Low shrinking resin composites are in the focus of research in posterior resin composite restoratives. In this context, the silorane-chemistry, incorporating ring-opening monomers and highly filled packable dimethacrylates seem to be most promising. The goal of this study was to investigate cuspal deflection after light-curing in extracted upper premolars (n= 10), using direct current differential transducers (DCDT), and adhesive interface integrity by scanning electron microscopy (SEM) evaluation, of two restorative systems: 1) Filtek™ Silorane/Silorane System Adhesive (3M ESPE); 2) Premise™ Packable/OptiBond FL (KERR). Data were analysed using a two-tailed t-test. A p-value < 0.05 was considered statistically significant. Filtek™ Silorane may reduce cuspal deflection associated to the polymerization process, but there is concern regarding durability of adhesive interface integrity. Premise™ Packable showed higher cuspal deflection and complete integrity of adhesive interface.