Evaluation of Use of Ultrasound for Greater Palatine Nerve Block and Inferior Alveolar Nerve Blocks: An Open Label Feasibility Study

Overview

Dental anesthesia is routinely performed based on anatomical landmarks which can be variable leading to repeated injections and failure. Ultrasonography can be used to guide these injections by identifying the nerves, accompanying blood vessels and the bony landmarks. 20 healthy adult patients will be selected to receive ultrasound guided greater palatine nerve block (gpn) (10 patients) or inferior alveolar nerve (ian) block (10 patients) depending on the dental procedure they are undergoing. The study will evaluate the feasibility and success rates of the ultrasound guided gpn and ian nerve block.

The study will be done on 10 adult patients belonging to asa physical status 1 or 2 undergoing dental procedures with indications for greater palatine or inferior nerve blocks. The study will be conducted in the dental clinic, university hospital, london health sciences centre. All subjects will receive the letter of information at least 4-6 hours before the study procedure. One of the investigators will obtain an informed consent prior to the procedure. All subjects will be clinically examined to rule out any contraindications to the block such as infection, allergy to local anesthetic and any known coagulopathic disorder. No sedation will be used. The study subjects will be positioned on the dental chair and requested to open the mouth as wide as possible. In patients undergoing dental procedure to the upper teeth posterior to canine, a linear hockey stick probe will be positioned long axis to the palate just medial to the alveolar ridge. A color doppler will be used to identify the greater palatine artery (gpa) and this artery will be traced to the greater palatine (gpn) foramen by moving the probe gradually posteriorly until the greater palatine foramen is visualized and the gpn and the gpa are seen to exit from the foramen. Using an oblique off-plane approach a 25g needle attached to a dental carpule of 2% lidocaine will be inserted to contact the nerve and a total of 1ml of local anesthetic is deposited around the nerve and the needle removed. In patients undergoing a dental procedure in mandible, the ian block will be done with the same probe. The ultrasound probe will be positioned so that it is facing laterally on the buccal mucosa close the retromolar area. A color doppler will be used to identify the inferior alveolar artery and a 25g needle coming in-plane to the probe from the anterior side of the probe will deposit the local anesthetic agent perineurally. Images will be stored pre-injection, during injection and post injection. One of the investigators will test for the sensory block in the distribution of gpn and ian. The sensory anesthesia is graded as no anesthesia, partial anesthesia and complete anesthesia for each of the nerve blocks. The time to perform the blocks and time to block onset will also be noted. The total procedure duration is counted form the time of starting the scan to the time of completion of injection. The block performance duration is documented from the time of starting the needle insertion to the end of injection. Time from the end of injection to onset of sensory analgesia will be considered as the onset time. The blocks will be tested at 2 minutes, 5 minutes and 10 minutes after the injection. For the gpn, the sensory block will be documented on the hard palate from the last molar to the canine on the blocked side specifically at the 1st premolar mesially. The areas that will be tested with the dental probe for ian are the buccal mucosa at the base of the first molar tooth (ian), the lower lip of the blocked side, the tip of the tongue (lingual nerve) as well as the lingual mucosa (lingual nerve ) and the buccal mucosa lateral to the molars on the block side (ian). Occurrence of any local hematoma or paresthesia during the procedure will be documented. The subjects will be contacted over the telephone at 24 hours for any residual paresthesia or numbness.