Patients
A single-blind randomized clinical trial study was conducted on 42 patients (84 cases) within 18 to 55 years-old by split-mouth design, whom were referred to the Oral and Maxillofacial Surgery Department. The patients needed bilateral IANB for posterior mandibular teeth extractions, and at least they had to have one lower molar tooth bilaterally, since each subject served as a control for its own. The cases were excluded in this study by having systemic disease, nervousness, limitation of mouth opening, infection, a history of a sensitivity reaction to the anesthetic solutions, ramus surgery or fracture, and any prescription changing the pain perception [17–19].
According to ethical approval, all individual participants that included in this study have informed and filled the consent from. After randomly selecting patients with proper criteria, the operation sites and techniques were randomized for the first surgery, and then the opposite site was implemented with the other method. The single-blind randomization has been completed with coins and letters (first letter of the method in a pocket).
Anesthetic solution and injection
In this study, an anesthetic solution was administered on the one side via the conventional method and the other side by the modified technique, considering randomization in which the same operator has done both procedures. The two techniques applied at least two weeks apart. The patients were in a semi-supine position in both techniques, and the operator positions were at 8 o’clock for a right IANB and at 10 o’clock for a left IANB, since the administrator was right-handed [4]. In each technique, a 27-gauge long needle was equally used with lidocaine 2% and epinephrine 1/80,000 in a 1.8 ml cartridge.
Conventional IANB
In the conventional IANB technique, the mouth should open widely considering three parameters, such as the injection height, the anteroposterior location of the needle, and the penetration depth. To determine the height of an injection, the left index finger or thumb was placed in the coronoid notch with an imaginary line extending posteriorly, which started from the fingertip in the coronoid notch to the deepest zone of PMR. This imaginary line should be parallel to the mandibular OP of the molar teeth, and it lies mostly 6–10mm above the OP. The barrel of the syringe was placed at the mouth corner on the contralateral side, while the insertion point was located at three fourth of the anteroposterior distance from the coronoid notch back to the PMR. The depth of the needle penetration was 20–25 mm toward a bone contact in the adult [4].
Modified IANB
In the planned modified technique, the injection anatomical landmarks were the PMF and the OP (Fig. 1a).
The anatomical landmarks have been displayed, to show injection point via the barrel of a syringe that is located to the contralateral side on the first molar or between first and second premolar
In this technique, the mouth should be open as wide as possible, and the barrel of the syringe located to the contralateral side on the first molar or between first and second premolar, upon the mouth corner allowance.
The needle enters mucosa just lateral (anterior) to the PMF (as Lateral hypothetical line to the PMF in Fig. 1b).
It shows that the needle injection point is just lateral to the pterygomandibular fold (Lateral hypothetical line to the PMF)
The needle entrance is about 5–15 mm above and parallel to the OP, which based on the vertical distance of OP to the MF in the digital panoramic radiography using a caliper (Fig. 2) [20, 21].
The needle injection height was determined by digital panoramic radiography using Castroviejo caliper, between two parallel presumed lines (superior-anterior MF and OP)
Additionally, an insertion should be continued until the needle tip contacts the bone in an advancement to the medial aspect of the ramus. At this point, after negative aspiration, approximately 1.5 cc of the cartridge was deposited in 60 seconds, while the residue was injected through the needle withdrawal to anesthetize the lingual nerve.
In conditions that the needle tip contacted the bone prematurely, the syringe and needle should be turned to the side to be operated on, which is a position that allows easier sliding of the needle along the ramus inner surface [16]. At the beginning of each method, the chronometer stated the injection time, and the surgeon observed the situation by establishing the exact time of anesthesia onset, accompanied by the patient that asserted the beginning of lip/chin numbness objectively. The technique was considered successful once confirming the anesthesia by the ipsilateral numbness of the lower lip and chin during 5 minutes [22].
Numbness of the lower lip and chin states the mental nerve anesthesia, which is a good indication for IAN anesthetizing, although the depth of anesthesia is not correlated [4]. In cases of no signs of anesthesia, in the first five minutes, the operator awaited another five minutes to evaluate the situation. However, failure procedure was considered by a condition that there was no sign of anesthesia after 10 minutes, although another cartridge was injected to continue the scheduled operation.
In any situation with incomplete anesthesia during EXT, a periodontal ligament (PDL) or intraosseous injection was administered [22]. Besides, in an IANB, the lingual nerve usually was anesthetized; otherwise, the anesthetic solution was injected about 0.3 ml (cc) from another cartridge into the lingual sulcus, while the long buccal should be anesthetized separately.
Statistic
Base on split-mouth design, the sample size was determined to compare proportions by assuming 10% difference in success rate concerning two techniques in paired groups. Therefore, the study required a sample size of 37 patients (paired or matched cases) to achieve a power of 90% with 5% significance to detect at least a difference of 0.10 between marginal proportions, which are success proportions showing at least 10% difference.
The Cochran-Mantel-Haenszel test was used by a 95% confidence interval to compare the success rates [23] between both techniques since it can analyze matched categorical data [24].