Objective To compare the penetration abilities of resin infiltration into proximal lesions in primary molars and permanent posterior teeth in vitro.Methods Extracted or exfoliated primary molars (n=32) and permanent posterior teeth (n =36) with proximal white spot lesions were selected. Roots of the teeth were removed, and the crowns were cut across the caries lesions perpendicular to the surface. Cut surfaces were examined with stereo microscopy and classified with respect to histological lesion extension (C1-C4) : Lesions confined to the outer half on enamel (C1) , lesions confined to the inner half on enamel (C2) , lesions confined to the outer half on dentin (C3), lesions extending into the inner half of dentin (C4) . C4 were excluded. Caries lesions were etched for 2 min with 15% hydrochloric acid gel and were subsequently treated for 5 min with resin infiltration. Thin sections from each lesion were prepared and specimens were observed with confocal laser scanning microscopy (CLSM) through a dualfluorescence staining technique. Lesion depth (LD) and penetration depth (PD) of resin infiltration were measured in primary molars and permanent posterior teeth in confocal microscopic images, and percentage penetration (PP) were calculated respectively. The date were collected and analyzed.Results There were no significant differences for overall PP in primary molars and permanent posterior teeth groups (P>0.05) . However, the penetration abilities in primary molars were slight higher than those in permanent posterior teeth in C1 group (P0.05) .Conclusion Resin infiltration have satisfied penetration abilities in primary molars and permanent posterior teeth with proximal initial lesions. The better penetration abilities of resin infiltration in primary molars are shown in C1 lesions than those in permanent posterior teeth.
