Influence of layering thickness on the color parameters of a ceramic system

Influence of Restorative Material on the Distribution of Loads to the Bone in Hybrid Abutment Crowns-In Vitro Study

Background: The objective of this study was to evaluate the load transmitted to the peri-implant bone by seven different restorative materials in single-unit rehabilitations with morse taper implants using a strain gauge. Materials: In a polyurethane block that simulated type III bone, a morse taper platform implant was installed (3.5 × 11 mm) in the center and 1 mm below the test base surface, and four strain gauges were installed around the implant, simulating the mesial, distal, buccal and lingual positions. Seven similar hybrid abutment crowns were crafted to simulate a lower premolar using different materials: 1-PMMA; 2-glass ceramic over resin matrix; 3-PEEK + lithium disilicate; 4-metal-ceramic; 5-lithium disilicate; 6-zirconia + feldspathic; 7-monolithic zirconia. All groups underwent axial and oblique loads (45 degrees) of 150 N from a universal testing machine. Five measurements (n = 5) were performed with each material and for each load type; the microdeformation data underwent statistical analysis. The data were obtained in microdeformation (με), and the significance level was set at p ≤ 0.05. Results: There was no statistically significant difference in the evaluation among the materials under either the axial load or the oblique load at 45 degrees. In turn, in the comparison between axial load and oblique load, there was a difference in load for all materials. Conclusion: The restorative material did not influence the load transmitted to the bone. Furthermore, the load transmitted to the bone was greater when it occurred obliquely at 45° regardless of the material used. In conclusion, it appeared that the different elastic modulus of each material did not influence the load transmission to the peri-implant bone.

Influence of Thickness of Opaque Porcelain and Alloy Color on the Final Color of Porcelain-Fused-to-Metal Restorations

Despite the advent of metal-free solutions, porcelain-fused-to-metal restorations (PFM) are still widely used. Particularly for the latest ceramic systems, scarce information is present in the scientific literature about the ideal opaque layer thickness and the alloy color impact to achieve the desired final color of PFM restorations. This study aimed to evaluate the influence of opaque thickness variation layered on different metal alloys on the final color of PFM restorations. Opaque porcelain of one metal−ceramic system (VITA VM13) was layered in four different thicknesses (0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm) on three differently colored dental alloys: a gold−platinum alloy (yellowish), a gold−palladium alloy (light grayish), and a nickel−chromium alloy (dark grayish). The veneering porcelain layered over the opaque was kept constant (Base Dentine 0.45 mm, Transpa Dentine 0.50 mm, and Enamel 0.20 mm). Sixty specimens were fabricated, five samples for each combination of alloy/opaque thickness. The color difference (ΔE) between specimen and reference was measured using a clinical spectrophotometer. The two-way ANOVA revealed that the thickness of both the opaque (p < 0.001) and the metal alloy (p < 0.001) significantly influenced the ΔE values. Gray-colored alloys covered by a 0.10 mm thick opaque layer enabled the closest color match, whereas this occurred for yellow-color alloys covered by a 0.15 mm thick opaque layer. In contrast, the samples covered by a 0.25 mm thick opaque layer obtained the worst ΔE.

Validation of a Hyperspectral Imaging System for Color Measurement of In-Vivo Dental Structures

A full comprehension of colorimetric relationships within and between teeth is key for aesthetic success of a dental restoration. In this sense, hyperspectral imaging can provide point-wise reliable measurements of the tooth surface, which can serve for this purpose. The aim of this study was to use a hyperspectral imaging system for the colorimetric characterization of 4 in-vivo maxillary anterior teeth and to cross-check the results with similar studies carried out with other measuring systems in order to validate the proposed capturing protocol. Hyperspectral reflectance images (Specim IQ), of the upper central (UCI) and lateral incisors (ULI), were captured on 30 participants. CIE-L*a*b* values were calculated for the incisal (I), middle (M) and cervical (C) third of each target tooth. ΔEab* and ΔE00 total color differences were computed between different tooth areas and adjacent teeth, and evaluated according to the perceptibility (PT) and acceptability (AT) thresholds for dentistry. Non-perceptible color differences were found between UCIs and ULIs. Mean color differences between UCI and ULI exceeded AT (ΔEab* = 7.39-7.42; ΔE00 = 5.71-5.74) in all cases. Large chromatic variations between I, M and C areas of the same tooth were registered (ΔEab* = 5.01-6.07 and ΔE00 = 4.07-5.03; ΔEab* = 5.80-8.16 and ΔE00 = 4.37-5.15; and ΔEab* = 5.42-5.92 and ΔE00 = 3.87-4.16 between C and M, C and I and M and I, respectively). The use of a hyperspectral camera has proven to be a reliable and effective method for color evaluation of in-vivo natural teeth.

Translucency of a Dental Porcelain Mixed by Two Ceramic Slurry Methods: A Bayesian Comparison

Background

The ceramics industry produces porcelain pastes using a controlled ratio of water and porcelain powder. Two methods are used to produce a dental porcelain paste: one-step mixing or incremental mixing.

Objective

To evaluate the optical properties of a feldspathic dental ceramic using two different ceramic paste preparation methods using a Bayesian approach.

Materials and Methods

Two groups of feldspathic porcelain discs, an incremental mixing group (n = 40) and a one-step mixing group (n = 40), were assessed. Groups were evaluated using spectrophotometry, and the translucency parameter (TP) of each sample was calculated. Surfaces were characterized by AFM and SEM. Statistical analysis was performed using a Bayesian approach.

Results

Translucency parameter values of the incremental mixing group ranged from 1.65 to 3.41, while values for the one-step mixing group ranged from 3.62 to 5.74, this difference being statistically significant. The lowest roughness was obtained on the surface of discs in the one-step mixing group.

Conclusions

Feldspathic porcelain with lower translucency and higher roughness was obtained using the incremental mixture method.

Color prediction of layered dental resin composites with varying thickness

OBJECTIVE

The aim of this study was to assess the accuracy of a Principal Components Analysis (PCA)-based method for reflectance reconstruction and color estimation of layered dental resin-based composites with different thicknesses.

METHOD

Bi-layered samples of different clinically relevant thicknesses were created using shades of VITAPAN Excell (VE), VITAPAN Dentine (VD) and VITA Physiodens (VP), combined with their corresponding enamel shades. Spectral reflectance of all samples was measured over a black background using a non-contact spectroradiometer with CIE 45^∘∕0^∘ geometry. Two different PCA-based models, built from two different configurations of known samples, were proposed to reconstruct the spectral data and color of unknown layered samples. Root Mean Square Error (RMSE), Goodness of Fit (GFC), as well as ΔE₀₀ with corresponding 50:50% acceptability and perceptibly thresholds (AT and PT) were used as performance assessment.

RESULTS

The 5-samples training set approach provided an average RMSE < 0.015 and GFC > 0.999 when measured and predicted spectral reflectances were compared, while for the 9-samples training set, RMSE < 0.0098 and GFC > 0.9999 were obtained. The overall mean color differences obtained with the 5-samples training set approach were ΔE₀₀ = 0.99 (AT% = 96.25% and PT% = 32.50%), while using the 9-samples training set resulted in lower overall mean color differences: ΔE₀₀ = 0.50 (AT% = 99.22% and PT% = 83.87%).

SIGNIFICANCE

Within the framework of this study, the two proposed PCA-based configurations allow the prediction of the spectral reflectance of layered dental resin-based composites of different shades and thicknesses, with a high degree of accuracy.

Effects of dentin and enamel porcelain layer thickness on the color of various ceramic restorations

OBJECTIVE

To investigate the effects of dentin and enamel porcelain layer thickness on the color of various ceramic restorations.

MATERIALS AND METHODS

Eighty specimens (shade A2 and A3, n = 10) (20 mm in length, 4 mm in width, 1.5 mm in thickness respectively) of casting ceramic (EM); alumina ceramic (AL); zirconia ceramic (ZR); and porcelain-fused-metal (PFM) were prepared. The color distributions of each specimen were measured at 4 places using a spectroradiometer. The dentin/enamel porcelain (D/E) layer thicknesses of the 4 places were 0.8/0.2 mm, 0.6/0.4 mm, 0.4/0.6 mm, and 0.2/0.8 mm. The color differences (ΔE₀₀ ) between the specimens and the corresponding color shade tabs were calculated. Data were analyzed using three-way repeated-measures ANOVA and Holm-Sidak pairwise comparisons (a = 0.05). The acceptability threshold (AT) was used to analyze the results.

RESULTS

The minimum ΔE₀₀ values were 1.31 (0.6/0.4 mm for EM), 1.41 (0.8/0.2 mm for AL), and 1.92 (0.2/0.8 mm for ZR) for shade A2, and 0.93 (0.6/0.4 mm for EM), 0.89 (0.8/0.2 mm for AL), and 1.34 (0.8/0.2 mm for ZR) for shade A3. Most of them were below AT value (1.8). For AL and ZR (shade A2) and ZR (shade A3), the D/E layer thicknesses of 0.8/0.2 mm and 0.6/0.4 mm had lower ΔE₀₀ values than 0.4/0.6 mm and 0.2/0.8 mm (p ≤ 0.001).

CONCLUSIONS

The dentin/enamel porcelain layer thickness that was most color-matched to the shade tab was different for various ceramic restorations. The color of shade A2 AL and ZR and shade A3 ZR was closer to the shade tab when dentin porcelain was thicker than enamel porcelain.

CLINICAL SIGNIFICANCE

Matching the shade of ceramic restoration to the shade tab color is a great challenge in esthetic dentistry. The dentin/enamel porcelain layer thickness is an important factor to influence the improved color matching.

Color stability of bulk-fill and universal composite restorations with dissimilar dentin replacement materials

OBJECTIVE

To determine color changes in bulk-fill composite and universal composite restorations with dissimilar dentin replacement materials in extracted teeth after staining in red wine.

MATERIALS AND METHODS

Cylindrical, 4 mm deep, class I cavities were prepared in 140 human molars. Bottom 2 mm was restored with Biodentine (Septodont), everX posterior (GC) or experimental HAP inserts. Each dentin replacement material was covered with a 2-mm layer of a universal composite Filtek Z250 or Z550 (3M ESPE) or Gradia Posterior (GC). Groups combining top composite layer and the underlying dentin replacement were designated as "composite_dentin replacement." Filtek Bulk Fill (3M ESPE) and Tetric EvoCeram Bulk Fill (Ivoclar Vivadent) were placed as a single 4-mm layer. Color measurements were performed using Vita Easyshade 4.0 (Vita Zahnfabrik) initially and after 48-hours storage in red wine at 37°C.

RESULTS

Color differences (ΔE_oo ) ranged between 2.1 ± 0.7 (Z250_HAP) and 7.8 ± 1.1 (Z550_everX). EverX resulted in higher ΔE_oo of the overlying composite than HAP (P < .001) and Biodentine (P = .006). Generally, ΔE_oo was affected more by decreasing lightness (ΔL') than changes in chroma (ΔC').

CONCLUSIONS

EverX resulted in higher ΔE_oo of the restoration than Biodentine and experimental HAP after staining in red wine. No significant differences in ΔE_oo may be expected in different composites with the same underlying dentin replacement material. The same was generally true for bulk-fill and universal composites.

CLINICAL SIGNIFICANCE

Similar extent of color changes may be expected in bulk-fill and universal composites. Highly translucent everX might exhibit greater color differences irrespective of the capping composite than non-translucent materials. Clinicians have a wider choice of composite materials to cover a particular dentin replacement material, for example, everX or Biodentine, as similar color differences may be expected in various overlying composite brands.

Comparação estética entre sistemas cerâmicos sobre substrato escurecido

Objetivo: O objetivo deste trabalho foi avaliar visualmente a possível influência de um substrato escurecido no resultado estético de coroas com infraestruturas de dissilicato de lítio ou zircônia. Metodologia: O delineamento foi observacional, transversal e descritivo. Para o experimento, foi selecionado um paciente com necessidade de coroas totais no 11 e 21, onde um dos dois elementos deveria ser escurecido. Uma coroa de dissilicato de lítio foi confeccionada sobre o substrato sem alteração de cor. Para o elemento escurecido foram confeccionadas uma coroa de dissilicato de lítio e uma de zircônia, criando-se duas situações clínicas. Sem conhecimento de qual material foi usado, os avaliadores responderam a um questionário que comparava o resultado estético das coroas de dissilicato de lítio ou zircônia com a coroa de dissilicato de lítio sobre o substrato normal, assim como as duas situações clínicas entre si. No total, 20 cirurgiões-dentistas participaram como avaliadores. Os avaliadores julgaram as restaurações como excelentes, aceitáveis ou inaceitáveis e, após, foi realizada uma análise descritiva das avaliações. Resultados: Os resultados demonstraram que houve diferença estética entre as restaurações de dissilicato de lítio e de zircônia, sendo que o dissilicato de lítio não conseguiu bloquear a cor do substrato, mesmo sendo utilizada uma pastilha opaca (MO). Conclusão: Concluiu-se que em casos de substrato escurecido está indicada a utilização de uma infraestrutura com opacidade suficiente, como a zircônia, podendo ocorrer diferenças visualmente perceptíveis e inaceitáveis caso seja utilizado um material translúcido como o dissilicato de lítio.

Optical properties of translucent zirconia: A review of the literature

Translucent monolithic zirconia is the newest option of zirconia-based ceramics, which aimed to substitute the opaque classic yttria-stabilized tetragonal zirconia polycrystal (Y-TZPs) in more demanding esthetic cases.

The aim of this review was to assess the available literature regarding the optical, chemical and mechanical properties of translucent zirconia ceramics.

This systematic review was developed according to the PRISMA (Preferred Reporting Items for Systematic Review and Meta-analysis) guidelines. An electronic literature search was undertaken through Medline (National Library of Medicine) via PubMed to identify relevant articles, published in the interval 2010-2018. The search was limited to the English language publications, in vitro studies of color and microstructure of translucent zirconia material.

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZPs) has excellent mechanical properties, but its intense white color and high opacity represent an esthetic limit. Cubic zirconia represents a new generation of dental ceramics with molecular structure and physical properties different from the conventional zirconia. Dental manufacturers created new formulations of this restorative material, introducing new cubic varieties of zirconia with improved optical properties. Translucent monolithic zirconia provides a new restorative option that combines strength with improved esthetics, due to its increased translucency. Translucent zirconia is indicated for anterior and posterior restorations but should be used carefully for discolored teeth, because the background color can affect the final esthetic appearance of the restoration.

Influence of implant abutment material and ceramic thickness on optical properties

STATEMENT OF PROBLEM

Anterior shade matching is an essential factor influencing the esthetics of a ceramic restoration. Dentists face a challenge when the color of an implant abutment creates an unsatisfactory match with the ceramic restoration or neighboring teeth.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of abutment material and ceramic thickness on the final color of different ceramic systems.

MATERIAL AND METHODS

Four experimental and control ceramic specimens in shade A3 were cut from IPS e.max CAD, IPS Empress CAD, and VITA Suprinity PC blocks. These specimens had thicknesses of 1.0 mm, 1.5 mm, 2.0 mm, and 2.5 mm, respectively, for the experimental groups, and 4 mm for the controls. Background abutment specimens were fabricated to yield 3 different shades: white zirconia, yellow zirconia, and titanium at a 3-mm thickness. All 3 ceramic specimens in each thickness were placed in succession on different abutment backgrounds with glycerin optical fluid in between, and the color was measured. A digital spectrophotometer was used to record the specimen color value in the Commission Internationale De L'éclairage (CIELab) color coordinates system and to calculate the color difference (ΔE) between the control and experimental groups. The Kruskal-Wallis test was used to analyze the effect of ceramic thickness on different abutments, and the pair-wise test was used to evaluate within the group (α=.05).

RESULTS

The color differences between the test groups and the control decreased with increasing ceramic thickness for every background material. In every case, significant differences were found between 1.0- and 2.5-mm ceramic thicknesses. Only certain 2.5-mm e.max CAD, VITA Suprinity PC, and Empress CAD specimens on yellow-shade zirconia or VITA Suprinity PC on titanium were identified as clinically acceptable (ΔE<3).

CONCLUSIONS

Increasing ceramic restoration thickness over the abutment background decreased the color mismatch. Increasing the thickness of ceramic on a yellow-shaded zirconia abutment rather than on titanium or white zirconia yielded a more esthetic color for the whole restoration.

The effect of powder A2/powder A3 mixing ratio on color and translucency parameters of dental porcelain

PURPOSE

The purpose of this study is to mix dental ceramic powder in varying ratios and evaluate the effect of the mixing ratio on color and translucency.

MATERIALS AND METHODS

The ceramic powder of shade A3 of the same product was mixed with the shade A2 of three products: IPS e.max Ceram (Ivoclar Vivadent, Schaan, Liechtenstein), Vintage Halo (SHOFU Inc., Kyoto, Japan), and Ceramco 3 (Ceramco-Dentsply, Burlington, NJ, USA) in the following fixed ratios (0 wt%, 25 wt%, 50 wt%, 75 wt%, and 100 wt%) and then fired. A total of 150 specimen of ceramic fired were manufactured in a regular size (W: 8.5 mm, L: 10.5 mm, and H: 1.5 mm). For color and translucency, L*, a*, and b* were measured and Two-way analysis of variance (ANOVA) and One-way analysis of variance (ANOVA) were used for data analysis (α=0.05).

RESULTS

The higher the mixing ratio was, L*, a*, and b* of IPS e.max Ceram were all increased, and L* of Vintage Halo was reduced and a* and b* were increased. L* and a* of Ceramco3 were reduced and b* of Ceramco3 was increased. Color difference (ΔE*ab) was increased in all three products as the mixing ratio got higher. Increased mixing ratios resulted in decreased translucency parameter (TP) values for IPS e.max Ceram but increased TP values for Vintage Halo and Ceramco3.

CONCLUSION

In this limited study, CIE L*, a*, and b* were influenced by the mixing ratio of the A3 powders and porcelain powder mixtures represented a various color and translucency.

Cyclic Loading Effect on Color Stability of Unshaded versus Shaded Zirconia

STATEMENT OF PROBLEM

Shaded versions of dental zirconia may improve initial color matching to teeth, but might change color with cyclic mechanical loading.

PURPOSE

The purpose of this study was to measure the color of unshaded and shaded zirconia dental ceramic before and after cyclic mechanical loading and calculate color differences (ΔE).

MATERIAL AND METHODS

Disk-shaped specimens (N = 30, Nobel Procera, 0.8 mm thick, 12 mm diameter) of unshaded or shaded zirconia (intrinsically shaded by small oxide modifications) were fabricated by the Nobel Biocare using standard CAD-CAM processing. Milled surfaces were polished. CIE L*a*b* values were measured (Konica Minolta spectrophotometer) before and after mechanical cycling (custom modified Leinfelder test machine, biaxial flexure loading, load = 80 N × 500,000 cycles, dry), and L*a*b* individual differences and ΔE color differences were calculated and compared (ANOVA, p < 0.05).

RESULTS

Mean L*a*b* values for the unshaded group before (U1 = 86.165, -0.887, 0.372) and after (U2 = 84.860, -0.805, 0.097) cyclic loading were compared to the shaded group before (S1 = 75.281, -0.679, 23.251) and after (S2 = 74.961, -1.233, 22.439) cyclic loading. All color variables for both unshaded and shaded groups were significantly different between before and after cyclic loading (p < .004) except for the L* value of the shaded group. The ΔE for unshaded (1.441 ± 0.495) versus shaded (1.252 ± 0.363) were statistically different but clinically the change would not be detectable at this point.

CONCLUSIONS

The color of the unshaded and shaded zirconia specimens was influenced by cyclic loading (p < 0.05). Color changes were detectable but small at levels up to 500,000 cycles, and remained clinically acceptable at that point.

CLINICAL SIGNIFICANCE

It is important to acknowledge any possible color changes that might occur in zirconia restorations, especially in the esthetic zone. Minor color changes that are individually imperceptible to the human eye within different restorative components may be compounded to produce clinically significant color change that is not aesthetically acceptable.

Translucency of ceramic materials for CEREC CAD/CAM system

OBJECTIVES

To compare translucency of the ceramic materials (CEREC CAD/CAM).

MATERIALS AND METHODS

Fifteen ceramic materials for CEREC CAD/CAM system were evaluated: IPS e.max HT/LT/MO, ZirCAD, Empress HT/LT; VITA Mark II, VITA AL; VITA YZ, VITA In-Ceram Spinell/Alumina/Zirconia; and Sirona InCoris AL; Sirona InCoris ZI/TZI. Specimens (0.5-mm and 1.0-mm thick; n = 10 each material) were cut from commercial blocks using a water-cooled diamond saw. Contrast ratio (CR = YB /YW ) was measured using a spectrophotometer with an integrating sphere. Kruskal-Wallis one way analysis of variance was performed followed by Dunn's multiple test for post-hoc.

RESULTS

CR varied from 0.35 to 1.00 and from 0.48 to 1.00 for 0.5 mm and 1.0 mm thicknesses, respectively. CR increased in the following order: IPS e.max HT (most translucent-least opaque), IPS Empress HT, VITA Mark II, IPS Empress LT, IPS e.max LT, In-Ceram Spinell, IPS e.max MO, VITA YZ, InCoris TZI, IPS e.max ZirCAD, InCoris ZI, In-Ceram Alumina, VITA AL, InCoris AL, and In-Ceram Zirconia (least translucent-most opaque).

CONCLUSIONS

The null hypothesis has been rejected because tested materials exhibited a wide range of CR. Translucency needs to be taken into account in different clinical situations, including considerations associated with thickness of restoration and/or particular layers.

CLINICAL SIGNIFICANCE

A wide range of translucency was identified for the ceramic materials tested. This variability has to be taken into account for the selection of the materials in different clinical situations also related to the thickness clinically required.

Color match of two different ceramic systems to selected shades of one shade guide

STATEMENT OF PROBLEM

There are no consistent indications given by dental manufacturers on how to layer ceramics to achieve a color match to a shade selected from a dental shade guide. The technique for ceramic layering relies primarily on the skill and experience of ceramists and is not easily predictable.

PURPOSE

The purpose of this study was to evaluate, using a clinical spectrophotometer, the ability to color match shades selected with the 3D-Master shade guide using 2 different ceramic systems.

MATERIAL AND METHODS

Two ceramic systems were selected for this study, the VITA Omega 900 and VITA VM 13. For both systems, shades 2M3, 3M2, 4M2 of the VITA 3D-Master shade guide were selected. Thirty ceramic discs, 15 mm in diameter, were fabricated with different layer thickness ratios of opaque dentin, dentin, and enamel, maintaining a constant overall thickness. A clinical spectrophotometer (VITA Easyshade) was used for color comparison. The measured ΔE values were statistically analyzed with a 3-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

The 3-way ANOVA showed that the ceramic system (P<.001), the selected shade (P<.001), and the layering scheme all significantly influenced the ΔE values (P<.001).

CONCLUSIONS

Both VITA VM 13 and VITA Omega 900 ceramic systems showed a color match with the shades 2M3, 3M2, and 4M2 of the VITA 3D-Master shade guide to be within the limits for clinical acceptability (ΔE≤ 3.3). VM 13 showed a statistically better color match. The layering scheme influenced the definitive color of the restoration.