Masking ability of bleach-shade resin composites using the multilayering technique

Effect of layering strategy and prolonged water aging on masking ability of composite resins

STATEMENT OF PROBLEM

Layered composite resins may adequately mask discolored substrates. However, whether color changes that occur over time affect masking ability is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of layering and water aging on the masking ability of 2 composite resins.

MATERIAL AND METHODS

Disk specimens (1.5 mm-thick and shade A1) from Charisma Diamond (CD) and Filtek Z350XT (Z350) were made according to the composite resin shade combination used in the layering strategies: bilayer for CD (enamel/dentin) and for Z350 (enamel/body and enamel/dentin) and trilayer for Z350 (enamel/body/dentin) (n=5). Color measurements were obtained with a spectrophotometer over an A3.5 ceramic substrate, and the whiteness index for dentistry (WID) was calculated. The specimens were aged in water at 37 °C and evaluated at different times: 24 hours, 1 week, 1 month, 2 months, 6 months, 12 months, 18 months, and 24 months. CIEDE2000 color differences (ΔE00) and WID differences (ΔWID) were calculated and interpreted by 50:50% color and whiteness perceptibility and acceptability thresholds. Changes among strategies and aging times were analyzed using the Kruskal-Wallis test (α=.05). Contrasts were made using the Mann-Whitney U test with Bonferroni correction (α=.001).

RESULTS

ΔE00 decreased from 24 hours to 2 months of aging. From 2 months onwards, ΔE00 increased for all layering strategies and times, without significant changes in lightness for CD (P>.004). Overall, for the CD restorative system, an increase in ΔWID was observed after 1 month of aging (P<.001), while for the Z350 restorative system, ΔWID decreased after aging (P<.001), except for the Z350 bilayer strategy (enamel + dentin) at 1 week and 2 months (P>.004). For all layering strategies and aging times, color differences were higher than the 50:50% perceptibility threshold for ΔE00 and, after 6 months, higher than the 50:50% acceptability threshold for ΔE00 and the 50:50% whiteness acceptability threshold.

CONCLUSIONS

The ability of the tested composite resins to mask a discolored substrate was affected by the layering approach applied and by prolonged water aging.

Masking ability of resin composites: A scoping review

OBJECTIVE

To map the existing evidence regarding the masking ability of resin composites.

OVERVIEW

The literature search was conducted electronically, based on the PRISMA Extension for Scoping Reviews-online protocol at https://osf.io/m2h67/ with no language or time restrictions. Two independent reviewers conducted the screening, and a third reviewer was consulted in case of disagreement. Studies that evaluated resin composite masking ability regardless of background, application technique, thickness, or number of layers were selected. The search found 2995 potentially eligible studies. After removal of duplicates (657), irrelevant articles (2323), 15 citations met the eligibility criteria based on title and abstract, and eight studies were included based on full text analysis (seven in vitro, and one case report). Acceptable masking ability is obtained by one layer of opaque shade resin composite or by the layering technique. A black background is masked with 1.0- to 2.0 mm-thick layers of opaque shade resin composites. Masking of the C4 background is achieved with one layer of 0.5- to 1.5 mm-thick opaque shade resin composite or by the layering technique using different combinations of enamel body and dentin shades with a final thickness of 1.5 mm.

CONCLUSIONS

Acceptable masking of C4 shade background is achieved with one layer of opaque shade composite at least 0.5 mm-thick or by different combinations of the layering technique, with a final thickness of 1.5 mm. Acceptable masking of the black background of the oral cavity is achieved with a resin composite of at least 1.0 mm opaque shade.

CLINICAL SIGNIFICANCE

The thickness of the resin composite layer required to achieve adequate masking is variable and depends on the translucency/opacity of the tested resin composites and the background shade.

Masking Ability of Bleach Shade Composite Resins in Different Thicknesses

Introduction

In recent years, the use of bleach shade composite resins has increased due to the high esthetic demands. The aim of the present study was to investigate the masking ability and translucency of several bleach shade composite resins.

Materials and Methods

In this in vitro study, 180 discs from 9 bleach shade composite resins of 5 brands (G-aenial Anterior, Gradia Direct, Charisma Diamond, Estelite Sigma Quick, and Renamel Microfill) in thicknesses of 0.5, 1, 1.5, and 2 mm were prepared. The color parameters of the specimens were measured in a CIE l ∗ a ∗ b ∗ system using a spectrophotometer. Masking ability and translucency parameters were calculated, and the influence of thickness, shade, and composite resin brand on these variables was analyzed using the Kruskal-Wallis and Mann-Whitney U tests.

Results

Both masking ability and translucency differed significantly among groups (p < 0.001), but only MA was different between different brands (p < 0.001). Higher thicknesses showed lower translucency in all pairwise comparisons (p < 0.001). 0.5 mm-thick specimens had lower masking ability than 1.5 mm- (p=0.016) and 2 mm- (p=0.035) thick ones. However, masking ability of other thickness pairs did not show a significant difference (p > 0.05). G-aenial Anterior and Renamel Microfill had the highest and lowest masking ability. Bleach white shades had lower masking ability and higher translucency than extrawhite bleach shades.

Conclusion

Translucency and masking ability of bleach shade composite resins differed in different thicknesses, composite resin brands, and shade groups.

Masking Ability of Monolithic and Layered Zirconia Crowns on Discolored Substrates

There is scarce information on the colorimetric behavior of monolithic and layered zirconia crowns in combination with various abutment colors. This study evaluated the masking ability on discolored substrates of monolithic and layered zirconia crowns. Anterior crowns were fabricated using 3Y-TZP zirconia and layering ceramic and divided into three groups: monolithic (ML), bi-layer (BL), and tri-layer (TL). The crowns were placed over eleven substrates (ND1-ND9, zirconia, metal), and CIE L*, a*, b*, C*, and h° color coordinates were measured in the cervical, middle, and incisal areas with a spectrophotometer. Masking ability was calculated using the color difference formula, and values were interpreted according to the perceptibility and acceptability thresholds. Data were analyzed statistically (α = 0.001). The L* coordinate was not significantly different between BL and TL crowns, regardless of the measurement area or substrate (p ≥ 0.001). In the middle area, the L* coordinate of the ML group was statistically different from the BL and TL groups only for zirconia and metal substrates, while in the incisal area, only for ND7 and metal substrates. The a* coordinate was significantly different between the ML and layered crowns for all measurement areas and substrates (except zirconia). The b* and C* coordinates differed significantly between the groups only in the cervical area (p < 0.001). The ML crown had better masking ability than the BL and TL crowns. However, the color differences for ML crowns were below the acceptability threshold for ND2, ND3, and ND7 substrates in the cervical and middle areas and below perceptibility threshold only for the incisal area. The lowest masking ability of the crowns was found for ND9 and metal substrates in all measurement areas.

Influence of manufacturing technique on the color of zirconia restorations: Monolithic versus layered crowns

OBJECTIVES

The study aimed to compare the color of monolithic and layered zirconia crowns fabricated using different brands in the cervical, middle, and incisal areas.

MATERIALS AND METHODS

A total of 45 crowns were fabricated from three brands (Katana, Nacera, Cercon) using three methods (monolithic = ML (n=5), cut-back + enamel = BL (n=5), cut-back + dentin + enamel = TL (n=5)). CIE L*, a* b*, C*, h° color coordinates were recorded with a dental spectrophotometer in cervical, middle, and incisal areas. Color differences between manufacturing techniques, tooth areas, and brands were calculated using the CIEDE2000(1:1:1) formula, and the values were compared to the perceptibility (PT₀₀ ) and acceptability thresholds (AT₀₀ ). Comparisons between color coordinates were analyzed statistically (Kruskal-Wallis and Mann-Whitney U tests, p < 0.001).

RESULTS

Significant differences were found between CIE L*, a*, b*, C*, h° coordinates of the zirconia crowns (p < 0.001), generally. The lowest color differences were obtained between BL and TL crowns in cervical and middle areas. Color differences between cervical and middle areas were mostly below PT₀₀ . An acceptable color difference was found between Katana and Cercon crowns.

CONCLUSIONS

The manufacturing technique and the brand influenced the color of zirconia crowns. Also, the color of the crowns varied from cervical to incisal.

CLINICAL SIGNIFICANCE

Reproducing the optical properties of teeth with ceramic crowns might be challenging, given the differences in the internal configuration of the enamel and dentine, as well as their complex behavior when interacting with light. When deciding whether to fabricate a monolithic crown in translucent zirconia or improve its appearance by layering with more translucent glass-ceramic, the clinicians and dental technicians must be aware of these procedures' effect on the final color of the restorations.