Normal Periodontal Bone Support
Healthy bone anchors the root right up to the CEJ.
- 0 mm: Bone level (from CEJ)
- 0: Mobility grade (physiologic only)
- 0%: Attachment loss (root support intact)
- 1–3 mm: Probing depth (healthy sulcus)
Cementoenamel junction as reference
CEJ marks where enamel meets root cementum.
Alveolar crest position
Healthy crest sits 1–2 mm below the CEJ.
Periodontal ligament function
PDL fibers cushion and anchor tooth to bone.
Early Horizontal Bone Loss
Plaque biofilm triggers the first measurable crestal bone loss.
- ~2 mm: Bone level (apical to CEJ)
- 0: Mobility grade (still firm)
- ~20%: Attachment loss (of root support)
- 3–4 mm: Probing depth (shallow pockets)
Biofilm-driven inflammation
Bacterial plaque inflames gingiva, triggering bone resorption.
Radiographic sign
Crestal bone flattens instead of following a sharp peak.
Reversibility window
Early loss is largely stabilized by scaling and cleaning.
Moderate Bone Loss & Grade 1 Mobility
Root support drops 30–50%, and the tooth starts to shift.
- ~5 mm: Bone level (apical to CEJ)
- 1: Mobility grade (<1 mm lateral shift)
- ~45%: Attachment loss (of root support)
- 5–6 mm: Probing depth (true periodontal pockets)
Lever-arm effect
Less bone means a longer unsupported crown lever arm.
Grade 1 mobility defined
Grade 1 is barely perceptible horizontal movement.
Treatment response
Scaling and root planing can still slow the loss.
Advanced Bone Loss & Grade 2 Mobility
Over half the root support is gone, mobility becomes obvious.
- ~8 mm: Bone level (apical to CEJ)
- 2: Mobility grade (1–2 mm lateral shift)
- ~70%: Attachment loss (of root support)
- 7–9 mm: Probing depth (deep pockets, furcation risk)
Furcation involvement
Multi-rooted teeth may show bone loss between roots.
Grade 2 mobility defined
Grade 2 movement is over 1 mm, clearly visible.
Functional impact
Chewing forces now accelerate further bone destruction.
Severe Bone Loss & Tooth Loss Risk
Support is nearly gone, and Grade 3 mobility risks exfoliation.
- ~11 mm: Bone level (apical to CEJ)
- 3: Mobility grade (depressible, rotates)
- ~92%: Attachment loss (of root support)
- Severe: Tooth loss risk (imminent without care)
Grade 3 mobility defined
Grade 3 moves in all directions, even vertically.
Prognosis
Root support this low usually means a hopeless prognosis.
Remaining options
Extraction and implant or bridge planning become priorities.