The significance of needle bevel orientation in achieving a successful inferior alveolar nerve block
Geoffrey Steinkruger, DMD, MS,
John Nusstein, DDS, MS,
Al Reader, DDS, MS,
Mike Beck, DDS, MA and
Joel Weaver, DDS, PhD
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ABSTRACT
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Background. The authors conducted a prospective, randomized, single-blinded, crossover study comparing the degree of pulpal anesthesia achieved with the use of a conventional inferior alveolar nerve (IAN) block administered with the needle bevel oriented away from the mandibular ramus or toward the mandibular ramus.
Methods. Fifty-one blinded subjects randomly received an IAN block injection administered with a 27-gauge needle; the needle bevel was oriented away from the mandibular ramus or oriented toward the mandibular ramus at appointments spaced at least one week apart, in a crossover design. The authors used a pulp tester to test molars, premolars and central and lateral incisors for anesthesia in four-minute cycles for 60 minutes. They considered anesthesia to be successful when two consecutive 80 readings (the maximum output on the pulp tester) were obtained within 15 minutes, and the 80 reading was sustained continuously for 60 minutes.
Results. When the needle bevel was oriented away from the mandibular ramus, successful pulpal anesthesia from the central incisor to the second molar was achieved in 24 to 90 percent of patients. When the needle bevel was oriented toward the mandibular ramus, successful pulpal anesthesia was achieved in 14 to 92 percent of patients. The results showed no significant difference between the two needle bevel orientations.
Conclusion. The authors concluded that using a 27-gauge needle with the bevel oriented away from the mandibular ramus was similar to using the same needle with the bevel oriented toward the mandibular ramus to administer successful IAN blocks in adults.
Clinical Implications. For IAN blocks administered with a 27-gauge needle, positioning the needle bevel away or toward the mandibular ramus does not affect anesthetic success.
Key Words: Needle bevel; inferior alveolar nerve block; local anesthesia
The inferior alveolar nerve (IAN) block is the most frequently used mandibular injection technique for achieving local anesthesia for dental treatment. However, the IAN block does not always result in successful pulpal anesthesia.1 Failure rates of 10 to 39 percent have been reported in experimental studies.1 Clinical studies in endodontics2–6 have found that the IAN block fails between 44 and 81 percent of the time. Therefore, it would be advantageous to improve the success rate of the IAN block.
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NEEDLE DEFLECTION
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Several authors have theorized7–9 that needle deflection is a cause of IAN block failure. Some authors,7–12 using in vitro methods, have reported that beveled needles, when passed through substances of varying densities, will deflect toward the nonbeveled side (that is, the needle will deflect away from the bevel). For the IAN block, Davidson8 recommended that the bevel of the needle be placed away from the mandibular ramus. Therefore, on insertion into the tissue, the needle will deflect toward the mandibular ramus, allowing for a more accurate injection.
Hochman and Friedman9 developed a bidirectional needle rotation technique designed to reduce needle deflection during insertion. The bidirectional technique relies on a penlike grasp that makes it possible to rotate the needle in a back-and-forth-motion, similar to the rotation described for use of endodontic hand files and acupuncture. The bidirectional technique is applicable using the CompuDent (Milestone Scientific, Livingston, N.J.) handle/needle assembly only, because the traditional syringe cannot be rotated easily owing to the thumb ring. Hochman and Friedman9 found that the bidirectional needle rotation technique cancelled the force vectors of needle insertion so the needle traveled in a linear path. They also demonstrated that a standard beveled needle that traverses 20 mm of tissuelike substance can deflect as much as 5 mm.
No clinical study has evaluated the importance of the needle bevel’s orientation toward the mandibular ramus.
Although Hochman and Friedman9 found less needle deflection in vitro with the bidirectional needle rotation technique, Kennedy and colleagues5 found no significant difference in success (no pain or mild pain on endodontic access or instrumentation) between the bidirectional rotation technique used with an IAN block and a conventional IAN block with the needle bevel oriented away from the mandibular ramus in patients with irreversible pulpitis. Both techniques were less than 57 percent successful in achieving pulpal anesthesia after an IAN block was administered.
Kennedy and colleagues5 conducted a study in which the bevel of the needle was away from the mandibular ramus, which theoretically would deflect the needle close to the mandibular ramus. However, no clinical study, to our knowledge, has evaluated the importance of the needle bevel’s orientation toward the mandibular ramus, theoretically deflecting the needle away from the ramus and the IAN. Therefore, the purpose of this prospective, randomized, single-blinded, crossover study was to compare the degree of pulpal anesthesia achieved with a conventional IAN block administered with the needle bevel oriented away from the mandibular ramus or toward the mandibular ramus.
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SUBJECTS, MATERIALS AND METHODS
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Fifty-one adults (23 women, 28 men) aged 20 to 46 years (mean age, 26 years) participated in this study. The subjects were in good health and were not taking any medications that would alter their perception of pain. The Ohio State University, Columbus, Human Subjects Review Committee approved the study, and we obtained written informed consent from each subject.
One of us (G.S.) administered all of the injections. The 51 blinded subjects randomly received an IAN block injection with the needle bevel oriented away from the mandibular ramus or the needle bevel oriented toward the mandibular ramus at one of two separate appointments spaced at least one week apart, in a crossover design (each subject received injections with both needle bevel orientations). All subjects received IAN block injections consisting of 2.2 milliliters of 2 percent lidocaine (44 milligrams) with 1:100,000 epinephrine (22 micrograms).
Using the crossover design, the dentist administered a total of 102 injections, and each subject served as his or her own control. Fifty-four IAN block injections were administered on the right side and 48 injections were administered on the left side. The side randomly chosen for the first injection was used for the second injection as well. The needle bevel orientation also was determined randomly. The test teeth were the first and second molars, first and second premolars, and lateral and central incisors. We used the contralateral canine tooth as the unanesthetized control to ensure that the pulp tester was operating properly and the subject was responding appropriately during each experimental portion of the study. Clinical examinations indicated that all teeth were free of caries and large restorations and patients were free of periodontal disease; in addition, none of the subjects had a history of trauma or tooth sensitivity.
Before the study, one of us (G.S.) randomly assigned to the two needle bevel orientations six-digit numbers from a random number table. Each subject was assigned randomly to one of the two needle bevel orientations to determine which was to be administered at each appointment. Trained research assistants recorded only the random numbers on the data collection sheets to blind the experiment.
Pulp tester.
At the beginning of each appointment and before any injections were administered, the research assistants tested the experimental teeth and control contralateral canine teeth three times with a pulp tester (Kerr, Analytic Technology, Redmond, Wash. [now SybronEndo, Orange, Calif.]) to record baseline vitality. After isolating the tooth to be tested with cotton rolls and drying it with gauze, the research assistant applied toothpaste to the probe tip and placed it midway between the gingival margin and the occlusal or incisal edge of the tooth.
The current rate on the pulp tester was set for 25 seconds and was increased from no output (0) to the maximum output (80). The research assistant recorded the number associated with the initial sensation, as reported by the patient. Trained research assistants performed all preinjection and postinjection tests. They were dental or hygiene students specifically trained in conducting clinical trials.
The authors considered anesthesia to be successful when they obtained two consecutive 80 readings (the maximum output) within 15 minutes.
Before administering the IAN block, the dentist determined the proper needle bevel orientation using a dental operating microscope (JedMed Instrument, St. Louis). Using a black permanent marking pen, he made a visual indicator (a dot) corresponding to the position of the needle bevel with respect to the long axis of the needle on the plastic hub of the needle assembly. The indicator was easily visible in the mouth during the injection, thus enabling proper orientation of the bevel. The dentist took care to ensure that minimal needle rotation occurred during insertion and placement of the needle during the IAN block.
Using a cotton-tip applicator, the dentist placed topical anesthetic gel (20 percent benzocaine) passively at the IAN block injection site for 60 seconds. He administered a standard IAN block1,13 using a 27-gauge 1
-inch Luer-Lok needle (Becton, Dickinson, Franklin Lakes, N.J.) attached to a 5-mL Luer-Lok syringe (Becton, Dickinson). We used the Luer-Lok syringe because we wanted to administer 0.4 mL of the lidocaine solution as we advanced the needle toward the target area to decrease the pain of needle placement. If we had used a standard dental syringe and administered 0.4 mL as the needle was advanced, only 1.4 mL would have been deposited at the target site. We wanted to ensure that a full-cartridge volume was deposited at the target site.
Anesthetic solution.
The clinician prepared the anesthetic solution by removing the contents from 1.8-mL cartridges of 2 percent lidocaine with 1:100,000 epinephrine and adding 2.2 mL of lidocaine to the 5-mL Luer-Lok syringe using a sterile technique. All anesthetic solution cartridges were checked to ensure that expiration dates were acceptable. The dentist administered 0.4 mL of anesthetic solution over a 10-second period as he advanced the needle. After reaching the target area and performing aspiration, he deposited 1.8 mL of the lidocaine solution over a one-minute period.
One minute after the dentist administered the IAN block, the research assistants pulp tested the first and second molars. At two minutes, they tested the first and second premolars. At three minutes, they tested the central and lateral incisors. At four minutes, they tested the control canine tooth. This cycle of testing was repeated every four minutes. At every fourth cycle, the research assistants tested the control tooth, the contralateral canine, with a pulp tester without batteries to test the reliability of the subject’s responses. Every minute for 15 minutes, the dentist asked each subject if his or her lip or tongue was numb. If the research assistant did not record profound lip numbness within 15 minutes, we considered the block to be unsuccessful and set up another appointment for the subject. All testing was stopped 60 minutes after the injection.
No response from the subject at the maximum output (80 reading) of the pulp tester was used as the criterion for pulpal anesthesia. We considered anesthesia to be successful when we obtained two consecutive 80 readings within 15 minutes, and the 80 reading was sustained continuously for 60 minutes (that is, for most restorative procedures, we would want the patient to experience numbness within 15 minutes and to remain numb for 60 minutes).
Statistical analysis.
With a nondirectional 
risk of .05 and a power of 80 percent, a sample size of 51 subjects was required to demonstrate a difference of ± 25 percent in anesthetic success. The researsch assistant recorded the time of anesthesia onset as the first of two consecutive 80 readings.
We used exact McNemar tests to analyze comparisons between the bevel orientation (that is, away or toward the mandibular ramus) nonparametrically for anesthetic success. We used the Wilcoxon signed ranks, matched pairs test to compare the onset of anesthesia between the two techniques. We considered comparisons to be significant at P < .05.
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RESULTS
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A total of 22 IAN blocks, 11 administered with the needle bevel oriented away from the mandibular ramus and 11 administered with the needle bevel oriented toward the mandibular ramus, did not result in profound lip numbness at 15 minutes (and were considered unsuccessful blocks). We scheduled these patients for subsequent appointments. Eventually, all 51 subjects experienced profound lip anesthesia with both needle bevel orientations.
Table 1
shows the rates of anesthetic success. For the needle bevel oriented away from the mandibular ramus, successful pulpal anesthesia ranged from 24 to 90 percent from the central incisor to the second molar. With the needle bevel oriented toward the mandibular ramus, successful pulpal anesthesia ranged from 14 to 92 percent. The results showed no significant difference between the two needle bevel orientations for any tooth. Figures 1 through 4 show the incidence of pulpal anesthesia (80 readings) for the two injection techniques for representative teeth.
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Figure 1. Incidence of first molar anesthesia as determined by the lack of response to electrical pulp testing at the maximum setting (80 readings) at each postinjection interval for the two needle bevel orientations.
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Figure 2. Incidence of second premolar anesthesia as determined by the lack of response to electrical pulp testing at the maximum setting (80 readings) at each postinjection interval for the two needle bevel orientations.
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Figure 3. Incidence of lateral incisor anesthesia as determined by the lack of response to electrical pulp testing at the maximum setting (80 readings) at each postinjection interval for the two needle bevel orientations.
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Figure 4. Incidence of central incisor anesthesia as determined by the lack of response to electrical pulp testing at the maximum setting (80 readings) at each postinjection interval for the two needle bevel orientations.
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The mean onset times of pulpal anesthesia for subjects who achieved pulpal anesthesia (that is, two consecutive 80 readings) are presented in Table 2. The results show no significant difference between the two needle bevel orientations.
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DISCUSSION
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We based our use of the pulp test reading of 80—signaling maximum output—as a criterion for pulpal anesthesia on the studies of Dreven and colleagues14 and Certosimo and Archer.15 These studies14,15 showed that when patients did not respond to an 80 reading, this ensured pulpal anesthesia in vital asymptomatic teeth. In addition, Certosimo and Archer15 demonstrated that electric pulp test readings of less than 80 resulted in pain during operative procedures in asymptomatic teeth. Therefore, using the electric pulp tester before beginning dental procedures on asymptomatic vital teeth will provide the clinician with a reliable indicator of pulpal anesthesia. Because all subjects reported that they felt profound lip numbness, despite pulp testing that revealed that subjects did not always achieve pulpal anesthesia (a reading of 80), asking the patient if his or her lip is numb indicates only whether soft-tissue anesthesia has been achieved, but does not guarantee that pulpal anesthesia has been achieved.
Anesthetic success.
Our study results show that anesthetic success was not significantly different when needle bevels were oriented away or toward the mandibular ramus when using a 27-gauge needle. Therefore, we do not think it is necessary to use commercial 27-gauge needles with markers indicating the needle bevel. For the most part, the results of our study were similar to the rates of anesthetic success and incidence of pulpal anesthesia reported in other studies of the IAN block.1 Neither of the needle bevel orientations provided complete pulpal anesthesia for mandibular teeth (Table 1
) (Figures 1 through 4), which could present meaningful clinical problems because the teeth might not be numb enough for procedures requiring complete pulpal anesthesia. Practitioners should consider supplemental techniques, such as intraosseous3,4,16–18 or periodontal ligament injections,2 when an IAN block fails to achieve pulpal anesthesia for a particular tooth. Because we studied a young adult population, the results of this study might not apply to children or elderly patients.
Needle gauge.
While Aldous10 reported that less deflection occurred with larger-gauge needles, Cooley and Robison7 found that the amount of deflection with 27- and 30-gauge needles was nearly identical. Robison and colleagues11 studied the deflection characteristics of 25-, 27- and 30-gauge needles and found that the majority of needles exhibited no statistical differences in the amount of deflection. Hochman and Friedman9 observed that 25-gauge needles deflected less than did 27-and 30-gauge needles in hydrocolloid and frankfurters. However, in wax, the 27-gauge needle deflected more than did the 30- and 25-gauge needles.9 Therefore, as these studies found, all needles deflect away from the bevel and the amount of deflection in relation to needle gauge seems to depend on the study. We selected the 27-gauge needle for our study because Malamed19 stated that one of the most commonly used (that is, most purchased) needles in dentistry is the 27-gauge needle. Future studies might address the association between different needle gauges and anesthetic success.
The 27-gauge needle used in the study was approximately 32 mm long with an ultrasharp, tribeveled needle tip. In comparing 20 sample needles under the dental microscope, we found that a standard Monoject (Kendall, Mansfield, Mass.) 27-gauge dental needle was identical to the needle we used in length and bevel characteristics. The only difference was that the Monoject dental needle passed through the hub to allow cartridge penetration, while the Becton Dickinson needle hub screws onto the disposable Luer-Lok syringe. Use of the Luer-Lok syringe allowed aspiration and delivery of the anesthetic solution in a manner similar to that of a dental aspirating syringe.
With regard to the pattern of fluid flow and the needle bevel, Cooley and Robison7 found that fluid was deposited on each side of the bevel, and the direction of the bevel did not appear to affect the pattern of fluid in the tissues. Future studies might address the pattern of fluid flow with different needle gauges.
The objective of the IAN block is to direct the needle into the pterygomandibular space as close to the IAN as possible so that the local anesthetic solution is deposited in close proximity to the nerve. Berns and Sadove,20 using radiopaque dyes and radiographs of needle placement, found that even with accurate needle placement, 25 percent of IAN blocks resulted in inadequate anesthesia. Using a medical ultrasonographic technique for needle placement for IAN blocks, Hannan and colleagues21 concluded that accurate needle placement did not result in more successful pulpal anesthesia. Galbreath22 reported that the course of anesthetic solution migration could not be predicted accurately; it was determined by the path of least resistance and by the fascial planes and structures encountered in the pterygomandibular space. The migration of anesthetic solution might help explain why accurate needle placement, or needle bevel orientation, may not result in pulpal anesthesia.
Both of the needle orientations in our study resulted in the same number of unsuccessful IAN blocks (that is, a lack of lip numbness within 15 minutes). Therefore, needle bevel orientation does not seem to affect the number of unsuccessful blocks. However, waiting 15 minutes before beginning the dental procedure might not guarantee adequate pulpal anesthesia.1 Using an electric pulp tester before dental procedures provides the clinician with a reliable indicator of pulpal anesthesia onset.
We found no significant differences in mean anesthesia onset times (Table 2). Therefore, needle bevel orientation does not seem to affect the time of onset of pulpal anesthesia. We did not measure the duration of pulpal anesthesia in our study because we ended testing at 60 minutes. Figures 1 through 4 show that pulpal anesthesia of at least 60 minutes’ duration after an IAN block is likely to occur in subjects in whom pulpal anesthesia is achieved.
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CONCLUSION
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The results of this study show that using a 27-gauge needle with the bevel oriented away from the mandibular ramus was similar to using a 27-gauge needle with the bevel oriented toward the mandibular ramus with regard to achieving pulpal anesthesia after administration of IAN blocks in adults.
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FOOTNOTES
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Dr. Steinkruger was a graduate student in endodontics, College of Dentistry, The Ohio State University, Columbus, at the time this study was conducted. He currently has a practice limited to endodontics in Charleston, S.C.
Dr. Nusstein is an associate professor and chair, Section of Endodontics, College of Dentistry, The Ohio State University, Columbus.
Dr. Reader is a professor and program director of advanced endodontics, Section of Endodontics, College of Dentistry, The Ohio State University, 305 W. 12th Ave., Columbus, Ohio 43210, e-mail "reader.2{at}osu.edu". Address reprint requests to Dr. Reader.
Dr. Beck is an associate professor, Section of Oral Biology, College of Dentistry, The Ohio State University, Columbus.
Dr. Weaver is a clinical professor and director of anesthesiology, Section of Oral Surgery, Oral Pathology and Anesthesiology, College of Dentistry, The Ohio State University, Columbus.
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REFERENCES
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- Nusstein J, Reader A, Beck M. Anesthetic efficacy of different volumes of lidocaine with epinephrine for inferior alveolar nerve blocks. Gen Dent 2002;50(4):372–5.[Medline]
- Cohen HP, Cha BY, Spangberg LS. Endodontic anesthesia in mandibular molars: a clinical study. J Endod 1993;19(7):370–3.[Medline]
- Reisman D, Reader A, Nist R, Beck M, Weaver J. Anesthetic efficacy of the supplemental intraosseous injection of 3 percent mepivacaine in irreversible pulpitis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84(6):676–82.[Medline]
- Nusstein J, Reader A, Nist R, Beck M, Meyers WJ. Anesthetic efficacy of the supplemental intraosseous injection of 2 percent lidocaine with 1:100,000 epinephrine in irreversible pulpitis. J Endod 1998;24(7):487–91.[Medline]
- Kennedy S, Reader A, Nusstein J, Beck M, Weaver J. The significance of needle deflection in success of the inferior alveolar nerve block in patients with irreversible pulpitis. J Endod 2003;29(10):630–3.[Medline]
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- Cooley R, Robison SE. Comparative evaluation of the 30-gauge dental needle. Oral Surg Oral Med Oral Pathol 1979;48(5):400–4.[Medline]
- Davidson MJ. Bevel-oriented mandibular injections: needle deflection can be beneficial. Gen Dent 1989;37(5):410–2.[Medline]
- Hochman MN, Friedman MJ. In vitro study of needle deflection: a linear insertion technique versus a bidirectional rotation insertion technique. Quintessence Int 2000;31(1):33–9.[Medline]
- Aldous JA. Needle deflection: a factor in the administration of local anesthetics. JADA 1968;77(3):602–4.
- Robison SF, Mayhew RB, Cowan RD, Hawley RJ. Comparative study of deflection characteristics and fragility of 25-, 27-, and 30-gauge short dental needles. JADA 1984;109(6):920–4.
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- Prohic S, Sulejmanagic H, Secic S. The efficacy of supplemental intraosseous anesthesia after insufficient mandibular block. Bosn J Basic Med Sci 2005;5(1):57–60.[Medline]
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- Berns JM, Sadove MS. Mandibular block injection: a method of study using an injected radiopaque material. JADA 1962;65:735–45.
- Hannan L, Reader A, Nist R, Beck M, Meyers WJ. The use of ultrasound for guiding needle placement for inferior alveolar nerve blocks. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87(6):658–65.[Medline]
- Galbreath JC. Tracing the course of the mandibular block injection. Oral Surg Oral Med Oral Pathol 1970;30(4):571–82.[Medline]
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ABSTRACT
NEEDLE DEFLECTION
