Change in jaw occlusive power by paralysis of masseter muscle with a neuromuscular blocker: Sion's masseter muscle paralysis.

STUDY OBJECTIVE: We aimed to determine whether jaw occlusive power decreases with the injection of neuromuscular blocking agents in masseter muscle - a method we named Sion's masseter muscle paralysis (SMP).

METHODS: A randomized, placebo-controlled animal study was conducted in which researchers were blinded to group allocation. We used 12 male mongrel dogs aged 10-12 months and weighing 30-35 kg. Four groups were formed: a conventional dose (CD) group (0.004 mg/kg succinylcholine in 4 ml normal saline [NS]); a high dose (HD) group (0.04 mg/kg succinylcholine in 4 ml NS); a placebo group (4 ml NS); and no intervention group. To measure the jaw occlusive power, 1 kg weight was hung sequentially on a specifically designed device on the animal's lower jaw. At -4, -2, 0', +2, +4, +6, +8, +10, +20, and +30 min, we measured the jaw occlusive power, oxygen saturation (SpO2 ), and end-tidal carbon dioxide (ETCO2 ).

RESULTS: After SMP, jaw occlusive power began to decline in CD and HD group. The arithmetical mean jaw occlusive power values at -4, -2, 0', +2, +4, +6, +8, and +10 min were 9.7, 9.7, 9.7, 8.7, 8.3, 7.3, 6.7, and 6.3 kgw in the CD group and 9.7, 9.3, 8.7, 8.0, 6.7, 5.0, 5.0, and 5.3 kgw in the HD group. No abnormalities in SpO2 or ETCO2 were detected.

CONCLUSION: Jaw occlusive power was decreased after SMP with succinylcholine, without inducing respiratory complication.