The clinical longevity of tooth-coloured restorations, whether direct or indirect, using composites and ceramics, greatly depends on the quality and stability of their marginal adaptation. In this issue, two interesting studies 7,15 bring this subject and lead us to an exciting discussion. Poor marginal adaptation of direct and indirect restorations exposes the dentin pulp complex to the oral e...

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors....

This study evaluated the polymerization shrinkage, flexural and compressive properties of low-shrinkage resin composites. For the study, four methacrylate-based and one silorane-based resin composites were light cured using three different light-curing units (LCUs) and their polymerization shrinkage, flexural (strength (FS) and modulus (FM)) and compressive (strength (CS) and modulus (CM)) prop...

The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated...

This study evaluated the effects of fiber nets and application techniques and flowable composites as a liner on microleakage and the effects of fiber nets on polymerization shrinkage in Class II MOD cavities. Standard MOD cavities were performed in 80 extracted third molars. The teeth were randomly divided into eight groups (n=10). Group 1: Filtek Supreme XT (bulk technique) (FSB); Group 2: Fil...

This study investigated the influence of modulated photo-activation on axial polymerization shrinkage, shrinkage force, and hardening of light- and dual-curing resin-based composites. Three light-curing resin composites (SDR bulk-fill, Esthet X flow, and Esthet X HD) and one dual-curing material (Rebilda DC) were subjected to different irradiation protocols with identical energy density (27 J c...

Despite daily perfecting both the composite material and light sources, the polymerization shrinkage of composite materials still remains a significant problem that compromises longevity of composite fillings. On average, the composite materials shrink 1-5% volume (1). Total shrinkage can be divided into preand postgelation phase. During the pregelation phase, the composite material is not comp...

The aim of this study was to evaluate the polymerization stress and degree of conversion of a composite submitted to different photoactivation protocols. The composite Filtek Z350 was placed in the central perforation of a photoelastic disc and polymerized using a LED-based curing unit (BluePhase II--Ivoclar Vivadent) with energy density of 12, 24 or 36 J/cm2 using the following photopolymeriza...

This study was conducted to determine whether novel experimental low-shrinkage dimethacrylate co-monomers could provide low polymerization shrinkage composites without sacrifice to degree of conversion, and mechanical properties of the composites. Experimental composites were prepared by mixing 28.6 wt% of bisphenol-A-glycidyl dimethacrylate based resin matrix (bis-GMA) with various weight-frac...

Thiol-ene systems demonstrate numerous advantageous polymerization properties in regards to rapid curing, high conversion, minimal oxygen inhibition, and reduced shrinkage stress. However, one of the drawbacks of thiol-ene systems is that commercially available monomers are not able to achieve the mechanical properties required for use as dental restorative materials. Methacrylate systems on th...