Lesley A. West

Evaluation of Regional Bond Strength of Resin Cement to Endodontic Surfaces

The purpose of this study was to test the feasibility of adapting a new microtensile testing technique to measure resin cement bond strengths to the cervical, middle, and apical thirds of root canals. Post spaces were created in extracted human teeth, and the roots were ground flat on one side to expose the canal and permit ideal placement of one of two resin cements (Panavia 21 or C&B Metabond). After 48 h of storage, serial 1-mm-thick cross-sections were cut to create 6-10 specimens per root. The first three specimens were from the cervical third, the next three were from the middle third, and the last three were from the apical third of the root. Each 1 x 1 x 8 mm specimen was pulled to failure in a miniature testing machine. The results indicated that both resin cements produced high bond strengths (12-23 MPa), and that bond strengths to the apical third were significantly higher (p < 0.05) than to the cervical or middle third with either cement. This new method shows promise for evaluating resin bond strengths within root canals.

Determination of Periodontal Ligament Cell Viability in Long Shelf-Life Milk

The purpose of this study was to determine the ability of long shelf-life milk to serve as a temporary storage medium for the maintenance of periodontal ligament (PDL) cell viability on avulsed teeth. PDL cells were plated onto 24-well culture plates and allowed to attach for 24 h. Minimal Essential Medium was replaced with regular pasteurized milk (refrigerated milk), long shelf-life milk (Parmalat), or Save-A-Tooth. Tap water served as the negative control, and Minimal Essential Medium served as the positive control. The tissue culture plates were incubated at 37 degrees C for 1, 2, 4, or 8 h. Cell viability was determined using a cell proliferation assay (CellTiter 96 AQ Assay) and absorbance read at 490 nm. ANOVA indicated that all media performed significantly better than tap water at all time periods. At 8 h, PDL cell viability in regular pasteurized milk and long shelf-life milk were significantly greater than in Save-A-Tooth (p < or = 0.001). There was no significant difference between regular pasteurized milk and long shelf-life milk at any time period. These results suggest that long shelf-life milk, which has the advantage of not requiring refrigeration, is as effective a storage medium for avulsed teeth as regular pasteurized milk and more effective than Save-A-Tooth.

Interpretation of periapical lesions comparing conventional, direct digital, and telephonically transmitted radiographic images

The purpose of this study was to evaluate direct digital radiography (DDR) and telephonically transmitted images versus conventional radiography in the interpretation of artificial periapical bone lesions. Five teeth were chosen from four cadaver jaw specimens. Three types of DDR images were evaluated: DDR stored images, DDR transmitted images, and DDR reversed images. A total of 150 DDR computer monitor images and 56 D-speed film images were evaluated by three endodontists and one endodontic graduate student. The Wilcoxon signed-ranks test was used for statistical analyses of the results. DDR reversed images were statistically inferior to DDR stored images, DDR transmitted images, and conventional radiography images (p < 0.0001). There were no statistically significant differences between DDR stored images, DDR transmitted images, and conventional film images in the ability of the evaluator to identify artificial periapical bone lesions (p > 0.05).

Antimicrobial activity of several calcium hydroxide preparations in root canal dentin.

The purpose of this study was to evaluate the antimicrobial activity of several calcium hydroxide (Ca(OH)2) preparations in root canal dentin infected with Enterococcus faecalis. Roots of extracted bovine incisors were prepared to standardized cylindrical test specimens of 5 mm in height; the smear layer was removed, and the specimens were incubated for 24 h at 37 degrees C in bacteriological culture medium that contained 7.0 x 10(4) colony forming units per milliliter of E. faecalis. The specimens were mounted in individual 4-mm diameter culture wells, and the test material was applied to fill the canal lumen. There were five treatment groups: group 1, a thick mixture of Ca(OH)2 USP (1.0 g/ml H2O); group 2, a thin mixture of Ca(OH)2 USP (0.1 g/ml H2O); group 3, Pulpdent TempCanal paste; group 4, sterile H2O (positive control); and group 5, 25 dentin specimens in sterile, uninoculated brain-heart infusion broth that were included as negative controls. Quantitative microbiological analysis of dentin at various depths was completed after 24 h. All groups showed a significant (p < 0.001) decrease in numbers of E. faecalis in all depths of dentin compared with the control. Groups 2 and 3 demonstrated significantly greater antimicrobial activity (73%-86% reduction) at all depths of dentin tested compared with group 1 (13%-26%) (p < 0.05). These results suggest that Ca(OH)2 can decrease the numbers of E. faecalis at all depths of dentinal tubules within 24 h and that thin preparations of Ca(OH)2 may be more effective in the elimination of E. faecalis from dentinal tubules than thick preparations.

In vitro antimicrobial activity of various medication preparations on E. faecalis in root canal dentin.

The purpose of this study was to evaluate the antimicrobial activity of several medication preparations in root canal dentin infected with Enterococcus faecalis. Roots of extracted bovine incisors were prepared to standardized cylindrical test specimens, 5 mm in height. The smear layer was removed and the samples were autoclaved and then incubated at 37 degrees C/5% CO2 for 24 h in brain-heart infusion (BHI) broth containing 7.0 x 10(4) colony forming units per ml of E. faecalis. The samples were washed in phosphate buffered saline and mounted to individual culture wells with sticky wax. Test medications were applied to fill the canal lumina; medication groups were: (a) sterile H2O (positive control); (b) a 10% mixture of 1.0 g Ca(OH)2 USP in 10 ml sterile H2O; (c) 10% Ca(OH)2 in 0.12% chlorhexidine gluconate (Peridex); (d) Peridex; and (e) uninoculated BHI (negative control). The samples were incubated at 37 degrees C/5% CO2 for 24 h. Dentin samples for quantitative microbiology were then obtained with consecutive sterile burs (ISO 029, 035, 042). All three experimental groups demonstrated significantly greater antimicrobial activity than the positive control (p < 0.001). Group 2 demonstrated significantly greater antimicrobial activity than Group 3 or Group 4 at all dentin depths (p < 0.05). These results suggest that 10% Ca(OH)2 may be more effective than Peridex or 10% Ca(OH)2 in Peridex for the elimination of E. faecalis from dentin tubules.

Use of the microscope in endodontics: A report based on a questionnaire

A survey regarding operating microscope (OM) usage and training was mailed to 3356 active members of the American Association of Endodontists (AAE) in the United States. Data from 2061 questionnaires indicate that 52% of the endodontists surveyed have access to and use the OM in their practice. The frequency of use as a function of years since completing endodontic training was as follows: < 5 yr, 71%; 6 to 10 yr, 51%; and > 10 yr, 44%. The OM was used most often for retrieval of separated instruments, root-end preparations, and root-end fillings. Of the respondents who use the OM, 36% report they do not use it as often as anticipated. The most common reasons reported were positional difficulties, inconvenience, and increased treatment time. The information collected from the survey reveals that the more training the operator has on the microscope, the more likely he or she is to use it for all procedures.

A Comparison of Fill Density Obtained by Supplementing Cold Lateral Condensation with Ultrasonic Condensation

The purpose of this study was to compare quantitatively the density of gutta-percha root canal fillings produced by cold lateral condensation with those produced by an ultrasonically energized spreader in a warm lateral condensation technique in artificial root canals. Thirty-degree simulated root canals in 30 transparent acrylic blocks were instrumented by using rotary files. The blocks were weighed. The canals were obturated with gutta-percha using cold lateral condensation without sealer and then weighed again. Two applications of warm lateral condensation were then performed on the same 30 canals using the UES. The blocks were weighed once more after each additional UES obturation treatment. The first heat application produced a 26.92% increase in weight over lateral condensation, and the second heat application produced an additional 5.95% increase. A one-way repeated measures ANOVA followed by the Tukey-Kramer test revealed that both applications of warm lateral condensation produced significant (p < 0.001) increases in weight. Results indicate that warm lateral condensation using a ultrasonically energized spreader results in denser gutta-percha fills by weight than cold lateral condensation.

Photoelastic comparison of stress induced by using stainless-steel versus nickel-titanium spreaders in vitro

The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may reduce the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty standardized models simulating curved canals (32 degrees) were formed within PL-2 photoelastic acrylic resin blocks. The canals were fitted with a gutta-percha point, and either a stainless-steel or nickel-titanium finger spreader was inserted. An Instron 4502 universal testing machine applied a vertical force of 20 Newtons to the spreader. Quarter wave and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lines showed that the stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals, thus reducing the concentration of stress and the potential for vertical root fracture.

Increased density of gutta-percha using a controlled heat instrument with lateral condensation.

The purpose of this study was to compare quantitatively the density of standard cold lateral gutta-percha condensation and warm lateral gutta-percha condensation using the System B heating instrument in a low-heat warm lateral condensation technique in an artificial root canal in vitro. Thirty-degree simulated root canals in 30 transparent acrylic blocks were instrumented using Gates-Glidden burs and Quantec (NT Company, Chattanooga, TN) rotary files. The canals were then obturated with gutta-percha using standard cold lateral condensation without sealer. Warm lateral condensation without sealer using the System B instrument at 101 degrees C was then performed on the same 30 canals. A second treatment of warm lateral condensation was then applied to these same canals. The blocks were weighed after the initial canal preparation and after each obturation treatment. Results showed warm lateral condensation of gutta-percha using the System B resulted in a significant increase in density by weight when compared with standard cold lateral condensation. A 23.97% increase in weight was realized after the first heat application, compared with standard lateral condensation. A second heat application produced an additional 2.59% increase in weight over that produced by the first heat application. Data were analyzed using a t test for repeated measures. Both increases were statistically significant (p < 0.001). Warm lateral condensation using the System B instrument results in denser gutta-percha fills by weight when compared with standard cold lateral condensation.

Obturation quality utilizing ultrasonic cleaning and sealer placement followed by lateral condensation with gutta-percha

The quality of canal obturation utilizing ultrasonic or hand instrument sealer placement followed by lateral condensation with gutta-percha was investigated. This in vitro study using the mesial roots of human mandibular molars showed the ultrasonic method of sealer placement resulted in a more thorough coverage of canal walls than when the sealer was placed with hand instruments. The difference was statistically significant (p less than 0.005). Ultrasonic sealer placement may be safely and effectively utilized when obturating a complex root canal system.