38
J. Dent. 1992;
20: 38-43
Effect of different storage methods on the performance of dental local anaesthetic cartridges J. G. Meechan and J. F. McCabe* Department Tyne, UK
of Oral Surgery
and *Dental Materials Science Unit, The Dental School, University
of Newcastle
upon
ABSTRACT Self-aspirating dental local anaesthetic syringe systems rely on deformation of rubber diaphragms contained in the anaesthetic cartridges to produce the aspirating force. A test has been developed which can examine the performance of these rubber diaphragms under functional conditions. This method could be useful in the production of standards for dental local anaesthetic cartridges. The test has been used to determine the influence of storage conditions on the performance of dental local anaesthetic cartridges. The results show that, with the cartridges investigated, storage at 37°C increased the amount of distortion per unit force of the aspirating diaphragms in comparison with storage at room temperature. However recovery of the diaphragms was unaffected. Storage at the higher temperature decreased the amount of force required to initiate movement of the cartridge rubber bung during injection. Soaking cartridges in alcohol did not affect the distortion of the aspirating diaphragms or the force needed to move the bung during injection, but did increase the degree of recovery of the diaphragm in the bung of self-aspirating cartridges. KEY WORDS: Anaesthesia (local), Delivery systems, Storage J. Dent. 1992;
20: 38-43
(Received 4 June 1991;
reviewed 2 July 1991;
accepted 2 August 1991)
Correspondence should be addressed to: Dr J. G. Meechan, Department of Oral Surgery, The Dental School, Framlington Place, Newcastle upon Tyne NE2 4BW, UK.
INTRODUCTION The wisdom of aspirating before the injection of dental local anaesthetic solution has been proclaimed for many years (Sicher, 1946; Jorgensen, 1952). Equipment has been developed to enable aspiration to be efficiently performed and there are now a number of self-aspirating systems available (Meechan, 1988). The performance of self-aspirating systems relies on an interaction between syringe and cartridge. The aspirating device in self-aspirating systems includes a rubber diaphragm in the cartridge. One of two diaphragms may be employed. In the Astra self-aspirating system (Cowan, 1972) the thin diaphragm contained in the rubber bung of the special self-aspirating cartridge is the aspirating device. In other systems such as the Aspiject (Craig and Rood, 1986) and Rotor (Meechan et al., 1987) it is the diaphragm at the base of the cartridge through which the needle passes that is deflected to create the aspirating o (1992) Buttenvorth-Heinemann 0300-5712/92/010038-06
Ltd.
force. It is important to ensure reliability of these components and thus it is desirable that certain standards related to performance are established. A British Standard for dental local anaesthetic syringes has recently been formulated (British Standards Institution, 1991) however there is no such standard for local anaesthetic cartridges. It has been shown that self-aspirating systems vary in their ability to aspirate when used clinically (Meechan and Blair, 1989) and when examined under controlled conditions in the laboratory (Meechan, 1988). Indeed, there are even significant variations in the performance of single systems due to the use of different cartridges (Blair and Meechan, 1985; Meechan et al., 1985). The purpose of the present investigation was to design a test that could be used to evaluate the performance of the cartridge rubber diaphragms under controlled conditions that mimicked clinical use. The effects of different storage conditions on the performance of the diaphragms and on the forces needed for injection were also investigated.
Meechan
MATERIALS
and McCabe:
8
39
of basal diaphragm
Ten cartridges of 3 per cent Citanest with octapressin were used in this test. The cartridge was placed in a Rotor syringe (John Quayle Dental Manufacturing Company, Worthing, UK) from which the plunger had been removed; no needle was attached. The loaded syringe was then placed on the load cell of the Instron testing machine in such a manner that the thumb-ring was depressed by the load cell. In this system pressure on the thumb ring pushes the cartridge down on to a nipple at the base of the syringe and this deflects the diaphragm at the base of the cartridge to produce the aspiration potential. The Instron was then used as described in the test above and each cartridge was subjected to two cycles. The trace obtained was similar to that shown in Fig. 1.
of performance
The same methods of calculating the aspiration potential and the recovery of the diaphragm were used for both bung and base diaphragms. Calculations were performed on the trace obtained at the second test cycle. The gradient of the slope of the first part (right hand side) of the trace obtained from the Instron testing machine is a measure of stiffness of the rubber diaphragm; the steeper the slope the stiffer the diaphragm and the less distortion per unit force. The more flexible the diaphragm
4 A
E s 3
i
4
of bung diaphragm
Ten cartridges of 3 per cent Citanest with octapressin from the same batch (Astra Pharmaceuticals, King’s Langley, UK) were used in this test. A cartridge was placed in an Astra self-aspirating syringe but no needle was attached. The loaded syringe was placed in the load cell of an Instron testing machine (Instron Ltd, High Wycombe, UK) in such a manner that the syringe was vertical and parallel to the direction of movement of the cross-head. The cross-head was set to move at a rate of 0.5 cm min-’ and was applied to the syringe plunger until a force of 10 N was generated. The cross-head was then reversed at the same speed until it was removed from contact with the plunger. Each cartridge was subjected to this cycle twice in quick succession. The paper in the recording console of the Instron was fed at a rate of 10 cm min-’ and Fig. 1 illustrates the type of trace obtained during one cycle, demonstrating the relationship of the trace to the deformation and recovery of the aspirating device.
Evaluation
cartridges
10
z"
Performance
of local anaesthetic
AND METHODS
Both the diaphragm in the bung of Astra self-aspirating cartridges and the diaphragm in the base of the cartridge were investigated independently. The test method used was designed to determine the deformation and recovery of the diaphragms under controlled conditions similar to those found during clinical use.
Performance
Performance
0
B
B
Fig. 7. Theshapeoftheforceversustimetraceobtainedfrom the lnstron testing machine.TheiIlustrationsatthetopofthe figure demonstrate the activity at the aspirating device in the Astra self-aspirating system in relation to the trace. The diagram also illustrates the components of the trace used to calculate the aspiration potential (B/A) and the recovery (y/ x) of the aspirating diaphragm.
the greater aspiration potential per unit force and thus the gradient of this part of the curve is inversely related to the aspiration potential. The aspiration potential of the diaphragm is given the numerical value of the inverse of the gradient of the first part of the slope measured between the 4 and 8 N points (Fig. 1). This part of the slope was chosen because it consistently produced a straight line and is the order of force used when injecting local anaesthetic solution clinically (Meechan, 1989). The next measurement taken was used to determine the degree to which the aspiration potential was realised. This is determined by the recovery of the rubber diaphragm. If, at the end of the aspirating manoeuvre, the diaphragm returns exactly to the position it occupied before deformation then all of the aspiration potential generated will be achieved. On the other hand, if the diaphragm falls short of its original rest position at the end of the aspirating manoeuvre then the full aspiration potential will not be obtained immediately. The recovery of the diaphragm was evaluated as follows. The force versus time trace obtained from the printer was divided into two components by dropping a vertical line from the peak of the trace (Fig. I). The point at which this line crossed the 0 N line was marked. The point on the right side of the Instron trace where the curve leaves the 0 N line represents the time at which the aspiration manoeuvre began, the equivalent point on the left of the trace corresponds to the time at which the aspiration manoeuvre ended. The distance x is thus a measure of the distortion of the diaphragm during the active phase of aspiration and the distance y the recovery to a final rest position. Complete recovery of the diaphragm to its pre-aspiration position would result in x = y. If recovery was not complete then x > y. The recovery of the diaphragm was evaluated by calculatingyl x and expressing this as a percentage.
40
J. Dent. 1992; 20: No. 1
Table 1. The effect of storage at 37°C on the aspiration potential and recovery of the diaphragm in the bung of Citanest cartridges
Aspiration potential (room temp.) Aspiration potential (37°C) Percent recovery (room temp.)
Percent recovery (37°C)
n
Mean
s.d.
10
0.272
0.044
10
10
10
0.379
85.8
86.0
0.117
12.0
Range
t
P level
2.71
< 0.02
0.04
n.s.*
0.250-0.370
0.250-0.588
66.f-98.0
10.9
61.3-94.9
*Not significant.
Table II. The effect of storage at 37 “C on the aspiration potential and recovery of the diaphragm in the base of Citanest cartridges
Aspiration potential (room temp.)
n
Mean
s.d.
10
0.227
0.030
Aspiration potential (37°C)
10
Percent recovery (room temp.)
,.
Percent recovery (37°C)
,.
0.260
97.9
97.2
0.018
1.6
1.7
Range
t
P level
2.98
< 0.01
1.02
n.s.*
0.189-0.294
0.25&0.294
94.7-l
94.3-l
00
00
*Not significant.
Effects of storage on performance The aspiration potential and diaphragm recovery were measured as described above in cartridges that had been stored under three different conditions. These were: 1. At room temperature in their packaging. 2. After storage at 37°C for 3 h. 3. After immersion in 70 per cent alcohol for 24 h. All tests were performed at room temperature and for regimes (1) and (2) took place immediately following removal from the storage condition. It has been established previously that, in those systems where the production of the aspirating force relies upon an interaction of the cartridge bung and syringe plunger, an important factor influencing aspirating ability is the force required to move the rubber bung (Meechan et al., 1985). The effect of the different storage methods described above on the forces needed to begin and maintain the movement of the rubber bung at a rate of 2.5 cm/min in Citanest cartridges was investigated in a manner previously reported (Meechan et al., 1985).
Ten cartridges of Citanest were used in each test and the results compared by Student’s t test.
RESULTS The results are presented in Tables Z-W. Storage at 37 “C increased the aspiration potential of the diaphragms in both the bung and base of the cartridges investigated (Tables Z and ZZ), however recovery was unaffected. Soaking cartridges in 70 per cent alcohol for 24 h did not affect the aspiration potential but did improve the recovery of the diaphragm in the bung of the cartridges investigated (Tables ZZZand IV). The temperature at which the cartridges were stored affected the forces necessary to move the cartridge bung during injection. The force required to initiate the movement of the bung was significantly lower after storage at 37 “C compared to that needed to move the bung in those kept at room temperature (Table V). Temperature did not affect the forces needed to keep the bung in motion. Soaking in alcohol did not alter the forces needed to move the bung in the cartridges used in the present investigation (Table VZ).
Meechan
and McCabe:
Performance
of local anaesthetic
cartridges
41
Tab/e 111.The effect of storage in 70 per cent alcohol on the aspiration potential and recovery of the diaphragm in the bung of Citanest cartridges
Aspiration potential (drv) . ,,
n
Mean
s.d.
10
0.297
0.068
Range
10
Percent recovery (dry)
,.
86.4
5.1
78.2-93.0
Percent recovery (alcohol)
,o
93.0
1.6
9 1.2-95.8
0.036
P level
1.03
n.s.*
3.86
< 0.01
0.227-0.454
Aspiration potential (alcohol)
0.272
t
0.238-0.370
*Not significant.
Table IV. The effect of storage in 70 per cent alcohol on the aspiration potential and recovery of the diaphragm in the base of Citanest cartridges
Aspiration ootential Idrv) I
n
Mean
s.d.
10
0.222
0.015
Range
t
P level
1.83
n.s.*
0.63
n.s.*
0.200-0.244
a,
Aspiration potential (alcohol)
10
Percent recovery (dry)
10
Percent recovery (alcohol)
10
0.236
96.2
96.5
0.019
1.5
1.1
0.208-0.270
93.4-98.5
95.2-98.4
*Not significant.
Table V. The effect of temperature on the forces required to move the bung in Citanest cartridges
Table VI. The effect of storage in 70 per cent alcohol on the forces required to move the bung in Citanest cartridges
n
Room temp.
37°C
n
No alcohol
Alcohol
10 10
8.5 k 1.9 3.9 k 1.5
3.7 f 0.5 3.0 + 3.8
10 10
6.5 f 0.6 4.0 f 0.6
6.1 ?I 0.8 3.9 k 0.8
Initiation force Maintenance force
Force (N), mean f s.d. Initiation force, t = 7.6; P < 0.001. Maintenance force, t = 1.7 (not significant).
DISCUSSION The test method described in this investigation can evaluate the performance of the rubber diaphragms contained in dental local anaesthetic cartridges. The method could be used to compare different designs of cartridges for use in self-aspirating systems and could be a useful part of a standard for cartridges. The test closely mimics the conditions under which cartridges function clinically and examines the cartridge/syringe interface that is important in self-aspirating systems. It was mentioned above that a standard now exists for syringes and it includes a test method to analyse the performance
Initiation force Maintenance force
Force (N), mean f s.d. Initiation force, t = 1 .I (not significant). Maintenance force,
t = 0.4 (not significant).
of self-aspirating systems. It is apparent that as one component of the aspirating device in self-aspirating systems is an integral part of the cartridge then some form of standardization is required for cartridges. It is suggested that a test method similar to that described in the present paper would be required in a standard for dental local anaesthetic cartridges. The calculations used in the evaluation of the aspiration potentials and the recoveries of the diaphragms were made on the second aspirating cycle in each case. The first application of force to the aspirating mechanism should not be used to determine the aspiration potential and
42
J. Dent. 1992; 20: No. 1
recovery because in practice this manoeuvre will have been completed before the first injection when confirming free flow of local anaesthetic through the needle. Thus the first loading of the aspirating device should never be the aspirating manoeuvre. Preliminary investigations performed when formulating the test method subjected the diaphragms to ten loading cycles and showed that there was no difference in performance between the second and tenth depressions (Meechan, 1989). The aspiration potential has been expressed without units as it has been used here as a basis of comparing performance. However, as the rate of descent of the crosshead and the speed at which the paper is fed through the printer in the Instron are constants, units could be assigned to the aspiration potential: for example the first mean aspiration potential in Table I of 0.272 computes to a distension of the rubber diaphragm (in the range of forces 4-8 N) of 0.17 mm/N. The results shown in the present study confirm an earlier report (Meechan, 1990) that different aspirating devices (namely the different diaphragms) vary in the amount of distortion produced under uniform loads and thus differ in their aspiration potential. The present study adds information related to the achievement of the aspiration potential by allowing assessment of the recovery of the diaphragm at the conclusion of the aspiration manoeuvre. These results show that immediate recovery is not 100 per cent at the loading rate employed in the test and that in the cartridges investigated the diaphragms in the base and bung differed in the amount of recovery achieved. The test method used mimicked the activity of the diaphragm during clinical use. It does not allow for any viscoelastic effects that may occur, that is a slower rate of recovery to the rest position. When employed clinically the injection is performed almost immediately following the completion of the aspirating manoeuvre and therefore viscoelastic effects are not important. The fact that recovery is not 100 per cent in the immediate postaspiration period can be visualized readily in the basal diaphragm as, after the use of a strong aspirating force, an impression of the nipple at the base of the syringe can be clearly seen in the rubber. It has been suggested that warming local anaesthetic cartridges avoids the discomfort produced by the administration of a cold solution (Roberts and Sowray, 1987b) and Westblade (1968) suggests that the injection solution should be within 3°C of body temperature. However, Oikarinen et al. (1975) claim that patients are unable to differentiate temperatures between 21°C and 37°C and Rood (1977) reported that subjects were unaware of temperature differences in injected solutions between 20°C and 35°C. Malamed (1986a) claims that cartridge warmers are not necessary and suggests that the temperature of the injected solution has decreased to room temperature by the time it leaves the needle. In addition, storage at the higher temperature increases the likelihood of microbial contamination and speeds up the rate of oxidation of adrenaline thus reducing the efficacy of
catecholamine-containing local anaesthetic solutions. Nevertheless some dental units contain cartridge warmers that operate at 37 “C. The results of the present study show that storage at 37°C affects the performance of dental local anaesthetic cartridges. The force required to initiate the movement of the bung in the cartridges investigated was significantly reduced at the higher temperature. The maintenance force was unaffected in the cartridges used in this study and as the aspirating ability of those systems which rely upon force generated from the rubber bung to create the aspiration potential is dependent upon the maintenance force then no adverse effect on aspiration should be produced. The finding of a lowering of the initiation force without a change in maintenance force supports the claim of Roberts and Sowray (1987b) that the heating of the cartridge allows a smoother syringe action during injection. The performance of both diaphragms were improved at the higher temperature in that the aspiration potential was increased without a change in recovery. Therefore storage at the higher temperature did not adversely affect aspirating ability in the cartridges examined. When dental local anaesthetic cartridges are received from the manufacturers the solution is free from microbiological contamination, however the outside of the cartridge is not sterile. To prevent entry of microorganisms into the solution when piercing the basal membrane with the needle a variety of recommendations have been made to disinfect the cartridge and some of these involve the immersion of the cartridge in alcohol (Roberts and Sowray, 1987a). This can lead to alcohol penetrating the rubber diaphragm and contaminating the anaesthetic solution (Roberts and Sowray, 1987a). This contamination can occur after storage in alcohol for 1 day (Malamed, 1986b). The results of the present study showed that immersion in alcohol for 24 h (which is longer than would be recommended) did not adversely affect the performance of the cartridges investigated and therefore it seems that soaking for less time will not reduce the aspirating ability. The only significant finding was an increase in the recovery of the diaphragm in the bung following storage in alcohol; aspiration potential and injection forces were unaffected. It should be mentioned that the tests used in the present study investigated only one make of cartridge from one manufacturer to reduce the number of variables which might influence the comparisons reported. Earlier work (Blair and Meechan, 1985; Meechan et al., 1985) has shown that cartridges of similar design from the same manufacturer using different materials (importantly different rubber to manufacture the bung) differ in their performance both clinically and in the laboratory. Thus the results of the present investigation should not be extrapolated to other local anaesthetic cartridges. In conclusion, a test has been presented that may be of use in a standard for dental local anaesthetic cartridges. This test specifically evaluates cartridge performance in relation to use in self-aspirating syringe systems. The
Meechan
and McCabe:
method of storing cartridges can affect physical properties, however, with those used in the present study keeping them at 37°C or in alcohol did not adversely affect aspirating ability when compared to cartridges maintained under dry conditibns at room temperature.
References Blair G. S. and Meechan J. G. (1985) Local anaesthesia in dental practice I. A clinical study of a self-aspirating system. Br. Dent. .I 159, 75-77. British Standards Institution (1991) Specification for Dental Cartridge Syringes. BS 7432: 1991. Cowan A (1972) A new aspirating syringe. Br. Dent. .I 133, 547-548. Craig D. C. and Rood J. P. (1986) A comparison of two passive aspirating systems. 1 Dent. 14, 180-182. Jorgensen N. B. (1952) Accidental intravenous injection of procaine in dentistry. J. South Carolina Dent. Assoc. 20, 17-20. Malamed S. F. (1986a, b) Handbook ofLocal Anesthesia, 2nd edn. St Louis, Mosby, a, pp. 85-87; b, p. 89. Meechan J. G. (1988) A comparison of three different automatic aspirating dental cartridge syringes. J. Dent. 16, 40-43.
Performance
of local anaesthetic
cartridges
43
Meechan J. G. (1989) The Administration and Effects of Dental Local Anaesthetics. PhD Thesis, University of Newcastle upon Tyne, UK. Meechan J. G. (1990) A laboratory investigation of a new design of self-aspirating syringe. J. Dent. 18, 163-166. Meechan J. G. and Blair G. S. (1989) Clinical experience in oral surgery with two different automatic aspirating syringes. In?. J. Oral Maxillofac. Surg. 18, 87-89. Meechan J. G., Blair G. S. and McCabe J. F. (1985) Local anaesthesia in dental practice II. A laboratory investigation of a self-aspirating system. Br. Dent. J. 159, 109-113. Meechan J. G., Blair G. S. and McCabe J. F. (1987) The Rotor self-aspirating syringe-a laboratory investigation. J. Dent. 15, 34-37. Oikarinen V. J., Ylipaavalnpemi P. and Evers H. (1975) Pain and temperature sensations related to local analgesia. Znt. J. Oral Surg. 4, 151-156. Roberts D. H. and Sowray J. H. (1987a, b) Local Analgesia in Dentistry, 3rd edn. Bristol, Wright, a, pp. 56-67; b, p.85. Rood J. P. (1977) The temperature of local anaesthetic solutions. J. Dent. 5, 213-214. Sicher H. (1946) The anatomy of mandibular anesthesia. J. Am. Dent. Assoc. 33, 1541-1557. Westblade A. G. (1968) Temperature changes and local anaesthesia. Aust. Dent. J. 13, 154-157.
Book Review Oral Candidosis. L. P. Samaranayake and T. Wallace MacFarlane. Pp. 265. 1990. Oxford, Wright (an imprint of ButteworthHeinemann). Hardback, f 60.00 Candida, Silver Fillings and the Immune System. B. Russel-Manning. Pp. 193. 1990. Lancaster, Greenward Press. Softback, f 12.95. Oral Candidosis appears to be the first, comprehensive textbook devoted solely to the topic The editors, both from Glasgow, have in addition to their own contributions, brought together a variety of contributors embracing many specialties. All are well known and widely respected in their fields. The general aspects of candida are covered in the first six chapters. Chapter 7 covers classification, then the next three look at ‘specific’ diseases, while the last three include laboratory diagnosis and antifungal agents. Aimed at medical and dental postgraduates and oral and medical microbiologists, the book will undoubtebly be useful. It cannot be recommended for widespread undergraduate consumption, although senior dental students would profit from selected perusal. The text is, in most chapters, detailed and critical although inevitably some references are repeated frequently within a short space, making tiresome reading; otherwise the use of references is excellent and very comprehensive. There is also repetition
of the text itself. The four common categories of acute pseudomembranous, acute atrophic, chronic atrophic and chronic hyperplastic candidosis are mentioned in general terms in many chapters, as is adherence. To a degree, this is inevitable in a multi-author text, but a little more pruning would have eliminated these irksome interludes, to allow more discussion in other areas, for instance, switching mechanisms. Illustrations are of good quality, although the colour section started shedding unbound leaves at the first opening. On balance, this is an excellent book, that has many virtues and few vices. It is up to date and contains a wealth of useful information. Price and binding apart, I recommend it to all with a clinical or research interest in the subject. Candida, Silver Fillings and the Immune System, by contrast, is abysmal. It attempts to ‘blame’ an increased incidence in candidosis on doctors, dentists, politicians, food producers and others with vested commercial interests; in fact, almost everyone gets a mention but the sufferer. It proceeds to take sideswipes at fluoride, silver (mercury) fillings, antibiotics, nickel crowns, birth control pills and radiation in no particular order and there is precious little science in this book. The few reasonable comments made are drowned in a sea of faddish cant. None the less, it is decidedly more readable than much good science and enlightening on the sort of pseudoscience that is used in argument against health professionals on many occasions. A. S. High
J. Dent. 1992;
20: 38-43
Effect of different storage methods on the performance of dental local anaesthetic cartridges J. G. Meechan and J. F. McCabe* Department Tyne, UK
of Oral Surgery
and *Dental Materials Science Unit, The Dental School, University
of Newcastle
upon
ABSTRACT Self-aspirating dental local anaesthetic syringe systems rely on deformation of rubber diaphragms contained in the anaesthetic cartridges to produce the aspirating force. A test has been developed which can examine the performance of these rubber diaphragms under functional conditions. This method could be useful in the production of standards for dental local anaesthetic cartridges. The test has been used to determine the influence of storage conditions on the performance of dental local anaesthetic cartridges. The results show that, with the cartridges investigated, storage at 37°C increased the amount of distortion per unit force of the aspirating diaphragms in comparison with storage at room temperature. However recovery of the diaphragms was unaffected. Storage at the higher temperature decreased the amount of force required to initiate movement of the cartridge rubber bung during injection. Soaking cartridges in alcohol did not affect the distortion of the aspirating diaphragms or the force needed to move the bung during injection, but did increase the degree of recovery of the diaphragm in the bung of self-aspirating cartridges. KEY WORDS: Anaesthesia (local), Delivery systems, Storage J. Dent. 1992;
20: 38-43
(Received 4 June 1991;
reviewed 2 July 1991;
accepted 2 August 1991)
Correspondence should be addressed to: Dr J. G. Meechan, Department of Oral Surgery, The Dental School, Framlington Place, Newcastle upon Tyne NE2 4BW, UK.
INTRODUCTION The wisdom of aspirating before the injection of dental local anaesthetic solution has been proclaimed for many years (Sicher, 1946; Jorgensen, 1952). Equipment has been developed to enable aspiration to be efficiently performed and there are now a number of self-aspirating systems available (Meechan, 1988). The performance of self-aspirating systems relies on an interaction between syringe and cartridge. The aspirating device in self-aspirating systems includes a rubber diaphragm in the cartridge. One of two diaphragms may be employed. In the Astra self-aspirating system (Cowan, 1972) the thin diaphragm contained in the rubber bung of the special self-aspirating cartridge is the aspirating device. In other systems such as the Aspiject (Craig and Rood, 1986) and Rotor (Meechan et al., 1987) it is the diaphragm at the base of the cartridge through which the needle passes that is deflected to create the aspirating o (1992) Buttenvorth-Heinemann 0300-5712/92/010038-06
Ltd.
force. It is important to ensure reliability of these components and thus it is desirable that certain standards related to performance are established. A British Standard for dental local anaesthetic syringes has recently been formulated (British Standards Institution, 1991) however there is no such standard for local anaesthetic cartridges. It has been shown that self-aspirating systems vary in their ability to aspirate when used clinically (Meechan and Blair, 1989) and when examined under controlled conditions in the laboratory (Meechan, 1988). Indeed, there are even significant variations in the performance of single systems due to the use of different cartridges (Blair and Meechan, 1985; Meechan et al., 1985). The purpose of the present investigation was to design a test that could be used to evaluate the performance of the cartridge rubber diaphragms under controlled conditions that mimicked clinical use. The effects of different storage conditions on the performance of the diaphragms and on the forces needed for injection were also investigated.
Meechan
MATERIALS
and McCabe:
8
39
of basal diaphragm
Ten cartridges of 3 per cent Citanest with octapressin were used in this test. The cartridge was placed in a Rotor syringe (John Quayle Dental Manufacturing Company, Worthing, UK) from which the plunger had been removed; no needle was attached. The loaded syringe was then placed on the load cell of the Instron testing machine in such a manner that the thumb-ring was depressed by the load cell. In this system pressure on the thumb ring pushes the cartridge down on to a nipple at the base of the syringe and this deflects the diaphragm at the base of the cartridge to produce the aspiration potential. The Instron was then used as described in the test above and each cartridge was subjected to two cycles. The trace obtained was similar to that shown in Fig. 1.
of performance
The same methods of calculating the aspiration potential and the recovery of the diaphragm were used for both bung and base diaphragms. Calculations were performed on the trace obtained at the second test cycle. The gradient of the slope of the first part (right hand side) of the trace obtained from the Instron testing machine is a measure of stiffness of the rubber diaphragm; the steeper the slope the stiffer the diaphragm and the less distortion per unit force. The more flexible the diaphragm
4 A
E s 3
i
4
of bung diaphragm
Ten cartridges of 3 per cent Citanest with octapressin from the same batch (Astra Pharmaceuticals, King’s Langley, UK) were used in this test. A cartridge was placed in an Astra self-aspirating syringe but no needle was attached. The loaded syringe was placed in the load cell of an Instron testing machine (Instron Ltd, High Wycombe, UK) in such a manner that the syringe was vertical and parallel to the direction of movement of the cross-head. The cross-head was set to move at a rate of 0.5 cm min-’ and was applied to the syringe plunger until a force of 10 N was generated. The cross-head was then reversed at the same speed until it was removed from contact with the plunger. Each cartridge was subjected to this cycle twice in quick succession. The paper in the recording console of the Instron was fed at a rate of 10 cm min-’ and Fig. 1 illustrates the type of trace obtained during one cycle, demonstrating the relationship of the trace to the deformation and recovery of the aspirating device.
Evaluation
cartridges
10
z"
Performance
of local anaesthetic
AND METHODS
Both the diaphragm in the bung of Astra self-aspirating cartridges and the diaphragm in the base of the cartridge were investigated independently. The test method used was designed to determine the deformation and recovery of the diaphragms under controlled conditions similar to those found during clinical use.
Performance
Performance
0
B
B
Fig. 7. Theshapeoftheforceversustimetraceobtainedfrom the lnstron testing machine.TheiIlustrationsatthetopofthe figure demonstrate the activity at the aspirating device in the Astra self-aspirating system in relation to the trace. The diagram also illustrates the components of the trace used to calculate the aspiration potential (B/A) and the recovery (y/ x) of the aspirating diaphragm.
the greater aspiration potential per unit force and thus the gradient of this part of the curve is inversely related to the aspiration potential. The aspiration potential of the diaphragm is given the numerical value of the inverse of the gradient of the first part of the slope measured between the 4 and 8 N points (Fig. 1). This part of the slope was chosen because it consistently produced a straight line and is the order of force used when injecting local anaesthetic solution clinically (Meechan, 1989). The next measurement taken was used to determine the degree to which the aspiration potential was realised. This is determined by the recovery of the rubber diaphragm. If, at the end of the aspirating manoeuvre, the diaphragm returns exactly to the position it occupied before deformation then all of the aspiration potential generated will be achieved. On the other hand, if the diaphragm falls short of its original rest position at the end of the aspirating manoeuvre then the full aspiration potential will not be obtained immediately. The recovery of the diaphragm was evaluated as follows. The force versus time trace obtained from the printer was divided into two components by dropping a vertical line from the peak of the trace (Fig. I). The point at which this line crossed the 0 N line was marked. The point on the right side of the Instron trace where the curve leaves the 0 N line represents the time at which the aspiration manoeuvre began, the equivalent point on the left of the trace corresponds to the time at which the aspiration manoeuvre ended. The distance x is thus a measure of the distortion of the diaphragm during the active phase of aspiration and the distance y the recovery to a final rest position. Complete recovery of the diaphragm to its pre-aspiration position would result in x = y. If recovery was not complete then x > y. The recovery of the diaphragm was evaluated by calculatingyl x and expressing this as a percentage.
40
J. Dent. 1992; 20: No. 1
Table 1. The effect of storage at 37°C on the aspiration potential and recovery of the diaphragm in the bung of Citanest cartridges
Aspiration potential (room temp.) Aspiration potential (37°C) Percent recovery (room temp.)
Percent recovery (37°C)
n
Mean
s.d.
10
0.272
0.044
10
10
10
0.379
85.8
86.0
0.117
12.0
Range
t
P level
2.71
< 0.02
0.04
n.s.*
0.250-0.370
0.250-0.588
66.f-98.0
10.9
61.3-94.9
*Not significant.
Table II. The effect of storage at 37 “C on the aspiration potential and recovery of the diaphragm in the base of Citanest cartridges
Aspiration potential (room temp.)
n
Mean
s.d.
10
0.227
0.030
Aspiration potential (37°C)
10
Percent recovery (room temp.)
,.
Percent recovery (37°C)
,.
0.260
97.9
97.2
0.018
1.6
1.7
Range
t
P level
2.98
< 0.01
1.02
n.s.*
0.189-0.294
0.25&0.294
94.7-l
94.3-l
00
00
*Not significant.
Effects of storage on performance The aspiration potential and diaphragm recovery were measured as described above in cartridges that had been stored under three different conditions. These were: 1. At room temperature in their packaging. 2. After storage at 37°C for 3 h. 3. After immersion in 70 per cent alcohol for 24 h. All tests were performed at room temperature and for regimes (1) and (2) took place immediately following removal from the storage condition. It has been established previously that, in those systems where the production of the aspirating force relies upon an interaction of the cartridge bung and syringe plunger, an important factor influencing aspirating ability is the force required to move the rubber bung (Meechan et al., 1985). The effect of the different storage methods described above on the forces needed to begin and maintain the movement of the rubber bung at a rate of 2.5 cm/min in Citanest cartridges was investigated in a manner previously reported (Meechan et al., 1985).
Ten cartridges of Citanest were used in each test and the results compared by Student’s t test.
RESULTS The results are presented in Tables Z-W. Storage at 37 “C increased the aspiration potential of the diaphragms in both the bung and base of the cartridges investigated (Tables Z and ZZ), however recovery was unaffected. Soaking cartridges in 70 per cent alcohol for 24 h did not affect the aspiration potential but did improve the recovery of the diaphragm in the bung of the cartridges investigated (Tables ZZZand IV). The temperature at which the cartridges were stored affected the forces necessary to move the cartridge bung during injection. The force required to initiate the movement of the bung was significantly lower after storage at 37 “C compared to that needed to move the bung in those kept at room temperature (Table V). Temperature did not affect the forces needed to keep the bung in motion. Soaking in alcohol did not alter the forces needed to move the bung in the cartridges used in the present investigation (Table VZ).
Meechan
and McCabe:
Performance
of local anaesthetic
cartridges
41
Tab/e 111.The effect of storage in 70 per cent alcohol on the aspiration potential and recovery of the diaphragm in the bung of Citanest cartridges
Aspiration potential (drv) . ,,
n
Mean
s.d.
10
0.297
0.068
Range
10
Percent recovery (dry)
,.
86.4
5.1
78.2-93.0
Percent recovery (alcohol)
,o
93.0
1.6
9 1.2-95.8
0.036
P level
1.03
n.s.*
3.86
< 0.01
0.227-0.454
Aspiration potential (alcohol)
0.272
t
0.238-0.370
*Not significant.
Table IV. The effect of storage in 70 per cent alcohol on the aspiration potential and recovery of the diaphragm in the base of Citanest cartridges
Aspiration ootential Idrv) I
n
Mean
s.d.
10
0.222
0.015
Range
t
P level
1.83
n.s.*
0.63
n.s.*
0.200-0.244
a,
Aspiration potential (alcohol)
10
Percent recovery (dry)
10
Percent recovery (alcohol)
10
0.236
96.2
96.5
0.019
1.5
1.1
0.208-0.270
93.4-98.5
95.2-98.4
*Not significant.
Table V. The effect of temperature on the forces required to move the bung in Citanest cartridges
Table VI. The effect of storage in 70 per cent alcohol on the forces required to move the bung in Citanest cartridges
n
Room temp.
37°C
n
No alcohol
Alcohol
10 10
8.5 k 1.9 3.9 k 1.5
3.7 f 0.5 3.0 + 3.8
10 10
6.5 f 0.6 4.0 f 0.6
6.1 ?I 0.8 3.9 k 0.8
Initiation force Maintenance force
Force (N), mean f s.d. Initiation force, t = 7.6; P < 0.001. Maintenance force, t = 1.7 (not significant).
DISCUSSION The test method described in this investigation can evaluate the performance of the rubber diaphragms contained in dental local anaesthetic cartridges. The method could be used to compare different designs of cartridges for use in self-aspirating systems and could be a useful part of a standard for cartridges. The test closely mimics the conditions under which cartridges function clinically and examines the cartridge/syringe interface that is important in self-aspirating systems. It was mentioned above that a standard now exists for syringes and it includes a test method to analyse the performance
Initiation force Maintenance force
Force (N), mean f s.d. Initiation force, t = 1 .I (not significant). Maintenance force,
t = 0.4 (not significant).
of self-aspirating systems. It is apparent that as one component of the aspirating device in self-aspirating systems is an integral part of the cartridge then some form of standardization is required for cartridges. It is suggested that a test method similar to that described in the present paper would be required in a standard for dental local anaesthetic cartridges. The calculations used in the evaluation of the aspiration potentials and the recoveries of the diaphragms were made on the second aspirating cycle in each case. The first application of force to the aspirating mechanism should not be used to determine the aspiration potential and
42
J. Dent. 1992; 20: No. 1
recovery because in practice this manoeuvre will have been completed before the first injection when confirming free flow of local anaesthetic through the needle. Thus the first loading of the aspirating device should never be the aspirating manoeuvre. Preliminary investigations performed when formulating the test method subjected the diaphragms to ten loading cycles and showed that there was no difference in performance between the second and tenth depressions (Meechan, 1989). The aspiration potential has been expressed without units as it has been used here as a basis of comparing performance. However, as the rate of descent of the crosshead and the speed at which the paper is fed through the printer in the Instron are constants, units could be assigned to the aspiration potential: for example the first mean aspiration potential in Table I of 0.272 computes to a distension of the rubber diaphragm (in the range of forces 4-8 N) of 0.17 mm/N. The results shown in the present study confirm an earlier report (Meechan, 1990) that different aspirating devices (namely the different diaphragms) vary in the amount of distortion produced under uniform loads and thus differ in their aspiration potential. The present study adds information related to the achievement of the aspiration potential by allowing assessment of the recovery of the diaphragm at the conclusion of the aspiration manoeuvre. These results show that immediate recovery is not 100 per cent at the loading rate employed in the test and that in the cartridges investigated the diaphragms in the base and bung differed in the amount of recovery achieved. The test method used mimicked the activity of the diaphragm during clinical use. It does not allow for any viscoelastic effects that may occur, that is a slower rate of recovery to the rest position. When employed clinically the injection is performed almost immediately following the completion of the aspirating manoeuvre and therefore viscoelastic effects are not important. The fact that recovery is not 100 per cent in the immediate postaspiration period can be visualized readily in the basal diaphragm as, after the use of a strong aspirating force, an impression of the nipple at the base of the syringe can be clearly seen in the rubber. It has been suggested that warming local anaesthetic cartridges avoids the discomfort produced by the administration of a cold solution (Roberts and Sowray, 1987b) and Westblade (1968) suggests that the injection solution should be within 3°C of body temperature. However, Oikarinen et al. (1975) claim that patients are unable to differentiate temperatures between 21°C and 37°C and Rood (1977) reported that subjects were unaware of temperature differences in injected solutions between 20°C and 35°C. Malamed (1986a) claims that cartridge warmers are not necessary and suggests that the temperature of the injected solution has decreased to room temperature by the time it leaves the needle. In addition, storage at the higher temperature increases the likelihood of microbial contamination and speeds up the rate of oxidation of adrenaline thus reducing the efficacy of
catecholamine-containing local anaesthetic solutions. Nevertheless some dental units contain cartridge warmers that operate at 37 “C. The results of the present study show that storage at 37°C affects the performance of dental local anaesthetic cartridges. The force required to initiate the movement of the bung in the cartridges investigated was significantly reduced at the higher temperature. The maintenance force was unaffected in the cartridges used in this study and as the aspirating ability of those systems which rely upon force generated from the rubber bung to create the aspiration potential is dependent upon the maintenance force then no adverse effect on aspiration should be produced. The finding of a lowering of the initiation force without a change in maintenance force supports the claim of Roberts and Sowray (1987b) that the heating of the cartridge allows a smoother syringe action during injection. The performance of both diaphragms were improved at the higher temperature in that the aspiration potential was increased without a change in recovery. Therefore storage at the higher temperature did not adversely affect aspirating ability in the cartridges examined. When dental local anaesthetic cartridges are received from the manufacturers the solution is free from microbiological contamination, however the outside of the cartridge is not sterile. To prevent entry of microorganisms into the solution when piercing the basal membrane with the needle a variety of recommendations have been made to disinfect the cartridge and some of these involve the immersion of the cartridge in alcohol (Roberts and Sowray, 1987a). This can lead to alcohol penetrating the rubber diaphragm and contaminating the anaesthetic solution (Roberts and Sowray, 1987a). This contamination can occur after storage in alcohol for 1 day (Malamed, 1986b). The results of the present study showed that immersion in alcohol for 24 h (which is longer than would be recommended) did not adversely affect the performance of the cartridges investigated and therefore it seems that soaking for less time will not reduce the aspirating ability. The only significant finding was an increase in the recovery of the diaphragm in the bung following storage in alcohol; aspiration potential and injection forces were unaffected. It should be mentioned that the tests used in the present study investigated only one make of cartridge from one manufacturer to reduce the number of variables which might influence the comparisons reported. Earlier work (Blair and Meechan, 1985; Meechan et al., 1985) has shown that cartridges of similar design from the same manufacturer using different materials (importantly different rubber to manufacture the bung) differ in their performance both clinically and in the laboratory. Thus the results of the present investigation should not be extrapolated to other local anaesthetic cartridges. In conclusion, a test has been presented that may be of use in a standard for dental local anaesthetic cartridges. This test specifically evaluates cartridge performance in relation to use in self-aspirating syringe systems. The
Meechan
and McCabe:
method of storing cartridges can affect physical properties, however, with those used in the present study keeping them at 37°C or in alcohol did not adversely affect aspirating ability when compared to cartridges maintained under dry conditibns at room temperature.
References Blair G. S. and Meechan J. G. (1985) Local anaesthesia in dental practice I. A clinical study of a self-aspirating system. Br. Dent. .I 159, 75-77. British Standards Institution (1991) Specification for Dental Cartridge Syringes. BS 7432: 1991. Cowan A (1972) A new aspirating syringe. Br. Dent. .I 133, 547-548. Craig D. C. and Rood J. P. (1986) A comparison of two passive aspirating systems. 1 Dent. 14, 180-182. Jorgensen N. B. (1952) Accidental intravenous injection of procaine in dentistry. J. South Carolina Dent. Assoc. 20, 17-20. Malamed S. F. (1986a, b) Handbook ofLocal Anesthesia, 2nd edn. St Louis, Mosby, a, pp. 85-87; b, p. 89. Meechan J. G. (1988) A comparison of three different automatic aspirating dental cartridge syringes. J. Dent. 16, 40-43.
Performance
of local anaesthetic
cartridges
43
Meechan J. G. (1989) The Administration and Effects of Dental Local Anaesthetics. PhD Thesis, University of Newcastle upon Tyne, UK. Meechan J. G. (1990) A laboratory investigation of a new design of self-aspirating syringe. J. Dent. 18, 163-166. Meechan J. G. and Blair G. S. (1989) Clinical experience in oral surgery with two different automatic aspirating syringes. In?. J. Oral Maxillofac. Surg. 18, 87-89. Meechan J. G., Blair G. S. and McCabe J. F. (1985) Local anaesthesia in dental practice II. A laboratory investigation of a self-aspirating system. Br. Dent. J. 159, 109-113. Meechan J. G., Blair G. S. and McCabe J. F. (1987) The Rotor self-aspirating syringe-a laboratory investigation. J. Dent. 15, 34-37. Oikarinen V. J., Ylipaavalnpemi P. and Evers H. (1975) Pain and temperature sensations related to local analgesia. Znt. J. Oral Surg. 4, 151-156. Roberts D. H. and Sowray J. H. (1987a, b) Local Analgesia in Dentistry, 3rd edn. Bristol, Wright, a, pp. 56-67; b, p.85. Rood J. P. (1977) The temperature of local anaesthetic solutions. J. Dent. 5, 213-214. Sicher H. (1946) The anatomy of mandibular anesthesia. J. Am. Dent. Assoc. 33, 1541-1557. Westblade A. G. (1968) Temperature changes and local anaesthesia. Aust. Dent. J. 13, 154-157.
Book Review Oral Candidosis. L. P. Samaranayake and T. Wallace MacFarlane. Pp. 265. 1990. Oxford, Wright (an imprint of ButteworthHeinemann). Hardback, f 60.00 Candida, Silver Fillings and the Immune System. B. Russel-Manning. Pp. 193. 1990. Lancaster, Greenward Press. Softback, f 12.95. Oral Candidosis appears to be the first, comprehensive textbook devoted solely to the topic The editors, both from Glasgow, have in addition to their own contributions, brought together a variety of contributors embracing many specialties. All are well known and widely respected in their fields. The general aspects of candida are covered in the first six chapters. Chapter 7 covers classification, then the next three look at ‘specific’ diseases, while the last three include laboratory diagnosis and antifungal agents. Aimed at medical and dental postgraduates and oral and medical microbiologists, the book will undoubtebly be useful. It cannot be recommended for widespread undergraduate consumption, although senior dental students would profit from selected perusal. The text is, in most chapters, detailed and critical although inevitably some references are repeated frequently within a short space, making tiresome reading; otherwise the use of references is excellent and very comprehensive. There is also repetition
of the text itself. The four common categories of acute pseudomembranous, acute atrophic, chronic atrophic and chronic hyperplastic candidosis are mentioned in general terms in many chapters, as is adherence. To a degree, this is inevitable in a multi-author text, but a little more pruning would have eliminated these irksome interludes, to allow more discussion in other areas, for instance, switching mechanisms. Illustrations are of good quality, although the colour section started shedding unbound leaves at the first opening. On balance, this is an excellent book, that has many virtues and few vices. It is up to date and contains a wealth of useful information. Price and binding apart, I recommend it to all with a clinical or research interest in the subject. Candida, Silver Fillings and the Immune System, by contrast, is abysmal. It attempts to ‘blame’ an increased incidence in candidosis on doctors, dentists, politicians, food producers and others with vested commercial interests; in fact, almost everyone gets a mention but the sufferer. It proceeds to take sideswipes at fluoride, silver (mercury) fillings, antibiotics, nickel crowns, birth control pills and radiation in no particular order and there is precious little science in this book. The few reasonable comments made are drowned in a sea of faddish cant. None the less, it is decidedly more readable than much good science and enlightening on the sort of pseudoscience that is used in argument against health professionals on many occasions. A. S. High
