Harold Gerstein

An initial investigation of the bending and torsional properties of nitinol root canal files

Root canal files in size #15 and triagular cross-sections were fabricated from 0.020-inch diameter arch wires of Nitinol, a nickel-titanium orthodontic alloy with a very low modulus of elasticity. A unique manufacturing process was used in which the fluted structure of a K-type file was machined directly on the starting wire blanks. The Nitinol files were found to have two to three times more elastic flexibility in bending and torsion, as well as superior resistance to torsional fracture, compared with size #15 stainless steel files manufactured by the same process. The fracture surfaces for clockwise and counterclockwise torsion were observed with the scanning electron microscope and exhibited a largely flat morphology for files of both alloy types and torsional testing modes. It was possible to permanently precurve the Nitinol files in the manner often used by clinicians with stainless steel files. These results suggest that the Nitinol files may be promising for the instrumentation of curved canals, and evaluations of mechanical properties and in vitro cutting efficiency are in progress for size #35 instruments.

Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance.

Abstract The mesiobuccal roots of 208 teeth were sectioned buccolingually from the mesial aspect and the canal configurations were categorized. One hundred one (48.5 per cent) had a single canal, 78 (or 37.5 per cent) showed two canals which merged toward a single apical foramen, and twenty-nine (14.0 per cent) displayed two distinct canals with separate apical foramina. The frequency of occurrence of the bifurcated or double canal must be taken into consideration when surgical treatment is planned and as a possible cause of otherwise unexplained failure. Case histories are presented to illustrate these situations.

A comparative bacterial microleakage study of retrofilling materials

Abstract An in vitro model system was used to evaluate the ability of poly-HEMA used as a retrofilling material to form a fluid-tight sealof the root canal space to prevent bacterial migration. Zinc-free amalgam and gutta-percha were also tested and found to have poor sealing ability compared with poly-HEMA. Several refinements of the in vitro model system are described, which should improve the systems suitability for testing the sealing ability of retrofilling materials.

Use of a hemostatic agent in the repair of procedural errors.

An innovative clinical approach is presented for the treatment of procedural errors. Three clinical cases are presented demonstrating the viability of using hemostatic agents in providing a matrix for the correction of furcal or post perforations and for obturating teeth with large apical foramina.

An in vitro comparison study to quantitate the debridement ability of hand, sonic, and ultrasonic instrumentation.

This study compared, histologically and quantitatively, the debridement ability of hand, sonic, and ultrasonic instrumentation on the mesial root canals of 50 human mandibular molars. The time of instrumentation per canal for each treatment group was also evaluated. Only those roots with canal curvature between 20 and 40 degrees were used in this study. The Cavi-Endo unit utilizing 2.6% NaOCl demonstrated a significantly greater percentage of canal cleanliness at the 1-mm level than any other treatment group except for the ENAC ultrasonic system. The ENAC ultrasonic system significantly cleaned a greater percentage of the canal than the sonic instrument or the Cavi-Endo/water group. Sonic instrumentation was not significantly better than hand instrumentation in canal cleanliness at the 1-mm level. Statistical analysis indicated no significant difference in canal and isthmus cleanliness at the 3-mm level. However, the Cavi-Endo unit utilizing 2.6% NaOCl exhibited the greatest percentage of canal and isthmus cleanliness. Sonic and ultrasonic instrumentation were significantly faster in preparing the root canal system than hand instrumentation in this study.

An investigation of the torsional and bending properties of seven brands of endodontic files

By using experimental procedures based on ADA specification no. 28, the clockwise and counter-clockwise torsion behavior and the cantilever bending properties were determined for five recently introduced brands of endodontic files and two traditional K files. Sizes #10, 15, 20, 25, and 30 were tested, with five replications of each brand size combination. Complete plots of bending or torsion moment as a function of angular deflection were obtained for bend angles to 90° and twist angles to where breakage occurred. In general, the recently introduced brands displayed the greatest elastic flexibility and the lowest resistance to permanent deformation. With only one exception, all groups of instruments either met or were relatively near the test limits in the current form of ADA specification no. 28. The wide variation in mechanical properties observed for these brands indicates that instrument selection by the endodontist should be made with due regard to individual clinical technique.

A Study of Mandibular and Maxillary Root Widths to Determine Dowel Size

Fifteen hundred permanent teeth were examined for mesiodistal widths of roots at the cervical, middle third, and apical third areas of the root. One hundred twenty-five teeth of each unit of the dentition, except second and third molars, were observed. These observations were recorded, and the means, standard deviations, 95% confidence intervals, and ranges were calculated. By use of the confidence interval, the optimal dowel size was selected.

A study of the cutting efficiency of seven brands of endodontic files in linear motion

A custom-designed apparatus was developed to evaluate the cutting ability of endodontic files in linear motion. Five recently introduced brands from different manufacturers were compared with two traditional K-type files, and sizes #20, 25, and 30 instruments were tested. Cutting efficiency was determined by measuring the depth of cut in a bovine bone specimen after 3-min periods. The experimental results indicated significant differences in the in vitro cutting efficiency among the seven brands. Wear was exhibited by all instruments, as a decrease in the depth of cut for each of three successive 3-min test periods.

A model for demonstrating an electronic canallength measuring device

An in vitro model for demonstrating an electroniccanal length measuring device is described.

Endosonics: Clinical impressions

During a 10-month clinical study at the Endodontic Department of Marquette University, we had the opportunity to use and evaluate the endosonic unit (Cavi-Endo). The unit was used for many procedures: preflaring, canal preparation, pathfinding, and the removal of obstructions, silver cones, and posts. Clinical radiographs are presented which demonstrate the various uses of endosonics along with a discussion of how the unit was used, types of problems encountered, and solutions to these problems. The general consensus among us is that the endosonic unit is a very valuable endodontic tool with a multiplicity of uses.