Effect of Cement Type and Loading Time on Glass-Fibre Posts

Objectives: To evaluate the effects of cement, loading time and measurement time on mechanical properties of teeth restored with fiberglass posts when subjected to cyclic loading.
Methods: Twenty extracted maxillary canines were endodontically treated to receive fiberglass posts (Reforpost). The teeth were randomly divided into two groups. In Group A, the posts were bonded to the tooth using Panavia F 2.0 - dual-polymerized adhesive resin cement and in Group B, RelyX U200-self-adhesive resin cement, was used. A standardized composite core was built on each tooth. Before loading, a metal ring was filled with self-polymerized acrylic resin and the center was filled with vinylpolysiloxane (VPS). The root portion of teeth were embedded into VPS upto cementoenamel junction. The groups were subdivided into two subgroups, one to be immediately loaded after cementation and the other was loaded after 24hours. Each specimen was subjected to cyclic loading (Bose Electroforce 3200) from 5 N to 50 N for 50000 cycles. Dynamic mechanical analysis provided storage stiffness (K’), viscoelastic energy dissipation ability (Tan Delta) and dynamic stiffness (K*) before and after cyclic loading. Three-way repeated measures ANOVA – f (cement, loading time and measurement time) with Satterthwaite correction was utilized to compare the measured parameters between the groups (significant, p<0.05).
Results: A significant difference was found between the measurement times before and after loading for the following parameters:Static stiffness (K’) (before: 1999.447±741.221 N/mm, after: 1692.049±670.678 N/mm, p=0.002); Tan Delta (before: 0.096±0.023, after: 0.114±0.033, p=0.006), and dynamic stiffness K*(before: 2007.991±741.306 N/mm, after: 1702.081±670.884 N/mm, p=0.002). No difference was found between the materials and the loading times (p>0.2352).
Conclusions: The tested resin cements and loading times (immediate or 24 hour delayed) did not make a difference in the parameters investigated but a significant decrease in static and dynamic stiffness, before and after loading, was noted. A significant increase in damping (tan delta) after cyclic loading is suggestive of increased micro damages or cracks in the tooth/post-core foundation.