Effect of time on the remineralisation of enamel by synthetic saliva aftercitric acid erosion

The aim of this in vitro study was to determine the influence of reminerali sation time on rehardening of surface-softened enamel after citric acid ero sion. Seven groups of 13 samples of human enamel were eroded in 0.3% citric acid at pH 3.2 for 2 h followed by profilometric measurements. Individual groups of specimens were placed in artificial saliva for 1, 2, 4, 6, 9 or 2 4 h. A control group was placed in isotonic saline for 24 h. After new prof ilometric measurements samples were ultrasonicated stepwise up to 480 s wit h profilometric measurements performed at 5, 30, 120, 240 and 480 s to meas ure the depth of surf ace softening. The control group had a softened surfa ce layer of mean thickness 2.9 mum. Mineral deposition was seen at all remi neralisation times by scanning electron microscopy. Exposure to artificial saliva for 1, 2 or 4 h produced a partial rehardening of the softened ename l; the additional surface losses produced by ultrasonication were lower and time delayed compared to the control group. Specimens remineralised for 6, 9 and 24 h showed little evidence of surface loss after ultrasonication, T he data suggest that a complete rehardening of the softened enamel in vitro is reached after a remineralisation time of 6 h. These data are of clinica l relevance to tooth wear. However, there is a need for studies in situ of enamel demineralisation and remineralisation. Copyright (C) 2001 S. Karger AG. Basel.