This study evaluated the shrinkage polymerization of two dual-curing resin cements during in vitro and in situ tests, using fiber Bragg grating with different curing time periods. The cements used were: Relyx ARC (dual conventional) and Relyx U200 (dual self-adhesive). For the in vitro experiment, the resin cements and the sensors were placed between two glass coverslips and afterwards were photoactivated for 40 s (N = 20). For the in situ experiments, 20 human teeth were prepared to receive root posts cemented with the same two resin cements. Two sensors were glued to the posts' surfaces at the coronal and apical thirds. Next, the cementation of the posts was photoactivated for 40 s. The sensors measured the strain for 60 min in both experiments. Data from in vitro and in situ experiments were analyzed by three-way ANOVA and Games-Howell multiple comparison procedures. Data from the coronal and apical thirds were analyzed by two-way ANOVA and T-test. The results showed that the polymerization shrinkage values are similar for the in vitro and in situ experiments, that contraction is greater after 5 minutes curing time compared to the contraction at 60 min, that both resin cements performed similarly and that the shrinkage measurement at the cervical third showed higher values than those at the apical third.