Safe and effective pain control is essential for today’s dental practice. Our current armamentaria for delivery of local anesthetic to the maxilla and mandible generally are adequate for most clinical situations. The most tried and true of all methods of delivery for mandibular anesthesia is the inferior alveolar nerve block, or the Halstead block, which uses traditional methods and directs the needle to the level of the mandibular foramen. This delivery technique has been available to dentists for more than a century; however, the reported incidence of inadequate local anesthesia with the inferior alveolar nerve block is significant (15 to 30 percent).1,2
Alternative local anesthetic delivery systems may offer some advantages over conventional techniques in certain situations.
More than 25 years ago, alternative delivery routes, such as the Akinosi3 and Gow-Gates4 block techniques, were promulgated in an effort to reduce this incidence of inadequate or incomplete anesthesia. Both of these techniques require anatomical approaches significantly above the level of the mandibular foramen. These alternative routes, particularly designed to enhance the effectiveness of mandibular local anesthesia, have yet to be universally adopted for routine use. This is most likely because of the more complicated nature of delivery (that is, higher and deeper into the head) and the potential for anatomical complications.5 Within the last 10 to 20 years, several alternative delivery methods have been introduced or revitalized for the dental community. These include the intraosseous, intraligamentary, computer-assisted and topical patch methods of delivery.
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INTRAOSSEOUS DELIVERY METHOD
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The intraosseous injection method involves the placement of anesthetic solution directly into the cancellous bone or marrow space adjacent to the tooth or teeth to be anesthetized, and allows for rapid onset of profound pulpal anesthesia.6–9 The site of injection involves the attached gingiva 2 millimeters apical to the gingival margin and interproximal relative to the teeth.
This route of delivery has been available in dentistry since the early part of the 20th century.10,11 Initially, the techniques involved gingival surgery to expose the cortical bone; a small round dental bur then was used to perforate the buccal cortical plate. Once the cortical opening had been prepared, the local anesthetic was deposited into the subjacent cancellous bone. Dentists found the method somewhat labor-intensive and often reported difficulty in maintaining sight of the small bony perforation for placement of the injection needle.
The method of intraosseous injection has been modified in recent years to address these concerns. Today, systems exist that consist of a perforator (approximately 27-gauge) designed to perforate both the gingiva and cortical bone (Stabident System, Fairfax Dental, Miami; X-Tip, Dentsply Maillefer, Tulsa, Okla.). These systems include a "guide sleeve" that is placed into the perforation to maintain its location and to direct the anesthetic needle into the cancellous bone.
The intraosseous injection most often is used to provide anesthesia to a single tooth.
Several authors have reported that the intraosseous injection of a local anesthetic is effective in providing pulpal anesthesia to teeth with irreversible pulpitis1,6–8,12–17 as a supplementary technique to the inferior alveolar nerve block, as well as to asymptomatic teeth as a primary or supplementary technique. However, we could find no evidence that the intraosseous injection provides effective pulpal anesthesia to teeth with irreversible pulpitis when the anesthetic is administered in an intraosseous manner alone. Intraosseous injections provide a duration of anesthesia that is shorter than that with mandibular block or infiltration; pulpal anesthesia has a duration of less than 60 minutes with vasoconstrictor and approximately 15 to 30 minutes without vasoconstrictor.17
Complications.
Problems of a localized nature with these injections include separation of the perforator needle from the plastic shank, which can occur occasionally; however, this has not proved to be a hazard.15 Second, localized infection can occur at the site of perforation and may require the use of oral antibiotics.6,13 Such infections occur more commonly than they do with typical injection techniques, but they still occur in only 3 percent of patients.
Increased heart rate.
The most significant concern with this route is the increased heart rate that occurs when using epinephrine- and levonordefrin-containing solutions.4–6,10–12,14,15 Blood pressure is not significantly changed, and heart rate usually returns to normal values within a few minutes.18 To avoid cardiovascular effects, clinicians should administer a local anesthetic without a vasoconstrictor.12,17,18 Of particular concern would be patients whose medical condition (that is, cardiovascular disease), drug regimens (for example, noncardioselective ß-blockers) or epinephrine sensitivity, or combination of the preceding might suggest caution.19 Several authors have suggested 3 percent mepivacaine as an alternative to intraosseous injections in such patients.12,17,18 Healthy patients likely will notice the heart rate increase with a lidocaine-epinephrine solution, but the increased rate in these patients should not be clinically significant.17,18
Although there is a short-lived effect on heart rate as a result of the vasoconstrictor, the plasma concentration of lidocaine delivered with the intraosseous injection is not toxic and is no greater than that seen after infiltration.20 Therefore, the intraosseous technique should not be considered an intravascular injection. In addition, if it were a true intravascular injection, little or no anesthetic effect would be observed.
Published contraindications to the use of intraosseous injection include the presence of gross periodontal disease or acute periapical infection.1 Intraosseous injections also are presumed to be contraindicated in cases in which the roots of the teeth are so close together that they preclude clear access to the interdental cancellous space, and where bone density would prevent entry into the cancellous space (for example, at the mandibular midline).21 Despite these contraindications, they appear to be based on anecdotal evidence, and no scientific studies have either confirmed or refuted them.
The intraosseous injection most often is used to provide anesthesia to a single tooth, but the manufacturer of the Stabident system claims that it can be used to anesthetize multiple teeth in the same quadrant, based on the site of injection and the volume of solution injected.21 According to Fairfax Dental, when the intraosseous injection is administered between the first premolar tooth and the canine tooth, one can anesthetize four teeth (first premolar, canine, lateral incisor and central incisor).21 However, no scientific proof exists for these claims.
In summary, intraosseous injection can be a useful adjunct to the dentist’s local anesthetic armamentarium when primary or supplemental anesthetic is desired. In addition, in patients with hyperemic pulps or when traditional anesthetic blocks yield inadequate or incomplete anesthesia, the intraosseous injection is a useful alternative. However, this method appears to have no advantage over the inferior alveolar nerve block as a primary means to achieve anesthesia.
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INTRALIGAMENTARY DELIVERY METHOD
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The periodontal ligament, or PDL, injection, also known as the intraligamentary injection, is occasionally used as the sole technique for anesthetizing a single tooth. It also can be used as a supplemental injection in situations in which a tooth continues to demonstrate pulpal sensitivity after the traditional injection has been administered. With this approach, the dentist inserts the needle through the gingival sulcus and into the periodontal ligament between the tooth and the alveolar bone. The needle is directed along the long axis of the tooth and as apically as possible. The dentist slowly injects a small volume of anesthetic solution under pressure to control the pain of the associated tooth.
Intraosseous injection can be a useful adjunct to the dentist’s local anesthetic armamentarium.
Smith and Walton22 reported that the route by which the anesthetic solution reaches the peri-apical tissue with a PDL injection is into and through the marrow spaces surrounding the tooth and not apically through the periodontal tissues, thus making this injection comparable to the intraosseous injection. D’Souza and colleagues23 suggested that it may be necessary to administer the PDL injection on all four sides of the tooth to achieve complete anesthesia because of its unpredictability.
From 1912 to 1923, this technique was described as the peridental injection.10,11 Repopularization of the PDL approach probably is the result of marketing new syringe devices that facilitate the delivery process, as well as an ongoing effort to supplement traditional anesthetic injection techniques, which can result in incomplete dental anesthesia, particularly in the mandibular area.
Although the new syringe devices may be used effectively and safely, they are not necessarily needed. The conventional anesthetic needle (27 gauge) and syringe can be used with equal effectiveness.1 However, one drawback to using the conventional syringe under conditions of extreme pressure is the potential for shattering the glass cartridge, potentially introducing shards of glass into the patient’s mouth and throat. The PDL syringe provides a metal or plastic covering for the cartridge for protection. If using traditional equipment, dentists can place a piece of transparent adhesive tape over the glass cartridge to preclude shattering in the event of breakage.1
The modern PDL technique, as described by Malamed24 and Walton and Abbott,25 involves slow injection (owing to back-pressure resistance in the PDL) of a relatively small volume (approximately 0.2 milliliters) (because of both the confined tissue space and design of special PDL injection devices) of anesthetic. We recommend adherence to this protocol to allow the patient to experience a more comfortable injection and postoperative course, even though the precise effects of rate of injection and quantity of anesthetic on pain have not been scientifically assessed. Postinjection discomfort most often is described24 as soreness of the soft tissue approximating the tooth and sensitivity to percussion or premature contact on closing. These symptoms usually resolve within two to three days.24
Researchers have recommended that the PDL injection should not be used when infection or significant inflammation exists at the injection site, as well as with primary teeth.1 Brannstrom and colleagues26 reported the development of enamel hypoplasia or hypomineralization in 15 permanent teeth after PDL injections adjacent to primary dentition, although this effect was the result of the local anesthetic solution, not the PDL injection itself. This suggests that an infiltration injection near a permanent tooth bud may result in hypoplasia. However, no scientific studies have confirmed that this problem is clinically significant, and a human clinical study of the phenomenon clearly is obviated by ethical considerations.
Another study of PDL injections in animals27 demonstrated that the ink marker did not penetrate the enamel organ or contact the permanent tooth buds, implying that the risk of mechanical damage to permanent tooth buds is minimal. Other concerns regarding this delivery method and route relate to potential tissue damage from injecting the anesthetic solution under pressure into a confined space, such as the PDL space. According to Walton and Garnick,28 and as addressed in a status report in JADA,29 the PDL injection causes slight damage to tissues not previously inflamed at the site of needle penetration only, and is safe in regard to periodontal tissues.
Froum and colleagues30 confirmed this type of mild histologic disruption with the PDL injection using the CompuDent local anesthetic system (formerly the Wand) (Milestone Scientific, Deerfield, Ill.) in an animal study. In that study, only mild, localized inflammation was noted at the injection site after administration of 1 mL of anesthetic, and no crestal bone loss or root resorption was found at various time periods (24 hours to 49 days) during which the animals were observed. The authors noted apical migration of the junctional epithelium in both control and experimental test sites.
The computer-controlled local anesthetic delivery system offers several advantages over conventional syringes.
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COMPUTER-CONTROLLED LOCAL ANESTHESTIC DELIVERY SYSTEM
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In the mid-1990s, the Wand local anesthetic delivery system was introduced into the U.S. dental marketplace. This device consists of a computer-controlled pump that drives local anesthetic from a conventional local anesthetic cartridge through plastic microtubing into a plastic handle to which a LuerLok needle (Becton, Dickinson, Franklin Lakes, N.J.) is attached. The computer-controlled flow is initiated by exerting pressure on a foot pedal. The pump allows administration of local anesthetic at two slow but constant rates, and the computer compensates for variation in resistance to flow. The device also enables the dentist to perform aspiration (via release of pressure from the foot pedal).
This system offers several advantages over conventional syringes, including excellent tactile sensation afforded by the lightweight plastic handle and the ability to rotate the needle as it is introduced into tissues, producing a "coring" penetration that minimizes needle deflection.31 The slow rate of anesthetic flow presumably reduces patient discomfort, which was demonstrated in a single-blind human clinical study comparing palatal injections administered with a traditional syringe vs. those administered via the computerized delivery system.32 After receiving injections of 0.45 mL of anesthetic, 48 (96 percent) of 50 subjects reported that the Wand injection was "more comfortable" (P < .001), a finding that was confirmed via visual analog scale analysis.
Ease of administration.
The device also allows relatively easy administration of PDL injections, because the operator only guides the needle into tissue, but does not have to generate injection pressure simultaneously with his or her hand. Disadvantages of the Wand include its relatively greater expense and a greater array of materials (that is, pump, tubing) that must be set up before the injections.
Anterior middle superior alveolar block.
An injection technique advanced by some dentists—apparently primarily on the basis of only one clinical observation reported via oral communication—for the Wand is the anterior middle superior alveolar, or AMSA, block.33 In this injection, the clinician introduces the needle into the palatal tissues adjacent to the maxillary premolars, and administers 0.6 to 0.9 mL of anesthetic. Friedman and Hochman33 claimed that this injection can produce anesthesia from the maxillary first molar to the central incisor on the injected side without producing anesthesia of buccal soft tissues, but this was based on only one case report in which the Wand was used. This technique can be further criticized on several grounds, including the following.
The scientific basis for routinely anesthetizing maxillary teeth with the proposed AMSA palatal injection is lacking. In certain patients, maxillary posterior teeth are innervated by posterior superior alveolar nerves, which travel with the greater palatine nerve to approach the apexes of the teeth. In addition, maxillary anterior teeth may receive innervation from anterior superior alveolar nerves traveling with the nasopalatine nerve. In such instances, the respective teeth could be anesthetized by nasopalatine injections, greater palatine nerve block injections or both. To date, there have been no scientific studies to support the manufacturer’s recommendation regarding the use of the AMSA palatal injection in place of conventional approaches.
Second, anesthesia of buccal soft tissues, especially in the posterior maxilla, is not unduly uncomfortable for most patients and frequently is desired, even for simple restorative procedures in which a rubber dam clamp is applied. Third, the posterior, middle and anterior superior alveolar nerves can be anesthetized safely and reliably via relatively painless injection on the buccal aspect of the maxilla.
Palatal injections reportedly are less painful when the Wand device is used instead of conventional syringes.32 A more recent study, however, evaluated three types of injections (that is, middle superior alveolar infiltration, palatal infiltration of maxillary first premolars and inferior alveolar block) in 40 subjects with a split-mouth design.34 Overall, the Wand produced less pain than a traditional syringe in 15 (83 percent) of 18 statistical comparisons, but statistical significance was found in only four (27 percent) of these 15 comparisons. Because the mean ratings for both injections were mostly "mild" pain, the authors advised that the clinical significance of the results should be interpreted with caution.34
A significant development in topical anesthesia occurred with the introduction of a bioadhesive patch impregnated with 10 or 20 percent lidocaine.
Furthermore, the dentist must evaluate the cost-effectiveness of the device, as well as the potential for improved patient comfort for some types of injections. Finally, it is important to remember from a scientific perspective that the pharmacological actions of dental local anesthetics are not affected by the type of syringe that is used to administer them, and intimate knowledge of neuroanatomy and pharmacology is the most important guide for the practitioner in administering effective local anesthetic nerve blocks.
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TOPICAL ANESTHETIC PATCHES
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A significant development in topical anesthesia occurred with the introduction of a bioadhesive patch impregnated with 10 or 20 percent lidocaine (Dentipatch, Noven Pharmaceuticals, Miami) containing 23 and 46 milligrams of local anesthetic, respectively. Clinical studies have confirmed its efficacy and safety, and it allows the operator to keep the anesthetic concentrated at a single site.35–38 Two scientifically based studies evaluated the effectiveness of the Dentipatch.
Active and placebo patches.
Hirsh and colleagues38 placed active (both 10 and 20 percent lidocaine) and placebo (no lidocaine) patches at maxillary and mandibular mucogingival (facial) sites and tested 32 to 35 subjects per group. Based on visual analog scores, the authors found that both active patches were significantly better than the placebo in reducing the pain of insertion of a 25-gauge dental needle. In another double-blind, multicenter trial,39 a similar protocol was used in 116 subjects. In that study, peak topical anesthesia occurred after a 15-minute application of 10 and 20 percent patches, with both active patches producing significantly better topical anesthesia than did placebo, and with no significant differences between the two active patches. Unfortunately, neither of these studies compared the lidocaine patch with the widely used 20 percent benzocaine ointment, nor did either study test the effectiveness of the lidocaine patch on palatal mucosa, a much more robust test.
Two more recent studies did compare the lidocaine patch with the commonly used topical anesthetic benzocaine (20 percent). In one well-designed study of 32 children aged 6 to 15 years, a statistically significant decrease in verbal indicators of pain resulted from the 15-minute application of the 20 percent (40-mg) patch compared with a one-minute application of 20 percent benzocaine gel (after palatal injections).40 However, the authors observed no statistically significant difference between the two topical regimens for reported pain or observed pain–motor responses.40
A similar, well-designed study of 60 adults also compared a 15-minute application of the 46-mg patch with a 30-second application of 20 percent benzocaine, with scaling and root planing and needlesticks (with and without actual injection of local anesthetic) as test stimuli. Based on verbal pain scores, the authors concluded that the patch reduced pain significantly better than did benzocaine gel and placebo for all painful stimuli tested.41
As Hirsh and colleagues38 pointed out, results from many studies of topical anesthetics are confused by variations in test protocols (for example, short contact times and testing with smaller [27-gauge] needles). Typically, topical anesthetics are used to anesthetize only the outer 1 to 3 mm of mucosa to reduce the pain of needle insertion. Also, evaluating the effect of a topical agent on the pain of subsequent local anesthetic injection is not scientifically appropriate for such trials, because topical anesthetic does not penetrate to the tissue depths at which the anesthetic solution is actually deposited.
Considerations.
However, the patch is considerably more expensive per application than are bulk forms of topical anesthetic (for example, benzocaine ointments), and the patch may not adhere well to some soft tissues (for example, alveolar mucosa in posterior areas). Once again, from a scientific perspective, the dentist must decide if this delivery system is cost-effective for his or her practice, including considerations of both the required application time (15 minutes) and the duration of topical anesthesia. He or she also should consider the fact that other topical anesthetics may be as effective in many application sites.
Because of the well-known discomfort associated with palatal injections, new topical anesthetic delivery systems will always be of great interest to the dental profession. In most cases, topical anesthetic is intended to provide preinjection desensitization of the mucosa, not of deeper structures. Variation in clinical study protocols of topical anesthesia, as well as differences in dentists’ expectations of the efficacy, depth and duration of topical anesthesia have led to controversy regarding the effectiveness of these anesthetics.36
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CONCLUSION
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Credit for the revived interest in these supplemental routes and local anesthetic delivery methods probably goes in large part to the device manufacturers in their attempt to simplify delivery techniques. As the information above illustrates, there are benefits and limitations inherent with each technique. The trend toward evidence-based dentistry mandates that our therapies be based on sound scientific knowledge whenever possible. Consequently, when electing to enhance his or her local anesthetic arsenal, the clinician must be knowledgeable beyond the marketing hype that usually accompanies any new product.
Unfortunately, no scientifically designed studies are available to support some aspects of the delivery systems addressed in this article. The ultimate safety and effectiveness of local anesthetic injections are still predicated on basic concepts and constructs that have become well-established over many years. Without knowledge and, more importantly, adherence to these basic tenets, the likelihood of therapeutic misadventure is greatly increased.
It is not our intent to minimize the importance of adjunctive injection techniques and devices. Rather, we hope that where scientific studies to substantiate them are lacking, dental investigators will appreciate their importance and initiate appropriate clinical trials.
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ABSTRACT
INTRAOSSEOUS DELIVERY METHOD
