Shrinkage Related Stress of Dual-Cure Post Cementation Materials

Objectives: Wide, irregular shapes of the coronal part of root canals can lead to thicker cement layers around endodontic posts. Thicker cement layers induce a higher shrinkage stress challenging the bonding interfaces. This investigation evaluates the differences in volumetric shrinkage and shrinkage stress of a self-adhesive universal resin cement compared to a dual-cure core build-up and post cementation composite.
Methods: 3M™ RelyX™ Universal Resin Cement (RUV) and DMG LuxaCore Z Dual (LUX) were compared. Shrinkage specimens were prepared according to Watts bonded disc method (D.C. Watts, A.J. Cash, Dent.Mater.1991,7,281-287): 100 mg material was applied into a brass ring (1mm height, 16mm inner diameter) bonded to a 3mm thick glass plate. Material was flattened with a 100µm cover slip. Slip movement during light-cure (20s, 3M™ Elipar™ S10 LED Curing Light) was recorded by a LVDT transducer. To analyze shrinkage stresses the deformation of a 2mm thick wall of a slot (2mm wide and 2.5mm deep) in an aluminum block was measured. The slot-shaped cavity was filled with the test material and light cured for 20s (3M™ Elipar™ S10). Shrinkage and stress induced deformation values were recorded 1h after light curing. Data was analysed by 2 sample t-test; p<0,05 indicates statistically relevant differences.
Results: RUV showed a significantly higher volumetric shrinkage but a significantly lower stress induced deformation than LUX (see table).
Conclusions: Test confirmed that the magnitude of shrinkage induced stress is multifactorial and not determined by shrinkage alone. The established clinical history of the materials investigated suggests that shrinkage induced stress at the levels observed is not critical.