Effect of low-elastic modulus liner and base as stress-absorbing layer in composite resin restorations.

Objectives: The aim of this study was to evaluate the effectiveness of liner and base materials to reduce the stress resulting from polymerization shrinkage. The null hypothesis tested was that the presence of low-viscosity liner and base materials under the composite resin restoration reduces the polymerization shrinkage stress.

Methods: A quasi-three-dimensional photoelastic model of a second premolar with a class I preparation was restored using four experimental groups (n=7): RC, resin composite (Filtek Z250); FLRC, flowable liner (Filtek Flow)+resin composite restoration; VLRC, resin-modified glass-ionomer liner+resin composite restoration; and VBRC, resin-modified glass-ionomer base+resin composite restoration.

Finite element analysis of weakened roots restored with composite resin and posts.

Finite element analysis (FEA) was used to investigate the influence of different post systems on the stress distribution of weakened teeth under oblique-load application. A maxillary central incisor root obtained from a sound tooth was weakened by partial removal of dentin inside the root canal. Seven two-dimensional numerical models, one from the sound tooth and six from the weakened root restored with composite resin and post systems were created as follows - ST: sound tooth; CPC: cast CuAl post and core; SSP: stainless steel post + composite core; GP: fiberglass + composite core; CP: carbon fiber + composite core; ZP: zirconium dioxide post + composite core; TP: titanium post + composite core.