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

Figure 1

A and B: acid-resistant double-sided tape perforated by rubber sheet punch (0.8  mm diameter), delimiting the adhesive bond area to the enamel. C: 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. D: application of the adhesive system according to the manufacturer (Adper Single Band 2, 3M ESPE, Sumaré, SP, Brazil). E: photoactivation for 20 seconds with an LED-type photoactivation device (Ultrablue D-2000. DMC, São Carlos, SP, Brazil), (900  mW/cm²). F, G, and H: acid-resistant tape first layer removal; Tygon® pipes placement, 0.8  mm internal diameter and 0.5  mm high, coinciding with tape demarcations. Pipes filled 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. I and J: 4% hydrogen peroxide with calcium (White Class with 4% calcium; FGM, Santa Catarina (SC), Brazil), using a 0.1 mL proportion of bleaching gel for 0.05 mL of artificial saliva, and conditioned during the bleaching process (2 (h), in a biological stove (37°C). Application delimitation of bleaching agent in 2 mm distance around the adhesive interfaces using a gingival barrier (TOP DAM, FGM, SC, Brazil). After bleaching gel was applied, specimens were washed using an air–water spray at approximately 5 cm from enamel surface, for 1 minute, and the gingival barrier was removed. Between sessions, specimens were stored in AS and conditioned in a biological stove (37°C). The gel was applied daily, according to the described duration for each group (Table 1). K: at the end of the dental bleaching systems for each group, samples were attached to a universal testing machine for the microshear test (Kratos Equipment’s LTDA, Cotia, SP, Brazil).