Microleakage of composite resins in cavities of upper primary molars

Objective. To improve the quality of resin restorations, studies are necessary not only of the physical properties of materials but also of the cavity geometry. We have evaluated marginal microleakage for two types of photo-curing composite resin applied to cavities with different marginal structures. Sample and methods. The test materials were 91 extracted upper primary molars. The two composite resins used in this experiment were Liner Bond II (LBII) and Photo Clearfil A (PCA). A class 1 cavity was created in each tooth; the cavity configuration was a round bevel, a straight bevel and a butt joint. The tooth was then restored with each composite resin. Each tooth was exposed to thermal cycles, followed by immersion in 0·2% basic fuchsin solution. Three sections, through the mesial, central and distal areas of each tooth were taken. The penetration of the dye was examined with a stereoscopic microscope. The sites of observation for examination of microleakage were awarded scores of between 0 and 7. Results. LBII–among the three marginal forms, absence of leakage was observed most frequently in the straight bevel group followed by the round bevel and the butt joint groups, in the mesial and distal sections. In the central section, the straight bevel did not show any scores of 0, 6 or 7. PCA–an absence of leakage in the mesial section occurred most frequently for the round bevel group. However, the absence of leakage in the central and distal sections was most frequent for the straight bevel group. Microleakage of the central section (with scores from 1 to 7) was frequently lower than that for the mesial and distal sections. Scores of 5 and above in the central section were observed only in the butt joint group. The frequency and mean score of leakage were clearly higher in LBII than in PCA, with one significant exception. For both composite resins, the butt joint group showed higher-mean scores of leakage than did either the round or straight bevel group, but for PCA, the mean score of the central section was lower than the other two sections in all groups. Conclusion. Our study shows that bevelling does reduce marginal leakage. This leakage was more frequently observed with the use of LBII than with PCA. However, the amount of tooth ground away was greater for the bevel-treated cavity. In considering these features, special care is necessary in selecting the bur for treating a bevelled cavity.