Efficiency Of Hand And Rotary Instruments In

JOURNAL OF ENDODONTICS Copyright © 2002 by The American Association of Endodontists

Printed in U.S.A. VOL. 28, NO. 8, AUGUST 2002

CLINICAL ARTICLES Efficiency of Hand and Rotary Instruments in Shaping Oval Root Canals
Roland Weiger, Prof Dr med dent, Ashraf ElAyouti, Dr med dent, and Claus Lost, Prof Dr med dent ¨

This study was designed to determine the efficiency of hand and rotaryinstruments in shaping oval root canals. Seventy-five oval canals were equally divided into three groups. The apical third was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars). The middle third with an oval cross-section was shaped with Hedstrom hand files using circumferential tech¨ nique, with 6% taper rotaryHero files in a circumferential filing movement or with rotary LightSpeed instruments in a step-back technique. Instrumentation was performed under clinical conditions in a phantom head. The teeth were sectioned at two levels in the middle third of the root. An assembly technique allowed comparing the canal outline before and after instrumentation. The photographed root sections were superimposedand traced under a stereomicroscope. The ratio of prepared to unprepared canal outline was calculated for each section. The lowest values were observed in the LightSpeed group (mean: 0.42; 95% confidence interval (CI): 0.37; 0.47). Significantly higher values were recorded in the Hero group (mean: 0.58; 95% CI: 0.53; 0.64) and in the Hedstrom group (mean: ¨ 0.56; 95% CI: 0.49; 0.62). Noinstrumentation technique was capable of completely preparing dentin walls of oval root canals. Circumferential filing of the middle third of oval root canals with either 6% taper Hero files or conventional Hedstrom hand ¨ files gave comparable results.

curved human root canals, which frequently have a round crosssection. Likewise, simulated root canals in resin blocks have a round shape where rotaryinstruments easily contact all canal walls and thus allow sufficient removal of resin material. A recent study (6) reported a high prevalence of oval root canals in human teeth. The percentage of root canals that deviated from a round shape at 5 mm from the apex was 56% for distal root canals of mandibular molars and 30% for the mandibular incisors. Also, in oval canals a circular cut using a rotaryinstrument left approximately 65% of the root canal unprepared at a level 5 mm from the apex (7). Circumferential filing with conventional hand files is advocated to shape canal recesses or fins that were not shaped during root canal preparation with instruments in a reaming or rotary motion. To our knowledge, there is no study dealing with the efficiency of rotary instruments that were pressedwith lateral pressure against the walls of oval root canals. This study compared circumferential preparation techniques with hand instruments or rotary nickeltitanium instruments with regard to their efficiency to shape oval root canals under simulated clinical conditions.

MATERIALS AND METHODS Extracted mandibular molars and incisors were used for this study. Radiographs were taken from oral andproximal aspects of the distal root of molars and of incisors. Roots were included if the width of the root canal in the proximal aspect was at least double that in the oral aspect. Roots with two separate root canals were excluded. Finally, a total of 75 single oval root canals was selected (45 distal canals of mandibular molars and 30 single root canals of mandibular incisors). Teeth werecleaned, and if necessary, a definite coronal reference plane was prepared by reducing the occlusal surface minimally using a fine diamond bur. The length of each tooth was measured with a measuring gauge to the nearest tenth of a millimeter. To divide the root canal into a coronal, middle, and apical third, the exact lengths of the root canals were determined. In molars, this was the distance from...