Effects of Low-temperature Plasma on Root Dentin Hardness and Elasticity

Objective: To evaluate the influences of low-temperature plasma (LTP) on root dentin hardness and reduced modulus using sodium hypochlorite (NaOCl) as a positive control.

Methods: Five extracted single-rooted human teeth were sectioned to provide thirty root dentin specimens. The samples were categorized into six groups (n=5 per group) based upon cutting directions (n=15 transverse discs and n=15 longitudinal segments) and three surface treatments: untreated (negative control), treated with 5.25% NaOCl for 10 minutes (positive control), and LTP treated for 10 seconds using a kINPen device and pure Argon (Ar) as the operating gas to deliver LTP jet at a flow rate of 5 l/min. On each sample, twenty-five nano-indentations were performed to the inter-tubular dentin following a trapezoidal loading function to a maximum load of 5000 µN and using a TriboIndenter equipped with a Berkovich tip. Hardness and reduced modulus were derived according to the Oliver-Pharr method; additionally, Young’s modulus was calculated and ANOVA was applied (α= 0.05).

Results: Compared to the untreated groups and regardless of the direction of tooth sectioning, hardness and reduced modulus of radicular inter-tubular dentin were decreased in LTP treated samples, and increased in NaOCl treated groups (ANOVA main effect, p< .05). These changes were more pronounced in horizontal than vertical sectioned specimens (interaction effect, p< .05).

Conclusion: The application of low-thermal plasma (LTP) and sodium hypochlorite (NaOCl) to root dentin resulted in significant, yet opposite, effects on root dentin hardness and reduced modulus compared to the untreated samples.