G. Sokołowski

Dental Resin Cements—The Influence of Water Sorption on Contraction Stress Changes and Hydroscopic Expansion

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.

Evaluation of alumino-silicate ceramic surface after different surface conditioning methods

Purpose: of this paper was to evaluate changes in alumino-silicate glass ceramic surface structure and the bond strength to composite material after different surface conditioning methods. Design/methodology/approach: Different conditioning methods of ceramic surface were applied: sandblasting, etching with hydrofluoric acid or both. Grounded ceramic surface served as control group. To evaluate changes of ceramic surface structure CLSM microscopy was used and profilometric analysis of ceramic surface was performed. Shear bond strength of composite material to ceramics was tested. Findings: The highest bond strength between tested alumino-silicate ceramics and composite material was obtained after sandblasting followed by 5 min 9% HF. Research limitations/implications: Further research should be conducted to evaluate the influence of surface treatment methods e.g. prolonged hydrofluoric etching time, on mechanical properties of ceramics. Practical implications: Extending HF etching time of glass-ceramic surface results in increased surface area and allows to obtain high bond strength to composite material. Originality/value: Results of the study applies to clinical situation as the clinical outcome and survival rate of dental all-ceramic prosthetic restorations depend on reliable bonding to tooth structures.

The effect of heat treatment simulating porcelain firing processes on titanium corrosion resistance

PURPOSE Corrosion resistance of titanium used in metal-ceramic restorations in manufacturing is based on the presence of oxide layer on the metal surface. The procedures used during combining metallic material with porcelain may affect the changes in oxide layers structure, and thus anticorrosive properties of metallic material. The aim of the study was an evaluation of potential changes in the structure and selected corrosion properties of titanium after sandblasting and thermal treatment applicable to the processes of ceramics fusion. METHODS Milled titanium elements were subjected to a few variants of the processes typical of ceramics fusion and studied in terms of resistance to electrochemical corrosion. The study included the OCP changes over time, measurements of Icorr, Ecorr and Rp as well as potentiodynamic examinations. Surface microstructure and chemical composition were analyzed using SEM and EDS methods. RESULTS The results obtained allow us to conclude that the processes corresponding to ceramic oxidation and fusion on titanium in the variants used in the study do not cause deterioration of its anticorrosive properties, and partially enhance the resistance. This depends on the quality of oxide layers structure. CONCLUSIONS Titanium elements treated by porcelain firing processes do not lose their corrosion resistance.