Effect of Multiple Stainless Steel Crowns on Salivary pH, Nickel, and Chromium Levels

Background: The use of stainless steel crowns (SSCs) in pediatric dentistry is widely used. Recently, there has been an increasing ecological and global public health concern associated with environmental contamination by metallic alloys. Aim of the study: To determine the in-vitro and in-vivo effect of multiple stainless steel crowns on the salivary pH, nickel and chromium levels at different periods.
Materials and methods: This study consisted of: I-In-vitro study: A total of 200 standard sizes of SSCs were divided into 4 groups (10 samples/each). Each sample/group contained 2, 4, 6, and 8 SSCs, respectively. All SSCs were trimmed 1mm circumferentially, smoothed, re-contoured, fitted, and cemented on standard crowns of plastic teeth models. Each group was placed in a closed container containing artificial saliva with a standard pH. II-In-vivo study: A total of 40 patients indicated for SSC restorations were selected, aged 5-9 years. Similar to in-vitro, they were allocated into 4 groups according to the numbers of SSCs restorations used. 5ml of unstimulated saliva was taken for pH, nickel, and chromium analysis at 5-intervals: baseline, and 1day, 1week, 2weeks, 1month, and 2-months post-cementation. Data analysis: The mean and standard deviations, one way ANOVA, and the Person correlation coefficient were used. The level of significance was adopted at p≤0.05.
Results: In both studies: The more the increase in the number of SSCs, the more the increase in acidity and release of ions. As regards pH value; within the groups at 5 intervals, there was only a significant difference in groups containing 8 SSCs and 6 SSCs, and between the intervals and the baseline (p≤0.05). The group that has 8 SSCs recorded the lowest pH value. Among groups: in-vitro: all groups showed a significant difference during 3-time intervals (p≤0.05) except at 2-months; the difference was not significant (p>0.05), while in-vivo, the difference was not significant (p>0.05). As regards the released ions: Within groups, both studies showed a significant difference among all intervals, and between the intervals and the baseline (p≤0.05). Among groups: In-vitro, all groups showed significant differences during the intervals (p≤0.05), while the only period showing no significant difference was at 2 months in the chromium group (p>0.05). The group that has 8 SSCs recorded the highest level and the difference was significant (p≤0.05). The peak level of the released ions and reduced pH value was at 1day and 1week for in-vitro and in-vivo study, respectively.
Conclusion: The released nickel and chromium ions were directly proportional to the number of stainless steel crowns whereas the pH value was inversely proportional. The maximum level recorded was 1day and 1-week post-cementation for in-vitro and in-vivo study, respectively. The peak released of ions was much lower than the toxic level or the level of dietary intake.