El proposito de este estudio fue evaluar los efectos en el area de accion y reaccion al aplicar clinicamente el diseno pendular de doble ansa (Uribe99) previamente evaluado in vitro. Se tomo una muestra por conveniencia de 10 sujetos, 5 Hombres 5 mujeres con promedio de edad 13.3 anos, a los que se les instalo el pendulo dejandose actuar hasta llegar a una relacion molar clase I definida por la posicion de la cuspide mesiobucal del primer molar superior en el surco bucal del primer molar inferior. La inclinacion del primer molar, segundo premolar e incisiva asi como su desplazamiento horizontal y vertical fueron evaluadas en cada paciente por medio de la diferencia entre la radiografia cefalica final e inicial, en las cuales se tenian marcas radiopacas de referencia para evitar error por una superimposicion de imagenes. La rotacion de los molares se evaluo por medio del oclusograma. El tratamiento con pendulo produjo un espacio promedio de 5.5 mm (±2.1), en el area de accion se produjo un desplazamiento distal molar promedio de 3,8 mm (±2.3), y en el area de reaccion un desplazamiento mesial del premolar promedio de 1,6mm (±0.8) y anterior de 0 mm (±1). Solo el desplazamiento molar fue estadisticamente significativo (p = 0.008). En cuanto a la inclinacion tambien solo la del molar fue estadisticamente significativo (p = 0.008), con un promedio de -12,3o (±6.7), mientras que la del premolar fue de 3.7o (±6.6) y la inclinacion anterior de 0o (± 1.6). Los Cambios verticales no fueron significativos: 0.9 mm (1.3) extrusion molar, 0.1 mm (±1.3) intrusion premolar, aumento a tercio inferior 1o (±1.8), ENA-Mn 1 mm (± 1,5) y una distorotacion molar de 4o. En general en los pacientes evaluados se observo que en el area de accion el desplazamiento distal del molar logrado con el pendulo es efectivo, con una minima reaccion o perdida de anclaje anteroposterior de premolares e incisivos y con minimos cambios verticales, sin embargo el movimiento es basicamente de inclinacion molar no controlada. ABSTRACT The purpose of this study was to evaluate the clinical effects in patients, in the areas of action and reaction, when using the previously reported pendulum twice loop design (Uribe/99), which was already tested in vitro. The sample consisted of 10 patients, 5 women and 5 men, 13.3 years old average, to? whom a pendulum was installed, which was left in position and activated until a class I molar relation was reached (determined by the position of the mesio-buccal cusp of the upper first molar, falling exactly onto the bucal sulcus of the lower first molar). The inclination of the first molar, second bicuspid and incisor, as well as its horizontal and vertical displacement were evaluated in every patient, by means of measuring the difference between the pre and post treatmentlateral cephalograms, which had radio marks to identify anatomical structures and avoid mistakes in the tracing by image superimposition. Molar rotation was evaluated with the aid of an oclusogram. The treatment with the pendulum resulted in an average space of 5.5 mm (±2.1), in the action area a distal displacement of the molar was obtained, average 3.8 mm (±2.3) and in the reaction area a mesial movement of 1.6 mm in average (±0.8) of the bicuspid, as well as an average of 0 mm of displacement (±1) in the anterior (incisal) region. The Orly statistically significant movement was that of the molar (p=0.008). Regarding tipping, only the molar movement was statistically significant (p=0.008) with an average of –12.3o (±6.7); the bicuspid’s inclination was 3.7o (±6.6) and in the anterior region was 0o (±1.6). Vertical changes were not significant: molar extrusion 0.9 mm (±1.3), premolar intrusion 0.1 mm (±1.3), inferior third increase of 1o (±1.8), ENA-Mn 1 mm (±1.5) and a distal rotation of the molar of 4o. In general, in the patients who were evaluated, it was observed that action area the distal displacement of the molar obtained with the pendulum is effective, with a slight reaction (anchorage loss) in the anteroposterior region of premolars and incisors and with minimal vertical changes. However, the movement is basically a non-controlled tipping of the first molar.