Eric M. Rivera

Bacterial retention in canal walls in vitro: Effect of smear layer

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 randomly 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.

Accuracy of the endex with variations in canal irrigants and formane size

Several electronic apex locators (EALs) are currently available. The manufacturer of a new device, the Endex, claims that it is accurate regardless of canal conditions. This study compared the accuracy of the Endex with that of the Exact-a-pex, the Sono-Explorer Mark III, and the Neosono-D SE as to the effects of fluids in the canal and variation in foramen size. Sixty extracted single-canaled teeth were divided into two groups (narrow and wide foramina), depending on whether the apical foramina permitted the tip of a #30 K file to pass through. An in vitro model was used, in which teeth were fitted in test tubes with the roots immersed in 1% agar in phosphate-buffered saline. Root canal lengths were measured in dry canals, then with ethanol, Xylocaine, and sodium hypochlorite in the canals by each electronic apex locator. These lengths were compared with those of the actual root canal lengths. No significant differences were noted among the instruments in dry canals regardless of the foramen size. The endex was generally superior to the other instruments examined in canals containing conductive fluids, especially where the apical foramen was widened.

Vertical root fracture in nonendodontically treated teeth

Vertical root fractures have been reported to occur primarily in endodontically treated teeth due to condensation forces and/or with post placement. This study describes 11 Chinese patients with 12 molars that developed vertical root fractures without endodontic or post procedures. These showed characteristics of a true vertical root fracture as confirmed after extraction. Fractured teeth showed a consistent pattern. The majority were severely attrited mandibular molars in males. All had clinically intact crowns with no or minimal restorations.

A three-dimensional finite-element stress analysis of an endodontically prepared maxillary central incisor

This study is an application of a three-dimensional Finite-Element Method to investigate the changes in stress characteristics of a prepared maxillary central incisor. The purpose of this study was to analyze stress distributions in this tooth after simulated canal preparation and static loading. A maxillary central incisor was embedded in acrylic, sectioned, photographed, and digitized. A three-dimensional finite-element model was generated by a computer and appropriately modified to simulate canal preparation. Data identified the highest stress magnitudes to be located between the middle and coronal thirds of the root; an area clinically observed to be prone to fracture during treatment. In addition, the magnitude of generated stresses was directly correlated with the simulated prepared canal diameter. The development of a validated three-dimensional finite-element method could identify areas that may predispose a tooth to structural failure during condensation loads.

Placement of calcium hydroxide in simulated canals: Comparison of glycerin versus water

Calcium hydroxide (Ca(OH)2) is an intracanal medicament used as an antimicrobial agent, temporary obturant, and for apexification. Placement should be controlled for the maximum biological effect. This study evaluated and compared the effectiveness of delivery of Ca(OH)2 mixed with water or with glycerin as to (a) length of placement and (b) density of fill at different levels. Fifty-six simulated canals with moderate curvature were prepared to #60 using the step-back technique. Ca(OH)2 was mixed with either water (28 canals) or glycerin (28 canals) into a thick paste and placed with lentulo spirals. Radiographs were made and blindly assessed. Results showed that glycerin was statistically significantly superior (p < 0.05) to water as to (a) length of fill and (b) density in the coronal, middle, and apical thirds. Of particular interest was the apical third, in which 0% of water and 50% of glycerin Ca(OH)2 pastes were completely dense.

Microleakage between endodontic temporary restorative materials placed at different times

Occlusal endodontic access preparations are occasionally made in teeth without removing the original restoration. However, microleakage between restorative materials that are placed at different times has not been extensively studied. Therefore, our objective was to compare microleakage at three areas: between an access opening restorative material and the cavity wall; between an additional material placed later to patch a secondary opening in the first restorative material and the original restorative material itself; and between the secondarily placed material and the cavity wall. Standard endodontic access preparations were made in 120 noncarious, nonrestored crowns of extracted human molars. These teeth were divided into six experimental groups. Another four molars were controls. The endodontic access cavities were restored with either IRM or amalgam as the primary restorative material. After 14 days, half of the primary restorations was removed, and this defect was filled with a secondary restorative material: IRM, Caviton, or a double seal of Caviton and IRM. Microleakage was measured linearly as the extent of basic fuchsin dye penetration under a stereomicroscope after thermal cycling (5 degrees and 55 degrees C for 100 cycles) and tooth sectioning. Wilcoxon signed-rank test was used for statistical analysis. Results indicated significantly less microleakage between primary and secondary restorative materials placed at different times than microleakage between primary temporary restorative materials and the access cavity wall, regardless of the type of primary restorative material used (IRM or amalgam).

Anaerobic tissue-dissolving abilities of calcium hydroxide and sodium hypochlorite

Closed root canals likely have an oxygen-free environment; most bacteria in canals are anaerobic. These bacteria and other debris are difficult to remove. Unknown is tissue dissolution with chemicals under these anaerobic conditions. This study evaluated and compared dissolving properties of calcium hydroxide (Ca(OH)2) and sodium hypochlorite (NaOCl) on bovine pulp tissue in aerobic and anaerobic environments. Sixty bovine pulp specimens were dried, then randomly divided into six groups. Groups A and B were immersed in Ca(OH)2 + water solution, whereas group C and D were in 2.5% NaOCl. Groups E and F (controls) specimens were placed in distilled water. Groups A, C, and E were incubated anaerobically, and groups B, D, and F were incubated under regular atmospheric conditions, all for 7 days. Percentages of weight loss were compared between groups. Results showed the following: (a) both chemicals partially dissolved pulp tissue, (b) anaerobic environment did not alter tissue-dissolving properties of Ca(OH)2 or NaOCl, and (c) Ca(OH)2 and NaOCl were equal and more effective than water.

Canal debridement: effectiveness of sodium hypochlorite and calcium hydroxide as medicaments.

The action of chemicals such as calcium hydroxide (Ca(OH)2) and sodium hypochlorite (NaOCl) that are used as tissue solvents may be enhanced by prolonged contact. The objective of this study was to determine if sealing Ca(OH)2 and NaOCl into the canal space would improve debridement of both the main canal and areas inaccessible to files. Mesial root canals of 75 freshly extracted mandibular molars were step-back hand-instrumented. Another six molars were controls. Either Ca(OH)2, NaOCl, or no medication was sealed in the canals for 1 or 7 days. Canals were finally irrigated with H2O and prepared for histological evaluation. The cleanliness of main canals and inaccessible areas (isthmi and fins) at the apical, middle, and coronal thirds was examined, scored, and compared by nonparametric statistical analysis. Results showed no significant differences among different groups in either the 1-day or 7-day time intervals in either the main canal or inaccessible areas. Instrumentation combined with NaOCl irrigation alone accounted for the removal of tissue in the main canal. In conclusion, in this system, prolonged contact with Ca(OH)2 and NaOCl was similarly ineffective; neither contributed significantly to canal debridement.

Evaluating the paper point technique for locating the apical foramen after canal preparation.

OBJECTIVE Despite not having been formally evaluated in the endodontic literature, claims have been made regarding the acceptability of the paper point technique (PPT) in estimating the location of the apical foramen (AF). Our aim was to investigate the repeatability and accuracy of PPT in estimating AF location in a cohort of dental patients. STUDY DESIGN Root canals with </=10 degrees of curvature (n = 71) in unsalvageable anterior and premolar teeth were measured using PPT as described in the literature. An endodontic file was cemented in each canal to the position indicated by PPT. Teeth were extracted and microscopic computerized tomography scanned. RESULTS The PPT was 0.5 mm short to 0.5 mm long of AF in 87% of the canals. Repeated measurements in a given canal were within 0.19 mm of each other 95% of the time. CONCLUSION For relatively straight root canals, PPT appears to be similar to current clinically acceptable techniques in estimating AF location.

Placement accuracy of electrically conductive gutta-percha

Conductive gutta-percha master cones (CGPMCs) with a surface conductive silver film have been developed for use with an electronic apex locator. Our research examined the accuracy of these CGPMC placed at working length (WL). Actual canal lengths of 30 extracted anterior teeth with mature apices were determined. Teeth were mounted in an in vitro system and canals step-back prepared. Each CGPMC was seated to the electronic WL as determined by the electronic apex locator and radiographs were made with the CGPMC in this position. Data showed (a) CGPMCs placed with the use of an electronic apex locator were at or within 1 mm short of WL in 36% of the teeth and (b) however, radiographic examination of the same CGPMC placements gave the appearance that 64% were at or within 1 mm short of WL.