Canal length estimation in curved root canals A comparison between conventional and direct digital radiography *Avinash M **Kamath PM

Transcription

1 Endodontology, Vol 14, 2002 Canal length estimation in curved root canals A comparison between conventional and direct digital radiography *Avinash M **Kamath PM ABSTRACT Direct Digital Radiographic (DDR systems make it possible to measure canal lengths by means of an on-screen measurement device that is based on a click measurement between two or more points Canal length was estimated by four methods: measurement on a conventional E-speed film radiograph and on-screen DDR measurement utilizing two clicks, six clicks and an unlimited number of clicks Thirty eight extracted human teeth with root curvatures ranging from 0 82 (Schneider s method were examined After gaining endodontic access, actual canal lengths were determined by visualizing the instrument tip at the apical foramen of the tooth with a positive occlusal/incisal reference point Teeth were mounted on a specially designed radiographic platform and radiographed using conventional techniques and DDR method (2 click, 6 click and unlimited clicks A two-way analysis (ANOVA and Karl Pearson s correlation coefficient indicated no significant differences between any of the methods, regardless of the canal curvature Both the radiographic methods nevertheless showed magnification when compared to the true canal length But interestingly, the 2-click measurement in the moderate and serve curvature groups was closer to the true canal length It was implied that this measurement offset the magnification error as it measured only a straight line between the two points of measurement instead of along the curve Key words Root canal length measurement, Direct digital radiography, curved canals Introduction Root canal therapy relies on establishment of an accurate and reproducible working length The working length establishes the apical extent of the preparation Accuracy of this length is essential if damage to the root apices * Former Post Graduate Student ** Professor and Head, Deptt of Conservative Dentistry and Endodontics, College of Dental Studies Mangalore (Manipal Academy of Higher Education 52 and peri apical tissues is to be avoided during instrumentation and obturation 1 Traditionally, conventional intra-oral radiography has been the basis for various techniques of determining working length Recently, with the introduction of Direct Digital Radiographic (DDR systems, newer avenues are being explored DDR is an emerging area of radiology that offers many potential benefits to an endodontic practice First described by Mouyen 2 in 1989, this is a filmless radiographic system based

2 Avinash and Kamath Canal length estimation on electronic generation of high-resolution computer images directly from an intra-oral sensor when irradiated by an x-ray beam Materials and Methods Direct Digital systems have three components : 1 Radio component is the solid state sensor 2 Visio component consists of video monitor and display processing unit 3 Graphy component is the storage module that provides a hard copy of the screen image using the same video signal Thirty-eight extracted adult human single and multirooted teeth with varying root curvatures were obtained To avoid confusion, extraneous roots on multirooted teeth were removed with straight fissure burs, so that only one root on each tooth remained Selection of Specimens Endodontic access cavity preparation Standard endodontic access was prepared in each tooth and canal patency verified with No 10 K file Two of the teeth were excluded due to excessive calcification precluding the passange of the patency file One more tooth was excluded as the patency file fractured apically while attempting negotiation, due to extreme curvature of the canal The advantages of this system over conventional radiography include instant image acquisition, eliminating messy developing solutions and associated processing errors, image enhancement, image manipulation to allow changes in contrast and brightness and reduced radiation to the patient Poor image resolution and high cost are the often cited disadvantages Determination of true canal length After establishing a small occlusal reference on each tooth with a straight fissure diamond, a No 15 K file with rubber stopper was inserted into the canal and advanced until the file tip was visualized at the foramen The stopper was set at the occlusal reference point and the file removed and set aside True canal length (CLT was determined for each tooth using a millimeter rule and 2x magnification Measurements were read to the nearest 05mm One of the more recent additions to the different DDR systems available commercially is the capability of on-screen point to point measurements using multiple additive clicks This capability allows for fast and accurate length estimation This study evaluated the accuracy of such a system in determining the canal length measurement over a range of canal curvatures The other purpose of this study was to determine its relevance with the commonly used radiographic method for working length estimation Measurement of canal curvature The teeth were mounted in acrylic tray Fig1 Radiographic Platform 53 Fig 2 Radiographic Platform (with mounted specimen attached to X-ray tube

3 Endodontology, Vol 14, 2002 material (DPI-RR cold curetm, using an ice cube tray as a base mould The teeth were held in the correct position by attaching them to the middle of a toothpick with wax The two ends of the toothpick rested on the edges of the ice cube mould The mounted teeth were then removed from the mould and placed in the radiographic platform as described by Sydney et al 3 Radiographic Platform This technique allows for a more consistent object to film distance (OFD and object to sensor distance (OseD It also allows the application of a more constant source to object distance The necessary materials for the fabrication of this device are : 1 A clamp (6 cms in diameter 2 A plastic ice cube mould (only one piece cut away from an ice cube tray 3 Two lids of gutta percha boxes (Dentsply, Malleifer 4 A plastic ruler and 5 Cynoacrylate adhesive (Fevi-Kwik, Pidilite Ind, Mumbai First, a rectangular ice cube mould was cut and one piece was detached One of the gutta percha lids was cut 3mm from one of its sides Using a carborundum disc, the ruler was cut longer than the clamp diameter, which must be adjusted to the X-ray tube The ruler was cemented to the clamp by means of cyanoacrylate adhesive The ice cube mould piece was cemented to the ruler, the base and the gutta percha lid piece Once the radiographic platform was assembled, it was painted black and connected to the X-ray tube by the clamp, which was previously adjusted to the correct diameter(fig1 and 2 Measuring canal curvature After placing the resin-mounted teeth into the ice-cube mould of the radiographic platform, conventional radiographs were taken using E speed film (Agfa Dentus, Belgium This radiograph was used to determine canal curvature Tracing of the radiograph was done on cephalometric tracing paper and Schneider s method 4 was employed to determine canal curvature This method involves drawing a line parallel to the long axis of the canal A second line is then drawn from the apical foramen to intersect with the point were the first line left the long axis of the canal The angle formed is then measured with a protractor The teeth were then grouped into three curvature groups Mild for curvatures < 20, moderate for curvatures > 20 and < 36 and severe for > 36 Collectively canal curvatures ranged from 0 82 Conventional and Digital Radiographic Imaging After determining canal curvatures, the No 15 K file was returned to the canal to the true canal length and fixed in place with light cured composite resin The resin mounted teeth were then placed on the radiographic platform and imaged using conventional and direct digital radiographic techniques Conventional radiographs were obtained using E-speed film (Agfa Dentus, Belgium, whereas digital radiographs were obtained on Dexis v30 system Both radiographs were obtained using a common X-ray source (J Morita, Japan, Optimal exposure time for each method was established during a pilot study Radiographic technique followed was the paralleling technique The paralleling technique (long cone or right angle technique derives its name from and produces improved images as the result of placing the film parallel with the long axis of the tooth and the central X-ray beam is directed at right angles to the teeth and film This orientation minimizes geometric distortion In addition, the use of a long source to object distance reduces the size of the apparent focal spot These factors result in images with less magnification and increased 54

4 Avinash and Kamath Canal length estimation definition The estimated canal length was then measured as the distance from the occlusal reference point to the most apical extent of the file visualized The following measurements were made: 1 Estimated canal length to the nearest 05 mm using a conventional radiographic technique (CL CR by means of calipers under X2 magnification 2 Estimated canal length to 01 of a millimeter using a two click measurement (one at the reference point and the other at the most apical extent of the file visualized on the DDR s on screen measurement device ( (Fig 3 3 Estimated canal length to 01 of a millimeter using a six click measurement (one at the reference point, one at the most apical extent of the file visualized and four intermediate clicks on the DDR s on screen measurement device ( 4 Estimated canal length to the 01 of a millimeter using unlimited number of clicks Table 1 Mild Curvature (< 20 Specimen Canal True CL Conventional Direct Digital Radiography No Curvature (CL T Radiotraphs (CL CR mm 232 mm 231 mm 231 mm 236 ( mm 192 mm 192 mm 192 mm 193 ( mm 238 mm 236 mm 236 mm 238 ( mm 233 mm 202 mm 202 mm 201 ( mm 247 mm 247 mm 247 mm 248 ( mm 287 mm 289 mm 289 mm 282 ( mm 205 mm 204 mm 204 mm 205 ( mm 236 mm 243 mm 243 mm 242 ( mm 23 mm 23 mm 23 mm 227 ( mm 221 mm 224 mm 224 mm 219 (7 Table 2 Moderate Curvature (20 < 36 Specimen Canal True CL Conventional Direct Digital Radiography No Curvature (CL T Radiotraphs (CL CR mm 21 mm 213 mm 218 mm 22 ( mm 23 mm 236 mm 232 mm 23 ( mm 195 mm 196 mm 20 mm 20 ( mm 185 mm 187 mm 194 mm 194 ( ,5 mm 235 mm 238 mm 239 mm 233 ( mm 255 mm 264 mm 269 mm 270 ( mm 26 mm 26 mm 263 mm 261 ( mm 21 mm 209 mm 222 mm 222 ( mm 195 mm 191 mm 193 mm 190 ( mm 25 mm 252 mm 253 mm 253 ( mm 21 mm 213 mm 218 mm 22 (8 55

5 using the DDRs on-screen measurement tool ( (Fig4 Group I CL T Group II CL CR Group III Group IV Group V Color, contrast and magnification of the digital radiographic images were adjusted to achieve the best possible image for viewing, just as would be available clinically As it was not possible to adjust conventional radiographic images, X2 magnification was used After obtaining measurements for conventional and radiographic images, 10 teeth each were grouped under the various curvature groups (slight, moderate and severe and compared with the true canal lengths (CL T Also, an overall comparison of the digitally obtained canal length was done with those obtained with the conventional radiographs and the true canal length Results and Analysis The true canal lengths as well as the canal lengths determined with the conventional and direct digital radiographic techniques of all the 56 Endodontology, Vol 14, 2002 Table 3 Severe Curvature (>36 Specimen Canal True CL Conventional Director Digital Radiography No Curvature (CL T Radiotraphs (CL CR mm 205 mm 192 mm 201 mm 198 ( mm 205 mm 174 mm 208 mm 211 ( mm 21 mm 186 mm 214 mm 214 ( mm 205 mm 195 mm 205 mm 205 ( mm 24 mm 241 mm 241 mm 242 ( mm 19 mm 187 mm 191 mm 191 ( mm 22 mm 221 mm 224 m 225 ( mm 195 mm 193 mm 200 mm 199 ( mm 225 mm 201 mm 231 mm 235 ( mm 235 mm 225 mm 238 mm 238 (7 specimens are listed according to the curvature in Tables 1, 2 and 3 Statistical tools employed were the Kari Pearson s coefficient of correlation and analysis of variance [ANOVA (Fishers F test Overall correlation between the true canal length and canal lengths obtained by the conventional radiographs and DDR system were found statistically to be very highly significant (p<0001 In other words, the canal lengths obtained by the conventional and DDR systems (2 chicks, 6 clicks and unlimited clicks were very much similar in values to the true canal lengths A comparison between the conventional radiographic length and that obtained by the DDR system also showed statistically a very highly significant correlation (Table 4 A correlation between the true canal length and the conventional and digital radiographic canal lengths in the various curvature groups also was found to be very highly significant statistically It is interesting to note that all the comparisons as listed in Table 5 showed very highly significant correlations except for the comparison between the 2 click digital radiographic canal length and the true canal lengths in the severe curvature group, which

6 Avinash and Kamath Canal length estimation Fig 3 Two click measurement Fig 4 Unlimited click measurement (8 showed just a statistically significant co-relation (p< 005 Correlations between the conventional radiographic length and the digital radiographic length for the different curvature groups were also drawn (Table 6 These results suggest a very highly significant correlation except for the comparison between the 2 click measurement on the DDR system and the conventional radiographic length in the moderate and severe curvature groups These exceptions showed a significant and highly significant co-relation respectively Therefore an overall analysis of the digital radiographic length in comparison with the conventional radiographic lengths suggests that a 2-click measurement differed in its estimation of canal lengths in the moderately and severely curved canal groups but only to such small a degree that it was not significant statistically (Tables Table 4 Overall Correlations CL-T CL-CR Pearson CL-CR 960 Correlation (r CL DDRUN P CL- CR CL DDrun and 6 Analysis of variance, ANOVA (Fishers F test showed no statistical significance (p>005 (Table 7 Discussion Working length establishes the apical extent of canal preparation and the apical stop The term working length is used to denote the distance between the apical limit of instrument and the point from which the measurement is made normally Failure to accurately determine the working length may lead to apical perforation and over filling with increased Table 5 Correlation between true canal length and other lengths GROUP r P <20 CL-T CL-CR <36 CL-T CL-CR >36 CL-T CL-CR

7 Endodontology, Vol 14, 2002 Table 6 Correlation between conventional and digital radiographic length GROUP r P <20 CL- CR <36 CL- CR >36 CL- CR incidence of post operative pain In addition, one might expect prolonged healing period and increased failure due to incomplete regeneration of cementum, periodontal ligament and alveolar bone Failure to determine tooth length accurately may also lead to incomplete instrumentation and under filling with attendant problems such as persistent pain and discomfort from inflamed shreds of retained pulpal tissue In addition, ledge formation may be developed, short of the apex, making adequate treatment or retreatment extremely difficult or impossible Finally, apical percolation may develop into the unfilled dead space at the apex This could result in a continued periradicular lesion and increased incidence of failure Therefore, an accurately determined working length is essential for endodontic success Since the advent of x-ray in dentistry by Edmund Kelles in 1899, radiography has been the mainstay in working length determination, although apex locators are an important adjuct The recently introduced DDR systems are also proving to be useful Various studies comparing conventional radiography and digital radiography have revealed no significant differences between the Table 7 ANOVA (Analysis of Variance - Fishers 'F' test F Sig (p NS NS NS CL- T NS CL- CR NS p< 005 significant <0001 very highly significant <001 highly significant >005 not significantr two Horner et al 6 noted no significant difference between the percentage of length of root canal visible in both the radiographic methods Similar studies were carried out by Hedrick et al 7 Leddy et al 8 Ong and Pittford 9 Garcia et al 10 and Burger et al 11 Most authors have recommended DDR owing to its superior features over conventional radiographs such as reduced patient exposure to radiation, filmless imaging, control of contrast, image enhancement and potential for computer storage and subsequent transmission of images But, DDR systems produce poorer image quality (poor resolution as determined by Walker et al 12 and Nelvig et al 13 Although many studies have compared conventional radiography with regard to canal length or working length determination, very limited studies have been done on the effects of canal curvature on the accuracy of the aforementioned system This study attempted to evaluate the same Statistical analysis revealed that there were statistically no significant differences between the true canal lengths (group I on the conventional and DDR canal length The level of significance was noted to be lesser in the correlation between the true canal length and the 2-click DDR measurement (which is just a straight line between two points in the severe curvature group The 2-click measurement gave a shorter canal length estimation than the true canal length in a few 58

8 Avinash and Kamath Canal length estimation specimens Each of those specimens which demonstrated such a finding affected the overall correlation coefficient resulting in a significance that was not very high An interesting point to note in the histograms depicted is that the 2 click measurement was not very highly significant in its co-relation with groups 2, 4 and 5 in the moderate and severe curvature groups when compared to the other co-relations All the other co-relations were very highly significant Thus, it was apparent that there was no significant difference between length estimation by either conventional radiography or direct digital radiography All radiographic methods however, over estimated the true canal length Although this was not statistically significant, the difference may be explained as the effect of magnification Magnification is defined as the enlargement of an object s image on the radiographic film It had been shown previously that magnification does affect length estimates Radiographic magnification increases as the OFD (object-film distance or OSD (object-sensor distance increases Because it is physically impossible to place either the film or the sensor directly against the tooth being imaged due to hard and soft tissue constraints, a certain degree of magnification is expected The effect of radiographic magnification error must be taken into consideration whenever a radiographic technique is used to determine canal length The use of a DDR system is no exception The thickness of the sensor must be considered when evaluating the effect of magnification on canal length estimates Distortion may also affect length estimation and is the result of unequal magnification of different parts of the object Magnification must be minimized by keeping the object as close to the film as possible and the SoF (Source film distance as large as possible Distortion on the other hand, can be minimized by using a paralleling technique to assist in positioning the object in the central part of the X-ray beam The on-screen measurement on the Dexis DDR system allows for rapid additive multiple point measurements of digital images, automatically tallying the measurements onscreen to a tenth of a millimeter Results of this experiment concur with similar studies that have found no statistical significance between RVG and D speed film for length estimation on ability to make accurate file length adjustments Empirically, it was expected that multiple measurements along the curve of a canal would be more accurate than a straight line measurement taken from the occlusal reference point to the apex This was based on the premise that if the measurement points were able to closely follow the curve, a truer estimate of the canal length would be obtained Experimentally, however, canal length estimates obtained using multiple clicks of the on-screen utility were not significantly different from those obtained using a starting and ending click But, with the 2 click measurement in the moderate and severe curvature groups, the canal length was closer to the actual canal length This may be explained by the fact that the DDR system always measures only a straight line between any two clicks Therefore, in a moderately or severely curved canal, the 2 clicks that connect the occlusal reference point and the apical extent of the instrument, would be straight line between the point instead of following the curve It is well known that a straight line is the shortest distance between any two given points This reductioni in length in the curved canals nullifies the magnification error to a certain extent, so that the canal length estimated is close to the true canal length As mentioned already, in conventional method for estimation of working length, a leeway of 1mm is to be deduced from the preoperative tooth length radiograph as a safety allowance for possible image distortion or 59

9 magnification Applying the results of this study to working length estimation, the following conclusions can be made 1 In the mild curvature groups, the magnification error must be accounted for in the DDR system 2 In moderate and severe curvature canals, the canal length is more or less the working length, as the magnification error is more or less compensated for by the two-click measurement on the DDR system Increasing the number of clicks may again result in magnification error, which should be taken into consideration Conclusion In conclusion, this study found that 1 There was no significant difference between canal length estimates obtained by conventional radiographic techniques and those using currently available DDR s on-screen measurement utilities 2 All the radiographic methods overestimated the true canal lengths although this was not statistically significant 3 The 2-click measurement in the moderate and severely curved canals did not corelate as significantly as the others in the canal length estimation, although this again was not statistically significant The 2-click measurement in these groups of teeth was closer to the true canal length due to the fact that the shortened canal length on the DDR offset the magnification error to a certain extent 4 It may be recommended that DDR systems be used in lieu of the conventional radiograph technique owing to their obvious advantages such as reduced 60 Endodontology, Vol 14, 2002 radiation exposure, ability to manipulate images (such as enhancement, control adjustments etc, instant image acquisition, the elimination of a radiographic film and the associated processing errors and easier documentation References 1 Ingle JI, Bakland LK, Peters OL, Buchanan SL, Mullaney TP Endodontic cavity preparation In: Ingle JI, Bakland LK, eds Endodontics 4th ed Baltimore: Williams & Wilkins, 1994; Mouyen F, Benz C, Sonnabend E, Lodter JP Presentation and physical evaluation of radiovisiography Oral Surg Oral Med Oral Pathol 1988; 65: Sydney GB, Batista A, de Melo LL The radiographic platform : a new method to evaluate root canal preparation in vitro J Endod 1991; 17: Schnieder WE A comparison of canal preparations in straight and curved root canals Oral Surg 1971; 32: Ingle JI, Bakland LK Endodontics (4th Ed 1994 Williams and Wilkins Pg Horner K, Shearer AC, Walker A, Wilson NHF Radiovisiography: an initial evaluation Int Endod J 1990; 168 : Hedrick RT, Dove SB, Peters DD, McDavid WD Radiographic determination of canal length: Direct Digital Radiography versus conventional radiography J Endod 1994;20 : Leddy BJ, Miles DA, Newton CW, Brown CE Interpretation of endodontic file lengths using radiovisiography J Endod 1994; 20 : Ong EY, Pittford TR Comparison of radiovisiography with radiographic film in root length determination Internat Endod J 1995; 28: Garcia AA, Navarro CT, Castello VU, Laliga RM Evaluation of a digital radiography to estimate working length J Endod 1997; 23 : Burger CL, MOrk TO, Hulter JW, Nicholl B Direct Digital radiography versus conventional radiography for estimation of canal length in curved canals J Endod 1999; 25 : Walker A, Horner K, Czajka J, Shearer AC, Wilson NHF Quantitative assenssment of a new digital imaging system Br J of Radiology 1991; 64: Nelvig P Wing K, Welander U Sens-A-Ray, a new system for direct digital intraoral radiography Oral Surg Oral Med Oral Pathol 1997; 74:818-23