Differences in the degree of infiltration of local anesthesia according to the site of injection in rats

This study was conducted for morphological and quantitative evaluation of the diffusional pattern of infiltration anesthesia according to the site of injection. The maxillary first molar of rats was anesthetized by local infiltration of 100 μL of 2% lidocaine containing trypan blue at a distance of 2 mm from the palatal mucogingival junction or mucobuccal fold over the root apex of the maxillary first molar. The frozen sections were prepared in order to measure the volume of the anesthetics using volume-calculating software. On the palatal side, the anesthetic infiltrated the submucosal layer at an infiltration volume of 0.51 ± 0.78 mm3. On the buccal side, the solution entered the space formed by the masseter muscles, the arcus zygomaticus, and the lacrimal gland, at an infiltration volume of 23.80 ± 13.16 mm3. The results indicate the infiltration volume depends on the injection site and that insufficient anesthesia or unnecessary numbness is expected.