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Papers by María Del Mar Pérez

Research paper thumbnail of Stability and Reproducibility of Radiometric Properties of Light Curing Units (LCUs). Part I: QTH LCUs

Dental Materials Journal, 2008

The present work is the second part of a study on the stability and reproducibility of the energy... more The present work is the second part of a study on the stability and reproducibility of the energy and spectral emission of some light curing units (LCUs). In this part, Part II, LED LCUs were investigated. Results revealed that these devices presented high stability and reproducibility in terms of their spectral emission, with values of VAF (variance accounting for) coefficient calculated from the Cauchy-Schwarz inequality all close to 100％. With respect to energy stability, the LED LCUs presented energy stability except for the third-generation LED LCUs which have several LEDs. For these devices, the law of reciprocity was not fulfilled as irradiance was not constant over exposure time. This result should be taken into account both in works examining the polymerization kinetics of dental materials as well as when these LED LCUs are used in clinical practice.

Research paper thumbnail of Recent Advances in Color and Whiteness Evaluations in Dentistry

Current Dentistry, 2019

Background: The final goal of color measurement or shade specification in dentistry is the reprod... more Background: The final goal of color measurement or shade specification in dentistry is the reproduction by prosthetic materials of all important appearance characteristics of natural oral structures. The application of color science in dentistry is an objective way to measure and evaluate such structures and dental materials in clinical practice and dental research. Methods: Literature on color science was reviewed to present new metrics to evaluate color differences of dental materials and dental structures. Visual acceptability and perceptibility values of color differences are reviewed and new whiteness indexes to describe whiteness in dentistry are presented. Results: In the last decade, the CIELAB 50:50% perceptibility and acceptability thresholds were set to 1.2 and 2.7, respectively, and the CIEDE2000 50:50% perceptibility and acceptability thresholds were set to 0.8 and 1.8. The CIEDE2000 color-difference formula became increasingly popular in dentistry. Developments in colo...

Research paper thumbnail of Predictive algorithms for determination of reflectance data from quantity of pigments within experimental dental resin composites

BioMedical Engineering OnLine, 2015

Background: Being able to estimate (predict) the final spectrum of reflectance of a biomaterial, ... more Background: Being able to estimate (predict) the final spectrum of reflectance of a biomaterial, especially when the final color and appearance are fundamental for their clinical success (as is the case of dental resin composites), could be a very useful tool for the industrial development of these type of materials. The main objective of this study was the development of predictive models which enable the determination of the reflectance spectrum of experimental dental resin composites based on type and quantity of pigments used in their chemical formulation. Methods: 49 types of experimental dental resin composites were formulated as a mixture of organic matrix, inorganic filler, photo activator and other components in minor quantities (accelerator, inhibitor, fluorescent agent and 4 types of pigments). Spectral reflectance of all samples were measured, before and after artificial chromatic aging, using a spectroradiometer. A Multiple Nonlinear Regression Model (MNLR) was used to predict the values of the Reflectance Factors values in the visible range (380 nm-780 nm), before and after aging, from % Pigment (%P1, %P2, %P3 and %P4) within the formulation. Results: The average value of the prediction error of the model was 3.46% (SD: 1.82) across all wavelengths for samples before aging and 3.54% (SD: 1.17) for samples after aging. The differences found between the predicted and measured values of the chromatic coordinates are smaller than the acceptability threshold and, in some cases, are even below the perceptibility threshold. Conclusions: Within the framework of this pilot study, the nonlinear predictive models developed allow the prediction, with a high degree of accuracy, of the reflectance spectrum of the experimental dental resin composites.

Research paper thumbnail of Are chroma tolerances dependent on hue-angle?

Color Research & Application, 2004

ABSTRACT Relationships between suprathreshold chroma tolerances and CIELAB hue-angles have been a... more ABSTRACT Relationships between suprathreshold chroma tolerances and CIELAB hue-angles have been analyzed through the results of a new pair-comparison experiment and the experimental combined data set employed by CIE TC 1–47 for the development of the latest CIE color-difference formula, CIEDE2000. Chroma tolerances have been measured by 12 normal observers at 21 CRT-generated color centers L*10 = 40, C*ab,10 = 20 and 40, and hab,10 at 30° regular steps). The results of this experiment lead to a chroma-difference weighting function with hue-angle dependence WCH, which is in good agreement with the one proposed by the LCD color-difference formula [Color Res Appl 2001;26:369–375]. This WCH function is also consistent with the experimental results provided by the combined data set employed by CIE TC 1–47. For the whole CIE TC 1–47 data set, as well as for each one of its four independent subsets, the PF/3 performance factor [Color Res Appl 1999;24:331–343] was improved by adding to CIEDE2000 the WCH function proposed by LCD, or the one derived by us using the results of our current experiment together with the combined data set employed by CIE TC 1–47. Nevertheless, unfortunately, from the current data, this PF/3 improvement is small (and statistically nonsignificant): 0.3 for the 3657 pairs provided by CIE TC 1–47 combined data set and 1.6 for a subset of 590 chromatic pairs (C*ab,10>5.0) with color differences lower than 5.0 CIELAB units and due mainly to chroma. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 420–427, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.20057

Research paper thumbnail of Color and translucency of zirconia ceramics, human dentine and bovine dentine

Human dentine Bovine dentine a b s t r a c t Objectives: Evaluate color and translucency of both ... more Human dentine Bovine dentine a b s t r a c t Objectives: Evaluate color and translucency of both non-colored and colored zirconia ceramics and compare them with corresponding properties of human dentine.

Research paper thumbnail of Firmness prediction in Prunus persica 'Calrico' peaches by visible/short-wave near infrared spectroscopy and acoustic measurements using optimised linear and non-linear chemometric models

Journal of the science of food and agriculture, Jan 15, 2014

In this work, near infrared spectroscopy (NIR) and an acoustic measure (AWETA) (two non-destructi... more In this work, near infrared spectroscopy (NIR) and an acoustic measure (AWETA) (two non-destructive methods) were applied in Prunus persica fruit 'Calrico' (n = 260) to predict Magness-Taylor (MT) firmness. Separate and combined use of these measures was evaluated and compared using partial least squares (PLS) and least squares support vector machine (LS-SVM) regression methods. Also, a mutual-information-based variable selection method, seeking to find the most significant variables to produce optimal accuracy of the regression models, was applied to a joint set of variables (NIR wavelengths and AWETA measure). The newly proposed combined NIR-AWETA model gave good values of the determination coefficient (R(2) ) for PLS and LS-SVM methods (0.77 and 0.78, respectively), improving the reliability of MT firmness prediction in comparison with separate NIR and AWETA predictions. The three variables selected by the variable selection method (AWETA measure plus NIR wavelengths 675 ...

Research paper thumbnail of Optical behavior of dental zirconia and dentin analyzed by Kubelka–Munk theory

Dental Materials, 2015

To use the Kubelka-Munk theory to evaluate the scattering (S), absorption (K) and transmittance (... more To use the Kubelka-Munk theory to evaluate the scattering (S), absorption (K) and transmittance (T) of non-colored and colored dental zirconia systems and human (HD) and bovine (BD) dentins. Two zirconia systems were used: ZC- ZirCAD (Ivoclar Vivadent) and LV-LAVA (3M ESPE). Specimens from each ceramic system were divided into 3 groups (n=5): ZC1 and LV1 (non-colored); ZC2 and LV2 colored to shade A1, and ZC3 and LV3 colored to shade A3. Five human and bovine anterior teeth were flattened and polished through 1200 grit SiC paper to expose the superficial buccal dentin. All samples were prepared to a final thickness of 0.5mm. Diffuse reflectance was measured against white and black backgrounds, using a spectroradiometer in a viewing booth with D65 illuminant and d/0° geometry. S and K coefficients and T were calculated using Kubelka-Munk's equations. Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. Spectral distributions of S, K and T were wavelength dependent. The spectral behavior of S and T was similar to HD (VAF≥96.80), even though they were statistically different (p≤0.05). The spectral behavior of K was also similar to HD, except for LV1 (VAF=38.62), yet all ceramics were statistically different from HD (p≤0.05). HD and BD showed similar values of S and T (p>0.05). The dental professional should consider the optical behavior differences between the zirconia systems evaluated and the human dentin to achieve optimal esthetics in restorative dentistry.

Research paper thumbnail of Stability and Reproducibility of Radiometric Properties of Light Curing Units (LCUs). Part I: QTH LCUs

Dental Materials Journal, 2008

The present work is the second part of a study on the stability and reproducibility of the energy... more The present work is the second part of a study on the stability and reproducibility of the energy and spectral emission of some light curing units (LCUs). In this part, Part II, LED LCUs were investigated. Results revealed that these devices presented high stability and reproducibility in terms of their spectral emission, with values of VAF (variance accounting for) coefficient calculated from the Cauchy-Schwarz inequality all close to 100％. With respect to energy stability, the LED LCUs presented energy stability except for the third-generation LED LCUs which have several LEDs. For these devices, the law of reciprocity was not fulfilled as irradiance was not constant over exposure time. This result should be taken into account both in works examining the polymerization kinetics of dental materials as well as when these LED LCUs are used in clinical practice.

Research paper thumbnail of Recent Advances in Color and Whiteness Evaluations in Dentistry

Current Dentistry, 2019

Background: The final goal of color measurement or shade specification in dentistry is the reprod... more Background: The final goal of color measurement or shade specification in dentistry is the reproduction by prosthetic materials of all important appearance characteristics of natural oral structures. The application of color science in dentistry is an objective way to measure and evaluate such structures and dental materials in clinical practice and dental research. Methods: Literature on color science was reviewed to present new metrics to evaluate color differences of dental materials and dental structures. Visual acceptability and perceptibility values of color differences are reviewed and new whiteness indexes to describe whiteness in dentistry are presented. Results: In the last decade, the CIELAB 50:50% perceptibility and acceptability thresholds were set to 1.2 and 2.7, respectively, and the CIEDE2000 50:50% perceptibility and acceptability thresholds were set to 0.8 and 1.8. The CIEDE2000 color-difference formula became increasingly popular in dentistry. Developments in colo...

Research paper thumbnail of Predictive algorithms for determination of reflectance data from quantity of pigments within experimental dental resin composites

BioMedical Engineering OnLine, 2015

Background: Being able to estimate (predict) the final spectrum of reflectance of a biomaterial, ... more Background: Being able to estimate (predict) the final spectrum of reflectance of a biomaterial, especially when the final color and appearance are fundamental for their clinical success (as is the case of dental resin composites), could be a very useful tool for the industrial development of these type of materials. The main objective of this study was the development of predictive models which enable the determination of the reflectance spectrum of experimental dental resin composites based on type and quantity of pigments used in their chemical formulation. Methods: 49 types of experimental dental resin composites were formulated as a mixture of organic matrix, inorganic filler, photo activator and other components in minor quantities (accelerator, inhibitor, fluorescent agent and 4 types of pigments). Spectral reflectance of all samples were measured, before and after artificial chromatic aging, using a spectroradiometer. A Multiple Nonlinear Regression Model (MNLR) was used to predict the values of the Reflectance Factors values in the visible range (380 nm-780 nm), before and after aging, from % Pigment (%P1, %P2, %P3 and %P4) within the formulation. Results: The average value of the prediction error of the model was 3.46% (SD: 1.82) across all wavelengths for samples before aging and 3.54% (SD: 1.17) for samples after aging. The differences found between the predicted and measured values of the chromatic coordinates are smaller than the acceptability threshold and, in some cases, are even below the perceptibility threshold. Conclusions: Within the framework of this pilot study, the nonlinear predictive models developed allow the prediction, with a high degree of accuracy, of the reflectance spectrum of the experimental dental resin composites.

Research paper thumbnail of Are chroma tolerances dependent on hue-angle?

Color Research & Application, 2004

ABSTRACT Relationships between suprathreshold chroma tolerances and CIELAB hue-angles have been a... more ABSTRACT Relationships between suprathreshold chroma tolerances and CIELAB hue-angles have been analyzed through the results of a new pair-comparison experiment and the experimental combined data set employed by CIE TC 1–47 for the development of the latest CIE color-difference formula, CIEDE2000. Chroma tolerances have been measured by 12 normal observers at 21 CRT-generated color centers L*10 = 40, C*ab,10 = 20 and 40, and hab,10 at 30° regular steps). The results of this experiment lead to a chroma-difference weighting function with hue-angle dependence WCH, which is in good agreement with the one proposed by the LCD color-difference formula [Color Res Appl 2001;26:369–375]. This WCH function is also consistent with the experimental results provided by the combined data set employed by CIE TC 1–47. For the whole CIE TC 1–47 data set, as well as for each one of its four independent subsets, the PF/3 performance factor [Color Res Appl 1999;24:331–343] was improved by adding to CIEDE2000 the WCH function proposed by LCD, or the one derived by us using the results of our current experiment together with the combined data set employed by CIE TC 1–47. Nevertheless, unfortunately, from the current data, this PF/3 improvement is small (and statistically nonsignificant): 0.3 for the 3657 pairs provided by CIE TC 1–47 combined data set and 1.6 for a subset of 590 chromatic pairs (C*ab,10>5.0) with color differences lower than 5.0 CIELAB units and due mainly to chroma. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 420–427, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.20057

Research paper thumbnail of Color and translucency of zirconia ceramics, human dentine and bovine dentine

Human dentine Bovine dentine a b s t r a c t Objectives: Evaluate color and translucency of both ... more Human dentine Bovine dentine a b s t r a c t Objectives: Evaluate color and translucency of both non-colored and colored zirconia ceramics and compare them with corresponding properties of human dentine.

Research paper thumbnail of Firmness prediction in Prunus persica 'Calrico' peaches by visible/short-wave near infrared spectroscopy and acoustic measurements using optimised linear and non-linear chemometric models

Journal of the science of food and agriculture, Jan 15, 2014

In this work, near infrared spectroscopy (NIR) and an acoustic measure (AWETA) (two non-destructi... more In this work, near infrared spectroscopy (NIR) and an acoustic measure (AWETA) (two non-destructive methods) were applied in Prunus persica fruit 'Calrico' (n = 260) to predict Magness-Taylor (MT) firmness. Separate and combined use of these measures was evaluated and compared using partial least squares (PLS) and least squares support vector machine (LS-SVM) regression methods. Also, a mutual-information-based variable selection method, seeking to find the most significant variables to produce optimal accuracy of the regression models, was applied to a joint set of variables (NIR wavelengths and AWETA measure). The newly proposed combined NIR-AWETA model gave good values of the determination coefficient (R(2) ) for PLS and LS-SVM methods (0.77 and 0.78, respectively), improving the reliability of MT firmness prediction in comparison with separate NIR and AWETA predictions. The three variables selected by the variable selection method (AWETA measure plus NIR wavelengths 675 ...

Research paper thumbnail of Optical behavior of dental zirconia and dentin analyzed by Kubelka–Munk theory

Dental Materials, 2015

To use the Kubelka-Munk theory to evaluate the scattering (S), absorption (K) and transmittance (... more To use the Kubelka-Munk theory to evaluate the scattering (S), absorption (K) and transmittance (T) of non-colored and colored dental zirconia systems and human (HD) and bovine (BD) dentins. Two zirconia systems were used: ZC- ZirCAD (Ivoclar Vivadent) and LV-LAVA (3M ESPE). Specimens from each ceramic system were divided into 3 groups (n=5): ZC1 and LV1 (non-colored); ZC2 and LV2 colored to shade A1, and ZC3 and LV3 colored to shade A3. Five human and bovine anterior teeth were flattened and polished through 1200 grit SiC paper to expose the superficial buccal dentin. All samples were prepared to a final thickness of 0.5mm. Diffuse reflectance was measured against white and black backgrounds, using a spectroradiometer in a viewing booth with D65 illuminant and d/0° geometry. S and K coefficients and T were calculated using Kubelka-Munk's equations. Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. Spectral distributions of S, K and T were wavelength dependent. The spectral behavior of S and T was similar to HD (VAF≥96.80), even though they were statistically different (p≤0.05). The spectral behavior of K was also similar to HD, except for LV1 (VAF=38.62), yet all ceramics were statistically different from HD (p≤0.05). HD and BD showed similar values of S and T (p>0.05). The dental professional should consider the optical behavior differences between the zirconia systems evaluated and the human dentin to achieve optimal esthetics in restorative dentistry.