use and misuse of equipment for dental local analgesia

Journal of Dentistry, 6, No. 2, 1978, pp. 133-146. Printedin Great Britain

Use and misuse of eaubment for ______ ---- ----- -- _ -,_-_,- ---_--_ - _ -

d&&I local analgesia J. D. Lilley, MSc, PhD, FDS, RCPS Department of Conservative Dentistry, University of Manchester

c. Russeli, MA, PhD Department of Bacteriology and Virology, University of Manchester

R. 0. Walker, CBE, FDS RCS (Eng and Edin) 6 Chad Road, Edgbaston, Birmingham

J. A. H. Waterhouse, MA, PhD Department of Social Medicine, University of Birmingham

ABSTRACT Changes in available equipment for dental local analgesia and increased official awareness of the hazards of transmissible disease prompted a survey of the practices in this regard currently followed by the dental profession. A 10 per cent sample of registered dentists was sent a questionnaire drawn up with a view to comparison with earlier studies.

The results indicated a growing awareness of the possible microbiological hazards and progressively better understanding of the ways in which to minimize them.

Nevertheless, a disturbing number of practitioners continues to employ inefficient methods. The need for authoritative guidance on the necessity and techniques of rendering discarded needles unusable and for the disposal of partly used cartridges is discussed in respect of social and legal responsibilities.

trwRnn1 rr-r~~hi II. I ll”Y”” I I”,. Thirteen years ago the results were published of a survey of the methods used in dental practice to sterilize local analgesic equipment (Walker and Geddes, 1965). That survey considered the syringe and the needle but not the analgesic cartridge. The possible hazards posed by the cartridge, and investigations into decontamination techniques, have recently been reported by Lilley and Russell (1975). In the 27 years since the dental implications were first pointed out, initially in German (Nocke, 1951), and later in English (Foley and Gutheim, 1956) there has been increasing awareness of the dangers of serum hepatitis (Department of Health and Social Security, 1975; Leading Article, British Medical Joumul, 1975). The risk of transmission of infection from one patient to another by multiple injection techniques has long been appreciated in relation to mass inoculations and medication by injection (Lurman, 1885; Murray, 1930; Borensztejn, 1948).

Hughes (1946) and Zuckerman (1964) demonstrated the need to sterilize or to replace the syringe after each usage, while Heathcote and Sherlock (1973) implicated both syringe and needle in the causation of disease. The role of these instruments and of the dental local analgesic cartridge in the epidemiology of serum hepatitis is now well documented (Medical Research Council, 1962; McLundie et al., 1968; Roberts and Sowray, 1970; Zuckerman, 1975). The occupational hazards have been highlighted by investigations by Jones et al. (1972) and Feldman and Schiff (1973) into the incidence of hepatitis-associated antigens among dental personnel; the need for particular care in the disposal of needles is apparent

134 Journal of Dentistry, Vol. ~/NO. 2

(Sims, 1974). The spread of viral hepatitis in association with drug abuse has been extensively reported, the transmission being effected by the communal, and insanitary, use of syringes and needles (Sullman and Zuckerman, 1971; Sherlock, 1973). As the possession of the drug is almost always illicit and the individuals involved frequently associated with crime, it is not surprising that the acquisition of the hypodermic, or intravenous, equipment is characte~sti~~y clandestine. It seems not ume~onable to expect the dental profession to accept a social responsibility for taking reasonable steps to prevent an unwitting supply of needles and syringes by rendering such equipment unusable after professional use. The increasing av~ability of disposable local analgesic ~uipment from the dental supply companies, and the concern expressed within the profession about the advisability of its use (British Dental Association, 1974; Owen, 1974) led the authors to believe that it would be instructive to carry out a fresh survey among the dental profession in Great Britain using a questionnaire which took into account the changes since the previous investigation was undertaken in 1961 and another (unpublished) survey conducted in 1969 from Birmingham. It is hoped thereby to identify areas of progress on the one hand or of concern on the other.

METHODS Every tenth practitioner in Tke Lkntists Register 1972 was sent the following question~re which was accompanied by an explanatory letter and a stamped addressed envelope.

Questions asked also in the earlier survey of 1961 (Walker and Geddes, 1965) are marked *. ~estions asked in the unpublished survey of 1969 are marked -l-. The wording in such cases was kept the same to permit direct comparison of the answers.

1. How many patients do you estimate you inject with local anaesthetic solution per day?*?

2. Do you always eject some anaesthetic through the needle prior to injection?*t 3. Do you aspirate in order to check the location of the needle tip?? 4. If ‘no’, why not?? 5. Do you continue to inject until the needle is withdrawn?*? 6. Do you predom~antly use:

a. A reusable needle? b. A sterile prepacked disposable needle?*

7. What factors influence this choice? 8. a. What gauge of needle do you use:

i. When aspirating?*+ ii. When not aspirating?

b. What lengths of needle do you use for each gauge used?? 9. For how many patients do you use one and the same reusable needle?*+

10. What precautions do you take for the safe disposal of used needles? 11. a. Which size of cartridge do you prefer, l-8 ml or 2-2 ml?

b. If you prefer the larger cartridge, is this because the smaller size may not contain sufficient anaesthetic for one injection site?

c. Do you find that you can use the larger cartridges to enable you to anaesthetize more than one patient?*t

12. In the type of cartridge which you usually use is the diaphragm on the end which is penetrated by the needle of (a) rubber, (b) rubber covered by metal foil diaphragm?

Lilley et al.: Dental local analgesia 135

13. When used at the chairside are the cartridges (a) taken as needed from the manufacturer’s carton, (b) taken from a special container in which they have been stored until needed?

14. If your answer to 13b is ‘yes’, a. Are the cartridges treated before storage? If so, how? b. Are the cartridges treated during storage? If so, how? c. Is the storage container (i) open to the atmosphere (this includes storage in a

drawer), (ii) in a heated compartment, e.g. in the unit? 15. Do you use a system distinct from the conventional cartridge id syringe? If ‘Yes’,

state system.? 16. Do you have facilities for a flame in your surgery, gas or spirit? 17. How is sterilization of equipment effected? Dry heat, boiling, autoclave.*? 18. If by boiling water, (a) timed or estimated time? (b)Are other instruments

sometimes added during this period?*+ If by dry heat, (a) for how long? (b) At what temperature?*?

19. How long have you been practising dentistry?*t 20. Is your practice:

a. Private, NHS, mixed, other. b. Urban, rural. c. Conservative, extraction and prosthetic, mixed?*

The data collected in this manner were transferred to punch cards for analysis.

RESULTS Of the 1850 questionnaires sent out, 706 completed forms were returned, i.e. 38.2 per cent response.

So that trends over the period since the first survey may be shown, each result given in the text is followed by three figures in parenthesis e.g. (12-l ; 13.4; 14.7). These refer to the three surveys in chronological order, namely, the 1961 Birmingham survey (Walker and Geddes, 1965), the 1969 Birmingham unpublished survey and the present Manchester survey carried out in 1974. Where no comparable figures can be quoted, as when the same question was not asked on every occasion, a dash has been inserted, e.g. (-; 13.8; 12.6).

In the tables the percentages shown have been determined on the basis of positive replies, i.e. ignoring respondents who did not reply to that particular question. In some cases several answers may have been given, i.e. the dentist used more than one method to achieve a specific end. In such instances the percentages shown were calculated on the basis of the total number of answers, not on the number of dentists.

Question 1 The mean number of patients injected per day by each dentist was 147 (12-l; 13.4; 14*7), although 2 dentists each injected more than 50 patients per day. Table I and Fig 1 show the distribution of the daily injection totals. On the basis of The Dentists Register 1972 this gives a conservative estimate of a quarter of a million patients injected each working day and this number is rising (150 000; 170 000; 250 000).

Questions 2,3,4 and 5 Only 12.6 per cent of dentists (-; 13.8; 12.6) aspirated to check the location of the needle.


Table 1. Gauge and length of needle used according to injection technique

Gauge of needle

No. of dentists Length of

No. of dentists

Aspira ring Not aspirating needle (in ) Aspira ring Not aspirating

21 1 0 <I 1 6 22 0 4 1 3 8 25 5 10 I+ 0 2 26 17 75 l$ 1 8 27 59 408 1; IO 58 28 1 1 14 6 23 30 2 22 1% 45 246

1: 2 18 2 1 9

Total 85 520 69 378

No. of patients Fig. 1. Number of patients injected per dentist per day in the three surveys. Black columns, Manchester, 1974; white columns, Birming- ham, 1969 (unpublished); stippled columns, Birmingham, 1961.

Of those who did not, 68.7 per cent said that they could not, i.e. did not use syringes which permitted aspiration, and 24.8 per cent did not believe it to be necessary. Almost all the dentists (98.6 per cent) routinely ejected some anaesthetic solution before injection, but only two-thirds (59-O; 71.2; 66-O) continued to inject while withdrawing the needle.

Questions 6 and 7 More than three-quarters of the dentists in the survey (-; 50-2; 78:2) stated that they used prepacked, sterile disposable needles predominantly. TabfeII shows the reasons for the


Tab/e II. Reasons for choice of disposable or reusable needles

557 disposable needle users 1%) 154 re-usable needle users ( % I Cost Convenience Infection risk cost Convenience Infection risk

Most important Second most

important Least important

0.9 12.9 89.5 51.2 57.3 12.8 4.2 83.7 9.4 24.4 35.0 29.8

94.9 3.4 1 .I 24.4 7.7 57.4

No. of patients Fig. 2. Number of patients injected with the same re-usable needle in the three surveys. Key as for Fig. 1.

choice given by these dentists and by the remainder who employed reusable needles. As might be expected, those using disposable needles gave most regard to the risk of infection and least to the cost involved, whereas those employing re-usable needles rated their low cost as more important a factor than any infection risk.

Question 8 Table I shows the gauge of needle preferred, the most popular being No. 27, whether aspirating or not. Similarly, aspiration did not affect the choice of length of needle, which was 18 in first, with 12 in second. Very few practitioners used other lengths.

Question 9 Although only 154 dentists employed re-usable needles (TableII), 292 answered this question; Table III and Fig. 2 show the distribution among them. Almost half (67; 29.6;


Table 111. Number of patients injected with one needle

No. of patients

Disposable needle users Re-usable needle users

No. %* No. %*

No data 402 _

1 135 90.0 2-4 10 6.7 5-9 2 1.3 10-14 2 1.3 15-19 0 0.0 20-24 1 0.7 25-29 0 0.0 30-34 0 0.0 35+ 0 0.0

12 _

7 4.9 39 27.5 48 33.8 26 18.4

5 3.5

2.0 6 4.2 2 1.4 33.6

3 2.1 6 4.2

Total 552 154

??Figures are percentages of replies.

Table IV. Precautions for safe disposal of used needles

Method No. of dentists using

each method

No reply No precautions Dustbin Dental waste bin Break or bend Incinerate Return to cover Special disposable container or tissue Dispose via local authority Boil and bury . Public tip

66 91 75

135

181 71 13 21

2

48.6) used one needle for one patient, but 17-5 per cent (34.0; 35.1; 17-5) used the same needle for 10 or more patients; the maximum number was 128 patients injected with the same needle. A separate analysis of the 154 dentists using reusable needles predominantly (Table III) shows that 7 used one needle per patient, whereas 48 (33.8 per cent) injected 10 or more patients with the same needle. Presumably, some dentists who usually use disposable needles answered this question in terms of their use of reusable needles.

Question 10 In Table IV are listed the ways in which needles were prepared for disposal after use. Some dentists used more than one method. No attempt to render the needles safe was made by 9 1 dentists, of whom 26.5 per cent were found to use their needles for 10 or more patients (in contrast to 17.5 per cent of all dentists). Further, 27.3 per cent of these 91 dentists boiled their needles to sterilize them, compared with only 17.6 per cent of all dentists. In view of the use of discarded syringes and needles by addicts and children (Steigmann et al., 1950; Levine and Payne, 1960; Sapira et al., 1968) it is disquieting to note that in only about one-third of cases were the needles made unusable.

Lilley et al.: Dental local analgesia

Tab/e V. Aseptic precautions taken by two groups of dentists*

Method Group 1 Group 2

Use prepacked sterile needles 78.2 46.8 Use of one needle for lO+ patients 17.6 38.7 Sterilize needle by boiling 17.6 40.0 Sterilize needle by antiseptic 4.0 12.7 Sterilize cartridge by boiling 2.1 14.3 Boil equipment for less than 10 min 14.7 43.4 Use dry heat for less than 60 min 80.5 100.0 Use dry heat at less than 160 ‘C 23.2 375

*Group 1 : all the dentists (706); group 2: dentists using a cartridge for more than one patient (47). Figures are the percentages in each group using the listed methods.

Tab/e V/. Distribution of methods of sterilizing equipment

Method Syringe Needle Cartridge

Dry heat 23.3 5.7 0.6 Autoclave 12.1 1 .3 0.2 Boiling 49.7 17.6 2.1 Antiseptic solution 10.7 4.0 18.6 Dipping in alcohol 1.2 0.9 13.2 Alcohol and flaming 0.4 0.4 11.5 Flaming end of cartridge 0.7 0.1 14.5 Prepacked sterile 1.8 70.0 39.2

Figures show the percentage of each method adopted for each article and ignore the dentists who did not reply.

Tab/e VII. Details of sterilization by heat*

Use of boiling water Use of dry heat

Total No. of dentists 403 Total No. of dentists 194 No. timing 93 Time less than 60 min 156 No. estimating time 303 Temperature less 45 Time less than 10 min 58 (14.7%) than 160°C Time 30 min or more 37 (9.3%) Both time less than 37 (19%) No. adding instruments 155 60 min and temp-

during boiling period erature less than 160 o C

*For recommended technique see Appendix.

139

Question 11 Two out of every three dentists (-; 65.9; 685) preferred cartridges containing 2.2 ml analgesic as against 1.8 ml, and of these, 65.2 per cent did so because the smaller size might contain insufficient solution for one site. However, 47 dentists (540; 24.5; l@O) of those using larger cartridges did so because they could treat more than one patient with one cartridge. The characteristics of this group of dentists are compared with those of their colleagues in respect of their methods of sterilization in Table V, which shows that they are


Table VIII. Sterilization of syringe according to needle usage*

Method Group 1 Group 2

Dry heat 22.2 24.8 Autoclave 17.3 1 .J Boiling 45.1 58.1 Antiseptic solution 7.4 12.0 Dipping in alcohol 1 .9 0.9 Alcohol and flaming 0.6 -

Prepacked sterile 5.6 0.9

“Group 1: dentists using one needle for one patient only (142 dentists); group 2: dentists using one needle for 5 or more patients (96 dentists). Figures are percentages of replies.

Tab/e IX. Methods of needle sterilization used by 135 dentists employing reusable needles for more than one patient

Method of sterilization

Use of method+ No. %

Details of method used

No. of dentists

Dry heat 36 21.4 Time less than 60 min 29 Temperature less than 7

160°C Autoclave 3 1 .B -

Boiling 98 58.3 Timing 24 Estimating time 65 Time/estimate less than 21

10 min Antiseptic solution 25 14.9 - Dipping in alcohol 4 2.4 - Alcohol and flaming 2 1 .2 - -

*Figures relate to methods not individuals so that the total (168) is greater than the number of dentists using such needles.

more likely to use one needle for a large number of patients, and less likely to use prepacked disposable needles.

Questions 13, 14 and 15 These relate to the manner in which the cartridge was treated and used. Very few dentists, O-9 per cent (-; 3.4; O-9) used any system other than the conventional cartridge and syringe. Fifty-four per cent placed cartridges in a special container from which they were taken as required. However, in only a few cases among these were the cartridges treated with antiseptic either before (10.2 per cent) or during (14.1 per cent) storage.

Questions 16, 17 and 18 Table VI shows the diversity of ‘sterilization’ techniques used. Disregarding the use of prepacked sterile needles, the commonest method of treating syringes and reusable needles was by boiling, and dry heat next. The most efficient method, autoclaving, was favoured by


relatively few. However, there had been an increase in the use of autoclaving (-; 9.4; 11.5) and dry heat (3.1; 22.3; 23.9) and a decline in the use of boiling water (91.0; 64.2; 54.3) over the period of the three surveys. In Table VII the methods of applying heat are further analysed to show the numbers failing to conform to acceptable standards (British Dental Association, 1974); for example, only 9.3 per cent boiled for 30 minutes or longer. The percentage of those adding extra instruments during the boiling period had declined (58.0; 45.5; 39.3). Of the 155 in the present survey who added extra instruments, only 20 timed the boiling and 5 of these did so for less than 10 minutes.

The distribution of methods of sterilizing syringes is not the same among the 142 dentists who used one needle for one patient as it is for the 96 who used one needle for 5 or more patients. Table WI shows the percentage of methods used in each group. A similar analysis showed that of those who used one needle for one patient, only 9.2 per cent boiled for less than 10 minutes (an ineffective period), whereas as many as 17.7 per cent of the 96 dentists using the same needle on 5 or more patients adopted similar unsatisfactory techniques. There is much greater disparity in the proportions of each group who used an autoclave.

It is of interest to consider separately the practice of the 135 dentists in the present survey who used the same needle for more than one patient. Table IX shows how they ‘resterilized their needles. Of those who boiled their needles, 21 (18.9 per cent) did so for less than 10 minutes; this contrasts with 14.7 per cent of all the dentists who boiled equipment (see Table VW).

As far as the cartridge is concerned, there seems to be a fairly even spread of preferred methods, if ‘prepacked sterile’ cartridges are excluded from consideration.

Table VI shows that only a small number flamed the cartridge, with or without alcohol, although only 1 per cent of dentists had neither a gas nor a spirit flame available. Further, 476 dentists (67.4 per cent) used cartridges which had rubber diaphragms covered by metal foil, somewhat more’suited to direct flaming than those with rubber only.

Question 19 The median number of years in practice of all the dentists in the survey was 15 (14; 17; 15). Fig. 3 relates the number of years in practice to the numbers using disposable needles, autoclaving syringes and using dry heat for 60 minutes at a temperature of 160 “C. There is a tendency for these methods, based on more recent knowledge or on only recently available equipment, to be used more by the younger than by the older practitioners.

Question 20 Table X indicates the distribution of dentists by the employing authority, type of practice and environment. The failure rate (74 per cent) in reply to the question on type of practice is extraordinary and invites speculation.

DISCUSSION

Comparison of the three surveys: Birmingham 1961, Birmingham 1969 and Manchester 1974 ‘The percentage responding to the questionnaires has declined successively over the period, from 52.6 to 49.6 to 38.2. This may reflect increasing resistance to form-filling or apprehension of the publicity associated with such self-evaluation, as noted by Prier (1973).


loa

I

??--, i i ; i

SO i

Fig. 3. Methods of sterilization as a function of years in practice. ??. . . * 0, All the dentists surveyed; ??-. -. ??; disposable needle users; e----e, autoclave users; ??-- 4, dry heat users (60 min at 160 “Cl.

Table X. Characteristics of practice

Employing authority No. Type of Practice No. Environment No.

Private NHS

Mixed Local authority Hospital School Forces Other No data

31 202

386 29 15 26

7 7 3

Conservative Extraction/

prosthetics Mixed No data

123 Urban 488 2 Rural 108

53 Mixed 42 528 No data 68

Although the total number of dentists on The Dentists Register has risen over the period (1961-1974), from c. 13 000 to c. 18 000, the number of patients injected per day per dentist has also increased slightly, from a mean of 12-l to 14-7. Thus the total number of patients injected each day has risen from c 150 000 to 250 000, i.e. 34.5 to 57.5 million in a working year of 46 5-day weeks. Allowing for the edentulous, it seems that the equivalent of the entire population must now be injected twice a year. Therefore the practices associated


Tab/e XI. Needle usage in Manchester and Birmingham surveys

Birmingham 1961

Birmingham 1969

Manchester 1974

Needle type: Prepacked sterile* _ 50.2 78.2

Reusable - 49 8 21.8

Reason: infection risk - 36.1 78.0 cost _ 29.1 11.4

Needle used for: 1 patient 7.0 i7.2) (4.9) 2-9 patients 59.0 (7.2) (4.9) lO+ patients 34.0 (35.1) (33.8) Median value 6.0 (6.0) (6.0)

??Prepacked needles were not generally available in 1961. Figures are percentages of positive replies. Figures in parentheses refer to re-users only.

with dental local analgesia have a significant, and increasing, potential role in the spread of transmissible disease.

There has been no appreciable change in the employing authority, type of practice or environment, for example, the percentage figures for private practice are 4-l ; 4.3; 4-4. An increase has taken place in the proportion of dentists who have been working for less than 5 years, from 12-O to 15.7 per cent, in line with the expansion in the dental student population. In all other respects, however, the samples of the dental profession involved in the three surveys may be regarded as comparable.

Table I shows that the gauge of needle most commonly used is 27, which confirms a trend seen in the two earlier surveys, and the preferred length is still 1% in. However, whereas in 1961 only 6.7 per cent of dentists used one needle per patient, this had risen to 48.6 per cent in 1974; in 1961 34 per cent of dentists injected more than 10 patients with one needle, but in 1974 the figure was down to 17-5 per cent.

In Table XI the data on the use of needles are compared. From this and from Tables II and III one may conclude that there has been an increased awareness of the risk of infection, a decrease in the importance attached to cost and, as a result, a considerable move towards the use of prepacked sterile needles. However, in respect of practitioners who inject with reusable needles, the number of patients per needle has not altered to any great extent, the median being 6 in each survey.

The fact that 99 per cent of practitioners in the most recent survey used the conventional cartridge and syringe compared with 96-6 per cent in the earlier survey is presumably the reason for there being no change in the proportion of dentists who aspirated before injections. Perhaps a related matter is the use of anaesthetic remaining after one injection for treatment of a subsequent patient. The preferred size of cartridge still seems to be greater than l-8 ml, some two-thirds of dentists using 2-2 ml in each survey. In 1961 as many as 54 per cent said that they re-used cartridges containing residual agent; in 1969 24.5 per cent of those using larger cartridges did so in order to use the residual agent for another patient; by the Manchester survey in 1974 this had dropped to 10 per cent. Table V shows the wide range of sterilizing techniques adopted by this small group of dentists. All these techniques


Tab/e X/l. Comparison of methods of sterilizing syringes and needles in the three surveys

Method Birmingham Birmingham

1961 1969 Manchester

1974

Dry heat 3,o 22.3 23.9 Boiling 91.0 64.2 54.3 Autoclaving - 9.4 11.5 Antiseptics 6.0 4.2 10.3 Dry heat for less 83.5 83.6 80.4

than 60 min ’ Dry heat at less 38.4 17.6 23.2

than 160 “C Boiling for less 34.0 14.6 14.6

than 10 min Boiling for more 15.0 12.1 37.4

than 20 min Boiling for 30 3.0 9.3

min or more Adding extra instruments 58.0 45.5 39.3

while boiling Boiling for more than 6.0 50.3

10 min without adding instruments

Figures given are percentages.

must be regarded as ineffective and their use is more likely to provide a route for transmission of infection from one patient to another. Similar conclusions may be drawn from Tables VIII and IX about other inefficient procedures.

In 1961 questions on methods of sterilization were not so searching as in 1974. The 1969 survey did not separate different items of equipment with respect to methods of sterilization so that only the overall results for treatment of syringes and reusable needles can be compared. Table XII gives data for the major methods of sterilization, showing a decline in the use of boiling and a rise in the use of dry heat and antiseptic solutions. There is evidence of an improvement in boiling procedures and there was an appreciable change in the times and temperatures used for sterilization by dry heat. The number of dentists adding extra instruments during boiling has declined but this remains a disturbing feature.

CONCLUSIONS The nature of the changes in the use of needles and analgesics and in the manner of sterilization revealed in these three surveys suggests a greater awareness of the possible microbiological hazards in the practice of local analgesia and a better understanding of the ways in which to minimize them. However, the wide diversity of methods employed for the disposal of used needles, and the continuing practice of treating additional patients with partly used cartridges underline the need for authoritative guidance to practitioners on the necessity and manner of rendering needles unusable and of discarding partly used cartridges. Such guidance should reinforce their social and legal responsibility (Health and Safety and Work etc. Act, 1974) to safeguard themselves and their staff against the hazards of transmissible disease, as well as the implementation of measures recommended for the well-being of the patient.


APPENDIX It may be of value at this point to reiterate recommendations made by the Dental Health Committee of the British Dental Association to the Representative Board in 1974 (British Dental Association, 1974):

1. A new disposable needle should be used for each patient requiring an injection. 2. A fresh cartridge should be used for each patient requiring a local anaesthetic. The

practice of retaining partly filled cartridges for use on other patients is condemned. 3. AU instruments used in the mouth should be sterilized in one of the following ways:

a. By autoclaving at 120 “C for 15 minutes. b. By exposure to dry heat at 160 “C for 1 hour. c. By continuously boiling in water (100 “C) for an uninterrupted 30 minutes; it must

be emphasized that this method should be regarded as the minimum for safety in destroying viruses. Practitioners should use an autoclave or dry heat sterilizer for their own safety and that of their staff and patients.

To the above may be added the recommendation for the sterilization of the cartridge diaphragm, i.e. direct flaming for 5 seconds (Lilley and Russell, 1975).

Acknowledgements The authors are grateful to Amalgamated Dental Co. Ltd for financial assistance to enable this survey to be carried out.

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use and misuse of equipment for dental local analgesia

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