Is Mandibular Molar Infiltration a Mental and Incisive Nerve Block?

Methods: Following ethical approval and a power calculation, 22 healthy volunteers received 1.8mL of 4% articaine with 1:100 000 adrenaline as a mandibular buccal infiltration adjacent to the second molar, first molar or canine teeth in a randomized double-blind crossover design.  Injections at the first molar and canine were considered equidistant from the mental foramen.  Responses of the second and first molars, first premolar, and lateral incisors were assessed using an electronic pulp tester over 47 minutes.  Successful anaesthesia was defined as no response to maximal stimulation over two or more consecutive tests.  Data were analysed using Chi-Squared. 

Results: The results are shown in the table. Injections equidistant from the mental foramen achieved success in each tooth type, suggesting a type of regional block either via the mental foramen or by direct entry to the inferior alveolar canal. Injections at the second molar failed to obtain anaesthesia in the lateral incisor suggesting that direct entry into the canal via the cortex is unlikely. There was no significant difference between anaesthetic success at the premolar between infiltrations equidistant from the mental foramen (p = 0.5), although first molar anaesthesia was significantly more likely following infiltration at that tooth compared to infiltration at the canine (p = 0.03). 

Conclusions: Anaesthesia following deposition of articaine in the mandibular buccal sulcus is achieved by infiltration in the second molar and by a combination of infiltration and block via the mental foramen at the first molar and canine.