QHI = Quigley Hein Index

Generally

QHI = Quigley Hein Index Smooth surface index, which divides the plaque on the smooth surfaces, which are colored with revalators, into 6 degrees.

Grade 0 =no plaque

Grade 1 =isolated plaque islands

Grade 2 =clearly contiguous plaque line at gingival and up to 1 mm

Grade 3 =Plaque expansion in the cervical third of the tooth

Grade 4 =Plaque expansion to the second third of the tooth

Grade 5 =Plaque expansion coronal to the cutting edge

The QHI is determined on the following teeth up to the age of 12 facial and oral: 16, 21, 24, 44, 41, 36. 

Index calculation                          

                              the severity levels

QHI = --------------------------------------------------------------------

                     Number of teeth used for evaluation

The QHI value should be less than 1.  (See also other oral hygiene indices).

References

1. Quigley GA, Hein JW: Comparative cleansing efficiency of manual and power brushing. JADA 65:26–29, 1962.
2. Turesky S, Gilmore ND, Glickman I: Reduced plaque formation by the chloromethyl analogue of victamine C. J Periodontol 41:41–43, 1970.