Saudi Journal of Oral Sciences

: 2014  |  Volume : 1  |  Issue : 2  |  Page : 105--109

The effect of different types of oral mouth rinses on the hardness of Silorane-based and Nano-hybrid composites

Rohit Ashok Antony Fernandez1, Marwan El Araby2, Mohamed Siblini2, Ayed Al-Shehri2,  
1 Department of Prosthodontics, Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Kingdom of Saudi Arabia
2 Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Kingdom of Saudi Arabia

Correspondence Address:
Dr. Rohit Ashok Antony Fernandez
Riyadh Colleges of Dentistry and Pharmacy, P.O. Box 84891, Riyadh 11681
Kingdom of Saudi Arabia


Background: The restorative materials used in dentistry are required to have long-term durability in the oral cavity. Effect of various fluids in the oral environment can affect the hardness of these restorations. This study was carried out to evaluate the effect of different mouth rinses on the hardness of Silorane and Nano-hybrid resin composites. Materials and Methods: Thirty specimens were prepared from each type of composite and stored in artificial saliva for 24 h at 37°C. They were then divided into six experimental groups based on the test solution and were immersed and stored for 24 h at 37°C. Thereafter, the specimens were washed, dried and the hardness was measured for each specimen by Vickers microhardness tester. Results: Nano-hybrid resin composite showed higher Vickers hardness number (VHN) than Silorane composite in any test solution. There was only a mildly significant difference in the mean VHN of Silorane composite immersed in alcohol-containing mouthwash compared with artificial saliva. However, there was a significant difference in the mean VHN of Nano-hybrid composite when immersed in different mouthwashes. Conclusion: The microhardness values of Silorane-based and Nano-hybrid resin composites were decreased after immersion in the mouthwashes. The hardness of Nano-hybrid composite immersed in artificial saliva showed the highest VHN and was significantly affected when immersed in other test solutions. Silorane-based composite is more resistant to alcohol-containing mouthwash than Nano-hybrid composite.

How to cite this article:
Antony Fernandez RA, El Araby M, Siblini M, Al-Shehri A. The effect of different types of oral mouth rinses on the hardness of Silorane-based and Nano-hybrid composites.Saudi J Oral Sci 2014;1:105-109

How to cite this URL:
Antony Fernandez RA, El Araby M, Siblini M, Al-Shehri A. The effect of different types of oral mouth rinses on the hardness of Silorane-based and Nano-hybrid composites. Saudi J Oral Sci [serial online] 2014 [cited 2020 Jan 25 ];1:105-109
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Full Text


The restorative materials used in dentistry are required to have long term durability in the oral cavity. One of the most important physical properties is the surface hardness, [1] which is the resistance of the material to indentation or penetration. The properties related to the hardness are strength, proportional limit and ductility. The hardness of a material is used to predict its wear resistance and its ability to abrade or be abraded by dental structures and other materials.[2]

It has been proven that Silorane composite has better properties in some physical, mechanical and chemical aspects; such as polymerization shrinkage, high fracture toughness, bond strength, low water sorption, high light ambient stability, and a high resistance to external staining.[3] However, it was also proven that it has low surface hardness and relatively low compressive strength.[2]

In an in vivo situation, it has been reported that food components and beverages may affect resin-composites.[4] Mouth rinses are considered one of these affecting factors, [5] and their use has become popular recently.[6] Mouth rinses are effective in the prevention and control of caries and periodontal disease, by the dissolution of plaque, and additionally to reduce oral malodor and are being recommended to patients by clinicians on a regular basis.[7]

The presence of alcohol in mouth rinse is used to dissolve plaque and as an antiseptic agent.[8] If the percentage of alcohol in the mouth rinse is >25% it may be implicated for oral carcinoma.[7] The alcohol in mouth rinses was also found to soften composite restorations, [9] and this effect was directly related to the percentage of alcohol present. Studies have shown that mouth rinse containing 7% or less alcohol have the same effects of alcohol-free mouth rinses on methyl methacrylate composites.[10] However, some studies have shown that both alcohol-containing and alcohol-free mouth rinse can reduce the hardness of restorative materials.[11] The aim of this study is to study whether alcohol containing mouthrinses have an impact on the hardness of silorane based composites.

 Materials and Methods

Five commercially available mouth rinses and two resin composites materials were used in this study. The mouth rinses used were Listerine Total Care (21.6% alcohol content), equaline minty fresh (15% alcohol content), Listerine Total Care Zero (Alcohol-Free) (Johnson & Johnson Healthcare Products Division of McNEIL-PPC, Inc), Aquafresh Extreme Clean (Contains Sodium Fluoride) (GlaxoSmithKline Consumer Healthcare) and Avohex mouth wash (Contains Clorhexidine) (MECP (Middle East Pharmaceutical Industries Co. Ltd) . The composites chosen for the study were Filtek P90 Low Shrinkage (Silorane-based) (3M™ ESPE™) and Filtek Z250xt (methyl methacrylate-based) (3M™ ESPE™).

For microhardness measurement, six rectangular silicon molds were made that measured 8 mm length × 4 mm width, and 3 mm in thickness. In each mold, ten holes with an internal diameter 3 mm were made to obtain cylindrical samples of 3 mm diameter × 3 mm height.

Each mold was placed on a microscope glass slide separated with a transparent matrix that was placed on a glass slab. An adequate amount of each composite material was placed and condensed using plastic instrument and condenser. Extruded excess was removed, and then another transparent matrix was placed on top covered with a microscopic glass slide and a glass slab on top. A load of 1000 g was then placed and pressed to extrude the excess material and obtain uniform specimens.

Each sample was light-cured individually for 40 s from the top and then an extra 40 s from the bottom using 3M ESPE Elipar S10 with a light intensity of not <450 mW/cm 2 .

The excess material was removed with a scalpel blade, and then the specimens were polished on one surface using an automata device with 600-grit silicon carbide abrasive paper.

A total of 60 specimens were fabricated, 30 specimens from each type of composite material. Each group was then immersed in 20 mL of artificial saliva to complete the postirradiation/postsetting polymerization in a dark bottle and incubated at 37°C for 24 h.[12] The specimens were removed from distilled water using tweezers and dried using filter paper. Each group of thirty specimens was further divided into 6 subgroups, each comprising of 5 specimens. Five of these subgroups were immersed in. A volume of 20 mL of their respective test solutions (mouth rinses) and 1 was immersed in artificial saliva (base line-control). The test solutions along with the specimens were contained in a dark amber bottle that was incubated at 37°C for 24 h.[13]

All specimens were then rinsed using distilled water and dried with filter paper for hardness measurement. Microhardness measurements of the specimens were obtained using a Vicker's microhardness tester (Micromet II model, Buehler Ltd., Lake Bluff, Illinois, USA), with a diamond indenter having a 136° apex angle. The specimens were inspected visually before testing to confirm the absence of any surface defects. Indentations were made by applying 300 g load for 15 s. Three indentations were created on the surface of each sample; each indentation on the surface was measured by a microscope, and a mean value was determined for each test sample. The results were converted to Vicker's microhardness values.

The results of Vickers hardness number (VHN) were subjected to two-way analyses of variance (ANOVA) and Duncan post-hoc test for multiple comparisons. Statistical analysis of the data was performed using commercial software (SPSS for Windows, version 16, SPSS Inc., Chicago, IL, USA).


Two-way of ANOVA revealed that there was a significant interaction between test materials and different immersion test solutions (P = 0.000). The effects of the mouth rinses on the hardness of both test materials were significantly different from the artificial saliva (base line-control) (P = 0.000).

Within each material (Silorane or Nano-hybrid), the effect of different immersion solution on the hardness of each composite was tested by one-way ANOVA. There was a slight significant difference in the hardness of Silorane immersed in different solutions (P = 0.043). However, Nano-hybrid composite immersed in different solutions showed highly significant difference in the hardness values (P = 0.000).

Independent t-test showed that the Nano-hybrid resin composite showed higher VHN than Silorane composite in any test solution (P = 0.000). The VHN of Nano-hybrid and Silorane resin composite in artificial saliva were 125.6 ± 11.54 and 67.84 ± 4.99, respectively.

Post-hoc Duncan test has been performed within each material for multiple comparisons [Figure 1] and [Table 1]. There was a significant difference in the mean VHN of Silorane immersed in the alcohol-containing mouth wash at a concentration of 21.6% or 15% and that immersed in artificial saliva (P < 0.05), the VHN were 62.49 ± 4.7, 62.71 ± 6.3, 67.84 ± 4.9, respectively. There was, however, no significant difference in the mean VHN values of Silorane-based composite immersed in sodium flouride-containing and chlorohexidine mouthwashes (P = 0.065).{Figure 1}{Table 1}

Concerning Filtek Z250xt, post-hoc Duncan test showed that there was a significant difference in the mean VHN of Nano-hybrid composite immersed in artificial saliva and those immersed in different mouthwashes (P = 0.000).

The hardness of Nano-hybrid composite immersed in artificial saliva showed the highest VHN of 125 ± 11.5 and was significantly higher than that immersed in other test solutions [Figure 2] and [Table 2]. Nano-hybrid composite immersed in alcohol 21.6% mouth wash had the VHN of 87.03 ± 9.8, which was significantly lower than those immersed in chlorohexidine, sodium fluoride 0.055%, alcohol 15% or alcohol-free mouthwashes (P = 0.000). Moreover, there was a significant difference between the mean VHN of Nano-hybrid composite immersed in chlorohexidine (105.24 ± 8.2) and that immersed in alcohol-free (115.16 ± 13.8).{Figure 2}{Table 2}


The present investigation was conducted to determine the surface hardness of two commercially available Silorane-based and Nano-hybrid composite restorative materials after exposure to different types of oral mouthrinses.

Filtek™ P90 Silorane (3M™ ESPE™) low shrink posterior restorative revealed significantly lower volumetric shrinkage and polymerization shrinkage stress values than the methacrylate based composites tested. Filtek Silorane is marketed as a posterior composite and posterior composites are designed to have higher wear resistance than anterior composites. As the wear resistance of dental materials has a significant impact on the clinical performances of restorations, hardness tests are used to predict the wear resistance of dental materials.[14]

Two dental composite restorative materials of shade (A3) were selected for this study. Both composites were from the same manufacturer (3M ESPE) to eliminate any variables in the manufacturing process. The specimens used for both testing materials were immersed in artificial saliva for 24 h, for elution of unreacted components from the resin-composites [15] and to allow for postirradiation and postsetting polymerization to occur.[12],[16] The specimens were immersed in the different test solutions for 24 h, which is equivalent to a minimum of 2 years of 2 min use as described by El-Badrawy et al. in 1993. [13]

Previous studies reported that the greatest change in the hardness of composites occurred within the first 7 days after exposure to ethanol.[17] In this study, it was found that the base line hardness values of Silorane-based composite were lower than that of Nano-hybrid resin composite (for samples of the control groups). Differences in hardness between the two composites could be attributed to the lower filler content (55 vol%) of the silorane-based composite.[18]

This study revealed that both alcohol-free and alcohol-containing mouth rinses had affected the hardness of both tested dental composites. This was in agreement with studies [5],[11] where it was reported that alcohol is not the only factor that has a softening effect on resin composite restorative materials. It was observed that alcohol-free mouth rinses showed the least difference in surface hardness, followed by sodium fluoride containing mouth rinses. Chlorhexidine showed a significant decrease in surface hardness of both the composites tested. This finding is in concurrence with a previous study, which stated that this may be attributed to the potentiating effect of chlorhexidine on the fluoride present in the filler of the composite. [19]

The highest reduction in the hardness of Nano-hybrid resin composite (Bis-glycidyl methacrylate [Bis-GMA]-based) was found in alcohol (21.6% or 15%) containing mouth rinses. This finding was in accordance with Kao [17] who 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.[5] Ethanol causes softening of the resin composite surface by removing the polymer structure as unreacted monomer, oligomers and linear polymers, [20] or imparts an opener structure to the polymer, decreasing its physical properties and increasing wear.[21] Ethanol in mouth rinses initially lowers the surface hardness of dental resin composite, but then approach a plateau approach by the 2 nd week.[22]

Furthermore, Listerine Total Care has a low pH equal to 3.57, [23] and high alcohol percentage which greatly affects the surface hardness of Nano-hybrid resin-composite.[9],[24] On the other hand, Listerine slightly affected the hardness of Silorane-based composite. This was in contradiction with the results of in vitro study by Yesilyurt et al. who concluded that hardness of Silorane-based composite was not influenced by ethanol significantly. In this research, there was a significant difference in the mean VHN of Silorane-based composite immersed in alcohol-containing mouthwash at concentration of 21.6% or 15% and that immersed in artificial saliva.

After conditioning, Silorane-based composite revealed a resistance to the softening effect of alcohol-containing mouthwashes, which could be due to the hydrophobicity of the resin matrix. This was in accordance with Yesilyurt et al. [18] Silorane-based composites exhibited more stable surface hardness than the Nano-hybrid composites, which could be chiefly due to the uptake of water by the polymers. It was already mentioned that Nano-hybrid composite had resin matrices composed of Bis-GMA, Bis-EMA, UDMA, and triethylene glycol dimethacrylate (TEGDMA). 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 had 3,4-epoxycyclohexyl-cyclopolymethylsiloxane. The cyclosiloxane backbone imparted hydrophobicity, thereby curtailing water sorption.[25]


Within the limitations of this study the following conclusions were derived.

The microhardness values of both Silorane-based (Filtek P90) and Nano-hybrid (Filtek Z250xt) resin composites were decreased after immersion in the selected mouthwashes.

Both Nano-hybrid and Silorane-based composites exhibited a reduction in surface hardness properties when immersed in both alcohol-free as well as alcohol-containing mouth rinses. Although Nano-hybrid composite immersed in artificial saliva showed the highest hardness value in this study, and was significantly higher than that immersed in other test solutions, the surface hardness properties of Nano-hybrid composites were adversely affected by the alcohol-containing mouth rinses.

Nano-hybrid composites showed higher surface hardness than Silorane-based composites, possibly owing to the variation in filler content. In contrast, Silorane-based composite exhibited more stable surface hardness than the Nano-hybrid composites when exposed to various different mouth rinses, possibly due to the hydrophobic property of the Silorane-based composite material.

Chlorhexidine mouth rinse showed significant reduction in surface hardness properties of both Nano-hybrid and Silorane-based composites.


We wish to extend our gratitude to the Physics Laboratory at the King Saud University, in Riyadh, Kingdom of Saudi Arabia for permitting us access to their facilities to carry out the required tests on our samples.


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