The amount and distribution of sclerotic human root dentine.

In low-power photomicrographs of ground sections of canine teeth, the amount of sclerosis increased with age linearly and was not markedly affected by the function of the tooth or external stimuli encountered during life. The pattern of distribution was similar in all teeth. Sclerosis started in the apical dentine adjacent to the cementum and extended coronally and towards the root canal, with increasing age. In the plane transverse to the long axis of the root, sclerosis appeared first at the mesial and distal sides so that the sclerotic zones formed a butterfly shape.