Purpose: To investigate the buffering capacity of restorative materials during a simulated carious and intrinsic erosive attack. Materials and Methods: Cavities with a volume of 130 μl were milled (Cerec MC XL) out of blocks of Ceram X Mono (CM), Quixfil (QX), Filtek Supreme (FS), Apa Fill 3 (AF), an experimental dual-curing composite containing a bioactive glass (EX), Dyract eXtra (DY), Beautifil (BE), Equia Fil (EQ), Telio CAD (TL) (negative control), TheraCal (TC; positive control), and extracted teeth (ED). 80 μl of lactic acid (pH 4.5) and hydrochloric acid (pH 2.6) were each pipetted into the cavities of two samples of each material. Change of pH in the solutions was measured continuously for 12 min using a calibrated pH electrode. Results: CM, AF, and FS (final pH 3.0-3.2) neutralized hydrochloric acid to a significantly lesser extent than did BE, EQ, DY and QX (final pH 5.0-5.6) (p 0.05, ANOVA Scheffé). The lactic-acid buffering capacity of CM, BE, and AF was equivalent (final pH 6.3-7.4) to that of ED (7.5), but was surpassed by FS (pH 8.0). pH values for EX and TC (final pH 9.2-11.3) increased significantly (p 0.05) in response to both acids. Conclusions: Conventional restorative materials do not buffer better than human teeth. However, the experimental composite demonstrates that buffering against carious and intrinsic erosive acid attacks is technically feasible. Keywords: buffering capacity, ion release, bioactive glass, secondary caries, composite, erosion