Polymerization shrinkage, modulus, and shrinkage stress related to tooth-restoration interfacial debonding in bulk-fill composites

Water sorption and solubility of bulk-fill composites polymerized with a third generation LED LCU

“…As a result, a number of clinical problems, such as microleakage, secondary caries, discoloration and postoperative sensitivity may arise. 4 In order to minimize the volumetric polymerization shrinkage, so to reduce stress at the tooth-composite interface 5 and achieve better mechanical properties along with adequate light penetration, 2 an incremental technique is needed, in which the composite is layered and light cured in increments of less than 2 mm. However, the incremental technique has a number of drawbacks, which include bond failures between increments due to contamination, the creation of voids, the more time required to place and polymerize each layer, and the difficulty in placement because of limited access during the conservative preparations.…”

“…Regular bulk-fills do not need an additional capping layer and can be used as a singlestep filling material. 5,8 With the spread of photopolymerizable dental composites, significant advances have been made in light curing units (LCUs) used in polymerization processes. Recently, the incorporation of different photoinitiators has led to the development of third generation polywave LED LCUs.…”

Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

“…63 The advantages of flowable bulk-fill composite is improved adaptation to cavity walls and reduced shrinkage stress due to its lower elastic modulus. 5 Reduction of shrinkage stress is another important claim for this new generation of bulk-fill composites. In fact, most bulk-fill composites available in the market did not represent any significant modification in monomeric composition.…”

“…Very recently, commercial materials based on stress-relieving moieties have been introduced in the market, both commercialized as bulk-fill materials. 5 For at least one of them, the underlying technology relies on free-radical addition fragmentation groups, which are the active moieties in covalent adaptable networks. In summary, this mechanism promotes rearrangemente of the network connectivity without reducing the overall crosslinking density or the final mechanical properties of the composite, even in glassy networks.…”

“…5 A gradual increase in viscosity of the resin material also occurs during the conversion, resulting in loss of its fluidity (gel-point) and flowing ability (vitrification). 4 Prior to vitrification, these materials are able to flow and partially relieve stresses.…”