In: Anesthesia28 Nov 2009
The use of the 80 reading as a criterion for pulpal anesthesia was based on the studies of Dreven et al and Certosimo and Archer. These studies showed that an 80 reading ensured pulpal anesthesia in vital asymptomatic teeth. Additionally, Certosimo and Archer demonstrated that electric pulp test readings less than 80 resulted in pain during operative procedures in asymptomatic teeth.
Even when using 3.6 mL of anesthetic solution, anesthetic success with the IAN block occurred 10%-58% of the time and failure occurred 20%-62% of the time (Tables 1 and 2). The central incisor showed the lowest success rate and the canines the highest (Table 1). The success and failure rates are similar to the results of previous studies in which a comparable method was used. Therefore, even after a clinically successful block (lip numbness), pulpal anesthesia in the anterior teeth may not be guaranteed. Theories of anesthetic failure for the IAN block have included cross-innervation, accessory innervation, accuracy of needle placement, anesthetic solution migration along the path of least resistance, central core theory, anxiety and psychological factors.
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Figure 2. Incidence of lateral incisor anesthesia as determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) at each postinjection interval for the 3 injection techniques.
The results of this study demonstrated that pulpal anesthesia for the lateral incisor can be improved with either a labial or lingual infiltration following an IAN block (Tables 1 and 2, Figure 2). However, only the combination of the IAN plus labial infiltration was statistically significant because of the higher failure rate with the IAN plus lingual infiltration (Table 2). Rood administered an IAN block, using 1.5 mL of 2% lig-nocaine with 1:80,000 epinephrine, in 20 patients. Following profound lip anesthesia and pulp testing at 10 minutes, 18 of 20 central incisors were responsive to the pulp tester. Rood then administered a labial infiltration of 1 mL of 2% lignocaine with 1:80,000 epinephrine over the central incisor apex; all the central incisors became nonresponsive to the pulp tester. The 100% success in Rood’s study may be due to the smaller number of patients used in his study or the fact that the labial infiltration was given over the central incisor apex. Regardless of the differences, the results of the study by Rood and the present study demonstrated significant improvement in pulpal anesthesia when a labial infiltration, over either the lateral or central incisor apex, was added to an IAN block. If we were to make clinical recommendations from this study, we would have to favor the IAN block plus labial infiltration for 2 reasons. First, the IAN block plus labial infiltration resulted in better pulpal anesthesia (Tables 1 and 2, Figure 2). Second, the clinician may be more familiar with the labial infiltration. Because we studied a young adult population, the results of this study may not apply to children or elderly patients.
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Adjacent teeth were anesthetized with the IAN block and infiltrations over the lateral incisor (Tables 1 and 2 and Figures 1 and 3). We would expect some spread of the anesthetic solution to adjacent teeth, and significant differences were shown for the central incisor (Tables 1 and 2). For the central incisor, the IAN block plus the labial infiltration resulted in the highest rate of anesthetic success (40%) and the lowest failure rate (15%), which would indicate that a distribution of the anesthetic solution occurred in this tooth even though the infiltration was centered over the lateral incisor. We could speculate that central incisor anesthesia may be better with a labial infiltration over the central incisor as shown by Rood. For the central incisor, the IAN block plus the lingual infiltration resulted in a lower rate of anesthetic success (38%) and a higher failure rate (25%) (Tables 1 and 2). Yonchak et al showed a lower success rate (no response to pulp testing) for the central incisor following a lingual infiltration, over the lateral incisor apex, using 1.8 mL of 2% lidocaine with 1:100,000 epinephrine (47% success rate) compared with a labial infiltration of the same amount of anesthetic solution (63% success rate). Therefore, the lower success rate for the central incisor of the IAN plus lingual infiltration may be related to the lower success rate of the lingual infiltration injection. For the canine, the failure rate of the IAN block plus a labial or lingual infiltration was decreased 5%-10% over the IAN block alone (Table 2). However, the differences were not statistically significant. Because the labial or lingual infiltration was centered over the lateral incisor apex, apparently only a small amount of the anesthetic solution was distributed to the canine. Perhaps infiltrating over the canine apex, following an IAN block, would provide a higher incidence of pulpal anesthesia.
Figure 3. Incidence of central incisor anesthesia as determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) at each postinjection interval for the 3 injection techniques.
Figures 1 through 3 show that the incidence of anesthesia (80 readings) for the IAN block alone gradually increased during the first 15-25 minutes, indicating a fairly slow onset of anesthesia. Previous studies have shown a slower onset of pulpal anesthesia for the anterior teeth when compared with the posterior teeth following an IAN block. Therefore, not only is there a decreased anesthetic success in anterior teeth, there is also a slower onset of pulpal anesthesia. When an infiltration was administered, over the lateral incisor apex, 6 minutes after the IAN block, the incidence of pulpal anesthesia for the lateral incisor increased gradually until it started to plateau at approximately 20 minutes (Figure 2). The slow increase is probably due to the time it takes for the anesthetic solution to pass through the cortical bone to reach the cancellous bone. Viagra Super Active
For the patients who achieved pulpal anesthesia in the lateral incisor, the duration of pulpal anesthesia for the 60 minutes was good for the IAN nerve block alone and the IAN block plus infiltration (Figure 2). The IAN plus infiltration injections helped to sustain a higher incidence of pulpal anesthesia, compared with the IAN block alone, during the 60 minutes.
The adjacent teeth showed a different pattern for the duration of anesthesia. For the IAN block alone, the central incisor showed a slight rise in pulpal anesthesia during the 60 minutes (Figure 3). However, the failure rate was 62% (Table 2). For the IAN block plus infiltrations, the central incisor (Figure 3) showed a gradual decline in pulpal anesthesia after approximately 40 minutes. Perhaps an infiltration over the central incisor apex would prolong the duration of pulpal anesthesia following an IAN block. The canine showed very little change in the duration of pulpal anesthesia with the IAN plus lingual infiltration (Figure 1). The duration of canine pulpal anesthesia with IAN plus labial infiltration started to decline after about 45 minutes (Figure 3). Generally, for the canine, the movement of the anesthetic solution from an infiltration over the lateral incisor apex did not contribute much to the incidence of pulpal anesthesia over the IAN block alone.
Clinically, an IAN block plus a labial infiltration would improve pulpal anesthesia in the lateral incisor, but the results were not 100%. The 12% failure rate (Table 2) is probably due to the initial failure of the IAN block and the fact that the infiltration injection could not completely overcome this failure. Another consideration would be cross-innervation from the contralateral IAN. Yon-chak et al and Rood demonstrated cross-innervation in the central and lateral incisor. Although administering bilateral IAN blocks plus a labial infiltration may be effective in achieving pulpal anesthesia, the considerable soft tissue anesthesia may be uncomfortable for the patient and the patient may feel unable to swallow. What would be an effective strategy for anesthetizing these teeth? Perhaps labial and lingual infiltrations following an IAN block would result in complete pulpal anesthesia. Further studies would need to be completed to determine the success for the lateral incisor and extent of anesthesia for the adjacent teeth using this strategy. Another method to anesthetize mandibular anterior teeth is the intraosseous injection. Although not specifically studied as a supplemental technique in mandibular anterior teeth, Coggins et al found a primary intraosseous injection of 1.8 mL of 2% lidocaine with 1:100,000 epinephrine resulted in a success rate (no response to pulp testing) of 78% in the lateral incisor. This success rate is higher than the 45% success rate (no response to pulp testing) of a labial infiltration, using 1.8 mL of 2% lidocaine with 1:100,000 epinephrine, reported by Yonchak et al. Additionally, the onset of pulpal anesthesia was immediate with the intraosseous injection, whereas the labial infiltration onset was around 8 minutes. Based on the results of the study by Coggins et al, we could extrapolate that an intraosseous injection after an IAN block should result in a reasonable success rate and fairly quick onset time. Therefore, practitioners should consider the supplemental technique of intraosseous anesthesia when an IAN block fails to provide pulpal anesthesia for anterior teeth.
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In conclusion, a labial infiltration, over the lateral incisor apex, of 1.8 mL of 2% lidocaine with 1:100,000 epinephrine following an IAN block significantly improved pulpal anesthesia for the lateral incisor compared with the IAN block alone.
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