title: Effect of 10% sodium ascorbate on the calcium: Phosphorus ratio of enamel bleached with 35% hydrogen peroxide: an in vitro quantitative energy-dispersive X-ray analysis.
abstract: OBJECTIVE
  The study assessed quantitatively the calcium and phosphorous loss from the enamel surface following bleaching with 35% hydrogen peroxide and reversal with 10% sodium ascorbate using energy-dispersive X-ray analysis (EDAX).
  
  
  METHODS
  Eight non-carious, freshly extracted human permanent maxillary central incisors without any visible defects were used. Each specimen was bleached with 35% hydrogen peroxide activated by light and reversed with sodium ascorbate antioxidant gel. The calcium and phosphorous content in weight percent of sound, bleached and reversed enamel was acquired using EDAX. The Ca/P ratio was calculated from the obtained data. One-way ANOVA followed by Post Hoc Tukey test was used for comparing the Ca/P ratio of sound, bleached and reversed enamel.
  
  
  RESULTS
  All the samples subjected to bleaching using 35% hydrogen peroxide showed a statistically significant decrease in the Ca/P ratio as compared with samples in which no bleaching procedure was performed (P-value < 0.01). The striking finding was that there was a significant increase in the Ca/P ratio on application of sodium ascorbate antioxidant gel when compared with the bleached enamel (P-value < 0.01).
  
  
  CONCLUSIONS
  The authors concluded that 35% hydrogen peroxide causes a significant decrease in the Ca/P ratio. This decrease in the Ca/P ratio can be restored by the application of 10% sodium ascorbate antioxidant gel.
authors: Department of Conservative Dentistry and Endodontics, Ragas Dental College, Chennai, India. poorniis@yahoo.com
authors: Saravanan
authors: S
authors: Poorni
authors: R Anil
authors: RA
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authors: Rajamani
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authors: Indira
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authors: S
authors: Ramachandran