Dentine hypersensitivity: the effects of brushing desensitizing toothpastes, their solid and liquid phases, and detergents on dentine and acrylic: studies in vitro.

Dentine exhibiting symptoms of dentine hypersensitivity has tubules open at the dentine surface and patent to the pulp. The mechanisms whereby dentinal tubules are exposed is ill understood but probably involves a variety of abrasive and/or erosive agents. This study in vitro examined the quantitative and qualitative effects of toothpastes, their solid and liquid phases and detergents on dentine and acrylic. Abrasion of dentine and acrylic were measured by surfometry. Morphological changes to dentine were assessed by scanning electron microscopy. Abrasion of dentine and acrylic by toothpastes increased with increasing brushstrokes with marked differences in the extent of abrasion between different pastes. Brushing dentine with water or detergents produced progressive abrasion but which appeared to plateau around 2 microm loss. Water and detergents produced minimal effects on acrylic. At 5000 strokes dentine abrasion by solid phases was less than the parent toothpastes but the ranking order of abrasivity was the same as the parent toothpastes. Loss of dentine produced by liquid phases was minimal and in the order of 1-2 microm. Observationally, all toothpastes removed at least the dentine smear layer to expose many tubules; with one desensitizing product leaving a particulate deposit occluding most tubules. The solid phases of the toothpaste produced identical morphological changes to the parent paste. The liquid phases and detergents all exposed dentinal tubules by 5000 strokes. Water had little or no effect on the dentine smear layer. It is concluded that toothpastes, solid phase, liquid phase and detergents have the potential to abrade or erode dentine to a variable degree and result in tubule exposure. The effects of the liquid phases and detergents appear limited to the removal of the smear layer. Such detrimental effects seen in vitro could have relevance to the aetiology and management of dentine hypersensitivity. Toothpaste formulations which despite exposing tubules have ingredients capable of occluding tubules may be an area of development for such products.