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 Table of Contents  
Year : 2017  |  Volume : 9  |  Issue : 2  |  Page : 55-59

Effect of four mouth rinses on microhardness of esthetic restorative material: An In vitro study

Department of Dentistry, Hassan Institute of Medical Sciences, Hassan, Karnataka, India

Date of Web Publication13-Apr-2017

Correspondence Address:
Rosamma George
Department of Dentistry, Hassan Institute of Medical Sciences, Hassan - 573 201, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jioh.jioh_21_16

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Aims and Objectives: This in vitro study is designed to evaluate the effect of four mouth rinses on the microhardness of esthetic restorative material. Materials and Methods: Forty specimens of resin composite (Filtek™ P60) material (3M ESPE St. Paul, MN, USA) with 3 mm diameter and 3 mm height were prepared using a plastic mold. The baseline microhardness values of the specimens were recorded using Vickers microhardness tester. The specimens were randomly allocated into four groups, each containing ten specimens as follows - Group I Listerine® (Johnson & Johnson), Group II Colgate Plax®, Group III Freshclor® (Group Pharmaceuticals), and Group IV AloeDent® (Optima, Bradford-Italy). The pH of all mouth rinses was recorded. Then, the specimens were immersed in 20 ml of respective mouth rinses and kept in an incubator at 37°C for 24 h. The change in the microhardness values of the specimens was recorded. The obtained result was subjected to statistical analysis using Wilcoxon signed rank, Kruskal–Wallis, and Mann–Whitney U-tests. SPSS software version 16 and Microsoft Excel version 7 were also used. The level of significance was set at P= 0.05. Results: There was reduction in the microhardness of all the specimens irrespective of the mouthwashes. Group I (Listerine®) showed significant reduction in the microhardness compared to Group II (Colgate Plax®), Group III (Freshclor®), and Group IV (AloeDent®), whereas there was no statistically significant difference between Group III and Group IV. Conclusion: All the mouth rinses showed reduction in surface hardness of the esthetic restorative material. High reduction of surface hardness was shown in Listerine® mouth rinse. There was no statistically significant difference between Freshclor® and AloeDent® mouth rinses.

Keywords: Microhardness, mouth rinse, pH, resin composites

How to cite this article:
George R, Kavyashree G. Effect of four mouth rinses on microhardness of esthetic restorative material: An In vitro study. J Int Oral Health 2017;9:55-9

How to cite this URL:
George R, Kavyashree G. Effect of four mouth rinses on microhardness of esthetic restorative material: An In vitro study. J Int Oral Health [serial online] 2017 [cited 2022 Oct 5];9:55-9. Available from:

  Introduction Top

In the recent years, there is a great research and development in the field of restorative dentistry. There is a marked increase in the use of composite resin as esthetics is the main concern for an individual.[1] However, resin re-restoration remains the most frequently performed restorative work.[1],[2] The oral environment influences the longevity, durability, and degradation of dental composite resins.[3],[4] Degradation of resin restoration may occur due to chemical degradation as the resin is unexposed to abrasion and compression.[5] Mechanical properties of the resins can be changed by water, saliva, drinks, and food.[5],[6] The wear resistance of a resin composite is affected when there is reduction in surface hardness.[7] Due to decrease in wear resistance, there may be increase in surface roughness, which is favorable for plaque accumulation, staining of resin composite, and finally early loss of the restoration, requiring re-restoration.[7],[8]

Dental caries and periodontal diseases can be prevented and controlled by regular use of mouthwashes.[9] Mouth rinses contain water, antimicrobial agents, salts, preservatives, and in some cases alcohol. The variation in the concentration of these substances affects the pH of the mouth rinses.[9],[10] Although mouthwashes are effective in reducing periodontal diseases and dental caries, there are some risks associated with them when used daily. The risks include dry mouth, pigmentation on tongue, an increase in the incidence of head and neck, and change in the physical properties of composite resin restorations.[11]

The alcohol in the mouthwashes influences the degradation of composite resins [11],[12] and this effect is found to be directly related to the concentration of alcohol.[12] Furthermore, low pH affects sorption; solubility and surface degradation of this restorative material.[12] Therefore, alcohol-free mouthwashes have been introduced into the market. However, studies have reported the fact that why both alcohol and alcohol-free mouth rinses can reduce the hardness of the restorative materials.[12]

Recently, manufacturers have introduced a new restorative composite material (Filtex™ P60®), which they claim to be resistant to wear in the oral environment. In addition, a new herbal mouth rinse (AloeDent ®) and an alcohol-free mouth rinse (Freshclor ®) are available in the market. As these products are recently introduced, there are no studies assessing the effect of these mouth rinses on the composite. Hence, the aim of the present study was to assess and compare the effect of these newly available mouth rinses (AloeDent ® and Freshclor ®) on the newly introduced restorative composite (Filtex™ P60®). This was studied by assessing the change in the surface microhardness of the restorative composite after exposure to the mouth rinses.

  Materials and Methods Top

Prior to the commencement of the study, ethical clearance was obtained from the Institutional Ethical Committee (IEC No. 78). The study was carried out at the Department of Dentistry, Hassan Institute of Medical Sciences, Hassan, India, and at Raghavendra Spectro Metallurgical Laboratory, Bengaluru, India.

Sample size calculation

Required sample size for this study was estimated using the following information (from previous studies) and assumption; (1) minimum difference expected between the groups and amount of variation within the group, i.e., standard deviation (both from previous studies), (2) level of significance set at 5%, and (3) power of the study: 80%.

Specimen preparation

A total of forty specimens of resin composite (Filtek™ P60, 3M ESPE) [Table 1] with 3 mm diameter and 3 mm height were prepared using a plastic mold. The mold was placed on a glass slide and filled with resin composite to a slight excess using Composite Filling Instrument (GDC Marketing Co., Hoshiarpur, Punjab, India), covered with a clear matrix strip, and another glass slide was placed on the top and gently pressed for 30 s to extrude excess material and to obtain a smooth surface. Each specimen was cured for 40 s from the top and bottom each, using LED Light Cure Unit (Blue phase C8, Astria at 800 mW/c). The baseline microhardness of each specimen was recorded using Vickers Micro Hardness Tester (Matsuzawa, Japan/MMT-X7A). Slot No. MMT 5421X) with a load of 40 g and a dwell time of 15 s.
Table 1: Product profile of resin composites used in the study

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The mouth rinses selected for the study were Listerine ®, Colgate Plax ®, Freshclor ®, and AloeDent ®. The pH of the mouth rinses was recorded using a digital pH meter (Servewell Instruments and Equipments Pvt. Ltd., Bengaluru) [Table 2].
Table 2: Composition, pH, and group allocation of mouth rinses used in the study

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The forty composite specimens were randomly divided into four groups (Group I–IV) of ten specimens each. Specimens of Groups I, II, III, and IV were immersed in 20 ml of Listerine ®, Colgate Plax ®, Freshclor ®, and AloeDent ®, respectively, for 24 h at 37°C, following which each specimen was removed from the mouth rinses and dried. They were rechecked for the surface microhardness as described previously.

The data were tabulated and subjected to statistical analysis.

Statistical analysis

The mean value of surface microhardness of all the four groups was calculated. The intragroup comparison was done using Wilcoxon signed rank test. For intergroup comparison, Kruskal–Wallis and Mann–Whitney U-tests were used. SPSS software version 16 (SPSS Inc., Chicago, IL, USA) and Microsoft Excel version 7 (Microsoft Corporation, NY, USA) were also used.

  Results Top

There was a significant reduction in the microhardness of all specimens after immersing in the mouth rinses (P < 0.05) [Table 3] and [Figure 1]. Specimens in Group I showed significant reduction in the microhardness compared to the other three groups. There was no statistically significant difference in the microhardness of specimens of Groups III and IV [Table 4] and [Figure 2].
Table 3: Intragroup comparison of changes in microhardness in each group

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Figure 1: Microhardness at before and after immersion

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Table 4: Intergroup comparison of microhardness

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Figure 2: Reduction in microhardness after immersion

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  Discussion Top

The ideal requirement of a restorative material is that it should function in the same manner as dental hard tissue in the dynamic oral environment.[12] To have long-term durability in the oral cavity, the restorative material should have sufficient hardness. Hardness is the resistance of a material to indentation or penetration.[12],[13] Strength, proportional limit, and ductility are related to hardness. Hardness has also been used to predict the wear resistance of a material and its ability to abrade or be abraded by opposing dental structures and materials.[14] Hence, when there is reduction in the hardness of resin material, there may be premature failure of resin restoration. Many new materials are developed so that their properties come closer to dental tissues. One such material is Filtex™ P60®.

Mouth rinses have been reported to affect the solubility of some restorative materials.[8] Asmussen [8],[9] reported that alcohol in the mouth rinses softens the resin composite restorations. Alcohol in mouth rinses is used as a solvent, taste enhancer, and antiseptic agent.[15] Ethanol, which is a component in various mouthwashes, may increase the hydrolytic degradation of composite-based materials.[16] Thus, there is an increasing demand for alcohol-free mouth rinses.[9] Freshclor ® (alcohol free) and AloeDent ® (herbal) are the newly introduced mouth rinses in the market and their effect on the surface hardness of restorative composite material (Filtex™ P60®) is not known. The surface hardness test is important because it may affect the surface properties of esthetic materials.[17],[18] The strength and rigidity of materials are related to the surface hardness property. Hence, the present study was undertaken to evaluate and compare the effect of alcohol-containing (Listerine ® and Colgate Plax ®), alcohol-free (Freshclor ®), and herbal (AloeDent ®) mouth rinses on the surface hardness of the newly introduced restorative composite material (Filtex™ P60®).

In the present study, alcohol-containing mouth rinses (Listerine ® and Colgate Plax ®) reduced the surface microhardness statistically more than alcohol-free (Freshclor ®) or herbal mouth rinses (AloeDent ®). The alcohol content of Listerine ® and Colgate Plax ® was 21.6%w/v and 11.6%w/v, respectively. Ethanol causes softening of the resin composite surface by removing the polymer structure as unreacted monomer, oligomers, and linear polymers [14],[18] or imparts an opener structure to the polymer, decreasing its physical properties and increasing wear.[19],[20] Ethanol in mouth rinses initially lowers the surface hardness of dental resin composite, but then makes a plateau approach by the 2nd week.[20]

In vitro studies have reproduced the subsurface and surface degradation of resin composites by storing them in ethanol,[12] and the mechanical properties of composite resins have been compromised by aging them in alcohol-containing solutions.[12],[15] The findings of these studies suggest the use of alcohol-free mouth rinses in patients with many resin restorations.

There was greater reduction in the surface microhardness of resin material from Listerine ® mouth rinse than Colgate Plax ®. This may due to the higher percentage of alcohol content of Listerine ® than Colgate Plax ®. Similar to our findings, Penugonda et al.[15] reported that the higher percentage of alcohol in the mouth rinses causes more reduction in the hardness of restorative materials. Carvalho et al.[16] and Almeida et al.[17] also showed higher sorption rate for nanofilled resin composites in ethanol than in water or saliva. Kao [18] revealed that both Bis-GMA- and urethane dimethacrylate (UDMA)-based polymers are susceptible to chemical softening by ethanol. This softening effect was found to be directly related to the percentage of alcohol in the mouth rinses.[18] Furthermore, Listerine ® has a low pH equal to 3.8[14] and a high alcohol percentage which greatly affect the surface hardness of resin composites.[17],[18] Low pH of active ingredients of mouthwashes may influence the surface hardness, wear, and color.[20] The acidity may change the polymeric matrixes of composite resin affecting dimethacrylate monomer present in their compositions.[20] A previous study suggested that, by lowering the solutions' pH, there is production of methacrylic acid that results in the sorption and hygroscopic expansion as a consequence of enzymatic hydrolysis and biodegradation.[21] It was observed that sodium fluoride-containing mouth rinses also reduce the surface hardness.[10],[20],[21] Sodium fluoride is one of the components of Colgate Plax ®, thus fluoride, along with its low pH, may have caused the reduction in the surface microhardness.

Alcohol-free mouth rinses have been shown to be as effective as alcohol-containing ones. However, in the present study, it has been found that alcohol-free mouth rinses also tend to reduce the surface microhardness of composites. Similarly, it was found that alcohol-containing and alcohol-free mouth rinses adversely affect the hardness of resin composites, glass ionomer cement, and fissure sealants, when compared to distilled water.[8] Other studies also reported that both alcohol-containing and alcohol-free mouthwashes affect the hardness of resin composites.[8],[10] Few authors [5],[11] have reported that alcohol is not the only factor that has a softening effect on resin composite restorative materials. AloeDent ® mouth rinse did not show a significant reduction of surface microhardness. This may be because of the absence of alcohol in it and also due to the near-neutral pH. Another herbal mouth rinse (HiOra) also showed less reduction in microhardness even though it had low pH. This was attributed to the absence of alcohol in it.

In the present study, all the mouth rinses irrespective of the presence or absence of alcohol or herbal mouth rinses resulted in reduction in the surface microhardness of the tested resin composite material compared to baseline values. This may be because of the alcohol content and acidic pH of the mouth rinses which would have caused acid erosion of the resin composite by acid etching and leaching the principal matrix-forming cations. Diab et al. also reported similar observations and concluded that mouth rinses with low pH are detrimental to the hardness of resin composites.[22]

However, the reduction of surface hardness of the resin was less compared to other studies. This may be because of the components of this new resin system. This resin (Filtek P60) consists of three major components. The majority of TEGDMA has been replaced with a blend of UDMA and Bisphenol A polyethylene glycol diether dimethacrylate (Bis-EMA). Both of these resins are of higher molecular weight and therefore have fewer double bonds per unit of weight. The high molecular weight materials also impact the measurable viscosity. The higher molecular weight of the resin results in less shrinkage, reduced aging, and a slightly softer resin matrix. In addition, these resins impart a greater hydrophobicity and are less sensitive to changes in atmospheric moisture.[13] Yesilyurt et al. concluded that hardness of silorane-based composite was not influenced by ethanol significantly, which could be due to the hydrophobicity of the resin matrix.[23] Except for Bis-EMA, all other molecules (Bis-GMA, UDMA, and TEGDMA) have hydroxyl groups, which promote water sorption. As for silorane-based composite, it has 3,4-epoxycyclohexyl-cyclopolymethylsiloxane. The cyclosiloxane backbone imparts hydrophobicity, thereby curtailing water sorption.[24]

The findings of our study suggest that it is preferable to use alcohol-free mouth rinses in patients with many resin restorations. However, the results of this in vitro study may not be directly related to the clinical situation where saliva may dilute or buffer the mouth rinses. Hence, further clinical studies are recommended to know the solubility behavior of different resin composites.

  Conclusion Top

  • All the mouth rinses tested in this study did not negatively affect the hardness of the tested dental composite
  • Listerine ® mouth rinse containing the highest amount of alcohol showed maximum reduction in microhardness of resin composite Filtek P60
  • The microhardness value of (FiltekP60) resin composites is decreased after immersion in the selected Listerine ® and Colgate Plax ® mouthwashes
  • Reduction in the surface microhardness in the tested composite was lower in alcohol free mouth rinses than in alcohol containing mouth rinse
  • All the mouth rinses used in the study irrespective of the presence or absence of alcohol reduced the microhardness of the tested composite resin composite.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4]

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