Influence of printing orientation on mechanical properties of aged 3D-printed restorative resins.

OBJECTIVE: To evaluate the influence of printing orientation on flexural strength (σf) and elastic modulus (E) of different 3D printing dental restorative resins. METHODS: Bar-shaped specimens (n = 20) were fabricated from two SLA-printed resins (FT- Formlabs Temporary, and FP- Formlabs Permanent) and two DLP-printed resins (DFT- Detax Freeprint Temp, and GCT- GC Temporary) using two building orientations (0º and 90º). The 3D-printed structures were aged (14 d) before submitted to three-point bending in 37ºC distilled water at a crosshead speed of 1.0 ± 0.3 mm/min until fracture to calculate the σf and the E values. The fractured surfaces were evaluated using stereomicroscopy and scanning electron microscopy (SEM) following fractography principles. Data were statistically analyzed using two-way ANOVA and Tukey post-hoc (α = 0.001). RESULTS: FP and FT showed significantly higher E values than DFT and GCT, irrespectively of printing orientation (p < 0.001). There was no statistical difference between the building orientations (0º and 90º) for the mean σf and E values for the resin materials evaluated. Fractographic characteristics were similar for the surface fracture from all the materials evaluated, showing typical brittle fracture behavior. SIGNIFICANCE: Printing orientation did not influence of flexural strength and elastic modulus values for the 3D-printed resin structures evaluated. Surface topography was mostly governed by the 3D printer type.

Optical behavior of 3D-printed dental restorative resins: Influence of thickness and printing angle.

OBJECTIVES: To evaluate the influence of thickness and printing angle on the optical properties of 3D-printed dental restorative resins. METHODS: Four 3D printing resin systems were evaluated: DFT-Detax Freeprint Temp; FP- Formlabs Permanent Crown; FP- Formlabs Temporary CB; and GCT- GC Temporary-. Samples from each material were printed at 0° and 90°, and polished up to 0.5, 1.0, 1.5 and 2.0 mm thickness. Scattering (S), absorption (K) and albedo (a) coefficients, transmittance (T%), light reflectivity (RI) and infinite optical thickness (X∞) were calculated using Kubelka-Munk's model. Data were statistically analyzed using Kruskal-Wallis¸ Mann-Whitney tests, and VAF coefficient. RESULTS: The spectral distribution on S, K, T%, RI,X∞ were wavelength dependent. Although the spectral behaviors were similar for all the specimens evaluated, the values of S, K, T% andX∞ presented significant differences between specimen thicknesses for all the materials used and for both printing orientations. Values for S and K increased, and T% and X∞ decreased. Significant differences between 0° and 90° were found for RI values at 0.5 and 1.0 mm thick samples, for S and K at 2.0 mm, for X∞ at 0.5 and 1.0 mm for DFT, and at 0.5 mm for FT. CONCLUSIONS: Optical properties of 3D-printed restorative resins vary between thicknesses, and could be affected by the building orientation. Therefore, these factors should be considered in order to improve the biomimetic potential of 3D-printed dental restorative resins. CLINICAL SIGNIFICANCE: Understanding the optical behavior of the 3D-printed restorative resins is essential to optimize their clinical performance.

The influence of printing angle on color and translucency of 3D printed resins for dental restorations.

OBJECTIVES: To evaluate the influence of printing orientation on color and translucency of 3D printing restorative resins. METHODS: Four 3D printing resin systems in the available shades (DFT-Detax Freeprint Temp- A1, A2,A3; FP-Formlabs Permanent Crown- A2,A3,B1,C2; FT- Formlabs Temporary CB- A2,A3,B1,C2; GCT-GC Temporary- Light, Medium) were evaluated. Three samples (10×10×1.2 mm) from each material were printed at two different printing orientations (0° and 90°) and polished to 1.00 ± 0,01 mm of thickness. Spectral reflectance was measured against black background using a calibrated spectroradiometer, CIE D65 standard illuminant and the 45°/0°geometry. Color and translucency differences were evaluated using CIEDE2000 metric (ΔE00) and 50:50% perceptibility (PT00 and TPT00) and acceptability (AT00 and TAT00) thresholds. RESULTS: In general, color changes due to printing orientation at (0° and 90°) were mainly produced by ΔL* or ΔC* . ΔE00 were above PT00 for all DFT shades, FP-B1, FP-C2, FT-A2 and FT-B1. Only for DFT-1, ΔE00 was above AT00. ΔRTP00 values were above TPT00 for DFT-A1, DFT-A3, FP-B1 and FT-B1, but lower than TAT00. The direction of the changes in translucency (ΔRTP00) depends on the material and shade. SIGNIFICANCE: The selection of building orientation (0° and 90°) for the 3D printed resins influence the visual color and translucency and therefore their esthetic appearance. These aspects should be considered when printing dental restorations using the evaluated materials.

Effect of thickness on color and translucency of a multi-color polymer-infiltrated ceramic-network material.

OBJECTIVES: To evaluate the effect of thickness on color and translucency of a multi-color polymer-infiltrated ceramic-network (PICN) material. METHODS: Specimens of 0.5, 1.0, 1.5 mm thicknesses were obtained by sectioning VITA ENAMIC® multiColor (E-MC) High Translucent CAD-CAM blocks (1M1-HT, 1M2-HT, 2M2-HT, 3M2-HT, and 4M2-HT). Spectral reflectance and color coordinates were measured on white and black backgrounds using a spectroradiometer, CIE D65 illuminant and CIE 45°/0° geometry. CIEDE2000 color and translucency differences (ΔE00 and ΔTP00 ) between thicknesses and adjacent layers were evaluated using their respective 50:50% perceptibility and acceptability thresholds (PT00 and AT00 ). RESULTS: In general, ΔE00 between thicknesses for all shades and layers were above AT00 in general. Chroma decreased from cervical to incisal layers with statistically significant differences (p < 0.05), and ΔE00 between sequential layers were above PT00 , for all shades and thicknesses. TP00 decreased from 0.5 to 1.5 mm and increased from cervical to incisal layers for all shades with statically significant translucency differences (p < 0.05). In general, for all thicknesses, TPT00 < ΔTP00 < TAT00 for sequential layers. CONCLUSIONS: The gradient in color and translucency of E-MC PICN material was influenced by the thickness of the CAD-CAM block. In addition, color and TP transition values between the layers depends on the thickness and shade. CLINICAL SIGNIFICANCE: The effect of thickness must be taken into account by dental technicians and dentists when CAD-CAM multicolor PICN materials are used.

Relevant optical properties for gingiva-colored resin-based composites.

OBJECTIVES: To evaluate the optical properties of gingiva-colored resin-based composites (GCRBCs). METHODS: Five discs (8 mm diameter x 1mm height) of 17 shades of GCRBCs were prepared. Diffuse reflectance was measured against white and black backgrounds using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Relative translucency parameter was calculated using ΔE00 (RTP00). Translucency differences were evaluated using published data of 50:50% translucency perceptibility (TPT00) and acceptability (TAT00) thresholds. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka-Munk's equations. Data were statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. RESULTS: The RTP00 values of the 17 evaluated shades ranged from 8.69 to 21.34. There were perceptible translucency differences (TPT00=0.62) between different shades of the same brand and between composites designated with the same shade of different brands. Spectral distributions of S, K and T were wavelength-dependent. Although the spectral behavior of the S and K coefficients and T% were similar for all the gingival composites evaluated, the values of these parameters presented statistically significant differences between shades, which would justify the differences found in the relative translucency parameter. CONCLUSIONS: The optical properties S, K and T% of GCRBCs were significantly different, resulting in perceptible translucency differences between the same shade of different commercial brands and between different shades of the same brand. CLINICAL SIGNIFICANCE: Translucency differences of gingiva-colored composites may significantly influence their masking ability affecting the clinician's choice of restorative material.

Visual and instrumental coverage error of two dental shade guides: an in vivo study.

OBJECTIVES: This study aims to evaluate in vivo the color agreement between natural teeth and dental shade guides by means of visual and instrumental coverage error ([Formula: see text]) index. MATERIALS AND METHODS: The color of the middle third of 735 incisors was visually determined by two evaluators using the Vita Classical (VC) and Vita 3D Master (V3DM) shade guides. The color match between the natural tooth and the shade tab was rated as poor (P), good (G), or optimum (O) by each observer. CIE color coordinates of the target teeth and shade tabs of VC and V3DM were instrumentally measured using a clinical spectrophotometer. Visual ([Formula: see text]) and instrumental ([Formula: see text]) coverage error indexes were computed using CIELAB and CIEDE2000 metrics for both shade guides. For [Formula: see text] calculation, only the concordant inter-observer determination on tooth shade rated as O-O or O-G was used. The results were evaluated using perceptibility (PT, [Formula: see text]= 1.2, [Formula: see text]= 0.8) and acceptability (AT, [Formula: see text]= 2.7, [Formula: see text]= 1.8) color thresholds for dentistry. RESULTS: VC and V3DM exhibited [Formula: see text] (2.5, 3.2, and 3.2, 2.7 CIELAB units; 1.9, 2.3, and 2.8, 2.4 CIEDE2000 units, respectively, for O-O and O-G match) and [Formula: see text] (4.7, 4.8, and 4.1, 4.6 CIELAB units; 3.3, 3.4, and 3.4, 3.6 CIEDE2000 units, respectively, for O-O and O-G match) values greater than 50:50% AT for both color difference formulas. [Formula: see text] contributes more than 50% (53.2-82.4% range) to the [Formula: see text] value. This contribution depends on the shade guide used and the quality of the visual rating. CONCLUSIONS: The evaluated shade guides exhibited visual coverage errors above acceptability thresholds, largely due to the contribution of the instrumental coverage error to the visual coverage error. CLINICAL RELEVANCE: It necessary to further improve commercially available dental shade guides to facilitate achievement of satisfactory esthetics results in clinical practice.

Color and optical properties of 3D printing restorative polymer-based materials: A scoping review.

OBJECTIVE: Color and optical properties are particularly crucial to mimic natural tooth. This scoping review aimed to present an overview of the literature published on color and optical properties of 3D printing restorative polymer-based materials. The literature search was performed in MED-LINE/Pubmed, Scopus and Web of Science. MATERIALS AND METHODS: The literature search was conducted in the three databases based on the question: "Are the optical properties and color adequately reported on polymer-based 3D printing dental restorative materials studies?" with no restriction on year of publication. Data were reported and synthesized following PRISMA-ScR statement. RESULTS: Nine studies fit the inclusion criteria. Five studies focused on evaluating only color stability; three articles assessed the color stability along with mechanical and morphological properties and only one study compared color parameters of 3D printed to conventional polymers. Two studies evaluated translucency parameter and no study was found evaluating scattering, absorption, and transmittance. CONCLUSIONS: Color and optical properties of 3D printed polymers that can be used in restorative dentistry are not adequately evaluated and characterized. Future studies on the influence of experimental printing conditions should include these physical properties to assist on improving esthetics. CLINICAL SIGNIFICANCE: This review shows the scarce literature existing on color and optical properties of 3D printing restorative polymer-based materials. These properties and their study are of outmost importance to create materials that mimic natural tooth to allow clinicians to obtain esthetically pleasant restorations.

Applications of artificial intelligence in dentistry: A comprehensive review.

OBJECTIVE: To perform a comprehensive review of the use of artificial intelligence (AI) and machine learning (ML) in dentistry, providing the community with a broad insight on the different advances that these technologies and tools have produced, paying special attention to the area of esthetic dentistry and color research. MATERIALS AND METHODS: The comprehensive review was conducted in MEDLINE/PubMed, Web of Science, and Scopus databases, for papers published in English language in the last 20 years. RESULTS: Out of 3871 eligible papers, 120 were included for final appraisal. Study methodologies included deep learning (DL; n = 76), fuzzy logic (FL; n = 12), and other ML techniques (n = 32), which were mainly applied to disease identification, image segmentation, image correction, and biomimetic color analysis and modeling. CONCLUSIONS: The insight provided by the present work has reported outstanding results in the design of high-performance decision support systems for the aforementioned areas. The future of digital dentistry goes through the design of integrated approaches providing personalized treatments to patients. In addition, esthetic dentistry can benefit from those advances by developing models allowing a complete characterization of tooth color, enhancing the accuracy of dental restorations. CLINICAL SIGNIFICANCE: The use of AI and ML has an increasing impact on the dental profession and is complementing the development of digital technologies and tools, with a wide application in treatment planning and esthetic dentistry procedures.

Optical behavior of one-shaded resin-based composites.

OBJECTIVE: To evaluate optical properties, and translucency and opalescence parameters of one-shaded resin-based composites. METHODS: Three one-shaded resin composites (OM - Omnichroma; VP - Venus Pearl; and VD - Venus Diamond) and a group-shaded resin composite (FU- Filtek Universal A2) were used. Three composite discs from each material were fabricated for each of the following thickness: 0.5, 1.0 and 2.0 mm. Diffuse reflectance was measured against white and black backgrounds using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Translucency parameter (TP) was calculated using ΔEab * and ΔE00. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka-Munk's equations, and a reflection spectrophotometer was used to measure the opalescence parameter (OP). Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. RESULTS: Spectral distributions of S, K and T were wavelength dependent, showing significant differences between materials of the same thickness and for different thicknesses of the same material (p < 0.001). OM showed the greatest translucency values for all thicknesses. Translucency decreased as thickness increased with statistically significant differences (p < 0.005). Values of ΔTPab and ΔTP00 between thicknesses were above of translucency thresholds for all materials. VP and VD showed the lowest OP values. SIGNIFICANCE: One-shaded resin-based composites showed different optical behavior than the group-shaded resin-based composite. Understanding the optical behavior of the one-shaded resin-based composites is essential to optimize their clinical performance.

Impact of short-term dental dehydration on in-vivo dental color and whiteness.

OBJECTIVE: To determine in-vivo chromatic and whiteness changes produced by short-term dental dehydration. METHODS: Spectral reflectance of 452 upper incisors (226 centrals and 226 laterals) of 113 participants were measured using a spectroradiometer at baseline and after short-term dehydration (minutes 2, 4, 6, 8 and 10). CIE L*a*b* color coordinates (L*, a*, b*, C*ab and hab) and whiteness index for dentistry (WID) were calculated. Color differences (ΔE00, ΔEab*) and whiteness differences (ΔWID) were computed and interpreted based on their respective 50:50% perceptibility (PT) and acceptability thresholds (AT). Statistical analysis was performed using the related samples Wilcoxon signed-rank test. RESULTS: L* showed an increasing trend with dehydration, while a*, b*, C*ab and hab have a decreasing tendency. All chromatic coordinates showed statistically significant differences (p < 0.003) at each interval of dehydration compared with baseline, except a* for all teeth. For ΔE00 and ΔEab* values were higher than PT after 2 min of teeth dehydration and higher than AT after 6 and 8 min, respectively. The percentage of teeth exceeding corresponding PT was higher than 50% after 2 min. WID index increased with dehydration time, while whiteness differences were clinically perceptible after 4 min. Statistically significant differences were found for WID between all dehydration intervals (except 8-10 min). The percentage of teeth exceeding whiteness PT was higher than 50% after 6 min of teeth dehydration. CONCLUSIONS: Short-term dental dehydration produces clinically unacceptable changes in tooth color and clinically perceptible increase in tooth whiteness level. CLINICAL SIGNIFICANCE: Clinical shade matching must be done within the first two minutes of any clinical procedure that requires precise chromatic determination but implies a risk of tooth dehydration.

Optical and colorimetric evaluation of a multi-color polymer-infiltrated ceramic-network material.

OBJECTIVE: To evaluate color, translucency parameter and optical properties (scattering (S), absorption (K) and transmittance (T)) of a multi-color polymer-infiltrated ceramic-network (PICN) material. METHODS: Samples of shades 1M1-HT, 1M2-HT, 2M2-HT, 3M2-HT, and 4M2-HT from VITA ENAMIC® multiColor (E-MC) High Translucent were fabricated (n = 3). CAD-CAM blocks were cut and polished to 1.00 ± 0.01 mm of thickness. Diffuse reflectance and color coordinates were measured against white and black backgrounds, using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Color and translucency differences were evaluated using 50:50% perceptibility (PT and TPT) and 50:50% acceptability (AT and TAT) thresholds. 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. RESULT: Mean C* and b* values increased from incisal to cervical layers with statistically significant differences (p < 0.05). In general, ΔE00 between sequential layers were above PT for all shades. In addition, translucency parameter (TP) increased from cervical to incisal and ΔTP00 values were greater than TPT00 and lower than TAT00 between all sequential layers. Layers from all shades showed similar spectral behavior for S (97.4% ≤ VAF), K (85.0% ≤ VAF) coefficients and T (95.3% ≤ VAF). However, these values presented significant differences (p < 0.05) from cervical to incisal layers. SIGNIFICANCE: The gradient in color and translucency of this novel CAD-CAM multi-color PICN material can assist dental technicians and dentists to reach greater esthetics than the pre-existing CAD-CAM monolithicmaterials.

Statistical errors in microleakage studies in operative dentistry. A survey of the literature 2001-2009.

The aim of this study was to assess the literature on microleakage of direct restorations in operative dentistry indexed in the ISI Web of Science, in order to assess the robustness of the statistical methodology used. Our database included 226 scientific papers (published between 2001 and 2009 in 22 journals) from the journal citation report categories 'Dentistry, Oral Surgery and Medicine' and 'Materials Science, Biomaterials'. We reviewed all articles to find potential mistakes that are commonly made at different stages in the scientific research process. Microleakage was assessed quantitatively in 50 (22.2%) studies and qualitatively in 176 (77.8%) studies. In all studies reviewed the statistical methods used were appropriate for the category attributed to the outcome variable, but in 13% of the total, the chi-square test or parametric methods were inappropriately used afterwards. When the appropriate statistical methods were applied in studies that had originally employed inappropriate methods to analyse their data, and in which the authors provided raw data, an alteration of the conclusions was necessary in 15.4% of these re-analysed studies. This survey also showed that the statistical methodology applied varies considerably for similar experimental designs. This could have an effect on statistical results; hence, a more standardized methodology should be implemented.

Dental ceramics: a CIEDE2000 acceptability thresholds for lightness, chroma and hue differences.

OBJECTIVES: To determine the visual 50:50% acceptability thresholds for lightness, chroma and hue for dental ceramics using CIEDE2000(K(L):K(C):K(H)) formula, and to evaluate the formula performance using different parametric factors. METHODS: A 30-observer panel evaluated three subsets of ceramic samples: lightness subset (|ΔL'/ΔE(00)| ≥ 0.9), chroma subset (|ΔC'/ΔE(00)| ≥ 0.9) and hue subset (|ΔH'/ΔE(00)| ≥ 0.9). A Takagi-Sugeno-Kang Fuzzy Approximation was used as fitting procedure, and the 50:50% acceptability thresholds were calculated. A t-test was used in statistical analysis of the thresholds values. The performance of the CIEDE2000(1:1:1) and CIEDE2000(2:1:1) colour difference formulas against visual results was tested using PF/3 performance factor. RESULTS: The 50:50% CIEDE2000 acceptability thresholds were ΔL' = 2.92 (95% CI 1.22-4.96; r(2) = 0.76), ΔC' = 2.52 (95% CI 1.31-4.19; r(2) = 0.71) and ΔH' = 1.90 (95% CI 1.63-2.15; r(2) = 0.88). The 50:50% acceptability threshold for colour difference (ΔE') for CIEDE2000(1:1:1) was 1.87, whilst corresponding value for CIEDE2000(2:1:1) was 1.78. The PF/3 values were 139.86 for CIEDE2000(1:1:1), and 132.31 for CIEDE2000(2:1:1). CONCLUSIONS: There was a statistically significant difference amongst CIEDE2000 50:50% acceptability thresholds for lightness, chroma and hue differences for dental ceramics. The CIEDE2000(2:1:1) formula performed better than CIEDE2000(1:1:1).

Color and translucency in silorane-based resin composite compared to universal and nanofilled composites.

OBJECTIVES: The purpose of this study was to determine the optical properties, color and translucency, of the new silorane-based resin composite and to compare it to universal dimethacrylate-based composites. METHODS: Six dimethacrylate-based resin composites and one silorane-based resin composite (all A2 shade) were studied. Color of non-polymerized and polymerized composites was measured against white and black backgrounds using a spectroradiometer. Changes in color (ΔE*(ab)), translucency (ΔTP) and color coordinates (ΔL*, Δa* and Δb*) were calculated for each resin composite. Results were evaluated using a one-way ANOVA, a Tukey's test and a t-test. RESULTS: The polymerization-dependent ΔE*(ab) ranged from 4.7 to 9.1, with the smallest difference for the silorane-based resin composite. The color changes of silorane-based composite were due to the changes of coordinates Δa* and Δb*. However, for the dimethacrylate-based composites, the color changes mainly originated by ΔL*and Δb*. The silorane composite exhibited the smallest TP values. Tukey's test confirmed significant statistical differences (p<0.05) between mean TP values of Filtek Silorane and each brand of dimethacrylate-based composites before and after polymerization. CONCLUSIONS: The new silorane-based restorative system showed different optical properties compared to clinically successful dimethacrylate composites. The silorane composite exhibited better polymerization-dependent chromatic stability, and a lower translucency compared to other tested products.

Prediction of color change after tooth bleaching using fuzzy logic for Vita Classical shades identification.

Tooth bleaching is becoming increasingly popular among patients and dentists since it is a relatively noninvasive approach for whitening and lightening teeth. Instruments and visual assessment with respect to commercial shade guides are currently used to evaluate tooth color. However, the association between these procedures is imprecise and the degree of color change after tooth bleaching is known to vary substantially between studies; there are currently no objective guidelines to predict the effectiveness of a tooth-bleaching treatment. We propose a new methodology based on fuzzy logic as a natural means of representing the imprecision present when modeling the color change produced by a tooth-bleaching treatment on the basis of a tooth's initial chromatic values. This system has the advantage of producing a set of interpretable fuzzy rules that can subsequently be used by scientists and dental practitioners. The fuzzy system obtained has the special characteristic whereby the rule antecedents correspond to prebleaching shades of the well-known Vita commercial shade guide. Additionally, the rule consequents directly correspond with the expected CIELAB postbleaching values for each Vita shade, thanks to a modification of the system's inference structure. Finally, the values of these postbleaching CIELAB coordinates have been associated with Vita shades by evaluating their respective membership functions, thereby approximating which posttreatment Vita shades are to be expected for each prebleaching shade.

Light polymerization-dependent changes in color and translucency of resin composites.

PURPOSE: To determine the influence of type of polymerization light on changes in color and translucency of resin composites. METHODS: 16 shades of commercial composites were analyzed. Specimens were polymerized with quartz-tungsten-halogen (QTH) and light-emitting diode (LED) polymerization light. Color of non-polymerized and polymerized composites was measured against white and black backgrounds using a spectroradiometer. Changes in color (deltaE'), translucency (deltaTP') and color parameters (deltaL', deltaC' and deltah') were calculated for each polymerization light. The differences among deltaE' values and among deltaTP' values obtained for each device were analyzed by two-way ANOVA. Multiple regression analysis was used to determine the influence of color parameters on deltaE' and deltaTP'. RESULTS: The results indicated that there was significant difference among the deltaE' and deltaTP' values obtained using QTH and LED light polymerization (P< 0.05). The prediction equations for deltaE' and deltaTP' based on the multiple regression analyses indicated that deltaE' was mainly caused by deltaC' for both lights. However deltaTP' was mainly caused by deltah' for LED light and by the deltaC' for QTH light. Changes in translucency significantly influenced the overall color changes after polymerization.

Stability and reproducibility of radiometric properties of light curing units (LCUs). Part I: QTH LCUs.

The present study, divided into two parts, analyses the stability and reproducibility of the spectral and energy emission of the present light-curing units (LCUs), quartz tungsten halogen (QTH) and light-emitting diodes (LEDs). In part I, QTH LCUs were studied. The results showed that the QTH LCUs studied presented high stability and reproducibility in terms of their spectral emission with VAF (variance accounting for) values from the Cauchy-Schwarz inequality, all close to 100%. With respect to the energy stability, the QTH LCUs studied can be considered stable under practical clinical conditions, although for some devices the initial irradiance value is critical. This result should be taken into account in those works which is researched in polymerization kinetics of dental materials as well as in clinical practice.

Stability and reproducibility of radiometric properties of light curing units (LCUs). Part II: LED LCUs.

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.

Study of the variation between CIELAB delta E* and CIEDE2000 color-differences of resin composites.

This study sought to assess the significance of the corrections introduced in the new CIEDE2000 color difference formula with respect to deltaE*ab. The purpose of which was to provide sounder knowledge, and hence more informed decision-making, about applying this new formula to dental resin composites. With two different hybrid composites, color differences were calculated between unpolymerized and polymerized resin composites, between polymerized resin composites of different thicknesses (1 and 2 mm), and between polymerized resin composites cured with halogen and LED light curing units (LCUs). The two formulas differed significantly, with VAB(E) (equal size) values higher than the inter-observer variability (VAB (E)=11%) and VAB(O) (original size) values greater than 25% for each of the data sets analyzed. Results obtained in this study agreed with and thus supported the recent recommendation of the Commission Internationale de l'Eclairage (CIE), whereby the new CIEDE2000 formula should be used to evaluate color differences of resin composites.

World dental research production: an ISI database approach (1999-2003).

The objective of this study was to obtain a geographic world map of scientific production in dentistry by analysing published papers. Articles and reviews in the Dentistry, Oral Surgery & Medicine category published from 1999 to 2003 were accessed through the ISI database. The data were analyzed quantitatively (number of documents, number of researchers, productivity, interannual variation rate and relative specialization index), qualitatively (weighted impact factor, relative impact factor, citation rate per document and top 5 publications) and socioeconomically (number of documents per inhabitant and per dentist and in relation to the country's GDP). The USA, UK, Japan and Scandinavian countries were found to be the most productive countries (number of publications). Publications from Scandinavian countries were also of high quality as measured by Impact Factor and Citation Rate, while the UK had one of the highest productivity rates (number of documents per researcher).