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An investigation into cavitational activity occurring in endosonic instrumentation
120
J. Dent. 1988; 16: 120-l
22
An investigation into cavitational activity occurring in endosonic instrumentation P. J. Lumley, A. D. Walmsley and W. R. E. Laird Department of Conservative Dentistry and Department Birmingham KEY WORDS: .I. Dent
1988;
of Dental Prosthetics and Periodontics,
University of
Ultrasound, Cavitation, Endodontics 16: 120-122
(Received 16 June 1987;
reviewed 13 August 1987;
accepted 2 December 1987)
ABSTRACT The ability of an oscillating endosonic file to generate cavitational activity has been determined using a chemical dosimetric solution (potassium iodide/carbon tetrachloride) which was passed over the tile. The amount of cavitational activity was quantified using spectrophotometric techniques. The results showed that cavitational activity could be detected with the endosonic instrument, but did not occur along the length of the file. It is probable that cavitation only provides minor benefit in ultrasonic root canal preparation.
INTRODUCTION The use of low frequency ultrasound in the preparation of root canals is increasing in popularity. The development of this technique has been associated primarily with Martin (1976) and Cunningham et al. (1982), and has been termed ‘endosonics’. More recently use of this technique has been reported by Nehammer and Stock (1985) and Stamos et al. (1985). To date, much of this work has been directed to reporting the methods of clinical usage of ultrasonic root canal instrumentation together with the observed effects. There has been little investigation into the fundamental aspects of systems which would allow a more formal appraisal of the technique (Walmsley, 1987). The current applications of ultrasound in endodontic therapy involve the use of a variety of files clamped to the end of a probelhandpiece which incorporates a magneto strictive transducer oscillating at about 25 kHz. The transducer vibrates in its longitudinal mode but the tiles are mounted essentially at right angles to the laminated stack so as to generate a flexural or transverse oscillating pattern. The tile is introduced into the root canal of the tooth to be treated and the generator power is switched on, thus inducing oscillation. It has been suggested (Martin et al., 1980) that the use of ultrasound results in increased efficiency in root canal preparation, due primarily to the biophysical effects of the ultrasound such as cavitation and acoustic microstreaming which are said to lead to increased cleansing of the root 0 1988 Butterworth t Co Publishers Ltd. 0300-5712/88/030120-03 $0340
canal system. Cavitational activity is thought to occur in the irrigant solution as it flows over the oscillating file in a manner similar to the ultrasonic descaling instrument (Walmsley et al., 1984), while acoustic microstreaming occurs around the cutting edges of the file. Cavitation is a broad spectrum of related acoustic phenomena ranging from linear pulsation of gas-filled bodies in low amplitude sound fields, which is termed ‘stable acoustic cavitation’, to the violent and highly destructive non-linear ‘explosive behaviour’ of vapourfilled cavities, known as ‘transient’ or ‘collapse-type cavitation’, which occurs in high amplitude sound fields. At present there are differing reports regarding the presence or absence of cavitational activity, although its presence has been assumed by some workers (Martin and Cunningham, 1985). Cavitational activity as measured by sonoluminescence, however, has been observed by Ahmad et al. (1987), and could be demonstrated both with the ultrasonic descaler and an endosonic instrument. This cavitational activity has been reported using the ENAC instrument (Osada Electric Co. Ltd, Tokyo, Japan), but only at high displacement amplitudes of the endosonic files and at a power setting greater than that recommended by the manufacturer (Ahmad et al., 1987). The occurrence of transient or collapse-type cavitation is frequently demonstrated using chemical dosimetric techniques. These are dependent upon the production of short-lived free radicals which are produced by the pyrolytic breakdown of water vapour by the high temperatures generated within the collapsing bubbles
Lumley
et al.: Endosonic
0.6r
cavitational
activity
121
T
(Noltingk and Neppiras, 1950). These free radicals then enter the surrounding solution where they may modify chemically other molecules (Weissler, 195 9). In the present study the oxidation of potassium iodide to iodine in the presence of carbon tetrachloride (Weissler, 1959) was used to monitor the level of cavitational activity occurring in the irrigant solution of an endosonic instrument, with the amount of iodine produced being a measure of the level of cavitational activity. MATERIALS AND METHODS The instrument used was a Cavi Endo (Dentsply International Inc., York, PA, USA) insert powered by an ultrasound generator, with K type files (Caulk Dentsply International Inc., Milford, DE, USA) being used for the investigation. The ultrasound generator was calibrated initially by shining a light on to an activated file and measuring the displacement amplitude at a specific power setting. The power setting chosen was that which produced the greatest displacement amplitude (85 pm). The dosimetric solution used consisted of 16.6 g of potassium iodide per litre of deionized water (0.5 M) with a 2 per cent addition of carbon tetrachloride. The solution was then stored in a light-protected bottle, shaken thoroughly to allow mixing of the constituents, and then allowed to stand for 10 min to allow any excess carbon tetrachloride to separate out. In view of the fact that the chemical reaction which results in the liberation of iodine can be affected by both light and heat, during test runs all samples were protected from the light and maintained at a constant temperature (20°C) by placing them in a water-bath with a top cover. The solution was protected from light by enclosing it in a surgical towel. During operation the irrigant solution was passed through an endosonic insert as it would be clinically and results obtained for a range of flow rates from 2 ml/min to 15 ml/min. For each flow rate the same volume of solution (15 ml) was collected. A control was established by passing the solution through the driver without the generator working. Experimental readings in respect of the working endosonic instrument were made with the solution passing through the activated driver, through the driver with a size 20 K type endosonic file, over the activated file but by passing the driver and finally by assessing the dosimetric solution from a small glass tube which had been exposed to the activated file for 1 min. The amount of cavitational activity in the collected solution was quantified using spectrophotometric techniques by measuring the change in optical density as compared to the unused solution at 350 nm which corresponds to the absorbtion spectrum of iodine. RESULTS For the endosonic instrument the pattern of cavitational activity appeared different for similar flow rates. Where
0
0
I
I
I
5
10
15
Flow
rate
(ml/min)
Fig. 7. Graph of changes in optical density comparing the ) with the driver and the driver on its own (-----oscillating size 20 file (- - - - -).
the irrigant solution was passed through the driver without a file in place cavitational activity was observed which decreased gradually as flow rate increased and then began to level out at higher flow rates (Fig I). With the tile inserted the amount of cavitational activity generated was similar to that of the driver alone, although at lower flow rates the rate of decrease was not so marked (Fig. I). However, cavitational activity did not occur either when the solution was passed through the driver without the generator working, or when the solution bypassed the driver and passed directly over the tile. DISCUSSION The size 20 K tile used in this study was selected as it demonstrated the greatest displacement amplitude (85 pm), and would therefore be most likely to generate cavitational activity. The amount of cavitational activity detected with the endosonic instrument appeared to decrease slowly with an increase in flow rate of solution, to a point at which, at a certain flow rate (7 ml/min), a rapid decrease was noted. Following this, cavitational activity tended to remain static for both the driver on its own and the size 20 K file and the driver. This may be explained by the observations that at lower flow rates a discrete drop of solution was held for about 1 s against the head of the driver (Fig. 2a), and was subjected therefore to greater exposure from the longitudinal oscillating head, resulting in a greater degree of cavitational activity. As the flow rate increased, however, the drop became less discrete and was not held against the driver for the same length of time, until at a rate in excess of 7 ml/min drop formation did not occur and the solution flowed freely along the file. At this stage a series of discrete drops of liquid (Fig. 2b) were seen at oscillatory nodes (points of minimal displacement amplitude), whereas at the anti-nodes (points of maximum
122
J. Dent.
1988;
16: No. 3
Fig. 2. a, Illustration of irrigant retention against the driver head at low flow rates and a displacement amplitude of 85 I.cm.b, The same solution as in a but at a greater flow rate flows along the file with discrete drops of liquid located at oscillatory nodes.
displacement amplitude) the liquid was dissipated as spray. At these high flow rates therefore the solution did not appear to be exposed to the energy in the driver for a sufficient period of time to allow the same amount of cavitation to occur. The irrigant solution was not exposed directly to the energy generated in the driver when it was passed over the working file alone and when the working file was driven to oscillate in the solution in the glass tube. The observation that cavitational activity was not detected in this situation may be explained by the fact that the displacement amplitude of the file was so low that there was an insufficient pressure change occurring which was able to
These conclusions agree with those of Ahmad et al. (1987) in that at the displacement amplitudes used during clinical use cavitational activity is not detected along the file. Acknowledgement
The authors would like to thank Dentsply Ltd for the loan of the instruments and tiles. References
CONCLUSIONS
Ahmad M., Pitt Ford T. R. and Crum L. A. (1987) Ultrasonic debridement of root canals. An insight into the mechanisms involved. .I Endodont. 13,93-101. Cunningham W. T., Martin H., Peller G. B. et al. (1982) A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg. 54, 238-241. Martin H. (1976) Ultrasonic disinfection of the root canal. Oral Surg. 42, 92-99. Martin H. and Cunningham W. T. (1985) Endosonics--the ultrasonic synergistic system of endodontics. Endodont. Dent. Traumatol. 1, 201-206. Martin H., Cunningham W. T., Norris J. P. et al. (1980) Ultrasonic versus hand tiling of dentin. A quantitative study. Oral Surg. 49, 79-8 1. Nehammer C. F. and Stock C. J. R (1985) Endodontics in practice: preparation and filling of the root canal. Br. Dent. J. 158, 285-291. Noltingk B. E. and Neppiras E. A. (1950) Cavitation produced by ultrasonics. Proc. Phys. Sot. (Lond.) B63, 674-685. Stamos D. G., Haasch G. C. and Chenail B. (1985) Endosonics: clinical impressions. J. Endodont. 11,
Cavitational activity does occur in association with the endosonic instrument. Such activity is present only in the solution as it flows through the driver and the part of the file closely associated with the driver. Cavitational activity is dependent on the flow rate of solution and does not occur along the length of the file. On the evidence presented it appears that cavitation is of little clinical value in endosonic instrumentation.
Walmsley A. D. (1987) Ultrasound and root canal treatment: the need for scientific evaluation. Znt. Endodont. J. 20, 105-l 11. Walmsley A. D., Laird W. R. E. and Williams A. R. (1984) A model system to demonstrate the role of cavitational activity in ultrasonic scaling. J. Dent. Res. 63, 1162-l 165. Weissler A. (1959) Some sonochemical reaction rates. J. Acoustic Sot. Am. 32, 283-284.
initiate cavitational activity. The cavitational activity which occurred during operation of the instrument tended to be restricted to the head of the driver and is not therefore considered to be of benefit in endosonic debridement of root canals as it is not present along the length of the tile and cannot be efficacious in the apical portion of the canal. This finding is contrary to earlier reports and expectations (Martin et al., 1980). In the clinical situation, however, the irrigant solution may be in contact with the driver for several seconds as it passes down and around the root canal and this might possibly result in ultrasonic bathing of the canal walls, although this is only likely to be of benefit in the coronal portion of the root canal system.
181-187.
Correspondence should be addressed to: Mr P. J. Lumley, Department of Conservative Dentistry, University of Birmingham, The Dental School, St Chad’s Queensway, Birmingham B4 6NN, UK.
J. Dent. 1988; 16: 120-l
22
An investigation into cavitational activity occurring in endosonic instrumentation P. J. Lumley, A. D. Walmsley and W. R. E. Laird Department of Conservative Dentistry and Department Birmingham KEY WORDS: .I. Dent
1988;
of Dental Prosthetics and Periodontics,
University of
Ultrasound, Cavitation, Endodontics 16: 120-122
(Received 16 June 1987;
reviewed 13 August 1987;
accepted 2 December 1987)
ABSTRACT The ability of an oscillating endosonic file to generate cavitational activity has been determined using a chemical dosimetric solution (potassium iodide/carbon tetrachloride) which was passed over the tile. The amount of cavitational activity was quantified using spectrophotometric techniques. The results showed that cavitational activity could be detected with the endosonic instrument, but did not occur along the length of the file. It is probable that cavitation only provides minor benefit in ultrasonic root canal preparation.
INTRODUCTION The use of low frequency ultrasound in the preparation of root canals is increasing in popularity. The development of this technique has been associated primarily with Martin (1976) and Cunningham et al. (1982), and has been termed ‘endosonics’. More recently use of this technique has been reported by Nehammer and Stock (1985) and Stamos et al. (1985). To date, much of this work has been directed to reporting the methods of clinical usage of ultrasonic root canal instrumentation together with the observed effects. There has been little investigation into the fundamental aspects of systems which would allow a more formal appraisal of the technique (Walmsley, 1987). The current applications of ultrasound in endodontic therapy involve the use of a variety of files clamped to the end of a probelhandpiece which incorporates a magneto strictive transducer oscillating at about 25 kHz. The transducer vibrates in its longitudinal mode but the tiles are mounted essentially at right angles to the laminated stack so as to generate a flexural or transverse oscillating pattern. The tile is introduced into the root canal of the tooth to be treated and the generator power is switched on, thus inducing oscillation. It has been suggested (Martin et al., 1980) that the use of ultrasound results in increased efficiency in root canal preparation, due primarily to the biophysical effects of the ultrasound such as cavitation and acoustic microstreaming which are said to lead to increased cleansing of the root 0 1988 Butterworth t Co Publishers Ltd. 0300-5712/88/030120-03 $0340
canal system. Cavitational activity is thought to occur in the irrigant solution as it flows over the oscillating file in a manner similar to the ultrasonic descaling instrument (Walmsley et al., 1984), while acoustic microstreaming occurs around the cutting edges of the file. Cavitation is a broad spectrum of related acoustic phenomena ranging from linear pulsation of gas-filled bodies in low amplitude sound fields, which is termed ‘stable acoustic cavitation’, to the violent and highly destructive non-linear ‘explosive behaviour’ of vapourfilled cavities, known as ‘transient’ or ‘collapse-type cavitation’, which occurs in high amplitude sound fields. At present there are differing reports regarding the presence or absence of cavitational activity, although its presence has been assumed by some workers (Martin and Cunningham, 1985). Cavitational activity as measured by sonoluminescence, however, has been observed by Ahmad et al. (1987), and could be demonstrated both with the ultrasonic descaler and an endosonic instrument. This cavitational activity has been reported using the ENAC instrument (Osada Electric Co. Ltd, Tokyo, Japan), but only at high displacement amplitudes of the endosonic files and at a power setting greater than that recommended by the manufacturer (Ahmad et al., 1987). The occurrence of transient or collapse-type cavitation is frequently demonstrated using chemical dosimetric techniques. These are dependent upon the production of short-lived free radicals which are produced by the pyrolytic breakdown of water vapour by the high temperatures generated within the collapsing bubbles
Lumley
et al.: Endosonic
0.6r
cavitational
activity
121
T
(Noltingk and Neppiras, 1950). These free radicals then enter the surrounding solution where they may modify chemically other molecules (Weissler, 195 9). In the present study the oxidation of potassium iodide to iodine in the presence of carbon tetrachloride (Weissler, 1959) was used to monitor the level of cavitational activity occurring in the irrigant solution of an endosonic instrument, with the amount of iodine produced being a measure of the level of cavitational activity. MATERIALS AND METHODS The instrument used was a Cavi Endo (Dentsply International Inc., York, PA, USA) insert powered by an ultrasound generator, with K type files (Caulk Dentsply International Inc., Milford, DE, USA) being used for the investigation. The ultrasound generator was calibrated initially by shining a light on to an activated file and measuring the displacement amplitude at a specific power setting. The power setting chosen was that which produced the greatest displacement amplitude (85 pm). The dosimetric solution used consisted of 16.6 g of potassium iodide per litre of deionized water (0.5 M) with a 2 per cent addition of carbon tetrachloride. The solution was then stored in a light-protected bottle, shaken thoroughly to allow mixing of the constituents, and then allowed to stand for 10 min to allow any excess carbon tetrachloride to separate out. In view of the fact that the chemical reaction which results in the liberation of iodine can be affected by both light and heat, during test runs all samples were protected from the light and maintained at a constant temperature (20°C) by placing them in a water-bath with a top cover. The solution was protected from light by enclosing it in a surgical towel. During operation the irrigant solution was passed through an endosonic insert as it would be clinically and results obtained for a range of flow rates from 2 ml/min to 15 ml/min. For each flow rate the same volume of solution (15 ml) was collected. A control was established by passing the solution through the driver without the generator working. Experimental readings in respect of the working endosonic instrument were made with the solution passing through the activated driver, through the driver with a size 20 K type endosonic file, over the activated file but by passing the driver and finally by assessing the dosimetric solution from a small glass tube which had been exposed to the activated file for 1 min. The amount of cavitational activity in the collected solution was quantified using spectrophotometric techniques by measuring the change in optical density as compared to the unused solution at 350 nm which corresponds to the absorbtion spectrum of iodine. RESULTS For the endosonic instrument the pattern of cavitational activity appeared different for similar flow rates. Where
0
0
I
I
I
5
10
15
Flow
rate
(ml/min)
Fig. 7. Graph of changes in optical density comparing the ) with the driver and the driver on its own (-----oscillating size 20 file (- - - - -).
the irrigant solution was passed through the driver without a file in place cavitational activity was observed which decreased gradually as flow rate increased and then began to level out at higher flow rates (Fig I). With the tile inserted the amount of cavitational activity generated was similar to that of the driver alone, although at lower flow rates the rate of decrease was not so marked (Fig. I). However, cavitational activity did not occur either when the solution was passed through the driver without the generator working, or when the solution bypassed the driver and passed directly over the tile. DISCUSSION The size 20 K tile used in this study was selected as it demonstrated the greatest displacement amplitude (85 pm), and would therefore be most likely to generate cavitational activity. The amount of cavitational activity detected with the endosonic instrument appeared to decrease slowly with an increase in flow rate of solution, to a point at which, at a certain flow rate (7 ml/min), a rapid decrease was noted. Following this, cavitational activity tended to remain static for both the driver on its own and the size 20 K file and the driver. This may be explained by the observations that at lower flow rates a discrete drop of solution was held for about 1 s against the head of the driver (Fig. 2a), and was subjected therefore to greater exposure from the longitudinal oscillating head, resulting in a greater degree of cavitational activity. As the flow rate increased, however, the drop became less discrete and was not held against the driver for the same length of time, until at a rate in excess of 7 ml/min drop formation did not occur and the solution flowed freely along the file. At this stage a series of discrete drops of liquid (Fig. 2b) were seen at oscillatory nodes (points of minimal displacement amplitude), whereas at the anti-nodes (points of maximum
122
J. Dent.
1988;
16: No. 3
Fig. 2. a, Illustration of irrigant retention against the driver head at low flow rates and a displacement amplitude of 85 I.cm.b, The same solution as in a but at a greater flow rate flows along the file with discrete drops of liquid located at oscillatory nodes.
displacement amplitude) the liquid was dissipated as spray. At these high flow rates therefore the solution did not appear to be exposed to the energy in the driver for a sufficient period of time to allow the same amount of cavitation to occur. The irrigant solution was not exposed directly to the energy generated in the driver when it was passed over the working file alone and when the working file was driven to oscillate in the solution in the glass tube. The observation that cavitational activity was not detected in this situation may be explained by the fact that the displacement amplitude of the file was so low that there was an insufficient pressure change occurring which was able to
These conclusions agree with those of Ahmad et al. (1987) in that at the displacement amplitudes used during clinical use cavitational activity is not detected along the file. Acknowledgement
The authors would like to thank Dentsply Ltd for the loan of the instruments and tiles. References
CONCLUSIONS
Ahmad M., Pitt Ford T. R. and Crum L. A. (1987) Ultrasonic debridement of root canals. An insight into the mechanisms involved. .I Endodont. 13,93-101. Cunningham W. T., Martin H., Peller G. B. et al. (1982) A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg. 54, 238-241. Martin H. (1976) Ultrasonic disinfection of the root canal. Oral Surg. 42, 92-99. Martin H. and Cunningham W. T. (1985) Endosonics--the ultrasonic synergistic system of endodontics. Endodont. Dent. Traumatol. 1, 201-206. Martin H., Cunningham W. T., Norris J. P. et al. (1980) Ultrasonic versus hand tiling of dentin. A quantitative study. Oral Surg. 49, 79-8 1. Nehammer C. F. and Stock C. J. R (1985) Endodontics in practice: preparation and filling of the root canal. Br. Dent. J. 158, 285-291. Noltingk B. E. and Neppiras E. A. (1950) Cavitation produced by ultrasonics. Proc. Phys. Sot. (Lond.) B63, 674-685. Stamos D. G., Haasch G. C. and Chenail B. (1985) Endosonics: clinical impressions. J. Endodont. 11,
Cavitational activity does occur in association with the endosonic instrument. Such activity is present only in the solution as it flows through the driver and the part of the file closely associated with the driver. Cavitational activity is dependent on the flow rate of solution and does not occur along the length of the file. On the evidence presented it appears that cavitation is of little clinical value in endosonic instrumentation.
Walmsley A. D. (1987) Ultrasound and root canal treatment: the need for scientific evaluation. Znt. Endodont. J. 20, 105-l 11. Walmsley A. D., Laird W. R. E. and Williams A. R. (1984) A model system to demonstrate the role of cavitational activity in ultrasonic scaling. J. Dent. Res. 63, 1162-l 165. Weissler A. (1959) Some sonochemical reaction rates. J. Acoustic Sot. Am. 32, 283-284.
initiate cavitational activity. The cavitational activity which occurred during operation of the instrument tended to be restricted to the head of the driver and is not therefore considered to be of benefit in endosonic debridement of root canals as it is not present along the length of the tile and cannot be efficacious in the apical portion of the canal. This finding is contrary to earlier reports and expectations (Martin et al., 1980). In the clinical situation, however, the irrigant solution may be in contact with the driver for several seconds as it passes down and around the root canal and this might possibly result in ultrasonic bathing of the canal walls, although this is only likely to be of benefit in the coronal portion of the root canal system.
181-187.
Correspondence should be addressed to: Mr P. J. Lumley, Department of Conservative Dentistry, University of Birmingham, The Dental School, St Chad’s Queensway, Birmingham B4 6NN, UK.