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.

The successful restoration of teeth requires a good connection between the inlay and natural tissue. A strong bond may improve retention and reinforce tooth structure. The purpose of this study was to evaluate the influence of cement layer thickness on contraction stress generated during photopolymerization, and to determine the changes in stress state of the cement occurring during aging in water (over 84 days). Two cements were used: resin composite cement (NX3) and self-adhesive resin cement (Maxcem Elite Chroma). A cylindrical sample made of CuZn alloy was used to imitate the inlay. The stress state was measured by photoelastic analysis. The contraction stress of the inlay restoration was calculated for cement layer thicknesses of 25 µm, 100 µm, 200 µm, and 400 µm. For both tested materials, the lowest contraction stress was observed for the thinnest layer (25 µm), and this increased with thickness. Following water immersion, a significant reduction in contraction stress was observed due to hygroscopic expansion. Applying a thin layer (approximately 25 µm) of composite and self-adhesive resin cements resulted in high levels of expansion stresses (over −6 MPa) after water aging.

Wstęp. Wybór określonego cementu protetycznego powinien być dokonywany w oparciu o warunki kliniczne, rodzaj wykonanego uzupełnienia protetycznego, jak również poprzez znajomość właściwości cementów protetycznych. Pojawienie się w ostatnich latach nowych cementów na bazie żywic (samoadhezyjnych, samotrawiących) o odmiennym składzie i mechanizmie wiązania skłania do porównania właściwości mechanicznych ww. cementów. Cel pracy. Porównanie właściwości mechanicznych wybranych cementów żywiczych.

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1) determined the rate of pinning of dislocations in copper single crystals during Co60 --irradiation by means of damping measurements at about 10 kHz. They found a pronounced minimum at 160 OK which they interpreted to be due to thermal conversion of the interstitials (2, 3). In the present paper similar damping measurements for 3 MeV-electron irradiation will be reported. In addition, here also the corresponding modulus measurements are given, which, as stated by Thompson and Buck (l), were not possible with sufficient accuracy in their case.In the present paper polycrystalline samples of 99.999% MARC0 copper were used (the same material a s in (1)). They were excited to torsional oecillations of about 5 lr~z at strain amplitudes of about lX10-? d he irradiation temperature was varied from 78 to 240 OK and the defect production rate was usually 1 . l x l O " defect psirs/cm 8 , leading during our irradiation times of 0.5 h to the same final defect concentration of about lo-' 88 in the experiment of Thompson and Buck. The background of decrement and modulus was determined by irradiation with lX1017 electrons/ cm and subsequent annealing for 5 min at 130 "C. After each irradiation run the sample was recovered in situ by annealing at 500 "C for 5 min which led reproducibly to the condition of the samples before irradiation. 2The number p of irradiation-induced pinning points per dislocation segment was determined in the usual way (4). Fig. 1 shows p vs. irradiation time for one set of irradiations. One recognizes that there are temperature-dependent systematic differences up to the factor two between the p-values obtained from modulus and decrement. Similar deviations have-been reported also by other authors ((4, 5), and also (1)). In analogy to (1) the mean slope of the pinning curves at the beginning has been taken ae the initial pinning rate b. It is plottea for two samples in Fig. 2.