Efficiency of different repair kits on bonding to aged dental resin composite substrates

Objectives: To assess the efficiency of intraoral repair kits on the tensile bond strength (TBS) of resin composites (RCs) to aged RC substrates.
Methods: 840 aged (six months, 37°C, distilled water) RC substrates (Tetric EvoCeram) were air-abraded (CoJet) with and without following phosphoric acid contamination or treated with silicon carbide (SiC) grinding paper. Seven repair kits were used as intermediate agents (Embrace First-Coat, CLEARFIL CERAMIC PRIMER, Tokuso Ceramic Primer, Monobond Plus+Heliobond; Scotchbond Universal, One Coat Bond and visio.link) for conditioning. Specimens were repaired using two direct RCs (Clearfil Majesty ES2 and Clearfil Majesty Posterior), stored in distilled water (37°C, 24h) and thermal aged (5°C/55°C, 10,000 cycles). The cohesive strength of the repair RCs (N=40) served as control and was determined by applying the RCs on the fresh polymerized substrates, followed by thermal-aging procedure. TBS and failure types were determined and evaluated with three-/one-way ANOVA, and chi-square test (p<0.05).
Results: The highest influence on the TBS was exerted by the intermediate agent (repair kit) (partial eta squared η_P² = 0.320, p<0.001), while the impacts of the repair RC (η_P² = 0.017, p<0.001) and surface pre-treatment (η_P² = 0.015, p=0.003) were significant but low. Except for Embrace First Coat and Tokuso Ceramic Primer, phosphoric acid contamination after air-abrasion maintains the TBS. The predominant type of failure was adhesive (46.2%), followed by cohesive (39.2%), while mixed (6.1%) or pre-failure (3.1%) was rarely observed.
Conclusions: Air-abrasion of aged substrates improved the repair strength inducing superior TBS compared with grinding the surface with SiC paper prior to repair, while the effect of phosphoric acid contamination is material dependent. Analyzed universal adhesives, as well as the combination between a universal primer and an adhesive were in-vitro efficient intermediate agents for repairing aged RCs, while the use of silane primers alone was less efficient.