Measuring plaque: without a recorded figure you do not know whether the patient is improving

At the end of a hygiene appointment the commonest judgement is that the patient has improved or worsened, and that judgement rests on a memory from six months earlier.

It is a weak basis. Clinical memory for something as graded as the quantity of plaque is unreliable over that interval, and tends to be coloured by how the patient presents that day.

An index solves the problem by producing a figure, which has two advantages: it is comparable over time and it can be shown to the person.

The O'Leary plaque index is the most practical for daily use. Presence of plaque is recorded on four surfaces per tooth after using a disclosing agent, and the percentage of surfaces with plaque is calculated.

Recording takes a few minutes and produces a figure the patient understands without explanation: a percentage is immediate where a description is not.

The commonly stated target is below twenty per cent, which is attainable and therefore useful as a goal. An unrealistic target discourages rather than directs.

The bleeding on probing index measures something different and complementary: not how well the patient cleans, but how the tissues are responding.

The percentage of sites that bleed is recorded, and it is more reliable than the plaque index as an indicator of inflammation, because plaque can be removed on the morning of the visit.

This is why the two indices should be read together. Low plaque with high bleeding indicates that the patient cleaned well only that day, or that a different factor is at play.

Their most effective use is not diagnostic but communicative. A patient who sees their percentage fall from fifty to twenty-five receives a concrete confirmation no generic compliment replaces.

The risk is using them as judgement rather than as a tool. An index presented as a report card produces defensiveness and pushes people away; presented as a shared measure it opens onto a goal.

It is worth recording the areas and not only the total, because the distribution says things the percentage hides: plaque concentrated in the right posterior segments suggests a technique problem in a right-handed patient.

In summary: clinical memory is unreliable over six months, the O'Leary index produces a comprehensible percentage, bleeding measures tissue response and the two are read together, the best use is showing improvement, and distribution says more than the total.