Considering the Two-Stage Injection Technique

One of the most important aspects of treating oral diseases is to ensure patients are free from pain during therapy. Because of this, many methods, techniques, agents, and equipment are dedicated to improving the patient and clinician experience with local anesthetic administration. Individual dental practices often use a unique blend of methodology, anesthetics, and devices during local anesthesia administration. These individual approaches are typically based on differences in patient populations, clinician gender, practice location, provider and staff training, and business operations.^1–3 This article includes an analysis of the two-stage injection technique designed to decrease the pain associated with local anesthesia administration.

When pain is experienced, the central nervous system detects and processes tissue damage and/or bodily danger (with the goal of removing the body from harm).⁴ Generally, type A and type C nerve fibers are involved during the dental injection process. The type A nerve fibers respond to mechanical stimulation and relay the sensation of pain described as sharp or vivid, while type C nerve fibers respond to thermal or chemical stimuli and are associated with dull or burning sensations.⁵ The process of local anesthetic injection and nerve fiber activation includes the needle penetrating mucosa and advancing to the target area (type A); anesthetic deposition (type A and type C); and removal of the needle (type A and type C).⁴

Introduction of the needle into the mucosa is the first step of the injection pain experience. Previous analysis of pain perception during this stage demonstrated a 14% to 22% incidence of moderate to severe pain with standard injection protocols.⁶ Considered the more painful stage of an anesthetic injection, the deposition of solution elicits intense responses due to the expansion of tissue, the rich sensory innervation seen intra­orally, and the chemical complexion and pH of the local anesthetic.⁴ Pain analyses for anesthetic deposition found an incidence of moderate to severe pain at 18% to 56%, during the anesthetic deposition stage.^7–10 Additionally, needle withdrawal can be associated with post-operative pain due to tissue damage or an expedited removal of the anesthetic delivery device.⁴ Post-operative pain has also been associated with the pH of the anesthetic, multiple injections, inadequate needle design, and poor injection technique.^4,11–13

TWO-STAGE INJECTION TECHNIQUE

Because injection technique is part of patients’ evaluation of care, oral health professionals are advised to deliver the least painful injection.^4,14 This fact led Levine to propose the “one-two injection” (or two-stage injection technique) in 1968, using two stages of anesthetic deposition to reduce pain. The first deposition is shallow and the second is directed at the targeted area.¹⁵ More recently, Walton and Torabinejad¹⁶ suggested the technique may decrease injection pain for any operative dental encounter with specific indications for apprehensive/anxious patients.

The first step in the two-stage injection technique is to prepare the mucosa by thoroughly drying the area (gauze and air) and applying a topical anesthetic gel (Figure 1). The next step is to introduce the needle into the mucosa at a depth of 2.0 mm to 5.0 mm, depositing 0.3 mL to 0.5 mL of anesthetic (Figure 2). After 5 minutes (Figure 3), the delivery device is re-introduced at the previous puncture zone (Figure 4), advanced slowly

to the target area for completed anesthetic deposition, and then withdrawn.

Although it can be applied at several injection sites, the two-stage injection technique is most often used with inferior alveolar nerve blocks (IANB). Anecdotal reports suggest that the two-stage injection technique is a better alternative for IANB compared to the traditional Halstead method. These reports propose the two-stage injection technique as a solution to the unreliable effect of topical anesthetic for IANB injections. Nakanishi et al,¹⁷ Meechan et al,¹⁸ and Nusstein et al,^6,10 re­ported that benzocaine (20%) topical gel did not consistently reduce the pain of needle-mucosa penetration with IANB injections. While current evidence points to an unreliability of topical benzocaine anesthetic for IANB injections, some reports have found a psychological connection with topical anesthetics as it relates to reducing the expectation of pain and a belief that the clinician is doing everything possible to reduce the pain.^10,19

Clinical studies evaluating the success of the two-stage injection technique to reduce pain are limited. Nusstein, Steinkruger et al¹⁰ did not find a difference in pain reported between men and women with the two-stage injection technique for the IANB needle insertion or fluid deposition using 2.2 mL of 2% lidocaine w/1:100,000 epinephrine. The investigators did report a difference in the pain response (less discomfort with the two-stage injection technique) during needle placement (advancing the needle through the mucosa) for women. In another study, using 2% lidocaine w/1:100,000 epinephrine to evaluate the patient pain experience, the investigators did not find the two-stage deposition of 0.2 mL to 0.4 mL to significantly reduce the pain experience during needle placement for men or women.²⁰ Sandeep et al²¹ found that the two-stage injection technique with 2.5 mL 2% lidocaine w/1:80,000 epinephrine produced a lower pain response from children when ad­ministration of anesthetic included infiltration or IANB injections. The authors also provided a modification to the technique described as the minimal deposition of anest­hetic agent ahead of needle advancement and placement. Additional research is needed to validate the two-stage injection technique and reach professional consensus.

ANESTHETIC SELECTION

Anesthetic selection for the two-stage injection technique depends on provider preference and patient characteristics. The technique is often associated with 4% prilocaine plain as the primary agent used for the shallow injection, followed by lidocaine or articaine for the target site anesthetic deposition.²²

Local anesthetics vary in their characteristics and effects. The use of 4% prilocaine plain is proposed as the primary agent for the two-stage injection technique because of the solution’s pH value of 6.0 to 7.0.²³ Several authors have proposed that the more acidic the anesthetic solution, the more likely a patient will report a higher pain score.^24–26 Anesthetics with vasoconstrictors have a lower pH value (3.0 to 5.0), while 4% prilocaine plain possesses the highest pH value (6.0 to 7.0), followed by 3% mepivacaine plain (4.5 to 6.8).²⁶

In an analysis of pain response and anesthetic administration, Nydegger²⁷ did not report any statistical difference between epinephrine-containing anesthetics and needle insertion pain across both genders (4% articaine w/1:100,000 epinephrine, 4% prilocaine w/1:200,000 epinephrine, and 4% lidocaine w/1:100,000 epinephrine). Of the study subjects, 86.1% reported none-to-mild (NM) pain for all anesthetics, and 13.9% reported moderate-to-severe pain (MS) with needle insertion. Additionally, the analysis did not find significant pain reporting difference with needle placement (84.5% NM/15.5% MS) or deposition of anesthetic (women: 60% NM/ 40% MS and men: 81.1% NM/18.9% MS) between the agents used. Abdulwahab et al²⁸ evaluated anesthetics and pain response with mandibular buccal infiltration for six local anesthetic formulations. Pain at injection site was evaluated using the Visual Analog Scale for Pain (VAS Pain), and a mean measurement was used to assess pain perception. All anesthetics demonstrated a mean VAS Pain score that correlated with mild pain response: 0.5% bupivacaine w/1:200,000 epinephrine (32.2 mm of VAS Pain 100 mm); 2% lidocaine w/1:100,000 epinephrine (26.2 mm); 4% articaine w/1:100,000 epinephrine (24.1 mm); 4% articaine w/1:200,000 epinephrine (24.1 mm); 3% mepivacaine, plain (22.9 mm); and 4% prilocaine w/1:200,000 epinephrine (21 mm).

Specific to analyses of 4% prilocaine plain and injection pain, Wahl, Schmitt, et al²⁹ found that 4% prilocaine plain caused significantly less pain than bupivacaine for maxillary buccal infiltration, posterior palatal infiltration, and IANB injections. In an earlier study that compared 2% lidocaine w/1:100,000 epinephrine and 4% prilocaine plain and pain reporting, Wahl, Overton, et al³⁰ did not find a statistically significant difference between the two agents and injection pain reported during maxillary buccal infiltration or inferior alveolar injections. Kramp et al³¹ demonstrated that the administration of 4% prilocaine plain resulted in the least perceived pain when compared to 2% mepivacaine w/1:20,000 levonordefrin and 2% lidocaine w/1:100,000 epinephrine. In a study completed at Temple University, the investigators re­ported that 4% prilocaine plain resulted in significantly lower pain scores than 2% lidocaine w/1:100,000 epinephrine, 3% mepivacaine plain, and 4% articaine, w/1:100,000 epinephrine.³²

TECHNIQUE CONSIDERATIONS

Many variables affect the success of the two-stage injection technique. Anesthetic selection should be a controllable variable; however, conclusive information on the best agent(s) is limited. Twenty-four studies were evaluated for this article. The majority found no significant difference between the anesthetics being tested 70.8%, (17 of 24 studies). Out of 17 studies that investigated different anesthetics with vasoconstrictors, 13 (76.5%) found no significant differences between the agents. Three of 14 studies (21.4%) that evaluated lidocaine found 2% lidocaine w/1:100,000 epinephrine to provide the least discomfort of the agents compared, and three of five (60%) analyses involving 4% prilocaine plain determined that the agent provided the least painful experience during injection. In one study comparing lidocaine 2% w/1:80,000 epinephrine and 4% articaine w/1:100,000, articaine was found to produce the least pain response.³³ Additionally, some correlation was observed with vasoconstrictor presence and higher discomfort. The completion of a comprehensive meta-analysis is needed to evaluate these observations and expand the evidence base for best practice.

Differences between pain response and gender have been proposed. Studies found women reported more pain than men for many injection types, especially during needle advancement.^10,27,34,35 A patient population with increased pain response will require a higher level of pain and anxiety management, as well as augmented techniques to provide the least painful encounter possible. Providers will need to evaluate the possible patient response to a second injection and address any concerns or fears he or she may have. If a patient is needle phobic, alternative methods should be considered, such as profound topical anesthetic agents, needleless syringes, anxiety/behavior management, or sedation.

Additionally, some reports have shown that the location of the injection site can result in higher pain perception (periodontal ligament and maxillary infiltrations are usually reported as less painful than IANB and palatal in­jec­tions).^36–38 Other considerations with the two-stage injection technique include presence of dental and/or needle phobias, patient’s ability to cooperate, and patient’s medical and dental history. Every oral health professional needs to understand the risks, benefits, recommendations, and regulations with the anesthetic agents and anesthesia techniques used in dental care.³⁹

Unfortunately, the available science on the two-stage injection technique, as well as the best anesthetic agents and pain response is limited. VAS Pain scoring with anesthetic agent comparisons is usually a secondary finding, if evaluated. There are also too few studies and reviews to achieve professional consensus on the benefits, risks, and best practices of the two-stage injection technique, and no studies were found that evaluated all available United States anesthetics within one cohort.

CONCLUSION

While the majority of dental patients report none to mild pain during dental injections, a significant percentage finds the process to be moderately to severely painful. Used in dentistry for more than 45 years, the two-stage injection technique has been proposed to reduce the pain response with local anesthetic injection. Anecdotal reports and dental professional opinions represent a favorable view of the technique. However, the evidence base to validate the methodology is fragmented. While many oral health professionals favor this technique, there is currently a lack of professional consensus as to the best practice of the two-stage injection technique.

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From Dimensions of Dental Hygiene. October 2016;14(10):53–56.