Resin matrix dental materials undergo contraction and expansion changes due to polymerization and water absorption. Both phenomena deform resin-dentin bonding and influence the stress state in restored tooth structure in two opposite directions. The study tested three composite resin cements (Cement-It, NX3, Variolink Esthetic DC), three adhesive resin cements (Estecem, Multilink Automix, Panavia 2.0), and seven self-adhesive resin cements (Breeze, Calibra Universal, MaxCem Elite Chroma, Panavia SA Cement Plus, RelyX U200, SmartCem 2, and SpeedCEM Plus). The stress generated at the restoration-tooth interface during water immersion was evaluated. The shrinkage stress was measured immediately after curing and after 0.5 h, 24 h, 72 h, 96 h, 168 h, 240 h, 336 h, 504 h, 672 h, and 1344 h by means of photoelastic study. Water sorption and solubility were also studied. All tested materials during polymerization generated shrinkage stress ranging from 4.8 MPa up to 15.1 MPa. The decrease in shrinkage strain (not less than 57%) was observed after water storage (56 days). Self-adhesive cements, i.e., MaxCem Elite Chroma, SpeedCem Plus, Panavia SA Plus, and Breeze exhibited high values of water expansion stress (from 0 up to almost 7 MPa). Among other tested materials only composite resin cement Cement It and adhesive resin cement Panavia 2.0 showed water expansion stress (1.6 and 4.8, respectively). The changes in stress value (decrease in contraction stress or built up of hydroscopic expansion) in time were material-dependent.

This paper describes a method of laser ablation for improving the hydrophobic properties of vulcanized rubber. The treatment was tested on acrylonitrile rubber (NBR) and styrene butadiene rubber (SBR) containing carbon nanotubes and soot as fillers. The surface layer of the vulcanizates was modified using a nanosecond-pulsed laser at 1060 nm wavelength. The parameters of the ablation process were congruent, so no chemical changes in the polymeric material were observed. Evaluation of the surface condition of the laser-textured samples was performed using a Leica MZ6 stereoscopic microscope, operating with MultiScan 8.0 image analysis software. The contact angles were determined for all the samples before and after the surface modification process. Following modification of the surface morphology, with the best parameters of laser ablation, the contact angle increased, reaching 147°, which is very close to the threshold of superhydrophobicity (150°). On the basis of the results from several tests, laser ablation with a fiber-pulsed laser can be considered a very useful method for producing rubbers with superhydrophobic surfaces.