Evaluation of modern bioactive restoratives for bulk-fill placement

ObjectiveTo investigate the impact of storage up to one year on the micro-mechanical properties of dental bioactive restoratives (R) used for bulk-application and their intermediate layer (IL) to dentin (D).MethodsOne giomer bulk-fill resin composite (RBC) and one glass-ionomer cement (GIC) were applied in 5-mm deep Class I cavities, which were prepared in 50 sound human molars. Specimens were stored in distilled water at 37 °C for 24 h, one week, one month, three months and one year. The variation in micro-mechanical properties (indentation modulus (YHU) and Vickers hardness (HV)) were determined in 100-μm steps in line-profiles located parallel to the tooth axis, starting 0.1 mm from the filling surface, through the IL in between R and D, and ending 300 μm in D.ResultsHV and YHU were influenced by the material (p < 0.001, partial eta-squared η2Pη2P = 0.011 and η2Pη2P = 0.395), immersion duration (η2Pη2P = 0.081, η2Pη2P = 0.081) and depth (η2Pη2P = 0.050, η2Pη2P = 0.091). The micro-mechanical properties progressively increased with immersion time in both restoratives, with a comparable time-dependency pattern, but to a different extent. IL showed weaker mechanical properties compared to more superficial cavity areas, which were maintained in RBC and even enhanced in GIC during storage. After one year of storage HV ranked in the following sequence: GIC: D: 61.4 ± 7.25-N/mm2, IL: 86.0 ± 23.63-N/mm2, R: 112.3 ± 30.36-N/mm2 and RBC: D: 67.2 ± 11.55-N/mm2, IL: 76.7 ± 18.88-N/mm2, R: 94.1 ± 12.28-N/mm2.ConclusionNo degradation with aging was identified in the giomer restorative. The gradual ascending transition in micro-mechanical properties from D through R identified in both restoratives might have a positive effect on the bond quality.Clinical significanceGiomers represent a new category of restoratives with promising clinical behavior and good mechanical stability up to one year of aging under simulated clinical conditions.