In Vitro Study On The Ion Release From Two Ni-Cr Dental Alloys

Objective: Through measurement of nickel ion release from two clinically used Ni-Cr alloys treated by acidic artificial saliva(AS) and AS with F－in short time and observation on nickel ion release changes and the physic and chemical changes of alloy surface before and after treatment, the corrosion behavior and biocompatibility of alloys in dynamic oral environment were discussed to provide theoretic basis for reasonable choice of alloys in clinical practice.Methods: (1) Preparation of alloy specimens: Two Ni-Cr alloys were selected: Heraenium S (alloy without Be) and TILITE P (alloy with Ti). Each type of alloy was cast into 18 specimens under the manufacture instructions. Dimension of the specimens was 18mm×12mm×1mm. No visible deformation and casting defects were observed in all the 36 specimens. Surfaces of specimens were ground and polished into clinically satisfaction. Specimens were rinsed, disinfected and dried. (2) Group and immerse test of alloys: Three different kinds of AS were used in this study: A pH6.8 AS, B pH4 AS, C pH4 AS with 0.1% F－. Specimens of Heraenium S were divided randomly into 3 groups: HA, HB, HC (n=6); Specimens of TILITE P were divided randomly into 3 groups: TA, TB, TC (n=6) . Group HA, TA were treated by pH6.8 AS; group HB,TB were treated by pH4 AS; group HC,TC were treated by pH4 AS with 0.1%F－. All the specimens were immersed in pH6.8 AS for one week before treatment. The pH6.8 AS represented the normal salivary environment in oral cavity. After one week's immersion the specimens were treated by pH6.8 AS, pH4 AS and pH4 AS with 0.1%F－ respectively for two hours, and the immersed solutions were sampled for detection; Group HA and TA were treated by pH 6.8 AS for two hours; Group HB and TB by pH4 AS; and Group HC and TC by pH4 AS with 0.1%F－. Specimens were immersed for another one week in pH 6.8 AS and the released solutions were sampled. (3) Measurement of nickel ion release : Nickel ion released to the immersed solutions were measured with Atomic Absorption Spectroscopy (AAS), and results were analyzed statistically. (4) Surface analysis: One specimen of each group after immersion was sampled for morphology and chemical analysis by SEM and EDS.Results: (1) Nickel ion release: There was no significant difference in nickel ion release from three groups of Heraenium S alloy specimens treated by AS A before treatment (P>0.05). Nickel ion release from the three groups in two hours' treatment by AS A, B and C respectively: group HA0.05). Nickel ion release from three groups of TILITE P alloys treated by AS A before treatment was not significantly different between each group (P>.05). Nickel ion release from the three groups in two hours' treatment by AS A, B, C respectively: group TA 0.05), and group TB and TC were greater than group A (P<0.05). Among them, nickel ion release from group TA after treatment was less than that before treatment (P<0.05), and ion release from group TB and TC after treatment was significantly greater than that before treatment (P<0.05). Nickel ion release from Heraenium S alloy treated by AS A before and after treatment was significantly greater than that of TILITE P respectively (P<0.05). Nickel ion release from Heraenium S alloy treated by AS B for one week before treatment was significantly greater than that of TILITE P (P<0.05); for the ion release in two hours and one week after treatment, Heraenium S was significantly less than TILITE P (P<0.05). Nickel ion release from Heraenium S alloy treated by AS C for one week before treatment was significantly greater than TILITE P (P<0.05); For two hours and one week after treatment nickel ion release was less significant than TILITE P (P<0.05). (3) SEM Observation: No obvious corrosion was obser...