Plaque Index — Free & Clinical | MedicalCalculatorHub

Plaque Index Calculator — Silness-Löe Scoring for Oral Hygiene Status

Silness-Löe Plaque Index with 0–3 scoring criteria for all tooth surfaces. Score 6 Ramfjord index teeth or full dentition, calculate mean plaque index, classify oral hygiene status, and generate clinical documentation.

CE Clinically reviewed byMedicalCalculatorHub Clinical Editorial Team · Jan 15, 2026

A 28-week pregnant patient presents for a routine periodontal recall. Hormonal gingivitis has flared through the second trimester, and before adjusting her maintenance interval, the hygienist needs an objective, reproducible measure of plaque accumulation — not just a visual impression from the chair.

What Is the Plaque Index?

The Plaque Index (PI) was developed by Silness and Löe in 1964 as a method for scoring the thickness of soft plaque at the gingival margin during clinical trials and routine patient monitoring. Unlike indices that measure how much of a tooth surface plaque covers, the Silness-Löe PI specifically measures plaque thickness in the gingival crevice — the deposit most closely linked to gingival inflammation. Each of four surfaces per tooth (mesial, distal, buccal, lingual) is scored on a 0–3 scale, and the mean of all scored surfaces gives the Plaque Index for that patient visit.

How to Score and Interpret Plaque Index Results

Run a periodontal probe along the gingival third of each surface being scored. A score of 0 means no plaque is detected at all; a score of 1 means plaque is only visible on the probe tip, not to the naked eye; a score of 2 means moderate plaque is visible without a probe; and a score of 3 means an abundant, visible accumulation fills the gingival pocket and margin. The full scoring criteria are below.

Silness-Löe Plaque Index scoring criteria
Score	Criteria	Detection method	Clinical significance
0	No plaque	No plaque on probe	No plaque present — ideal
1	Film of plaque	Run probe along margin — plaque visible on tip	No plaque present — ideal
2	Moderate plaque	Visible to naked eye	No plaque present — ideal
3	Abundant plaque	Visible to naked eye	No plaque present — ideal

Once every surface is scored, sum the values and divide by the number of surfaces scored to get the mean PI. That mean score maps onto the classification and recall table below.

Mean Plaque Index classification and recall interval
Mean PI	Classification	Recall interval	Clinical action
0	Excellent	12 months	Positive reinforcement, maintenance
0.1–0.9	Good	6–12 months	Oral hygiene reinforcement, fluoride
1.0–1.9	Fair	3–6 months	OHI + professional polishing; identify problem areas
2.0–3.0	Poor	3 months	Intensive OHI, scaling, caries risk assessment; CAMBRA if indicated

The Ramfjord Index Teeth Protocol

In epidemiological surveys, scoring is commonly limited to the six Ramfjord index teeth — teeth #3, #9, #12, #19, #25, #28 (universal numbering) — chosen to represent all regions of the dentition. Each of the four surfaces is scored 0–3, and the mean score across all 24 surfaces (6 teeth × 4 surfaces) gives the mean plaque index. This protocol reduces chairside assessment time while maintaining statistical validity for population comparisons.

Clinical Significance of the Plaque Index

Löe and Silness demonstrated a strong correlation between the Plaque Index and the Gingival Index — higher plaque scores consistently predicted higher gingival inflammation scores in the same patients. A mean PI below 1.0 is associated with clinical gingival health in most populations, while a PI above 2.0 is consistently associated with generalized gingivitis and elevated risk of periodontitis progression. Because it is quick to record and highly reproducible between examiners, PI remains a standard outcome measure in periodontal research and a practical chairside tool for tracking a patient's response to oral hygiene instruction over time. For a fuller picture of gingival inflammation alongside plaque thickness, it can be paired with a Gingival Index Bleeding calculator.

When to Use This Calculator

Use the Plaque Index at a new-patient baseline exam, at periodontal maintenance recalls to track whether home care is improving, immediately before and after oral hygiene instruction to demonstrate progress to the patient, in clinical research comparing oral hygiene interventions, and during pregnancy periodontal monitoring given the hormonal sensitivity of gingival tissue. It is equally applicable to natural teeth and implant abutment surfaces, where a stricter target of PI below 0.5 is often used to reduce peri-implant mucositis risk.

Frequently Asked Questions

What are the Silness-Löe plaque index scores 0, 1, 2, and 3?

0 = No plaque. 1 = Thin film at gingival margin, visible only by running a probe along the tooth surface. 2 = Moderate accumulation visible to the naked eye at the gingival margin and in the gingival pocket. 3 = Abundance of soft matter within the gingival pocket and on the gingival margin and tooth surface.

How is the mean plaque index calculated?

Sum the scores from all surfaces assessed. Divide by the total number of surfaces scored. For the 6 Ramfjord teeth protocol: sum of all 24 surface scores ÷ 24 = mean PI. For full dentition: sum of all surface scores ÷ total surfaces examined. The result ranges from 0 to 3.

What is the treatment goal for plaque index?

The clinical treatment goal is a mean Plaque Index of less than 1.0, which is associated with an absence of clinical gingivitis in most populations. In periodontal maintenance patients and implant patients, the goal is PI <0.5 to minimise peri-implant mucositis risk.

Is the Silness-Löe Plaque Index the same as the Oral Hygiene Index (OHI-S)?

No. Silness-Löe measures plaque thickness at the gingival margin on a 0–3 scale per surface. The Greene-Vermillion OHI-S measures the area of the tooth surface covered by debris and calculus. They're complementary — not interchangeable — and any report should specify which index was used.

How often should Plaque Index be reassessed in periodontal maintenance patients?

Match the recall interval to the classification found at the last visit: 12 months for excellent, 6–12 months for good, 3–6 months for fair, and 3 months for poor — until the mean PI drops below 1.0.

Can the Plaque Index be used to monitor peri-implant plaque?

Yes. The same 0–3 criteria are commonly applied to implant abutment surfaces. Many clinicians use a stricter target of PI <0.5 for implant patients given the elevated risk of peri-implant mucositis.

About This Calculator's Clinical Basis

This calculator implements the Plaque Index exactly as published by Silness and Löe in 1964, without modification to the underlying 0–3 scoring criteria for individual tooth surfaces. The scoring logic was checked against the original description of the index and against subsequent clinical literature that has used it as a standard outcome measure, including studies applying it during pregnancy and in periodontal maintenance populations.

Clinical significance thresholds shown here (excellent, good, fair, poor, and the <1.0 treatment goal) reflect classification ranges reported in the periodontal literature summarizing outcomes at each PI band, and the associated recall intervals reflect commonly used periodontal maintenance scheduling. Research demonstrates a strong association between elevated Plaque Index scores and gingival inflammation, and the index continues to be used in both epidemiological surveys and individual patient monitoring because it is fast to record and highly reproducible between examiners.

Content on this page is reviewed periodically by the MedicalCalculatorHub Clinical Editorial Team against current periodontal literature and updated when scoring guidance changes. This calculator is a documentation and screening aid; it does not diagnose periodontal disease and does not replace a comprehensive clinical periodontal examination by a licensed dentist or dental hygienist.