Hall technique crowns (HTCs) alter the occlusion temporarily, potentially affecting jaw muscles, particularly the masseter -the primary jaw-closing muscle.To assess masseter muscle activity (MMA) in children treated with a unilateral HTC.In 12 children treated with a single HTC, bilateral MMA was recorded with surface electromyography (sEMG) for ten cycles of Rest-Position (RP) and Maximum-Voluntary-Clenching (MVC) over 20 seconds immediately-pre (P ), immediately-post (P ), at two weeks-post (P ) and at six weeks-post (P ) HTC cementation. T-test, ANOVA and post hoc statistics were used (p<0.05).baseAs expected, MMA was low at rest and increased during maximal jaw clenching (p<0.0001). MMA (mean±SD) increased significantly (p<0.001) between RP and MVC at: P [from 1.60 μV.s (±0.96) to 5.40(±2.30)]; P [1.57(±1.15) to 3.75(±1.87)]; P [1.39(±0.54) to 5.54(±1.45)] and finally P [1.46(±0.56) to 6.45(±2.56)]. Rest-MMA at P , P , P & P remained unchanged (p=0.18) while P clench-MMA reduced by a third at P (p<0.001), returned to and exceeded baseline levels at P (p=0.822), and P (p<0.001) respectively.baseThis pilot study showed that Hall technique crowns may affect masseter muscle activity in children. Clench-MMA was reduced immediately post-treatment but returned to and later exceeded baseline levels at two and six weeks, respectively. Rest-MMA remained unchanged.