear layer through the scanning electron microscopy. Twenty four single rooted teeth were selected, instrumented and irrigated with various solutions and the specimens were processed for scanning electron microscopy. It was found that though both EGTA and EDTA completely removed the smear layer, EDTA caused erosion and conjugation of the tubules, whereas, EGTA effectively removed the smear layer without inducing any erosion. It was thus concluded that EGTA can be effectively used as an alternative chelator for the removal of the smear layer.

Chelating Agents↗
PubMed2001

Comparison of the cytotoxic effects and smear layer removing capacity of oxidative potential water, NaOCl and EDTA.

UNLABELLED: This study compared the smear layer removing capability and cytotoxicity of NaOCl, EDTA and Oxidative Potential Water (OPW). Fifteen extracted single-rooted human upper incisors were examined in three groups. The root canals were enlarged to the apical foramen with K files to size #60 and irrigated with: (a) NaOCl followed by OPW, (b) OPW during and after instrumentation and (c) NaOCl followed by EDTA and NaOCl. The effect of these irrigants on the smear layer was evaluated using a scanning electron microscope. In vitro cytotoxicity of these irrigants was examined by MTT colorimetric assay. We found that the combination of NaOCl and OPW as well as the application of OPW alone, failed to remove the smear layer from the apical third, whereas the EDTA and NaOCl combination achieved complete removal. OPW, when used during and after instrumentation, removed the smear layer in the middle third more effectively than NaOCl followed by OPW. EDTA exerted more cytotoxic effects at all concentrations tested when compared with OPW and NaOCl. IN CONCLUSION: (a) OPW was less cytotoxic than other irrigants but did not effectively remove the smear layer, (b) treatment with EDTA followed by NaOCl efficiently removed of the smear layer, but their cytotoxicity should be considered during endodontic therapy.

Animals↗
PubMed1992

Origination and progression of microleakage in a restoration with a smear layer-mediated dentinal bonding agent.

Several recently marketed dentinal bonding agents modify, but do not remove, the smear layer. Some controversy exists as to whether the smear layer should be left in place or completely removed from preparations to be restored with composite resin systems. This study utilized scanning electron microscopy with energy dispersive x-ray analysis to evaluate the pathway of microleakage in a composite resin restorative material that utilizes a smear layer-mediated dentinal bonding agent. Microleakage occurred at the smear layer-dentin interface and progressed into both the smear layer and dentinal tubules, suggesting that the smear layer acts as a pathway for microleakage.

Composite Resins↗