July 1, 2001
by David Isen, BSc, DDS
In 1853, Pravex invented the syringe. Almost 150 years later, there have been few changes to the original design. In the early 1920s, Cook Laboratories added the ability for the syringe to accept a local anaesthetic cartridge and in the mid 1950s; the syringe was given the ability to aspirate.1 Over the past six years, the design of the syringe and the mode of local anaesthetic delivery has suddenly changed drastically with the advent of computer controlled injection devices. There are currently at least six different computer controlled injection devices available today, three in North America, one in Brazil and two in Japan. This paper will discuss the rationale behind computer controlled anaesthetic delivery and review the three available systems in North America.
The premise behind computer controlled injection devices is in part, that they can do what our hands cannot. That is, to deliver local anaesthetic at a constant rate despite the density of the tissue. In an area of dense or tight tissue like the palate or the anterior buccal fold, an injection of local anaesthetic is especially painful because there is little room for the local anaesthetic to expand the tissues. Decreasing the pain during these injections is difficult because in these tight tissues, if using a needle and syringe, the dentist must push harder in order to infuse the anaesthetic. The result of pushing harder, which is unavoidable, is to cause more pain. A study was done to measure the injection pressure created when a dentist pushes local anaesthetic through a standard needle and syringe into the oral tissues. Pressures were found to vary between 330-660 psi. The higher pressures were due to the dentist pushing harder and to the density of the tissues. The denser tissues resulted in an increased injection pressure.2 Increased injection pressures elicit more pain.
A computer can be programmed to push the local anaesthetic out at a constant rate despite the density of the tissues. That is, the computer does not have to push harder in areas of dense tissue in order to release the anaesthetic solution. Instead, the computer ejects the anaesthetic at the same rate whether injecting into the palate, an area of high resistance, or the maxillary posterior buccal fold, an area of low resistance where there is room for tissue expansion. This programmed rate is slow so that the tissues are expanded gently, possibly resulting in less pain. For example, The Wand will not allow the pressure of injection to increase above 400 psi3 and the Comfort Control Syringe releases local anaesthetic at approximately 200 psi. This theoretically will result in less pain during the injection. A study done by Gibson et al compared The Wand with the traditional needle and syringe where pediatric subjects were rated for their response to the injection. This study reported significantly less signs of pain, less movement and less crying during a palatal injection with The Wand vs. the traditional needle and syringe but found no significant differences during buccal injections.4 In a second study, dentists were injected in the palate with The Wand and with a traditional needle and syringe and asked to rate the pain of both injections. The subjects were blind as to which injection they were receiving. These dentists reported 2-3 times more pain with the traditional injection as compared to The Wand.5
General advantages of computer controlled injections include:
Possible decrease in pain during the injection. Especially in areas of dense, tight tissue.
Less effusion of local anaesthetic to areas away from the desired injection location due a slower injection rate. Some proponents of computer controlled injections theorize that this may result in more profound local anaesthesia and less post-operative pain.
These products may be practice builders. Patients may be interested and impressed with this technology.
The ability to do periodontal ligament injections without the worry of the increased pressure that is required to push the solution into the PDL space.
General disadvantages of computer controlled injections include:
Set up, breakdown and disinfecting time.
Because the injections are given slowly, the needle will remain in the tissue for a longer time. Anxious patients may have difficulty with this.
Some systems have disposable pieces that push the cost of use higher and require re-ordering.
In the mid 1990s, Milestone Scientific Inc. released the first computer controlled delivery system into the North American marketplace. The Wand (Fig. 1) met with great excitement in the dental profession and initial purchases were so brisk that dentists found themselves on a waiting list in order to purchase a machine. However because of a few glitches, the popularity of The Wand died down but to their credit, Milestone addressed the difficulties that dentists were encountering. As a result, they have improved their product, now called The Wand Plus.
The Wand Plus has three components; a table-top base unit, a foot pedal and a handpiece. The base unit is called a microprocessor and this is where the foot pedal and the local anaesthetic cartridge are attached. The microprocessor is a drive unit that recognizes signals from the foot pedal and as a result, it delivers the local anaesthetic by advancing a plunger into the anaesthetic cartridge. The local anaesthetic is pushed into a disposable tubing system and this connects to the handpiece and needle. Because the local anaesthetic cartridge is on the table-top machine and not in the handpiece, a standard dental needle cannot be used. There is no need for the cartridge perforating end of the needle and thus, a luer lock needle is required.
The system has two possible rates of local anaesthetic delivery both controlled from the foot pedal. The slow speed allows for a cartridge to be dispensed in four minutes and the fast speed will dispense a cartridge in about one minute. The manufacturers suggest that injections should begin with the slow speed to initially anaesthetize the tissues as painlessly as possible. Then at some point, when the operator decides that the tissues are properly anaesthetized, the pedal is depressed again and the machine will change to the fast speed of injection. It is also suggested that only the slow speed be used for PDL and palatal injections. Aspiration is also controlled from the foot pedal or it can be controlled from the base unit.
The tubing and the handpiece are disposable items to be used one per patient. The disposable cost is approximately $1.50. The Wand Plus retails for approximately $2,150.00 Canadian funds and can be purchased in Canada through Synca.
Advantages of this device include:
An extremely comfortable, light and easy to maneuver handpiece.
No vibration in the handpiece since it does not have a motor or electrical components in it.
A two-speed system with an initial slow speed for a less painful injection. The operator has the ability to change speeds anytime during the injection.
Because the local anaesthetic cartridge is not on the handpiece, the assistant can add another cartridge to the base unit while the needle remains in the patient’s mouth.
Disadvantages of this device include:
A comparatively long aspiration cycle that takes approximately five seconds. This however is a vast improvement since the old Wand system had a 14-second aspiration cycle.
The inability to use a full local anaesthetic cartridge. The tubing must initially be purged of air and this is done by running anaesthetic solution through the tubing. Some of the anaesthetic is lost in this process by being expressed out of the handpiece. As well, the tubing will never be completely emptied of anaesthetic. These two situations result in the loss of between 0.3-0.4 mls of local anaesthetic.
There is ongoing maintenance required. The plunger on the base unit has an o-ring on it that is part of the aspiration system. This o-ring must be lubricated on a regular basis to maintain the reliability of the aspiration. The Wand Plus has an audible signal to remind the owner when to carry out this lubrication.
The Wand is not compatible with standard needles. It requires luer lock needles.
The design of this product is such that the local anaesthetic cartridge is not inside the handpiece but on the counter-top microprocessor. Therefore it is not in the dentist’s line of sight during the injection. The dentist therefore would not know if this machine was actually injecting unless there was some signal to indicate that an injection was actually occurring. As a result, an audible beep has been programmed into the computer and this beep carries on throughout the course of the injection.
The second computer controlled device to be described is the Quicksleeper (Fig. 2). This machine was invented in France by Dr. Alain Villette in 1991. It is available in Canada through Quebec Dentaire. It is the only local anaesthetic delivery device that allows the ability to perform all intraoral local anaesthetic injection techniques. The extra feature that gives the Quicksleeper this ability is a built-in motor in the syringe/handpiece that renders the syringe both an injector and a perforator of bone. That is, the handpiece of the Quicksleeper has the ability to perform an intraosseous injection via a motor driven perforation of the cortical plate of bone. A standard dental needle that attaches to the syringe spins as the motor rotates the handpiece thus acting as a perforator.
The Quicksleeper is controlled by a double foot pedal. One pedal activates the rotation of the handpiece and this pedal is depressed if the operator wants to perform an intraosseous injection. The second pedal initiates the injection of the local anaesthetic. If a standard technique such as a block or infiltration is being used, only the injection pedal is pressed. The amount of anaesthetic desired is pre-chosen by pressing a button on the counter-top base of the machine. The operator can chose volumes of 1/4, 1/2, 3/4, or a full cartridge. Once the injection is initiated, the Quicksleeper begins injecting slowly and the injection speed gradually accelerates. This once again takes advantage of the initial slow injection being less painful. This initial slow speed can be bypassed by a double press of the foot pedal.
The Quicksleeper retails for $6,000.00 Canadian funds. The team working closely with this device suggest that this cost is offset by the fact that it can perform an intraosseous injection. An intraosseous injection allows for immediate local anaesthesia and it is therefore suggested that it is a boost to productivity. Immediately following the administration of local anaesthetic, the procedure can be commenced.
The following are advantages of the Quicksleeper:
This device has a motor driven ability to perforate the cortical plate of bone and thus perform an intraosseous injection.
It is compatible with standard dental needles.
There are no disposable components and therefore there is no ongoing cost.
There is an initial slow speed that automatically accelerates for a possible less painful injection.
The following are disadvantages of the Quicksleeper:
The handpiece is relatively heavy weighing 240 g. as compared to a standard syringe that weighs 80 g. This weight may be difficult for a small-handed dentist to control.
The Quicksleeper is the most expensive of the three devices.
The operator cannot control when the injection speed increases.
THE COMFORT CONTROL SYRINGE
The final device to be discussed was released in February 2001 by Dentsply — Midwest. It is called the Comfort Control Syringe or CCS (Fig. 3). In the early 1990s, Dr. Mark Smith, a dentist from London, ON, invented a device that he incorporated into his practice as the sole local anaesthetic delivery method. After perfecting the system, he released the rights of this device to Dentsply.
This system differs from the other two in that there are no foot pedals. Instead, there are two components, a base unit that can be wall mounted or table-top and a syringe. Many of the functions of the computer can be controlled directly from the syringe during the injection process. The base unit allows the dentist to program one of five different injections by pressing a single button. The five buttons marked on the base unit are block, infiltration, PDL, intraosseous and palatal. Each of these injections has a specific corresponding rate of local anaesthetic delivery associated with it. For example, the rate of injection for an infiltration (the fastest injection) is 0.017 ml/sec, which corresponds to the delivery of one cartridge in 80 seconds. This compares to the rate for the palatal injection (the slowest injection) that is set at 0.008 ml/sec, which allows for the delivery of one cartridge in 4 minutes. If at any point in the injection process the dentist decides that he/she wants to speed up the process, a double rate button can be pushed on the syringe and the injection will take half the amount of time.
Once the injection technique is decided upon, and the appropriate button has been pressed, the device is ready to inject. There are three buttons on the syringe that control the remainder of the injection process. The first button is the start/stop button, the next button is the aspiration function and the last button is the double rate function. Once the start button is pressed, the injection begins at a preprogrammed, slow speed for 10 seconds. That is, despite the type of injection chosen by the operator, the computer will always begin the process with an extremely slow 10-second injection. This will theoretically anaesthetize the tissues in as painless a manner as possible and once this 10 second phase has elapsed, the computer will automatically change speeds to the rate of injection previously chosen by the operator.
The base unit has three digital readouts that provide the dentist with feedback during the injection. These displays show the rate of injection (chosen by the operator), time elapsed during the injection, and the cumulative volume injected. The volume reading is important during injections such and the PDL injection where the dentist may wish to give a precise amount per root or simply for charting purposes.
There is a disposable component with the CCS. It is a clear plastic cartridge sheath that attaches the cartridge to the syringe. This cannot be sterilized and therefore one is used per patient. They cost approximately 30 cents each. The CCS itself retails for $1,300-1,400 Canadian funds.
The following are advantages of the CCS:
A wide range of injection speeds, controlled by the operator.
An initial, extremely slow rate, 10 second injection to possibly decrease the pain associated with tissue expansion.
The ability to control the computer directly from the syringe thus eliminating the need for a foot pedal.
A digital readout showing the volume injected.
The CCS is compatible with standard dental needles.
The CCS is the least expensive of the above three products.
Disadvantages of the CCS include:
Due to the fact that the CCS can be controlled by hand, the syringe must contain a certain amount of electronic equipment and this adds bulk to its’ circumference. A dentist with a very small hand may have difficulty negotiating the buttons due to the increased circumference of the syringe. The circumference of the CCS syringe is 112mm compared to 36mm for a traditional syringe, and 17mm for The Wand.
Because of the electronics in the syringe, the operator will feel a slight amount of vibration in the syringe while the injection occurs. This will not affect the anaesthesia but it certainly is a feeling that is different from the traditional syringe or The Wand which both have no such vibration. The vibration in the Quicksleeper is very minimal.
It takes some practice for the dentist to get used to maneuvering their fingers to press the buttons on the syringe.
With the increasing number of computer controlled local anaesthetic delivery systems available, one has to wonder if these devices are the wave of the future. More research is certainly required before we can scientifically say that these machines deliver a less painful injection however common sense suggests that a slow injection is less painful. Those in the industry who have invented, sold and based their entire practices around such devices are firm believers that a computer controlled injection is less painful than a standard needle and syringe injection and many also suggest that less volume of local anaesthetic is required for what results in more profound anaesthesia. Once again, these suggestions require scientific study. Which device to choose is purely the choice of the operator. Each has their own set of “bells and whistles” and they each have a unique feel to them. With the descriptions listed above, the dentist in the market for one of these machines can begin to decide if there is a place for this technology in their practice.
Dr. Isen maintains a private practice in Toronto.
Oral Health welcomes this original article.
1.Jastak JT, Yagiela JA, Donaldson D, Local Anesthesia of the Oral Cavity. W.B. Saunders Co. Toronto, 1995.
2.Pashley EL, Nelson R, Pashley DH, Pressures created by dental injections. J Dent Res 1981;60:1742-1748.
3.Froum SJ, Tarnow D, Caiazzo A, Hochman MN, Histologic response to intraligament injections using a computerized local anesthetic delivery system. A pilot study in mini-swine. J Perio Sept 2000, 1453-1459.
4.Gibson RS, Allen K, Hutfless S, Beiraghi S, The Wand vs. traditional injection: a comparison of pain related behaviors. Ped Dent 22(6):458-62, Nov-Dec 2000.
5.Hochman M, Chiarello D, Hochman CB Lopatkin R, Pergola S, Computerized local anesthetic delivery vs. traditional syringe technique. New York State Dental J 63(7): 24-9, Aug-Sept 1997.
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