Introduction: The aim of this study was to determine the influence of the loss of the first molar in the masticatory efficiency, by Nakamura’s test, in young subjects. Materials and Method: The sample included healthy subjects according to (CDI/TTM), 19 with loss of the first molar and 19 controls with complete dentition. The electromyographic activity was registered by electrodes, located unilaterally in the anterior temporal and superficial masseter muscles, while the subjects were chewing raw carrot, in cubes of 1.3×1.3 cm, in ten masticatory shocks, Nakamura’s test. The statistical analysis was performed by the T and U tests of Mann-Whitney. Results: No statistically significant differences were observed in the masticatory efficiency between both groups. In relation to the electromyographic Activity, statistically significant differences were observed, where the control group with complete dentition presented the highest averages, concluding that the young men with loss of the first molar present a decrease of the masticatory efficiency, with a major VC according to Nakamura’s test, and a minor electromyographic activity of the previous Temporary muscles and superficial masseters of the right and left side.