Exploratory Study Of New Methods For Color Matching Based On The Color Space Of Natural Teeth

Color is one of the most important factors affecting the aesthetic outcome of porcelain restoration.Harmonious color matching of artificial restorations with natural dentition will greatly improve the aesthetic effect of dental restorations.However,color matching is still remains as one of the most challenging tasks in esthetic dentistry.In present study,color distributions(L*,a*and b*)of maxillary central incisors of the given population were measured and analysed.The metal-ceramic samples were fabricated with the mixture of porcelain powders to create a color database.An optimized shade guide was developed base on the color space of maxillary central incisors and the color database of porcelain powder mixtures.Besides,a novel compuer color matching system based on the back-propagation neural network model was also developed and evaluated.Partl Evaluation of the applicability of three shade guides for the given population Objectives:To analyse the color distributions of maxillary central incisors in Wuhan,and to evaluate the applicability of three shade guides for the given population.Materials and methods:Color coordinates(L*,a*and b*)of 236 maxillary left central incisors and three shade guides were measured using a spectroradiometer(PR-650 Spectra Scan).Color space of the maxillary left central incisors were analysed.The coverage errors of three shade guides were calculated.Results:For the color coordinates(L*,a*and b*)of all maxillary left central incisors,the mean L*values were 73.1 ±5.0,the mean a*values were 1.5± 1.3 and the mean b*values were 13.5±3.4.The range of values for color coordinates(L*,a*and b*)were 55.4?89.9,-0.8-7.3 and 5?27.4,respectively.The coverage errors of three shade guides(Vitapan Classical?Vintage Halo and Chromascop)were 3.44±2.19,4.16±2.53 and 4.92±2.65,respectively.There were significant difference in coverage errors among the three shade guides(P<0.01).The Vitapan Classical shade guide has the lowest coverage error in the three shade guides,Conclusion:Color coordinates of maxillary central incisors are distributed in a flat,long and narrow area of the color space.In this study,none of the shade guides have adequate coverage and logical arrangement in the color space of natural teeth.The Vitapan Classical shade guideis more suitable for color matching in the given population.Part 2 Development and clinical evaluation of an optimized shade guideObjectives:To develop and evaluate an optimized shade guide based on the color space of maxillary central incisors and the color database of porcelain powder mixtures.Materials and methods:56 metal-ceramic tabs were fabricated according to porcelain powder mixtures.Color coordinates of all the metal-ceramic tabs were measured by a Spectroradiometer(PR-650 Spectra Scan)to create a color database.An optimized shade guide was designed according to the color space of maxillary central incisors and the color database of porcelain powder mixtures.Coverage errors of the 56 metal-ceramic tabs,the optimized shade guide and Vitapan Classical shade guide were calculated.The optimized shade guide was evaluated clinically by comparing with Vitapan Classical shade guide.Results:The mean coverage errors of the 56 metal-ceramic tabs,the optimized shade guide and Vitapan Classical shade guide were 2.79±2.01,2.93±2.00 and 3.44±2.19,respectively?Significant difference of coverage errors was found between the optimized shade guide and Vitapan Classical shade guide(P<0.01).There was no significant difference in coverage errors between the optimized shade guide and the 56 metal-ceramic tabs(P>0.05).The mean color difference of the optimized shade guide was 3.62±1.22 while Vitapan Classical shade guide was 5.34±2.04.The mean color difference of the optimized shade guide was significant lower than that of Vitapan Classical shade guide(P<0.001).Conclusion:Coverage error of the shade guide can be reduced by improving the color distributions of the shade guide in the color space of natural teeth.The optimized shade guide made a better performance than Vitapan Classical shade guide.Part 3 Development and clinical evaluation of a novel computer color matching modelObjectives:To develop and optimize a novel computer color-matching system based on the BP neural network model and to explore the feasibility of the optimized computer color matching model.Materials and methods:Metal-cermic tabs were fabricated by proportionally mixing porcelain powders.Color coordinates of metal-cermic tabs were measured using a Spectroradiometer(PR-655 Spectra Scan).A computer color matching system based on BP neural network model was developed according to the 'color coordinates-porcelain powders formulas' database.Genetic algorithms and Levenberg-Marquardt algorithms were used to improve the convergence and generalization performance of traditional BP neural network.The feasibility and accuracy of the computer color matching system based on the optimized BP neural network model was evaluated by comparing with visual shade matching.Results:The mean color difference of the optimized BP neural network model(AE=1.11 ±0.23)was significantly lower than that of the traditional BP neural network model(A E=2.34±0.70)(P=0.009).The mean color difference of the computer color matching system based on the optimized BP neural network model(AE=1.89± 0.75)was significantly lower than that of visual shade matching(AE=3.54±1.11)(P<0.001),as well as the clinically tolerable threshold 2.69(P<0.001).Conclusion:Combining Genetic algorithms and Levenberg-Marquardt algorithms with BP algorithm will greatly improve the generalization and accuracy of BP neural network.The newly developed CCM system was superior to the traditional visual color-matching system.