Keith V. Krell

Anatomical and histological features of C-shaped canals in mandibular second molars

The mandibular second molar has many root canal variations. This investigation used two evaluation methods to examine the canal morphology of mandibular second molars having C-shaped canals. Fifteen extracted mandibular second molars with a conical root and C-shaped canal orifice were separated into two groups. A polyester cast resin technique allowed three-dimensional visualization of the root canal system in eight teeth; the remaining seven molars were prepared for histological examination in cross-section in the coronal, middle, and apical thirds for study under the light microscope. The results illustrated that C-shaped canals in mandibular second molars can vary in number and shape along the length of the root with the result that debridement, obturation, and restoration in this group may be unusually difficult.

Endodontic retreatment: evaluation of gutta-percha and sealer removal and canal reinstrumentation.

To examine the appearance of root canal walls after retreatment, 80 extracted teeth were chemomechanically prepared using a stepback flare technique and obturated with gutta-percha and either Roths 801 or AH26 sealers. Four techniques were used to remove gutta-percha and sealer: method 1—heat and files; method 2—heat, files, and Cavi-Endo; method 3—chloroform and files; and method 4—chloroform, files, and Cavi-Endo. The teeth were sectioned longitudinally and the amount of debris remaining was quantitated. The results showed that no technique removed all debris. When AH26 was the sealer, method 4 was significantly less effective. When Roths 801 was the sealer, method 1 was significantly less effective. Teeth obturated using Roths 801 sealer were significantly cleaner after reinstrumentation.

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.

An in vitro histological comparison of the step-back, sonic, and ultrasonic instrumentation techniques in small, curved root canals

The effectiveness of different methods of root canal instrumentation in small, curved canals was assessed by histological examination. Compared were the step-back hand instrumentation technique, sonic instrumentation with the Endostar 5, and ultrasonic instrumentation with the Cavi-Endo and PZ-KTec prototype systems. Eighty root canals in freshly extracted humanteeth were randomly placed into these four instrumentation groups of 20 teeth each. Five uninstrumented canals served as controls. Following canal preparation and histological processing, coronal, middle, and apical cross-sections were examined for areas of remaining debris and predentin, the percentage of planed canal walls, and percentage of increase in canal area. The results showed significant differences among the four canal preparation methods in all evaluation categories.

Comparison of ethylenediamine tetraacetic acid and sodium hypochlorite on the apical seal of endodontically treated teeth

This study evaluated the effect of a chelating agent on the apical seal of endodontically treated teeth. The root portions of freshly extracted, single-rooted, human teeth were instrumented while irrigating with a 2.5% solution of NaOCl. Step back flaring was done using either NaOCl alone or an aqueous solution of REDTA in combination with NaOCl for irrigation. The teeth were obturated with gutta-percha and Grossmans sealer. Apical leakage was evaluated by measuring the linear penetration of a 1% solution of methylene blue dye. The results showed no significant differences in dye penetration between the groups regardless of the irrigating solution used.

The conservative retrieval of silver cones in difficult cases

The retrieval of silver cones from root canal spaces is often complicated when no “handle” is present in the chamber. Two techniques are presented that utilize the ultrasonic scaler to aid in dislodging the silver cone.

Vertical root fracture and relative deformation during obturation and post cementation

There are several speculated etiologies of vertical root fractures such as pressure exerted during post placement and excessive forces during lateral condensation. However, there are no reports comparing these two forces by use of the same measurement system. This study determined and compared on single-rooted teeth (1) the amount of strain to the root that occurs during obturation and post cementation and (2) the incidence of incomplete and complete vertical root fractures occurring during the aforementioned procedures. Canals of 32 extracted maxillary central incisors were step-back prepared. Teeth were randomly divided into negative and positive controls and experimental groups. The amount of root distortion was recorded with a strain gauge during each of the following procedures: (1) lateral condensation, and (2) lateral condensation plus cementation of a cast gold post. Relative deformations were compared statistically. Teeth were examined by transillumination and stereomicroscopy for incomplete and complete fractures and compared among groups. Data showed significantly more relative deformation with placement of a post and loading than with obturation alone. The accumulation of strain from both procedures did not significantly increase incidence of vertical root fractures. The results indicate that stresses from cementation of posts is more likely to cause relative deformation of roots.

An in vitro comparison of five root canal length measuring instruments

Several new root canal length measuring instruments (RCLMI) have recently been introduced claiming superiority over older systems. The purpose of this study was to compare five models of these instruments with respect to their accuracy under a given set of specified conditions. The five RCLMI tested were: the, Exact-a-pex, the Endocater, the Neosono-D, the Apex Finder, and the Sono-Explorer, Mark III. The conditions tested were the accuracy of the instruments in determining the working length, the consistency of measurement following canal instrumentation and with conductive gutta-percha points in place, and the operation of the RCLMI in the presence of fluids frequently found in root canals during endodontic treatment. An in vitro model was used to test these instruments. A set of 20 teeth was tested using the conditions specified above. All data were compared using the mean difference from the actual canal length of the teeth. The results indicated that there were no significant differences among measurements derived from the five instruments, under the specified conditions. There was a slight variation of the measurements by all instruments when they were used following instrumentation and with the use of conductive gutta-percha points. When fluids were present in the canals, the reliability of the RCLMI depended on the electrical conductivity of the fluid tested. The poorest results were obtained when either sodium hypochlorite or blood were present in the canals.

Irrigation patterns during ultrasonic canal instrumentation. Part I. K-type files

This study examined the irrigation patterns of K-type endosonic files in 20 straight and 20 curved artificial canals. One-half of each group was inverted during instrumentation. Canals were instrumented sequentially using an ultrasonic endodontic unit and #15, 20, and 25 K-type files. A food color dye was placed into the reservoir for the irrigant. The time for total irrigant penetration in the canal was recorded for each file size. The #15 file required the greatest time for penetration in all groups and straight canals required longer instrumentation times for complete irrigant penetration when compared with curved canals. The irrigant could not advance to the most apical extent until the file could “freely” vibrate. Use of ultrasonic files should result in irrigant penetration to the most apical extent of the instrument.

Using ultrasonic sealers to remove fractured root posts

The removal of an existing cast or cemented stainless steel post has proved difficult, time consuming, and to require excessive removal of tooth structure. The use of the ultrasonic scaler alone and in combination with other techniques provides a conservative, efficient method for retrieval of broken posts from root canal spaces. The primary advantage of these techniques in the removal of posts is the conservation of remaining tooth structure.