Evaluation of the colour stability of three different nano composites after bleaching with 10% carbamide peroxide: A spectrophotometeric study.

INTRODUCTION

Smile is the first thing that people notice on meeting a person. It plays such a crucial role in appearance that the aim to achieve the perfect white smile tops the outlook check list. Popularity of aesthetic dentistry has led to a scenario where unaesthetic restoration are being replaced by aesthetic restorations. Due to high aesthetic requirements, most patient for tooth bleaching also opt for aesthetic composite restorations.

The use of more aesthetically pleasingcomposite restorationshas drastically increased. Nanofilled composites claims to have a more considerable colour stability due to their filler characteristics.Introduction of nanotechnology has enabled the nano scale incorporation of nanofiller particles into the resin matrix of composites which has resulted in a substantial upgradation in the overall mechanical and aesthetic properties in comparison with the conventional, conventional resins.¹)

Bleaching is a relatively safe aesthetic treatment for whitening the teeth. ⁽²⁾ The contents of the available home and the in - office agents of bleaching include either hydrogen peroxide, carbamide peroxide or sodium perborate. Bleaching fundamentally is an oxidation process by which the molecules causing discoloration are chemically modified ⁽³⁾

However, one drawback of this procedure is that theteeth reverts back to the original color after a period of time. ⁽⁴⁾Satisfactory results persist only for 1-2 years and patient should be advised regarding the need for re-bleaching procedures ⁽⁵⁾ Hence maintenance therapy of bleaching has become a requisite.

Cases planned for full mouth aesthetic rehabilitation may require teeth bleaching in conjunction with composite restoration. Composites used in such cases should have adequate colour stability to ensuring a limited or insignificant colour change with the bleaching maintenance therapy.

Bleaching agents tend toimpart some colour change in composite restorations. This impactdepends on the composition of the materialtoo.6 Certain studies have concluded that the effect of bleaching treatment with peroxide on the color of composite restorations is not clinically perceptible.^7,8

In assessing chromatic differences, generally two systems are used: the Munsell color system and the Standard Comision Internationale de L, Eclairage (CIELAB) Color System. The American Dental Association advices the use of the CIELAB color differential system. Colour stability can be assessed by the CIELAB colorimetric values which can be procured from a spectrophotometer.³

This study was aimed at the spectrophoto metric evaluation the colour stability three commercially available nano composites after bleaching procedure.

Materials and methods

Characteristics of the three different nano composite materialsselected for this studyare presented according to the manufacturers in (Table 1). Composite materials of shade A2 was selected. 60 samples were prepared based on the material used. Specimens were divided into three groups containing 20 samples each:

Group A (n = 20): ceram.x® SphereTEC™ one universal (Densply Asia)

Group B (n = 20): Filtek Z250 XT (3M EPSE)

Group C (n = 20):Tetric N-Ceram ( Ivoclar Vivadent)

The specimens were fabricated using plastic disc molds 10 mm in diameter and 2 mm in depth covered by polyethylene sheets and pressed flat with glass plates (Figure 1). The composite materials were placed incrementally in two stages and cured for 20 seconds after each increment with a LED curing light system through the glass and polyethylene sheets on the top and bottom of the specimens. The composite specimens were polished with a Soflex disc (3M dental products) starting with coarse discs and ending with extra fine discs. Once the specimens were light cured, they were stored in distilled water to complete their polymerization for 24 hours.

Specimens in the three groups were further subdivided into 2 subgroups of 10 specimens each. The specimens were bleached following the manufacturer’s instructions.

Control Subgroup(n=10): Immersed in distilled water

Test Subgroup(n=10): Opalescence PF was applied once daily for 4 hours for a total duration of 2 weeks.

After each cycle of treatment, specimens were cleaned using a soft brush for a duration of 1 min. In between treatment phases, the specimens were immersed in vials filled with distilled water at room temperature. Distilled water was refreshed daily in all groups.

Color Change Measurement

Delta a*, delta b*, delta L*, delta H and delta C color parameters were evaluated in test specimens before and after the 2 week bleaching treatment and in control specimens at baseline and after 2 weeks of storage in distilled water using a spectrophotometer ( DATA COLOR 800) in accordance to the CIE-L*a*b* color space ( Figure 2). CIE L* parameter were as follows: (Table 2)

Statistical analysis

The impact of the type of composite and bleaching agent on delta a*, delta b*, delta L*, delta H and delta C was analyzed with two-way ANOVA. If there was a significant interaction effect, oneway ANOVA was used. Tukey’s HSD test was carried out for multiple comparisons.The level of significance was set at P<0.05. The sample size had been estimated using the GPower software v. 3.1.9.2

Results

Among the A2 shade before bleaching procedure Filtek Z250 XT showed a lighter shadein accordance to the L parameters.Hue value was of A2 shade increased from

Tetric N-Ceram to ceram.x® followed by Filtek Z250 XT. (Figure 3)

After bleaching Tetric N-Ceram showed the lowest L value compared to Filtek Z250 XT and ceram.x®.

The test specimens showed the delta E values of 4.17±2.21, 1.91±1.40 and 1.63±1.40 for Filtek Z250 XT, ceram.x® andTetric N-Ceram respectively after bleaching.ceram.x® presented with the least difference in the colour change in accordance to the delta E values.There was a statistically significant difference of the total colour values of Tetric N-Ceram and Filtek Z250 XT. (Table 3, 4, 5)

After bleaching Tetric N-Ceram showed the lowest L value compared to Filtek Z250 XT and ceram.x®.

The test specimens showed the delta E values of 4.17±2.21, 1.91±1.40 and 1.63±1.40 for Filtek Z250 XT, ceram.x® andTetric N-Ceram respectively after bleaching.ceram.x® presented with the least difference in the colour change in accordance to the delta E values.There was a statistically significant difference of the total colour values of Tetric N-Ceram and Filtek Z250 XT. (Table 3, 4, 5) 

Discussion

Swift et al. concluded from his study that the satisfactory results of bleaching onlypersist for 1-2 years and patient should be advised regarding the need for re-bleaching procedures for 1 week every year.⁵ The data procured from the studyby Moghadam FV et al clearly indicated that bleached teeth reverted back to the original color.⁴ All this affirmed the need for a maintenance therapy for the bleaching procedure.

To assess the performance of an aesthetic material in clinical situations, colour stability is an important in vitro analysis. Three recently introduced nanocomposites were selected in the present studyas there was a high demandin the use of nanocomposites owing to their superior properties. These nano composites have gained universal usage because of their advantage of better strength, aesthetics and lower shrinkage. According to Nair et al, itwas deduced that the nanofilled composites with their advanced filler characteristics have a higher color stability compared to the microfilled composite resins.9 The shade A2 was made use in this studyas it is currently the most commonly used shade in dentistry.⁹

The delta E values of the test specimens were 4.17±2.21, 1.91±1.40 and 1.63±1.40 for Filtek Z250 XT , ceram.x® and Tetric N-Ceram respectively after bleaching of which Tetric N-Ceram and Filtek Z250 XT showed statistically significant colour change. No consensus has been reached on the clinically perceptible ΔE value. Values of 1, 2, more than 3 and even more than 3.7 have been reported to be the clinically perceptible ΔE.^10,11,12

Kim JH et al stated thatcross-linking within nano-filled composite make them less prone to change in colourby bleaching procedure.¹³ Better results of ceram.x® could be due to is composition of organically modified ceramic nano particles comprising polysiloxane back bone. These nanoceramic particles can be best described as inorganic – organic hybrid particles where the inorganic siloxane part imparts the strength and the organic methacrylic part makes the particles compatible and polymerizable with the resin matrix.¹⁴

Lower colour stability of Tetric N Ceram could be due of the fillers in it, barium and strontium respectively. These are difficult to incorporate into the resin matrix, when compared with zirconia fillers.9

A study by Al Nuaimi et al reported that composite restorative material with large filler particle size has more color instability than a composite with small fillers.⁽¹⁵⁾Average particle size of Tetric N-Ceram, Filtek Z250 XT and ceram. x® were 40nm,5-20nm and 10nmrespectively which were consistent with the test values.⁽¹⁴⁾ When comparedwith ceram.x®,Filtek Z250 XTshowed a higher filler content. This could aid in the higher colour stability of ceram.x®.

Conclusion

The current study revealed that ceram. x® presented with best results of clinically accepted colour stability following the use of Opalescence PF bleaching agent.From the clinical stand point while planning for full mouth aesthetic rehabilitation in conjunction with bleaching procedure it is important for the clinician to select a combination ofcomposite and bleaching agent which results in no or minimal colour change.