Evaluation of the effect of three different post etching surface treatments of feldespathic ceramic on the shear bond strength to composite resin

The clinical porcelain repair system is almost entirely dependent on the integrity of the bond between porcelain and composite resins.   The preferred manner of conditioning the fitting surface of the ceramic restoration is by etching with hydrofluoric acid followed by the application of a silane coupling agent and bonding resin to achieve a high bond strength. Hydrofluoric acid etching of silica-based ceramics produces insoluble silica-fluoride salts, which can interfere with the bond strength to the resins.

The aim of this study is to evaluate shear bond strength of composite resin to porcelain treated with phosphoric acid compared to ultrasonic cleaner and air-water spray following hydrofluoric acid etching.

66 porcelain disks (Super Porcelain EX3, Noritake) of 8 mm diameter and 3 mm thickness were fabricated and stored in distilled water for 10 days. Porcelain surfaces were abraded with number 023 football shaped bur, etched with 9.5% Hydrofluoric acid and rinsed with water.  The disks were randomly divided into 3 groups: Group 1:  without any additional treatment    Group 2: Etching with 35% phosphoric acid for 30 seconds followed by water spray rinse.    Group 3: Ultrasonic cleaning in distilled water for 5 minutes.Silane and porcelain bonding resin (Bisco Inc.) was applied on the bonding surface of porcelain disks, according to manufacturerchr('39')s instructions. The composite samples (AELITE All Purpose Body) of 4 mm diameter and 3 mm thickness were bonded to the porcelain disks following fixation of a plastic mold on the center of disks.Study samples were stored in distilled water in room temperature for 1 week. Shear bond strength of each specimen was determined using universal testing machine following thermocycling protocol. (1000 cycles between 5°C and 55°C) The fracture modes (adhesive, cohesive, mixed) were examined under scanning electron microscopy at ×25 magnification. Data were analyzed by one-way ANOVA, post hoc Tukey’s test and post-hoc Dunnettchr('39')s t-test.

For both group 2 (P=0.015) and 3 (P<0.0001) the mean bond strength were significantly different from group 1. The bond strength values were significantly higher in group3 compared with group 2. (P=0.011) The highest and lowest bond strength was achieved in group 3 and 1, respectively.

According to increased bond strength between composite resin and ceramic following application of phosphoric acid and ultrasonic cleaning, they are both effective methods for post etching ceramic treatment, whereas regarding to the highest shear bond strength in group 3, ultrasonic cleaning is more recommended than phosphoric acid application.