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 Table of Contents  
Year : 2016  |  Volume : 3  |  Issue : 1  |  Page : 1-5

Effect of varying concentrations of home bleaching agents on hardness of a resin composite: An in vitro study

Department of Conservative Dentistry and Endodontics, KSR Institute of Dental Science and Research, Thiruchengode, Tamil Nadu, India

Date of Web Publication18-Oct-2016

Correspondence Address:
Dr. S Hari Baskar
Dental Clinic, Opp. Lakshmi Theatre, Chittode, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2229-3019.192467

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Aim: To evaluate the effect of 10%, 20% and 35% Carbamide Peroxide home bleaching agent on hardness of a microfilled resin composite. Materials and Methods: Forty specimens of micro filled resin composite(Z250, 3M ESPE) were prepared using moulds with dimensions of 4mm diameter x 2mm thickness and cured with a LED polymerization unit (LEDition - Ivoclar Vivadent). The specimens were polished with coarse, medium, fine and super fine polishing discs (Sof-lex, 3M ESPE) and were stored in distilled water at 37?C in an incubator for 24 hours. Specimens were then divided into four groups of 10 specimens each. One group was selected as the control group (not treated with bleaching agents) and was stored in artificial saliva for 7 days at 37?C. The other three groups were treated with 10%, 20% and 35% carbamide peroxide gels respectively (Opalesence PF 10%, Opalesence PF 20% and Opalesence PF 35%, Ultradent) as per the manufacturer’s instructions over a period of 7 days. The specimens were subjected to Shore Durometer for 15 seconds and checked for hardness. The results were analyzed using ANOVA and Post hoc Bonferroni tests. Results: There was no significant difference in the hardness of the specimens belonging to Group A, Group B or Group C when compared with the Control Group. Conclusion: It can be confirmed based on the results of this study that the hardness of the Micro filled Composite resin was not affected by10%, 20 % or 35% carbamide peroxide bleaching gels when used as per the manufacturer’s instructions. Restorations done using microfilled composite resins can be retained after bleaching procedures.

Keywords: Bleaching, composite resin, microfilled, microhardness, carbamide peroxide

How to cite this article:
Baskar S H, Jayakumar M, Kumar S. Effect of varying concentrations of home bleaching agents on hardness of a resin composite: An in vitro study. J Indian Acad Dent Spec Res 2016;3:1-5

How to cite this URL:
Baskar S H, Jayakumar M, Kumar S. Effect of varying concentrations of home bleaching agents on hardness of a resin composite: An in vitro study. J Indian Acad Dent Spec Res [serial online] 2016 [cited 2019 Jul 16];3:1-5. Available from: http://www.jiadsr.org/text.asp?2016/3/1/1/192467

  Introduction Top

Advances in dental materials have allowed practitioners to perform a variety of procedures to improve the appearance of patient’s smiles. Resin composites accommodate a wide range of applications for both anterior and posterior restorations. Composite resins have provided us with the opportunity to make invisible restorations possible and achieve optical properties of natural teeth.

Several esthetic procedures have been described in the literature to improve the appearances of smiles and these include alterations in the form, texture, position, and color of the teeth. The most conservative of them all is bleaching.[1],[2],[3] Bleaching, although not new to dentistry, has recently become very popular. It has the advantage of being minimally interventive and is very safe when used correctly. The introduction of carbamide peroxide at-home bleaching agent has created resurgence in use of bleaching because of its relative ease of application, safety of the material used, lower cost, and high percentage of successful treatment.

There are concerns regarding the effect of bleaching agents on resin composites due to their organic matrix, which is more prone to chemical alteration when compared with inert metal or ceramic restorations.[4] Bleaching agents may have a varying influence on physical properties of restorative materials including its hardness. The estimation of hardness may indicate the deteriorating effects of bleaching agents on the restorative material.

Some studies found a reduction in surface microhardness after the bleaching process[5],[6] whereas some others did not.[7],[8]

The aim of this in vitro study was to evaluate and compare the effects of bleaching agents with carbamide peroxide at concentrations of 10%, 20%, and 35% on the hardness of a microfilled composite resin.

  Materials and Methods Top

The resin-based composite material evaluated in the current study is Filtek Z250—a microfilled composite resin [Table 1].
Table 1: Materials Used In The Study

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Specimen fabrication

Ethyl vinyl acetate molds were made to dimensions of 4 mm diameter × 2 mm height. The resin was packed into the molds and polymerization was carried out using Light Emitting Diode polymerization unit (Ivoclar Vivadent Inc, New York) for 20 s as per the manufacturer’s recommendations. A total of 40 specimens were prepared.

The specimens were polished with coarse, medium, fine, and superfine polishing discs (Sof-lex discs, 3M ESPE, St Paul, MN) [Figure 1].
Figure 1: Mold for sample preparation

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Grouping of specimens

The specimens divided into four groups consisting of 10 each. The specimens were stored in distilled water in an incubator at 37°C for 24 h in  Petri dish More Detailses before they were exposed to the bleaching agents.

Ten specimens were selected as the control group with no bleaching treatment and they were stored in artificial saliva (Wet Mouth, ICPA) at 37°C in an incubator. The artificial saliva was replaced every day during the period of the study [Figure 2] and [Figure 3].
Figure 2: Samples stored in artificial saliva

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Figure 3: Samples placed inside an incubator

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Bleaching procedure

Bleaching procedure was carried out as per the manufacturer’s instructions. The top surfaces of the specimens were covered with the bleaching gel to a thickness of 1 mm.

Control group (n = 10)—The specimens were not exposed to bleaching agents.

Group A (n = 10)—They were exposed to Opalescence PF 10% bleaching gel for duration of 8 h.

Group B (n = 10)—They were exposed to Opalescence PF 20% bleaching gel for duration of 4 h.

Group C (n = 10)—They were exposed to Opalescence PF 35% bleaching gel for duration of 30 min.

The bleached specimens were thoroughly cleaned with a soft toothbrush under flowing distilled water and incubated at 37°C in artificial saliva for the remaining time of the day. The bleaching procedure was carried out for 7 consecutive days [Figure 4].
Figure 4: Samples exposed to the bleaching agent

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Hardness test

The specimens were removed from artificial saliva, washed, and stored in distilled water at 37°C in an incubator 24 h before they were tested for hardness. The specimens were tested with a Digital Shore D Durometer.

Statistical analysis

Statistical analysis was done using ANOVA with P < 0.05 and post hoc Bonferroni tests [Table 2] and [Table 3], [Figure 5].
Table 2: Results of Shore-D hardness tests

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Table 3: Mean microhardness values (MPa) and statistical results: post hoc Bonferroni test

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Figure 5: Comparison of mean microhardness values of control group and experimental groups

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  Results Top

There was no significant difference in the hardness of the specimens belonging to Group A, Group B, or Group C when compared with the Control Group.

However, when multiple comparison post hoc—Bonferroni test was used to individually compare three bleaching agent groups, there was a statistically significant difference in hardness among them [Figure 6].
Figure 6: Comparison of mean microhardness values of the three experimental groups after bleaching

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  Discussion Top

Physical properties of a restorative material have implications on the quality and durability of restorations. A reduction in hardness due to erosion of organic matrix may enhance the roughness and wear of restorations and may decrease their wear resistance.[9]

When bleaching is performed in the clinical setting, the physical alteration of tooth-colored restoratives is an important consideration. Bleaching agents affect the color lightening of discolored tooth structure through decomposition of peroxides into free radicals. The free radicals result in a breakdown of the large pigmented molecules in the enamel into smaller, less pigmented molecules through either oxidation or reduction.

Carbamide peroxide containing bleaching gels are usually unstable and immediately degrade into approximately one-third hydrogen peroxide and two-thirds urea on contact with tissue and saliva. Hydrogen peroxide breaks down into free radicals after degradation of carbamide peroxide inducing oxidative cleavage of polymer chains leading to chemical softening of dental materials.[10]

The ability of a material to abrade or to be abraded by opposing dental structures or materials or any chemical softening has implications on clinical durability of dental restorations.[11] The mechanical properties of composite resins are determined by the interaction of several factors, such as composition, degree of conversion of polymer chains, filler volume-fraction, filler particle size and distribution, and the interfacial properties between the filler and resin matrix.[12],[13] Thus, the higher filler content of Filtek Z250 micro-filled composite may have contributed to the higher hardness performance.

One of the factors that cause decrease in surface hardness of resin composite after bleaching treatment is due to the oxidation and degradation of resinous matrix.[14]

The resin composite used in this study consists of about 60% inorganic filler loading by volume and this must have been high enough to be closely packed together to resist oxidation and degradation of matrix, thus resisting the softening effect of bleaching agents.

Another factor that affects the integrity of hardness of resin composites is the degree to which filler is bonded to resin matrix. The bonding of inorganic fillers to resin matrix may be adequate to resist the effect of bleaching treatments in the resin composite used in this study.

Resin composites are also reported to be highly susceptible to chemical softening due to presence of Bis-GMA monomer.[15] The presence of Bis-GMA monomer in the resin used in this study must be low that it did not cause any significant reduction in hardness even after bleaching with 10%, 20%, or 35% bleaching gels.

Filler particles are usually much harder than the polymer matrix and if they are closely spaced, they shelter the intervening matrix polymer. Filler particles are much harder than the polymer matrix and resist wear well. If filler particles are closely spaced, they shelter the intervening matrix polymer due to ``microprotection.’’ In microfilled composites, the particles are extremely small, and the interparticle spacing is very small.[16] Use of 10% Carbamide peroxide bleaching agent affected the hardness of various resin composites like nano-filled, low shrink, and hybrid types but not the microfilled type.[17]

  Conclusion Top

Within the limitations of this study, it can be concluded that none of the bleaching agents Opalescence PF 10%, Opalescence PF 20%, or Opalescence PF 35% used in this study produced any significant change in the hardness of the bleached groups when compared with the control group.

Though there were significant changes among the groups themselves, there was no significant change in them when compared with the control group.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Haywood VB, Heymann HO. Nightguard vital bleaching: How safe is it. Quintessence Int 1991;22:515-23.  Back to cited text no. 1
Haywood VB. History, safety, and effectiveness of current bleaching techniques and applications of the nightguard vital bleaching technique. Quintessence Int 1992;23:471-88.  Back to cited text no. 2
White DJ, Kozak KM, Zoladz JR, Duschner H, Gotz H. Peroxide interactions with hard tissues: Effects on surface hardness and surface/subsurface ultrastructural properties. Compend Contin Educ Dent 2002;23:42-8.  Back to cited text no. 3
Cooley RL, Burger MK. Effect of carbamide peroxide on composite resins Quintessence Int. 1991;22:817-21.  Back to cited text no. 4
de Freitas PM, Basting RT, Rodrigues JA, Serra MC. Effects of two 10% peroxide carbamide bleaching agents on dentin microhardness at different time intervals. Quintessence Int 2002;33:370-5.  Back to cited text no. 5
Yap AU, Wattanapayungkul P. Effects of in-office tooth whiteners on hardness of tooth-colored restoratives. Operat Dent 2002;27:137-41.  Back to cited text no. 6
Yu H, Li Q, Hussain M, Wang Y. Effects of bleaching gels on the surface microhardness of toothcolored restorative materials in situ. J Dent 2008;36:261-7.  Back to cited text no. 7
Polydorou O, Hellwig E, Auschill TM. The effect of at-home bleaching on the microhardness of six esthetic restorative materials. J Am Dental Assoc 2007;138:978-84.  Back to cited text no. 8
Abu-Bakr N, Han L, Okamoto JM, Hickel R. Changes in mechanical properties and surface texture of compomer immersed in various media. J Prosthet Dent 2000;84:444-52.  Back to cited text no. 9
De Freitas PM, Basting RT, Rodrigues JA, Serra MC. Effects of two 10% peroxide carbamide bleaching agents on dentin microhardness at different time intervals. Quintessence Int 2002;33:370-5.  Back to cited text no. 10
Atash R, Van den Abbeele A. Bond strengths of eight contemporary adhesives to enamel and to dentine: An in vitro study on bovine primary teeth. Int J Paediatr Dent 2005;15:264-73.  Back to cited text no. 11
Bream M, Lambrechts P, Vanherle G. Clinical relevance of laboratory fatigue studies. J Dent 1994;22:97-102.  Back to cited text no. 12
Ferracane JL, Berge HX, Condon JR. In vitro aging of dental composites in water-effect of degree of conversion, filler volume, and filler/matrix coupling. J Biomed Mater Res 1998;42:465-72.  Back to cited text no. 13
Taher NM. The effect of bleaching agents on the surface hardness of tooth colored restorative materials. J Contemp Dent Pract 2005;6:18-26.  Back to cited text no. 14
Wu W, McKinney JE. Influence of chemicals on wear of dental composites. J Dent Res 1982;61:464-8.  Back to cited text no. 15
Bayne SC, Taylor DF, Heymann HO. Protection hypothesis for composite wear. Dent Mater 1992;8:305-9.  Back to cited text no. 16
MQ AlQahtani. The Effect of 10% carbamide peroxide bleaching agent on microhardness of four types of direct resin based restorative materials. Operat Dent 2013;38:316-23.  Back to cited text no. 17


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1], [Table 2], [Table 3]

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