| Lithium disilicate glass-ceramic possesses higher mechanical strength than otherdental glass-ceramics and meanwhile demonstrates excellent translucency characteristicsdue to the unique nature and distribution of Li2Si2O5crystals. Therefore, it has beenconsidered as the ideal aesthetic restorative material with board applications in cosmeticdentistry. Currently, IPS products manufactured by Ivoclar Vivadent Corporate are theonly commercial dental lithium disilicate glass-ceramics with high cost. In order to breakthe technological monopoly of foreign manufacturers and to promote the application ofall-ceramic restorations in China, new products with independent intellectual propertyrights and lower cost need to be developed. Property improvement and color matching aretwo main difficulties of developing new dental ceramics. In the previous study, a novel dental lithium disilicate glass-ceramic has been produced. In the present study, the effectof the sintering time and zircon-based ceramic pigments on the microstructure andproperties of experimental lithium disilicate glass-ceramic were investigated, in order toimprove the properties of the experimental glass-ceramic by optimizing the sintering timeand to investgate whether zircon-based tricolor pigments can be used to color theexperimental glass-ceramic. Moreover, computer color matching of the experimentalglass-ceramic was conducted to procure pigment formulations matching with the color ofthe Vitapan Classical shade guide. Besides, the color matching accuracies of threecomputer color matching methods were evaluated with the aim of establishing colormatching database for further color research. Furthermore, the effect of veneeringporcelain on the color of the experimental glass-ceramic was studied. And finally, themicrostructure and properties of the experimental glass-ceramic were compared with thoseof commercial dental lithium disilicate glass-ceramics. Based on these studies, we aimedto develop a novel dental lithium disilicate glass-ceramic product with intellectualproperty. The present study includes three parts:Part I: property analysis of the experimental lithium disilicate glass-ceramic1. Glass-ceramics derived from the SiO2-Li2O-K2O-Al2O3-ZrO2-P2O5system wereproduced by a two-stage sintering cycle with a primary thermal treatment at700oCfollowed by a secondary thermal treatment at900oC. The periods during which thematerials were subjected to each temperature level (700oC/900oC) were the following: A,1h/1h; B,2h/2h; C,3h/3h; D,4h/4h; E,5h/5h; F,6h/6h; G,8h/8h. The XRD resultsrevealed that all groups had a similar crystalline structure though the sintering times weredifferent. The main crystalline phase corresponds to Li2Si2O5and the minor phasescorrespond to Li2SiO3and Li3PO4. SEM analysis showed an interlocking microstructureof rod-shaped Li2Si2O5crystals in all specimens. However, the glass-ceramics producedwith different sintering times showed different crystal sizes and spatial distribution. Thetranslucency parameters (TP) of the glass-ceramics studied were not affected by sinteringtime since similar TP values were observed in all specimens. The glass-ceramic sinteredduring5h in each temperature level (700oC/900oC) showed the highest flexural strength (308±25MPa).2.1.0wt.%zircon-based tricolor pigments (praseodymium zircon yellow, ferrumzircon red and vanadium zircon blue) were added into the experimental glass-ceramic andtheir effects on the microstructure and properties of the experimental glass-ceramic wereinvestigated. The results revealed that the three pigments had no significant effects on thethermal property, crystalline phase composition, microstructure and flexural strength ofthe experimental glass-ceramic. Although significant differences (P<0.05) were observedbetween the translucencies of the uncolored and1.0wt.%zircon-based pigment coloredceramics, the translucencies of the latter were sufficient to fabricate dental restorations.These results indicate that the zircon-based tricolor pigments could be used as thecolorants of the experimental glass-ceramic.Part II: computer color matching of the experimental lithium disilicate glass-ceramic3. Monochrome colored experimental glass-ceramic samples with gradient addedconcentrations of zircon-based tricolor pigments were fabricated. The effect of thepigments on the chromatic values and reflective spectrums of the monochrome sampleswere investigated. The results indicated that the relationship between the addedconcentration of pigments and the chromatic values was consistent with the basic law ofpigmentation, and that the spectral reflectance data of monochrome samples could be usedto establish the database of computer color matching.4. Computer color matching methods based on Kubelka-Munk theory, namely,tristimulus matching method and spectrophometic matching method, were applied forcolor matching of the experimental glass-ceramic with Vitapan Classical shade guide. Theresults showed that the samples sintered according to the pigment formula provided bythese two computer color matching methods both achieved similar colors with the shadetabs of Vitapan Classical shade guide. However, spectrophometic matching method wassuperior to tristimulus matching method in color matching precision, and the average colordifferences (ΔE) between the matching samples of these two methods and the target shadetabs were10.8±2.1and14.0±2.2, respectively. 5. Computer color matching method based on BP artificial neural network was usedto match the color of the experimental glass-ceramic with Vitapan Classical shade guide.The results demonstrated that the samples sintered according to the pigment formulaprovided by BP artificial neural network also obtained similar colors with the shade tabsof Vitapan Classical shade guide. Moreover, this method showed better color matchingaccuracy than both tristimulus and spectrophometic matching methods, with smalleraverage color differences between the matching samples and the target shade tabs(6.3±1.2).6. IPS e.max Ceram veneering porcelain was fired on the experimental glass-ceramiccore materials and the colors of the samples fired with veneering porcelain were evaluated.Additionally, the effect of repeated firing according to the firing program of IPS e.maxCeram on the color of A2colored experimental glass-ceramic was investigated, in order todetermine color stability of the colored experimental glass-ceramic. The resultsdemonstrated that average color differences between the samples fired with veneeringporcelain and the target shade tabs were reduced to3.5±0.4. Moreover, repeated firing hadno significant effect on the color of the experimental glass-ceramic.Part III: comparative analysis on the microstructure and properties of dental lithiumdisilicate glass-ceramics7. The microstructure and properties of the experimental glass-ceramic and IPSe.max Press ceramic blocks were compared, with aim to analyze the relationship betweenthe properties and microstructure of lithium disilicate glass-ceramic. The results showedthat the crystalline phase composition, microstructure and mechanical properties of theexperimental glass ceramic were similar to those of IPS e.max Press ceramic blocks. Thetranslucency parameters of the experimental glass ceramic were higher than those of IPSe.max Press HO ceramic blocks but lower than those of MO ceramic blocks. The resultsverified that the experimental lithium disilicate glass-ceramic possesses sufficientperformance that comply with the requirements of dental aesthetic restorative materialsand demonstrates ideal application prospects. |
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