Osseointegration is the direct structural union of living bone with the surface of a load-bearing implant, first described by Brånemark. New bone forms outward from existing cortical bone across the implant surface as osteoblasts lay down osteoid that then mineralizes. The fraction of the implant surface in direct contact with bone — bone-to-implant contact (BIC) — grows logistically toward a ceiling set by surface conditions, but only if micromotion at the interface stays below roughly 50–150 µm; above that threshold, fibrous tissue forms instead of bone and integration stalls or reverses.
dBIC/dt = k(roughness) · BIC · (BICmax − BIC)
k ∝ osteoblast attachment sites (↑ with Ra)
if load > safe AND week < 6: k → k·0.12, BICmax → BICmax − overload
- Surface roughness — a rougher, micro-textured surface (e.g. sandblasted/acid-etched titanium, "SLA") gives osteoblasts more anchor points and raises the growth-rate constant k; a machined-smooth surface integrates slower and to a lower ceiling.
- Mechanical load — force transmitted through the implant. Moderate load during healing is fine, but overload in the first ~6 weeks causes micromotion that disrupts the fragile early bone-implant bond, sharply slowing growth and capping the maximum BIC ever reached — even causing active bone loss if severe.
- Time speed — how fast simulated weeks elapse; slow it down to watch individual growth nodes mineralize, or speed it up to see the whole healing timeline.
- Reset — starts a fresh implant at week 0 with 0% contact.
Real-world relevance: this exact trade-off — rough enough to integrate fast, but protected from overload during early healing — is why dental and orthopedic surgeons prescribe a period of reduced chewing or weight-bearing ("immediate" vs "delayed" loading protocols) after placing an implant.