Majinah Ahmad

The validity of using simulated root canals as models for ultrasonic instrumentation

The validity of using simulated root canals in resin blocks for evaluating the effects of ultrasonic root canal instrumentation was examined. Curved canals in resin blocks and in natural teeth were ultrasonically instrumented using the Cavi-Endo unit at power setting 1. Canal shapes were compared qualitatively and quantitatively from photographs and subtraction macroradiographs of simulated canals and teeth, respectively. The following measurements were taken: apical and coronal areas, changes in width at the elbow and at 0.5 mm apical to the elbow, and apical transport width. Qualitatively, there did not appear to be any differences in the manner of removal of material along the length of the canal in both test models. Quantitatively, there was a similarity in the following: areas of canal walls removed, the incidence of elbows, the change in width at the region of the elbow, and the apical transport width. The lack of differences showed that the ultrasonic file cut in a similar fashion in both test models and indicated that simulated canals are valid models for evaluating the effects of ultrasonic instrumentation.

Effectiveness of ultrasonic files in the disruption of root canal bacteria

The physical mechanisms of ultrasound, namely cavitation and acoustic streaming, generated by the Enac-Osada ultrasonic unit were investigated for effectiveness in disrupting Streptococcus mitis. In addition, the bactericidal effect of ultrasound in the presence of 2.5% sodium hypochlorite was examined. Bacterial suspensions were irradiated directly with ultrasound in simulated root canals, and the viability of bacteria was examined after growth on a blood agar medium under anaerobic conditions at 37 degrees C for 5 days. The results indicated that ultrasound per se failed to disrupt bacteria but resulted in increases in the viable counts; the former was considered to be because of the lack of cavitation and the latter because of the dispersal effects of acoustic streaming. The 2.5% sodium hypochlorite solution demonstrated powerful bactericidal activity.

A Comparison Using Macroradiography of Canal Shapes in Teeth Instrumented Ultrasonically and by Hand

Forty teeth with severely curved canals were divided into two groups and the root canals were prepared either ultrasonically or with hand instruments. Canal shapes were compared qualitatively and quantitatively using subtraction macroradiography; this allowed the pre- and postinstrumented canal shapes to be viewed on the same print. The times to carry out instrumentation and the incidence of elbows were recorded. In addition, the following measurements were taken from the radiographs using a digitizer: apical and coronal areas, distance of elbow from canal curvature, change in width at elbow and 0.5 mm apical to it, and apical transport width. Subjective evaluation revealed that no difference was apparent between the methods as to the places where the dentin was removed; both instruments exhibited unequal dentin removal along the canal length with more removal occurring coronally. The quantitative results indicated an absence of differences in the following: the time of instrumentation, the incidence of elbows, the distance of elbow from the point of curvature, the change in width at the region of the elbow, and the apical transport width. These findings indicated that ultrasonic files behaved similarly to hand instruments when used in a filing action.

Comparison of Two Ultrasonic Units in Shaping Simulated Curved Canals

The effects of ultrasonic instrumentation on the preparation shape of curved simulated canals were investigated. Measurements of the displacement amplitudes of the files were made to examine the possible relationship between displacement amplitude and the cutting ability of the file. Twenty-five simulated canals in clear resin blocks were instrumented using a Cavi-Endo unit at a power setting of 1 with differing times of instrumentation and with water as irrigant. Another group of 25 canals received similar treatment but were instrumented with an Enac unit at a power setting of 1. The canal shape and the incidence of elbow formation were evaluated using various measurements taken from photographic prints of the canals. All canals exhibited unequal removal along the canal with more removal occurring coronally. The Enac group exhibited a higher incidence of elbows which occurred further apically than those in the Cavi-Endo group. There was no significant difference between groups in the amount of apical canal enlargement. Coronally, the Enac appeared to cut significantly better. The Enac also caused significantly greater apical deviation and change in width. In both units more elbows were formed following instrumentation, with less flexible files having smaller displacement amplitudes.