Anatomic feasibility of a modified 3-distal site anesthesia injection method for impacted mandibular third molar extraction using cone-beam computed tomography

Abstract

Background: Various injection methods have been used to improve the success rate of inferior alveolar nerve (IAN) block and reduce the pain and complications. But these methods also have their advantages and disadvantages. A modified 3-distal site anesthesia injection method proposed in 2015 was used clinically with satisfactory results at some dental clinics in China. This study aimed to determine the feasibility of this modified 3-distal site anesthesia injection method for extraction of an impacted mandibular third molar from an anatomical point of view.

Methods: Three-dimensional (3D) reconstruction and analysis of the mandibles was performed using cone-beam computed tomography (CBCT) scanning to measure the simulated needle insertion depth, infiltration distance, and other important parameters. These parameters were compared with an actual depth of 20 mm and a theoretic infiltration distance of 10 mm. The main parameters were compared between males and females.

Results: Sixty-three CBCT datasets were imported into Simplant OMS software for 3D reconstruction. The left simulated insertion depth did not differ from 20 mm, while right insertion depth was >20 mm (P<0.05). The bilateral infiltration distances were <10 mm (P<0.05) and articaine blocked the IAN. The widths of the mandibular rami were greater than the syringe length (21 mm), thus it was not possible for the syringe to reach the distal edge of the mandible. There was no difference in the simulated needle insertion depth and infiltration distance between the left and right (P>0.05). The bilateral simulated insertion depths, infiltration distances, widths of the mandibular rami, and height of the left mandibular foramen in females were less than in males (P<0.05), while there was no difference in the height of the right mandibular foramen and bilateral insertion angles (P>0.05).

Conclusions: The modified 3-distal site anesthesia injection method was shown to block the IAN based on anatomic evidence derived from 3D analysis on the measurements by CBCT.

Keywords: Anesthesia injection; cone-beam computed tomography (CBCT); distal insertion site; inferior alveolar nerve (IAN).

Figure 1

The schematic diagram of modified 3-distal site anesthesia injection method. Anesthetic was injected by a syringe needle into the periosteum of the mesiobuccal and lingual insertion sites to anesthetize the corresponding gums and mucosa, respectively. At the distal site of the impacted mandibular third molar, a needle was inserted and slipped inward for 20 mm after contacting the bone surface. When the needle touched the end and blood could not be withdrawn, anesthetic was injected to block the IAN. IAN, inferior alveolar nerve.

Figure 2

The points, lines, and surfaces based on 3D measurements. (A) Points 1–16 are set according to the sequence from IM to RIntersection; (B) setting lines; (C) planes in coronal view; (D) planes in transverse view. IM, midpoint between the mesial incisal tips of both mandibular central incisors.

Figure 3

Schematic diagram of the left infiltration distance. Points LInEnd and RInEnd were the theoretical bilateral insertion end sites. The line, LMnF-LInEnd, was the theoretical minimum distance for the anesthetic to infiltrate. There was a left difference (LDifference) between the actual depth of needle insertion (20 mm) and the line length (LRamusAnt-LInEnd). The LDifference and LMnF-LInEnd were set as the right-angle sides of a triangle, and the length of the hypotenuse was the left actual distance for the anesthetic to infiltrate (LWAnesthetic).