Odontologo

Copyright C Munksgaard 2000

Endod Dent Traumatol 2000; 16: 101–106
Printed in Denmark . All rights reserved

Endodontics &
Dental Traumatology
ISSN 0109-2502

A survey of interfacial forces used during
filing of root canals
Regan JD, Sherriff M, Meredith N, Gulabivala K. A survey of
interfacial forces used during filing of root canals. Endod Dent
Traumatol 2000; 16: 101–106. CMunksgaard, 2000.
Abstract – The pattern of dentine removal during endodontic instrumentation is influenced by many factors including the interfacial forces applied by the operator. The aim of this study was to
investigate the influence of operators and different sizes and types of
instruments on the magnitude of these interfacial forces. Singlerooted teeth were mounted on a cantilevered aluminium beamto
which two pairs of single element strain gauges were joined in a
half-bridge configuration and mounted at right angles to each
other. The strain gauges were connected to an analogue-to-digital
converter fitted in a micro-computer via conditioning amplifiers.
This enabled strains to be recorded over a period of time. Twenty
operators instrumented root canals using a series of hand instrumentsfor 1 min each. The mean interfacial forces used by operators demonstrated a wide variation ranging from 9.06 g to
149.42 g (range of forces from 0–331 g) but there was a consistency
in the relative magnitude for each operator. The 20 operators could
be divided into 13 groups which were significantly different (aΩ
0.05) from each other. There were significant differences (aΩ0.05)
between theforces used for each of the K-Flex files (15, 25, 35, 45,
and 70), the force increasing with the file size. There was also a
significant difference (aΩ0.05) in the forces used between the
Flexofile (.25) and the .25 K-Flex and Hedstrom files. However,
¨
there was no significant difference between the K-Flex and Hedstrom files.
¨

The aim of filing root canals is to remove dentine in
a controlledmanner so as to produce a preconceived
taper. Achieving this depends upon the cutting properties of the instrument, the physical properties of the
dentine and the nature of the interaction between the
two. The properties of the instrument dictate its mode
of use which may involve a push-pull motion, a rotational motion or a combination of both. Conventional
ISO files are generally designed toremove dentine
optimally in the push-pull motion. Other variables
which affect the efficiency of this action include the
flexibility or rigidity of the instrument, the sharpness
of the cutting edges, the presence or absence of irrig-

J. D. Regan1, M. Sherriff2,
N. Meredith1, K. Gulabivala1
1
Eastman Dental Institute for Oral Health Care
Sciences and 2United Medical and Dental School,Guy’s Hospital, University of London, UK

Key words: interfacial forces; root canal
preparation
K. Gulabivala, Eastman Dental Institute, 256,
Gray’s Inn Road, London, WC1X 8LD, England, UK
Accepted September 11, 1999

ant (1) and the magnitude of interfacial forces used
(2). The significance of this last factor has not been
thoroughly investigated.
The great majority of endodonticinstrumentation
studies make no reference to the interfacial forces applied to the root canal walls (3–6). A small number of
studies have evaluated the cutting efficiency of various
instruments and have controlled or considered controlling the interfacial force. The selected interfacial
force has either been chosen arbitrarily (7) or been
based on pilot studies (8, 9). A recent study (2) investigatedstroke rate and loading using hand, sonic and
ultrasonic instruments.
101

Regan et al.

Fig. 1. Schematic diagram showing longitudinal section of the force
measuring unit. tΩtooth sample; pΩplaster; bΩbrass well; aΩaluminium beam; sΩstrain gauges; cΩcasing.

The aim of the present study was to investigate the
magnitude of the interfacial forces applied to root canal walls by 20...