Changes in the stress state of metal inlay restorations bonded with selected resin cements
Assoc. Prof. Kinga Bociong1, Dr. Krzysztof Sokołowski2, Prof. Jerzy Sokołowski1, Dr. Michał Krasowski3, Dr. Agata Szczesio-Włodarczyk3
1 Medical University of Lodz, Department of General Dentistry,
2 Medical University of Lodz, Department of Restorative Dentistry,
3 Medical University of Lodz, University Laboratory of Materials Research
Objectives
The resin materials used in the cementation of inlays exhibit polymerization shrinkage which may affect the integrity of the interface between the cement and the tooth structure. This study investigates changes in the stress state of metal inlay restorations bonded with cement during water aging (56 days).
Materials and Methods
Three types of cements were employed: adhesive resin cement (NX3, Variolink Esthetic), self-adhesive cement (Maxcem Elite Chroma, Breeze), and universal adhesive cement (Nexus Universal, G-cem One). A cylindrical sample made of CuZn alloy (type MM54, Huta Będzin) was utilized to simulate the inlays. Using metal inlays of 5.90 mm in diameter, 50 µm of cement layer were obtained. Photoelastic analysis with a circular transmission polariscope (FL200, Gunt) was employed to measure the stress state. The epoxy resin plates were imitate tooth tissue. The cements were photopolymerized according to the manufacturer’s instructions, with lamp output irradiance of 1450 mW/cm2.
Results
Total stress observed after 0.5 h from polymerization for all cements were close to 4 MPa. After water immersion, a notable reduction in contraction stress occurred due to hygroscopic expansion. After two months (56 days), Variolink Esthetic (1.0±0.9 MPa), Breeze (-1.0±0.9 MPa), G-Cem One (0.9±0.8 MPa), and Nexus Universal (-0.4±0.7 MPa) showed stress close to zero. However, NX3 and MaxCem Elite Chroma showed high hydroscopic expansion stress, -6.5 MPa and -5.5 MPa, respectively.
Conclusions
All tested cements generated contraction stress, which decrease during immersion in water. Dynamic of this stress dropping is connected with type/composition of cement.