Comparison among different systems of electronic injection.

Transcription

1 Pain and anesthesia Comparison among different systems of electronic injection. A. Villette professional training evaluation 1 The greater the interior diameter of the needle, the less painful the injection? 2 Palatal anesthesia is always painful 3 The injection speed is the only element that generates pain 4 A surface anesthesia is essential in order to realise a painless infiltration in the attached mucosa 5 The position of the bevel of the needle does not have any importance in the appearance of pain. False D True D 6 A needle having a 45 angle to the surface of the mucosa will allow its painless penetration For about the past ten years, different electronically controlled systems have appeared on the market that claim to diminish the pain during the different injections performed in dentistry. The objective is to improve the anesthesia practice, reduce the level of stress and especially the patient s level of apprehension. The arguments set forth to validate these new materials gather, every which way, the control of the pressure, of the flow (2,3), the speed of injection, the control of the position and penetration of the needle, the needle with a greater bore to decrease the pain from the injection. All these arguments are presented as determining and well-controlled factors. However, no serious study allows certifying that such and such parameter is effectively controlled and contributes to the improvement of the result, and to what extent. The answers to these questions are available on the ID internet site: L'INFORMATION DENTAIRE n

2 SCIENTIFIC & CLINICAL Equipment and methods The study on the technical characteristics and ergonomics of different assisted injection systems for oral anesthesias must allow the determination of those that are the most likely to respond to the practitioners' and patients need for comfort. We expect to study the different systems which make it possible to perform these assisted injections and to compare the technical characteristics stated in the presentation files delivered with these systems. i There are 5 devices that were studied: a Japanese device called Anaeject imported by Septodont (fig.1) two American devices, the Wand from the Milestone company, formerly imported by Henry Schein (fig. 2) the CCS from the Dentsply company, which is not marketed in Europe (fig. 3). two French devices, the Sleeperone and the Quicksleeper, both from the Dental hi tec We discover in these 5 injection systems the presence, or not, of 3 factors company (fig 4a and 4b).. which can contribute to the control of the painful factors when performing All the devices studied authorise an assisted the injection: injection. We will further discuss the fact that it could controlling by spinning the orientation of the needle bevel, be controlled by a micro controller and not by a the possibility of pen grip with the foot control, micro processor as certain advertisements suggest. the acceleration of the progressive injection. Results Anaeject: allows the positioning of the needle while spinning, has an injection that progressively accelerates and can be stopped at any moment. It doesn t require any other consumables but the needle and the cartridge. On the other hand, it does not at all make the pen grip at all possible, it is not equipped with a foot control. We have added to these criteria the fact that the additional consumables are necessary, or not, which contributes to the cost of the anesthesia. The Sleeperone and Quicksleeper devices allow the spinning of the needle, the pen grip, they have a foot control and a progressive acceleration. They do not require additional consumables. The Wand: allows the needle positioning by spinning and the pen grip, it is equipped with a foot control. On the other hand, it has no progressive acceleration and requires additional consumables besides the needle and the cartridge. Summary table of the results Control of the needle bevel (spinning) Foot control Pen grip Gradual acceleration of the injection progressive No consumables The CCS: does not allow the positioning by spinning of the needle bevel, nor the pen grip (three different device contacts on the handpiece), it does not have a foot control. No progressive acceleration and requires consumables besides the needle and the cartridge. 974 L'INFORMATION DENTAIRE n

3 Discussion Starting from having an anesthesia done by a classical manual syringe, using a cartridge and a 40-hundredths 16 mm needle which has a normal wall (0.095 mm thick), we could emphasize the parameters involved in an injection. We are studying their involvement in decreasing pain. Control of the pressure and the injection speed. The injection is done by using the set of elements presented in Photo no. 5. An anesthetic injection consists of the transfer of a liquid contained in a glass cartridge, through a needle, in a living tissue that varies in density. The conditions of this transfer meet the rules of the fluid mechanics. There are two rules that are imposed on us: - the liquids are incompressible. - the liquids integrally transfer pressures. It is compulsory to use the rubber piston (or an assimilated material) of the cartridge, as an intermediary, when making an injection. This rubber piston is the only deformable element. It is elastic, in the mechanical sense of the term, meaning it takes back its initial shape after the constraints to which it is subject have disappeared. It is the only elastic element of the injection system (fig. 6). We will disregard the elasticity of the practitioner s palm, since we are studying systems where it does not contribute to the injection. The liquid (incompressible) takes its place inside a tissue, derived from elements that can be either displaced or deformed. This is the case of the palatal mucosa that whitens upon injection (liquid displacement). The anesthetic takes its place by pushing back cumulatively, first the vascular liquids (whitening), then the extra- and intra-cellular liquids, which leads to a potential distress of the tissue. This is the case for the free mucosa that inflates, taking the shape of a blister (tissue deformation). In the case where the liquid is injected in a particularly defensible loose cellulous tissue that does not offer any significant resistance (R close to 0, the deformation of the piston of the cartridge is also close to 0), we can consider that controlling the speed of the injection piston will also make it possible to control the flow (the flow is defined as the liquid quantity injected within a time unit). We must always place the flow below the pain threshold, i.e. 1 ml/minute (1,3). In the case of injection made in a dense tissue, resistant to injection, R increases. It is now that we consider the notion of pressure. The pressure is defined as the force to be exerted on the syringe piston, in reference to the surface of the cartridge piston. This pressure is directly proportional to the resistance offered by the tissue when being penetrated by the liquid. The pressure compresses the rubber piston till it transfers the necessary force to the liquid, in order to penetrate in the tissue. If the resistance is constant for a constant speed, then the flow will be constant. If resistance is not constant, the flow will depend upon the elasticity of the rubber piston, which will compress or slacken based on the resistance of the tissue. From this observation, we can assert that no system can claim to control the injection speed and pressure in a tissue offering resistance. Low resistance Strong resistance L'INFORMATION DENTAIRE n

4 SCIENTIFIC & CLINICAL No system whatsoever can claim to control the advance speed of the syringe piston. Thus we cannot talk about controlled systems, but about electronically assisted systems. As far as the arguments of enlarged bore needles are concerned (having the same exterior diameter, 0.08 mm thickness of the wall instead of 0.09 mm) which decrease the pain upon injection, their use in loose cellulous tissue would not serve any purpose, since the tissue will not suffer due to a more or less variable flow (deformation). On the other hand, in a dense tissue offering a resistance, the very same needle, for the same injection speed will have a greater flow inside the tissue than a needle with a normal bore, which will increase the flow, thus the pressure and consequently the pain. We see only that the purpose achieved is contrary to the purpose sought (fig. 7). In summary, we will say that the injection speed has to be inversely proportional to the resistance of the tissue. If in a loose tissue the speed can be constant and quick from the very beginning of the injection, in a dense tissue, the injection will have to be very slow in the beginning and progressively increase. In both cases, the maximum speed will remain under the pain threshold. This is why a good system must have an acceleration of the injection and allow this to be stopped, then start again at a slower speed. Needle orientation In the literature, concerning the positioning of the bevel, for Hayashihara (2), an orientation of the bevel is required, for Machtou (3), the needle is oriented parallel to the surface of the mucosa. The other authors don t speak about this. It is known that the penetration of the bevel, no matter its position, is painless in a loose cellulous tissue. 7. Diagram injection speed 8. After surface anesthesia, penetration of the needle and compression of the mucosa with a cotton bud. On the other hand in an attached mucosa, it is said and written that the penetration (especially of the palatal mucosa) is unavoidably painful (1). For many patients, palatal anesthesia is very traumatic (4). Therefore, we will have a surface anesthesia before penetration of the needle and compression of the mucosa with a cotton bud during penetration. (1.3.4) (fig.8) A study of a needle shows that the working extremity is formed by a tube cut by a plan (fig. 9). The angle formed by this plan and the axis of the needle is generally between 12 and 14. If the needle is u sed as in Photo no. 8, we will have to make it penetrate more than 1 mm before injecting. This will generate the pain which we systematically encounter in the case of injection in an attached mucosa. If, on the other hand, the bevel is flatly positioned (fig. 10), so that it penetrates only the superficial layers of the mucosa (which are the non-innerved scaling layers), this angle allows an immediate injection. To achieve this result, we have to perfectly control three elements: the positioning of the bevel on the needle axis (its spinning), the angulation of this bevel against the mucosa (position of the syringe against the mucosa), the penetration of the needle into the mucosa (the "entrance" of the needle by several tenths of millimetres ). Pen grip Controlling these three elements is possible if the system enables: spinning the needle on its axis (rotational positioning), Flow = speed x surface Different flow Identical injection speed Surface 2 Surface L'INFORMATION DENTAIRE n

5 a grip that allows an easy appreciation of the angle formed by the needle and the mucosa, using support points (the only specific means making it possible to control the penetration of the needle). From now on, we should note that the placement of the support points must be close to the working point, like for example holding a turbine handpiece to prepare a tooth. This catch is called pen grip and requires a foot control. Conclusion From this study, we can conclude that: no system can claim to control neither the flow nor the pressure upon injection in a dense tissue since each cartridge has a deformable piston. anesthesia in an attached mucosa, universally considered painful, can, in the absence of surface anesthesia, be painless if the ergonomics of the device used enables a perfect control of the positioning of the bevel and the penetration of the needle, and the injection needing to be smooth and progressive, enlarged bore needles have no clinical justification. If we take into account these parameters, then we can have a painless anesthesia in an attached mucosa. Now it seems obvious that electronically assisted devices are an asset in our practice but also that their ergonomics contributes to decreasing pain. The practitioner s dexterity does the rest. Bibliography 1. Gaudy J F, Arreto CD, Alimi D., Brulê S, Donnadieu S, Landru MM. Manuel d'analgésie en odontostomatologie, 2nd edition, Paris, 2005, Masson. 2. Hayashihara H. Application clinique d'anaeject : Comparaison des systèmes d'injection électroniques. Le Chirurgien- Dentiste de France, numero 1237/1238 : 53-59,15 december Machtou P, Bronnec F. Anesthésie palatine alraumatique. Information dentaire, Vol. 87 (4l): Malamed SF. Handbook of local anesthesia, ed 5, St Louis, 2005, Mosby. 5. Palm A M, Kirkegaard II, Poulsen S, The Wand versus traditional injection for mandibular nerve block in children and adolescents: perceived pain and time of onset, Pediatric Dentistry ; 26 (6) : , The working end of a needle is formed by a tube cut by a plan, whose angle with the axis of the needle is generally between 12 and Bevel in a flat position to penetrate only the superficial layers of the mucosa. Author's address Dr Alain Villette 66. avenue des Marronniers F Cholet L'INFORMATION DENTAIRE n