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 »  Home  »  Endodontic Articles 6  »  Electronic determination of root canal length in primary teeth with and without root resorption
Electronic determination of root canal length in primary teeth with and without root resorption
Introduction - Materials and methods.

J. Mente, J. Seidel, W. Buchalla & M. J. Koch
Poliklinik für Zahnerhaltungskunde, Ruprecht-Karls-University, Heidelberg, Germany.
Indiana University School of Dentistry, Oral Health Research Institute, Indianapolis, Indiana, USA.

Pulpectomy is an important treatment option in primary teeth with infected pulps (Fuks & Eidelman 1991, Yacobi et al. 1991). Although pulpectomy is generally accepted as a safe procedure for primary teeth (Coll & Sadrian 1996), various factors must be borne in mind before starting treatment: long appointments may be tiring for young patients and the results of diagnostic procedures which require a child’s cooperation (e.g. vitality testing) are less reliable compared with adult patients (Nowak 1999).
There are also specific problems which are characteristic of primary teeth: root canal walls are often thin and instrumentation of the canal may result in perforation or root fractures. In addition, the primary teeth are resorbed during eruption of their permanent successors.
Radiographic determination of root canal length may give misleading results when lateral canals are present. Therefore, one of the critical aspects of pulpectomy in primary teeth is the presence of root resorption (Coll & Sadrian 1996). Minor degrees of resorption may not be obvious radiographically and more extensive resorption should be considered as a contraindication for root canal treatment (Nowak 1999). Electric root length determination may be helpful in overcoming the shortcomings of radiographic examination in teeth with resorption. The aim of this study was to evaluate whether initial resorption of primary teeth affects the accuracy of an electrical root canal measuring device.

Figure 1. Flow diagram of the different steps of the study.

Flow diagram of the different steps of the study

Materials and methods.
Twenty-four extracted maxillary primary incisors were selected and stored in 4% formaldehyde solution for up to 4 weeks before examination. An overview of the methodology is given in Figure 1. Half of the teeth (n = 12) showed obvious signs of external resorption. The teeth were placed in the aperture of the lid of a high-density polyethylene vessel containing 35 mL 0.9% saline in such a way that the root was completely submersed in saline (Weiger et al. 1999). At the bottom of the vessel a metal screw was connected to one electrode of a Tri Auto ZX device (Morita, Dietzenbach, Germany). The Tri Auto ZX device is an apex locator that simultaneously calculates the ratio of two impendances in the same canal using two different frequencies (Vajrabhaya & Tepmongkol 1997). The crowns of the teeth were shortened using a diamond bur to obtain a defined reference point. Two examiners ( J. M. and M. J. K.) independently determined root canal length. A size 053 K-file or 073 Hedstroem file (VDW, Munich, Germany) was connected to the second electrode of the Tri Auto ZX device. The diameter of the endodontic instrument was chosen according to the canal size (between ISO 30 and 90); no preparation of the canal was performed. The endodontic instrument was inserted until the 0.5 mm distance diode became illuminated. The penetration depth of the instrument was marked using a silicone stop and measured using a millimetre scale. Care was taken not to remove pulpal tissue during instrumentation of the canal in order to ensure that the situation for the second examination was identical. The values were recorded to an accuracy of 0.5 mm.

Radiographic examination.
After the second electronic measurement of root canal length, the instrument was inserted to the previously determined length. A radiograph of the tooth was exposed with an instrument in situ (K-file or Hedstroemfile) and a metal stopper (3.05 mm in diameter, Fig. 2) for reference using a 60-kV tube (Heliodent DS, Sirona, Bensheim, Germany; exposure time 0.16 s) and an Ultra Speed D film (Eastman Kodak, Rochester NY, USA). Films were developed using an XR 24 Nova (Dürr Dental, Bietigheim-Bissingen, Germany) device. A third examiner ( J. S.), using a lens with 2-fold magnification, estimated the distance between the acceptable working length and the instrument tip on the radiographs. The acceptable working length was defined as the point at which the apical constriction was reached. In those cases where resorption had occurred (e.g. Fig. 2) and/or where there were lateral orifices, the acceptable working length was defined as that point where the instrument was just surrounded by dentine in the right-angled projection of the root axis. The radiographs were then digitized using a scanner (CanoScan 2700F, Canon, Tokyo, Japan) at a resolution of 970 648 dpi. The digitized radiographs were also analysed for the distance between instrument tip and maximum acceptable working length. For this purpose a software program for endometric measurements (Square Root! 2.0, Brücklmeier & Nolt, Berlin, Germany) was used as described previously (Buchalla et al. 1999). The agreement between radiographic and the electric measurement was calculated.

Figure 2. In vitro radiograph of a tooth (resorption group) with a metal stopper (? = 3.05 mm - large arrow) for calibration and a silicon stopper for length determination (small arrow).

In vitro radiograph of a tooth with a metal stopper for calibration and a silicon stopper for length determination

After the radiograph was taken, the teeth with the endodontic instrument were dehydrated step-wise by immersion in varying concentrations of ethanol (80%, 90%, 95%, 100%) for 12-hour periods and subsequently immersed in methylsalicylate for 24 h. After clearing, the teeth were photographed at a magnification of 2and the resulting slides were scanned at a resolution of 970 648 dpi. These digitized images were analysed for distance between tip of instrument and acceptable working length, and tip of instrument and tip of the root, using the same endometric software (SquareRoot! 2.0).

Statistical analysis.
Statistical analysis was performed using SPSS for Windows 10.0 (SPSS Inc., Chicago, IL, USA). Inter-examiner reproducibility of the electric root length measurement was analysed with Cronbachs intra class correlation coefficient, confidence interval, and inter–item reliability coefficient.