Volumetric Shrinkage and Polymerization Shrinkage Stress In Different Bulk Fill Composite Resins
Ghannam, Mousa G.
MetadataShow full item record
The volumetric contraction associated with polymerization, and its associated shrinkage stress, are a huge limitation of resin-based composites. Volumetric shrinkage occurs when the intermolecular distance of monomers in the organic matrix of composites is reduced, as a result of the formation of covalent bonds. This contraction causes internal stresses to form within the composite if it is constrained within the oral environment, which becomes transferred to the tooth structure during cavity restoration. This process produces tensile forces at the bonding interface, which have the potential to cause bond failure, micro leakage, marginal gap formation, secondary caries, cuspal deflection, pulpal irritation and post-operative sensitivity. Various modifications of the monomer system have led to the manufacturing and release of innovative bulk-fill composites with lower viscosity and shrinkage stress. However, no formal investigation of the relationship between polymerization shrinkage and shrinkage stress in these new composites has been done. We hypothesized that there is a significant difference between the volumetric shrinkage and shrinkage stress between conventional nano-hybrid composites, and that there is a correlation between these two properties. Depth of cure (DOC), polymerization shrinkage and shrinkage stress were measured for: Filtek Supreme Ultra (control), Tetric EvoCeram, SureFIl SDR and Filtek Bulk Fil. There was no difference between the bottom/top hardness ratio across different composites. There was no consistent correlation found between volumetric shrinkage and polymerization shrinkage stress. All the bulk-fill composites demonstrated significantly lower polymerization shrinkage stress compared to the control. SureFil SDR and Filtek Bulk Fill had significantly higher and lower volumetric shrinkage compared to that of the control, respectively.