Periodontal probes: probing force changes the reading more than the markings do

The periodontal probe produces the data on which diagnosis, prognosis and treatment planning rest. It is also the instrument with the greatest variability between operators.

The principal variable is not the probe but the force applied. The same pocket measured with different forces yields different values, and the difference can exceed a millimetre.

The reference force is around 0.20 to 0.25 Newtons, corresponding to very light pressure. It is far less than most operators apply instinctively.

Excessive force carries the tip beyond the junctional epithelium into connective tissue, and returns a pocket deeper than the real one. In inflamed tissue the overestimate is greater.

Pressure-controlled probes address this with a spring mechanism that yields beyond a threshold. They are the instrument of choice in clinical trials and long-term monitoring.

Among manual probes, markings differ and are not interchangeable. The UNC-15 has marks at every millimetre with highlighted bands; the Williams omits four and six; the CPI has a coloured band between 3.5 and 5.5.

Switching markings between one review and the next introduces a reading error that adds to the force error, which is why standardising the instrument across the practice is worthwhile.

The CPI probe is designed for rapid screening rather than detailed diagnosis. Using it to record depths in a complex periodontal case loses resolution.

Probing should be performed at six sites per tooth, not four. Interproximal sites carry the deepest pockets, and limiting oneself to buccal and lingual surfaces systematically underestimates the disease.

The tip is kept parallel to the long axis and walked along the sulcus, not inserted and withdrawn at isolated points. The value recorded is the deepest found at that site.

On implants plastic or titanium probes are used to avoid scratching the surface, and the values are interpreted differently: peri-implant tissue offers less resistance, and penetration is greater at equal force.

Bleeding on probing should be recorded alongside depth, because it is the indicator that distinguishes a stable pocket from an active one, and its repeated absence has good predictive value for stability.

In summary: light force matters more than the probe chosen, one marking is standardised across the practice, six sites per tooth are recorded, and on implants non-metallic tips are used with differently interpreted readings.