THE EFFECT OF SHORT TERM WATER STORAGE ON FRACTURE TOUGHNESS AND MICRO HARDNESS OF A LOW-SHRINKAGE SILORANE AND DIMETHACRYLATE BASED NANOHYBRID COMPOSITES

Objectives: The purpose of this study was to assess the effect of water storage on the fracture toughness (K1C), and micro-hardness of a low shrinkage silorane based and a nanohybrid dimethacrylate composite resin materials.
Materials and Methods: Two types of composite resins were selected: nano hybrid methacrylate based (Grandio) and microhybrid silorane based (Filtek P90). For fracture toughness test, a total of 40 single edge notched bar-shaped specimens were prepared and stored in distilled water for 24hrs and 6 weeks. The effect of water uptake on fracture toughness following each storage regimen was determined by loading the specimens to failure in a 3-point flexure strength test setup using a universal testing machine. For Vickers hardness test, 40 disc shaped specimens (height 2 mm, diameter 5 mm) were prepared from each composite material and subjected to testing after 24 hours and six weeks of water storage. The fractured surface was examined using scanning electron microscopy (SEM) to determine the failure pattern following both storage periods.
Results: Statistical analysis (T=8, p<0.0001) revealed that the 24hrs fracture toughness of Silorane was singnificantly higher (1.65±0.12 MP a.m1/2) than Grandio (1.11±0.12 MP a.m1/2). After six weeks storage in water the two materials showed a significant decrease (T=13.5, P<0.001) in fracture toughness with Silorane still exhibiting a higher fracture toughness
(1.22±0.07 MPa.m1/2) compared to Grandio (0.56 ± 0.08 MPa.m1/2).
Silorane showed a highly significant difference in VHN (67.18±1.33) compared to Grandio (42.37±0.73) at the 24 hrs period. After 6 weeks storage in water, a significant decrease was observed in VNH of Grandio (30.55±0.71) while Silorane did not show any decrease in VHN (67.44±1.16). SEM imaging findings were consistent with the results
Conclusions: Within the limitations of this study, Silorane P90 exhibited higher fracture toughness and microhardness compared to Grandio nanohybrid composite in both storage periods. Although water storage decreased fracture toughness of Silorane it still remained significantly higher than Grandio. VHN of Silorane was not significantly affected by water storage after six weeks, while, Grandio showed a highly significant decrease in VHN following water storage.