When fractures of fixed partial dentures occur, they cause an aesthetic and functional dilemma both for the patient and the dentist. Re-make of the entire restoration is an option, but not always desirable. Previous studies have provided several options for ceramic reparation, but there is limited consensus about this issue. The aim of this study was to test the shear bond strength due to four different etching agents for ceramic repair. The goal was to find a substitute for hydrofluoric acid as etching agent with less toxicity. Ideally, the repair of ceramics must meet both functional and aesthetic requirements. A total of 70 square shaped feldspathic porcelain disks of dimensions 10 mm x 10 mm x 3 mm were produced and embedded in cylindrical polyethylene walled poly(methyl methacrylate) (PMMA) blocks (16 mm diameter and 12 mm thick). All specimens were wet-ground with silicon carbide papers down to P4000. For one of the groups ten cylindrical ceramic specimens (diameter 5 mm and 2.5 mm high) were made and wet-ground to P4000. The blocks were divided into 7 groups with 10 specimens for each group. In six of the groups composite cylinders were bonded to the porcelain with different pretreatments of the porcelain. As etching agents 9% hydrofluoric acid (HF), 35% phosphoric acid (PO), 15% hydrochloric acid (HCl) and 15% potassium fluoride/hydrogen fluoride (KF center dot HF) were tested. This study compared a one-part (activated) silane and a new two-part silane. In one group two porcelain specimens were bonded with composite veneer cement. All the specimens were thermocycled for 5000 cycles from 5 degrees C to 55 degrees C before shear bond test. The best overall result was obtained in group 6 (two porcelain specimens bonded with veneer cement), and the mean shear bond strength was 24.5 MPa. The lowest values were obtained in group 4 with 35% phosphoric acid, and group 5 with 15% hydrochloric acid as the etching agent (6.5 and 0.8 MPa, respectively). Pretreatment with either 9% HF or 15% KF center dot HF as the etching agent combined with two-part silane gave good adhesion for porcelain reparations. (C) Koninklijke Brill NV, Leiden, 2009