Periodontal ligament injection: spread of the solution in the dog

Investigations of the spread of anesthetic solutions administered with the periodontal ligament injection have reported conflicting findings. The purpose of this investigation was to study the distribution of the injected fluid by macroscopic and microscopic techniques. One third of the liquid of the carpules (2% lidocaine with 1:100,000 epinephrine) was replaced with India ink as a marker. Injections were made with a pressure syringe, (Ligmaject) at 90 sites in 12 dogs. Twenty-five control sites were injected with a marked solution without a vasoconstrictor (3% mepivacaine). Seven dogs were killed within 24 h; the others after 5 days. Spread of the ink was studied in undemineralized slices, in three-dimensional cleared specimens, and in histological sections. The solution usually reached the alveolar crest, seeped under the periosteum, and entered into bone marrow spaces alongside vascular channels. The ink spread along the path of least resistance, influenced by the intricacies of anatomical structures and fascial planes, rather than penetrating into the periodontal ligament or in the root canal. In the controls without a vasoconstrictor the spread was more diffuse. Five days postoperatively, carbon particles were present only within macrophages.