Methods: In a randomised controlled trial, 40 enamel specimens measuring 2x2x3 mm were prepared from human first molars exhibiting MIH (n=10 per group). The sterilisation treatments were: gamma irradiation (total exposure: 4080 Gy), cold plasma (38 minute cycle, Sterrad® NX system) and ethylene oxide (24 hour cycle of sterilization in an AN-74ix). In fourth control group, we used thymol solution (1%: specimens where immersed into solution for at least 24 hours). Nanohardness of enamel specimens was measured at baseline (B), after sterilisation (S) and after demineralisation (D: citric acid, 0.3% w/v, pH3.20, 10s). Nanohardness data were analysed by analysis of co-variance (ANCOVA).
Results: All specimens showed reduction in enamel nanohardness (% change±SD) at (S) point, thymol -1.35±3.37, Cold Plasma -18.04±16.38, ethylene oxide -6.19±8.54, and GAMA -3.62±14.02. Cold plasma group was the only statistically different group compared to other groups (p<0.05). All groups had reduction in enamel nanohardness at subsequent demineralisation (D) point. The percentage reduction in the hardness was -26.78±13.32, -19.86±13.88, -19.51±10.65, and -18.34±13.48 respectively. Groups were not statistically different.
Conclusion: in this study, ethylene oxide and GAMA irradiation did not affect the surface mechanical properties of hypomineralised enamel. Therefore, the use of ethylene oxide as a sterilisation method is recommended in future in situ/vivo research on hypomineralised enamel due to its ease of use, low cost and low risks.