Objectives: This in vitro study evaluated the influence of different glass ionomer liners and curing techniques on microleakage of resin composite restorations. Methods: Class V root preparations were made in 120 bovine incisors, randomly divided into twelve groups, according to liner and curing technique. The resin composite system (Single Bond + Z100) was inserted and polymerized in one increment. Experimental resin groups: 1, 4, 7, 10- no liner; groups 2, 5, 8,11- resin modified glass ionomer liner (Vitrebond); groups 3, 6, 9, 12- conventional glass ionomer liner (Ketac Bond). Curing techniques: groups 1, 2, 3- conventional exposure (450mW/cm2/40s) [a]; groups 4, 5, 6 - ramp technique (100 - 800mW/cm2/15s + 800mW/cm2/25s) [b]; groups 7, 8, 9 - pulse delay (200mW/cm2/3s + 3 minutes delay + 600mW/cm2/30s) [c] and groups 10,11,12- high intensity (1600mW/cm2/3s) [d]. Teeth were thermocycled and immersed in 0.5% basic fuchsin, sectioned, and dye penetration was measured (Image Tool). Results: No significant difference in leakage (two-way ANOVA, Tukey test, a= 0.05) among conventional and ramp or pulse delay techniques was seen. High intensity groups showed significantly greater penetration compared to other curing techniques. No significant difference existed in marginal leakage between liner types, but microleakage was significantly higher in groups restored using no liner. No relationship between filling technique and light curing method was observed. Conclusions: Use of glass ionomer liners reduced microleakage, while high intensity curing yielded the greatest dye penetration. Curing units: [a],[b],[c] Quartz-tungsten-halogen; [d] Plasma arc.

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