The fact that bisphenol-a-glycidyl methacrylate (bis-GMA)-based cements contain an uncured surface is believed to play an important role when determining the surface curing properties of the cements. Therefore, in the present study, the bone-bonding strength of cement plates having an uncured surface on one side and a cured surface on the other side has been evaluated. These cement plates were composites of a bis-GMA-based resin with either an apatite- and wollastonite-containing glass-ceramic (AW-GC) powder or a hydroxyapatite (HA) powder, respectively designated AWC and HAC. The amount of each of these powders in a composite cement was 70 wt %. We formulate the hypothesis that the uncured surface of a cement plate is bioactive having bone-bonding properties. The goal of the present study was to indicate the bone-bonding strength of the uncured surfaces of AWC and HAC and compare the strength with the respective cured surfaces by a detaching in vivo test, as well as to histologically examine the bone-cement interface. Each plate has been implanted into the tibiae of male Japanese white rabbits, taking care to retain the surface properties, and the so-called "failure load has been measured using a detaching test followed 8 weeks after implantation. The failure load for AWC-plates at the uncured surface (2.05 +/- 1.11 kgf, n = 8) was significantly higher than AWC at its cured surface side (0.28 +/- 0.64 kgf, n = 8). The failure load for HAC-plates at the uncured surfaces (1.40 +/- 0.68 kgf, n = 8) was significantly higher than HAC at its cured surface (0.00 +/- 0.00 kgf, n = 8). Failure loads for AWC at its uncured and cured surfaces were both higher than for HAC, although not significantly. Direct bone formation has been observed histologically for both AWC and HAC on the uncured surfaces, and a Ca-P-rich layer was observed only at the uncured surface of AWC. These findings strongly suggest that uncured surfaces are useful for exposing a bioactive filler on a surface of composites, being very effective in inducing bone bonding.