Rehardening of surface softened and surface etched enamel in vitro and by intraoral exposure

The rehardening of surface-softened and surface-etched enamel was investigated in vitro and by intraoral exposure. Surface-softened enamel was obtained by treatment with 0.1 M acetic acid buffer solution (pH = 5.5) for 3 h. Surface-etched enamel was obtained by the acid etch procedure used in clinical situations (37% phosphoric acid gel, 30 s). The enamel lesions were treated in vitro, with calcifying solutions for 8 h or were carried for 48 h in an intraoral appliance. Changes at the enamel surfaces were investigated by surface microhardness measurements. Following the treatment with calcifying solutions a significantly greater indentation length was observed in surface-etched than in surface-softened enamel. No significant difference in indentation length between both types of enamel lesions was observed following intraoral exposure. It was concluded that the initial rate of rehardening between both types of enamel lesions is comparable. At his stage remineralization occurs in microspaces created in the slightly destroyed enamel structures. The influence of the etch pits on the indentation length becomes dominating when remineralization continues. An obliteration of etch pits was observed in enamel samples treated with the calcifying solution with the highest degree of saturation. It was suggested that freshly prepared highly supersaturated calcifying solutions can be used to enhance mineral appositions in accidental etch pits.