Internationa} Bndodontic lourml (1992) 2 5 , 8 8 - 9 2
Variables affecting electronic root canal measurement Y, N, WU, J. N. SHI. L, Z. HUANG & Y. Y, XU* Department ofEndodontics, School ofDentistry, and 'Department o/Statistics, Fourth Militory Medical Universita,
X n , China
Summary This study was conducted in two parts. In thefirstpart, 20 single-rooted teeth that had been scheduled for extraction were investigated. The electronic root canal lengths were measured in vivo with a Dental SonoExplorra- type Y-III, and the actual canal lengths were Doeasured afiter extraction ofthe teeth. The rate of agreement of the two measurements was 77.5% within a range of ±0,5 mm, while it was 100% at ±2,0nun, which is acceptable clinicaUy, In the second part, there were 19 emulated canals whose lengths and apical foramen sizes were known beforehand. Experiments revealed a negative correlation between the areas ofthe apical foramina and the difference between the electronic and the actual root cmud lengths. This relationship was shown by the linear regression equation: y = 0,6 - 1.6x, With the exception of the smallest areas of foramina, electronic root canal length measurements were less than the actual lengths. Keywords: apical constriction, apical foramen, root canal measurement, working length. Introduction It is very important to obtain an accurate value for the length ofa root canal for successfiii root canal treatment. Sunada (1958) suggested the theory of biological characteristics and invented the method of electronic root canal measurement (ERCM). Huang (1987) discovered that the constant value of impedance was a purely physical phenomenon, which could be reproduced with simulated devices in the laboratory. On the basis of this finding, Huang (1987) suggested the theory of electronic characteristics, A series of electronic devices has since been developed, and their accuracy has been demonstrated in Correspondence: Dr Wu You-Nong, Department of Endodontics, School of Dentistry, Fourth MlUtary Medical Universtty, Xlan, Shaanxi 71O032,China.
88
clinical experiments {Thaoetal. 1987), The Dental SonoExplorer type Y-III is a very recent instrument and is easy to operate because it makes two kinds of sound, but there have been no reports on its accuracy to date. The factors that influence tbe accuracy of ERCM have always concerned both instrument designers and users. Huang (1987) considered that the size of the apical foramen was a decisive influencing factor, but that this required further study. The aim of this study was to determine the accuracy of the Dental Sono-Explorer type Y-IU in a clinical experiment, and tofindhow the length of electronic measurements changed with the size of the apical foramen in a laboratory experiment. Materials and methods CUnical experiment With each patient's consent, 20 single-rooted teeth, which were going to be extracted from 11 patients because of extensive caries or periodontai disease, were used. The Dental Sono-Explorer type Y-III (Huadong Electron Tube Factory, Nanjing, China) (Fig. 1) was used. The relationship between the reamer tip and the apical foramen was indicated by signals from a buzzer and indicator lamps. The precision ofthe vernier callipers (Measuring and Cutting Plant, Wuxi, China) that were used was 0,02 mm. Local anaesthesia was routinely given before tooth extraction. The tooth crown was then cut across with a high-speed drill. The cut surface of the root was smoothed with a diamond bur and cleaned with a cotton wool roll, the saliva was carefully isolated, the pulp tissue was not removed (Zhao et al, 1987), and ERCM was tiien performed according to the manufacturer's manual. A size 15 reamer was smoothly introduced as an electric probe into the root canal until the burner sounded intermittently and a single lampflashed.The rubba: stop on the reamer shank was adjusted to touch the cut surface of Ihe root positively; the reamer was then pulled out, with care being taken to avoid touching the stop. The
Electronic root canal measuretnent
89
distance between the stop and the tip of the reamer was measured with I'ernier callipers. The ERCM was thus ohtaioed. The root was then extracted in the normal way. washed and dried. The original reamer was introduced into the root canal until the very tip ofthe reamer could just be seen at the apical foramen. The actual length was then determined by measuring the distance from the stop to the tip ofthe reamer. The measurement was performed by two operators. A and B. and was repeated three times in order to derive the mean. The data were subjected to analysis of variance.
Laboratory experiment A twist drill. 0.5 mm in diameter, was used to bore 30 holes through a 10.5-mm-thick plastic block (Chemical Plant, Baoji. China), to make simulated root canals. All these canals were enlarged with K-flles of different sizes. The area of each apical foramen was measured with a TAS plus image analysis system (Ernst Leitz Wetzlar GmbH, Germany), and ] 9 canals ivith varying areas of foramen were selected for investigation. The plastic blocks were kept suspended in a glass container filled with normal saline by four screws. The distance from the surface of the liquid to the top of the plastic block was approximately 1.0 mm (Fig. 2). A smooth probe was introduced into each canal and moved up and down several times to let liquid in and air bubbles out. The iength of each simulated canal was measured with the Dental Sono-Explorer type Y-IIl five times, and the mean v^alue was calculated. The relationship between ERCM lengths and the areas of the apical foramina was analysed statistically.
Results
Fig. 1. tental Sono-Explorer Type Y-IIl
ranged from -'0.5509 mm to 4-0.5509 mm. smaller than that of repeated measurements by one operator. Thus the error of the methods could be neglected. The mean error of repeated measurements ranged from — 0.7151 mm to -1-0.7151 mm. which was relatively larger; the error was mainly due to two teeth measured by operator B, suggesting that ERCM may not be accurate in some individual teeth. For this reason the length should be measured several times with the electronic device, and the mean value taken.
Clinical experiment The plus sign indicated that the ERCM length was longer than the actual length, whereas the minus sign indicated that the ERCM length was shorter than the actual length. Among the canals measured by operator A. eleven were longer {0.02 to 0.86 mm) and nine were shorter (— ] .01 to — 0.02 mm). Among the same canals measured by operator B, twelve were longer (0.09 to 0.50 mm) and eight were shorter ( - 1 . 4 1 to - 0.01 mm). There were 77.5% within the range —0.5 to -1-0.5 mm (Table 1 and Fig. 3). Analysis of vadaoce was performed. The mean error between operators A and B was almost zero, and indicated that it was easy to master the measuring technique. The mean error of the two methods
Laboratory experiment All ERCM lengths were shorter than their actual lengths, with the exception of the two with the smallest apical foramina (Table 2). A negative correlation was found between the areas of the apical foramina and ERCM length ( r = - 0 . 8 8 4 8 , P
Variables affecting electronic root canal measurement Y, N, WU, J. N. SHI. L, Z. HUANG & Y. Y, XU* Department ofEndodontics, School ofDentistry, and 'Department o/Statistics, Fourth Militory Medical Universita,
X n , China
Summary This study was conducted in two parts. In thefirstpart, 20 single-rooted teeth that had been scheduled for extraction were investigated. The electronic root canal lengths were measured in vivo with a Dental SonoExplorra- type Y-III, and the actual canal lengths were Doeasured afiter extraction ofthe teeth. The rate of agreement of the two measurements was 77.5% within a range of ±0,5 mm, while it was 100% at ±2,0nun, which is acceptable clinicaUy, In the second part, there were 19 emulated canals whose lengths and apical foramen sizes were known beforehand. Experiments revealed a negative correlation between the areas ofthe apical foramina and the difference between the electronic and the actual root cmud lengths. This relationship was shown by the linear regression equation: y = 0,6 - 1.6x, With the exception of the smallest areas of foramina, electronic root canal length measurements were less than the actual lengths. Keywords: apical constriction, apical foramen, root canal measurement, working length. Introduction It is very important to obtain an accurate value for the length ofa root canal for successfiii root canal treatment. Sunada (1958) suggested the theory of biological characteristics and invented the method of electronic root canal measurement (ERCM). Huang (1987) discovered that the constant value of impedance was a purely physical phenomenon, which could be reproduced with simulated devices in the laboratory. On the basis of this finding, Huang (1987) suggested the theory of electronic characteristics, A series of electronic devices has since been developed, and their accuracy has been demonstrated in Correspondence: Dr Wu You-Nong, Department of Endodontics, School of Dentistry, Fourth MlUtary Medical Universtty, Xlan, Shaanxi 71O032,China.
88
clinical experiments {Thaoetal. 1987), The Dental SonoExplorer type Y-III is a very recent instrument and is easy to operate because it makes two kinds of sound, but there have been no reports on its accuracy to date. The factors that influence tbe accuracy of ERCM have always concerned both instrument designers and users. Huang (1987) considered that the size of the apical foramen was a decisive influencing factor, but that this required further study. The aim of this study was to determine the accuracy of the Dental Sono-Explorer type Y-IU in a clinical experiment, and tofindhow the length of electronic measurements changed with the size of the apical foramen in a laboratory experiment. Materials and methods CUnical experiment With each patient's consent, 20 single-rooted teeth, which were going to be extracted from 11 patients because of extensive caries or periodontai disease, were used. The Dental Sono-Explorer type Y-III (Huadong Electron Tube Factory, Nanjing, China) (Fig. 1) was used. The relationship between the reamer tip and the apical foramen was indicated by signals from a buzzer and indicator lamps. The precision ofthe vernier callipers (Measuring and Cutting Plant, Wuxi, China) that were used was 0,02 mm. Local anaesthesia was routinely given before tooth extraction. The tooth crown was then cut across with a high-speed drill. The cut surface of the root was smoothed with a diamond bur and cleaned with a cotton wool roll, the saliva was carefully isolated, the pulp tissue was not removed (Zhao et al, 1987), and ERCM was tiien performed according to the manufacturer's manual. A size 15 reamer was smoothly introduced as an electric probe into the root canal until the burner sounded intermittently and a single lampflashed.The rubba: stop on the reamer shank was adjusted to touch the cut surface of Ihe root positively; the reamer was then pulled out, with care being taken to avoid touching the stop. The
Electronic root canal measuretnent
89
distance between the stop and the tip of the reamer was measured with I'ernier callipers. The ERCM was thus ohtaioed. The root was then extracted in the normal way. washed and dried. The original reamer was introduced into the root canal until the very tip ofthe reamer could just be seen at the apical foramen. The actual length was then determined by measuring the distance from the stop to the tip ofthe reamer. The measurement was performed by two operators. A and B. and was repeated three times in order to derive the mean. The data were subjected to analysis of variance.
Laboratory experiment A twist drill. 0.5 mm in diameter, was used to bore 30 holes through a 10.5-mm-thick plastic block (Chemical Plant, Baoji. China), to make simulated root canals. All these canals were enlarged with K-flles of different sizes. The area of each apical foramen was measured with a TAS plus image analysis system (Ernst Leitz Wetzlar GmbH, Germany), and ] 9 canals ivith varying areas of foramen were selected for investigation. The plastic blocks were kept suspended in a glass container filled with normal saline by four screws. The distance from the surface of the liquid to the top of the plastic block was approximately 1.0 mm (Fig. 2). A smooth probe was introduced into each canal and moved up and down several times to let liquid in and air bubbles out. The iength of each simulated canal was measured with the Dental Sono-Explorer type Y-IIl five times, and the mean v^alue was calculated. The relationship between ERCM lengths and the areas of the apical foramina was analysed statistically.
Results
Fig. 1. tental Sono-Explorer Type Y-IIl
ranged from -'0.5509 mm to 4-0.5509 mm. smaller than that of repeated measurements by one operator. Thus the error of the methods could be neglected. The mean error of repeated measurements ranged from — 0.7151 mm to -1-0.7151 mm. which was relatively larger; the error was mainly due to two teeth measured by operator B, suggesting that ERCM may not be accurate in some individual teeth. For this reason the length should be measured several times with the electronic device, and the mean value taken.
Clinical experiment The plus sign indicated that the ERCM length was longer than the actual length, whereas the minus sign indicated that the ERCM length was shorter than the actual length. Among the canals measured by operator A. eleven were longer {0.02 to 0.86 mm) and nine were shorter (— ] .01 to — 0.02 mm). Among the same canals measured by operator B, twelve were longer (0.09 to 0.50 mm) and eight were shorter ( - 1 . 4 1 to - 0.01 mm). There were 77.5% within the range —0.5 to -1-0.5 mm (Table 1 and Fig. 3). Analysis of vadaoce was performed. The mean error between operators A and B was almost zero, and indicated that it was easy to master the measuring technique. The mean error of the two methods
Laboratory experiment All ERCM lengths were shorter than their actual lengths, with the exception of the two with the smallest apical foramina (Table 2). A negative correlation was found between the areas of the apical foramina and ERCM length ( r = - 0 . 8 8 4 8 , P
