Polymerisation Shrinkage Stress and Flexural Strength of a New Nano-Composite

The purpose of this study was to determine and compare the polymerisation shrinkage stress and flexural strength of different nano-composites.

Methods:

The composites tested were: Tetric EvoCeram (TE-Ivoclar Vivadent), Filtek Supreme XTE (FS-3M ESPE), Estelite Sigma Quick (ES-Tokuyama), IPS Empress direct (IE-Ivoclar Vivadent), Herculite ultra XRV (HU-Kerr), Esthet-X HD (EX-Dentsply) and Venus Pearl (VP-Heraeus Kulzer). After 24h flexural strength was measured with 7-10 specimens (25x2x2mm) per group in a universal testing machine (Zwick Z1445) with a crosshead-speed of 0.75 mm/min (standard EN ISO 4049:2000). To determine polymerisation shrinkage stress, cylindrical cavities (diameter 4mm) were prepared in Araldit B epoxy resin plates (40x40x4mm) and pretreated with the Rocatec system (3M ESPE) to ensure bonding of the resin composites. The resin composite specimens (n=5-10) were exposed to light for 60s with a QTH curing device (Translux Energy, Heraeus Kulzer). The samples were stored dark and dry (23°C) during the first hour and after that in distilled water (37°C). Polymerisation shrinkage stress data (MPa) 24h post exposure were calculated based on the diameter of the isochromatic curves of first order, obtained from the Araldit plates. Statistical analysis was carried out using One-way ANOVA and Scheffé (flexural strength) and Tamhane (shrinkage stress) post hoc test (p≤ 0.05).

Results:

After 24h the following mean values for shrinkage stress/flexural strength in MPa were recorded.

Some significant differences between composites in shrinkage stress and flexural strength were found.

Conclusions:

In this test VP showed the most pronounced combination of low shrinkage stress and high flexural strength. This may be promising for good clinical performance, which need to be verified in clinical studies.