Study of the adhesion of microhybrid and nanohybrid diacrylic composite resins to dental hard tissues

Objective. The aim of the present study is to compare the adhesive capacity of the microhybrid and nanohybrid diacrylic composite resins to enamel, dentin and cement. Materials and method. Standardized cavities were made at the cervical level on the vestibular surfaces of 8 maxillary third molars without caries or fractures. The cavities were filled with microhybrid (Filtek Z250 – 3M ESPE), respectively nanohybrid composites (Filtek Z550 – 3M ESPE), half of the teeth also receiving an intermediate layer of flowable composite (Gradia Direct LoFlo – GC). All of them were subjected to a thermocycling process (300 cycles in water of 5°C/55°C). After the isolation of the teeth with nail polish, they were introduced into 1% methylene blue for 24 hours. Subsequently, they were embedded in an epoxy resin (EpoThinTM 2 – Buehler), polished and sectioned mesiodistally with Beta Grinder/Polisher-Buehler. Sections were selected where the greatest degree of methylene blue penetration was detected to be analyzed by optical polarized light microscopy (Axio Imager A1m – Zeiss). Results. All teeth showed microinfiltration of the cement, while only half showed it also in enamel. There are no microinfiltration differences between micro- and nanohybrid composite resins. The intermediate layer of flowable composite does not influence microinfiltration.