Effects Of Acid Etching Methods On The Dentin Structure And The Hardness Of Moderate Dental Fluorosis

Objective: To compare the changes of surface structure,roughness,dentin tubule diameter,and interfacial microhardness of moderate fluorosis dentin treated by different acid etching methods,we analyzed the differences of nanoscale physical structure and micromechanical properties of dentin interface under different acid etching methods,in order to provide some theoretical reference for the selection of acid etching methods in the treatment of fluorosis dentin restoration.Methods: After slicing and polishing 40 human moderate fluorosis isolated tooth samples collected,they were divided into 4 groups of 10 samples each using the random number table method.F0 was the control group;FA group was treated with full acid etchant(Eco-Etch 37% phosphoric acid)for 15s;FB group was treated with 37% phosphoric acid(Eco-Etch 37% phosphoric acid)for 15s followed by 10% sodium hypochlorite(NaCIO)for 20s;FC group was treated with sixth generation two-component self-etching bonding agent(Kuraray Philo SE Bond pretreatment agent)for 60s.The dentin surface morphology was observed using Atomic Force Microscopy(AFM)and the surface roughness and dentin tubule diameter values were measured.The Vickers hardness of the dentin surface was measured by micro Vickers hardness tester.SPSS 26.0 statistical software was applied for data analysis.Results: 1.AFM has a significant advantage in the observation of dentin microstructure;AFM shows that the distribution of dentin tubules in the middle layer of moderate fluorosis teeth is irregular,the size of the tubule mouth varies,and some tubule mouths can be seen as obvious narrowing and deformation of the lumen.37% phosphoric acid will obviously demineralize the peritubular intertubular dentin,the dentin tubule mouth increases,showing a "small bottom mouth large" deep funnel shape."The combined treatment of 37%phosphoric acid + 10% sodium hypochlorite further demineralized the dentin,reducing the area of the remaining intercanal dentin,further increasing the size of the dentin tubules,and opening more secondary dentin tubules.The dentin interface of the self-etching treatment group(Coliflu SE Bond pretreatment agent)was still visible as debris and impurities,and the demineralization of peri-and intertubular dentin was not obvious,and the dentin tubule mouth was "crater-like invagination".2.In this experiment,acid etching treatment groups could increase the surface roughness of the middle layer dentin of moderate fluorosis teeth(P ﹤ 0.05).The combined 37%phosphoric acid + 10% sodium hypochlorite treatment group did not show any statistical difference in increasing the surface roughness of dentin compared with the 37%phosphoric acid group(P > 0.05).3.In this experiment,both the 37% phosphoric acid group and the 37% phosphoric acid +10% sodium hypochlorite combined treatment group could significantly increase the diameter of dentin tubules(P < 0.05);no statistically significant difference was seen between these two groups(P > 0.05).There was no significant difference in the diameter of dentin tubules after self-etching cement treatment compared with the control group(P >0.05).4.Both the 37% phosphoric acid group and the 37% phosphoric acid combined with 10%NaCIO treatment group significantly reduced the microhardness values of the dentin surface(P < 0.05),while there was no significant difference in the surface microhardness values of the dentin in the self-etching group compared with the control group(P > 0.05).Conclusion: Under the present experimental conditions: 1,all three acid etching treatments increased the surface roughness and dentin tubule diameter at the dentin interface of moderate fluorosis dentin,and the 37% phosphoric acid and 37% phosphoric acid combined with 10% NaCIO treatments had significant effects.2,The hardness of dentin was reduced after all three acid etching treatments,among which,37% phosphoric acid and 37% phosphoric acid combined with 10% NaCIO treatment reduced the hardness significantly.3.The self-etching treatment has a good retention rate of dentin hardness while increasing the roughness of dentin surface,which has some advantages in the bonding restoration of fluorosis dentin.