This study contains the first part of a research project in which the applicability of fracture mechanics parameters to predict failure of a restored tooth was investigated. Fracture mechanics parameters have been used in dental research before, but were restricted to comparative studies between various brands of composites. The critical values of the opening mode stress intensity factor (KI), its equivalents, the strain energy release rate (GI), and the J integral (JI), were measured with single-edge notched-bend (SENB) specimens of dental composite in a three-point bend test. The measured values of KIc for Silux (KIc = 0.99 +/- 0.03 MNm-3/2) and P-30 (KIc = 1.88 +/- 0.12 MNm-3/2), compared with values from the literature, show quantitative agreement. The J integral was computed by means of finite element analysis (FEA) on a two-dimensional model of the SENB specimens. The critical value of the J integral (measured with SENB specimens, notch depth-to-width ratio (a/W) = 1/2) was used to predict failure of specimens having an arbitrary geometry. In this study, failure was predicted for SENB specimens with notch depth-to-width ratio (a/W) = 1/4 and 3/4. The predicted deflection and load at failure correspond well with the measured deflection and load.