Internal adaptation of resin composite restorations with different thicknesses of glass ionomer cement lining

Aim The aim of the present study was to investigate the effect of the thin or thick placement of resin‐modified glass ionomer cement (RMGIC) lining on the adaptation of resin composite restorations bonded with two types of adhesive. Methods Sixty deep occlusal cavities were prepared and divided into two groups: etch‐and‐rinse adhesive (Single Bond 2) or self‐etching adhesive (Clearfil SE Bond). Specimens were further divided into three subgroups: no lining (control), lined with 0.5 mm‐thin RMGIC, or lined with 1 mm‐thick RMGIC (Vitrebond). Each cavity was bonded, restored with resin composite, and sectioned to obtain two specimens. One specimen was stained with 2% methylene blue, and dye staining at the pulpal floor and cavity walls was calculated. Other specimens were investigated for micro‐gap formation using scanning electron microscopy (SEM). Results For Single Bond 2, dye staining was not significantly different among the three groups. For Clearfil SE Bond, lining absence showed the lowest dye staining at the pulpal floor. Dye staining of 0.5 mm‐thin RMGIC significantly increased, but 1 mm‐thick RMGIC tended to reduce dye staining. Comparing the two adhesives, there was no significant difference in dye staining. From the SEM images, micro‐gaps were more frequently observed in the 0.5 mm‐thin lining groups. Conclusions RMGIC should be placed as a thick lining, if indicated.