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 »  Home  »  Endodontic Articles 13  »  Effect of X-ray beam angulation and intraradicular contrast medium on radiographic interpretation of lower first molar root canal anatomy
Effect of X-ray beam angulation and intraradicular contrast medium on radiographic interpretation of lower first molar root canal anatomy
Introduction - Materials and methods.

H. J. Naoum, R. M. Love, N. P. Chandler & P. Herbison
Departments of Oral Rehabilitation, Stomatology, Preventive and Social Medicine, University of Otago, Dunedin, New Zealand.

Successful root canal treatment requires effective chemo-mechanical debridement to eradicate intraradicular infection and proper canal shaping to facilitate obturation. The root canal geometry may have a direct impact on the thoroughness and extent of debridement and canal shaping (Peters et al. 2001). Many methods have been used to investigate root canal anatomy in vitro, each has its own advantages and disadvantages with variable degrees of accuracy and procedural complexity. However, with the exception of radiography, these methods cannot be applied in vivo. Usually, the processes either destroy the specimen rat best preclude the unimpeded entry of instruments into the root canal.
Careful preoperative assessment of root canal anatomy obtained from a diagnostic radiograph is a key prerequisite for thorough canal preparation and, ultimately, successful therapy. The technique of choice for endodontic radiography is the long cone paralleling technique, which creates an accurate radiograph with minimal distortion and a high level of reproducibility (Fava & Dummer 1997). Intentional alteration of the X-ray beam angulation may provide additional information not readily available from the orthoradial view. The recommended horizontal beam angulation for identification of two canals in one root is dependent on the amount of separation and divergence between canals and is reported to lie between 20 and 408 (Walton 1973, Klein et al. 1997, Martinez-Lozano et al. 1999). In assessing the canal configuration of mandibular first molar teeth, a 308mesial horizontal beam angulation was suggested to provide additional detail not provided by 0 or 208 angulation (Walton1973).
Contrast media are radiopaque substances that can be introduced into various parts of the body to artificially alter subject contrast (Whaites1992).The use of radiopaque materials to enhance the contrast of a root canal system is not new. Barrett (1925) presented radiographs from clinical cases where radiopaque material had been forced into empty root canals to demonstrate the presence of lateral branches. Other investigators have used a variety of radiopaque materials to study canal anatomy in extracted teeth. Similar principles of removing the pulp tissue and introducing radiopaque material with the aid of centrifuging or vacuum were used (Barker et al.1969, Lowman et al.1973, Hession 1977, Mayo et al. 1986, Thomas et al.1993). Although this method reveals the complex anatomical characteristics of the root canal system, it cannot be applied in vivo. More recently, Scarfe et al. (1995) passively injected contrast medium into the root canal to determine the presence of lateral and secondary canals. Similarly, to improve radiographic interpretation, Shearer et al. (1996) injected iohexol contrast medium passively into the root canals of extracted human teeth. Contrast medium may have many applications in endodontic radiography, e.g. to improve radiographic interpretation of root canal systems in teeth with aberrant anatomy, for the detection of root perforations and ledges and in the diagnosis of internal resorption. Shearer et al. (1996) concluded that contrast media could be a valuable aid in radiographic interpretation of root canal systems and suggested the need for further clinical studies to assess the efficacy of this technique. The aims of this study were to compare the accuracy of evaluator interpretation of the root canal anatomy on radiographs taken at 0 or 308mesial angulation without or with radiopaque contrast medium introduced into the root canal by incremental passive injection or infusion under vacuum. Furthermore, the effectiveness of the passive injection technique was assessed by comparing it to the laboratory-accepted method to introduce the contrast medium into the root canal system.

Materials and methods.
Twenty extracted human mandibular first molar teeth with sound roots and mature apices were collected. Unimpeded coronal access to canals in the mesial and distal roots was gained and canal patency was ensured using a size 8 K-file (Caulk, Dentsply, Milford, DE, USA). In order to avoid cutting and modifying the canal anatomy and plugging the openings of small lateral canals by dentinal debris, pulp tissue from each canal was removed with 20 mL 2.5% NaOCl irrigation using a 31- gauge needle (Endo-Eze, Ultradent Products, UT, USA) and mechanical agitation with blunted size 8 K-files. Each canal was then irrigated with 10 mL of water and dried with paper points.
The body of a dried human mandible was split in half, longitudinally, using a rotating saw with the plane of section extending mesiodistally. The teeth and cancellous bone were removed, leaving the buccal and lingual cortical plates intact. To simulate cancellous bone, a silicone laboratory putty (Bayer Dental, Dormagen, Germany) was mixed with sawdust and the roots of each sample were embedded in the putty mixture between the cortical plates such that each tooth was custom-fitted into the bone. The cortical plates were held together on a wax base on the rotating table of a jig attached to a film holder and beam-aiming device. Angulations were scribed onto the rotating part of the jig to indicate the horizontal angle of the X-ray beam. A soft tissue equivalent to15-mmplasticine was attached with in the beam alignment ring (Fig. 1). The sample and dental X-ray unit were positioned to obtain a 26-cm focal spot-object distance and a 2-cm object-film distance. Conventional E-speed radiographic film (Kodak Co., Rochester, NY, USA) was exposed ata 0or 308mesialhorizontal angulation (Walton 1973) with the X-ray unit operating at 65 kVp, 8 mA, for 0.44 s (Gendex, Milan, Italy). These settings were determined in a pilot study to produce the best quality radiographs.

Figure 1. Jig for standardized radiographic images:
a, soft tissue equivalent in aiming ring;
b, section of mandible with tooth in position;
c, film holder;
d, angle indicator.

Jig for standardized radiographic images

Iohexol is a tri-iodated, nonionic, water-soluble contrast medium with low osmotic pressure and a molecular weight of 821.14 (iodine content 46.4%). The product has been tested in both in vitro and in vivo and has been shown to be safe (Aakhus et al.1980, Mutzel et al.1980). To aid visual reference of contrast medium in the root canal, one drop of 0.1% methylene blue dye was mixed with 1mL of iohexol radiopaque contrast medium (Omnipaque1, Nycomed, Birmingham, UK). Increments of the mixture were injected passively into the canals with a 31-gauge needle placed to the most apical level possible. A blunt size 8 K-file was introduced1mmshort of the apical foramen after the first increment and manipulated in each canal for 1min. File insertion was repeated for another minute after the second increment to enhance penetration of the contrast medium and expel air bubbles. A second pair of radiographs was taken at the previous angles and settings. The teeth were then removed from their moulds and immersed in iohexol and subjected to vacuum (24 in. mmHg_1) for 2min. The vacuum was reapplied for further 2 min until air bubbles ceased escaping from the access cavity. Samples were carefully cleaned without disturbing the canals and replaced into their moulds for repositioning in the mandible and a third pair of radiographs exposed. All films were developed in an automatic processor (All-Pro 2000M, Hicksville, NY, USA) using Kodak GBZ developer and fixer solutions (Kodak Co., Rochester, NY, USA).
The mesial root on all images (Fig. 2) was examined and assessed by three evaluators, a specialist endodontist and two experienced general practitioners. The assessment included the number of visible canals, whether the canal(s) was visible along the entire length of the root, the location of the canal terminus in relation to the radiographic apex, configuration of canal(s) based on Pineda (1973), level of multiple canals merging and the presence of lateral canals. The aim of the experiment was explained to the evaluators who were given verbal instructions and schematic diagrams to assist them in their answers. The evaluators were first allowed to examine and assess images not included in the study by answering the assessment questionnaire. Points of confusion were clarified using the schematic drawings of the possible findings as re-enforcement of assessment criteria may improve evaluator agreement (Reit 1987, Saunders et al.1999). The images were examined with a x2 magnifier on a light viewing box (Magni Viewer III, Proyrex, Tokyo, Japan) with peripheral light excluded. No time limit was set for assessments and the image sequence was randomized for the evaluators. The viewing was conducted in two sessions no less than 1week apart. Finally, to accurately determine the root canal anatomy, each tooth was rendered transparent (Fig. 3) with a clearing technique (Kelsen et al.1999), and examined using a stereomicroscope (Olympus, Tokyo, Japan) at x10 magnification and the same assessment criteria. Evaluation of the cleared teeth represented the gold standard.

Figure 2. Representative images of the 0 and 308 radiographs without and with contrast medium.
A and B; 0 and 308 radiographs without contrast medium,
C and D; 0 and 308 radiographs with contrast medium introduced by passive injection,
E and F; 0 and 308 radiographs with contrast medium introduced by vacuum.

Representative images of the 0 and 30 radiographs without and with contrast medium

The experimental data were compared to the gold standard using logistic regression with the standard errors adjusted for clustering on samples. The Kappa test was applied to determine the interevaluator reliability. To determine the intraevaluator reliability, radiographs of four samples were randomly selected and reassessed after 3 months by the three evaluators. Data were analysed using the Kappa test and values were defined as: 0.81-1.00 represented very good agreement, 0.61-0.80 represented good agreement and 0.41-0.60 represented moderate agreement (Landis & Koch1977).

Figure 3. The mesial root of the specimen in Fig. 2 following clearing.

The mesial root of the specimen in Fig. 2 following clearing