Purpose: To evaluate the clinical, biochemical, and microbiological reactions to nanocomposite containing amorphous calcium phosphate (ACP) in comparison to a traditional composite restorative material in early childhood caries. Materials and Methods: Eighteen teeth were restored with the test material (ACP-containing resin) and 18 teeth were restored with the control material (traditional composite, TC) in fourteen paediatric patients using a split-mouth design. One caries- and restoration-free intact tooth in each patient was selected as the healthy control. Gingival crevicular fluid (GCF) and supragingival plaque samples were collected at baseline before the treatment and also on days 1, 7, 14 and 30 after treatment. Unstimulated whole saliva samples were obtained from each patient at baseline, and 1 and 6 months after restoration. GCF and saliva samples were assayed for IL-17A, IL-17F IL-17A/F, IL-17E, OPG and RANKL levels by ELISA, and plaque composition was assessed using RT-PCR. Results: Clinical evaluation indicated no statistically significant differences between the two restorative materials according to the FDI criteria surface lustre, material retention and marginal adaptation properties. Pro-inflammatory IL-17 levels decreased statistically significantly at 6 months compared to baseline and 1-month values (p 0.05). The baseline pro-inflammatory IL-17 cytokine levels in GCF samples around the carious teeth were higher than those obtained around the healthy teeth (p 0.05), but similar in GCF from the ACP-test and TC teeth. Microbiological findings were similar in the ACP and T groups. Conclusion: It may be suggested that both ACP-containing and traditional resin composites show similar antimicrobial and biochemical effects in early childhood caries. Schlagwörter: amorphous calcium phosphate, cytokines, early childhood caries, GCF, plaque, saliva