Dr. Wedad Y. Awliya

The Effect of Bleaching Agents and Whitening Tooth pastes On Color Stability and Microhardness of Some Restorative Materials.

By Dr. wedad Y. Awliya Associate Professor, Department of Restorative Dental Science, College of Dentistry, King Saud University, Riyadh, Saudi Arabia P.O. box 5967 Riyadh 11432 E-mail [email protected]

1 ABSTRACT

The purpose of this study was to compare the effect of office, home bleaching gels, and whitening tooth pastes on color stability and microhardness of composite resins and resin modified glass-ionomer cement. A total of 35 disc specimens from three restorative materials (Z250, Esthet-X and Fuji II) were fabricated. Specimens of each material were divided into 7 groups each group contains 5 specimens. First group was treated with Opalescence Xtra office bleaching gel, the second group was treated with Nite-White home bleaching gel following manufacturer’s instructions. Third group was treated with Signal 2 cavity fighter regular tooth paste. Fourth, fifth and sixth groups were treated with whitening tooth pastes (Crest Extra whitening, Advance White, and

Aquafresh Whitening). The seventh group was stored in saline to serve as control. Color and Vickers surface microhardness of each specimen were recorded before and after treatments. Results indicated significant color change and reduction in microhardness of Esthet-X composite resin after treatment with

Opalescence Xtra bleaching gel. However, microhardness of Esthet-x was significantly increased by all tooth pastes used in the study. Although microhardness of Z250 composite resin was significantly affected by Opalescence

Xtra bleaching gel, its color stability was not affected by any of the used products. Fuji II LC showed significant color change and reduction in

2 microhardness with both bleaching gels and significant color change and increase in microhardness with all tooth pastes.

Key Words: Bleaching Agents, Whitening Tooth Pastes, Microhardness, Color,

Restorative Materials.

3 INTRODUCTION

The requirement for esthetic benefits is high lightened by rapid growth of tooth whitening products. Home vital bleaching or mouthguard bleaching has attracted the interest of patients due to its high success rates, ease of use and media publicity.1,2 This procedure utilizes low concentrations of hydrogen peroxide (3% to 7%) or carbamide peroxide (10% to 22%).3,4 The in-office bleaching products contain strong oxidizing agent, (30%-37% hydrogen peroxide), used under the dentist’s control.5 The influence of various concentrations of bleaching agents on physical properties, surface morphology and color change of tooth structure and different restorative materials, has been investigated in several in vitro-studies simulating the clinical situations as closely as possible.6,7,8,9,10,11 The results of these studies were controversial. Some studies showed that 35% hydrogen peroxide and 10-16% carbamide peroxide alter enamel surface morphology, deteriorate the surface of existing restorations and induce bacterial adhesion.6,7 However, other investigations revealed no significant change in enamel or existing restoration physical properties due bleaching agents.8,9 Moreover, some studies reported increase in enamel or composite resin surface hardness following bleaching.10,11

In addition to regular tooth pastes, which commonly used to remove plaque in order to prevent caries and periodontal disease, a considerable number of whitening tooth pastes, have been developed.12 Manufacturers claimed that

4 whitening tooth pastes are formulated to remove extrinsic dental stain rather than to change the natural tooth color through a bleaching action.13 In fact, these whitening tooth pastes contain some abrasive particles such as natural calcium carbonate and silica microgranules which abrade tooth surface, thus removing stains.14 Some formulation of whitening tooth pastes may also contain small percentage of hydrogen or carbamide peroxide.15 In addition , baking soda has been introduced in some formulation of whitening tooth pastes to act as anti-halitosis and anti-bacterial.16 Concern has been also raised regarding the high abrasive action of baking soda.17 Little is known about the effect of these whitening tooth pastes on soft tissues, tooth structure and physical properties of restorative materials.

The appearance of natural teeth and restorative materials varies according to color and translucency.18 The esthetic properties of an existing restoration are important factors that affect clinical success. Although the initial color match of a light-polymerized restoration may be established, long-term color changes can occur because of surface staining, marginal staining, and microleakage. Drastic color changes to existing restorations may compromise esthetics; therefore it is important to understand the effect of the whitening products including the daily used whitening tooth pastes on color of restorative materials.

The purpose of this study was to determine the color change and surface microhardness that might occur in two light-polymerized composite resins and

5 resin modified glass-ionomer cement as a result of using some whitening tooth pastes, home and office bleaching agents.

MATERIALS AND METHODS

Shade A2 from three restorative materials was selected for this study:

Z250 (3M/ESEP), Esthet-X (Dentsply), and Fuji II LC (GC international).

Compositions of the different materials are listed in Table 1. The restorative materials were injected into round Teflon mold (10 mm in diameter and 1.5 mm deep), covered with Mylar strip, and pressed between glass plates. After 10 seconds curing with a wide tipped Prismetics curing unit (LD Caulk/Dentsply

Int.), the top glass plate was removed in order to have the tip of the curing light closer to the samples. Then each specimen was polymerized for another 50 seconds. Thirty five specimens from each material were fabricated and stored in darkness at room temperature for 24 h to allow optimum conversion. The specimens of each material were divided randomly into seven groups (n=5).

One regular tooth paste, three whitening tooth pastes and two bleaching gels were selected as treatment products (Table 2). The control group was stored in saline. Baseline color measurement of each specimen was done before treatment using Spectrophotometer (PSD 1000, Ocean Optics, FL, USA). Surface microhardness measurements were also recorded before treatment using

Beuhler Micromet II tester with a Vickers diamond indenter. Three measurements were made on top surface of each disk. A load of 300 g was

6 applied to the surface of each specimen for 12 seconds. Then the treatments of each group were performed: In the home bleaching group (Nite-White) specimens were immersed for 4 hours daily in fresh bleaching gel following the manufacturer’s direction. The specimens were rinsed with deionized water after each treatment, and then stored in deionized water between treatments. The home bleaching treatments were continued for one month. For the office bleaching group (Opalescence Xtra Boost), specimens were immersed in the bleaching gel, following manufacturer’s direction, for 15 minutes. After agitation every 5 min., the gel was removed by suction tip; specimens were then rinsed with deionized water. A new gel was applied after 15 minutes for three times.

Then the same procedure was repeated after one week, keeping the samples in deionized water between treatments. For the tooth pastes groups: specimen surfaces, in each group, were brushed with an electric tooth brush (Colgate

ActiBrush) for two minutes twice daily, with a new brush tip for each tooth paste.

The tooth brush held perpendicular on the surface of the specimens with no pressure application as described by others.19 The same procedure was repeated for 30 days. Following each treatment, samples were rinsed with deionized water and stored in deionized water between treatments.

After finishing all treatments, color and microhardness were measured.

Color change was measured according to the following formula:

2 2 2 1/2 ∆E* = [(L*o - L*I) +(a*o – a*I) +(b*o – b*I) ]

7 ∆ E* = color change, L* = luminance reflectance, a* = red-green color coordinate, b* = yellow-blue color coordinate, O = baseline, and I = after treatment.

Color change ∆E* data and microhardness values were analyzed by Two-way analysis of variance (ANOVA) and Post Hoc Tukey’s test at 0.05 significance level to compare between the different groups.

RESULTS:

The mean and slandered deviation values of color change ∆E* of the specimens produced by each of the products used in the study are summarized in Table 3.

Two-way ANOVA showed that both the restorative materials and whitening products were significant. Significant interaction also, was found between the restorative materials and the treatment products (P=0.000).

Z250 composite resin showed the most color stability among the other materials. Although some color change was noticed with some of the treatment products, it was not clinically significant. Color of Esthet-X composite resin was significantly affected after treatment with Opalescence Xtra office bleaching gel

(P=0.000) and Crest Extra whitening tooth paste (P=0.000).

Fuji II LC was found to be the least resistance to color change. Although all the tooth pastes and the bleaching gels used in the study caused significant color

8 change of Fuji II, Opalescence Xtra bleaching gel caused the most significant color change (P=0.000)

Microhardness

The results of microhardness testing are shown in Figures 1-3. Two- way analysis indicated significant difference by type of the treatment product

(P=0.000). Significant interaction was also, found between the restorative materials and the whitening products (P=0.000).

The microhardness of the three restorative materials was significantly reduced after treatment with Opalescence Xtra bleaching gel. In addition, microhardness of Fuji II was significantly reduced by Nite-White home bleaching gel (P≥0.05).

However, microhardness of Z250, Esthet-X and Fuji II was significantly increased, after one month brushing, with all the tooth pastes used in this study.

Esthet-X and Fuji II specimens treated with Crest extra whitening tooth paste were significantly harder than the specimens treated with the other tooth pastes.

DISCUSSION

An unacceptable color match of the restorative materials to natural teeth still one of the major causes for replacement of anterior restorations.20 Discoloration can be evaluated visually and by using specified equipments. Spectrophotometer has been used in many previous studies to measure color change (∆E*) by

9 comparing the values before and after treatment according to the formula previously mentioned.21,22,23 Because the ability of the human eye to appreciate differences in color differs from individual to individual (as it is a combination of eye characteristics and skill of the operator), three different intervals were used for distinguishing color differences. Values of ∆E*< 1 were regarded as not appreciable by the human eye. Value of ∆E*< 3.3 were considered appreciable by skilled operators, but considered clinically acceptable, while value ∆E* >3.3 were considered appreciable also by non-skilled persons and for that reason it is clinically not acceptable.24,25,26

The effect of bleaching agents and Whitening tooth pastes on color and microhardness of restorative materials was investigated in this study because their whitening action was different. Peroxide in bleaching gels decomposes into free radicals that attack the organic molecule releasing other radicals. These radicals break down large pigmented molecules responsible for color stain into smaller less pigmented molecules hence removing discoloration and brighten the inherent color.27 On the other hand, whitening tooth pastes help to control stain by way of abrasives incorporated in the product that remove pellicle in addition to dental stains.14 Recently, certain types of chemicals have been also incorporated into some of the whitening tooth pastes that may help to reduce stain by a chemical action through stain inhibition and or direct stain removal.

These chemicals include enzymes, detergents and oxygenating agents. 15

10 In this study Opalescence Xtra bleaching gel significantly changed the color of Esthet-X composite resins and Fuji II resin modified glass-ionomer cement, however, color of Z250 was not affected. The alteration in color of

Esthet-X composite resin could be attributed to oxidation of surface pigments and amine compound, which have also been indicated as responsible for color instability of restorative materials over time.28 Differences in color change between different materials might be a result of different resin, filler content, initiation components and different degrees of conversion of resin matrix to a polymer.29,30 Although both composite resins, Z250 and Esthet-X, are microhybride and have similar filler content (60% by volume), Esthet-X have smaller filler particle size hence higher resin content. The higher resin contents of a material, the lesser its resistance to oxidation.31 Also, it has been stated that resin materials using UDMA, such as Z250 composite resin, show more color stability than BisGMA resin.32 The presence of HEMA in Fuji II resin modified glass-ioinomer cement increases the susceptibility of the material to water sorption and disintegration hence changing its color.33

The softening of restorative materials by strong oxidizing agents, such as the 37% hydrogen peroxide in Opalescence Xtra, has been also reported in other investigations.6,7 This support the reduction in microhardness of the three restorative materials used in this study. Although Nite-White bleaching gel contains 10% carbamide peroxide which upon application breaks down into 3% hydrogen peroxide and 7% urea, it causes significant reduction in microhardness

11 of Fuji II resin modified glass-ionomer cement. Chemical softening of a restorative material might occur if bleaching products have solubility parameters similar to that of resin matrix.34 Reduction in Fuji II microhardness is the result of erosion of glass-ionomer matrix, wash-off and release of metal cations from the surface by the peroxide subsequently reducing its microhardness. 35,36

Increase in surface microhardness of the three restorative materials in this study was noticed after treatment with all tooth pastes. This increase in surface microhardness might be a consequence of incorporating abrasives in the tooth pastes such as silica, hydrated silica, calcium carbonate and tri-phosphate.14

Calcium carbonate is included in Signal 2 regular; tri-phosphate is an ingredient in Aquafresh Whitening, while silica is among the ingredients of all the tested tooth pastes. It was thought that these abrasives will loosen the stained matrix; however, the exact quantitative information on their abrasive action is unclear.

Sodium Bicarbonate, which is an active ingredient in Crest Extra Whitening and

Advance White tooth pastes, was reported also to have high abrasive action.16

The incorporation of abrasives in tooth pastes may help to physically remove stain but since virtually all tooth pastes contain abrasives some benefit may be expected even by regular products. In this study no significant difference in color or microhardness was found between specimens treated with the regular tooth paste (signal 2) and the other whitening tooth pastes except Crest Extra

Whitening. The concept of whitening formulations containing specific chemicals that reduce or inhibit stain independent of physical effect would appear to be

12 particularly attractive since reduced staining may be apparent in sites of dentition where the abrasive effects of tooth paste would be less obvious. Although

Advance White tooth paste contains hydrogen peroxide in addition to abrasives, it did not show significant difference in color or microhardness from the other tooth pastes. Concisely, it was anticipated that the increase in surface microhardness of the three restorative materials in this study attributed to action of the abrasives, aided by the tooth brush, which produces smooth and hence harder surface

Esthet-X and Fuji II specimens showed significantly high color change and increase in microhardness when treated with Crest Extra Whitening tooth paste.

This could be credited to structural integrity of the restorative materials, as previously mentioned, and to material interaction with different ingredients of the tooth pastes. The combined abrasive action of hydrated silica and sodium bicarbonate in addition to softening effect of citric acid in Crest Extra whitening could produce smooth and hard surface of Esthet-X and expose surface silica core in Fuji II thus increasing their surface microhardness and changing color. 37

The results of this study indicated that both bleaching agents and tooth whitening products might affect color and microhardness of existing restoration and this effect is material dependant. Nevertheless, problem with color matching of anterior restorations after bleaching will occur even if the restorations are unaffected. If the restoration match the color of teeth perfectly before bleaching, they may no longer match once the teeth have become lighter and brighter as a

13 result of bleaching. Hence, the restorations may require replacement. Therefore, patients should be advised that existing anterior restorations may not match the natural teeth after bleaching, and replacement may be required.

CONCLUSIONS

● The effect of bleaching gels or whitening tooth pastes on color and

microhardness was material dependent.

● Color of Z250 composite resin was not affected by any of the bleaching

gels or tooth pastes used in the study. However, its microhardness was

significantly reduced by Opalescence Xtra bleaching gel and increased by

all the tooth pastes.

● Significant color change and reduction in microhardness of Esthet-X

composite resin was noticed after treatment with Opalescence Xtra

bleaching gel. However, microhardness Esthet-X was significantly

increased by all tooth pastes used in the study

● Fuji II LC showed significant color change and reduction in microhardness

with both bleaching gels and significant color change and increase in

microhardness with all tooth pastes.

● Existing restorations might not match the color of the teeth after

bleaching and therefore, they might require replacement.

● Surface integrity of restoration might be affected by brushing tooth pastes

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Table 1. Restorative Materials Used In The Study And Composition

Material Manufacturer composition Z250 3M/ESPE Dental products Bis-GMA, UDMA, Bis-EMA

(Hybride composite Ziroconia/silica filler (60% by resin) Vol) particle size:0.01-3.5 µm Esthet-X Dentsply DeTrey GmbH Bis GMA, Bis EMA, TEGDMA,

(Hybride with micro Barium fluoro alumino boro matrix composite resin) silicate (particle size <1 µm)

(60% by Vol)

Nano –sized Silicon Dioxide Fuji II LC GC international, Corp., Co-polymer of maleic acid and

(Resin modified glass- Tokyo, Japan acrylic acid, 2-HEMA, water ionomer cement) Fluoro alumino silicate glass

20 Table 2. The treatments products used in the study and their ingredients

Whitening products Manufacturer Composition Opalescence Xtra Ultradent products Inc. 37% chemically activated

Boost (office 505 west 10200 South. Hydrogen peroxide. bleaching) South Jordan Utah 84095,

USA. Nite-White (home Discus Dental 8550, 10% Carbamide Peroxide bleashing) Higuera street, Culver city,

CA 90232, USA Signal 2 cavity Binzagar Lever Limited, SA Calcium Glycerophosphate, fighter Calcium Carbonate, Sorbitol,

Water, Silica, Sodium Lauryl

Sulfate, Sodium

Monofluorophosphate, Mix of

flavors, cellulose gum, Trisodium

Phosphate, Sodium Saccharin,

Formaldehyde, Cl 12490 Crest Extra Procter & Gamble, GM Aqua, Hydrated Silica, Sorbitol,

Whitening Glycerin, PEG-6, Sodium Lauryl

Sulfate, Tetrapotassium, Sodium

Bicarbonate, Citric Acid,

Pyrophosphate, Aroma,

Carbomer, Carnauba, Cellulose

Gum, Limonene, Sodium

21 Fluoride, Sodium Saccharin,

Triclosan, Xanthan Gum, Cl

74160, Cl 77891 Advance White Arm & Hammer, Church & Sodium Fluoride, Sorbitol,

Dwight Co., Inc, USA Sodium Bicarbonate , Hydrogen

Peroxide, Glycerin, Silica, Water,

Sodium Lauryl Sulfate, Sodium

Saccharin, Mix of flavors,

cellulose gum, Sodium Lauryl

Sulfate, Titanium Dioxide, Aquafresh Whitening GlaxoSimithKline, UK Hydrated Silica, water, Sorbitol,

Glycerin, Pentasodium, Tri-

Phosphate, PEG-6 Sodium, Lauryl

Sulfate, flavor, Titanium Dioxide,

Xanthan Gum, Sodium hydroxide,

Sodium Saccharin, Sodium

Fluoride, Cl 73360, Cl 74160

Table 3. Mean and standard deviations of color change ∆E after treatment with the different whitening products.

Treatment Restorative materials Z250 Esthet-X Fuji II LC Opalescence Xtra 1.9 (0.52)a 7.9 (7.46)*b 9.6 (1.46)* Nite-White 0.6 (0.35)a 2.1 (1.77) a 6.2 (1.88)*ab

22 Signal 2 cavity 1.2 (0.43)a 1.3 (0.40) a 3.5 (0.77)* fighter Crest Extra 1.6 (1.19)a 5.1 (0.91)*a 5.0 (1.54)* whitening Advance White 1.1 (0.68)a 1.8 (0.44)a 5.8 (1.04)*a Aquafresh Whitening 1.2 (0.16)a 1.3 (0.32)a 6.9 (0.92)*b Saline (control) 0.9 (0.60)a 1.0 (0.76)a 0.9 (0.60) * Means significantly different from Control (P<0.05)

Means with the same letter are not significantly different

23 Mean Vicker Hardness Values of Z250 Composite Resin Before and After Treatment with the different Whitening Products

Before treatment After treatment

0 Opalescence Nite-White Signal 2 Crest Extra Advance Aquafresh Saline Xtra cavity fighter Whitening White Whitening

Figure 1.

24 Mean Vicker Hardness Values Of Esthet-X composite resin After Treatment With The Different Whitening Products

Before treatment After treatment 100 90 80 70 60 50 40 30 20 10 0 Opalescence Nite-White Signal 2 cavity Crest Extra Advance White Aquafresh Saline Xtra fighter Whitening Whitening

Figure 2.

25 Mean Vicker Hardness Values Of Fuji II LC After Treatment With The Different Whitening Products

Before treatment After treatment

90 80 70 60 50 40 30 20 10 0 Opalescence Nite-White Signal 2 Crest Extra Advance Aquafresh Saline Xtra cavity fighter Whitening White Whitening

Figure 3.