| Background In recent years,zirconia prosthesis has been widely used because of its excellent chemical stability,biocompatibility and aesthetics.With the rapid development of computer aided design and manufacturing(CAD/CAM)technology in oral restoration,the full-contour zirconia crowns have been used more and more in clinic without manual operation.Conventional zirconia commonly used in dentistry is often milled after sintering,resulting in serious waste of materials,while a novel self-glazed zirconia is prepared by 3D gel deposition approach followed by a milling of internal surface of the green bodies during which the possible local plastic deformation enable the elimination of grains defect.Different processing approaches may cause different surface properties,ultimately affecting bacterial adhesion.Therefore,the purpose of our study was to study the surface microstructure and properties of zirconia prepared by two different methods,and to further clarify the effects of these surface factors on bacterial adhesion and biofilm formation.Objective The purpose of this study was to compare the surface microstructure and properties of zirconia fabricated by two different manufacturing processes and further clarified how these surface factors affect the bacterial adhesion and biofilm formation.Material and Methods The research was divided into the following two parts: 1?Surface properties of materials(1)Two different commercially available zirconia were cut into the same size(diameter 15 mm,thickness = 1.0 mm)and were divided into four groups(n=10): 1)UCZ group(unpolished conventional zirconia):Manufactured by milling the partially sintered blanks;2)USGZ group(unpolished self-glazed zirconia):Manufactured by the precision additive 3D gel deposition approach;3)PCZ group(polished conventional zirconia):Manufactured by milling the partially sintered blanks and then polished;4)PSGZ group(polished self-glazed zirconia):Manufactured by the precision additive 3D gel deposition approach and then polished.(2)Scanning electron microscopy(SEM),Atomic force microscope(AFM)and contact angle measuring system were used to characterize the surface properties of four groups of zirconia.2?In vitro and in vivo experiments(1)In vitro experiment: Two different commercially available zirconia were cut into the same size(diameter 15 mm,thickness = 1.0 mm)and were divided into four groups(n=3).Spectrophotometer and CLSM(Confocal laser scanning microscopy)were used to measure the quantity and biofilm thickness of Streptococcus mutans after 24 h cultured.(2)In vivo experiment: Two different commercially available zirconia were cut into the same size(diameter 3 mm,thickness = 1.0 mm)and were divided into four groups(n=8).Eight healthy volunteers wore oral acrylic maxillary splint,and with four specimens were randomly inserted into the appliances for 24 hours,then the biofilm coverage and biofilm thickness were observedResults(1)The SEM images showed nanometer grains can be found on the surfaces of both UCZ and USGZ.At the magnification of 5000 ×,the surface structure of USGZ was more(2)uniform and dense,while the surfaces of PCZ and PSGZ were smoother.At the magnification of 50,000 ×,it appeared that the average grain size of UCZ was relatively larger than that of USGZ.Polishing could flatten the surface of both PCZ and PSGZ,which were smoother than UCZ and USGZ under high magnification,but some shallow scratches were still available,especially on PCZ.(2)The results of surface roughness showed that UCZ had the highest surface roughness(Ra = 45.9 ± 2.6 nm),followed by the USGZ(Ra = 33.0 ± 2.5 nm),PCZ(Ra = 16.6 ± 1.7 nm)and PSGZ(Ra = 8.0 ± 1.2 nm).The surface roughness of the conventional zirconia was significantly higher than that of self-glazed ziconia in both unpolished and polished groups(P < 0.001).The surface roughness of conventional zirconia and self-glazed zirconia decreased significantly after polishing(P < 0.001).(3)The results of contact angle showed that the contact angle in PSGZ group was(79.5 ± 2.0°),followed by the PCZ(78.4 ± 1.8°),USGZ(47.5 ± 3.0°)and UCZ(44.7 ± 1.4°).The contact angle was identified on UCZ,which was significantly lower than for USGZ(P < 0.05);however,PCZ showed no significant difference compared to PSGZ(P = 0.26).The contact angles of CZ and SGZ increased significantly after being polished(P < 0.001).The results showed that the surface free energy of UCZ group was the highest(48.6 ± 1.7 m J/m2),followed by the USGZ(46.2 ± 1.1 m J/m2),PCZ(46.2 ± 1.1 m J/m2)and PSGZ(44.9 ± 2.4 m J/m2).Statistical analysis indicated significant differences between UCZ and USGZ,UCZ and PCZ(P < 0.05).In addition,the surface free energy of polished CZ and SGZ,increases obviously.(4)The results of MTT assay within 24 hours showed that the bacterial formation rate of SGZ surface in unpolished group and polished group was significantly lower than that in CZ group,and there was significant difference between the two groups(P < 0.05).Meanwhile,the biofilm formation of Streptococcus mutans decreased significantly in the polished groups(P < 0.001).(5)CLSM images of in vitro study revealed that the values for the polished groups were significantly lower than those of unpolished groups in both CZ and SGZ.The biofilm thickness in UCZ group was significantly higher than that in USGZ group(P < 0.05)while PCZ and PSGZ showed no significant difference(P = 0.75).(6)CLSM images of in vivo study revealed that there was only significant difference between USGZ and PSGZ(P < 0.05).However,the mean values were different.The lowest surface coating coverage was PSGZ with a mean of 10.4 %,followed by PCZ with 12.2 %,USGZ with 13.9 % and UCZ showed the highest surface coating coverage with 15.5 %;There was no significant difference in biofilm thickness among different zirconia ceramic materials(P > 0.05).The highest biofilm thickness was measured on UCZ with a mean of 15.21 ?m,followed by USGZ with 15.19 ?m,PCZ with 14.08 ?m and the lowest was on PSGZ with a mean of 13.8 ?m.Conclusion(1)Due to different manufacturing approaches,the size and distribution of zirconia surface grains produced by conventional approach and 3D gel approach were different,which can lead to different surface properties such as surface roughness,contact angle and surface free energy.Besides,surface properties significantly changed after being polished.(2)When we can assure the cutting accuracy of zirconia prosthesis,both zirconia produced by conventional approach and 3D gel approach can meet the clinical standards.Besides,zirconia prepared by 3D gel approach showed the superior effect to zirconia prepared by conventional approach in decreasing the bacterial adhesion.Polishing is an indispensable step to reduce bacterial adhesion when we need to modify the occlusal and adjacent surfaces of the prosthesis... |
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