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Glass ionomer cements have assumed an important role in dental practice. They are effective, release more fluoride than silicate cements, and can reduce enamel solubility by as much as 52 percent. A study was conducted to compare the bonding strength of glass ionomer with composite resin between two different surfaces that had undergone different degrees of etching. Forty-eight glass ionomer samples were divided into two groups. The first group was prepared with a glass-smooth surface; the second group was prepared by smoothing the surface with a teflon instrument while the glass ionomer was still in the fluid state. Each group was divided into four subgroups. One subgroup was not etched, the other three subgroups were etched for 15, 30 and 60 seconds, respectively. It was determined that a composite resin will not bond to an unetched, glass-smooth glass ionomer. Since the bond between a composite resin and a glass ionomer is a mechanical one, the bond is enhanced by surface roughness. Disturbing the surface with an instrument produces more roughness than etching a smooth surface. However, the study revealed that for instrument-disturbed surfaces, the bonds were strongest in the subgroup that was not etched and in the group that was etched for 15 seconds. There was a slight decline for the subgroups etched for 30 and 60 seconds. The authors cannot account for this decline, and speculate that it may be a result of the glass ionomer becoming less retentive as a result of the loss of some of its surface particles. (Consumer Summary produced by Reliance Medical Information, Inc.)