Comparative Study on Anesthetic Potency: METHODS

In: Dental treatment

1 Feb 2010

Subjects and Method of Observation of Anesthetic Effect

The subjects studied were 35 male Japan White rabbits weighing between 1.9 and 2.1 kg. This study was conducted in compliance with the Guidelines for the Treatment of Experimental Animals at the Tokyo Dental College and in accordance with the guidelines of the Japanese government. A 22-gauge in-dwelling catheter (Angiocath, Becton Dickinson, Sandy, Utah) was inserted into the auricular vein of each rabbit. The rabbits were anesthetized with the administration of 25-50 mgAg thiopental (Ravonal, Tanabe Seiyaku, Osaka, Japan). Tracheotomy was performed under spontaneous breathing, and the trachea was intubated with a 14-16 French size pediatric endotracheal tube (Blue Line Tracheal Tube, Portex, Kent, UK). Each rabbit was administered 0.5 mgAg vecuronium (Masclulax, Organon Technica bv, Boxtel, Netherlands) intravenously to prevent movement during preparation, then put on a respirator (Harvard Apparatus Dual Phase Control Respirator Pump, Central Kagaku Boeki, Tokyo, Japan), and ventilated with room air.

Anesthetic potency was evaluated by EMG of the digastric muscle during electrical stimulation at the mandibular incisor. The dental cavity of the incisor was performed by a dental drill. Under irrigation, a round bar #3 (Hager & Meisinger GmbH, Dusseldolf, Germany) was used to create an opening in the pulp chamber of approximately 1.5 mm in diameter from the labial side at the cervix. Two epoxy-coated silver acupuncture needles were placed approximately 3 mm apart on the pulp and were fixed there. After the electrodes for stimulation were installed, the rabbit was maintained in a supine position. The neck was slightly extended, and the head was fixed with a plaster to restrain free movement of the head. Two leads for the EMG were placed laterally on the same side as the tooth in which the stimulating electrode had been installed. After completing the surgical preparation, the rabbit was weaned from the respirator after recovery from thiopental and vecronium and spontaneous breathing was stabilized. An electrode stimulator (Stimulator DPS-05, Dia Medical System, Tokyo, Japan) was used to apply electrical pulp stimulation of an intensity of 10-15 V for a single stimulus 1 millisecond in duration at 30-60-second intervals. The EMG lead was connected to an amplifier (Bioelectric Amp 7923-1B, NEC-Sanei, Tokyo, Japan), and the results were visualized with an oscilloscope (Synchroscope SS-5703, Iwa-saki Electric, Tokyo, Japan) and printed out on a recorder (Omniace RT-3104, NEC-Sanei) (Figure 1).
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Figure 1. Illustration of experimental method

Figure 1. Illustration of experimental method. (A) Stimulating electrode; dental pulp of the mandibular incisor. (B) EMG electrode; digastric muscle. (C) Measurement of administration.

Local Dental Anesthetics

The four anesthetics studied were 4% articaine with 12 fxg/mL epinephrine (A12 group) (Ubistesinforte®, ESPE, Seefeld, Germany), 4% articaine with 6 |xg/mL epinephrine (A6 group) (Ubistesin®, ESPE), 2% lidocaine with 12.5 |xg/mL epinephrine (L group) (Xylo-caine®, Astra, Osaka, Japan), and 3% propitocaine with 0.03 IU/mL felypressin (P group) (Citanest®-Octapres-sin®, Astra).

Injection Site of Anesthetics and Observation Period

The stability of the EMG was confirmed by repeated electrical stimulation to the dental pulp, and the amplitude of the EMG of the digastric muscle during this period was adopted as a control. Local anesthetics were injected into the lingual side of the dental root of the mandibular incisor. This area was confirmed through palpation of the bulging bone. The anesthetic was injected by the extraoral method in approximately 5-7 seconds using a 1-mL disposable syringe with a 26-gauge needle. The control EMG measurement was observed 20 minutes after completing the preparation of the experiment. Thereafter, EMG measurements were made at 2, 3, 5, 10, 12, 15, and 20 minutes after the administration of the local anesthetics. Bilateral mandibular incisors of a single rabbit were used for the experiment.

Dosage Setting of Local Anesthetics and Assessment of Anesthetic Potency

A preliminary experiment was performed in order to determine the adequate dosage of anesthetic in several rabbits. First, the maximal dosage that did not induce change on the EMG of the digastric muscle and the minimal dosage at which it showed flatness of the EMG were used to determine the standard dosages. By increasing or decreasing by 0.05-mL increments from the 2 standard dosages, the range of injection volumes was determined. As a result, the range of dosages was 0.025-0.18 mL for 4% articaine with 12 |xg/mL epinephrine, 0.03-0.5 mL for 4% articaine with 6 |xg/mL epinephrine, 0.1-0.5 mL for 2% lidocaine with 12.5 |xg/mL epinephrine, and 0.15-0.5 mL for 3% propitocaine with 0.03 IU/mL felypressin. In cases where a dosage of 0.5 mL or more was needed, the injection of such a large amount resulted in direct invasion of the digastric muscle itself, which caused the disappearance of the EMG wave. Therefore, injections of more than 0.9 mL were excluded. canadian antibiotics

Figure 2. Example of probit analysis

Figure 2. Example of probit analysis for 2% lidocaine with epinephrine (2 minutes).

Statistical Analysis

Effectiveness (where effectiveness = number of EMG measurements that showed loss of the jaw-opening re­flex at the particular time point measured/total number of EMG measurements made at that time point) was determined for each time point at which EMG measurements were made for each anesthetic. Probit analysis was used to determine the ED50 and ED95 values. The ED50 or ED95 of local anesthetics was calculated from a linear regression line of anesthetic volume and the probit value, where the volume was plotted on the abscissa and the probit value of the potency rate of anesthetics was plotted on the ordinate. A 95% confidence interval was determined for each ED50 and ED95 (Figure 2). The difference between 2 anesthetics was considered to be significant when the confidence intervals did not overlap. The probit analysis was performed using statistical analysis of Soft SPSS. kamagra uk

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