Effect of Staining and Aging on Translucency Parameter of CAD-CAM Materials

Abstract

Objectives

To evaluate different intervals of exposure to staining solutions and artificial aging on translucency parameter (TP₀₀) of CAD-CAM materials.

Material and Methods

One millimeter thick square-shaped specimens (N = 288) were cut from Cerasmart (CS), IPS e.max (IE), Lava Ultimate (LU), Shofu HC (SH), Vita Enamic (VE), and Vita Suprinity (VS) and were divided into laboratory and chairside polishing. Reflection wavelength spectra, CIE D65 standard illuminant, 2 ° standard observer, SCI, UV included, SAV aperture, 6 mm diameter, were recorded at 10 nm sensitivity against white and black calibration tiles using a benchtop spectrophotometer. Subsequently, they were converted into CIEDE 2000 TP₀₀. After baseline measurements (T0), the specimens were divided as follows (n = 8): staining in coffee (C) and wine (W), for 60 (T1) and 120 hours (T2), and accelerated artificial aging (A). Artificial aging (ISO 4892-2 standard) was performed in two cycles of 150 KJ/m², for T1 and T2, respectively. TP measurements were repeated at T1 and T2. Data of TP₀₀ retention were submitted to analysis of variance and Fisher’s PLSD multiple comparison test (α=0.05).

Results

Fisher’s PLSD critical differences among materials, time intervals and staining/aging were 0.16, 0.11 and 0.11, respectively. SH showed the highest TP₀₀ followed by LU > CS > IE = VS > VE. For all time intervals, the lowest TP₀₀ retention was observed with C. W, and A presented similar values.

Conclusions

Translucency Parameter was a time and staining/aging-dependent material. In majority of cases, it decreased upon staining/aging.

Introduction

The introduction of computer aided design – computer aided manufacturing (CAD-CAM) systems in prosthodontics allowed faster production of dental restorations with higher mechanical strength compared to handmade porcelain restorations (1). In-office full digital workflow has been incorporated in daily routine, from intraoral 3D scanning to chairside CAD-CAM of restorations, because it is time saving, it reduces the quantity of patient visits to the office, and eliminates the need of a dental technician (2, 3). At the same time, new CAD-CAM materials, such as lithium silicate/disilicate ceramics, resin nanoceramics (RCN) and polymer-infiltrated ceramic-network (PICN) have been introduced and quickly have been accepted as materials of choice (4, 5). These new materials are almost fully manufacturer processed, thus minimizing human related errors (6-8).

In the era of esthetic dentistry, the goal is to provide patient functional restorations whilst mimicking natural tooth appearance. Translucency, along with color, texture, size and shape, influences the appearance and optical properties of restorations.

Finishing and polishing affect the surface texture and roughness (9, 10), which associated with in-mouth material aging and consumption of dark colored beverages, such as coffee, tea, red wine, and coke can provoke alterations in color and in translucency parameter (TP) of restorations (11-17). In vitro tests can be used to compare different materials under the same conditions and to predict the clinical performance (18). This study aimed to compare the TP of lithium silicate/disilicate ceramics, RCN and PICN CAD-CAM materials upon exposure to staining solutions and artificial aging (19, 20). The null hypothesis was that there were no differences in TP a) among materials, b) caused by different intervals of c) immersion in staining solutions and exposure to artificial aging. In addition, comparisons between laboratory and chairside polished specimens, and correlation between TP₀₀ and TP_ab were evaluated.

Material and Methods

Six CAD-CAM materials: Cerasmart (GC, Tokyo, Japan); IPS e.max CAD (Ivoclar Vivadent, Schaan, Liechtenstein); Lava Ultimate (3M ESPE, St. Paul, MN); Shofu HC (Shofu, Kyoto, Japan); Vita Enamic (Vita Zahnfabrik, Bad Säckingen, Germany); Vita Suprinity PC (Vita Zahnfabrik) (Table 1) were tested for the translucency parameter (TP₀₀) at baseline and after exposure to artificial aging or staining in coffee and red wine.

Table 1. Materials, acronym, type, composition, and shade.

Material, acronym, type	Composition	Shade
Cerasmart (CS), resin nanoceramic	71% SiO2 and barium glass nanoparticles, BisMEPP, UDMA, DMA	A2 LT
IPS Emax CAD (IE), lithium disilicate glass ceramic	57–80% SiO2, 11–19% Li2O, other oxides	A2 LT
Lava Ultimate (LU), resin nanoceramic	80% SiO2 and ZrO2 nanoparticle, 20% BisGMA, UDMA, BisEMA, TEGDMA	A2 LT
Shofu HC (SH), resin nanoceramic	61% ZrSiO4-based glass and SiO2, UDMA, TEGDMA	A2 LT
Vita Enamic (VE), polymer-infiltrated ceramic-network	58–63% SiO2, 20–23% Al2O3, 9–11% Na2O, 4–6% K2O, 0.5–2% B2O3, < 1% ZrO2, < 1% CaO, 14% UDMA, TEGDMA	2M2 T
Vita Suprinity PC (VS), zirconia reinforced lithium silicate	56–64% SiO2, 15–21% Li2O, 8–12% ZrO2, 1–8% other oxides	A2 T

BisGMA - bisphenol A glycidil methacrylate, UDMA – urethane dimethacrylate, BisEMA – ethoxylated bisphenol A dimethacrylate, TEGDMA - triethylene glycol dimethacrylate, BisMEPP - 2,2-bis (4-methacryloxypolyethoxyphenyl) propane

One millimeter thick square shaped specimens (N = 288), were cut from CAD-CAM blocks (shade A2 or similar) with a precision sectioning blade (IsoMet 15LC, Buehler, Lake Bluff, IL) and mounted in a precision cutter (IsoMet 1000, Buehler). After that they were sequentially pre-polished under water cooling with #180; 320; 400; 600 SiC papers (Buehler) using Ecomet 6 grinder/polisher (Buehler). Specimens of each material were divided into two groups: laboratory polished and chairside polishing protocols. Polishing of all specimens was performed by the same operator (R.N.T.). Laboratory polishing was performed sequentially under water cooling with # 800, 1200, 2400, and 4000 SiC papers (15 seconds per grit) in an Ecomet 6 grinder/polisher at 250 rpm under light hand pressure. Chairside polishing was performed as recommended by each manufacturer (Table 2). Light hand pressure with a low-speed handpiece (maximum 15,000 rpm) was used to polish for 30 seconds per step.

Table 2. Chairside polishing steps for materials: Cerasmart (CS), IPS e.max (IE), Lava Ultimate (LU), Shofu HC (SH), Vita Enamic (VE) and Vita Suprinity (VS).

Material	Chairside polishing steps
CS	Cremaster finishing and polishing kit (Shofu) 1) Ceramaster CA-0123 at 20000 rpm 2) Cotton buff + Diapolisher paste at 15000 rpm (GC)
IE	OptraFine Assortment (Ivoclar Vivadent) 1) Finisher F at 15000 rpm 2) Polisher P at 15000 rpm 3) Nylon brush + Optrafine diamond paste at 7000rpm
LU	Polishing Set for 3M ESPE Lava Ultimate (Meisinger, Centennial, CO) 1) Polishing 9507P-050 at 10000 rpm 2) High-gloss polishing 9507H-050 at 10000 rpm 3) Cotton buff + DirectDia paste at 10000 rpm (GC)
SH	Ceramaster finishing and polishing kit (Shofu) 1) Ceramaster CA-0123 at 20000 rpm 2) Cotton buff + Diapolisher paste at 15000 rpm
VE	Vita Enamic Polishing Set Clinical (Vita Zahnfabrik) 1) Pre-polishing VI – EB14m at 9000 rpm 2) High-gloss polishing VI – EB14f at 6000 rpm
VS	Vita Suprinity Polishing Set Clinical (Vita Zahnfabrik) 1) Pre-polishing VI – SS4m at 9000 rpm 2) High-gloss polishing VI – SS4f at 6000 rpm

Specimens were cleaned with deionized water in an ultrasonic cleaner (Branson Ultrasonics, Brookfield, CT) for 10 minutes, and air-dried for 20 seconds for baseline TP₀₀ (T₀) measurements, after which they were randomly divided into 3 subgroups (n=8): coffee or wine staining, and accelerated artificial aging. The samples were stored in staining solution in an incubator at 37 °C in the dark for 60 (T₁) and 120 hours (T₂) (solutions were changed once a day). Coffee was prepared by mixing 6 table spoons of ground coffee (Folgers Classic Roast Medium, The Folger Coffee, Orrville, OH) to 600 ml of boiling water. Cabernet Sauvignon red wine (Frontera, Concha y Toro, Santiago, Chile) was used for red wine staining. Artificial accelerated aging was performed according to International Organization for Standardization (ISO) 4892-2 standard, using a xenon lamp weathering and lightfastness test chamber (Suntest XXL+ machine, Ametek Atlas, Mount Prospect, IL). The artificial aging cycle consisted of light exposure (102 minutes) and water spraying (18 minutes) under artificial daylight (CIE D65 illuminant) at constant temperature (37 °C ± 3 °C) and relative humidity (50% ± 10%), with a black panel temperature of 65 °C and irradiance control in the 300 to 400 nm interval of 60 W/m². The total energy delivered for artificial accelerated aging was 150 kJ/m² (T₁) and 300 kJ/m² (T₂), respectively. Measurements were repeated upon each storage period and aging cycle (T₁ and T₂).

Reflection values were recorded using a bench top spectrophotometer Ci7600 (X-Rite, Grand Rapids, MI) at 10 nm sensitivity with the following setup: CIE D65 standard illuminant, 2 degrees 1931 standard observer, specular component included (SCI), UV component included, small area view (SAV) aperture, and 6-mm in diameter (21, 22). Prior to measurements, the spectrophotometer was calibrated according to the manufacturer's instructions. Reflection spectra measurements were performed against white and black calibration tiles, thus providing comparisons within the same phase of the experiment. Reflection spectra data were converted into CIELAB and CIEDE 2000 color coordinates and the respective TP_ab and TP₀₀ values were calculated utilizing the following formulas (23):

where, L, a, and b denote lightness, green-red and blue-yellow coordinates, respectively, against white (*_W) and black (*_B) backgrounds.

Where L’, C’ and H’ denote lightness, chroma and hue respectively, against white (*_W) and black (*_B) backgrounds. R_{T (rotation function) accounts for the interaction between} C’ and H’ _{differences in the blue region.} S_L, S_C, and S_H adjust the total color difference for variation in the location of the color difference specimen over *_W and *_B in L*, a*, b*coordinates. The kL, k_C, and k_H are correction terms (24).

Data of TP₀₀ retention were analyzed using the analysis of variance (Minitab 16, Minitab, and State College, PA). Fisher’s PLSD multiple comparison test was calculated (α=0.05). TP_ab and TP₀₀ values were submitted to a scatterplot to generate R²-values. TP₀₀ differences of TP < 0.6 and ≤ 2.6 corresponding to the 50:50% perceptibility threshold (PT) and 50:50% acceptability threshold (AT) were used to interpret the results (25).

Results

Mean baseline TP₀₀ (s.d.) values and retention (%) upon exposure to coffee (C), wine (W) and aging (A) for T0-T1, T0-T2 and T1-T2 interval comparisons are presented in the Table 3. Fisher’s PLSD critical differences among materials, time intervals and staining/aging were 0.16, 0.11 and 0.11, respectively (p < 0.001, power = 1.0).

Table 3. Baseline TP₀₀ (s.d.) values and retention percentage upon exposure to coffee (C), wine (W) and aging (A) for T0-T1, T0-T2 and T1-T2 interval comparisons.

Material	C	W	A
CS	12(0.4)/100.5/96.9/96.4	12.4(0.4)/98.9/98.7/99.8	12.3(0.3)/99.3/97.6/98.3
IE	11.6(0.6)/97.9/98.5/100.6	11.5(0.2)/101.0/98.7/97.7	11.9(0.8)/97.6/97.9/100.3
LU	13.2(0.2)/93.5/90.4/96.7	13.3(0.6)/95.3/93.8/98.4	13(0.2)/98.7/98.1/99.4
SH	13.5(0.2)/94.2/91.1/96.7	13.6(0.5)/95.8/94.7/98.9	13.3(0.3)/97.5/97.0/99.5
VE	8.7(0.2)/93.8/89.6/95.5	8.5(0.1)/93.6/91.1/97.4	9.2(0.1)/99.9/99.3/99.4
VS	11.4(0.6)/96.6/95.2/98.6	11.5(0.7)/96.8/97.7/100.0	11.8(1.3)/96.6/97.5/100.9

SH showed the highest TP₀₀ followed by LU > CS > IE = VS > VE. For all time intervals (T0-T1, T0-T2 and T1-T2), the lowest TP₀₀ retention was observed with C. W and A presented similar values.

Figure 1 presents the comparison between corresponding TP_ab and TP₀₀ values, the coefficient of determination (R²), and an equation to calculate TP₀₀ values based on known TP_ab values.

Figure 1.

Scatterplot of TP_ab and TP₀₀ values to generate R²-value and equation.

The results of t test for TP₀₀ from laboratory and chairside polished specimens showed no significant difference between them (p-value = 0.67). A comparison between the corresponding TP₀₀ and TP_ab values, the coefficient of determination (R²), and an equation to calculate TP₀₀ values based on known TP_ab values are presented in Figure 1. The opposite equation, to calculate TP_ab values based on known TP₀₀, was as follows: TP_ab = 1.1 TP₀₀ + 2.8 (R² = 0.97).

Discussion

The instability of color and translucency can affect the esthetics of a restoration, and depending on the severity may lead to the need of its replacement (26). Restorations involving high chroma dental remnant and endodontic posts are very challenging regarding translucency of restorative material. In such cases, high translucent materials are not acceptable because they cannot mask the background properly. The higher the TP value, the more translucent the material becomes. Therefore, lower TP stands for decreased translucency of the same material after staining and aging, or lower translucency between different materials.

It was observed that Shofu HC presented the highest TP₀₀, followed by Lava Ultimate and Cerasmart, respectively. IPS Emax and Vita Suprinity showed intermediate values, while Vita Enamic presented the lowest TP₀₀ values. Higher TP values were reported for RNC materials, such as Shofu HC, Lava Ultimate and Cerasmart, compared to other materials (27-29). Conversely, similar TP values between RNC and PICN have been reported (11). It can be hypothesized that similar refractive index between the inorganic filler and the organic phase in RNC contributes to this result. The grain size, chemical composition, crystalline structure and internal flaws have been related to TP change of dental ceramics (6, 30). Zircon dioxide reinforced glass ceramics presents 4 to 8 times smaller grain size compared to lithium disilicate ceramics (7).

Coffee provoked the greatest TP changes, followed by red wine and artificial aging, which showed to be alike. It was reported that yellow stain molecules with low polarity present in coffee are attracted by the polymer network leading to greater color changes (31) and that coffee and wine affect translucency and color significantly (12, 32). The TP₀₀ mean values and TP₀₀ retention decreased from T0-T1 to T0-T2. Therefore, the null hypothesis that there were no differences in TP among materials, caused by different intervals of immersion in staining solutions and exposure to artificial aging was rejected.

The t-test comparison results showed no difference between TP₀₀ of laboratory and chairside polished specimens. This is in agreement with previous studies which showed similar TP values with different finishing and polishing protocols for the same material (27, 28). Since digital workflow from 3D scanning to chairside polishing has been implemented in office routine, we only presented the data on chairside polished specimens. Additionally, since a high correlation was observed between the values obtained by TP₀₀ and TP_ab formulas, conversion equations between them were presented in order to allow the comparison of the results of studies using only 1 of these formulas.

The clinical visual evaluation of differences in translucency is complex and difficult (33). The implementation of visual thresholds facilitated the evaluation of color and translucency, contributing to the follow-up of restorations and quality control of materials (34). Although the statistical analysis had shown significant differences among staining solutions and aging, the baseline ΔTP₀₀ among them were graded as excellent match (below 50:50% perceptibility threshold, 0.6), except the comparison between red wine and artificial aging for Vita Enamic (ΔTP₀₀ = 0.7) which was graded as an acceptable match, still below the 50:50% TP acceptability threshold, 2.6 (25). The ΔTP₀₀ graded as excellent match was observed for comparisons between coffee and red wine (0.0 to 0.5) for all time intervals. For the comparisons between red wine and artificial aging, excellent match was observed for all ΔTP₀₀ except for VE (0.7) at T0-T2 interval, which was graded as acceptable match. For the comparisons between coffee and artificial aging, excellent match was noticed, except for LU (0.7 and 1.0) at T0-T1 and T0-T2, respectively, for SH (0.8) and VE (0.8) at T0-T2 interval. The comparisons between time intervals showed acceptable match for LU (0.8), SH (0.7) and VE (0.8) stained with red wine for T0-T2 interval, for LU (0.9 and 1.3) and SH (0.8 and 1.2) stained with coffee for T0-T1 and T0-T2 intervals, respectively. The ΔTP₀₀ graded as acceptable match was also recorded for VE (0.9) for T0-T2 interval. Excellent match was observed for all other experimental conditions.

The continued exposure to staining and aging imposed in this in vitro study was harsher than in mouth in vivo challenge. Moreover, in the present study, both surfaces of specimens were exposed to staining and aging, which might have increased the ΔTP. However, in vitro comparisons among materials under the same test conditions can provide results to guide material selection. Intraorally, staining and aging of restorations can be further associated with oral hygiene, smoking and tooth whitening. Further research combining previously mentioned factors and repolishing of material surface should be considered, despite the fact that complex combinations mimicking in vivo scenario hinder information of isolated variables.

Conclusions

Limited by the findings of this study, the following conclusions were made: Translucency Parameter (TP) was a time and staining/aging-dependent material; Shofu HC exhibited the highest TP, followed by Lava Ultimate and Cerasmart, respectively. Lower values were recorded for IPS Emax, Vita Suprinity and Vita Enamic; Coffee caused the greatest decrease in TP, followed by wine and aging, which showed similar effects. Staining and artificial aging-dependent changes in TP were increased with the increase of exposure; No difference in TP was found between laboratory and chairside polished specimens. TP₀₀ and TP_ab values were highly correlated.