Abstract Objective: To evaluate morphologically and morphometrically the sequential healing and osseointegration events at moderately rough implant surfaces with and without chemical modification. Particularly the role of bone debris in initiating bone formation was emphasized. Material and methods: Solid, screw-type cylindrical titanium implants (SSI) (n촹), 4mm long and 2.8mm wide, with either chemically modified (SLActives) or sandblasted and acid-etched (SLAs) surface configurations were surgically installed in the retromolar region of 28 human volunteers. After 7, 14, 28 and 42 days of submerged healing, the devices were retrieved with a trephine. Histologic ground sections were prepared and histomorphometrically analyzed. Linear measurements determined fractions of old bone (OBIC), new bone (NBIC), soft tissue (ST) and bone debris (BD) in contact with the SSI surfaces. Results: Healing was uneventful at all installation sites. Sixty-one percent of all devices were suitable for morphometric analyses. All implant surfaces were partially coated with bone debris and new bone formation was observed as early as 7 days after installation. There was a gradual increase in NBIC, whereas OBIC, ST and BD progressively decreased over time. NBIC after 2 and 4 weeks was higher on SLActives than on SLAs surfaces, albeit statistically not significant. The BD : ST ratio changed significantly from 7 to 42 days (from 50 : 50 to 10 : 90 for SLActives; from 38: 62 to 10 : 90 for SLAs) (Fisher's exact test, Po0.01). Conclusion: Both SLActives and SLAs devices became progressively osseointegrated, while old bone on the device surface was gradually resorbed. The decrease in BD : ST ratio suggests that bone debris, created during implant installation and adhering to moderately rough surfaces, significantly contributed to the initiation of bone deposition and mediated the connection between the old bone and the new bone on the implant surface.