Abstract: Objective　To evaluate the mechanical properties of Bis-GMA/TEGDMA resin composites containing zirconia fillers conditioned by two different phosphate ester monomers. Methods　Two different phosphate monomers solutions (MDP and PENTA) were prepared in advance, and then the zirconia fillers were mixed with MDP or PENTA at the ratio of 1ml/1g. The zirconia fillers before and after the treatment were added to the Bis-GMA-based experimental resin composites at a ratio of 5% (Bis-GMA: TEGDMA = 7:3, silicon oxide treated by silane: zirconia = 55:5), and four resin composites were obtained: group A, without zirconia fillers (control group); group B, with untreated zirconia fillers (ZrO2); group C, with MDP-treated zirconia fillers (MDP- ZrO2); group D, containing PENTA-treated zirconia fillers (PENTA- ZrO2). The morphology and structure of the resin composites containing zirconia fillers were observed by scanning electron microscopy (SEM), and the composition and distribution of elements were analyzed by EDS. The three-point bending test samples were prepared according to the ISO 4049, and the bending strength test was performed using a universal testing machine. One-way analysis of variance (ANOVA) followed by Tukey's post-hoc least significant difference test was used to evaluate the three-point bending strength in SPSS 21.0 statistical software. Results　The SEM showed that the zirconia fillers treated by MDP and PENTA were uniformly dispersed in the resin composites. There was no agglomeration in the fillers containing untreated zirconia. The EDS showed that the resin composite containing zirconia fillers treated by MDP and PENTA had the most Si content, followed by O and the least Zr content. Mapping showed that the three elements were evenly distributed in the materials. There was no significant difference in the values of three-point bending strength between the MDP-ZrO2 and the PENTA-ZrO2, but the values were significantly higher than that of ZrO2 group. The four groups of resin composites all obtained higher elastic modulus values, and there was no significant difference between the groups. Conclusions　Adding both MDP and PENTA-conditioned zirconia fillers can improve the flexural strength of the resin composite without affect its elastic modulus, and there was no significant difference in the effect of two phosphate monomers.

Key words: resin composite, phosphate ester monomers, flexural strength, filler, surface treatment