Effect of surface treatments and adhesives
on composite repair strength
Objective: To evaluate the effect of surface treatments and bonding systems on the repair bond strength between composites, using an improved micro-tensile test method.
Method: Thirty six composite cylinders (Tetric Evo Ceram) were fabricated, stored in water for two weeks followed by thermal cycling (5000X between 5 and 55 ⁰C) and served as a substrate. The cylinders were mechanically roughened using 320 grit silicon carbide sandpaper, etched with 37% phosphoric gel, rinsed with water and divided equally into three experimental groups; 1: Unchanged surface, 2: Sandblasting with CoJet® sand (Microetcher II) and 3: Silane coating (Bis-Silane™). Each experimental group received the following three bonding systems; a: Adhese One, b: Clearfil SE and c: Adper Scotchbond MP. Fresh composite was placed and cured on top of the prepared substrate cylinders. The cylinders were placed in distilled water for a week and thermocycled. Four composite cylinders that underwent the same two ageing procedures served as controls. The cylinders were serially sectioned perpendicular to the bonding surface in an automatic cutting machine, producing 10–20 test specimen rods from each cylinder, approximately 1.1 × 1.1 mm. The specimens were mounted in a universal testing machine and the tensile strength calculated based on the force at fracture and specimen dimension. Fracture surfaces were examined and the type of fracture noted.
Result: The mean tensile strength of composite control was 54.5±6.0 Mpa and ranged from 26.4±6.8 to 49.9±10.4 MPa for the repaired groups. There was a statistical difference between all groups (p<0.05). The highest repair strength was obtained in the silane + Clearfil group. Clearfil also had the highest repair strength within each surface treatment group. Most fractures were of the adhesive type.
Conclusion: The highest repair bond strength was achieved by using freshly mixed silane solution on the substrate in addition to an adhesive, rendering a thin bonding layer.