Dose-dependent effects of gamma-ray irradiation on SLA-treated titanium Grade 4: An in vitro evaluation of its physical, chemical and surface properties

BACKGROUND: Gamma-ray sterilization is commonly used for dental implants, but may alter their physical, chemical and surface properties. OBJECTIVES: The present study compared gamma-ray irradiation doses of 15 kGy and 25 kGy in terms of their effects on the physical (microhardness), chemical (titanium (Ti) ion release) and surface (morphology and hydrophilicity) properties of sand-blasted, large-grit, acid-etched (SLA) Ti Grade 4 (G4) implants. MATERIAL AND METHODS: A total of 48 cylindrical Ti G4 samples (4 mm in diameter, 8 mm in thickness) were irradiated using cobalt-60 (Co-60) gamma radiation at 0 kGy (non-irradiated), 15 kGy or 25 kGy doses. Post-irradiation analyses included testing Vickers hardness (HV), Ti ion release in simulated body fluid (SBF) after 2 weeks, the water contact angle (θ), and scanning electron microscopy (SEM) for morphology assessment. Statistical significance was set at α = 0.05. RESULTS: Gamma-ray irradiation significantly impacted all measured properties. The mean hardness decreased from 536.5 HV (non-irradiated) to 251.3 HV (15 kGy) and 203.8 HV (25 kGy) (p < 0.001); no significant difference was observed between 15 kGy and 25 kGy. Titanium ion release increased with a radiation dose: 44.68 μg/L (non-irradiated); 93.75 μg/L (15 kGy; p = 0.0292 vs. control); and 218.98 μg/L (25 kGy; p < 0.001 vs. control and 15 kGy). The water contact angles approached 0° postirradiation, indicating a shift to superhydrophilicity, significantly different from the moderately hydrophilic control (p = 0.0085), with no difference between the radiation doses (p = 0.1266). The SEM analysis revealed more pronounced micro-damage and roughness at 25 kGy. CONCLUSIONS: Both 15 kGy and 25 kGy significantly altered surface properties, but 25 kGy induced greater Ti ion release and micro-damage. Within the study limitations, 15 kGy is recommended as the preferred sterilization dose, as it maintains sterility while minimizing mechanical degradation and excessive Ti ion release as compared to 25 kGy.