Influence of Prolonged Dental Bleaching on the Adhesive Bond Strength to Enamel Surfaces

Figure 2

A: 4% hydrogen peroxide with calcium (White Class with 4% calcium; FGM, SC, Brazil) (PH4), using a 0.1 mL proportion of bleaching gel for 0.05  mL of AS, and sample packaging, during the bleaching process 2 h in a biological stove (37°C). B: placement of the customized acetate trays proportioned with PH4 and AS. C and D : acid-resistant double-sided tape perforated with rubber sheet punch (0.8 mm diameter), delimiting the enamel adhesive bond area. E: conditioning with 35% phosphoric acid (Adper Scotchbond 3M ESPE, Sumaré, SP, Brazil) for 30 seconds; gel removal with an air–water spray for 30 seconds, drying with air jets. F: application of adhesive system according to manufacturer’s recommendations (Adper Single Bond 2, 3M ESPE, Sumaré, SP, Brazil). G: photoactivation using an LED-type photoactivation device with 900 mW/cm² (Ultra Blue D-2000. DMC, SP, Brazil). H, I, and J: acid-resistant tape first layer removal; Tygon® pipes placement, 0.8 mm diameter and 0.5 mm high, coinciding to tape demarcations. Filling of the pipes with Filtek Z350 XT composite resin (3M ESPE, Sumaré, SP, Brazil) and photoactivation for 40 seconds. Two cylinders of composite resin were made in each tooth. After 24 h of storage in distilled water (37°C), removal of Tygon® pipes, and the second layer of tape with the aid of scalpel blade n°12. The resin cylinders were examined with a stereoscopic microscope (40x). K: at the end of the dental bleaching systems in each group, samples were attached to a universal testing machine for the micro-shear test (Kratos Equipment’s LTDA, Cotia, SP, Brazil).