| Abstract|| |
This is an in vitro reflection spectrophotometric studs, which evaluated the color stability of Ionomer and resin composite materials in, various environmental solutions. Three Ionomer based esthetic restorative materials were used:-Glass Ionomer(GIs), resin modified glass Ionomer(RMGIs), and compomers.
A light cured resin bonded composite (RBC) was used as control. Disk type specimens were prepared and aged in four different solutions (deionized water, 75% ethanol. 0.1 mole acetic acid solution & 10% hydrogen peroxide) . for 1,7,14,21,28 and 56 days. The color changes were measured by a reflection spectrophotomer. In deionized water, all specimens showed an acceptable color stability. In ethanol, resin modified glass ionomers(RMGIs) showed the maximum color change, whereas the compomer showed a slightly significant color change. In acetic acid all the test materials showed color changes, ie maximum by glass ionomers (GIs), followed by compomers (Polyacid modified composites- PMCs) & resin modified glass ionomers (RMGls). I0% hydrogen peroxide solution resulted in degradation and high degree of color change for chemicalcured GIs. The light cured resin-modified Glass Ionomers (RMGIs) and compomers (PMC'S) showed high color change in 10% hydrogen peroxide solution. The light-cured composite (RBC-control), showed insignificant color change in all the experimental solutions.
|How to cite this article:|
Ahmed KI, Sajjan G. Color stability of ionomer and resin composite restoratives in various environmental solutions: An invitro reflection spectrophotometric study. J Conserv Dent 2005;8:45-51
|How to cite this URL:|
Ahmed KI, Sajjan G. Color stability of ionomer and resin composite restoratives in various environmental solutions: An invitro reflection spectrophotometric study. J Conserv Dent [serial online] 2005 [cited 2020 Apr 3];8:45-51. Available from: http://www.jcd.org.in/text.asp?2005/8/1/45/42726
| Introduction|| |
Newer dental materials developed for esthetic enhancement are now chosen for their excellent mechanical properties as well as esthetic qualities. With the advent of Buonocore's acid etching technique, dentistry has moved towards a more conservative procedure. The trend is to use materials, which adhere to the tooth structure and hence limit the excessive removal of tooth material that was done traditionally. The glass
Ionomers (GIs) and resin-bonded restoratives (RBCs) have been subjects of interest for dentists for the past few decades. Under oral conditions these esthetic restorations could be exposed to the combined effects of light, moisture, stain and mechanical wear, which often results in visibly detectable and esthetically undersirable color changes. GIs have been criticized for their lack of color stability almost since they were introduced, as stated by Bern et al. The RBC's have better color stability but lack the fluoride releasing properties, which are necessary in many of the cases. These limitations of these materials led to the introduction of hybrid materials:- the resin modified glass ionomers (RMGIs) and the compomers (PMCs), which have both, the components of glass ionomers and resins ,in various percentages.
GIs are sensitive to organic acid solutions. Organic acids are present in dental plaque or food intake, which could be either acetic, propionic or lactic acid. Hydrogen peroxide produces color changes in RBCs and RMGIs. Also, most of the mouth resins used contain ethonal which has softening effect and deteriorates the polymer surface, as stated by Eric Asmussen(1984).
Therefore, the present study was conducted to evaluate the degree of color stability of polyacid based restoratives in various environmental solutions.
| Materials and Methods|| |
The study samples comprised of 3 commercial polyacid based esthetic restorative materials:- chemically cured glass ionomers (GIs)-Fuji II, Resin modified glass ionomers (RMGIs)-Fuji II LC and polyacid modified composites (PMCs)-Dyract respectively. A light cured resin based composite (RBC)-Z100, was used as a control material
Twenty discs of each material, with a diameter of 8mm and thickness of 1.65mm were prepared, by placing the materials in the Teflon moulds and following the manufacturers instructions. In case of the light cured materials, the specimens were exposed for 40 seconds each. The surfaces of chemical cured specimens were coated by varnish (GC varnish) and the surfaces of the light cured specimens were polished with soflex discs (3M), in order to remove any defective setting layers. The specimens were placed in an environmental oven at 37° c, at 100% relative humidity for 24 hours, before placing them in the test solutions. 5 samples of each material were placed in the 4 different environmental solutions viz; deionized water (control), 0.1 mole of acetic acid solution, 75% ethanol solution and 10% hydrogen peroxide for 1, 7, 14,21,28 & 56 days. Concomitant color changes were recorded using a reflection spectrophotomer.
Baseline measurement (Lo, ao, bo) of specimens were performed before aging treatments. CIE values (Ln, an,bn) were measured after 1, 7, 14,21,28,&56 days of environmental aging in the solution. The change in color (ΔE) was calculated using the following equation ΔE = [(L n -L o ) 2 + (b n -b o ) 2 ] 12. Descriptive statistics on color change that includes, mean and standard deviation values were calculated for each of the four materials, observed at 1, 7, 14,21,28 & 56 days. Possible difference among materials for each solution were analyzed by analysis of variance technique following by Mann Whitney test for pairwise comparison. Multivariate analysis (2way Anova) was performed to test the difference between materials, between solutions and materials by solutions interactions. The color change (ΔE) data were analyzed using minitac (version 13.1 USA) statistical software package.
| Results|| |
As seen in graph l, in deionized water (control solution), Fuji II, Dyract showed negligible color change. There was significant color change with Fuji II LC at the end of the first day (ΔE =2.55), but remained stable for upto 56 days with an increase in ΔE = 0.5 . the control group (Z-100) showed a color change upto ΔE =1.64.
As seen in graph II, in ethanol, on the first day, Fuji II and Dyract had insignificant color change (ΔE =1.45, 1.85 respectively), whereas Fuji II LC was more color stable (ΔE=0.06). But later, Fuji II LC showed an increase in ΔE upto 5.53 on the 56th day. Fuji II showed color change ΔE =3.09 - ΔE 73.3 is perceivable to the naked eye) however, it is not perceivable to the naked eye, whereas dyract gave a perceivable color change (ΔE =3.46) after 56 days.
As seen in graph III, in acetic acid, all the materials showed perceptible color change (ΔE 73.3). Fuji II on the first day showed color change (ΔE) = 3.75 and finally on the 56th day Fuji II showed the maximum color change (ΔE =18.34). Fuji II LC on the first day gave color change ΔE =3.79, on 56 th day gave color change (ΔE)=8.14. The color change with Dyract increased upto 12.59. Z- 100 showed minimal color change (ΔE =1.39).
As seen in CR-IV, in hydrogen peroxide, on the rust day, Fuji II and Fuji II LC showed significant color changes (ΔE =5.69, 3.66 respectively) Dyract and Z100 had minimal color changes- 0.75, 0.58 respectively. From the 7 th to 21 st day, there was an increase in ΔE drastically with Fuji II (AE =15.15, 21 st day). After which no readings could be taken as the specimens deteriorated. +E for Fuji II LC increased up 11.39 on the 7 th day, then decreased upto 6.49 on 28 th day and again increased in upto 9.89 on the 56 th day. Dyract showed color change (+E)<3.3 upto 21 days (+E =2.4), after which it touched 8.36 on the 56 th day. As usual Z 100 showed unperceivable color change (+E =1.16).
| Discusssion|| |
Color changes in esthetic restorative materials have been attributed to a wide variety of possible causes. Wear or chemical degradation can increase the susceptibility of these materials to extrinsic staining. Other causative factors that may contribute to the change in color of esthetic restorative materials include: stain accumulation, dehydration, water sorption. leakage, poor bonding and surface roughness. In this study CIE lab (standardized commission international de eclairage) color system is used, as recommended by the American Dental Association. According to this system, all colors in nature are obtained through blending of three basic colors (i.e., red, blue and green) in certain proportions.
L * - Depicts the lightness/value
A * - Depicts chromacity in the red-green axis
B a - Depicts chromacity in the yellow blue axis.
In the present study Z- 100 (RBC) was taken as control, as it is already documented that RBC is more color stable when compared to the test materials, as according to Bum et al & Vargas et al. Deionized water was taken as the control solution as the rest of the testing conditions were aqueous in nature.
75% of ethanol was used, as according to FDA it is a recommended food simulators and should be considered clinically relevant. Also 0.1 mole acetic acid & 10% hydrogen peroxide should be considered clinically relevant as they are present in plaque/ aerated drinks and bleaching agents respectively.
The restorative depicted in graph I are as follows:
In Deionized water (control solution), Fuji II, Dyract showed negligible color change as these test materials were stable in the presence of water. on the first day Fuji II LC showed significant color change ΔE=2.55, when compared to the other test materials. This can be explained by the fact that the acid base reaction in resin modified cements proceeds more slowly, as some of the water in the cement is replaced by watersoluble monomers. Research has been done and found that resin modified cements have the potential to up take water from the environment. The uptake of water by the resin matrix may account for the changes in color parameters. This is in accordance with the results reported by Yap and Bum. Once the water sorption took place +E remained stable for upto 56 days (ΔE =3.0). However ΔE =3 was less than the perceivable limits. Z-100 showed a minimal change of ΔE =1.64 on the 56 th day.
The results depicted in graph II are as follows:
In ethanol, Fuji II had no perceptible color change (ΔE =3.09) on the 56 th day. On the 1 st day Fuji II LC was quite color stable (ΔE =0.06), but shot up on 14 th and 21 st day and reached a value of 5.53 on the 56th day. Dyract had a slight perceptible colorchange (ΔE =3.46). Z-100 (control) was most color stable (ΔE =1.99) on the 56 th day.
This can be explained by the fact that, though the resin component in RMGI is lesser compared to compomer or composite, the resin here is hydrophilic and the filler content is minimal. The solvent such as ethanol penetrates the resin matrix, the polymer chains expand and the monomer may leach out. It has also been reported by Eric Asmussen (1984), that the ethanol has a softening effect on the resin matrix. As the filler content increases these changes can be reduced. Therefore Fuji II LC showed the largest color difference of ΔE=5.53, followed by Dyract (ΔE =3.46), Fuji II showed upto 3.09 and Z 100 (control) upto 1.99. These results are in accordance with that found by Bum.
The results depicted in graph III are as follows:
In acetic acid, all materials except Z - 100 showed perceptible color change. (ΔE =>3.3) for the first day. Subsequently, Fuji II showed maximum color change AE =18.34 followed by Dyract and Fuji II LC for the 56th day, Z-100 showed minimal color change. For Fuji II it can be explained by the fact, that due to the degradation of metal polyacrylate salts that were not stabilized during the initial stage of the setting reaction, a noticeable color change was observed. Light cured resin modified GI was an exception and showed significantly lesser discoloration upto 21 days. This could be attributed to the protection given by the resin matrix from acid attack to the glass ionomer component. Also for compomer, previous research has showed that, low pH media affects the surface integrity of compomer. Under acidic conditions the compomer surface is appreciably softened with loss of structural ions from the glass phase. As a result individual particles dissociate from each others and show a rough surface with the presence of voids.
The results of this study is in accordance with that reported by Neamat et al and Bum et al.
The results depicted in graph IV are as follows:
In hydrogen peroxide on the first day Fuji II and Fuji II LC showed significant color change, ΔE =5.69 and 3.66 respectively. This can be explained and also has been supported by several research works that dental whitening agents (10% H 2 O 2 ) could change the surface texture of these restorations. These restorative materials are stained easily by mechanical adsorption when their surface roughness, or surface chemistry has been altered by chemical degradation, which was particularly seen with that of GIs. In case of RMGIs. the change in color could be due to the oxidation of the residual chemical ingredient (reaction activator), as when compared to Dyract and Z 100, which had minimal, color change of 0.75 to 0.58 respectively.
Till the 14 th day there was an orderly increase in ΔE for Fuji II and Fuji II LC upto 12.35 and 11.39 respectively, whereas Dyract was 1.54 and Z- 1 00=0.64. On the 21 st day ΔE reduced from 11.39 to 8.74 in the case of Fuji II LC, whereas Fuji II gave a reading of 15.15. The decrease in was AE in the case of Fuji II LC is due to chipping and delamination of the damaged surface layer in hydrogen peroxide solution. After delamination, fresh surfaces were exposed and these gave rise to a recording of less color change than the damaged surface layer.
On the 28 th day Fuji II LC showed an even lower ΔE value of about 6.49, but in case of Fuji II no reading could be elicited as most of the samples had completely deteriorated in 10% Hydrogen peroxide solution. Dyract showed a significant color change of (ΔE =5.26, whereas Z-100 had a minimal of 0.87. On the 56th day there was an increase in ΔE value of 9.89 with Fuji II LC, and with Dyract it was 8.36 while Z-100 maintained a minimal of 1.16.
The discoloration of compomer could be explained by the oxidation of residual inhibitor. Z- 100 again was resistant against discoloration when compared to other materials because of its higher filler content and chemistry of the resin matrix. The above result is in accordance to that obtained by Bum.
In deionized water the value (L) of all the materials decreased. In ethanol all materials exhibited darkening and a shift towards the blue chromatic axis (b). In acetic acid all materials exhibited increase in lightness (L) and a shift towards the yellow axis (b). In hydrogen peroxide, all the materials exhibited an increase in lightness (L) and a shift towards the blue axis (b).
Therefore the following conclusion can be made based on the study:
- In ethanol, RMGI showed a perceptible color change, therefore when a RMGI restoration is placed; ethanol containing mouth rinses should be avoided. If the patients are a habitual drinker then GI or RBC may be used as even compomer showed a slightly perceptible color change.
- In acetic acid (present in plaque, diet), GI showed the maximum color change followed by compomer. Though RMGI showed color change, it was lesser when compared to GI or compomer. Therefore if a fluoride containing restorative has to be placed then RMGI would be the material of choice and since RMGI has a tendency to be come lighter in Acetic acid, a slightly darker shade may be selected in such a situation.
- In hydrogen peroxide (patients indicated for bleaching), GI completely dissociated, RMGI showed varying amounts of color change with delamination of the surface. Compomer showed a perceptible color change. The best material would be RBC. But if a fluoride- containing restorative is demanded in a situation, then compomer would be the next best material of choice. Since compomer had the tendency to lighten and become bluish, a slightly darker and yellower shade may be selected in such a clinical situation.
- RBC showed the best results in terms of color stability, hence if the situation is not very insisting on the fluoride containing esthetic restorative then RBC showed be used.
- Very few studies have been done to determine the intrinsic staining of the esthetic restorative materials by these environmental solutions. Hence extensive research have to be done in these directions as these environmental solutions largely mimic intra oral conditions to which the restoratives are subjected.
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Khaja Iftheqar Ahmed
Bapuji Dental College and Hospital, Davangere
Source of Support: None, Conflict of Interest: None