Resumen de Characterization of dental biomaterials by means of optical methods
- español
CARACTERIZACIÓN DE BIOMATERIALES DENTALES MEDIANTE MÉTODOS ÓPTICOS Descriptores: Propiedades ópticas y rugosidad de biomateriales dentales.
RESUMEN Actualmente, la obtención de biomateriales capaces de sustituir tejidos es una realidad que despierta gran interés social y en la que concentra sus esfuerzos una parte importante de la comunidad científica internacional. La puesta en marcha de tratamientos que empleen biomateriales de nueva generación pasa, sin duda, por la realización previa de estudios que analicen el comportamiento y las características reales de estos materiales. Los resultados de tales estudios condicionarán, en gran medida, el éxito de las futuras aplicaciones que se lleven cabo en el terreno biosanitario. Antes de poder desarrollar todo su potencial, es imprescindible conocer en detalle cómo son y cómo se comportan los materiales que ya están siendo generados.
Para profundizar en el conocimiento de los nuevos biomateriales es de vital importancia estudiar sus propiedades ópticas. Ello es independiente de que las funciones del tejido restaurado no sean propiamente las visuales. Por ejemplo, comprender la propagación de la radiación láser en estos materiales es crucial para establecer los efectos de muchos tratamientos médicos actuales, que se basan en la irradiación del tejido con este tipo de fuentes. También las técnicas de diagnóstico inocuas más recientes tienen su fundamento en la respuesta óptica de los medios biológicos. De hecho, para el desarrollo de futuras aplicaciones terapéuticas y diagnósticas es imperativo conocer las relaciones entre propiedades ópticas y biológicas de los tejidos y, por consiguiente, de los biomateriales.
Por ello, la presente Tesis Doctoral persigue como objetivo general aplicar métodos ópticos a la caracterización de biomateriales empleados en odontología para la reparación y sustitución de tejidos dentales (dentina y esmalte), tales como cerámica de zirconia y resinas de composite.
El contenido de esta Tesis Doctoral se estructura del siguiente modo: El capítulo I es una introducción donde se describe el contexto y los antecedentes. En el capítulo II, se expone la motivación incluyendo los objetivos específicos de la Tesis. Cada uno de los cuatro capítulos comprendidos entre el III y el VI responde a uno de los objetivos específicos perseguidos.
El capítulo III tiene como objetivo específico realizar medidas que permitan determinar con precisión los valores del factor de anisotropía de esparcimiento en biomateriales dentales y analizar comparativamente el comportamiento que presenta la anisotropía de esparcimiento en dichos biomateriales y en los tejidos dentales que están destinados a sustituir. El objetivo que se aborda en el capítulo IV es aplicar el algoritmo IAD para obtener valores precisos de los coeficientes de absorción y esparcimiento de biomateriales dentales incorporando los valores del factor de anisotropía de esparcimiento previamente calculados. El capítulo V tiene por objetivo realizar medidas encaminadas a evaluar el efecto de los biomateriales dentales sobre el estado de la luz polarizada. El objetivo que aborda el capítulo VI es realizar una inspección microtopográfica no invasiva que permita evaluar con precisión los principales parámetros de rugosidad de biomateriales dentales a través de un sistema de triangulación óptica y complementar la información sobre rugosidad con el resultado de medidas del brillo especular.
En cada uno de estos capítulos se incluyen los antecedentes, la metodología empleada, los materiales analizados, los resultados obtenidos, su discusión y las referencias citadas. En el capítulo VII se recogen las conclusiones finales y el capítulo VIII contiene las publicaciones científicas que son fruto del trabajo desarrollado en la presente Tesis Doctoral. Finalmente, el capítulo IX está dedicado a las fuentes de financiación que han hecho posible dicho trabajo.
Las contribuciones más novedosas que aportará esta Tesis Doctoral se pueden resumir en los siguientes puntos: Evaluación de la función de fase de esparcimiento y del factor de anisotropía de esparcimiento, g, a partir de medidas experimentales (no a partir de modelos, simulaciones o aproximaciones teórico-empíricas) en resinas de composite y cerámicas de zirconia para aplicaciones dentales. Comprobación de la idoneidad del método experimental empleado para obtener los valores de g con una precisión tal que permita establecer comparaciones entre materiales y distinciones entre un mismo material en diferentes condiciones (distintos espesores de la muestra y distintas longitudes de onda). Esto se comprueba, incluso, para tejidos dentales humanos (esmalte y dentina).
Determinación de los coeficientes de absorción y esparcimiento (¿a y ¿s) de resinas de composite y cerámica de zirconia mediante el algoritmo IAD a través de la incorporación de valores experimentales del factor de anisotropía de esparcimiento, g, considerando los cambios espectrales de dicho factor y del índice de refracción. Corroboración de la idoneidad del método experimental empleado para obtener los valores de ¿¿a y ¿¿¿¿ con una precisión que permita analizar comparativamente distintos materiales.
Realización, en condiciones de repetividad, de medidas encaminadas a valorar el efecto de tejidos dentales humanos (esmalte y dentina) y resinas de composite sobre el estado de la luz polarizada, proporcionando la incertidumbre asociada a los ángulos de desviación del plano de polarización.
Evaluación de los principales parámetros de rugosidad (Ra, Rq, Rsk y Rku) en resinas de composite y cerámicas de zirconia, -proporcionando información, no sólo sobre la rugosidad media, sino también sobre la distribución superficial de alturas-, mediante el uso de un sistema microtopográfico no invasivo basado en triangulación óptica. Comprobación de la idoneidad de este sistema para obtener los principales parámetros de rugosidad con una precisión tal que permita establecer comparaciones entre materiales y distinciones entre un mismo material en diferentes condiciones (tratamiento superficial en composites y proceso de sinterización en cerámica de zirconia).
Aportación de una información tan relevante como es la incertidumbre asociada a todas y cada una de las magnitudes determinadas experimentalmente (factor de anisotropía, coeficientes de absorción, esparcimiento y atenuación, profundidad de penetración óptica, ángulo de desviación del plano de polarización, parámetros de rugosidad y porcentaje de brillo). Esto constituye una importante novedad pues se obvia de forma generalizada en los trabajos que estudian biomateriales y, concretamente, biomateriales destinados a aplicaciones dentales, de modo que no es posible conocer la precisión de los valores de las magnitudes facilitados, ni en qué medida las comparaciones establecidas se basan de diferencias significativas.
- English
CHARACTERIZATION OF DENTAL BIOMATERIALS BY MEANS OF OPTICAL METHODS KEYWORDS Optical properties and roughness of dental biomaterials INTRODUCTION Light propagation in biological media is characterized by the absorption coefficient, the scattering coefficient, the scattering phase function, the refractive index, and the surface conditions (roughness). The surface properties are intimately related with the optical properties in a material, since the way that light is reflected by the material depends not only on its composition but also on its microstructure.
In dentistry, aesthetic failure is one of the most widespread reasons for restoration replacement. Aesthetic restoration involves a visible match of the optical properties of restorative material and natural teeth. These optical properties are determined by light absorption and scattering by the medium¿s surface and interior. Some of the main appearance properties of restorative materials, such as the perceived color and translucency, are intimately related with light-scattering properties [1, 2]. More than 80% of patients are reportedly aware of color and appearance differences between the restoration and the adjacent natural teeth [3]. The rough surface of a treated tooth not only affects the appearance, for example superficial staining, but also increases penetration of bacteria and plaque retention. This results in a higher risk of cavities and gingival inflammation [4]. Therefore, maintaining the smooth surface of a restoration is of utmost importance for its success [5].
Among the methods based on solving the radiative transport theory, the Inverse Adding-Doubling (IAD) algorithm is an alternative for determining optical properties. The combination of the IAD algorithm with the Monte Carlo simulations [6-8], leads to a more precise determination of optical properties than the previously used Kubelka Munk theory [9-11]. This is because the IAD method enables a separate determination of absorption and scattering parts with high precision. This is not provided by the Kubelka Munk absorption and scattering coefficients (K and S), since S is made up of the radiative theory¿s absorption and scattering coefficients (¿¿a, ¿¿¿¿ and g). For this same reason, Kubelka Munk theory does not allow any separation between pure scattering and its direction.
In contrast, with the IAD method, scattering can be separated into pure scattering (with the scattering coefficient ¿s) and its direction (with the scattering anisotropy factor g). In addition, the use of Monte Carlo simulations minimizes systematic errors by taking into account the measuring geometry, radiation losses at border lines, and the wavelength dependent refractive index. Moreover, with the knowledge of the ¿¿a, ¿¿¿¿ and g, color can be evaluated from simulated reflectance values without additional measurements [12-14]. The IAD method along with inverse Monte Carlo simulations has been broadly used to study biological and turbid media [15-20]. As a result, its suitability for dental biomaterials is expected.
Optical methods have the most important role for non-invasive inspection of surfaces. The increasing range of surface types, measurement limitations and tolerance requirements has demanded a major research effort in the development of different methods, systems and metrological techniques. The profilometric inspection seems to be insufficient in many instances. Among the optical methods, triangulation-based ones have gained a major status thanks to their flexibility, reliability and robustness. Optical triangulation has for a long time proved to be an invaluable tool for microtopographic evaluation of surfaces in the industrial and scientific fields [21]. Successful applications in life sciences have also been performed [22, 23]. Particularly, triangulation-based microtopographic inspection of treated tooth surfaces has proved to provide valuable insights in order to evaluate the quality of dental enamel stripping (a technique widely used in dentistry).
Gathering of optical and roughness parameters may assist the development of potential applications useful for clinical practice, such as laser-based techniques and treatments. Furthermore, this data may allow the advance of other calculation models as a basis for the optimization of new biomaterial composition. For example, in the future, the determination of optical and roughness parameters could be used along with the development of new dental biomaterials. This would allow comparisons between experimental compositions and available materials of known properties, thus revealing the most suitable material compositions.
Currently, dental-resin composites are among the most common and widely used materials for replacing enamel. Dental nano-filled resin composites have recently been introduced [24]. Nanotechnology applied to dental composites has provided filler particles that are dramatically smaller, can be dispersed in high concentrations and are polymerized into the resin system with molecules designed to be compatible when coupled with a polymer. Since this molecular manufacturing provides other unique characteristics, optical properties of nanocomposites could differ when compared with those of conventional composites (hybrids and micro-hybrids).
With the intention of avoiding the infrastructure of metallic prostheses, structural ceramics have been improved and progressively more employed in restorative dentistry. One ceramic material currently used to replace dentine in an irreversibly diseased tooth is yttrium cation-doped tetragonal zirconia polycrystal (3Y-TZP). The microstructure of 3Y-TZP ceramics for dental applications consists of small equiaxed grains with diameter sizes depending on the sintering temperature [25]. The sintered ceramic for dental applications is fabricated using computer-aided design and manufacturing (CAD/CAM) procedures from pre-sintered zirconia ceramic. This ceramic material arose as a versatile and promising biomaterial because of its good mechanical and biological properties [26, 27]. However, its roughness and optical characterizations have not been completely developed.
The fulfillment of optimal quality and final success in biomedical application of dental-resin composites and zirconia ceramics calls for thorough studies to assess the appropriate material properties.
MOTIVATION AND OBJECTIVES Currently, obtaining biomaterials capable of replacing tissue is an issue that arouse widespread interest in society and on which an important part of the international scientific community is concentrating its efforts. The implementation of treatments that use new generation biomaterials happens, no doubt, by the prior accomplishment of studies to analyze the behavior and the actual characteristics of these materials. The results of such studies will condition, to a large extent, the success of future applications to be carried out in the biomedical field. Before they can be developed to their full potential, it is essential to know in detail how the materials already being generated are and how they behave.
In order to deepen the knowledge of new biomaterials it is vital to study their optical properties, even if the main function of the restored tissue is not visual. For example, comprehension of laser radiation propagation in these materials is crucial to establish the effects of many current treatments, which are based on tissue irradiation with laser sources. The latest harmless diagnostic techniques also have their foundation in the optical response of biological media. In fact, for the future development of therapeutic and diagnostic applications, it is imperative to know the relationships between optical and biological properties of tissues and, thus, of biomaterials.
Therefore, the present Thesis pursues the next goals: Main objective: To apply optical methods to characterize biomaterials used in dentistry for substitution of dental tissues (dentine and enamel), such as zirconia ceramic and dental-resin composites.
Specific objectives: 1.-Perform measurements for precise determination of the scattering anisotropy values of dental biomaterials. Comparatively analyze the behavior showed by the scattering anisotropy in these biomaterials and in the tissues that they are meant to replace.
2.-Apply the IAD algorithm to achieve precise values of the absorption and scattering coefficients of the dental biomaterials, using the scattering anisotropy factor values previously obtained.
3.-Perform measurements to evaluate the effect of dental biomaterials on the polarized light state.
4.-Complete a microtopographic non-invasive inspection to evaluate with precision the main roughness parameters of the biomaterials by means of an optical triangulation system. Complement the information about roughness with specular gloss measurements.
The subsequent contents of this PhD thesis are structured as follows: Each chapter between III and VI corresponds to one of the specific objectives pursued. Each of these chapters includes the state of the art, the methodology, the materials analyzed, the results obtained, their discussion and the references quoted. In chapter VII the final conclusions are gathered and chapter VIII contains the publications due to the work developed in the present Thesis. Finally, chapter IX is dedicated to the funding sources that have made this work possible.
The following table shows the relationship between the specific objectives, the chapters of this Thesis and the scientific publications included in the database Web of Science produced by the Institute for Scientific Information (ISI).
Table 1. Relationship between specific objectives, chapters and publications included in the database Web of Science, of the Institute for Scientific Information (ISI).
Specific objective/ Chapter/ Publications in Web of Science (ISI).
1.- Perform measurements for precise determination of the scattering anisotropy values in dental biomaterials. Comparatively analyze the behavior showed by the scattering anisotropy in these biomaterials and in the tissues that they are meant to replace./ III/ Fernández-Oliveras, A., Rubiño M. and Pérez M. M., ¿Scattering anisotropy measurements in dental tissues and biomaterials¿. J. Eur. Opt. Soc.-Rapid Publ. 7, 12016-1-12016-8 (2012). Fernández-Oliveras, A., Pecho, O. E., Rubiño, M. and Pérez, M. M., ¿Measurements of scattering anisotropy in dental tissue and zirconia ceramic¿. Proc. SPIE 8427, 84272C-1-6 (2012).
Fernández-Oliveras, A., Carrasco, I. M., Ghinea, R., Pérez, M. M. and Rubiño, M., ¿Comparison between experimental and computational methods for scattering anisotropy coefficient determination in dental-resin composites¿. Proc. SPIE 8427, 84272B-1-7 (2012).
2.- Apply the IAD algorithm to achieve precise values of the absorption and scattering coefficients of the dental biomaterials including the scattering anisotropy factor values previously obtained./ IV/ Fernández-Oliveras, A., Rubiño M. and Pérez M. M., ¿Scattering and absorption properties of biomaterials for dental restorative applications¿. Submitted (2013). Fernández-Oliveras, A., Rubiño M. and Pérez M. M., ¿Determination of optical properties in dental restorative biomaterials using the inverse-adding-doubling method¿. Proc. SPIE, In press (2013).
3.- Accomplish measurements for evaluating the effect of dental biomaterials on the polarized light state./ V/ Fernández-Oliveras, A., Pecho, O. E., Rubiño, M. and Pérez, M. M., ¿Measurements of optical polarization properties in dental tissues and biomaterials¿. Proc. SPIE 8001, 80012Y-1-7 (2011).
4.- Complete a microtopographic non-invasive inspection to evaluate with precision the main roughness parameters of the biomaterials by means of an optical triangulation system. Complement the information about roughness with the results of specular gloss measurements./ VI/ Fernández-Oliveras, A., Costa, M. F. M., Pecho, O. E., Rubiño, M. and Pérez, ¿Rugometric and microtopographic non-invasive inspection in dental-resin composites and zirconia ceramics¿. Proc. SPIE, In press (2013). Fernández-Oliveras, A., Costa, M. F. M., Yebra, A., Rubiño, M. and Pérez, M. M., ¿Gloss measurements and rugometric inspection in dental biomaterials¿. Proc. SPIE, In press (2013).
Chapter III. SCATTERING ANISOTROPY EXPERIMENTAL ANALYSIS AND COMPARISON WITH DENTAL TISSUES Understanding the behaviour of light propagation in biological materials is essential for biomedical engineering and applications, and even more so when dealing with incoming biomaterials. Many methods for determining optical parameters from biological media assume that scattered light is isotropically distributed over all angles. However, an angular dependence of light scattering may exist and affect the optical behaviour of biological media. The present work seeks to experimentally analyze the scattering anisotropy in different dental tissues (enamel and dentine) and their potential substitute biomaterials (hybrid dental-resin, nano-filled composite, and zirconia ceramic) and comparatively study them. Goniometric measurements were made for four wavelengths in the visible range, allowing a spectral characterization of the materials studied. Previously, for each material, measurements were made with two different sample thicknesses at the same wavelength, checking the behaviour of the angular scattering profile. The asymmetry of experimental phase functions was considered in the recovery of the scattering anisotropy factor. The results demonstrate that the thicker sample yielded a less forward-directed scattering profile than did the thinner sample. The biomaterials analysed show angular scattering comparable to those of the tissues that they may replace. Comparisons can be made by virtue of the low uncertainties found.
Chapter IV. DETERMINATION OF SCATTERING AND ABSORPTION PROPERTIES USING THE INVERSE-ADDING-DOUBLING METHOD The physical understanding of the optical properties of dental biomaterials is mandatory for their final success in restorative applications. Light propagation in biological media is characterized by the absorption coefficient, the scattering coefficient, the scattering phase function, the refractive index, and the surface conditions (roughness). We have employed the IAD method to combine transmittance and reflectance measurements performed using an integrating-sphere setup with the results of the previous scattering-anisotropy goniometric measurements. This has led to the determination of the absorption and the scattering coefficients. The aim was to optically characterize two different dental-resin composites (nanocomposite and hybrid) and one type of zirconia ceramic, and comparatively study them. The experimental procedure was conducted under repeatability conditions of measurement in order to determine the uncertainty associated to the optical properties of the biomaterials. Spectral variations of the refraction index and the scattering anisotropy factor were also considered. The whole experimental procedure fulfilled all the necessary requirements to provide optical-property values with lower associated uncertainties. The effective transport coefficient presented a similar spectral behavior for the two composites but completely different for the zirconia ceramic. The results demonstrated that the scattering anisotropy exerted a clearly distinct impact on the optical properties of the zirconia ceramic compared with those of the dental-resin composites.
Chapter V. MEASUREMENTS OF OPTICAL POLARIZATION PROPERTIES: EFFECT ON POLARIZED LIGHT STATE Since biological tissues can have the intrinsic property of altering the polarization of incident light, optical polarization studies are important for a complete characterization. We have measured the polarized light scattered off of different dental tissues and biomaterials for a comparative study of their optical polarization property. The experimental setup was composed by a He-Ne laser, two linear polarizers and a detection system based on a photodiode. The laser beam was passed through one linear polarizer placed in front of the sample, beyond which the second linear polarizer (analyzer) and the photodiode detector were placed. First, the maximum laser-light intensity (reference condition) was attained without the sample in the laser path. Then, the sample was placed between the two polarizers and the polarization shift of the scattered laser light was determined by rotating the analyzer until the reference condition was reached. Two dental-resin composites (nanocomposite and hybrid) and two human dental tissues (enamel and dentine) were analyzed under repeatability conditions at three different locations on the sample: 20 measurements of the shift were taken and the average value and the uncertainty associated were calculated. For the human dentine the average value of the polarization shift found was 7 degrees, with an associated uncertainty of 2 degrees. For the human enamel and both dental-resin composites the average shift values were found to be similar to their corresponding uncertainties (2 degrees). The results suggest that although human dentine has notable polarization properties, dental-resin composites and human enamel do not show significant polarization shifts.
Chapter VI. RUGOMETRIC INSPECTION FOR DETERMINATION OF ROUGHNESS PARAMETERS AND MEASUREMENTS OF SPECULAR GLOSS In dental applications, optimizing appearance is desirable and increasingly demanded by patients. The specular gloss is among the major appearance properties of dental biomaterials, and its relationship with surface roughness has been reported. Roughness and gloss are key surface aspects that complement each other. We have experimentally analyzed the specular gloss and surface roughness of two different types of dental-resin composites and pre-sintered and sintered zirconia ceramics. We have studied two shades of both composite types and two sintered zirconia ceramics: colored and uncolored. Moreover, a surface treatment was applied to one specimen of each dental resin. Gloss measurements were performed with a standardized reflectometer and the corresponding gloss percentages were calculated. All the samples were submitted to rugometric non-invasive inspection with the MICROTOP.06.MFC laser microtopographer in order to determine meaningful statistical parameters such as the average roughness (Ra), the root-mean-square deviation (Rq), the skewness (Rsk), and the kurtosis of the surface height distribution (Rku). For a comparison of the different biomaterials, the uncertainties associated to the measure of the surface gloss and roughness were also determined. The differences between the two shades of both kinds of composites proved significant in the case of the roughness parameters but not for the specular gloss. Among the dental resins, the nanocomposite presented the highest values and, for the zirconia ceramics, the pre-sintered sample registered the lowest ones. The composite performance may have been due to cluster-formation variations. Except for the composites with the surface treatment, the sample surfaces had approximately a normal distribution of heights. The surface treatment applied to the composites increased the average roughness and moved the height distribution farther away from the normal distribution, but the changes in the specular gloss were significant only for the A2 enamel nano-composite. The surface treatment applied to the dental-resin composites increased the average roughness. For the zirconia ceramic the sintered process resulted in an increase in the surface roughness -without affecting the height distribution- and a decrease of the specular gloss, corroborating that the relationship between the gloss and the roughness shows the expected behavior.
CONCLUSIONS 1.- Angular-scattering measurements were made for a spectral characterization of the dental tissues and biomaterials in the visible range. Previously, measurements had been made with different sample thicknesses, checking the behaviour of the angular-scattering profile. g values had similar spectral variations, except for the human dentine. The thicker samples yielded a less forward-directed scattering profile than did the thinner samples.
The uncertainty corresponding to g values fell within the range of 0.00011 and 0.005. Zirconia g values were considerably closer to the isotropy (g = 0) than the composites¿ g values, which were strongly forward-directed (near to 1). The angular scattering profiles indicated the presence of a more pronounced forward-directed scattering in the nano-filled dental-resin than in the hybrid dental-resin composite. For the zirconia ceramic, the outcome of sintering displayed an optical behaviour more similar to that of dentine tissue, in terms of scattering anisotropy.
The dental-resin composites and the human enamel showed a similar angular scattering behaviour. On the other hand, the zirconia ceramic presented a scattering angular behaviour more similar to that of the human dentine. This is valuable for biomedical applications, since it means that, in terms of angular scattering behaviour, the biomaterials are comparable to the tissues that they are meant to replace.
2.- The IAD method was used to combine the results of the goniometric measurements with transmittance and reflectance measurements performed using a laser-integrating-sphere-based setup. The experimental procedure was conducted under repeatability conditions of measurement and fulfilled all the necessary requirements to provide optical-property values with lower uncertainties. Therefore, this procedure is advisable for the comparative analysis of different materials.
The results agreed with the application of the diffusion theory, since the reduced scattering coefficient had values much higher than the absorption coefficient. The scattering anisotropy had clearly distinct impacts on the optical properties of zirconia ceramic and dental-resin composites. The absorption coefficient had similar spectral variation for both dental-resin composites, but thoroughly different for the zirconia ceramic. In the case of the scattering coefficient, the spectral values appeared to follow more parallel trends for the three biomaterials, with higher values for the nanocomposite. The effective transport coefficient of the zirconia ceramic presented not only higher values but also a different spectral behavior compared with the composites. The effective mean free path seemed to show somewhat dissimilar spectral trends for each dental biomaterial, with a marked increment at 632.8 nm in the case of the hybrid composite.
3.- Dental-resin composites and human enamel did not show significant polarization shifts. However, optical polarization properties of human dentine were found to be different. Nevertheless, differences between nanocomposite and hybrid dental-resin composite did not proved to be significant in terms of their optical polarization behavior.
4.- Dental-resin composites and pre-sintered and sintered zirconia ceramics were submitted to rugometric non-invasive inspection performed with the MICROTOP.06.MFC laser microtopographer. Gloss measurements were conducted using a glossmeter device. The experimental procedure was conducted under repeatability conditions of measurement in order to determine the uncertainty related to gloss and roughness parameters.
The surface treatment applied to the dental-resin composites not only increased the average roughness but also changes the symmetry and shape of the surface-height distribution, moving it farther away from the normal distribution. However, the changed in the specular gloss due to the surface treatment were significant only for the A2 enamel nano-composite. The sintering process of the zirconia ceramics appeared to increase the average roughness and reduce the specular gloss, without notably affecting the symmetry or shape of the surface-height distribution.
The differences between the two shades of both kinds of composites were significant in the case of the roughness parameters but not for the specular gloss. In comparisons of both composite types with similar shades, the gloss percentage proved to be similar or slightly lower in the case of the nanocomposite. In addition, the roughness parameters Ra and Rq presented higher values for this dental-resin composite.
The experimental methods used for determining the optical properties and the surface roughness parameters were shown to be suitable for comparison between materials by virtue of the low uncertainties found.
