Divisions of the maxilla. The arrow shows the site of the injection. The maxilla was divided into 6 parts, which were called as follows: 1, right incisive part (including the right incisor); 2, left incisive part (including the left incisor); 3, right maxillary part (including right molars; the zygomatic arch was removed); 4, left maxillary part (including left molars; The zygomatic arch was removed); 5, right palatal part; and 6, left palatal part. The palatal mucosa and nerves running in the maxilla (maxillary nerves) were detached from parts 3 and 4.

Concentrations of (A) ropivacaine and (B) lidocaine in the right palatal mucosa, maxillary part, and maxillary nerve. After 0.5% ³H-ropivacaine or 2% ¹⁴C-lidocaine was infiltrated into the right palatal mucosa proximal to the first molar of rats, each radioactivity in palatal mucosa (○) , maxillary bone (□) , or maxillary nerve (Δ) was measured with a liquid scintillation counter. The concentration (ng/mg wet weight) of ropivacaine or lidocaine was calculated from the specific radioactivity. Data are mean ± SD (n  =  8). (A) The ropivacaine level in the palatal mucosa reached the maximum 0.5 minutes after the injection, and significantly decreased after 2, 5, and 10 minutes compared with the maximum level (P < .01). There was no significant difference in the anesthetic level between 2 and 5 minutes or between 5 and 10 minutes. The maximum level in the maxillary part was observed 0.5 minutes after the injection. The levels significantly decreased after 2 minutes (P < .01), and did not significantly change thereafter (P < .01). In the maxillary nerve, ropivacaine level reached the maximum after 0.5 minutes, and decreased to 10.4% of the maximum level after 2 minutes. (B) The lidocaine level in the palatal mucosa reached the maximum 0.5 minutes after the injection, and significantly decreased after 2 (P  =  .028), 5, and 10 minutes (P < .01). There was no significant difference in the lidocaine level between 2 and 5 minutes. The level after 10 minutes was significantly lower than that after 5 minutes (P < .01). The maximum level of lidocaine in maxillary part was observed 2 minutes after the injection. There was no significant difference in the lidocaine level between 2 and 5 minutes. In the maxillary nerve, the lidocaine level reached the maximum after 0.5 minutes, and, unlike ropivacaine, lidocaine level slowly decreased in length of time.

Chromatogram of ropivacaine and lidocaine and radioactive metabolites derived from ³H-ropivacaine and ¹⁴C-lidocaine in the palatal mucosa and maxilla. ³H-ropivacaine and ¹⁴C-Lidocaine were separated by thin-layer chromatography (TLC). The area from the lower end of the plate to the solvent front is divided into 1–9 zones. Spots were visualized with ultraviolet lamp (wavelength : 253.7 nm). Authentic ropivacaine and lidocaine were detected in zone 5 and zone 4, respectively. Radioactive substances that were extracted from the palatal mucosa (B and D) and maxilla (C and E) 1 hour (□) and 24 hours (▪) after the injection of 0.5% ³H-ropivacaine and 2% ¹⁴C-lidocaine into the right palatal mucosa proximal to the first molar were separated by TLC. Radioactive substances in each silica gel zone were scratched from the plate and ³H and ¹⁴C radioactivity in the zone was measured with the liquid scintillation counter. The radioactivity in each zone as a percentage of the total radioactivity on the TLC plate was calculated. Data are mean ± SD (n  =  4). In the palatal mucosa (B), 91.0% of total ³H-radioactivity was detected in zone 5, and 87.7% in the maxilla (C) 1 hour after the injection. 89.5% of ¹⁴C-radioactivity was detected in zone 4 in the palatal mucosa (D) and 92.9% in the maxilla (E).

Tissue affinity of ropivacaine and lidocaine in vitro. The affinity of ropivacaine and lidocaine for oral tissues was evaluated by equilibrium dialysis. (A) The amounts of ropivacaine and lidocaine in palatal mucosa, maxillary nerve, brain, and liver after equilibrium dialysis for 26 hours. The radioactivity was converted to the amount of local anesthetic per wet weight of each tissue (nmol/mg wet weight). The uptakes of ropivacaine by the palatal mucosa and maxillary nerve were twice and 12 times higher than those of lidocaine, respectively. (B) The amounts of ropivacaine and lidocaine in maxilla and serum after equilibrium dialysis. The level of local anesthetic per protein content of each tissue was calculated (nmol/mg protein). The amount of lidocaine in the maxilla was 3.7 times higher than that of ropivacaine.