Dahl, B.L. Antibacterial effect of two luting cements on prepared dentinin vitroandin vivo.The antibacterial effect of a polycarboxylate cement (Durelon®) and a zinc phosphate cement (De Trey's Zink Zement Improved®) was studiedin vitroandin vivo.Forin vitroexperiments a streptomycin resistant strain ofStreptococcus mutans (Strep. mutansPRSR) was used. In one experimental series 1 ml of an overnight bacterial culture was suspended in 20 ml of nutrient agar, and poured to set in Petri dishes. Holes 5 mm in diameter were punched in the gel and filled with freshly mixed cement. The antibacterial effect was estimated by measuring the diameter of the zone of bacterial growth inhibition surrounding the holes after 24 h. In another experimental series two cavities were cut into the dentin of newly extracted human third molars. On the floor of both cavities a circular disc of filter paper saturated withStrep. mutansPRSR was placed. A sterile brass cylinder with freshly mixed cement covered one of the paper discs for 15 min. Both discs were then transferred to a streptomycincontaining growth medium of trypticase soy broth (TSB) and incubated at 37°C for 6 days. Scrapings from the cavity floor subjacent to the paper discs were also incubated. Bacterial growth was recorded as positive, no growth as negative.In vivovital crown and bridge abutments with preparations into the dentin were used from several patients. Discs of filter paper saturated with the patient's own saliva were placed on sprayed and dried dentin and covered with freshly mixed cement as described above. Again, after 15 min the paper disc was liberated from the cement, placed in TSB and incubated for 6 days, as were scrapings from the dentin subjacent to the disc.In the gel diffusion test the zinc phosphate cement exhibited the strongest antibacterial properties, while in the otherin vitrotest the poly-:arboxylate cement appeared to be most strongly antibacterial againstStrep. mutansPRSR.In vimpositive cultures were obtained with both ce, ments, indicating that the saliva always contains some bacteria resistant to the antibacterial effect of the cements studied.