[In vitro study of non-thermal atmospheric plasma influencing the surface properties of dentin]

Objective: To study the influence of non-thermal atmospheric pressure plasma (NTAPP) on dentine surface temperature, wettability and morphology of collagen fibrils under different treatment condition. Methods: Helium was used as the operating gas at the flow rate of 3, 4, 5 L/min respectively. The plasma jet was operated at various input power of 8, 9, 10, 11 W. Thermal accumulation on human dentine surface (6 specimens per group, acquired from Department of Stomatology, The First Affiliated Hospital of Xi'an Medical University and Department of Stomatology, The Second Affiliated Hospital of Xi'an Medical University) of each group was measured continuously at 5 s intervals for 60 s by infrared thermography. Mean values were calculated and temperature curves were drawn. Dentine surface contact angles were measured after NTAPP treatment for 5, 10, 15, 20 s with gas flow rate and input power described above. The micro structure of the collagen fibrils of the negative control group (without NTAPP treatment) and NTAPP treatment groups (5 L/min gas flow rate, input power of 8, 9, 10, 11 W and treating time for 5, 10, 15, 20 s) was observed by field emission scanning electron microscopy (FE-SEM). All data were analyzed by SPSS 18.0. Results: Input power, gas flow and treatment time all showed significant influences on dentine surface temperature and wettability (P<0.01). Dentine temperature rose along with time. The greater input power was, the higher dentine temperature was. The greater gas flow rate was, the faster the temperature rose. Dentine surface temperature reached the highest point of (35.10±0.24) ℃ with NTAPP treatment for 60 s, at input power of 11 W and flow rate of 5 L/min. The contact angles of each experimental group decreased with time, and significant differences were found in the contact angles between the experimental groups and the negative control group (75.57°±1.45°). The contact angles showed a decreasing trend as the input power and the gas flow rate increased. The contact angles reached the lowest point of 13.19°±2.01° with NTAPP treatment for 20 s, at input power of 10 W and flow rate of 5 L/min. The FE-SEM results showed that, along with the increase of input power and extension of time, the demineralized collagen fibrils were destroyed in varying degrees. The collagen fibrils were curled, fractured, fused, and even disappeared. Conclusions: NTAPP could significantly increase the surface temperature, modify dentine wettability and alter the micro structure, which was significantly influenced by input power, gas flow rate and treating time.