Comparative Study on Anesthetic Potency: DISCUSSION

In: Dental treatment

3 Feb 2010

Anasthetic potency

Study Method

There are several reports on observations of anesthetic potency of local anesthetics in the teeth. Previous animal models that have been used to study the effects of local dental anesthetics involved the use of the method of Buldring et al, in which the skin contraction response was measured, and the Herr and Jones procedure, in which changes in rat tail elevation or vocalization, respectively, in response to electric stimulation were measured. However, these methods do not consider the effect of the anesthetic’s penetration into tissues before reaching the pulp nor the effect of using a vasoconstrictor with the anesthetic. Therefore, these studies didn’t simulate the clinical setting. Nearly all studies used the maxillary incisor tooth, where cortical bone is relatively thin and local anesthetics penetrate easily. In this study, we used the mandibular incisor as an injection site (where penetration of the injection anesthetics solution to the dental pulp is difficult because of thick cortical bone) and we used the research methods of Grief fie and Brunei, which entails observation by EMG of the jaw-opening reflex of the digastric muscle, specifically observation of the efficacy of the local anesthetic through loss of the reflex over time. The results were then analyzed with the probit method to determine the ED50 and ED95 values. The jaw-opening reflex is induced by a pain stimulus, and this reflex involves at least 2 neural pathways: one causes relaxation of the jaw-closing muscle and the other causes contraction of the jaw-opening muscle. This reflex may be a defensive mechanism that protects oral tissue from a pain stimulus in the oral cavity. With this model, (1) it is easier to monitor and record EMGs of the digastric muscle compared with the somatosensory-evoked potential, (2) reproducibility is sufficient, (3) quantitative evaluation is possible, and (4) effects due to differences among the digastric muscle of different animals are minimized by using probit analysis. Using this model, higher dosages (ED50 or ED95) were judged as having a weaker anesthetic potency. The reason for the extraoral administration of the local anesthetic at the mandibular incisor was because lingual administration of the local anesthetic was easier since rabbit incisor roots are located toward the lingual side of the mandible.

Comparison of Anesthetic Potency

It has been suggested that articaine has a quick onset and a strong anesthetic effect; however, there has been no comparative quantitative study of the efficacy of articaine with other local anesthetics. The A12 group showed local anesthetic potency at lower dosages at all observation points compared with the P and L groups, and the difference in dosage is statistically significant at all of the observation points. Since no increase in dosage was required over time, it can be assumed that the A12 group had fast onset and a long duration of anesthetic effect. This supports the characteristics of articaine that have already been re­ported. In this study, we found a difference in efficacy and anesthetic duration between articaine with 6 (xg/ mL epinephrine and that with 12 |xg/mL epinephrine, showing the tendency that added amounts of epineph­rine contributed to a stronger effect than lidocaine. Comparing the ED50 values among the anesthetics, it was found that the A12 group showed 3.6-4.2 times the anesthetic efficacy of the L group, which suggests the possibility that a lower dosage of articaine can pro­duce the same anesthetic effect as a given dosage of lidocaine. Sitzmann and Lindorf reported that an ar­ticaine solution had higher bone permeability based on experimental results that showed that articaine had su­perior anesthetic efficacy on the mandibular tooth com­pared with lidocaine. Further, Takai et al reported that 4% articaine with 10 |xg/mL epinephrine showed dou­ble the anesthetic efficacy in infiltration anesthesia on volunteers compared with lidocaine with 12.5 |xg/mL epinephrine. On the other hand, Vahatalo et al re­ported that there was no significant difference in the effects of 4% articaine with 5 |xg/mL epinephrine and 2% lidocaine with 12.5 |xg/mL epinephrine upon infil­tration anesthesia procedures on volunteers. Cowancompared the anesthetic efficacy between 4% articaine with 5 |xg/mL epinephrine and 2% lidocaine with 12.5 |xg/mL epinephrine in infiltration anesthesia or in con­duction anesthesia at foramen mentale and reported that the success rate of articaine was only 94% while that for lidocaine was 100%. Haas et al and Donaldson et al reported that articaine administered through infiltration anesthetic procedures showed the same level of efficacy as propitocaine. Sommer et al compared anesthetic efficacy on the ulnar nerve and reported that articaine without a vasoconstrictor showed an anesthetic effect of shorter duration than mepivacaine. When summarizing past studies, it is suggested that there was no significant difference in clinical local anesthetic efficacy between articaine and other local anesthetics when the epinephrine concentration was low, at around 5 |xg/ mL. The strong anesthetic efficacy of the A12 group in this study is suggested to be the result of the high concentrations of both articaine and epinephrine.
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The L group showed stronger efficacy than the P group up to 5 minutes after administration, and there was no change in dosage level over time at all observation points. As a result of the above, the anesthetic onset of the L group was swift, and the anesthetic effect was maintained for over 20 minutes. The ED50s of the L group were 1.2-2.0 times higher than those of the P group. This result closely resembles those of past reports, which have indicated that the L group showed 1.3-1.5 times the efficacy of the P group, which supports the applicability of this experimental model in comparing the efficacy of local anesthetics.

To attain a particular anesthetic effect, a significantly higher dosage level for the P group was needed than for the other 3 groups at the 2- and 3-minute points and up to the 5-minute point, showing the weaker anesthetic efficacy for the P group. Further, to attain a particular anesthetic effect, the dosages of the P group at the 2-, 3-, and 5-minute points were significantly higher than the other measurement points of the P group, which suggests the need for massive doses of this agent for swift onset and duration of anesthetic efficacy. However, the P group did show the same level of local anesthetic efficacy as the L group after the 10-minute point. For the P group to attain the same anesthetic effect as the L group, there was a need to wait 10 minutes. Because the P group also required an increase in dosage level after 12 minutes, there was a significant difference between the P group and the other groups; however, it is suggested that this was due to the limits of the experimental model. In other words, after 20 minutes, the P group required massive dosages, over 0.5 mL, to attain the same anesthetic efficacy as the other agents, which resulted in an extremely large standard deviation in the dosage level. This may be the reason for being unable to identify a statistically significant difference.

A characteristic that was common to all 4 groups was that a specific amount of time was required before onset of the anesthetic effect. For all agents, it was necessary to wait 5-10 minutes after administration to attain sufficient anesthetic efficacy. In other words, to attain satisfactory local anesthetic efficacy for clinical use, there is a need to wait more than 5 minutes after administration of the local anesthetics before further treatment is begun. On the other hand, there is a need to increase the dosage level when (1) a swift anesthetic efficacy is needed, such as 2 or 3 minutes after administration, or (2) the duration of the anesthetic effect needs to be extended.

The A12 group showed efficacy at lower dosages, the shortest time before onset, and a longer duration of efficacy compared with the other 3 agents. This is an extremely desirable feature to a clinical dental practitioner, and thus it is suggested that 4% articaine with 12 |xg/ mL epinephrine is a highly potent local anesthetic for clinical use.
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In conclusion, we provided electrical stimulation to the dental pulp of rabbits to determine anesthetic potency by observing the loss of the jaw-opening reflex of the digastric muscle through measurements made by EMG. Probit analysis was used to analyze the data. We found that there was a need to increase the dosage level of the local anesthetic drugs to attain a quick onset or to extend the duration. Comparing the dosage required to attain a particular anesthetic effect, we found that efficacy was in the order of 4% articaine with 12 |xg/ mL epinephrine, 4% articaine with 6 |xg/mL epinephrine, 2% lidocaine with 12.5 |xg/mL epinephrine, and 3% propitocaine with 0.03 IU/mL felypressin.

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Blog invites submissions of review articles, reports on clinical techniques, case reports, conference summaries, and articles of opinion pertinent to the control of pain and anxiety in dentistry.