Before we understand what subgingival calculus is let us first know what the word calculus means in dentistry.

Calculus is the mineralized bacterial plaque that is formed on the surface of the natural teeth and on the dentures or dental prosthesis.

Depending upon the location of the calculus in relation to the gingival margin, weather it is located below the gingival margin or above the gingival margin it is classified in to supragingival calculus and subgingival calculus.

Subgingival calculus is located below the crest of the marginal gingiva and therefore is not visible on routine clinical examination.

The location and extend of subgingival calculus maybe evaluated by careful tactile perception with a delicate dental instrument such as an explorer.

A person named Clerehugh et al used a World Health Organization #621 probe to detect and score subgingival calculus.

Subsequently, these teeth were extracted and visually scored for subgingival calculus. An agreement of 80 % was found between these two scoring methods.

Subgingival calculus is typically hard and dense and frequently appears dark brown or greenish black in color while being firmly attached to the tooth surface.

Subgingival calculus and supra gingival calculus generally appear together, but one may be present without the other.

Microscopic study demonstrate that deposition of subgingival calculus usually extend nearly to the base of periodontal pockets in chronic periodontitis but do not reach the junctional epithelium.

When the gingival tissues recede, subgingival calculus becomes exposed and is therefore reclassified as supragingival.

Thus suprgingival calculus can be composing of both supragingival calculus and previous subgingival calculus.

A reduction in gingival inflammation and probing depths and a gain in clinical attachment can be observed after the removal of subgingival calculus and plaque.