Effect of ionizing radiation on properties of restorative materials

To evaluate the effect of ionizing radiation from high energy X-ray on properties of restorative materials. Study materials (3M-ESPE) were: Z250—microhybrid resin-based composite (Filtek Z-250); Z350—nanofilled resin-based composite (Filtek Z-350XT); VIT—resin-modified glass ionomer cement (Vitremer); and KME—conventional glass ionomer cement (Ketac Molar Easymix). Sixty bar-shaped and cylinder-shaped specimens were fabricated from each material. Specimens were light activated (980 mW/cm2, Radii, SDI) for 60 s (3 × 20 s for Z250 and Z350) and 120 s (3 × 40 s for VIT) and thirty specimens from each shape were irradiated (IR) with 1.8 Gy/day for 39 days (total IR = 70.2 Gy). IR and non-irradiated (NI) specimens were evaluated for flexural strength (σ, n = 30) followed by fractography (SEM), diametral tensile strength (DTS, n = 30), hardness (H, n = 10), surface roughness (Ra, n = 10) and chemical composition (n = 3). The IR effect on each material property was statistically analyzed using Student’s t test (α = 0.05). Data from σ and DTS were also analyzed using Weibull statistics. IR significantly increased the mean σ values of VIT and KME and the mean DTS value of VIT (p < 0.05). IR increased Ra and H values for VIT and decreased H value for Z-250 (p < 0.05). The remaining materials and properties were not significantly affected by IR (p > 0.05). There was no significant change on materials composition after IR. The recommended radiotherapy protocol for head and neck cancer altered some material properties, mainly for glass ionomer cements. Such variations on material properties are not related to chemical composition changes.