0099-2399/91/1710-0491/$03.00/0 JOURNAL OF ENDODONTICS Copyright 9 1991 by The American Association of Endodontists
Printed in U.S.A.
VOL. 17, NO. 10, OCTOBER1991
A New Model System for Measuring Intracanal Temperatures R. Norman Weller, DMD, MS, FICD, FACD, Joseph J. Jurcak, DDS, Dennis L. Donley, DDS, and James C. Kulild, DDS, MS, FICD
A new model system was developed which allows intracanal temperature measurements to be recorded during repeated obturations of a human tooth root canal. A human central incisor was embedded in clear orthodontic resin and sectioned longitudinally. Sixteen thermocouples were secured at 2-ram intervals along two surfaces of the root canal. The thermocouples were connected to a computerized temperature recording system to measure intracanal temperatures produced by high-temperature thermoplasticized injectable gutta-percha. The system was capable of recording 16 simultaneous temperatures every second with an accuracy of a hundredth degree centigrade. There was a linear increase in the recorded temperatures in the root canal. However, the actual temperatures were lower than expected.
The purpose of this article was to report a new model system which accurately records temperatures produced in vitro in a natural tooth. This system also allows repeated obturations of the same tooth so that a direct comparison of different materials or techniques can be made. MATERIALS AND METHODS A human maxillary central incisor tooth was completely embedded in a block of clear orthodontic resin (Caulk/Dentsply, Milford, DE). Four mesiodistal alignment holes were drilled through the resin block perpendicular to the long axis of the tooth apical to the level of the cementoenamel junction. Two of the holes were drilled on the facial side of the tooth and the other two were drilled on the palatal side. The tooth was then sectioned longitudinally in a buccolingual direction through the center of the root canal using a Buehler Isomet low-speed saw (Buehler Ltd., Evanston, IL). During experiments the two halves of the block could then be reapproximated and secured with bolts placed in the four alignment holes. The crown of the embedded tooth was removed by a model trimmer to expose the middle third of the pulp chamber (Fig. 1). A #6 round bur in a slow-speed handpiece was
The ability to obturate a root canal system by one of the presently available warm gutta-percha techniques has stimulated interest in the temperature increases produced during these procedures. Prior investigations have measured intracanal temperatures produced during thermomechanical root canal obturation procedures (1, 2) and vertical condensation of warm gutta-percha (3), and also the temperatures produced on the external root surface using heated pluggers within the root canal (4). Various model systems have been developed to accurately measure these temperatures. These models include in vitro thermocouples embedded in acrylic blocks that simulate root canals (5), and the in vivo placement of thermocouples on the overlying bone of teeth in dogs (6). Goodman et al. (3) developed a model system to monitor the intracanal temperature changes produced during the vertical compaction of warm gutta-percha. Their system consisted of six thermocouples placed at 2-mm intervals along one side of the root canal of a sectioned and embedded premolar tooth. The first thermocouple was placed 2 mm from the anatomical apex. The tooth was embedded in an acrylic block and the thermocouples connected to a millivolt recorder which produced strip charts of the recorded intracanal temperatures.
FtG 1. Embedded tooth with crown removed to expose middle third of pulp chamber.
491
492
Weller et al.
Journal of Endodontics
FIG 2. Components of tooth model system. F~G3. Separated tooth model showing eight holes drilled in each side of root for insertion of thermocouples.
used to establish straight line access to the root canal. The halves of the root were then separated and the access preparation was evaluated for adequacy. All of the component parts of the model system are shown in Fig. 2. The working length was established by visually placing the tip of a #10 K-Flex file (Kerr, Romulus, MI) 1 mm short of the anatomical root apex on one of the root halves. This 16m m working length would be constant throughout the use of this model. The two halves of the block were reapproximated and secured with the four alignment nuts and bolts. The canal was then prepared using a standard step-back method to a #60 K-Flex file at the established working length. Saline irrigation was employed throughout the instrumentation procedure. The two halves of the resin block were separated and the quality of the root canal preparation was visually examined to ensure equal preparation in both halves of the root. By using a 0.021-inch drill bit, eight holes on each side of the root were hand drilled at right angles to the root canal through the root to the outer surface of the acrylic block. The initial hole was drilled through the mesial half of the tooth at the established working length. Subsequent holes were then drilled every millimeter, alternating between the distal and mesial halves of the root. The eight holes on each side of the root were 2 m m apart. A total of 16 holes was drilled in this manner (Fig. 3). A type K chromel-alumel thermocouple (Omega Engineering Inc., Stamford, CT) was placed in each hole from the resin side of the block until it was flush with the root canal surface (Fig. 4). This position was verified with the aid of a stereomicroscope (Wild MPS 51 S; Wild, Heerbrugg, Switzerland) (Fig. 5). Each thermocouple was then secured in its correct position with a cyanoacrylate ester (Zapit; MDS Products, Inc., Anaheim Hills, CA). The two wire leads of each thermocouple were connected to the appropriate channel of an AIM 7 thermocouple input module (Keithley Data Acquisition and Data Control, Cleveland, OH). This module was interfaced to a personal computer (Zenith Data Systems Corp., St. Joseph, MI) using a Labtech Notebook data acquisition software program (Laboratory Technologies Corp., Wilmington, MA) (Fig. 6). This computer program was configured to simultaneously record input from the 16 thermocouples in the root canal model. The sampling rate was set at one
r"
. .
16ram
X. \
"/ J/
J I
.- 2mm
F~G 4. Diagram of the two wires of each thermocouple inserted in holes drilled in each side of the root.
FiG 5. Stereomicroscopic verification of the thermocouple position along the canal wall.
Intracanal Temperatures
Vol. 17, No. 10, October 1991
measurement per second for each thermocouple with an accuracy of a hundredth degree centigrade. After all of the thermocouples were secured and calibrated, the mesial and distal halves of the block were united and secured (Fig. 7). The root canal model was obturated 10 times without sealer using a high-temperature thermoplasticized injectable guttapercha system (Obtura; Texceed, Costa Mesa, CA). The temperature control was adjusted to the highest setting on the unit. A silicone spray (Dentsply International, York, PA) was applied to each half of the root canal before each obturation to facilitate removal of the gutta-percha mass. The computerized temperature recording system was started and the intracanal baseline temperature was recorded for 5 s before obturation of the root canal. Following the manufacturer's instructions, the needle of the Obtura syringe was placed to within 3 m m of the working length and the gutta-percha was injected as the needle was withdrawn from the canal. Each obturation required an average of 25 to 30 s to complete. Intracanal temperature measurements were recorded for an additional 120 s after the gutta-percha was injected. Each temperature measurement cycle lasted a total of 155 s. The collected data files were recorded, printed, and the highest temperature at each thermocouple level was tabulated.
493
FIG 6. Computer hardware connected to each of the 16 thermocoupies attached to the root of the tooth.
RESULTS The temperature of the injected gutta-percha recorded at each level within the root canal is presented in Table 1. The recorded temperatures ranged from 31.40 to 86.26~ There was a linear increase in the mean temperatures inside the root canal from the apex to the coronal opening. The average baseline temperature in the root canal was 30.10~ DISCUSSION The model system in this report, although similar to the one used by Goodman et al. (3) has several distinct modifications. First, the split tooth design permits repeated obturations in the same root canal system. This reduces variables encountered when different teeth are used during an investigation. Second, the number of thermocouples in this model was increased from 8 to 16 and they were positioned on both halves of the root surface to allow temperature recordings at l-ram intervals along the root canal surface. Third, the most apically located thermocouple in this new model was positioned at the working length and not 2 m m from the anatomical apex. Temperatures recorded at the working length using thermal techniques are clinically significant since they are very near the apical foramen and the adjacent periodontal tissues. Fourth, the model system in the present report used a computerized program that provided a printout of temperature recordings at 1-s intervals to an accuracy of a hundredth degree centigrade. This printout listed temperatures recorded at all 16 thermocouples with each one in a separate column. This listing allowed accurate temperature monitoring along the length of the canal wall and also easy tabulation of the results. The temperatures reported by Goodman et al. (3) were recorded to the nearest degree centigrade on a printed strip
FIG 7. Tooth model secured with alignment nuts and bolts showing the 16 thermocouples attached to the block with cyanoacrylate ester.
TABLE 1. Intracanal temperatures (~ produced by hightemperature thermoplasticized injectable gutta-percha T*
High
Low
Mean
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
36.52 41.23 51.91 42.97 43.30 48.38 45.69 62.07 55.74 67.79 66.60 65.71 72.90 79.09 86.26 57.34
31.40 33.39 34.88 35.62 37.40 34.67 41.00 43.50 45.09 50.97 46.58 48.72 44.74 63.85 62.01 39.43
33.68 36.41 36.96 38.66 39.45 41.89 42.84 49.16 48.65 56.56 55.62 57.04 54.19 71.15 75.22 47.36
* T, intracanal thermocouple level in mm from anatomical root apex.
494
Weller et al.
chart. These temperature recordings would have had to have been visually extrapolated from the chart. This method could have resulted in some inaccurate temperature interpretations. Also, as the plugger was inserted deeper into the root canal during the obturation procedures, some of the printer needles recording the temperatures at the different levels became superimposed. As a result, some of the thermocouples were disconnected from the recording device. A further advantage of this new model system is that it allows flexibility in positioning the thermocouples. By attaching thermocouples at different positions along the external as well as internal surface of the root, more detailed temperature investigations can be performed. The results in Table 1 indicate a linear temperature increase from the apex at each level within the root canal. The highest recorded temperature at level 15 was at the level of the second largest cross-sectional area of gutta-percha mass. However, the largest area of gutta-percha mass, found at level 16, reflected a large temperature decrease. This decrease was probably due to the effects of room temperature air on the gutta-percha at this most coronal level. The results obtained in this investigation have clinical relevance. The highest intracanal gutta-percha temperatures recorded in this study in areas of relatively larger masses of gutta-percha coupled with an accompanying decrease in the thickness of the radicular dentin may create temperatures on the root surface which could have a detrimental effect on periradicular tissues. A decrease in thickness of radicular dentin may result from incompletely formed roots, internal resorption, or overprepared canals. Since thermoplasticized injectable gutta-percha is some times used in clinical situa-
Journal of EndodonUcs
tions where a large intracanal preparation or defect exists, the resulting root surface temperatures may become clinically significant in these areas of thinner root dentin. Further research is needed to determine these root surface temperatures. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the United States Army or Department of Defense. The authors would like to thank Mr. Jack Homer, assistant chief, Department of Clinical Investigation, Eisenhower Army Medical Center, Fort Gordon, GA, for his technical assistance and Dr. David H. Pashley, professor of oral biology, Medical College of Georgia, School of Dentistry, Augusta, GA, for the use of some of the computer hardware. Dr. Weller is director and Dr. Kulild is assistant director, Endodontic Residency Program, U.S. Army Dental Activity, Fort Gordon, GA. Dr. Jurcak is assistant chief, endodontics, Fort Benning, GA. Dr. Donley is chief, endodontics, Fort Huachuca, AZ. Address requests for reprints to COL James C. KulUd, U.S. Army Dental Activity, Fort Gordon, GA 30905-5660.
References 1. Fors U, Jonasson E, Bergquist A, Berg J-O. Measurements of the root surface temperature during thermo-mechanical root canal filling in vitro. Int Endod J 1985;18:199-202. 2. Hardie EM. Heat transmission to the outer surface of the tooth during the thermo-mechanical compaction technique of root canal obturation. Int Endod J 1986;19:73-7. 3. Goodman A, Schilder H, Aldrich W. The thermo-mechanical properties of gutta-percha. Part IV. Thermal profile of the warm gutta-percha packing procedure. Oral Surg 1981 ;51:544-51. 4. Hand RE, Huget EF, Tsaknis PJ. Effects of warm gutta-percha technique on the lateral periodontium. Oral Surg 1976;42:395-401. 5. Figdor D, Beech DR, Waterson JG. Factors affecting heat generation in the McSpadden Compaction Technique [Abstract 22]. J Dent Res 1983;62:405. 6. Gutmann JL, Rakusin H, Powe R, Bowles WH. Evaluation of heat transfer during root canal obturation with thermoplasticized gutta-percha. Part II. In vivo response to heat levels generated. J Endodon 1987;13:441-8.
Printed in U.S.A.
VOL. 17, NO. 10, OCTOBER1991
A New Model System for Measuring Intracanal Temperatures R. Norman Weller, DMD, MS, FICD, FACD, Joseph J. Jurcak, DDS, Dennis L. Donley, DDS, and James C. Kulild, DDS, MS, FICD
A new model system was developed which allows intracanal temperature measurements to be recorded during repeated obturations of a human tooth root canal. A human central incisor was embedded in clear orthodontic resin and sectioned longitudinally. Sixteen thermocouples were secured at 2-ram intervals along two surfaces of the root canal. The thermocouples were connected to a computerized temperature recording system to measure intracanal temperatures produced by high-temperature thermoplasticized injectable gutta-percha. The system was capable of recording 16 simultaneous temperatures every second with an accuracy of a hundredth degree centigrade. There was a linear increase in the recorded temperatures in the root canal. However, the actual temperatures were lower than expected.
The purpose of this article was to report a new model system which accurately records temperatures produced in vitro in a natural tooth. This system also allows repeated obturations of the same tooth so that a direct comparison of different materials or techniques can be made. MATERIALS AND METHODS A human maxillary central incisor tooth was completely embedded in a block of clear orthodontic resin (Caulk/Dentsply, Milford, DE). Four mesiodistal alignment holes were drilled through the resin block perpendicular to the long axis of the tooth apical to the level of the cementoenamel junction. Two of the holes were drilled on the facial side of the tooth and the other two were drilled on the palatal side. The tooth was then sectioned longitudinally in a buccolingual direction through the center of the root canal using a Buehler Isomet low-speed saw (Buehler Ltd., Evanston, IL). During experiments the two halves of the block could then be reapproximated and secured with bolts placed in the four alignment holes. The crown of the embedded tooth was removed by a model trimmer to expose the middle third of the pulp chamber (Fig. 1). A #6 round bur in a slow-speed handpiece was
The ability to obturate a root canal system by one of the presently available warm gutta-percha techniques has stimulated interest in the temperature increases produced during these procedures. Prior investigations have measured intracanal temperatures produced during thermomechanical root canal obturation procedures (1, 2) and vertical condensation of warm gutta-percha (3), and also the temperatures produced on the external root surface using heated pluggers within the root canal (4). Various model systems have been developed to accurately measure these temperatures. These models include in vitro thermocouples embedded in acrylic blocks that simulate root canals (5), and the in vivo placement of thermocouples on the overlying bone of teeth in dogs (6). Goodman et al. (3) developed a model system to monitor the intracanal temperature changes produced during the vertical compaction of warm gutta-percha. Their system consisted of six thermocouples placed at 2-mm intervals along one side of the root canal of a sectioned and embedded premolar tooth. The first thermocouple was placed 2 mm from the anatomical apex. The tooth was embedded in an acrylic block and the thermocouples connected to a millivolt recorder which produced strip charts of the recorded intracanal temperatures.
FtG 1. Embedded tooth with crown removed to expose middle third of pulp chamber.
491
492
Weller et al.
Journal of Endodontics
FIG 2. Components of tooth model system. F~G3. Separated tooth model showing eight holes drilled in each side of root for insertion of thermocouples.
used to establish straight line access to the root canal. The halves of the root were then separated and the access preparation was evaluated for adequacy. All of the component parts of the model system are shown in Fig. 2. The working length was established by visually placing the tip of a #10 K-Flex file (Kerr, Romulus, MI) 1 mm short of the anatomical root apex on one of the root halves. This 16m m working length would be constant throughout the use of this model. The two halves of the block were reapproximated and secured with the four alignment nuts and bolts. The canal was then prepared using a standard step-back method to a #60 K-Flex file at the established working length. Saline irrigation was employed throughout the instrumentation procedure. The two halves of the resin block were separated and the quality of the root canal preparation was visually examined to ensure equal preparation in both halves of the root. By using a 0.021-inch drill bit, eight holes on each side of the root were hand drilled at right angles to the root canal through the root to the outer surface of the acrylic block. The initial hole was drilled through the mesial half of the tooth at the established working length. Subsequent holes were then drilled every millimeter, alternating between the distal and mesial halves of the root. The eight holes on each side of the root were 2 m m apart. A total of 16 holes was drilled in this manner (Fig. 3). A type K chromel-alumel thermocouple (Omega Engineering Inc., Stamford, CT) was placed in each hole from the resin side of the block until it was flush with the root canal surface (Fig. 4). This position was verified with the aid of a stereomicroscope (Wild MPS 51 S; Wild, Heerbrugg, Switzerland) (Fig. 5). Each thermocouple was then secured in its correct position with a cyanoacrylate ester (Zapit; MDS Products, Inc., Anaheim Hills, CA). The two wire leads of each thermocouple were connected to the appropriate channel of an AIM 7 thermocouple input module (Keithley Data Acquisition and Data Control, Cleveland, OH). This module was interfaced to a personal computer (Zenith Data Systems Corp., St. Joseph, MI) using a Labtech Notebook data acquisition software program (Laboratory Technologies Corp., Wilmington, MA) (Fig. 6). This computer program was configured to simultaneously record input from the 16 thermocouples in the root canal model. The sampling rate was set at one
r"
. .
16ram
X. \
"/ J/
J I
.- 2mm
F~G 4. Diagram of the two wires of each thermocouple inserted in holes drilled in each side of the root.
FiG 5. Stereomicroscopic verification of the thermocouple position along the canal wall.
Intracanal Temperatures
Vol. 17, No. 10, October 1991
measurement per second for each thermocouple with an accuracy of a hundredth degree centigrade. After all of the thermocouples were secured and calibrated, the mesial and distal halves of the block were united and secured (Fig. 7). The root canal model was obturated 10 times without sealer using a high-temperature thermoplasticized injectable guttapercha system (Obtura; Texceed, Costa Mesa, CA). The temperature control was adjusted to the highest setting on the unit. A silicone spray (Dentsply International, York, PA) was applied to each half of the root canal before each obturation to facilitate removal of the gutta-percha mass. The computerized temperature recording system was started and the intracanal baseline temperature was recorded for 5 s before obturation of the root canal. Following the manufacturer's instructions, the needle of the Obtura syringe was placed to within 3 m m of the working length and the gutta-percha was injected as the needle was withdrawn from the canal. Each obturation required an average of 25 to 30 s to complete. Intracanal temperature measurements were recorded for an additional 120 s after the gutta-percha was injected. Each temperature measurement cycle lasted a total of 155 s. The collected data files were recorded, printed, and the highest temperature at each thermocouple level was tabulated.
493
FIG 6. Computer hardware connected to each of the 16 thermocoupies attached to the root of the tooth.
RESULTS The temperature of the injected gutta-percha recorded at each level within the root canal is presented in Table 1. The recorded temperatures ranged from 31.40 to 86.26~ There was a linear increase in the mean temperatures inside the root canal from the apex to the coronal opening. The average baseline temperature in the root canal was 30.10~ DISCUSSION The model system in this report, although similar to the one used by Goodman et al. (3) has several distinct modifications. First, the split tooth design permits repeated obturations in the same root canal system. This reduces variables encountered when different teeth are used during an investigation. Second, the number of thermocouples in this model was increased from 8 to 16 and they were positioned on both halves of the root surface to allow temperature recordings at l-ram intervals along the root canal surface. Third, the most apically located thermocouple in this new model was positioned at the working length and not 2 m m from the anatomical apex. Temperatures recorded at the working length using thermal techniques are clinically significant since they are very near the apical foramen and the adjacent periodontal tissues. Fourth, the model system in the present report used a computerized program that provided a printout of temperature recordings at 1-s intervals to an accuracy of a hundredth degree centigrade. This printout listed temperatures recorded at all 16 thermocouples with each one in a separate column. This listing allowed accurate temperature monitoring along the length of the canal wall and also easy tabulation of the results. The temperatures reported by Goodman et al. (3) were recorded to the nearest degree centigrade on a printed strip
FIG 7. Tooth model secured with alignment nuts and bolts showing the 16 thermocouples attached to the block with cyanoacrylate ester.
TABLE 1. Intracanal temperatures (~ produced by hightemperature thermoplasticized injectable gutta-percha T*
High
Low
Mean
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
36.52 41.23 51.91 42.97 43.30 48.38 45.69 62.07 55.74 67.79 66.60 65.71 72.90 79.09 86.26 57.34
31.40 33.39 34.88 35.62 37.40 34.67 41.00 43.50 45.09 50.97 46.58 48.72 44.74 63.85 62.01 39.43
33.68 36.41 36.96 38.66 39.45 41.89 42.84 49.16 48.65 56.56 55.62 57.04 54.19 71.15 75.22 47.36
* T, intracanal thermocouple level in mm from anatomical root apex.
494
Weller et al.
chart. These temperature recordings would have had to have been visually extrapolated from the chart. This method could have resulted in some inaccurate temperature interpretations. Also, as the plugger was inserted deeper into the root canal during the obturation procedures, some of the printer needles recording the temperatures at the different levels became superimposed. As a result, some of the thermocouples were disconnected from the recording device. A further advantage of this new model system is that it allows flexibility in positioning the thermocouples. By attaching thermocouples at different positions along the external as well as internal surface of the root, more detailed temperature investigations can be performed. The results in Table 1 indicate a linear temperature increase from the apex at each level within the root canal. The highest recorded temperature at level 15 was at the level of the second largest cross-sectional area of gutta-percha mass. However, the largest area of gutta-percha mass, found at level 16, reflected a large temperature decrease. This decrease was probably due to the effects of room temperature air on the gutta-percha at this most coronal level. The results obtained in this investigation have clinical relevance. The highest intracanal gutta-percha temperatures recorded in this study in areas of relatively larger masses of gutta-percha coupled with an accompanying decrease in the thickness of the radicular dentin may create temperatures on the root surface which could have a detrimental effect on periradicular tissues. A decrease in thickness of radicular dentin may result from incompletely formed roots, internal resorption, or overprepared canals. Since thermoplasticized injectable gutta-percha is some times used in clinical situa-
Journal of EndodonUcs
tions where a large intracanal preparation or defect exists, the resulting root surface temperatures may become clinically significant in these areas of thinner root dentin. Further research is needed to determine these root surface temperatures. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the United States Army or Department of Defense. The authors would like to thank Mr. Jack Homer, assistant chief, Department of Clinical Investigation, Eisenhower Army Medical Center, Fort Gordon, GA, for his technical assistance and Dr. David H. Pashley, professor of oral biology, Medical College of Georgia, School of Dentistry, Augusta, GA, for the use of some of the computer hardware. Dr. Weller is director and Dr. Kulild is assistant director, Endodontic Residency Program, U.S. Army Dental Activity, Fort Gordon, GA. Dr. Jurcak is assistant chief, endodontics, Fort Benning, GA. Dr. Donley is chief, endodontics, Fort Huachuca, AZ. Address requests for reprints to COL James C. KulUd, U.S. Army Dental Activity, Fort Gordon, GA 30905-5660.
References 1. Fors U, Jonasson E, Bergquist A, Berg J-O. Measurements of the root surface temperature during thermo-mechanical root canal filling in vitro. Int Endod J 1985;18:199-202. 2. Hardie EM. Heat transmission to the outer surface of the tooth during the thermo-mechanical compaction technique of root canal obturation. Int Endod J 1986;19:73-7. 3. Goodman A, Schilder H, Aldrich W. The thermo-mechanical properties of gutta-percha. Part IV. Thermal profile of the warm gutta-percha packing procedure. Oral Surg 1981 ;51:544-51. 4. Hand RE, Huget EF, Tsaknis PJ. Effects of warm gutta-percha technique on the lateral periodontium. Oral Surg 1976;42:395-401. 5. Figdor D, Beech DR, Waterson JG. Factors affecting heat generation in the McSpadden Compaction Technique [Abstract 22]. J Dent Res 1983;62:405. 6. Gutmann JL, Rakusin H, Powe R, Bowles WH. Evaluation of heat transfer during root canal obturation with thermoplasticized gutta-percha. Part II. In vivo response to heat levels generated. J Endodon 1987;13:441-8.
