Primary Stability

Primary stability refers to the mechanical stability of an implant immediately after it is placed — the initial grip of the implant threads in bone before biological integration has occurred. It is one of the most important factors influencing whether an implant can be immediately loaded and how likely it is to successfully integrate.

How it is measured

• Insertion torque: The force (in Ncm) required to drive the implant to its final position. High torque generally indicates good bone engagement. Values above 35 Ncm are typically considered adequate; values above 45 Ncm may allow immediate loading.
• ISQ (Implant Stability Quotient): Non-invasive measurement using resonance frequency analysis. ISQ above 70 generally indicates excellent primary stability.

What affects primary stability?

• Bone density and quality — denser bone gives better grip
• Implant diameter and length — larger implants engage more bone
• Implant thread design — certain thread geometries provide better initial grip
• Surgical technique — undersizing the preparation in softer bone can improve stability

Secondary stability

As osseointegration proceeds, biological stability (secondary stability) gradually replaces mechanical stability. There is typically a dip in total stability at around 3–4 weeks as primary stability reduces before secondary stability has fully developed — this is why overloading during this window is particularly risky.