Dentinal tubule penetration of root canal sealers after root canal dressing with calcium hydroxide

The purpose of this study was to evaluate the dentinal tubule penetration of root canal sealers after root canal dressing with calcium hydroxide (Ca(OH)2). Forty-two single-rooted teeth were instrumented to size 60. Six teeth served as the control group, and the remaining teeth were assigned to two groups. Root canals of the first group were filled with the Ca(OH)2 paste; the second group was filled with TempCanal, and all were incubated for 7 days. The samples were either irrigated with only NaOCl or with EDTA, followed by NaOCl to remove Ca(OH)2. All of the teeth were obturated with CRCS, AH26, and Ketac Endo by a lateral condensation technique. The specimens were then kept at the same conditions for another 7 days, and then all of the roots were prepared for scanning electron microscopic evaluation. Scanning electron microscopic examination revealed that Ca(OH)2 was not completely removed from the root canal surfaces, and root canal sealers did not penetrate into the dentinal tubules when only NaOCl was used. EDTA followed by NaOCl irrigation resulted in complete removal of Ca(OH)2 and root canal sealers penetrated into the dentinal tubules.

Influence of entrapped air on the accuracy of leakage studies using dye penetration methods

Entrapped air can inhibit dye penetration resulting in failure to demonstrate existing voids. A new approach to study dye penetration was developed in which the entrapped air was evacuated before the dye was introduced. This method was compared with the regular technique of passive dye diffusion. Uniformly prepared root canal specimens were filled with AH26. Two different sizes of standardized voids were created in the specimens. Specimens were either immersed passively in 2% methylene blue for a week or placed in a chamber with 100 mtorr absolute pressure, after which the dye was introduced while the vacuum was maintained. Leakage was measured stereomicroscopically. Controls with no voids showed insignificant external leakage. Passive dye penetration resulted in incomplete filling of the voids regardless of size of the voids, whereas vacuum dye delivery resulted in complete filling of the voids. Results of this study suggest that entrapped air produces artifacts in passive immersion technique; therefore, the sample should be evacuated prior to the dye introduction in order to demonstrate the full extent of void in future dye penetration studies.

A 1-year follow-up study on leakage of four root canal sealers at different thicknesses

Determination of leakage using a fluid transport model allows measurement of leakage in a longitudinal manner. Leakage of four sealers at three different thicknesses in 225 bovine root sections, after storage in water for 1 year, was measured again using the same methodology. The change in seal over time for each sealer was observed. The results after the second measurement showed that every sealer produced the best seal when the sealer layer was the thinnest. AH26, Ketac-Endo and Tubli-Seal showed a reduction in leakage over time and gave significantly less leakage than Sealapex (P<0.005). Sealapex showed significantly more leakage after storing in water for 1 year (P<0.005). Therefore, the long-lasting seal of sealer may, among other influencing factors, depend on the layer thickness and the solubility of the material.

Bacterial leakage versus dye leakage in obturated root canals

AIM

The aim of this study was to compare in vitro bacterial and dye leakage tests, commonly used to determine the seal of root canal fillings.

METHODOLOGY

Ninety-six single-rooted teeth had their crowns removed at the cemento-enamel junction and their roots instrumented to ISO size 60 within 1 mm of the apex. Three groups of 30 roots were obturated by lateral condensation using gutta-percha and one or other of the sealers. AH26, Ketac Endo, or Roth's 801 sealer. Three roots were used as negative controls and three roots as positive controls. The roots were then exposed at their coronal end first for 38 days to soy broth containing Staphylococcus epidermidis and thereafter for 48 h to basic fuchsin. Bacterial leakage was recorded when the challenging organism could be recovered from the apical end. Dye leakage was checked by microscopy of transverse sections of the apical tip at the end of the experiment.

RESULTS

For the bacterial experiment, there was no significant difference amongst the three sealer groups. The dye experiment showed significantly greater leakage in the AH26 compared to the Ketac Endo group. No correlation between the results of the two tests could be seen.

CONCLUSIONS

The results of this study suggest that the molecular size of the penetrating agent may not be the relevant parameter when attempting to determine an appropriate test for the sealability of root canal fillings.

Distinctive, rapid, and easy labeling of diffuse plaques in the Alzheimer brains by a new methenamine silver stain

We have developed a new methenamine silver (MS) stain for detecting diffuse plaques distinctively on paraffin-embedded tissue sections of Alzheimer-type dementia, Down's syndrome, and mentally normal aged brains. This rapid and easy method selectively labels amyloid-related component of senile plaques, but not of kuru plaques found in Gerstmann-Sträussler syndrome. Our MS stain shows almost the same staining pattern as that of the beta protein immunostaining with formic acid pretreatment. Therefore, new MS stain is appropriate to routine or screening studies for senile plaques including diffuse plaques.

Adhesion of sealer cements to dentin with and without the smear layer

The influence of a smear layer on the adhesion of sealer cements to dentin was assessed in recently extracted human anterior teeth. A total of 120 samples was tested, 40 per sealer; 20 each with and without the smear layer. The teeth were split longitudinally, and the internal surfaces were ground flat. One-half of each tooth was left with the smear layer intact, while the other half had the smear removed by washing for 3 min with 17% EDTA followed by 5.25% NaOCl. Evidence of the ability to remove the smear layer was verified by scanning electron microscopy. Using a specially designed jig, the sealer was placed into a 4-mm wide x 4-mm deep well which was then set onto the tooth at a 90-degree angle and allowed to set for 7 days in 100% humidity at 37 degrees C. This set-up was then placed into a mounting jig which was designed for the Instron Universal Testing Machine so that only a tensile load was applied without shearing or applying preloading forces. The set-up was subjected to a tensile load at a crosshead speed of 1 mm per min. The results show significant differences (p less than 0.001) among AH26, Sultan, and Sealapex, with AH26 being the strongest and Sealapex being the weakest. The only significant difference with regard to the presence or absence of the smear layer was found with AH26, which had a stronger bond when the smear layer was removed.

Long-term evaluation of the influence of smear layer removal on the sealing ability of different sealers

The purpose of this study was to examine the effect of the smear layer on apical microleakage over 16 wk. One hundred and four extracted human teeth were assigned to four groups treated as follows: group A1--smear layer was left intact and canals were obturated with gutta-percha and Roth 811; group A2--smear layer was left intact and canals were obturated with gutta-percha and AH26; group B1--smear layer was removed and canals were obturated with gutta-percha and Roth 811; and group B2--smear layer was removed and canals were obturated with gutta-percha and AH26. Microleakage was measured by the electrochemical method. In parallel, 12 teeth were examined under a scanning electron microscope. The results indicated that the smear layer removal resulted in a statistically significant reduction of microleakage values in groups obturated with AH26. The presence or absence of smear layer had no significant effect on the sealing ability of Roth 811.

Leakage of four root canal sealers at different thickness

Sealers play a key role in sealing the root canal system. Fluid transport under a headspace pressure of 50 kPa (0.5 atm) through four sealers, AH26, Ketac-Endo, Sealapex and Tubli-Seal at a thickness of 0.05, 0.25 or 3 mm, was determined using 240 standard bovine root sections which were obturated with either sealer only or sealer combined with standard gutta-percha cylinders. AH26 and Sealapex sealed more tightly than Ketac-Endo or Tubli-Seal when used without gutta-percha; AH26, Ketac-Endo, and Sealapex sealed more tightly than Tubli-Seal when the sealer layer was 0.25 mm thick, while Ketac-Endo sealed more tightly than the other three sealers when the sealer layer was 0.05 mm thick. These findings indicate that the thickness of the sealer layer influences the sealing ability of a root canal filling.

A comparative study of the apical leakage of four root canal sealers and laterally condensed gutta-percha

Previous studies have shown that lateral condensation of gutta-percha and sealer can provide an adequate apical seal. The purpose of this study was to compare the level of apical dye penetration when different sealers were used. One-hundred twenty-five teeth with single root canals were biomechanically prepared using the step-back technique and irrigation with EDTAC and 1% NaOCl solutions. The teeth were divided into five groups of 25 teeth each. The control group root canals were filled with laterally condensed gutta-percha and no sealer and the other four groups were filled with laterally condensed gutta-percha and either Apexit, Sealapex, Tubli-Seal, or AH26 sealer. After storage in 100% humidity at 37 degrees C for 48 h, the root surfaces were coated with nail varnish (except at the apex) and placed in 2% methylene blue dye solution and centrifuged at 3 x g for 3 min. The roots were sectioned transversely at 1-mm intervals to determine the following mean levels of dye penetrations: Apexit, 1.67 mm; Sealapex, 2.28 mm; Tubli-Seal, 1.95 mm; AH26, 0.82 mm; and gutta-percha alone, 8.37 mm. This study demonstrated that a root canal sealer should be used in conjunction with laterally condensed gutta-percha and that AH26 sealer provides a significantly better apical seal than the other sealers.

Incidence of invasive cervical resorption in bleached root-filled teeth

Invasive cervical resorption, a form of external root resorption, has been reported to be associated with intra-coronal bleaching of root-filled teeth and this has raised concerns about carrying out such bleaching procedures. The purpose of the present study was to examine the incidence of invasive cervical resorption in root-filled teeth which had been bleached using a standardized technique. Three observers examined records and radiographs from a total of 158 patients, whose bleaching treatment had been carried out in a specialist endodontic practice. The sample comprised 204 teeth with a review period of between 1 and 19 years. One-hundred-and-fifty-one teeth (77.94 per cent) had an associated history of traumatic injury. All teeth had been treated with a combination of thermocatalytic and 'walking bleach' procedures using 30 per cent hydrogen peroxide. In 54.41 per cent of teeth, gutta-percha and AH26 root-fillings were kept at the height of the cemento-enamel junction while 18.63 per cent were below and 26.96 per cent were above the CEJ. Sealing cement was not placed over the gutta-percha and AH26 root-fillings in any of the teeth in the study. It was found that a total of four teeth from the sample group (1.96 per cent) had developed invasive cervical resorption during the review period. All of these teeth had a history of traumatic injury and the level of gutta-percha was at the CEJ.(ABSTRACT TRUNCATED AT 250 WORDS)

Standardization of various applications of methacrylate embedding and silver methenamine for light and electron microscopy immunocytochemistry

The use of butyl-methyl-methacrylate embedding and the application of the silver methenamine (SM) method as a poststaining of the immunoperoxidase-DAB (IP) procedure led to the standardization of several useful methods for the visualization of tissue antigens at the light and electron microscope level. These procedures included: 1) Standardization of the actual methacrylate embedding; 2) The IP-SM method with and without periodic acid oxidation, which provided 100% intensification of the IP staining; 3) The IP-SM method made it possible to stain semithin sections (0.5 micron), and this in turn, permitted a) clear visualization under the light microscope of the intracellular distribution of antigens and, b) staining, in several adjacent sections, of roughly the same cytoplasmic region of the same cell with different primary antisera; 4) a double immunostaining whereby the first antigen in the sequence was revealed by the IP-SM method and the second by the IP procedure; 5) standardization of the IP and the IP-SM methods for post-embedding staining of ultrathin methacrylate sections. The combined application of methacrylate embedding and the IP-SM, and the use of an appropriate fixative, resulted in an ultrastructural immunocytochemical procedure characterized by a good immunoreactivity of the tissue sections, a strong and selective immunoreaction and a well preserved ultrastructure.

Efficacy of removing glass ionomer cement, zinc oxide eugenol, and epoxy resin sealers from retreated root canals

Removal of gutta-percha and various sealers was assessed during retreatment of the root canal system. Sixty root canals were prepared and obturated with gutta-percha and Ketac-endo, Roth's 801 cement, or AH26. After 14 days, the canals were retreated by hand or ultrasonic technique and the retreatment time was recorded. The roots were split and the amount of debris that remained on the canal walls in three separate levels was recorded by use of a dissecting microscope. The mean scores were compared by one-way and two-way ANOVA. The total score was significantly the highest for Ketac-endo (p less than 0.04), followed by AH26 and Roth's 801 cement. The largest amount of debris was consistently found in the apical third, and generally it was comparable for both retreatment techniques. The ultrasonic technique was significantly faster than the hand technique for all sealers tested (p less than 0.0004, p less than 0.0003, p less than 0.02, respectively). Hand retreatment of Ketac-endo was the slowest, whereas ultrasonic retreatment of Roth's 801 cement was the fastest. The results indicated that Ketac-endo endodontic sealer can be effectively removed from the root canal by ultrasonic instrumentation.

Comparison of apical leakage in root canals obturated with various gutta percha techniques using a dye vacuum tracing method

In this study, residual apical microlumina remaining after obturation with five different gutta-percha obturation methods were traced with an efficient vacuum method. Seventy-nine human maxillary anterior teeth were instrumented and divided into five groups. The groups were obturated with single-cone techniques, lateral condensation, vertical condensation, Thermafil, and Ultrafil techniques. All specimens were immersed in a vacuum flask containing 2% methylene blue dye solution. The air was evacuated with a vacuum pump to an absolute pressure of 75 torr for 30 min. The roots were sectioned longitudinally and the linear extent of dye penetration was measured. Group mean linear dye penetration values were: single-cone technique, 1.55 +/- 0.95 mm; lateral condensation, 2.25 +/- 1.46 mm; vertical condensation, 2.61 +/- 2.61 mm; Thermafil 1.41 +/- 1.16 mm; and Ultrafil 3.51 +/- 4.70 mm. There were no statistically significant differences between the gutta-percha obturation methods. The clinical implications of these findings are discussed.

Kinetics of hydrolysis of methenamine

The kinetics of degradation of methenamine were studied in citrate--phosphate buffers between pH 2.0 and 7.4 at 37.5 degrees. GLC was used to monitor the rate of hydrolysis. The conversion of methenamine to formaldehyde was found to be pH dependent in the buffers of constant ionic strength, with the reaction half-life decreasing from 13.8 hr at pH 5.8 to 1.6 hr at pH 2.0. The kinetics of degradation also were measured at 47, 57, and 67 degrees, and the reaction obeyed the Arrhenius relationship. At pH 2.0, the activation energy was calculated to be 23.5 kcal/mole; at pH 5.1, it was 12.0 kcal/mole.