Objectives: The purpose of this study was to evaluate the effect of instrument lubricant on the cohesive strength of resin composite layers.
Method and materials: Clear acrylic molds were filled with 3 increments of a hybrid resin composite using a metal instrument. The first increment (shade A2) was inserted to a height of 4 mm and light cured, followed by a 1-mm-high second increment (shade A1). The composite instrument was then wiped with 1 of 7 lubricants before insertion of a 1-mm-high third increment (shade A1): (1) isopropyl alcohol gauze, 70% v/v (AL); (2) acetone (AC); (3) Adper Single Bond Adhesive (SB); (4) One-Step Adhesive (OS); (5) D/E Bonding Resin (DE); (6) Scotchbond Multi-Purpose Adhesive (SP); (7) Tescera Sculpting Resin (TE). No lubricant was used in the control group (CT). A final 4-mm-high increment (shade A2) was inserted and light cured. The blocks were sectioned to obtain 48 sticks for each group. Sticks were fractured with an Instron machine. Statistics were computed using 1-way analysis of variance and Duncan's test.
Results: Outcomes were as follows (mean +/- SD, MPa; same letters indicate significant differences at a confidence level of 95%): TE = 96.7A +/- 17.8; SP = 93.6AB +/- 9.6; DE = 93.4AB +/- 16.2; OS = 91.9AB +/- 19.5; AC = 90.1ABC +/- 12.2; SB = 89.9ABC +/- 14.5; AL = 88.8BC +/- 16.8; CT = 84.7C +/- 8.3.
Conclusions: Although the difference between Tescera Sculpting Resin and alcohol was statistically significant, Tescera Sculpting Resin is recommended only for indirect composite restorations. The lubricant used to reduce stickiness between the resin composite used for direct restorations and the composite instrument did not significantly reduce bond strengths.