|Figure 1. Gate principal of nerve sensation and pain.|
Among healthcare professionals, dentists are often referred to as the local anesthesia experts, since providing localized anesthesia is an integral part their daily routine. Yet this is the one aspect that most patients dread when thinking of going to the dentist. Furthermore, it is often what prevents certain patients from having treatment.
Local anesthesia, as it pertains to dental treatment, can be divided into 2 areas: administration and depth/duration. Both areas influence the patient experience, and most patients would indicate that their area of fear and anxiety relates more to the administration portion of the experience than how profound the anesthesia is. Often, patients tense up just at the thought of being “stuck” by the needle, and will delay or avoid treatment until tooth pain outweighs the perceived pain caused by injection of the needle. Treating pediatric patients can be even more of a challenge than apprehensive adults. If the appointment starts off with elevated patient emotions related to a painful injection, the rest of the appointment spirals down into a challenging patient management issue.
Dentists, being the “local anesthesia experts” with an understanding of pain conduction and certain modifications in injection technique, can greatly improve the dental treatment experience for the patient.
This article will address how pain is transmitted, methods to make local administration a more pleasant experience, along with a brief overview of anesthetics used and their selection influencing anesthetic duration and depth.
PAIN CONDUCTION: UNDERSTANDING THE HOW AND WHY OF DENTAL PAIN
In 1965, Canadian psychologist Ronald Melzack and British physiologist Patrick Wall1 described the gate control theory of nerve conduction. Their paper, “Pain Mechanisms: A New Theory,” was described as “the most influential ever written in the field of pain.”1 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 fibers, but opened when the slow-conducting “pain” fibers transmitted a high volume and intensity of sensory signals. They went further to state the gate could be closed again if these signals were countered by renewed stimulation of the large fibers. So 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 fibers, traveling at about 2 meters per second; whereas, an impulse such as a vibration is conducted rapidly along thick myelinated A-beta nerve fibers at a rate of 75 meters per second. When these 2 sensations occur at the same time, the sensation of vibration reaches the sensory area of the brain first, causing a release of inhibitory interneurons, thus preventing the activation of projection neurons in the dorsal horn of the spinal cord; this results in a closure of the gate, and the sensation of pain is blocked (Figure 1).
|Figure 2. DentalVibe, a lightweight cordless local anesthesia augmentation device with illuminated intraoral tip.||Figure 3. Disposable tip shown attached to the DentalVibe unit.|
|Figure 4. DentalVibe disposable tips come in both adult and pediatric configurations.||Figure 5. DentalVibe, retracting the cheek with the tip resting on the ascending ramus of the mandible, as an inferior alveolar
injection is administered.
|Figure 6. DentalVibe retracting the lip and in position, as a mental injection is administered.||Figure 7. DentalVibe tips placed on the hard palate, during a palatal injection.|
The vibrations stimulate mechanoreceptors (Pacinian corpuscles) and primary endings in the muscle spindle.2,3 This is contributed by Meissner’s corpuscles in the skin and mucous membranes.4 Some have suggested that the larger fibers within the area, directly affected when stimulated, achieve maximum pain reduction.5 The neural gate responsible for this lies within the dorsal horn of the spinal cord and inhibits the transmission of pain to the higher centers of the brain. This provides a basis to explain why, for example, after bumping one’s 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, since more than a third of the somatosensory cortex cells in the brain are devoted to sensory input from the mouth.6 Vibration stimuli are easily applied in the orofacial area, and have been used to raise the threshold of pain from pulpal, periodontal, and postsurgical origins.7,8 It has also been suggested that, when light to moderate pressure is combined with the vibration stimulation of the underlying bone, pain tolerance is improved during stimuli application.9 Previously, the use of vibration stimuli, with regard to local anesthetic administration, has focused on vibrating the needle or vibrating a cotton swab at the injection site for topical relief. Nanitsos et al,9 in a study investigating pain associated with local anesthetic 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 on which only one car can drive on 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. So, when a sensation, such as the feel of the needle piercing the tissue, occurs while a stronger stimulus is occurring, this pain sensation is unable to merge. 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 that 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, we would be constantly stimulated after dressing by the clothing rubbing our 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 (pulsing it in a nonuniform manner), the brain is not able to adapt to it and it continues to block the pain transmission during the injection process.
A TECHNIQUE FOR IMPROVING THE PATIENT EXPERIENCE
The DentalVibe (DentalVibe) is a cordless, rechargeable, lightweight handheld device designed to aid in improving the local anesthetic experience (Figure 2). 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 (Figure 3). 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. They should not be autoclaved/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 (Figure 4).
|Figure 8. DentalVibe retracting the lip and in position, as a maxillary buccal injection is administered.||Figure 9. BeeGentle (CAO Group) topical anesthetic varnish.|
|Figure 10. The Wand STA (Aseptico) Anesthesia System (shown with single-use needle attached).||Figure 11. Single-use needle for The Wand, demonstrating the ergonomics of the hand-held portion.|
|Figure 12. The Wand STA with a 30-gauge needle being introduced into the periodontal injection space to provide local anesthesia to a single tooth.|
The device provides pulsed percussive micro-oscillations at the terminal tips of the disposable end. These vibrations use a proprietary technology (VibraPulse [DentalVibe]) to gently stimulate the sensory receptors at the site to be injected, effectively closing the neural pain gate. As discussed earlier, varying the vibration prevents the brain from adapting to the stimuli, allowing the vibration to block the pain sensation.
In nature, pressure makes great diamonds, but the wrong amount of pressure applied when employing this technique can affect the gating capability of the vibrations. With this in mind, the unit was designed with a voltage regulated power supply capable of boosting power to the tip when excess pressure is made on the site; this may occur when retracting the cheek tissues and if the patient is resisting the process by tensing the muscles. Additionally, the tip was specifically designed with a pressure-sensing feature that 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 at the site to be injected for the practitioner to feel the bony landmark, but not enough to stop the tip from vibrating.
The DentalVibe can be utilized with any injection technique, including inferior alveolar (Figure 5), mental (Figure 6), palatal (Figure 7), and buccal maxillary (Figure 8). If desired, this device can be utilized with a topical anesthetic, and also in combination with ancillary devices such as the CompuDent (Milestone Scientific) and single tooth anesthesia (STA) anesthesia systems (Aseptico) if chosen by the practitioner, the combination of which can cut anesthetic delivery time in half.
- Demonstrate to the patient what the vibrating tip will feel like by contacting the tip to his or her finger. This is especially recommended for pediatric patients to help avoid startling the patient when the tip is inserted intraorally.
- 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 (IA), contact with the medial aspect of the mandible is imperative.
- Maintain light to moderate pressure for 5 seconds prior to insertion of the needle into the mucosa.
- Insert the anesthetic needle into the soft tissue between the 2 prongs (as close to one of the 2 prongs as possible), using a standard anesthetic technique while maintaining pressure and vibration with the DentalVibe tip.
- Withdraw the needle from the soft tissue after administration of the anesthetic, keeping the DentalVibe tip on the site with pressure and vibration.
- Continue to apply pressure and vibration to the site for 5 seconds after withdrawal of the needle to help distribute the anesthetic and speed onset of anesthesia.
These are good adjuncts to assist in administering local anesthetic. An application is placed over the site to be injected and allowed to take effect for 2 to 3 minutes prior to injection. Topical anesthetics are available in either a liquid or gel form, with the gel form being easier to keep in the intended location while awaiting its effects. There are several negatives to the use of topical anesthetic. 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 anesthetic. Taste and general spread of the topical action may be a hindrance in pediatric cases, or to those adults who object to their entire mouth feeling numb. Topicals available are usually lidocaine, benzocaine, or triple-anesthetic agents (containing benzocaine combined with tetracaine, prilocaine, or other topical anesthetic agents).
Recently, topical anesthetics have been formulated as varnishes, allowing application to the area without spreading to other sites in the mouth by the tongue and/or cheeks. One product fitting this category is a 20% benzocaine topical varnish (BeeGentle [CAO Group]). It is formulated in a water insoluble base that, when applied to the tissue, forms an insoluble ﬁlm upon contact with moist tissue. The ﬁlm releases benzocaine at a constant rate during a 20- to 30-minute period. The varnish forms a white ﬁlm on the soft tissue that remains in place until physically removed, or until it is slowly dissolved by the saliva. BeeGentle has an ethanol-based solvent and is honey ﬂavored, providing a more pleasant taste for those patients who have issues with flavoring typically found in topical anesthetics. The author has found this product very useful in some patients (in lieu of local anesthetic administration) when scaling and root planing. It is particularly useful when used for patients with mild inflammation and pockets less than 5 mm, and with 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. Then, it should be allowed to dry for 2 minutes, allowing the topical to exert its effects (Figure 9).
There is a misconception among practitioners with regard to needle gauge that the smaller the gauge, the less the patient feels the needle. 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.10-14 Injections in the oral cavity place the tip of the needle in close proximity to blood vessels. Therefore, it is important that the aspiration of the syringe be performed prior to administration of the local anesthetic 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.15,16 Additionally, as gauge decreases, the needle is more likely to deflect during insertion, resulting in inaccurate injections or potential breakage upon injection.17 Use of a smaller gauge needle requires more pressure to express the solution from the needle, thus creating a fast-moving stream of anesthetic that can cause some hydrostatic damage during injection; this may result in more pain during anesthetic administration than would occur when using a larger gauge needle, even with injecting a greater volume of anesthetic.17
It is recommended that a 27-gauge needle meets the best of all worlds, allowing positive aspiration, less chance of needle deflection, increased strength with lower potential for breakage, and improved patient comfort.
THE WAND: SINGLE TOOTH ANESTHESIA
Providing local anesthesia in some patients can be a challenge, especially in the mandibular arch. Infiltration is difficult to achieve in the mandible due to the denser nature of the bone compared to the more vascular lower density maxilla. This leads to issues when relying on block anesthetic techniques and may not provide adequate anesthesia for some procedures.
Alternative techniques have been available to supplement the standard injection techniques, including periodontal injections and intraosseous application of anesthetic. Periodontal injections can be a challenge. This is because they cannot be readily administered with a standard anesthetic syringe due to the pressure required to place the anesthetic in the periodontal ligament space. Special syringes have been developed that increase the leverage, thereby increasing the amount of pressure exiting the needle. This also allows for less effort on the part of the practitioner. But, these still are not easy to routinely use.
With these issues in mind, a computerized anesthesia device was introduced approximately 20 years ago: The Wand (Aseptico). More recently, an advanced version, called the STA, was offered (Figure 10). The STA system has several advantages over the traditional syringe and periodontal injection syringes. It provides pressure sensing (Dynamic Pressure Sensing Technology), allowing metered flow of anesthetic. In addition, it provides a sensing of the periodontal injection space so that needle position is maintained throughout the procedure. This enables a precise STA-intraligamentary injection to anesthetize a single tooth comfortably, safely, and predictably. This system also eliminates the usual and associated anesthetic effects that bother patients, namely a numb tongue and cheek. From the author’s experience, this technology has helped with apprehensive patients and those who dread the lingering anesthetic effects that typically last for hours after the dental care has been completed. The literature has reported that patient comfort was improved when the STA System Unit was used to administer anesthetic in adult patients.18-20
The Wand may be used with other anesthesia techniques, such as blocks, infiltrations, and palatal injections, and is not limited to periodontal injections. The unit provides slow-metered administration and has needles available in 30-gauge/0.5-inch (for periodontal injections and palatal injections), 30-gauge/1.0-inch (infiltrations, periodontal ligament, and palatal), and 27-gauge/1.25-inch (for blocks and infiltrations) (Figure 11). Each needle, and attached tubing connection to the carpule at the unit, is single-patient use and should be disposed of via a sharps container when treatment is completed. When utilizing the STA for a periodontal injection technique, the 30-gauge needle is introduced into the periodontal injection space, and the unit senses the back pressure as it infiltrates anesthetic, thus providing improved comfort for the patient with automatic pressure so the solution is administered at a constant rate (Figure 12). This also provides easier administration (less hand fatigue) as compared to doing manual periodontal injections that require significant hand pressure to force the anesthetic into the periodontal space.
LOCAL ANESTHETIC AGENTS
Lidocaine (Xylocaine, Octocaine)
Lidocaine, an amide anesthetic agent first introduced in 1948, exhibits twice the potency of procaine (the common local anesthetic agent at the time) and half of the toxicity. It produces a greater depth of anesthesia with a longer duration than comparable volumes of procaine.
It is available in 4 formulations: a 2% solution without vasoconstrictor (plain), a 2% solution with 1:200,000 epinephrine (a vasoconstrictor), a 2% solution with 1:100,000 epinephrine, and a 2% solution with 1:50,000 epinephrine. Lidocaine, without a vasoconstrictor, has a soft-tissue anesthetic duration of one to 2 hours, but only a pulpal duration of 5 to 10 minutes. Therefore, it is of limited use for most dental procedures. Formulations with the vasoconstrictor epinephrine have a pulpal duration of one to 1.5 hours and a soft-tissue range of 3 to 5 hours. The 1:50,000 epinephrine formulation may be advantageous for hemostasis in surgical sites, but has no significant advantage for duration of pulpal anesthesia. There are no benefits between the 1:200,000 and 1:100,000 formulations, but a greater toxicity safety factor is present when using the 1:200,000 formulation. (See drugs.com/mtm/lidocaine-injection.html.)
Mepivacaine (Carbocaine, Polocaine)
Introduced in 1960, a 2% solution of mepivacaine has the same potency and toxicity ratings equivalent to a 2% solution of lidocaine. The greatest advantage of mepivacaine is its less vasodilating activity when compared to lidocaine, and it can be used reliably as a nonvasoconstrictor-containing solution for procedures of short duration. Mepivacaine is available on the US market as either a 3% plain solution (no vasoconstrictor) or as a 2% solution with 1:20,000 levonordefrin (a vasoconstrictor also provided under the name neocobefrin). The plain solution has a pulpal anesthetic duration of 20 to 40 minutes with a soft-tissue duration of 2 to 3 hours. The vasoconstrictor containing solution has a pulpal duration equivalent to that of lidocaine with vasoconstrictor (one to 1.5 hours) and soft-tissue duration of 3 to 5 hours.
As the levonordefrin vasoconstrictor in mepivacaine is less likely to produce cardiac side effects (such as palpitations) than epinephrine, it may be the anesthetic 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. Therefore, it may not be the anesthetic to use in patients with severe hypertension and blood pressure. It also has a higher potential for interaction with tricyclic antidepressants such as amitriptyline hydrochloride. (Also see the Web sites: drugs.com/mtm/mepivacaine.html, drugs.com/pro/carbocaine.html, and drugs.com/mtm/polocaine.html.)
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 anesthesia. It is available only as a 0.5% solution with 1:200,000 epinephrine. Bupivacaine may exhibit a slightly slower onset time in some patients, taking approximately 6 to 10 minutes compared with 2 to 7 minutes for lidocaine or mepivacaine. The longer duration of anesthesia 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 1.5 to 7 hours are common with soft-tissue anesthesia of 5 to 12 hours, making this very suitable as an adjunct for patients undergoing surgery to provide long-duration anesthesia. When administered via infiltration technique, bupivacaine provides anesthetic depth and duration comparable to other local anesthetic agents. (Also see: drugs.com/cdi/marcaine-solution.html.)
Prilocaine, also first introduced in 1960, is slightly less potent but considerably less toxic than lidocaine as a local anesthetic agent. As with mepivacaine, prilocaine produces less tissue vasodilation than lidocaine, and may be used in a plain solution form for short-duration procedures. Prilocaine is available as a 4% plain solution (no vasoconstrictor), or with 1:200,000 epinephrine in a 4% anesthetic solution. The plain solution has a pulpal duration of 40 to 60 minutes with soft-tissue anesthesia for 2 to 3 hours. The duration of anesthesia with plain prilocaine is more dependent upon the type of injection given than noted with other anesthetics. Infiltration injections of prilocaine plain may only provide 5 to 10 minutes of pulpal anesthesia 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 to 60 minutes of anesthetic duration, which is suitable for many dental procedures. The vasoconstrictor-containing version of prilocaine provides pulpal anesthesia for 1.0 to 1.5 hours (durations similar to lidocaine and mepivacaine) with a potentially longer soft-tissue duration of 3 to 8 hours.
Prilocaine (as noted by some practitioners) has a greater efficacy in patients who are difficult to anesthetize, including patients with a past or present history of substance abuse, as they tend to be fast metabolizers. 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 paraesthesia with the use of prilocaine and articaine, particularly for inferior alveolar and lingual nerve block injections; this appears to be related to the higher concentration of anesthetic (a 4% solution compared to the 2% solution found with other anesthetics) more so than to the particular anesthetic itself. Additionally, since the concentration is twice as strong as 2% solution, half the total amount of anesthetic can be administered safely; care should be given in pediatric patients as the safe amount, based on the patient’s body weight, can be very low. (Also see the Web sites: drugs.com/pro/prilocaine-hydrochloride-injection.html and drugs.com/pro/citanest-plain-dental-injection.html.)
Articaine (Septocaine [Septodont], Articadent [DENTSPLY Pharmaceutical])
Articaine is an analogue of prilocaine in which a benzene ring moiety found in all other amide local anesthetics 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 4% solution with 1:100,000 epinephrine. Currently, a 1:200,000 epinephrine formulation is also available. A pulpal anesthesia duration of approximately one hour, with soft-tissue anesthesia for 2 to 4 hours, is typically observed. Articaine has a slightly faster onset of action (1.4 to 3.6 minutes), and reports of a longer and perhaps more profound level of anesthesia has been reported, in general. With a greater ability to diffuse through tissues, articaine has become a very widely used anesthetic in the European, US, 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 anesthesia for tooth extraction. Similar results have been claimed for the mandibular anterior and premolar teeth with buccal infiltrations. As discussed with prilocaine, there are reports of a significantly increased risk of nerve paresthesia with the use of these 4% anesthetic solutions, particularly for inferior alveolar and lingual nerve block injections. This warrants caution in the use of these anesthetic agents. (See also the Web sites: drugs.com/mtm/septocaine.html and drugs.com/pro/articadent.html.)
Infected sites that are to receive dental treatment are a particular challenge to adequate local anesthesia. As the pH becomes more acidic as seen in areas of infection, local anesthetics are converted to a nonusable form at the site, thus requiring greater volumes of anesthetic and increasing safety issues. Articaine is not affected by low pH in the injection site, unlike other local anesthetic agents, and has been reported by the author (as well as others) to provide better and more profound anesthesia in infected areas that will undergo either extraction or endodontics.
Many patients avoid dental treatment for fear of the pain associated with the needle or during treatment. Whether these fears are valid or not, they prevent patients from seeking the dental care that they need. Local anesthesia is the cornerstone of dental treatment. Proper management, through better techniques during administration, can allay the patient’s fear of the needle, making the patient more likely to return for future treatment. Additionally, the selection of the right anesthetic agent, appropriate for 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.
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Disclosure: Dr. Kurtzman reports no discloures.