Abstract
Objectives
The purposes of this study were to evaluate color shifting at the boader of resin composite restorations after placement in human tooth cavities in vitro.
Methods
Twenty extracted human premolars with an A2 shade were used in this study. Cylindrical shaped cavities (3.0 mm or 1.5 mm depth; 2.0 mm diameter) were prepared in the center of the crowns. One of four resin composites of A2 shade (Clearfil AP-X, AP; Clearfil Majesty, MA; Tetric N Ceram, TNC; Ceram X mono, CX) was placed in the cavity, and the color was measured at four points (0.4 mm × 0.4 mm) on the restored teeth (area 1: tooth area 1.0 mm away from the border of resin composite restoration; area 2: tooth border area 0.3 mm away from margin of resin composite restoration; area 3: resin composite border area 0.3 mm away from margin of resin composite restoration; area 4: resin composite area at the center of resin composite restoration) using a spectrophotometer (Crystaleye). The color of each area was determined according to the CIELAB color scale. Color differences (Δ E *) between the areas of 1 and 2, 2 and 3, 3 and 4, and 1 and 4 were calculated, and also the ratio of Δ E *23 to Δ E *14 as a parameter of the color shifting at the border of resin composite restoration, was determined. The data were statistically analyzed using two-way ANOVA, and Dunnett’s T3 and t -test for the post hoc test.
Results
For all materials, the Δ*23 were significantly lower than Δ E *14, in which Δ E *23 were significantly influenced by the materials although there were no significant differences in the Δ E *14 between the materials. Additionally, Δ E *12 were significantly higher than Δ E *34. For the 3.0 mm cavity depth group, the lowest Δ E *23/14 ratio was seen in CX = MJ < TNC < AP. For the 1.5 mm cavity depth group, TNC dramatically reduced the Δ E *23/14 ratio, and the lowest ratio was seen in TNC = CX < MJ < AP.
Significance
All resin composite restorations in the tooth cavities produced the color shifting of resin composite and tooth at the border. For deep cavity, resin composites with higher diffused light transmission property showed higher color shifting at the border, while for shallow cavity, the straight-line as well as diffused light transmission of resin composite affected the color shifting at the border. Clinically, diffused light transmission property of resin composites may contribute to the color shifting at the border of resin composite restoration regardless of cavity depth, resulting in better color matching.
1
Introduction
Light-cured resin composites are widely used with the direct filling technique for esthetic restoration of anterior and posterior teeth. The color rendition of resin composite restorations is influenced and perceived by several factors; color (hue, value and chroma) and the optical properties (translucency, opalescence, straight-line and diffusion light transmission characteristics) of resin composite, texture and luster of the surface, cavity size and location . The light transmission characteristics of resin composites are significant factor in their color appearances . In addition, the translucency of resin composites would affect color matching of resin composite restoration .
However, the problem of color matching resin composite to the surrounding tooth is still remained. It is difficult to accurately match the color because of the limited color variations of resin composites and because tooth color is influenced by the type of tooth, the site and its age . On the other hand, it has been clinically observed that the perceived color difference between tooth and resin composites is less than would be expected from viewing the colors in isolation, even though their color matching is not perfect . This phenomenon is often called the ‘chameleon effect’ among dental manufacturers and professionals. This ‘chameleon effect’ phenomenon is thought to be caused by the color shifting of resin composite, resulting from the color reflection from surrounding tooth.
Discovering the mechanisms of the color shifting of resin composites toward the color of the surrounding tooth would improve the esthetics of resin composite restorations and simplify shade matching through a reduction in the number of the shades . Paravina et al. evaluated the color change of resin composites when placed in a mold made of another color of resin composite which mimicked dental hard tissue. They indicated that the color shifting effect increases with an increase in the translucency parameter, and with a reduction in the size of restoration and the initial color difference between the inner and outer resin composites moreover, it was dependent upon the kind of resin composite and its’ shade . However, there is no published research on the color shifting at the border of resin composite restoration in tooth cavity when placed in cavities of human teeth.
Recently, dental color measuring devices using digital imaging have been introduced, which can measure the color of teeth and esthetic materials in the oral environment . Crystaleye (OLYMPUS, Tokyo, Japan) is a dental spectrophotometer, which can capture a digital image of a specimen using 7 LEDs as an illumination source without contacting an object, and transfer the spectral data to a personal computer and analyze the color of a randomly selected small area (2.0 mm × 2.0 mm to 0.4 mm × 0.4 mm) using the CIELAB system . The purpose of this study was to investigate the ‘chameleon effect’ on the color appearance of resin composite restorations in human tooth cavity. The color differences (Δ E *) between four small areas (resin composite, tooth, composite-border and tooth-border areas) on restored human teeth, which were placed with four resin composite in different depth cavities, were measured using Crystaleye and the color shifting at the boarder of resin composite restorations was evaluated. The null hypotheses tested were that the kind of resin composite and the cavity depth does not affect the color shifting of resin composite restoration in cavities of human teeth.
2
Materials and methods
In this study, the following four commercial resin composites of A2 shade were used: Clearfil AP-X (AP; Kuraray Medical Inc., Tokyo, Japan), Tetric N Ceram (TNC; Ivoclar Vivadent, Amherst, NY, USA), Clearfil Majesty (MA; Kuraray Medical Inc.), and Ceram X mono (CX; Dentsply Caulk, Milford, DE, USA) ( Table 1 ).
| Materials | Composition | Manufacturer | Batch number |
|---|---|---|---|
| Cleafil AP-X | Filler: 85 wt% (71 vol%) silicated barium glass filler of 0.7 μm and | Kuraray Medical (Tokyo, Japan) | 00994A |
| Silicated silica filler of 0.1–1.5 μm | |||
| Base resin: Bis-GMA, TEGDMA | |||
| Clearfil Majesty | Filler: 78 wt% (66 vol%) silicated barium glass filler of 0.7 μm and | Kuraray Medical (Tokyo, Japan) | 00048A |
| Pre-polymerized organic filler of 100 μm | |||
| Base resin: Bis-GMA, hydrophobic dimethacrylate | |||
| Tetric N Ceram | Filler: 57 wt% (81 vol%) Ba–Al silicate glass filler of 0.4–0.7 μm and | Ivoclar Vivadent (Amherst, NY, USA) | L58657 |
| Ytterbium fluoride of 0.2 μm and spheriod mixed oxide of 0.12–0.16 μm | |||
| Base resin: Bis-GMA, Bis-EMA, triethyleneglycole | |||
| Ceram X mono | Filler: 76 wt% (57 vol%) inorganically glass filler of 1.3 μm and | Dentsply Caulk (Milford, DE, USA) | 810001496 |
| Metacryl acid modified nanofiller of 10 nm and | |||
| Organically modified ceramic of 2–3 nm | |||
| Base resin: dimethacrylate | |||
2.1
Specimen preparation
Extracted human maxillary premolars without endodontic treatment or restorations, stored at 4 °C water, were used in this study, according to a protocol approved by the Human Research Ethics Committee, Tokyo Medical and Dental University, Japan. Twenty teeth of A2 shade were selected by measuring their colors using a dental spectrophotometer (Crystaleye, OLYMPUS, Tokyo, Japan). In order to evaluate the effect of back ground color of tooth on color appearance, cylindrical shaped cavities (1.5 mm or 3.0 mm depth; 2.0 mm diameter) were prepared in the center of the crowns by using cylindrical diamond bar (#D11, ISO 108 010, GC, Tokyo, Japan) which was marked at 1.5 mm or 3.0 mm from the top of the bar.
One of four resin composites was randomly selected and placed in each cavity without the application of any adhesive system. After photo-polymerization for 60 s using a light-curing unit (XL3000, 3M ESPE, St. Paul, MN, USA) with a light output >600 mW/cm 2 , the resin composite restorations were finished and polished using silicon carbide disks with mild hand pressure.
2.2
Color measurement of restored tooth
After storage at 37 °C in water 24 h, the colors were measured at four points (0.4 mm × 0.4 mm) on the restored teeth (area 1: tooth area 1.0 mm away from the border of resin composite restoration; area 2: tooth border area 0.3 mm away from the restoration margin; area 3: resin composite border area 0.3 mm away from the restoration margin; area 4: resin composite area at the center of resin composite restoration) using a spectrophotometer (Crystaleye) ( Fig. 1 ). In order to closely measure the color value at the border of resin composites and tooth without crossing over, the center of the measurement area (0.4 mm × 0.4 mm) was necessary to be at least 0.3 mm away from the margin.
Crystaleye uses seven LEDs (Light Emitting Diode) as an illumination source with 45°/0° geometry . The Crystaleye was positioned to capture the tooth image. Prior to data acquisition, the instrument was calibrated using a calibration plate (OLYMPUS Inc.). The capture time was 0.2 s. The spectral data from the tooth were acquired from the captured image of the tooth. The reflectance values from 400 to 700 nm with 1 nm intervals for each pixel were transferred from the spectrophotometer to a personal computer (Endavor NJ 2000; EPSON, Nagano, Japan) and also were converted into CIELAB (Commission Internationale de l’Eclarirage) color coordinates L * (differences in lightness), a * (green-red coordinate) and b * (blue-yellow coordinate).
After color measurement of the restored tooth with one of four resin composites, the resin composite was removed carefully using a superfine diamond bar, and then another resin composite selected at random, was re-filled, the color measured, and removed repeatedly for each tooth as previous mentioned. The Δ E * values [Δ E * = (Δ L *2 + Δ a *2 + Δ b *2 ) (1/2) ] were calculated as color differences in between two different areas (1 and 2, 2 and 3, 3 and 4, and 1 and 4), and ratio of <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE23∗’>ΔE∗23ΔE23∗
Δ E 23 ∗
to <SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE14∗’>ΔE∗14ΔE14∗
Δ E 14 ∗
was also determined.
2.3
Statistical analysis
The data of <SPAN role=presentation tabIndex=0 id=MathJax-Element-3-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE12∗’>ΔE∗12ΔE12∗
Δ E 12 ∗
, <SPAN role=presentation tabIndex=0 id=MathJax-Element-4-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE23∗’>ΔE∗23ΔE23∗
Δ E 23 ∗
, <SPAN role=presentation tabIndex=0 id=MathJax-Element-5-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE34∗’>ΔE∗34ΔE34∗
Δ E 34 ∗
, <SPAN role=presentation tabIndex=0 id=MathJax-Element-6-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE14∗’>ΔE∗14ΔE14∗
Δ E 14 ∗
, and <SPAN role=presentation tabIndex=0 id=MathJax-Element-7-Frame class=MathJax style="POSITION: relative" data-mathml='ΔE23∗/ΔE14∗’>ΔE∗23/ΔE∗14ΔE23∗/ΔE14∗
Δ E 23 ∗ / Δ E 14 ∗
obtained in this study were analyzed by two-way ANOVA (materials and depth) and Dunnett’s T3 for post hoc multiple comparisons between the investigated materials. The data were also analyzed using a t -test to compare statistical differences between the cavity depth groups. All statistical procedures were performed at the confidence level of 95% using the Statistical Package for the Medical Science (SPSS Ver.11 for Windows).
2
Materials and methods
In this study, the following four commercial resin composites of A2 shade were used: Clearfil AP-X (AP; Kuraray Medical Inc., Tokyo, Japan), Tetric N Ceram (TNC; Ivoclar Vivadent, Amherst, NY, USA), Clearfil Majesty (MA; Kuraray Medical Inc.), and Ceram X mono (CX; Dentsply Caulk, Milford, DE, USA) ( Table 1 ).
| Materials | Composition | Manufacturer | Batch number |
|---|---|---|---|
| Cleafil AP-X | Filler: 85 wt% (71 vol%) silicated barium glass filler of 0.7 μm and | Kuraray Medical (Tokyo, Japan) | 00994A |
| Silicated silica filler of 0.1–1.5 μm | |||
| Base resin: Bis-GMA, TEGDMA | |||
| Clearfil Majesty | Filler: 78 wt% (66 vol%) silicated barium glass filler of 0.7 μm and | Kuraray Medical (Tokyo, Japan) | 00048A |
| Pre-polymerized organic filler of 100 μm | |||
| Base resin: Bis-GMA, hydrophobic dimethacrylate | |||
| Tetric N Ceram | Filler: 57 wt% (81 vol%) Ba–Al silicate glass filler of 0.4–0.7 μm and | Ivoclar Vivadent (Amherst, NY, USA) | L58657 |
| Ytterbium fluoride of 0.2 μm and spheriod mixed oxide of 0.12–0.16 μm | |||
| Base resin: Bis-GMA, Bis-EMA, triethyleneglycole | |||
| Ceram X mono | Filler: 76 wt% (57 vol%) inorganically glass filler of 1.3 μm and | Dentsply Caulk (Milford, DE, USA) | 810001496 |
| Metacryl acid modified nanofiller of 10 nm and | |||
| Organically modified ceramic of 2–3 nm | |||
| Base resin: dimethacrylate | |||
2.1
Specimen preparation
Extracted human maxillary premolars without endodontic treatment or restorations, stored at 4 °C water, were used in this study, according to a protocol approved by the Human Research Ethics Committee, Tokyo Medical and Dental University, Japan. Twenty teeth of A2 shade were selected by measuring their colors using a dental spectrophotometer (Crystaleye, OLYMPUS, Tokyo, Japan). In order to evaluate the effect of back ground color of tooth on color appearance, cylindrical shaped cavities (1.5 mm or 3.0 mm depth; 2.0 mm diameter) were prepared in the center of the crowns by using cylindrical diamond bar (#D11, ISO 108 010, GC, Tokyo, Japan) which was marked at 1.5 mm or 3.0 mm from the top of the bar.
One of four resin composites was randomly selected and placed in each cavity without the application of any adhesive system. After photo-polymerization for 60 s using a light-curing unit (XL3000, 3M ESPE, St. Paul, MN, USA) with a light output >600 mW/cm 2 , the resin composite restorations were finished and polished using silicon carbide disks with mild hand pressure.
2.2
Color measurement of restored tooth
After storage at 37 °C in water 24 h, the colors were measured at four points (0.4 mm × 0.4 mm) on the restored teeth (area 1: tooth area 1.0 mm away from the border of resin composite restoration; area 2: tooth border area 0.3 mm away from the restoration margin; area 3: resin composite border area 0.3 mm away from the restoration margin; area 4: resin composite area at the center of resin composite restoration) using a spectrophotometer (Crystaleye) ( Fig. 1 ). In order to closely measure the color value at the border of resin composites and tooth without crossing over, the center of the measurement area (0.4 mm × 0.4 mm) was necessary to be at least 0.3 mm away from the margin.
Crystaleye uses seven LEDs (Light Emitting Diode) as an illumination source with 45°/0° geometry . The Crystaleye was positioned to capture the tooth image. Prior to data acquisition, the instrument was calibrated using a calibration plate (OLYMPUS Inc.). The capture time was 0.2 s. The spectral data from the tooth were acquired from the captured image of the tooth. The reflectance values from 400 to 700 nm with 1 nm intervals for each pixel were transferred from the spectrophotometer to a personal computer (Endavor NJ 2000; EPSON, Nagano, Japan) and also were converted into CIELAB (Commission Internationale de l’Eclarirage) color coordinates L * (differences in lightness), a * (green-red coordinate) and b * (blue-yellow coordinate).
After color measurement of the restored tooth with one of four resin composites, the resin composite was removed carefully using a superfine diamond bar, and then another resin composite selected at random, was re-filled, the color measured, and removed repeatedly for each tooth as previous mentioned. The Δ E * values [Δ E * = (Δ L *2 + Δ a *2 + Δ b *2 ) (1/2) ] were calculated as color differences in between two different areas (1 and 2, 2 and 3, 3 and 4, and 1 and 4), and ratio of ΔE∗23
Δ E 23 ∗
to ΔE∗14
Δ E 14 ∗
was also determined.
2.3
Statistical analysis
The data of ΔE∗12
Δ E 12 ∗
, ΔE∗23
Δ E 23 ∗
, ΔE∗34
Δ E 34 ∗
, ΔE∗14
Δ E 14 ∗
, and ΔE∗23/ΔE∗14
Δ E 23 ∗ / Δ E 14 ∗
obtained in this study were analyzed by two-way ANOVA (materials and depth) and Dunnett’s T3 for post hoc multiple comparisons between the investigated materials. The data were also analyzed using a t -test to compare statistical differences between the cavity depth groups. All statistical procedures were performed at the confidence level of 95% using the Statistical Package for the Medical Science (SPSS Ver.11 for Windows).
3
Results
The result of ΔE∗12
Δ E 12 ∗
, ΔE∗23
Δ E 23 ∗
, ΔE∗34
Δ E 34 ∗
, ΔE∗14
Δ E 14 ∗
of the 3.0 mm and 1.5 mm cavity depth groups are shown in Figs. 2–5 . Two-way ANOVA revealed that the value of ΔE∗23
Δ E 23 ∗
(the color difference between resin composites and tooth at the border) was significantly affected by materials ( p < 0.001) and cavity depth ( p < 0.001). There were significant interactions between the materials and cavity depth for the value of ΔE∗23
Δ E 23 ∗
( p = 0.001). On the other hand ΔE∗12
Δ E 12 ∗
(the color change of tooth), ΔE∗34
Δ E 34 ∗
(the color change of resin composites) and ΔE∗14
Δ E 14 ∗
(the color difference between resin composites and tooth) were not significantly affected by materials ( p = 0.104, p = 0.457 and p = 0.167, respectively) and cavity depth ( p = 0.108, p = 0.119 and p = 0.10, respectively).
