Study Of The Effects Of Surface Modified Nano-oxides On Maxillofacial Elastomers

Extraoral maxillofacial prostheses are widely used for restoring missing facialstructures due to resection, trauma, or congenital anomalies. Materials used forthis purpose are silicone elastomers. However, because of their limitations ofphysical properties and certain environmental factors, they usually becomeaging, harder and color degradation. Nano oxide, as a kind of ultraviolet lightabsorber, is more stable and has better property of enhancing silicone elastomer.Our group firstly introduces it into maxillofacial elastomer, and investigates thetentative confirmation. The purpose of of our research focus on the effects onthe physical properties, color stability and biological safety performance ofmaxillofacial elastomer after adding surface modified nano-oxides by properconcentrations. When patients wear the maxillofacial prosthesis, the compoundmaterials can resist outdoor environmental factors and partial mechanical forcein order to avoid aging in long term. Then the service life of prosthesis can be extended.Part I Study of surface modification of nano-sized TiO₂and ZnOwith silicane coupling agent.This part consists of3experiments:â‘ Nano-sized TiO₂and ZnO were treated with different content of KH-570.The nano-sized TiO₂and ZnO before and after modification werecharacterized by virtue of several analysis means.â‘¡The evaluation of UV-ray shieding properties of surface modifiednano-sized TiO₂and ZnO;â‘¢Evaluations of mechanical properties of silicone elastomer by addingsurface modified nano-sized TiO₂and ZnO with different concentrations.The results are showed as follows:â‘ The surface performance of nano-sized TiO₂and ZnO modified with silanecoupling reagent （KH-570） had changed from hydrophilic to hydrophobic,the KH-570was bound on the surface of nano-sized TiO₂and ZnO particles,a firm chemical bonding of KH-570to nano-sized TiO₂and ZnO and a layerof organic coating layer formed. The best concentration of KH-570coatedon the surface of nano-sized TiO₂and ZnO was about5wt%.â‘¡Both of nano-sized TiO₂and ZnO have the better UV-sheildingperformance.â‘¢KH-570surface modified nano-sized TiO₂and ZnO at concentrations of2.0wt%and2.5wt%improved the overall mechanical properties of thesilicone A-2186maxillofacial elastomer.Part II After different aging conditions, the evaluations of mechanical properties and color stability of silicone elastomerA-2186by adding nano-sized TiO₂and ZnOâ‘ The evaluation of mechanical properties of silicone elastomer A-2186byadding nano-sized TiO₂and ZnO after artificial agingThe results showed below:a) For tensile strength, compared with control group, both ZnO groups andTiO₂groups improved the tensile strength before and after artificial aging（p<0.05）; ZnO with2.5wt%concentration groups showed the smallestchanges （p<0.05）;b) For tear strength, TiO₂at2.5wt%concentration with no pigments group hadthe greatest changes （p<0.05）; When mixed with pigments, ZnO at1.0wt%showed smallest changes （p<0.05）;c) For elongation, there was significant difference among the type ofnano-oxides （p<0.05）; control group had the greatest changes after artificialaging （p<0.05）; TiO₂at2.0wt%concentration group had the smallestchanges （p<0.05）;d) For hardness, after artificial aging, specimens of control groups become4-7times harder than all nano-oxide groups （p<0.001）.Above all results, the conclusion was: Both of nano-sized TiO₂and ZnOimproved mechanical properties of silicone elastomer A-2186after subjected toartificial aging.â‘¡The evaluation of color stability of silicone elastomer A-2186by addingnano-sized TiO₂and ZnO after artificial aging and outdoor aginga) Artificial aging condition Yellow pigments mixed with all three nano-oxides at all intervals increased E*values significantly from3.7up to8.4. When mixed pigment groups wereconsidered, TiO₂at2.0wt%, and2.5wt%exhibited the smallest color changes,followed by ZnO respectively （p<0.001）.The smallest color differences,observed for nano-oxides groups, were recorded for TiO₂at2.0wt%and2.5wt%.When the nano-oxides were tested at all concentrations, TiO₂groups had theleast color change. All E*values of the mixed pigment groups were below the50:50%acceptability threshold （E*=1.2–2.3, below3.0）.b) Outdoor aging conditionFor the exposure periods, there were significant differences from each other. Allspecimens of12months exposure showed the greatest color changes （p<0.001）;Nano ZnO at1.0wt%concentration with no pigments showed the smallest colorchange; however, after mixed with three pigments, nano TiO₂at2.5wt%showedthe smallest color differences; Compared with control group, all E*values ofthe mixed groups were below the50:50%acceptability threshold （E*=0.6-2.6,below3.0）.Above all results, the conclusion were: Nano TiO₂and nano ZnO protected bothpigmented and nonpigmented silicone A-2186from color degradation. Exposureperiods had significantly affected the color change. Outdoor aging made greatercolor changes than artificial aging.Part III Evaluations on the biocompatibility of silicone elastomerA-2186with nano TiO₂and nano ZnOBefore the clinical application, a series of experiments should be done todetermine the biological safety of silicone elastomer A-2186with nano TiO₂and nano ZnO according to standards GB/T16175-1996. The results of biologicaltests were as below:â‘ Cytotoxicity test, the result showed that the cytotoxicity index of siliconeelastomer A-2186with nano TiO₂and nano ZnO were in grade I, whichindicated that the materials had no cytotoxicity;â‘¡Skin irritation tests, the primary irritation index of silicone elastomerA-2186with Nano TiO₂and nano ZnO were all zero. The response types ofirritation tests were all minimal. The data showed that these materials didn’thave skin irritaion under the experimental condition.â‘¢Intracutaneous irritation tests, the results showed there were no obviousintracutaneous irritations.â‘£Skin sensitization tests, the scores of skin reaction of silicone elastomerA-2186with Nano TiO₂and nano ZnO were all zero. Sensitization rates ofthe two groups were also zero. There are no potential of skin sensitizationunder the experimental conditions.⑤Oral mucous membrane irritation tests, there were no local or systemicabnormal response in the groups of Nano TiO₂and nano ZnO. The scores oferythematous response were all zero and the histopathological findings werealso normal. There had no irritating response to oral mucous membraneunder the experimental conditions.