Curettes: a blunt blade burnishes calculus instead of removing it

The curette is the basis of manual periodontal instrumentation, and its performance depends almost entirely on one condition that is seldom checked: the edge of the blade.

A worn blade does not cut the deposit: it compresses and burnishes it. Residual calculus becomes smoother and harder to detect with the probe, and the next appointment starts from a worse position.

The clinical signal is recognisable. If the instrument slides across the surface instead of engaging the deposit, and more pressure is needed for any effect, the blade needs sharpening.

The visual check is equally simple: a sharp blade does not reflect light along its edge, because the edge is a line. A worn blade shows a reflective surface along the margin.

Universal curettes have two cutting edges and a blade angled at ninety degrees to the shank. They serve throughout the mouth and suit supragingival removal and shallow subgingival work.

Gracey curettes have a single working edge and an angle of about seventy degrees, which lets the blade adapt to the root surface at the correct inclination without thinking about angulation.

This is why they are preferred in periodontal therapy: the geometry does part of the work, and reduces the risk of damaging cementum through a wrong angle.

Gracey numbering corresponds to precise sites. The 1-2 and 3-4 are for anteriors, the 5-6 for anteriors and premolars, the 7-8 and 9-10 for buccal and lingual surfaces of posteriors.

The 11-12 are for mesial surfaces of posteriors and the 13-14 for distal. Using a curette on a site it was not designed for forces an incorrect angulation.

Versions with extended shank and reduced blade serve in deep pockets, where a standard blade cannot reach the base without traumatising the tissue.

Sharpening should be scheduled maintenance rather than a response to an instrument that no longer cuts. A maintained blade needs a few passes; one left to blunt requires metal removal that shortens the instrument's life.

The commonest error in sharpening is altering the original angle. A blade sharpened at the wrong angle loses the geometry that makes the curette suited to its site.

In summary: a worn blade burnishes instead of removing, a sharp edge reflects no light, Gracey curettes belong on the sites they are numbered for, and sharpening is scheduled maintenance rather than repair.