Determination of
root canal curvatures before and after canal
preparation (part
II): A method based on numeric calculus
D. Sonntag Dr. Med. dent.1; S.
Stachniss-Carp, Dr. rer. nat.2; C. Stachniss3; and V. Stachniss, Prof. Dr. med.
dent.1
1 Department of Operative
Dentistry, Philipps-University, Marburg, Germany
2 Department of Mathematics,
Philipps-University, Marburg, Germany
3 Institute of Computer Science,
Albert-Ludwigs-University, Freiburg, Germany
Abstract
The aim of this paper is to
present a new method based on numeric calculus to
provide data on any type of root
canal curvature at any point of the long axis of
the canal.
Twenty severely curved,
simulated root canals were prepared with
rotary FlexMaster® and Profile®
instruments in the crown-down technique
and manually in the step-back
technique.
The inner and outer curvatures were
registered in a system of
coordinates before and after preparation in increments
of 0.5 mm.
Using an equalising
function, the curvatures were first represented
in graphic and algebraic form.
The
maximum and the mean curvature as well as
the length of the arc from the
apical foramen to the point of maximum curvature
were determined mathematically.
An
increase in maximum curvature was
registered for all four shaping
systems investigated. The radius of the inner curvature
decreased by 0.5–1.2 mm in the
manual systems as a result of the preparation.
The Profile® system displayed the
smallest changes in radius (−0.9 mm)
even with the outer curvature, and
manual preparation with stainless steel files
the most pronounced change (−1.8
mm).
The point of maximum curvature at
the inner curvature was displaced
by 1.6 mm to the apical foramen through
manual preparation with Ni-Ti
files.
At the outer curvature, the maximum displacement
(1.8 mm) recorded was also the
result of preparation with Ni-Ti hand
files, while a displacement of
only 0.3 mm to the apical foramen was recorded
with the other systems.
The method
offers a means of determining curvatures
precisely without random
specification of reference points.
The method is also
capable of registering only minor changes in
curvature in the two-dimensional long axis of the canal.
Introduction
The objective of root canal
preparation is to clean and
shape the canal.
The root canal
should be conically prepared
but changed as little as possible
in its original shape.
However, no rotary preparation
technique available to
date is fully capable of
preventing modifications to canal
morphology, such as zips, elbows,
transportation or
straightening.
Displacement of the canal axis or
excessive removal of
material at the inner curvature
may result in stripping or
perforation (1).
The prognosis of teeth damaged in
this
way is dubious and surgical
intervention is necessary in
most cases (2).
For some decades, new files and
techniques have been
tested and evaluated with the aim
of minimising these
problems.
The transportation of
the long axis of the root
canal has been investigated by
numerous authors with
reference to mechanical serial sections
or virtual CT sections
(3–5).
Root canal curvature and
curvature modification
induced by rotary preparation of
the root canal have
(ìCT) with a high spatial resolution of 33 ìm (13).
In vivo,
less
precise methods are generally applied, with the
two-dimensional
radiographic representation of a threedimensional
long
axis of the canal being in any case inadequate.
The
accuracy could be enhanced here by taking
recourse
to and following up some precise mathematical
methods
already presented.
The
aim of the present study was to present an optimised
method
providing data on root canal curvature at
any
point of a two-dimensional long axis.
This method
should
permit even slight mechanically induced changes
in the curvature
of the long axis of the canal to be shown
in clinical
radiographs.
with
a new one.
The blocks were photographed in a
purpose-designed
stand (Fig. 1; precision mechanics
workshop,
Philipps University, Marburg, Germany) in a
reproducible
position with a digital camera (Camedia
C2500L,
Olympus, Tokyo, Japan) against a plotting paper
background
and the image data were stored in a PC (Compaq
Computer
Corp., Houston, USA).
The methylene blue
solution
was then flushed out of the canals with water to
prevent
any obliteration due to drying of the dye.
The
numbered blocks were randomised to the individual
groups
and issued individually to the operators for
preparation.
The resulting assignments were entered in a
coding
list showing the operator and the preparation system
of
each root canal.
The operator was also assigned a
number
to facilitate allocation in sequence of treatment
(Table
1).
Following
a theoretical refresher course on how to use
the
preparation systems, each student prepared one simulated
root canal up to
size ISO 35 with each of the four
