SMT (Satisfiability Modulo Theories) solvers are automatic verification engines suitable to discharge important classes of proof obligations generated in applying formal construction of software and hardware designs. In this paper, we present a new approach to combine decision procedures and propositional solvers into an SMT-solver. This approach is based on the generation of model equalities by decision procedures. We show the soundness and completeness of the proposed approach using an original abstract framework to represent and reason about SMT-solvers. We then present an algorithmic version of the new SMT-solving approach and discuss practical aspects of our implementation.