The Periodontitis Severity Index (PSI) was developed to assess the severity of periodontitis and distinguishes between clinically healthy and inflamed sites. Periodontitis is diagnosed on the concurrence of clinically apparent marginal inflammation and vertical loss of supporting periodontium. In the presence of marginal inflammation, the PSI is directly proportional to the percentage of bone loss. The severity of the associated clinical inflammation does not seem to be related to the severity of the tissue loss.
Clinical Inflammation Score
Signs of gingival inflammation -ANY of the following:
(1) edema
(2) suppuration
(3) bleeding upon provocation
(4) increased crevicular fluid flow
(5) color deviation
If none of these findings are present, the clinical inflammation score is 0.
If any one of the these findings are present, the clinical inflammation score is 1.
Bone Loss Score
A Schei ruler is used to determine the percentage of bone loss for a tooth surface from the radiograph.
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Bone Loss in percent
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Bone Loss Score
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0
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0
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1-10%
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1
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10-20%
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2
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20-30%
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3
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30-40%
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4
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40-50%
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5
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50-60%
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6
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60-70%
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7
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70-80%
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8
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80-90%
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9
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90-100%
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10
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Periodontal Severity Index
For each mesial (medial) and distal tooth surface, the following is calculated:
periodontal severity index (PSI) =
= (clinical inflammation score) * (bone loss score)
mean periodontal severity index =
= SUM (all PSI scores) / (total number of surfaces)
Interpretation:
• A PSI of 0 can occur if either no bone loss has occurred or if the gingiva is healthy.
• maximum PSI: 10
