Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Objective: To evaluate the effects of unilateral and bilateral premature loss of posterior occlusal support on mandibular bone dimensions in growing rats. Materials and Methods: Thirty female Wistar rats (5 weeks old) were randomized into three groups: control, unilateral mandibular molar teeth extraction, and bilateral mandibular molar teeth extraction. After 8 weeks, animals were sacrificed and acrylic rapid-prototyped templates of the mandibles were constructed. Mandibular length, ramus height, intercondylar distance, and body weight were measured and analyzed by one-way analysis of variance (Tukey test as post hoc test; alpha = .05). Results: Mandibular length and intercondylar distance were significantly shorter in experimental animals, while no difference was observed for ramus height and body weight. Conclusions: Unilateral and bilateral premature loss of posterior occlusal support in growing rats results in a smaller mandible at skeletal maturity. (Angle Orthod. 2012;82:242-246.)822242246Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)