Influence of saliva contamination on resin bond durability to zirconia - effect of cleaning methods

Indiana University-Purdue University Indianapolis (IUPUI)Background and Rationale: As compared with glass-based ceramics, zirconia has gained considerable popularity in restorative dentistry due to its superior mechanical properties. Clinically, however, zirconia ceramics pose a significant challenge regarding the achievement of a reliable and durable bond to resin-based cements. Thus far, it has been established that zirconia bond to resin-based cements can be enhanced after different surface conditioning methods, such as airborne particle abrasion with aluminum oxide particles. Meanwhile, another major issue pertaining to bonding of ceramic restorations is related to its potential contamination before cementation. Briefly, after sandblasting and clinical try-in procedures, zirconia can be contaminated with saliva and/or blood. As with many metals, zirconium shows a strong affinity towards the phosphate group found in saliva and other fluids, which reacts with the zirconia surface and makes bonding very difficult. Recently, a new cleaning agent called Ivoclean® (Ivoclar-Vivadent), which is an alkaline suspension of zirconium oxide particles, has been introduced in the market to remove contamination from zirconia in an effort to improve bonding to resin cements. Objective: The purpose of this study was to evaluate the influence of saliva contamination and the effect of several cleaning methods, including Ivoclean on resin bond strength to zirconia. Materials and Methods: Eighty square-shaped specimens (ϕ = 12 mm x 12 mm x 3 mm) of yttria-stabilized full-contour zirconia (Diazir®, Ivoclar-Vivadent, Amherst, NY) were sectioned from zirconia blocks using a water-cooled diamond blade. Then, these specimens were embedded in acrylic resin, and their surfaces gradually finished with silicon carbide papers (600 grit to 1200 grit). The prepared zirconia surfaces were sandblasted with 50-μm aluminum oxide particles for 15 s, under 2.5 bars and from distance of 10 mm. After sandblasting the specimens were cleaned in an ultrasonic bath containing distilled water for 5 min and air-dried for 10s. All samples were equally divided into 4 groups (n = 20) according to the cleaning method. Airborne particle abraded specimens without contamination was served as the control group. Remaining groups were contaminated with saliva, and subjected to different cleaning protocols, namely: Ivoclean®, 70% isopropanol, and no treatment. Two resin cement buttons (Multilink – Ivoclar-Vivadent, Amherst, NY) were built over each zirconia surface and light-cured following the manufacturer recommendations. The influence of contamination and surface cleaning methods on ceramic bond durability were examined after 24 h on half of the samples in each group (n = 10, n = 20), and the other half (n = 10, n = 20) specimens will undergo 6000 thermocycles (TC) before shear bond testing in the universal testing machine. Conclusion of Expected Outcomes: The shear bond strength of resin cement to zirconia led to a significant improvement after cleaning with Ivoclean both immediately and after thermal aging