Introduction:Today, chitosan has a wide usage in Dentistry. Due to its penetration into tooth tissues, inhibition of the acid penetration and anti-demineralization capabilities, chitosan may interfere with the etching mechanism in the bonding restorations. The aim of this study was to evaluate the effect of chitosan with different concentrations and molecular weight on the shear bond strength (SBS) of composite to deciduous teeth's enamel.
Materials & Methods:In this in vitro trial, 50 deciduous anterior human maxillary teeth, which extracted because of orthodontic treatment plan, were selected and divide evenly between groups. In the control specimens, Filtek Z250 composite were packed on buccal teeth surfaces after using self-etch primer  single bond universal and light-cured. In four next groups the teeth were immersed into chitosan solution with low and high molecular weights and 5 mg/ml and 2.5 mg/ml concentrations for 60 seconds and restored with composite as control groups. The SBS of composite to the teeth enamel were determined with Universal testing machine. Data was analyzed by SPSS-18 software using one-way ANOVA and p<0.05 was considered significant.  
Results:The SBS to enamel in the control specimens were 20.98 ± 6.31 MPa. The values were 17.92 ± 7.25, 16.02 ± 6.03, 13.26 ± 5.18 and 17.67 ± 8.95 MPa in the pretreatment with low molecular weight chitosan in 2.5 mg/ml , low molecular weight chitosan in 5 mg/ml , high molecular weight chitosan in 2.5 mg/ml and high molecular weight chitosan with 5 mg/ml concentrations respectively. No significant differences were found regarding SBS between groups. (P>0.05)
Conclusion:Despite a slight reduction in SBS of the composite to the enamel of the treated compare to control, use of chitosan in different concentration and molecular weight did not interfere with the SBS of composite to the enamel of deciduous teeth.