This investigation evaluated the effect of glass and polyethylene fiber inserts on the microleakage of Class II composite restorations with gingival margins on root surfaces. Fifty-four intact molars were sterilized with Gamma irradiation and mounted in acrylic bases. Class II slot cavities were made on both proximal sides of each tooth (3 mm wide, 1.5 mm deep) with the gingival margin on the root surface. The teeth were divided into nine groups, according to the technique of restoration and type of bonding agent. Filtek P-60 (3M/ESPE) was used to restore all cavities. Two types of fiber inserts were used: glass fiber (Ever Stick, StickTech) and polyethylene (Ribbond-THM), with three bonding agents being employed: Scotch Bond Multipurpose (3M/ESPE), Clearfil SE Bond (Kuraray) and Xeno IV (Dentsply). In the experimental groups, 3 mm long fiber inserts were inserted into restorations at the gingival seat. The control groups had no fiber inserts. The restorations were made incrementally and cured with LED light (UltraLume5, Ultradent). The restored teeth were stored in water for two weeks, then thermocycled for 3000 cycles (5 degrees C and 55 degrees C). The tooth surfaces were sealed with nail polish, except at the restoration margins. The teeth were immersed in 2% procion red dye solution, sectioned and dye penetration was assessed to determine the extent of microleakage according to a six-point scale. The fiber groups generally showed reduced microleakage scores compared to the control groups. The Clearfil SE Bond (Kuraray)/Filtek P-60 (3M/ESPE) combination produced the lowest degree of microleakage, irrespective of fiber type. However, the glass fiber groups were more consistent in reducing microleakage than the polyethylene groups. The use of fiber inserts significantly reduced gingival microleakage in Class II composite restorations with gingival margins in dentin, irrespective of the adhesive used. Clearfil SE Bond (Kuraray)/Filtek P60 (3M/ESPE) produced the lowest microleakage scores.
