The effect of radiotherapy and surface treatment on immediate repair bond strength of two CAD/CAM materials

Abstract Background Patients undergoing radiotherapy often have limited tolerance for extensive restorative procedures. Therefore, repair of defective restorations using minimally invasive approaches is preferred. This study investigated the effects of radiotherapy and surface treatment on the repair micro-shear bond strength (µSBS) and nanoleakage (NL) of two water-stored CAD/CAM materials. Methods Eighty CAD/CAM specimens were stored in water for 6 months and assigned to eight groups according to irradiation exposure (irradiated or non-irradiated), material type [lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar-Vivadent, Liechtenstein) or CAD/CAM composite blocks (Grandio Blocs, VOCO, Germany), and surface treatment (abrasive bur or abrasive bur + silicon carbide (SiC) conditioning bur). For each material, irradiated specimens (single 6 meV irradiation dose) and non-irradiated specimens were initially prepared using an abrasive bur. Half of the specimens were subsequently conditioned using a SiC bur, while the remaining half received no additional SiC bur conditioning. Three composite cylinders were bonded to each specimen and subjected to µSBS testing at a crosshead speed of 0.5 mm/min. Fracture modes was evaluated using stereomicroscopy and NL was qualitatively assessed for the presence or absence of silver nitrate deposits using SEM. Data were analyzed using ANOVA followed by Tukey’s post hoc test (α = 0.05). Results µSBS was significantly influenced by irradiation ( p < 0.0001), material type ( p < 0.0001), and surface treatment ( p = 0.039). The highest µSBS value (29.50 ± 3.13 MPa) was observed in non-irradiated CAD/CAM Resin Composite specimens treated with AB and SiC, whereas the lowest value (8.78 ± 1.72 MPa) was recorded in irradiated lithium disilicate specimens treated with AB alone. No significant difference in bond strength between surface treatments was found for the lithium disilicate material ( p = 0.423), whereas the Resin composite showed a significant difference ( p = 0.03). Adhesive failure predominated in lithium disilicate specimens (72.3%), while mixed failure predominated in CAD/CAM composite specimens (50%). No silver nitrate deposition was detected with respect to material type, irradiation, or surface treatment. Conclusion For irradiated patients, SiC conditioning bur seemed to be considered as extra step that does not enhance the repair SBS of CAD/CAM materials evaluated in this study.