Dentine specimen preparation
teeth, dentine
A total of 180 dentine fragments were obtained from the cervical area of the root of extracted human premolars. The teeth had been taken from a pooled biobank (details under Ethical Aspects). The fragments were embedded in acrylic resin and these specimens were then ground flat with abrasive silicon carbide paper discs of grain size 18 µm until 300 µm of the root surface was removed. The specimens were further ground with abrasive silicon carbide paper discs of 9 µm grain size to remove another 30 µm of the dentine surface. Final polish was performed with the paper discs with grain size of 3 µm for 2 min. Grinding and polishing procedures were performed with a polishing machine under constant cooling (EXAKT-Apparatebau, Otto Herrman, Nortedstedt). Between each type of paper disc and after the final polish, the specimens were rinsed and sonicated for 1 min. The specimens were stored in tap water until the beginning of the experiment when they were rinsed and sonicated for 1 min. Then, the initial profile of a central area (3 mm × 1 mm) was analyzed with an optical profilometer, and an adhesive tape was placed on two parts of the dentine surface, with a distance of 1.5 mm between them, where the treatments and challenges were performed. The specimens were kept in a humid chamber during the whole experiment.