Objective. The authors conducted a study to identify and quantify the reasons used by dentists in The Dental Practice-Based Research Network (DPBRN) for placing restorations on unrestored permanent tooth surfaces and the dental materials they used in doing so. Methods. A total of 229 DPBRN practitioner-investigators provided data from their practices regarding 9,890 consecutive restorations in 5,810 patients. Information the practitioner- investigators provided included their reasons for restoring the teeth, the specific teeth and surfaces they restored and the restorative materials they used. Results. Primary caries (85 percent of teeth, 8,351 of 9,890) and noncarious defects (15 percent, 1,479 of 9,890) were the main reasons participants gave for placing restorations. Participants placed restorations necessitated by caries most frequently on occlusal surfaces (49 percent, 4,091 of 8,351). They used amalgam for 47 percent of the molar restorations and 45 percent of the premolar restorations. They used directly placed resin-based composite (RBC) for 48 percent of the molar restorations, 50 percent of the premolar restorations and 93 percent of the anterior restorations. Conclusion. DPBRN practitioner-investigators cited dental caries on occlusal and proximal surfaces of molar teeth as the main reasons for placing restorations on previously unrestored tooth surfaces. RBC was the material they used most commonly for occlusal and anterior restorations. Amalgam remains the material of choice to restore posterior teeth with proximal caries, although the authors noted significant differences in the use of amalgam and RBC by dentists in various regions of the DPBRN.