A clinical trial to treat dental osseous lesions with bioactive glass granules of narrow size range (300 to 360 μm) has been conducted since early spring 1990. This study followed an animal study in which the osseous tissue repair properties of bioactive glass granules of narrow size range and hydroxyapatite granules were compared for up to 2 years of implantation. The therapeutic response to the bioactive glass material exceeded the response to the hydroxyapatite as evidenced by very extensive osteoconduction, as well as the capacity to cause differentiation of osteoprogenitor cells to osteoblasts. The clinical study was started by virtue of the bioactive glass granules of narrow size range eliciting expeditious bone tissue formation throughout a defect. In this clinical study 87 patients and 106 defects were treated. The indications selected were apical resection areas, cystic defects, extraction sites, and defects of the alveolar ridge due to surgery or resorption. After insertion, the particles remained well in place and only small changes in the contours of the restored defects were seen, at the most up to 2 months postinsertion. At 3 months the application sites had fully solidified. Radiographic analysis indicated that the material integrated into the bone tissue, and at 6 months any difference between glass particles and bone tissue had nearly disappeared. The few initial cases with limited clinical results were caused by factors unrelated to the glass granules, mostly the surgical technique. By adapting the surgical technique, no unfavorable clinical results were subsequently experienced. The follow-up, exceeding 3 years, demonstrated that bioactive glass granules of narrow size range constitute a valuable material to aid in the repair of dental bone lesions. (Implant Dent 1993;2:151–156)