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| Year : 2014 | Volume
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| Issue : 3 | Page : 261-265 |
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| The effect of different beverages on surface hardness of nanohybrid resin composite and giomer |
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Saijai Tanthanuch1, Boonlert Kukiattrakoon2, Chantima Siriporananon1, Nawanda Ornprasert1, Wathu Mettasitthikorn1, Salinla Likhitpreeda1, Sulawan Waewsanga1
1 Department of Conservative Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla, Thailand
2 Maxillofacial Prosthodontics Rehabilitation Research Unit, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla, Thailand
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| Date of Submission | 12-Nov-2013 |
| Date of Decision | 27-Feb-2014 |
| Date of Acceptance | 11-Mar-2014 |
| Date of Web Publication | 2-May-2014 |
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 Abstract | | |
Aims: To investigate the effects of five beverages (apple cider, orange juice, Coca-Cola, coffee, and beer) on microhardness and surface characteristic changes of nanohybrid resin composite and giomer.
Materials and Methods: Ninety-three specimens of each resin composite and giomer were prepared. Before immersion, baseline data of Vicker's microhardness was recorded and surface characteristics were examined using scanning electron microscopy (SEM). Five groups of discs (n = 18) were alternately immersed in 25 mL of each beverage for 5 s and in 25 mL of artificial saliva for 5 s for 10 cycles. Specimens were then stored in artificial saliva for 24 h. This process was repeated for 28 days. After immersion, specimens were evaluated and data were analyzed by two-way repeated analysis of variance (ANOVA), Tukey's honestly significant difference (HSD), and a t-test (α = 0.05).
Results: Microhardness of all groups significantly decreased after being immersed in the tested beverages (P < 0.05). SEM photomicrographs presented surface degradation of all groups.
Conclusions: The effect of these beverages on the surface of both restorative materials also depended upon the exposure time and chemical composition of the restorative materials and beverages. Keywords: Beverage; giomer; microhardness; resin composite
How to cite this article:
Tanthanuch S, Kukiattrakoon B, Siriporananon C, Ornprasert N, Mettasitthikorn W, Likhitpreeda S, Waewsanga S. The effect of different beverages on surface hardness of nanohybrid resin composite and giomer. J Conserv Dent 2014;17:261-5 |
How to cite this URL:
Tanthanuch S, Kukiattrakoon B, Siriporananon C, Ornprasert N, Mettasitthikorn W, Likhitpreeda S, Waewsanga S. The effect of different beverages on surface hardness of nanohybrid resin composite and giomer. J Conserv Dent [serial online] 2014 [cited 2022 Aug 13];17:261-5. Available from: https://www.jcd.org.in/text.asp?2014/17/3/261/131791 |
| Introduction | |  |
Nanohybrid resin composite, the newest resin composite restorative material, is becoming popular because it combines physical, mechanical, and esthetic properties. It incorporates a high volume fraction of filler particles with a wide particle size distribution (5-100 nm). [1] The compressive and diametral strength, and the fracture resistance of the nanohybrid resin composite is equivalent to or higher than those of other composites (hybrid, microhybrid, and microfilled-resin composite). [1]
Giomer is a relatively new innovative filler technology of resin composite as an esthetic direct restorative material for anterior and posterior teeth restoration. Similar to a traditional methacrylate-based composite, the giomer chemical composition encompasses inorganic filler particles and organic-resin matrix. [2],[3] In place of applying purely glass or quartz as the typical fillers, the giomer encompasses inorganic fillers (ranges between 0.01 and 5 μm) that are derived from the complete or partial reaction of ion-leachable fluoroboroaluminosilicate glasses with polyalkenoic acids in water before being interfaced with the organic matrix. [2],[3] This created a stable glass-ionomer phase on a glass core in which they induced an acid-base reaction between acid reactive fluoride containing glass and polycarboxylic acid in the presence of water and developed as a prereacted glass ionomer (PRG) filler. [4] The pre-action can involve only the surface of the glass particles (called surface PRG (S-PRG)) or almost the entire particle (termed fully PRG (F-PRG)). [4]
Nowadays, people are interested in healthy drinks and fruit juice. A recent study suggested that drinking apple cider can help maintain good health as well as help one detox. [5] However, consumption of acidic food, fruit juices, soft drinks, coffee, tea, or wine, can result in surface damage and decrease hardness, esthetic quality, and other properties of resin composite and giomer. [6],[7],[8],[9],[10],[11] There are a number of studies reporting the different surface hardness effects of beverages on resin composite and giomer, [7],[10],[12],[13] but only a few of the studies reported effects of apple cider, orange juice, Coca-Cola, coffee, and beer on surface hardness of nanohybrid resin composite and giomer. In addition, the previous studies [7],[12] presented the continuous immersion of resin composite in the selected beverages. However, during consumption, drink contacts only shortly with the tooth surfaces before it is washed away by saliva. This study was then designed to simulate the washing effect of saliva of an individual drinking by cyclic specimen immersion. Therefore, the objectives of this study were to compare the effects of different beverages (apple cider, orange juice, Coca-Cola, coffee, and beer) on surface hardness and surface characteristic changes of nanohybrid resin composite and giomer and to investigate the pH and titratable acidity of different beverages.
| Materials and methods | | |
Specimen preparation
Ninety-three disc-shaped specimens (10.0 mm in diameter and 2.0 mm in thickness) were made from each nanohybrid resin composite and giomer using a polytetrafluoroethylene cylindrical mold. The details of these materials are given in [Table 1]. A mylar strip and a glass slide were then placed over the filled mold after which light pressure (20 N) was applied. The glass slide and the mylar strip had mirror flat surfaces. This method was able to provide a smooth surface on each specimen. The specimens were polymerized for 40 s with a light-activated polymerization unit (Elipar 2500, 3M ESPE, St Paul, MN, USA) to ensure a complete polymerization. [14] The light intensity was verified with a measuring device (Cure Rite, L.D. Caulk, Milford, DE, USA). No mechanical preparation or abrasions of specimens were performed.
The pH and titratable acidity measurements
Five beverages were used in this study: Apple cider, orange juice, Coca-Cola, coffee, and beer [Table 2]. The pH of each beverage was determined using a pH meter (Orion 900A, Orion Research, Boston, MA, USA). Ten pH readings of the freshly prepared drinks were obtained in order to give a mean pH measurement for each beverage.
To determine titratable acidity (buffering capacity), [15] 20 mL of each beverage was added by 0.5 mL increments of 1 mol/L sodium hydroxide (NaOH). The amount of NaOH required to reach pH levels of 5.5, 7.0, and 10.0 was recorded. The titrations for each beverage were also repeated 10 times to obtain a mean value.
Beverage immersion and microhardness testing
Ninety-three discs of each nanohybrid resin composite and giomer were divided into five groups of 18 specimens, the rest of three samples (before immersion) were subjected to scanning electron microscopy (SEM) (JSM model 5800LV, JEOL, Tokyo, Japan) observations. Each group was subjected to surface microhardness measurement to obtain a baseline value. The hardness value (kg/mm) of each specimen was determined using a microhardness tester (Micromet II, Buehler, Lake Bluff, IL, USA) with a diamond Vickers indenter. A load of 0.3 N was applied to the surface for 10 s. Five indentations, equally spaced over a circle, were made on the surface of each specimen.
After that, at room temperature (about 25°C), the specimens were alternately immersed in 25 mL of a beverage for 5 s and in 25 mL of artificial saliva for 5 s for 10 cycles. [7] The same protocol was used with different beverages used in this study for 28 days consecutively. In order to maintain the original pH level of the beverages, they were refreshed daily throughout the experiment. The specimens' immersion protocol simulated an individual eating acidic food, sour fruits, and drinks. [7] After the immersion sequence was completed, the specimens were rinsed with deionized water, blotted dry, and subjected to post-immersion surface microhardness testing. The surface hardness test was carried out at the following intervals, before immersion and then subsequently at 7, 14, 21, and 28 days. Gradual changes in surface microhardness were recorded at each time interval.
Surface micromorphology analysis
Using SEM, the effect of each beverage on the surface micromorphology of the materials before and after immersion were determined. Three specimens of each restorative material from each of the five beverages at day 28 were examined.
Statistical analysis
Surface microhardness values were tested for significant differences (at α = 0.05) using two-way analysis of variance (ANOVA) with repeated measurement, Tukey's honestly significant difference (HSD), and a t-test for multiple comparisons.
| Results | | |
The mean pH and standard deviations (SDs) and titratable acidity of beverages with 1 mol/L NaOH is shown in [Table 3]. The microhardness values of the materials used before and after immersion are reported in [Table 4]. | Table 3: The mean pH and standard deviation (SD) and titratable acidity (volume of NaOH (mL) to bring the pH to 5.5, 7.0, and 10.0) in beverages tested
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 | Table 4: Mean microhardness and standard deviations (SDs) of materials tested immersed in different beverages at different times
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SEM photomicrographs of the nanohybrid resin composite and giomer, before and after the 28 day of immersion period in the different beverages, are presented in [Figure 1] and [Figure 2], respectively. The Coca-Cola group produced the roughest specimen surface. | Figure 1: Scanning electron microscopy (SEM) photomicrographs of nanohybrid resin composite (×300): (a) Before immersion (b) after immersion in apple cider (c) orange juice (d) Coca-Cola, (d) coffee, and (e) beer
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 | Figure 2: SEM photomicrographs of giomer (×300): (a) Before immersion (b) after immersion in apple cider (c) orange juice (d) Coca-Cola (d) coffee, and (e) beer
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| Discussion | | |
Microhardness values of all groups decreased from the initial week of immersion until the end of the 28 days period and the greatest change in hardness shown occurred within the first 7 days. The specimens were not exposed to any mechanical forces so any observed change in hardness would be from a chemical reaction or dissolution. The decreasing in microhardness related to the pH and the titratable acidity of beverages as seen from SEM photomicrographs.
According to the SEM results of this present study, both materials tested became rougher after soaking in the beverages. Beautifil II giomer became rougher than the Premise resin composite, because average filler particle size of Beautifil II is 0.8 mm and Premise is 0.4 mm. After soaking in the beverages, dislodgement of filler particles resulting in Beautifil II giomer became rougher than the Premise resin composite.
Coca-Cola is a popular soft drink with the lowest pH among the beverages in the present study. After immersing the specimens in the beverages, Coca-Cola produced the roughest surface. It has been reported that a low pH in acidic food and drink induces erosive wear in materials. [16] Although Coca-Cola is the lowest tritratable acidity, but Coca-Cola is a carbonate beverage containing carbonic acid and phosphoric acid which promotes dissolution and easily eroded the materials. [17] The erosive potential of an acid drink is not exclusively dependent on its pH, is also strongly influenced by its tritratable acid content in beverages. [18],[19] The pH values present only a measure of the free hydrogen ion concentration. It does not present the hydrogen ion remaining in the undissociated form. Thus, the potential degradation of acidic agents should be considered for both the pH value and titratable acidity.
Apple cider has the highest tritratable acidity in this study of beverages, while orange juice as a fruit drink has higher tritratable acidity than the other three groups of beverages, thus indicating erosive potential. Some beverages appear to be less erosive than others within the same pH. It may also be possibly related to the type of acid used in beverage's formulations. [20] Apple cider and orange juice are composed of citric acid while Coca-Cola is composed of phosphoric acid and carbonic acid. Phosphoric acid softens materials more than citric acid and carbonic acid. However, citric acid has been shown to be aggressive for dental hard tissues and resin-based restorative materials. [13] The influence of the acidity increasingly dissolves the matrix, along with any unstable glass particles in a low pH value drink. High acidity might have a greater softening effect on the resin matrix, thus promoting the dislodgement and leaching out of filler particles and reducing the load resistance of restorative materials. [13] In comparison to a giomer, resin composite was found to be less affected by low pH beverages or acid solution. [13] Therefore, Premise resin composite exhibited less change in surface hardness values than Beautifil II giomer.
The results of this present study showed that microhardness decreased from the 1 st week until the end of the 28 days period of immersion in coffee. Although the pH of coffee is nearly 7, coffee is composed of water, and the effect of water uptake can degrade polymer materials. [21] When polymer materials absorb water, coupling agents cause hydrolysis and loss of chemical bond between filler particles and the resin matrix. Filler particles dislodge from the outer surface of the material [22] causing surface roughness and decreasing hardness. The effect upon the resin matrix and the degradation of the resin-filler interface and inorganic fillers may also play a role in the reduction of surface hardness. [23] This may explain why Premise resin composite, which contains silica/barium glass, shows hardness decrements when exposed to beverages. Factors which influenced water absorption of polymer-based materials included the types of resin. A hydrophobic resin like hydroxyethylmethacrylate absorbs more water than one like bis-GMA. Filler loading may affect the water absorption of materials, with higher filler loading expecting to show a lower uptake. [22] The last factor which influences water absorption of polymer-based tooth-color filling materials is the presence of voids during the mixing or producing of these materials. However, water absorption values of resin composites are significantly less than giomer restorations. [23]
The result of this present study also showed that microhardness decreased from the first week until the end of the 28 days period of immersion in beer, accompanied with the data of McKinney and Wu. [24] Wine and 9% volume alcohol beverages cause significant increases in the degree of corrosion because alcohol in beverages soften polymer matrices and dislodge filler particles, resulting in a rapid decrease in microhardness. [25]
The limitations of this study included incomplete replication of the complex oral environment and disregard for the effects of temperature change. Whilst further studies may examine the in vivo effects of beverages and this study could not completely replicate the complex oral environment, this study at least confirms the erosive potential of certain acidic juices, soft drink, coffee, and alcoholic beverages; which are a potentially damaging factor that the public should be aware of.
| Conclusion | | |
Within the limitation of this study, the following conclusions were drawn: All the beverages used significantly reduced the surface hardness of the both materials, particularly at the end of the 28 days immersion period. Immersion in Coca-Cola caused more surface hardness reduction over time than other beverages. In addition, giomer showed significantly greater reduction in surface hardness than nanohybrid resin composite. The effect of these beverages on the surface of both restorative materials also depended upon the exposure time and chemical composition of the restorative materials and beverages.
| References | | |
| 1. | Beun S, Glorieux T, Devaux J, Vrevena J, Leloup G. Characterization of nanofilled compared to universal and microfilled composites. Dent Mater 2007;23:51-9. 
|
| 2. | Gordan VV, Mondragon E, Watson RE, Garvan C, Mjor IA. A clinical evaluation of a self-etching primer and a giomer restorative material: Results at eight years. J Am Dent Assoc 2007;138:621-7.
|
| 3. | Sunico MC, Shinkai K, Katoh Y. Two-year clinical performance of occlusal and cervical giomer restorations. Oper Dent 2005;30:282-9.
|
| 4. | Lien W, Vandewalle KS. Physical properties of a new silorane-based restorative system. Dent Mater 2010;26:337-44.
|
| 5. | Baskaran SA, Amalaradjou MA, Hoagland T, Venkitanarayanan K. Inactivation of Escherichia coli 0157: H7 in apple juice and apple cider by trans-cinnamaldehyde. Int J Food Microbiol 2010;141:126-9.
|
| 6. | Hengtrakool C, Kukiattrakoon B, Kedjarune-Leggat U. Effect of naturally acidic agents on microhardness and surface micromorphology of restorative materials. Eur J Dent 2011;5:89-100.
|
| 7. | Wongkhantee S, Patanapiradej V, Maneenut C, Tantbirojn D. Effect of acidic food and drinks on surface hardness of enamel, dentine, and tooth-coloured filling materials. J Dent 2006;34:214-20.
|
| 8. | Tanthanuch S, Patanapiradej V. Effect of Thai wine on surface roughness and corrosion of various tooth-coloured filling materials. J Dent Assoc Thai 2009;52:100-8.
|
| 9. | Sarrett DC, Coletti DP, Peluso AR. The effects of alcoholic beverages on composite wear. Dent Mater 2000;16:62-7.
|
| 10. | Han L, Okamoto A, Fukushima M, Okiji T. Evaluation of flowable resin composite surfaces eroded by acidic and alcoholic drinks. Dent Mater J 2008;27:455-65.
|
| 11. | Okte Z, Villalta P, Garcia-Gody F, Lu H, Powers JM. Surface hardness of resin composites after staining and bleaching. Oper Dent 2006;31:623-8.
|
| 12. | Wu W, McKinney JE. Influence of chemicals on wear of dental composites. J Dent Res 1982;61:1180-3.
[PUBMED] |
| 13. | Erdemir U, Yildiz E, Eren MM, Ozel S. Surface hardness of different restorative materials after long-term immersion in sports and energy drinks. Dent Mater J 2012;31:729-36.
|
| 14. | Poggio C, Lombardini M, Gaviati S, Chiesa M. Evaluation of Vickers hardness and depth of cure of six composite resins photo-activated with different polymerization modes. J Conserv Dent 2012;15:237-41.
[PUBMED]  |
| 15. | Cairns AM, Watson M, Creanor SL, Foye RH. The pH and titratable acidity of a range of diluting drinks and their potential effect on dental erosion. J Dent 2002;30:313-7.
|
| 16. | Coombes JS. Sports drinks and dental erosion. Am J Dent 2005;18:101-4.
[PUBMED] |
| 17. | Bagheri R, Tyas MJ, Burrow MF. Subsurface degradation of resin-based composites. Dent Mater 2007;23:944-51.
|
| 18. | Grando LJ, Tames DR, Cardoso AC, Gabilan NH. In vitro study of enamel erosion caused by soft drinks and lemon juice in deciduous teeth analysed by stereomicroscopy and scanning electron microscopy. Caries Res 1996;30:373-8.
|
| 19. | Maupomé G, Díez-de-Bonilla J, Torres-Villaseñor G, Andrade-Delgado LC, Castaño VM. In vitro quantitative assessment of enamel microhardness after exposure to eroding immersion in a cola drink. Caries Res 1998;32:148-53.
|
| 20. | Lussi A, Jaeggi T, Zero D. The role of diet in the aetiology of dental erosion. Caries Res 2004;38:34-44.
|
| 21. | Göpferich A. Mechanisms of polymer degradation and erosion. Biomaterials 1996;17:103-14.
|
| 22. | Santos C, Clarke RL, Braden M, Guitian F, Davy KW. Water absorption characteristics of dental composites incorporating hydroxyapatite filler. Biomaterials 2002;23:1897-904.
|
| 23. | EL-Sharkawy FM, Zaghloul NM, Ell-kappaney AM. Effect of water absorption on color stability of different resin based restorative materials in vitro study. Int J Compos Mater 2012;2:7-10.
|
| 24. | McKinney JE, Wu W. Chemical softening and wear of dental composites. J Dent Res 1985;64:1326-31.
[PUBMED] |
| 25. | Ferracane JL, Marker VA. Solvent degradation and reduced fracture toughness in aged composites. J Dent Res 1992;71:13-9.
|
Correspondence Address:
Boonlert Kukiattrakoon
Department of Conservative Dentistry, Maxillofacial Prosthodontics Rehabilitation Research Unit, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla
Thailand
 Source of Support: Faculty of Dentistry Research Fund, Prince
of Songkla University,, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-0707.131791
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4] |
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