Preventive and removing action on hydroxyapatite (HA) stains by polyvinylpyrrolidone (PVP) 5% in vitro

Aim. To evaluate the efficacy of PVP 2%, 5% or 10% over removal stain on HA. Methods. HA was stained in a tube by a Lipton Black Tea solution stirred. Stained HA was filtered, washed and dried. The stained HA powder was used for the test after two weeks. It was divided in 4 tubes to undergo different treatments: control: the tube was filled with water; test 2%: with a solution PVP 2%; test 5%: with a solution PVP 5%; test 10%: with a solution PVP 10%. All tubes were stirred for 5 minutes. HAs were filtered, washed and then dried. The HAs (test 2%, 5%, 10% and control) were imaged in the same picture and processed with Adobe Photoshop to calculate L*a*b* and ΔE*ab. Results. The stained HA treated with 2%, 5% or 10% PVP or control to remove stains gave the following colour parameters: water treated HA L 65 a 21 b 23, PVP 2% treated HA L 65 a 20 b 24, PVP 5% treated HA L 67 a 21 b 23, PVP 10% treated HA L 67 a 20 b 21; ΔE*ab were respectively 1.4, 2.2 and 3.5 for 2%, 5% and PVP 10% compared to control. Discussion: ΔL (luminance, strictly linked to white intensity) compared to control suggests that solutions 5% or 10% PVP are capable to remove stains from HA but this effect is not clearly visible by not expert eye. L for stained HA treated with PVP 2% is not different from control. There is no considerable difference between the solution 5% and 10%. Conclusions. results suggest that 5% and 10% PVP solutions are capable to reduce staining.