This clinical trial was performed to evaluate the nano-filled resin modified glass ionomer (RMGI) -with a brand name of "Ketac Nano"- as a filling material for the treatment of caries in primary teeth. Children aged 5-8 years were selected and treated with either Ketac Nano or another conventional RMGI called Vitremer. Then, the treated children were evaluated at baseline, after one yeat and after two years. The hypothesis to be tested in the present study was: The clinical performance of nano-filled RMGI (Ketac Nano) in class I primary molars will differ from that of its preceding conventional RMGI (Vitremer).

First, shear bond strength of each material to primary molars dentin specimens were measured (n=10) using a notched-edge crosshead. Independent sample t-test was used for statistical analysis. Then, a split mouth designed clinical trial was performed in which nano-filled RMGI; Ketac Nano (KN) and conventional RMGI; Vitremer (VR) were used to restore class I cavities of primary molars. Each material group (n=30) was evaluated according to the modified United States Public Health Service (USPHS) regarding marginal discoloration, marginal adaptation, color match, anatomic form and recurrent caries, at baseline, after one year and after two years. Wilcoxon signed- rank test and Chi-square test were used for statistical analysis.

Inclusion Criteria:

• The presence of a bilateral identical pair of primary molars in the same arch containing initial occlusal caries (a minimum of two pits or fissures without any cusp destruction).

Exclusion Criteria:

• Handicapped or uncooperative children and children with extensive or rampant caries.