In health care dentists are often referred to as the local anaesthesia experts as we provide localized anaesthesia as an integral part of what is performed daily. When thinking of going to the dentist, this is the one aspect that most patients dread and often what prevents patients from seeking treatment.
Local anaesthesia as it pertains to dental treatment can be divided into two areas: administration and depth/duration. Both of these areas influence the patient experience and most patients would indicate that their area of fear and anxiety relates more to the administration part of the experience then how profound the anaesthesia is. Many patients experience stress just at the thought of being “stuck” by the needle and will delay treatment or avoid it until tooth pain outweighs the perceived pain caused by injection of the needle. Treatment of pediatric patients can be more of a challenge than apprehensive adults. If the application of local anaesthetic starts the appointment off with patient emotions related to a painful injection, the rest of the appointment just gets worse and becomes a pediatric management situation.
As the “local anaesthesia experts” we can, with an understanding of pain conduction and modification of technique, greatly improve the dental treatment experience for the patient. This article will provide an overview of how pain is transmitted, methods to make local anaesthetic administration a more pleasant experience, and a brief overview on anaesthetic s used and their selection influencing anaesthetic duration and depth.
Single Tooth Anaesthesia (STA) — The Wand
Providing local anaesthesia in some patients can be a challenge especially in the mandibular arch. Successful anaesthesia by infiltration is difficult to achieve in the mandible due to the denser nature of the bone compared to the more vascular, less dense maxilla. This leads to issues when relying on block anaesthetic techniques and may not provide adequate anaesthesia for some procedures.
Alternative techniques have been available to supplement the standard injection techniques which include periodontal injections and intraosseous application of anaesthetic. Periodontal injections (PDL) can be a challenge as they can not be readily administered with a standard anaesthetic syringe due to the pressure required to place the anaesthetic in the periodontal ligament space. Special syringes have been developed that increase the leverage thereby increasing the amount of pressure exiting the needle with less effort on the part of the practitioner. But these still are not easy to routinely use.
With these issues in mind, a computerized anaesthesia device was introduced approximately 20 years ago. The Wand (Aseptico Inc., Seattle, WA, USA) was introduced and more recently, an advanced version, the STA was offered (Fig. 1). The STA Single Tooth Anaesthesia System® Unit has several advantages over the traditional syringe and PDL syringes. It provides Dynamic Pressure Sensing (DPS™) Technology, allowing metered flow of anaesthetic and sensing of the PDL space so that needle position is maintained throughout the procedure. The needle and “wand” design provides a thin ergodynamic portion that is used intraorally. The STA may be used with other anaesthesia techniques such as blocks, infiltrations and palatal injections and is not limited to PDL injections. The unit provides slow metered fluid administration and has needles available in 30 gauge, ½ inch length (for PDL and palatal injections), 30 gauge, 1 inch (infiltrations, PDL and palatal) and 27 gauge, 1¼ inch (for blocks and infiltrations) (Fig. 2). Each needle and attached tubing assembly is single patient use and should be disposed of via a sharps container when treatment is completed.
The STA-Intraligamentary injection can anesthetize a single tooth comfortably, safely, and predictably providing better comfort not only for the tooth being treated and eliminating the anaesthetic effects that bother patients, namely a numb tongue and cheek (Fig. 3). From the author’s experience, this has helped with apprehensive patients and those who dread the lingering anaesthetic effects that typically last for hours after dental care. The literature has reported that patient comfort was improved when the STA Single Tooth Anaesthesia System® Unit was used to administer anaesthetic in adult patients.1,2
How and Why of dental pain conduction
In 1965, Canadian psychologist Ronald Melzack and British physiologist Patrick Wall, described the gate control theory of nerve conduction. Their paper, “Pain Mechanisms: A New Theory”, (Science: 150, 171-179, 1965) was described as “the most influential ever written in the field of pain.” They suggested a gating mechanism within the dorsal horn of the spinal cord that closed in response to normal stimulation of the fast conducting “touch” nerve fibres, but opened when the slow conducting “pain” fibres transmitted a high volume and intensity of sensory signals. They went further to state that the gate could be closed again if these signals were countered by renewed stimulation of the large fibres. Based on the stimuli, this can either permit a pain sensation to travel up the spinothalamic tract to the brain or block those signals from being perceived as pain.
The sensation of pain is conducted slowly along thin, unmyelinated, C nerve fibres traveling at about two meters per second. Whereas, an impulse such as a vibration is conducted rapidly along thick, myelinated, A beta nerve fibres at a rate of 75 meters per second. When these two sensations occur at the same time, the sensation of vibration reaches the sensory area of the brain first, causing a release of inhibitory interneurons which prevents the activation of projection neurons in the dorsal horn of the spinal cord, resulting in a closure of the gate and the sensation of pain is blocked (Fig. 4).
The vibrations stimulate mechanoreceptors (Pacinian corpuscles) and primary endings in the muscle spindle.3,4 This is contributed to Meissner’s corpuscles in the skin and mucous membranes.5 Some have suggested that the larger fibres within the area directly affected when stimulated achieve maximum pain reduction.6 The neural gate responsible for this lies within the dorsal horn of the spinal cord and inhibits the transmission of pain to the higher centres of the brain. This provides a basis to explain why after bumping your hand, rubbing it reduces and sometimes negates the pain sensation as long as the stimuli of rubbing is ongoing.
Utilization of this theory has importance in the oral cavity due to its higher sensitivity where more than a third of the somatosensory cortex cells in the brain are devoted to sensory input from the mouth.7 Vibration stimuli are easily applied in the orofacial area and have been used to raise the threshold of pain from pulpal, periodontal and post surgical origins.8,9 It has also been suggested that when light-to-moderate pressure is combined with the vibration stimulation of the underlying bone improves pain tolerance during stimuli application.10 Previously, the use of vibration stimuli with regard to local anaesthetic administration has focused on vibrating of the needle or vibrating a cotton swab applied to the site for topical relief. Nanitsos et al., reported in a study investigating pain associated with local anaesthetic oral administration found that vibration applied during injection decreased the pain perceived.
From a more simplistic standpoint we can think of the nerve as a single lane road, only one car can drive up the road at a time. If a sensation is traveling up the “road” it is like a line of cars driving bumper-to-bumper not allowing any car to merge from a side road. When a sensation, such as the feel of the needle piercing the tissue occurs, when a stronger stimulus is occurring, this pain sensation is unable to merge and therefore the brain doesn’t perceive it as intensely or at all in some cases when a stimulus has been applied prior to the needle.
But what sensation works the best at blocking that pain conduction? The brain is continually bombarded with stimuli and as a protection mechanism to help filter out some of the noxious stimuli, the brain quickly adapts to constant stimuli. We have all walked into a room to smell an offensive odor, only to find that we do not notice that odor after a few minutes. If the brain didn’t filter out constant stimuli then we would be constantly stimulated after dressing with the clothing rubbing the skin. This relates to the vibration stimulus and the gating theory of nerve conduction. If a constant vibration would be applied the brain would quickly adapt and the patient would sense the introduction of the needle through the mucosal tissue. By varying the vibration, with pulsations in a non-uniform manner the brain is not able to adapt to it and it continues to block the pain transmission during the injection process.
The DentalVibe® is a cordless rechargeable lightweight handheld device designed to aid in improving the local anaesthetic experience (Fig. 5). A latex-free disposable tip attaches to the end of the unit, illuminating the area to be injected and when activated provides oscillating vibration to the terminal fork (Fig. 6). The tip serves an additional purpose, allowing retraction of tissue to improve visibility to the area to be injected. The tips are designed for single patient use and should not be autoclaved or cold-sterilized as this alters the material making them ineffective to conduct the vibrations. Tips are available in both a pediatric (short) and adult (long) configuration and selection depends on patient oral cavity size and accessibility (Fig. 7).
The device provides pulsed percussive micro-oscillations at the terminal tips of the disposable end. These vibrations use a proprietary VibraPulse® technology gently stimulating the sensory receptors at the site to be injected, effectively closing the neural pain gate. As discussed, varying the vibration prevents the brain from adapting to the stimuli and allows the vibration to block the pain sensation.
Pressure makes great diamonds but the wrong amount can affect the gating effect of the vibrations. With this in mind, the unit was designed with a voltage regulated power supply which is capable of boosting power to the tip when excess pressure is made on the site, which may occur when retracting and the patient is resisting the process by tensing the cheek. Additionally, the tip was specifically designed with a pressure sensing feature which shuts the unit off if excessive force is applied during use. So how much pressure should be applied? The author recommends placing sufficient pressure on the bony structure in the site to be injected that the practitioner can feel the bony landmark but not enough to stop the tip from vibrating.
The DentalVibe® can be utilized with any injection technique including; the inferior alveolar nerve block (Fig. 8), the mental block (Fig. 9), palatal injections (Fig. 10) and maxillary paraperiosteal injections (Fig. 11). This device can be utilized with a topical anaesthetic if desired and also in combination with ancillary devices such as the CompuDent and STA anaesthesia systems (Milestone Scientific, Livingston, NJ) if chosen by the practitioner. The combination of which can cut anaesthetic delivery time in half.
Tips on utilization for the DentalVibe®:
1. Demonstrate to the patient what the vibrating tip will feel like by contacting the tip to their finger. This is especially recommended for pediatric patients and avoids startling the patient when the tip is inserted intraorally.
2. Activate the tip and place on the injection site maintaining contact with the soft tissue. The tip is also used to retract the cheek or tongue aiding in visualization. For the mandibular block (IAN), contact with the medial aspect of the mandible is imperative.
3. Maintain light to moderate pressure for five seconds prior to insertion of the needle into the mucosa.
4. Insert the anaesthetic needle into the soft tissue between the two prongs (as close to one of the two prongs as possible) using a standard anaesthetic technique while maintaining pressure and vibration with the DentalVibe® tip.
5. Withdraw the needle from the soft tissue after administration of the anaesthetic, keeping the DentalVibe® tip on the site with pressure and vibration.
6. Continue to apply pressure and vibration to the site for five seconds.
A misconception exists with regard to needle gauge among practitioners, that the smaller the gauge the less the patient feels the needle. Yet clinical studies have demonstrated that there is no difference in perceived pain between 30-gauge (smaller gauge), 27-gauge (medium gauge) and 25-gauge (larger gauge) needles.11-15 Injections in the oral cavity place the tip of the needle in close proximity to blood vessels and thus it is important that aspiration be performed prior to administration of the local anaesthetic to lessen the chance of injecting into a vessel. Larger gauge needles permit more accurate aspiration than smaller gauge needles, as more pressure is required to withdraw fluid back through the smaller gauge needle than is required for a larger gauge needle.16,17 Additionally, as gauge decreases, the needle is more likely to deflect during insertion resulting in inaccurate injections or potentially break upon injection.18 Use of a smaller gauge needle requires more pressure to express the solution from the needle. Thus, creating a fast-moving stream of anaesthetic , which may cause some hydrostatic damage during injection. This may result in more pain during anaesthetic administration than would result from using a larger gauge needle even with injecting a greater volume of anaesthetic .19
Thus, it is recommended that use of a 27-gauge needle meets the best of all worlds, allowing positive aspiration, less chance of needle deflection, increased strength so lower potential for breakage and provides comfort to the patient.
Local anaesthetic agents:
Lidocaine (e.g. Xylocaine, Octocaine)
Lidocaine an amide anaesthetic agent was first introduced in 1948, exhibiting twice the potency of procaine the common local anaesthetic agent at the time and half the toxicity. It produced a greater depth of anaesthesia with a longer duration than comparable volumes of procaine.
Available in 4 formulations: a two percent solution without vasoconstrictor (plain), a two percent solution with 1:200,000 epinephrine (a vasoconstrictor), a two percent solution with 1:100,000 epinephrine (a vasoconstrictor), and a two percent solution with 1:50,000 epinephrine. Only the formulations with 1:100,000 and 1:50,000 epinephrine are available for dentistry in Canada. Formulations with the vasoconstrictor epinephrine have a pulpal anaesthetic duration of one to one and a half hours, and a soft-tissue range of three to five hours. The 1:50,000 epinephrine formulation may be advantageous for hemostasis in surgical sites but has no significant advantage for duration of pulpal anaesthesia. There are no differences between the 1:200,000 and 1:100,000 formulations but a greater safety factor toxicity wise is present when using the 1:200,000 formulation.
Mepivacaine (e.g. Carbocaine, Polocaine)
Introduced in 1960, a two-percent solution of mepivacaine has the same potency and toxicity ratings equivalent to a two-percent solution of lidocaine. The greatest advantage of mepivacaine is its decreased vasodilating property than lidocaine and can be used reliably as a non-vasoconstrictor-containing solution for procedures of short duration. Mepivacaine is available on the U.S. market as either a three-percent plain solution (no vasoconstrictor) or as a two-percent solution with 1:20,000 levonordefrin (a vasoconstrictor also provided under the name Neo-Cobefrin). The plain solution has a pulpal anaesthetic duration of 20-40 minutes with a soft tissue duration of two to three hours. The vasoconstrictor-containing solution has a pulpal duration equivalent to that of Lidocaine with vasoconstrictor (1-1.5 hours) and a soft-tissue duration of three to five hours.
As levonordefrin vasoconstrictor in mepivacaine is less likely to produce cardiac side effects, such as palpitations, than epinephrine on a mcg-to-mcg basis, it may be the anaesthetic to select in those patients with severe cardiac issues or sensitivity to epinephrine. Care should be taken as it is more likely to increase blood pressure and so may not be the anaesthetic to use in patients with severe hypertension it also has a higher potential for interaction with tricyclic antidepressants such as amitrityline hydrochloride.
Bupivacaine (e.g. Marcaine)
Released in the United States in 1983, bupivacaine is an analogue of mepivacaine that exhibits a fourfold increase in potency and toxicity and a remarkable increase in the duration of anaesthesia. It is available only as a 0.5 percent solution with 1:200,000 epinephrine. Bupivacaine may exhibit a slightly slower onset time in some patients, taking approximately six to ten minutes compared with two to seven minutes for lidocaine or mepivacaine. The longer duration of anaesthesia for bupivacaine is achieved primarily via regional nerve block injection techniques with mandibular blocks frequently having greater duration than maxillary blocks. When used as a block, pulpal durations of one to seven hours are common with soft-tissue anaesthesia of five to twelve hours making this very suitable as an adjunct in patients undergoing surgery to provide long-duration anaesthesia. When administered via infiltration technique, bupivacaine provides anaesthetic depth and duration comparable to other local anaesthetic agents.
Prilocaine (e.g. Citanest)
Prilocaine, also first introduced in 1960, is slightly less potent but considerably less toxic than lidocaine as a local anaesthetic agent. As with mepivacaine, prilocaine produces le
ss tissue vasodilation than lidocaine and may be used in a plain solution form for short-duration procedures. Prilocaine is available as a four-percent plain solution (no vasoconstrictor) or with 1:200,000 epinephrine in a four-percent anaesthetic solution. The plain solution has a pulpal duration of 40-60 minutes with soft-tissue anaesthesia for two to three hours. The duration of anaesthesia with plain prilocaine is more dependent upon the type of injection given than noted with other anaesthetic s. Infiltration injections of prilocaine plain may only provide five to ten minutes of pulpal anaesthesia and may not be suitable for most procedures that will take more then a few minutes. Yet when used as a block injection it typically provides 40-60 minutes of anaesthetic duration suitable to many dental procedures. Whereas, the vasoconstrictor-containing version of prilocaine provides pulpal anaesthesia for one to one and a half hours with durations similar to lidocaine and mepivacaine with a potentially longer soft-tissue duration of three to eight hours.
Prilocaine, it has been noted by some practitioners, has a greater efficacy in patients who are difficult to anesthetize, such as those patients with a past or present history of substance abuse. An additional advantage is a decrease in cardiac side effects due to the lower vasoconstrictor concentration. Relative contraindications for prilocaine include a patient history of methemoglobinemia, anemia, cardiac or respiratory failure due to hypoxia. A precaution has been raised by reports of an increased risk of nerve paresthesia with the use of prilocaine and articaine, particularly for inferior alveolar and lingual nerve block injections which appears related to the higher concentration of anaesthetic (a four-percent solution compared to the two-percent solution found with other anaesthetics) more so then the particular anaesthetic itself. Additionally, since the concentration is twice as strong as two percent solution, half the total amount of anaesthetic can be administered safely and care should be given in pediatric patients as the safe amount which is based on the patient’s body weight can be very low.
Articaine (e.g. Septocaine, Articadent)
Articaine an analogue of prilocaine in which the benzene ring moiety found in all other amide local anaesthetics has been replaced with a thiophene ring. Although not released in the United States until April 2000, articaine has been available in Germany since 1976 and in Canada since 1983 in a number of formulations. Initially, one formulation was approved in the United States, a four percent solution with 1:100,000 epinephrine, today a 1:200,000 epinephrine formulation is also available. Pulpal anaesthesia duration of approximately one hour with soft-tissue anaesthesia for two to four hours is typically observed. Articaine has a slightly faster onset of action (1.4 to 3.6 minutes), reports of a longer and perhaps more profound level of anaesthesia have been reported in general. With a greater ability to diffuse through tissues, articaine has become a very widely used anaesthetic in the European, USA and Canadian markets. The tissue diffusion characteristics of articaine are not well understood. In a percentage of patients, an injection into the buccal maxillary vestibule results in adequate palatal anaesthesia for tooth extraction. Similar results have been claimed for the mandibular anterior and premolar teeth with buccal infiltrations. As discussed with prilocaine, reports of a significantly increased risk of nerve paresthesia with the use of these four-percent anaesthetic solutions particularly for inferior alveolar and lingual nerve block injections, warrants practitioner caution in the use of these anaesthetic agents.
Infected sites that are to receive dental treatment are a particular challenge in achieving adequate local anaesthesia. As the tissue pH becomes more acidic as seen in areas of infection local anaesthetics are converted to a non-usable form at the site thus requiring greater volumes of anaesthetic and increasing safety issues. Articaine has been reported by the author as well as others providing better more profound anaesthesia in infected areas that will undergo either extraction or endodontics.
A good adjunct to assist in local anaesthetic , a topical anaesthetic is placed over the site to be injected and allowed to take effect for two to three minutes prior to injection. Topical anaesthetic s are available in either a liquid or gel form with the gel form being easier to keep in the intended location while awaiting its affects. There are several negatives to use of topical anaesthetic . Penetration is usually only about 3 mm so it will assist in the initial “pinch” of the needle but the patient may feel the needle as it moves deeper into the site to deposit the anaesthetic . Taste and general spread of the topical action may be a hindrance in pediatric cases or to those adults that object to their entire mouth feeling numb. Topicals available are usually lidocaine, benzocaine or triple anaesthetic s which contain benzocaine combined with tetracaine, prilocaine or other topical anaesthetic agents.
Recently, topical anaesthetic s have been formulated as varnishes allowing application to the area without spread to other sites in the mouth by the tongue or cheeks. One product fitting this category is BeeGentle™ a 20 percent benzocaine topical varnish (CAO Dental, West Jordan, UT) formulated in a water insoluble base which when applied to the tissue forms an insoluble lm upon contact with moist tissue. The lm releases benzocaine at a constant rate over a 20-30 minute period. The varnish forms a white lm on the soft tissue that remains in place until physically removed or until slowly dissolved by saliva. BeeGentle has an ethanol based solvent and is honey-avored which should give a more pleasant taste in those patients who have issues with flavoring typically found in topical anaesthetics. The author has found this product very useful in some patients in lieu of local anaesthetic administration when scaling and root planing (patients with mild inflammation and pockets less than 5 mm) and minor laser soft tissue procedures. When using this product it is advised that the material be brushed on using the disposable brush tip provided with the syringe of topical and allowed to dry for two minutes allowing the topical to exert its affects (Fig. 12).
Frequently patients avoid dental treatment because of the fear of the pain associated with the needle. Whether these fears are valid or not they prevent patients from seeking the dental care they need. Local anaesthesia is the cornerstone of dental treatment and management through better techniques during administration can allay the patient’s fear of the needle, which makes them more likely to return for future treatment. Additionally, selection of the right anaesthetic agent dependent upon the treatment to be rendered can make treatment less stressful for both the patient and practitioner and provide greater comfort in the period following treatment. Improvement in these areas of dental care can be a practice builder as happy patients are the best practice promoters.OH
Gregori M. Kurtzman,
DDS, MAGD, FPFA, FACD, DICOI, DADIA
Dr. Kurtzman is in private general practice in Silver Spring, Maryland, USA. He has lectured internationally on the topics of restorative dentistry, endodontics and implant surgery and prosthetics, removable and fixed prosthetics, periodontics and has over 390 published articles. He can be reached at firstname.lastname@example.org.
Oral Health welcomes this original article.
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