Community Periodontal Index (CPI)
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Direct answer
Ten index teeth, six sextants and a ball-ended probe are all the Community Periodontal Index needs to grade a population's periodontal status in minutes. Developed by Ainamo and colleagues in 1982 as the CPITN and renamed CPI in the WHO's 1997 Basic Methods, it scores each sextant by its worst finding: code 0 healthy, 1 bleeding on probing, 2 supra- or subgingival calculus felt during probing, 3 shallow pocket 4-5 mm, 4 deep pocket 6 mm or more, X excluded sextant, 9 not recorded. The WHO CPI probe carries a 0.5 mm ball tip with markings at 3.5 and 5.5 mm (extended probes add 8.5 and 11.5 mm), so pocket depth is read off the black band rather than estimated.
What you must remember
- Index teeth: 17, 16, 11, 26, 27 in the maxilla and 37, 36, 31, 46, 47 in the mandible — ten teeth standing for six sextants; for subjects under 20 years, only six index teeth (16, 11, 26, 36, 31, 46) are examined and third molars are never scored.
- Codes verbatim: 0 healthy, 1 bleeding on probing (gentle probing, about 10 g force — about the pressure that blanches a fingernail without pain), 2 calculus or overhang felt, 3 pocket 4-5 mm, 4 pocket 6 mm or deeper, X excluded (fewer than two functional teeth in the sextant), 9 not recorded.
- Probe design: 0.5 mm ball end to detect calculus and limit penetration, black band from 3.5 to 5.5 mm for pocket coding.
- Scoring sites: probe six sites per tooth (mesio-, mid- and disto-buccal, plus the lingual sweep where relevant), walking circumferentially; the sextant score equals the worst site.
- Loss of attachment is recorded separately: 0 (0-3 mm), 1 (4-5 mm), 2 (6-8 mm), 3 (9-11 mm), 4 (12 mm or more), using the cementoenamel junction as the fixed reference — this is what distinguishes current disease from cumulative destruction.
- CPITN to CPI (1997): the original index assumed code 2 meant "needs scaling" and codes 3-4 meant "needs complex treatment"; CPI retained the scoring but dropped the automatic treatment-need interpretation.
- Population output: percentage of subjects with healthy sextants, with bleeding, calculus, shallow or deep pockets.
Scoring a mouth, sextant by sextant
Examine a 40-year-old tea-shop worker the way a survey does. Start at 17: probe the buccal mesial, mid and distal sites, then sweep the lingual. Bleeding appears at 17-16 after ten seconds and you feel a rough ledge of calculus below the gingival margin at 16 — the sextant already carries at least code 2, so further bleeding elsewhere in it changes nothing. Move to 11: firm, pink, no bleeding on probing, sextant scores 0. At 26 the black band disappears up to its upper edge — 5.5 mm at the base of the pocket — code 3. At 36 the ball tip sinks past the 5.5 mm mark entirely: code 4, and that sextant is the person's summary score. Now record loss of attachment separately: at 36 the CEJ-to-pocket-base distance reads 7 mm — code 2. His CPI score is 4 with loss of attachment 2, and in a survey table he enters the "periodontal pocket" column. Multiply this by two hundred mouths and the district learns, for instance, that half its adults have pockets but almost nobody with healthy sextants — an argument for a scaling programme, not merely oral hygiene instruction.
Where students slip
The classic mark-loser is treating CPI and loss of attachment as one recording. They are two separate entries on the WHO assessment form: a mouth can show code 1 (bleeding only) yet have 6 mm of attachment loss from old destruction — active disease and accumulated damage are different questions. The second slip is mechanical: pocket depth is measured from the gingival margin (a moving landmark), attachment loss from the cementoenamel junction (a fixed one), which is why recession adds to attachment loss without adding to pocket depth. Finally, remember the force: an exploratory 10-20 g, not a stabbing push that manufactures bleeding and inflates code 1.
Frequently asked questions
Which ten teeth are examined in CPI and why?
17, 16, 11, 26, 27 and 37, 36, 31, 46, 47; they represent all sextants, erupt early, are most commonly retained, and index periodontal status efficiently without full-mouth examination.
What does a CPI code 3 mean?
A periodontal pocket of 4-5 mm — the black band on the probe (3.5-5.5 mm) remains partly visible at the base of the sulcus or pocket.
How does CPI differ from the original CPITN?
The 1997 WHO revision kept identical scoring but removed CPITN's automatic equation of codes with treatment needs, making CPI a pure status measurement.
How is loss of attachment recorded and why separately?
As codes 0-4 measured from the cementoenamel junction, because pocket depth reflects current anatomy while attachment loss reflects lifetime cumulative destruction.
What is the X code in CPI?
A sextant excluded because it contains fewer than two functional teeth, distinguished from 9, which simply means not recorded.