Objective <p>The study aims to evaluate the effect of contouring instruments on the porosity and immediate quality of direct dental restorations.</p> Materials and methods <p>Fifteen human molars with 30 Class II and 10 Class V cavities were restored by five voluntary dentists using three contouring instruments (conventional steel, silicone-tipped and diamond-like carbon coated-instruments) and three filling materials (Admira Fusion, Filtek Supreme XTE and Fuji II LC). The restorations were evaluated for immediate quality, porosity and number of pores using stereomicroscope and micro-computed tomography. Statistical analysis included the Shapiro‒Wilk test for normality, one-way ANOVA with Holm‒Sidak post hoc test for normal data, Kruskal‒Wallis ANOVA and Dunn’s test for non-normal data, and Fisher’s exact test for restoration quality comparisons. Statistical significance level was set at <i>p</i> &lt; 0.05.</p> Results <p>The proportion of restorations with acceptable immediate quality was higher for the restorations that had been contoured using a diamond-coated non-stick contouring instrument compared to the restorations that had been contoured using a conventional steel instrument (<i>p</i> = 0.033). The number of pores and porosity were similar for restorations that had been contoured with different contouring instruments. However, the number of pores and porosity were lowest in the restorations made of Filtek Supreme XTE followed by Admira Fusion and Fuji II LC.</p> Conclusion <p>The use of diamond-like carbon-coated contouring instruments increased the proportion of acceptable composite restorations compared to conventional steel instruments.</p> Clinical relevance <p>Non-stick contouring instruments should be considered for wider use.</p>