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The effect of tooth age on colour adjustment potential of resin composite restorations

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A. Tanaka a, M. Nakajima a,*, N. Seki b, R.M. Foxton c, J. Tagami a,d a Cariology and Operative Dentistry, Oral Restitution Department, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-4-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan b Dental Education Development Section, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-4-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan c Division of Conservative Dentistry, King’s College London Dental Institute at Guy’s, King’s and St Thomas’ Hospitals, King’s College London, London Bridge, London SE1-9RT, UK d Global Center of Excellence (GCOE) Program; International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo Medical and Dental University, 1-4-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan

article info

abstract

Article history:

Objectives: The purpose of this study was to investigate the effect of tooth age on colour adjustment

Received 23 January 2014

potential of resin composite restorations in human teeth.

Received in revised form

Methods: Twenty extracted human premolars with an A2 shade, extracted for orthodontic reasons from

6 August 2014 Accepted 11 September 2014 Available online xxx Keywords: Tooth age Colour shifting Colour adjustment Colour of resin composite Light transmission characteristics

younger patients(20–28 yrs) (younger teeth) and periodontal reasons from older patients(45–69 yrs) (older teeth), were used in this study. Cylindrical shaped cavities (3.0 mm depth; 2.0 mm diameter) were prepared in the centre of the crowns on the buccal surface. One of four resin composites of A2 shade (Kalore, KA; Solare, SO; Clearfil Majesty, MJ; Beautifil II, BF) was placed in the cavity, and the colour was measured at four areas (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 centre of resin composite restoration) using a spectrophotometer (Crystaleye). The colour of each area was determined according to the CIELAB colour scale. Colour differences (DE*) between the areas of 1 and 2, 2 and 3, 3 and 4 and 1 and 4 were calculated, and also the ratio of DE*area 2–3 to DE*area 1–4 (DE*area 2–3/1–4), DE*area 3–4 to DE*area 1–4 (DE*area 3–4/1–4) and DE*area 1–2 to DE*area 1–4 (DE*area 1–2/1–4) as a parameter of the colour shift in resin composite restoration, were determined. Moreover, the light transmission characteristics of the resin materials and dentine discs from the younger and older teeth were measured using a goniophotometer. The data were statistically analyzed using two-way ANOVA, and Dunnett’s T3 and t-test for the post hoc test.

Results: DE*area 2–3 (colour difference between resin composite and tooth at the border) and DE*area 1–4 (colour difference between resin composite and tooth) of the older teeth groups were significantly larger than those of younger teeth groups (p < 0.05). The DE*area 2–3/1–4 (mis-match rate in colour shifting at the border) of the older teeth groups was larger than that of the younger teeth groups (p < 0.05). DE*area 3–4/1–4 (colour shifting rate of resin composite side) was significantly larger in older teeth than younger teeth (p < 0.05), while DE*area 1–2/1–4 (colour shifting rate of tooth side), was significantly smaller in older teeth than younger teeth (p < 0.05). In each tooth group, there were no significant differences in DE*area 2–3, DE*area 1–4, DE*area 2–3/1–4, DE*area 3–4/1–4 and DE*area 1–2/1–4 between the materials (p > 0.05). Analysis of the light transmission properties indicated that older dentine transmitted more light, while younger dentine exhibited greater light diffusion and transmitted less light.

Conclusions: The colour shifting effects at the border of the resin composite restorations were influenced by the age of the tooth. This behaviour might be influenced by the light transmission characteristics of dentine in restored teeth.

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Clinical significance: The potential for colour adjustment of resin composite restorations may be less in older teeth than younger teeth.

# 2014 Published by Elsevier Ltd.

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19 * Corresponding author. Tel.: +81 3 5803 5483; fax: +81 3 5803 0195. E-mail address: [email protected] (M. Nakajima). http://dx.doi.org/10.1016/j.jdent.2014.09.007 0300-5712/# 2014 Published by Elsevier Ltd.

Please cite this article in press as: Tanaka A, et al. The effect of tooth age on colour adjustment potential of resin composite restorations. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.09.007

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1.

Introduction

Direct resin composite restorations are widely used because of their superior adhesion to tooth substrates, excellent aesthetics, acceptable longevity, and relatively low cost. However, the problem of colour matching resin composite to the surrounding tooth still remains. It is difficult to accurately match the colour of restorative materials with limited colour shades to teeth because tooth colour is influenced by tooth type, site and age.1–3 Clinicians, researchers and manufacturers face the challenge of colour matching a synthetic restorative material to a natural living tooth. The colour appearance of resin composite is influenced and perceived by various factors: their colour (hue, value and chroma) and optical properties (translucency, opalescence, straight-line and diffusion light transmission characteristics).4–7 It is well known that translucent materials can reflect a colour from the surrounding substrate, leading to shifting of the colour. Actually, the perceived colour difference between resin composite and surrounding tooth is less than would be expected from viewing the colours in isolation, even though their colour matching is not perfect.8–10 This colour shifting effect at the border of resin composite restoration is often called the ‘chameleon effect’ among dental manufacturers and professionals. Discovering the mechanisms of the colour shifting of resin composites towards the colour of the surrounding tooth would improve the aesthetics of resin composite restorations and simplify shade matching through a reduction in the number of the shades.10–12 Paravina et al.10–12 evaluated the colour adjustment potential of resin composites when placed in a mould made of another colour of resin composite which mimicked dental hard tissue. It was found that the colour shifting effect increases with an increase in the translucency parameters, and with a reduction in the size of restoration and the initial colour difference between the inner and outer resin composites. Tsubone et al.13 also evaluated the colour shifting effect of resin composite restorations in human tooth cavities. They

revealed that the colour shifting at the border of resin composite restorations was caused on the tooth side as well as on the resin composite side, in which the colour shifting effect of the tooth side was larger than that of resin composite side. Physiological ageing processes affect the morphological and optical characteristics of the tooth. It is well known that teeth are light in young people, but become yellow and darker with age, raising aesthetic concerns.14–16 Moreover, ageing results in a transparent layer in dentine, which is due to thickening of the peritubular dentine and occlusion of the dentinal tubules by mineral deposition.17–19 Changes in the light transmission characteristics of dentine might affect the colour matching and colour shifting of resin composite restorations in human teeth. However, there are few published articles on how changes in the optical properties of dentine with age affect the colour matching of resin composite restorations in human teeth.20–24 Therefore, the purpose of this study was to investigate the effect of tooth ageing on the colour adjustment potential of resin composite restorations in human teeth. The null hypothesis tested was that the age of the tooth does not affect the colour adjustment potential of resin composite restorations in human tooth cavities.

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Materials and methods

In this study, the following four commercial resin composites in shade A2 were used: Kalore (KA; GC America Inc., Alsip, USA), Solare (SO; GC, Tokyo, Japan), Clearfil Majesty (MJ; Kuraray Noritake Dental Inc., Tokyo, Japan), and Beautifil II (BF; Shofu Dental Corp., Kyoto, Japan) (Table 1).

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Specimen preparation

Human premolars, extracted for orthodontic reasons from younger (20–28 yrs) (younger teeth) and periodontal reasons from older (45–69 yrs) patients (older teeth), stored at 4 8C water, were used in this study, according to a protocol

Table 1 – Resin composite materials used in this study. Composition

Manufacturer batch number

Kalore (A2)

Filler: 82 wt% (71 vol%) 30–35 wt% pre-polymerized filler, 20–30 wt% fluoroaluminosilicate glass, 20–33% wt%, 1–5 wt% silicon dioxide nanofiller Base resin: UDMA, DX-511

GC America Inc., 10111021 Alsip, USA GC Inc., 1102171 Tokyo, Japan

Solare (A2)

Filler: 73 wt% (64 vol%) pre-polymerized filler of 16 mm, silica glass of 0.85 mm, fumed silica of 16 mm Base resin: UDMA, DX-511

Clearfil Majesty (A2)

Filler: 78 wt% (66 vol%) silanated barium glass filler, pre-polymerized organic filler Micro filler (glass filler): mean 1.5 mm Nano filler: mean 20 nm Base resin: Bis-GMA, TEGDMA, hydrophobic aromatic dimethacrylate

Kuraray Noritake 00081 A Dental Inc. Tokyo, Japan

Beautifil II (A2)

Filler: 83.3 wt% (68.6 vol%) multi-functional glass and S-PRG filler based on fluoroboraluminosilicate glass Particle size range: 0.01–4.0 mm (mean 0.8 mm) Base resin: Bis-GMA, TEGDMA

Shofu, 031120 Kyoto, Japan

Material

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approved by the Human Research Ethics Committee, Tokyo Medical and Dental University, Japan (No. 725). A dental spectrophotometer (Crystaleye, OLYMPUS, Tokyo, Japan) was used for colour measurements and selection of twenty shade A2 teeth (ten younger teeth and ten older teeth). Crystaleye uses seven LEDs (Light Emitting Diode) as an illumination source with 45/0-degree geometry.25 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 teeth were acquired from the captured images of the teeth. 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 converted into CIELAB (Commission Internationale de l’Eclarirage) colour coordinates L (differences in lightness), a (green-red coordinate), b (blue-yellow coordinate) and also VITAPAN classical shade.26–28 In order to evaluate the colour adjustment potential of resin composite restorations, cylindrical shaped cavities (3.0 mm depth; 2.0 mm diameter) were prepared in the centre of the crowns on the buccal surface using a cylindrical diamond bur (#D11, ISO 108 010, GC, Tokyo, Japan), which was marked at 3.0 mm from the top of the bur. One of four resin composites was randomly selected and placed using a bulk filling technique in each cavity without the application of any adhesive system in order to easily remove the filled resin composite from the cavity.13 After photopolymerization for 60 s using a light-curing unit (XL3000, 3M ESPE, St. Paul, MN, USA) with a light output >600 mW/cm2, the resin composite restorations were finished and polished using silicon carbide disks with mild hand pressure.

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After storage at 37 8C in 100% relative humidity for 24 h, the colours were measured at four areas (0.4 mm  0.4 mm) on the restored teeth (area 1: tooth area 1.0 mm away from the border of the resin composite restorations; 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 centre of resin composite restoration) using a spectrophotometer (Crystaleye) (Fig. 1). In order to closely measure the colour value at the resin composite-tooth border without crossing over, it was necessary for the centre of the measurement area (0.4 mm  0.4 mm) to be at least 0.3 mm away from the margin.13 After colour measurement of the restored tooth with one of four resin composites, the resin composite was carefully removed using a superfine diamond bur. A different randomly selected resin composite was placed in the cylindrical shaped cavity, and the colour was measured. This process was repeated for each tooth until each of the four resin composites were measured.13 The DE values [DE = (DL2 + Da2 + Db2)½] were calculated as colour differences in between two different areas (1 and 2, 2 and 3, 3 and 4 and 1 and 4) and ratios of DE*area 2–3 to DE*area1–4, DE*area3–4 to DE*area1–4 and DE*area1–2 to DE*area1–4 were also determined.

Colour measurement of restored teeth

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Fig. 1 – The colour measurement areas (0.4 mm T 0.4 mm) on the restored tooth: area 1: tooth area of 1.0 mm away from the border of resin composite restoration; area 2: tooth boarder area of 0.3 mm away from margin of resin composite restoration; area 3: resin composite border area of 0.3 mm away from margin of resin composite restoration; area 4: resin composite area of the centre of resin composite restoration.

2.3. Measurements of light transmission characteristics of resin composite and dentine

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Resin composite discs (6.0 mm in diameter) were made and covered with celluloid strips on glass plates, which were separated by 0.5 mm thick spacers. After light curing for 60 s from the top and bottom sides, the strips and glass plates were removed. Five discs were prepared for each material. All the specimens were stored at 37 8C in 100% relative humidity for 24 h before measurement of light transmission characteristics. From additional younger and older human premolars, ten 0.5 mm-thick dentine slabs each were prepared from the coronal labial region using a low speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under water-cooling. Both surfaces were polished with diamond pastes down to 1/4 mm particle size. For each resin composite and dentine specimen, the twodimensional distribution graph of transmitted light intensity (incidence angle: 08, measurement range: 908 to +908) was obtained using a goniophotometer (Model GP-200, Murakami Color Research laboratory, Tokyo, Japan) under regulated conditions (sensitivity: 950; volume: 580). KA and SO specimens were measured using double neutral density filters (ND-10; Transmittance 10% and ND-50; Transmittance 50%, Murakami Color Research laboratory, Tokyo, Japan), while MJ, BF and dentine specimens were measured without filter. The light beams converge onto a pin hole through a condenser lens and are converted into a parallel beam through the collimator lens. These light beams reach the specimen plane through the beam iris. The light transmitted from the specimen plane is fed to receptor via a telescope lens and receiving iris. The light transmission and diffusion properties of a specimen can be obtained by measuring the light intensity. Using the distribution graph, the straight-line light transmission property was calculated from the peak gain at 08 angle (G0), and the

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transmitted light diffusion property was calculated as the diffusion factor (DF) using the following formula: Diffusion factor(%) = {(B708 + B208)/2} B58100 The total area of the graph was calculated as the whole amount of transmitted light (Area) with image J software (image J 1.47 for Windows).

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The colour data were analyzed by two-way ANOVA (materials and teeth) with Dunnett’s T3 and t-test for post hoc test. The light transmission characteristics data were analyzed by t-test (teeth) and by one-way ANOVA with Dunnett’s T3 for post hoc multiple comparisons test (resin materials). All statistical procedures were performed at a confidence level of 95% using the Statistical Package for the Medical Science (SPSS Ver.11 for Windows).

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The results of DE*area 1–4 (colour difference between resin composite and tooth) and DE*area 2–3 (colour difference between resin composite and tooth at the border) of the younger and older tooth groups are shown in Figs. 2 and 3. Two-way ANOVA revealed that DE*area 1–4 and DE*area 2–3 were significantly affected by age of tooth (DE*area 1–4: p < 0.001; DE*area 2–3: p = 0.002), while not significantly affected by materials (DE*area 1–4: p = 0.401; DE*area 2–3: p = 0.215). There were no significant interactions in DE*area 1–4 and DE*area 2–3 between age of tooth and materials (DE*area 1–4: p = 0.678; DE*area 2–3: p = 0.210). For all the materials except for SO, the older teeth exhibited significantly higher DE*area 1–4 and DE*area 2–3 values than the younger teeth. Regardless of the materials and age, DE*area 2–3 was significantly lower than DE*area 1–4 ( p < 0.05). The results of the ratios of DE*area 2–3 to DE*area 1–4 (DE*area 2–3/ 1–4; mis-match rate in colour shifting at the border), DE*area 3–4

Statistical analysis

Result

Fig. 2 – The DE*area 1–4 values (colour differences between the area of 1 and 4) in younger and older tooth groups of all materials (KA: Kalore, SO: Solare, MJ: Clearfil Majesty, BF: ) indicates significant differences Beautifil II). The line ( in each material between younger and older teeth (p < 0.05). There were no significant different in each tooth group between the materials (p > 0.05) (N = 10).

Fig. 3 – The DE*area 2–3 values (colour differences between the area of 2 and 3) in younger and older tooth. (KA: Kalore, SO: Solare, MJ: Clearfil Majesty, BF: Beautifil II). The line ) indicates significant differences in each material ( between younger and older tooth (p < 0.05). There were no significant different in each tooth group between the materials (p > 0.05) (N = 10).

to DE*area 1–4 (DE*area 3–4/1–4; colour shifting rate of resin composite side) and DE*area 1–2 to DE*area 1–4 (DE*area 1–2/1–4; colour shifting rate of tooth side) are depicted in Figs. 4–7. DE*area 2–3/1–4, DE*area 3–4/1–4 and DE*area 1–2/1–4 were calculated to compare the colour shifting effect between the tooth groups because the DE*area 1–4 values were different between the younger and older tooth. Two-way ANOVA revealed that the DE*area 2–3/1–4, DE*area 3–4/1–4 and DE*area 1–2/1–4 were significantly affected by the age of the tooth (p = 0.001, 0.0258 and 0.003, respectively), while not significantly affected by materials (p = 0.118, 0.749 and 0.562, respectively). There were no significant interactions in DE*area 2–3/1–4, DE*area 3–4/1–4 and DE*area 1–2/1–4 between the age of the tooth and materials

Fig. 4 – The ratio of DE*area 1–2, DE*area 2–3 and DE*area 3–4 values with DE*area 1–4 value (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 of the centre of resin composite restoration) in younger and older tooth (KA: Kalore, SO: Solare, MJ: Clearfil Majesty, BF: Beautifil II).

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Fig. 5 – The DE*area 2–3/1–4 values (the ratio of DE*area 2–3 to DE*area 1–4: mis-match rate in colour shifting at the border) in younger and older tooth (KA: Kalore, SO: Solare, MJ: ) indicates Clearfil Majesty, BF: Beautifil II). The line ( significant differences in each material between younger and older tooth (p < 0.05). There were no significant different in each tooth group between the materials (p > 0.05) (N = 10).

Fig. 7 – The DE*area 1–2/1–4 values (the ratio of DE*area 1–2 to DE*area 1–4: colour shifting rate of tooth side) in younger and older tooth (KA: Kalore, SO: Solare, MJ: Clearfil ) indicates Majesty, BF: Beautifil II). The line ( significant differences in each material between younger and older tooth (p < 0.05). There were no significant different in each tooth group between the materials (p > 0.05) (N = 10).

(p = 0.537, 0.409 and 0.416, respectively). For all the materials except BF, the younger tooth was significantly lower DE*area 2–3/ 1–4 than the older tooth (p < 0.05). Regardless of the materials, the older tooth was significantly lower DE*area 3–4/1–4 and higher DE*area 1–2/1–4 than the younger tooth (p < 0.05). The results of DF (diffusion transmission property), G0 (straight-line transmission property) and Area (amount of transmitted light) of younger and older dentine are shown in Table 2. The younger dentine showed significantly lower G0 and Area values, and higher DF value than the older dentine (p < 0.05). The results of DF, G0 and Area values of resin composites are shown in Table 3. For the DF values, MJ and BF

were significantly higher than KA and SO (p < 0.05), while for the G0 values, KA and SO were significantly higher than MJ and BF (p < 0.05). Furthermore, the Area values were significantly different among all the materials (p < 0.05).

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Discussion

The results of this study require rejection of the null hypothesis that the age of the tooth does not affect the colour adjustment potential of resin composite restorations in human tooth cavities. Paravina et al.12 demonstrated that, when a restoration is placed, a complex colour interaction between dental materials and hard tissue occurs, originating from their translucency, layering and blending effects. Tsubone et al. reported that ‘colour shifting’ occurred at the border of resin composite restorations using extracted human premolars for orthodontic reasons.13 In this study, the DE*area 2–3 values (colour difference between resin composite and tooth at the border) were smaller than DE*area 1–4 values (colour difference between resin composite and tooth) in both the extracted human premolars for orthodontic reasons (younger tooth groups) and for periodontal reasons (older tooth groups)

Table 2 – DF, G0 and area values of dentine. Fig. 6 – The DE*area 3–4/1–4 values (the ratio of DE*area 3–4 to DE*area 1–4: colour shifting rate of resin composite side) in younger and older tooth (KA: Kalore, SO: Solare, MJ: ) indicates Clearfil Majesty, BF: Beautifil II). The line ( significant differences in each material between younger and older tooth (p < 0.05). There were no significant different in each tooth group between the materials (p > 0.05) (N = 10).

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Q4

DF

G0

Area

Younger

47.5 1 (9.01)

11.4 a (5.91)

3.90  10 4A (8.38  103)

Older

36.8 2 (6.19)

32.1 b (11.2)

5.93  10 4B (9.06  103)

Mean (SD); Different superscript letters in each column indicates statistically differences (p < 0.05).

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Table 3 – DF, G0 and area values of resin composites. DF

G0

Area

Kalore

5.811 (0.36)

1.08  10 3a (1.77  102)

5.64  10 6A (6.41  105)

Solare

3.14 2 (0.18)

1.41  10 3a (1.50  102)

7.51  10 6B (3.77  105)

Clearfil majesty

34.0 3 (1.87)

32.2 b (2.50)

8.61  10 4C (3.59  103)

Beautifil II

37.93 (2.03)

57.6 c (2.50)

7.70  10 4D (1.94  103)

Mean (SD); Different superscript letters in each column indicates statistically differences (p < 0.05).

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(Figs. 2 and 3). These results indicate that a ‘colour shifting effect’ at the border of the resin composite restorations was produced in the older teeth as well as the younger teeth. However, the older teeth exhibited larger DE*area 1–4 and DE*area 2–3 values than the younger teeth (Figs. 2 and 3). This result indicates that the colour matching of the A2 shade resin composite restorations placed in 3.0 mm deep cavities was inferior in the older teeth compared to younger teeth. Additionally, the older teeth exhibited larger DE*area 2–3/1–4 values (mis-match rate in colour shifting at the border) than the younger teeth (Fig. 5). These results would indicate that an older tooth has poorer colour adjustment potential at the border of a resin composite restoration than a younger tooth. Therefore, resin composite restorations in older teeth might require more accurate colour matching compared to placement in a younger tooth. The previous study using younger teeth demonstrated that a reduction of the colour difference at the border of resin composite restoration was produced by colour shifting on the tooth side as well as on the resin composite side, in which the colour shifts on the tooth side were larger than those in the resin composite.13 In this study, in order to compare the colour shifting effects of the resin composite and tooth sides among the younger and older tooth groups, the ratio of DE*area 3–4 to DE*area 1–4 (DE*area 3–4/1–4; colour shifting rate of resin composite side) and DE*area 1–2 to DE*area 1–4 (DE*area 1–2/1–4; colour shifting rate of tooth side) were calculated. The older teeth exhibited significantly higher DE*area 3–4/1–4 and lower DE*area 1–2/1–4 values than the younger teeth (Figs. 6 and 7). These results indicate that colour shifting on the tooth side was smaller in the older teeth than in the younger teeth, whereas colour shifting on the resin composite side was larger in the older teeth than the younger teeth (Fig. 4). These colour shifting effects in the younger and older teeth might be influenced by the optical properties of the restored tooth. Ageing and physiological changes in the individual subject would cause large variations in the light transmission characteristics of dentine.17 It is well known that the dentinal tubules are narrowed by thickening of the peritubular dentine with ageing and occasionally occluded with mineral deposition.17 The occluded tubules form a so-called transparent layer in dentine, which has a higher straight-line light transmission property because of the similar refractive index between intratubular dentine and the occluded tubule lumens.17 The area of transparent dentine increases with age and is

influenced by neither functional nor external factors.18,19 In this study, there were different light transmission characteristics between the younger and the older dentine (Table 2). That is, the G0 values (the straight-line light transmission property) and Area values (whole amount of transmitted light) of the older teeth were significantly larger than those of the younger teeth, while the DF values (light diffusion property) of the older teeth were smaller than those of the younger teeth. These results indicate that older dentine can transmit larger quantities of light and that younger dentine exhibits higher light diffusion and transmits less light. These different light transmission characteristics of dentine might affect the colour shifting at the border of the restorations and produce significant differences in the colour adjustment potential of resin composite restoration between younger and older teeth. This means that a larger quantity of the light passing through the lateral wall of dentine in an older tooth cavity to the resin composite may increase colour shifting of resin composite at the border of the restoration, and, conversely, diffusion of the light passing through resin composite to the dentine side of a younger tooth restoration could produce colour shifting of the surrounding tooth. Moreover, if the light passing through resin composite could be better reflected from the cavity floor, the colour matching of resin composite restorations might be improved by a blending effect with colour of cavity floor dentine. The dentine of older teeth has a higher light transmission property and therefore poorer colour adjustment potential for resin composite restorations than the dentine of younger teeth, which has a higher light diffusion property. The optical properties of resin composites are determined by many factors such as resin matrix composition, filler composition and content, pigment and other additives.17 The shape of the filler particles as well as particle size and filler content would significantly affect the light transmission characteristics including the light diffusion characteristics.29 KA and SO, which are UDMA-based materials, and MJ and BF which are Bis-GMA/TEGDMA-based resin materials, were used in this study (Table 1). The filler compositions of KA and BF are 82.0 and 83.3 wt%, respectively, and SO and MJ are 73.0 and 78.0 wt%, respectively. The DF values of KA and SO were significantly lower than those of MJ and BF, whereas the G0 values of KA and SO were significantly higher than those of MJ and BF. Moreover, the Area values of SO and KA were larger than MJ and BF (Table 3). These results indicate that KA and SO exhibit higher light transmission with higher straight-line light transmission, while MJ and BF exhibit less light transmission with higher light diffusion. However, with regards to the use of resin composite with various light transmission characteristics, the colour shifting effect of D E*area 2–3/1–4, DE*area 3–4/1–4 and DE*area 1–2/1–4 values showed no significant differences between the materials. On the other hand, for BF only, there was no significant difference in D E*area 2–3/1–4 value (mis-match rate in colour shifting at the border) between the older and younger teeth, and for SO only, there were no significant differences in D E*area 1–4 (colour difference between resin composite and tooth) and D E*area 2–3 (colour difference between resin composite and tooth at the border) values between the older and younger teeth. In this study, the optical properties of resin composite

Please cite this article in press as: Tanaka A, et al. The effect of tooth age on colour adjustment potential of resin composite restorations. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.09.007

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materials would affect the colour shifting of resin composite restorations in human teeth. However, the effects of straight-line light transmission property, light diffusion property and whole amount of transmitted light of resin composites were not clarified on colour matching of resin composite restorations in human teeth. Clinically, for successful colour matching of resin composite restorations, BF and SO, whose colour appearances were not influenced by the age of the tooth, appear to be user-friendly materials. In addition, the colour adjustment potential of resin composite restorations might be influenced by the storage period after filling. Further research is required in order to improve the colour adjustment potential of resin composite restorations in the various types, sites and ages of teeth in long-term storage. Within the limitations of this study, it was concluded that resin composite restorations in older teeth exhibited less potential for colour adjustment than younger teeth. The colour shifting effects at the borders of resin composite restorations were influenced by the age of the teeth. For the younger teeth, colour shifting was larger than in the resin composite. For the older teeth, colour shifting of the resin composite increased, while colour shifting of the teeth decreased. These different behaviours might be influenced by the light transmission characteristics of dentine in restored teeth.

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Acknowledgements This work was supported by the Global Center of Excellence (GCOE) Program; International Research Center for Molecular Science in Tooth and Bone Diseases at Tokyo Medical and Q3 Dental University, and a Grant-in Aid from the Japan Society for the Promotion of Science (JSPS No. 22791829).

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Please cite this article in press as: Tanaka A, et al. The effect of tooth age on colour adjustment potential of resin composite restorations. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.09.007

The effect of tooth age on colour adjustment potential of resin composite restorations.

The purpose of this study was to investigate the effect of tooth age on colour adjustment potential of resin composite restorations in human teeth...
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