Effect of different enamel surface preparations on the micro-tensile bond strength of resin composite to bleached enamel

Aim: This study was carried out to investigate the effect of different enamel surface treatments on micro-tensile bond strength of resin composite to bleached enamel
Materials and methods: 56 human premolars were used in this study. Teeth were divided into two main groups group 1: unbleached enamel (10 teeth) while group 2: bleached enamel (40 teeth). Then group 2 was subdivided into 4 subgroups (10 each) according the enamel surface treatment employed after bleaching and before bonding to composite either no treatment, grinding with diamond stone to remove 0.5mm of the surface, air abrasion using the air abrasion system (AquaCare-Velopex International) and combination of grinding and air abrasion. Each subgroup as well as the control group was further divided into two classes (5 each) according to the aging time either 24 hours or 3 months. Another six specimens were used as representative for the enamel surface topography after treatments for scanning electron microscopy SEM testing. Specimens of group 2 were polished and mounted in an acrylic block (five teeth in each block) with slight lingual inclination from their long axis to facilitate bleaching and light application. For in office bleaching, Philips ZOOM in-office light-activated bleaching gel was used in this study. After the in-office bleaching, teeth were subjected to at home bleaching using Night White ACP system for successive 7 days. The bleached teeth were divided into four subgroups according the enamel surface treatment employed after bleaching and before bonding as mentioned before. All enamel specimens either unbleached (control) or bleached and prepared specimens were bonded to Filtek Universal Restorative composite (3M ESPE, St Paul, MN, USA) using Single Bond universal adhesive (3M ESPE, St Paul, MN, USA). For immediate subgroups and classes, the specimens were stored in distilled water for only 24h after resin composite bonding. While for the three-month classes, the specimens were stored for three months in distilled water at room temperature. For micro-tensile bond strength test, specimens were longitudinally cut into a series of 1 mm thick slabs by means of a water-cooled diamond blade of thickness 0.5 mm in a low speed micro-slicing machine. By rotating the specimen 90o and sectioning it again lengthwise (five cuts), four sticks of about 1 mm2