Effect of Instrument Lubricants on Microtensile Strength of Resin-Based Composites

Objectives: o investigate the effect of using instrument lubricants (ILs) on the microtensile bond strength between increments of a resin-based composite (RBC).
Methods: One RBC (Filtek supreme XTE, 3M, USA) and three classes of IL were investigated: solvents; bonding agents; and wetting resins. Master blocks (10 mm height x10 mm width x10 mm length) of the RBC were made by building up successive 2.5 mm thick increments, each of which were polymerised using a 40s light illumination with intensity 1020 mW/cm2 (Elipar, DeepCure, 3M ESPE, Germany) An IL was applied using a dentine adhesive brush between the second and third increments, with a group that received no IL used as a control. Next the blocks were sectioned to produced ‘stick-shaped’ specimens with 1± 0.1 mm2 cross-section and 10± 0.1 mm length and stored at 37°C in distilled water for either 24hours or 7days post-polymerisation.

Prior to testing in tension, specimens were placed on custom designed attachment plates and held in place with cyanoacrylate glue. The specimens were then tested using an Instron-5567 testing machine at 1 mm/min until the fracture. ANCOVA with Tukey post-hoc test was then used to assess the data for statistically significant differences (p<0.05).
Results: Both solvents and bonding agents were statistically significant different to the control (P<0.05). They both reduced the microtensile strength at both baseline and after 7 days. The solvent values were in range 17-39 MPa with the lowest values in the Isopropyl group. The bonding agents group range was 25-36 MPa. The wetting resins did not reduce the microtensile strength values and had a range of 36-57 MPa.
Conclusions: Conclusion: Only wetting resins maintained the microtensile bond strength between increments, while solvents and bonding agents reduced it