Modern local anaesthetics have transformed the practice of dentistry. However  a proportion of  injections fail to achieve pulpal anaesthesia.   This trial set out to find if  the addition of mannitol to lidocaine with epinephrine improved its efficacy.

Forty patients were randomised to receive  an inferior alveolar nerve (IAN) block  in 3 separate appointments spaced at least 1 week apart the following anaesthetics

• 1.8 mL solution of 36 mg lidocaine with 18 µg epinephrine (control solution);
• 2.84 mL solution of 36 mg lidocaine with 18 µg epinephrine (1.80 mL) plus 0.5 M mannitol (1.04 mL);
• 5 mL solution of 63.6 mg lidocaine with 32 µg epinephrine (3.18 mL) plus 0.5 M mannitol (1.82 mL).

Following the injection teeth were tested blindly with an electric pulp tester at 4-minute cycles for 60 minutes post injection.  No patient response with the pulp tester at maximum output was considered to represent pulpal anaesthesia. The main outcome was mean percentage total pulpal anaesthesia which was defined as  the total of all the times of pulpal anaesthesia over the 60 minutes. Pain of solution deposition and postoperative pain were also recorded.

They found  that

• 2.84 mL of lidocaine with epinephrine plus 0.5 M mannitol was significantly better than 1.8 mL of lidocaine with epinephrine for the molars and premolars.
• 5 mL of lidocaine with epinephrine plus 0.5 M mannitol was statistically better than 1.8 mL of lidocaine with epinephrine and 2.84 mL of lidocaine with epinephrine plus 0.5 M mannitol for all teeth except the central incisor.
• Solution deposition pain and postoperative pain were not statistically different among the mannitol formulations and the lidocaine formulation without mannitol.

The authors concluded

 adding 0.5 M mannitol to lidocaine with epinephrine formulations significantly improved effectiveness in achieving a greater percentage of total pulpal anaesthesia compared with a lidocaine formulation without mannitol for IAN block.

Wolf R, Reader A, Drum M, Nusstein J, Beck M. Anesthetic efficacy of combinations of 0.5 m mannitol and lidocaine with epinephrine in inferior alveolar nerve blocks: a prospective randomized, single-blind study. Anesth Prog. 2011 Fall;58(4):157-65.