In the recent years, restorative dentistry has advanced greatly, leading to increased use of composite resins as aesthetics have become important concern for patients.¹ Dental composite has become a material of choice for direct restoration.² The restorative materials should last long in the oral cavity. Surface hardness, which is the resistance of the material to indentation or penetration is an important property because it effects the proportional limit, ductility and strength. The hardness of a material serves as an indicator to predict its wear resistance and potential to abrade or be abraded by dental structures and other materials.³ Resin composites consist of polymeric matrix, filler particles, and silane-coupling agent that links the matrix to fillers. In the oral environment, these materials can degrade over time due to water absorption, temperature changes and mechanical stress. Water plays a major role in this process by weakening the resin matrix, leading to reduced hardness and the deterioration of resins physical and mechanical properties.⁴ Although the polymerized composite material initially have sufficient hardness to withstand the masticatory load, they begin to degrade when exposed to oral environment. Factors such food, organic solvents, water, thermal changes, mechanical cycling influence surface degradation, crack propagation and hardness of the material. This degradation may lead to material break down over time, ultimately influencing the clinical longevity of the restoration.² In an in vivo situation, food components and beverages has been reported to affect properties of resin composites. Mouthrinses are among the factors that affect resin restorations, and have gained widespread popularity in recent years. They are commonly recommended by clinicians for prevention and control of dental caries, periodontal diseases, plaque reduction and in management of oral malodor.³ Mouthrinses can be alcohol, peroxide, or fluoride containing.⁵ Mouthrinses contain water, antimicrobial agents, salts, preservatives and sometimes alcohol. Variations in the concentration of these components affect the pH of mouth rinses. Alcohol containing mouth rinses may soften the resin restorations, with the effect increasing as the alcohol concentration rises. Additionally, low Ph enhance sorption, solubility and surface degradation of resin composites.⁶ Ayurvedic mouthwashes are typically alcohol and chemical free, containing time-tested herbal oils and extracts – like neem oil, clove, and peelu – that support oral health. Hence, they serve as a viable alternative to the chemical mouthwashes. However, frequent mouth rinse use may adversely affect oral tissues and restorative materials. They can alter the surface roughness of dental materials potentially increasing plaque retention, staining, and compromising patient comfort.⁵ The type of restorative material also influences the degradation of restorative materials.⁶ Previous studies have indicated conflicting findings regarding the influence of mouthrinses on the mechanical and physical properties of composites, including hardness and roughness.⁷ Furthermore, many commercially available mouthrinses have not yet been evaluated for their impact on the restorations.⁶ Hiora K mouth rinse is commercially available alcohol free mouth rinse enriched with herbal ingredients. It also contains natural potassium that reduces tooth sensitivity from varied etiologies and also restores the mineral composition of teeth, strengthening them as a result.⁸ Hence the aim of this in vitro study was to evaluate the effect of commercially available herbal mouthrinse on microhardness of various restorative composite resin materials.

MATERIALS AND METHODS

The 3-month in-vitro study was conducted in the Department of Pediatric and Preventive Dentistry, College of Dental Sciences, Davangere, in collaboration with the Department of Mechanical Engineering, Manipal Institute of Technology, Manipal, India. The study evaluated three restorative materials divided into three groups: Group I (Reveal HD Bulk fill, BISCO, USA), Group II (Filtek Z350 XT Nanohybrid, 3M ESPE, USA), and Group III (Filtek P60 Microhybrid, 3M ESPE, USA).

Specimen preparation:

A total of 54 cylindrical specimens were fabricated using a Teflon mold, with 18 specimens prepared for each composite material group, measuring 6mm in diameter and 2mm in thickness. The mold was then placed on a glass slide and filled with resin composite to a slight excess using composite filling instrument covered with a clear matrix strip and another glass slide was placed on top and gently pressed for 30 s to extrude excess material to obtain a smooth surface. Each specimen was cured for 40 s from the top and another 40 s from the bottom using LED light cure unit (Blue phase C8, Ivoclar Vivadent, Astria) at 800 mW/cm². Immediately following polymerization, the specimens were stored in distilled water in a dark container that were maintained in a humidor at 37°C for 24 hours, to allow post-polymerization, before taking the baseline microhardness measurement. After 24 hours, the specimens were subjected to surface polishing with abrasive disks (Sof-Lex, 3M ESPE, St. Paul, USA) under continuous water irrigation. Abrasive disks were applied in decreasing order of abrasiveness (10 s each), in a slow-speed handpiece. To avoid micro-crack formation polishing time was limited to 10 s for each step. The samples were inspected visually before and after testing to confirm the absence of any surface defects or pores. Each group had 18 specimens. The specimens were further divided into two different subgroups (n = 9) in terms of immersion medium (artificial saliva and herbal mouthrinse) to test the microhardness of each composite resin materials.

For Microhardness Assessment:

The specimens were divided into three main groups according to composite resin materials. Each group was then subdivided into two different subgroups (n = 9) according to the immersion mediums artificial saliva and herbal mouth rinse. The pre immersion baseline micro hardness values of the specimens were recorded using Knoop micro hardness tester (Buehler Mmt- 3, Waukagen Lake, Bluff, II, USA) with a dwell time of 15 s and a load of 50 gf. Next, the specimens were then immersed in 20 ml of immersion mediums artificial saliva and herbal mouth rinse respectively. They were then kept in a dark glass container in an incubator at 37°C for 12 h. Following immersion, each specimen was blotted dry with a filter paper and checked for post immersion micro hardness using the same micro hardness tester previously mentioned for base line values. The data was tabulated and subjected to statistical analysis.

Statistical Analysis: The recorded values were entered in Microsoft Excel and subjected to statistical analysis by SPSS. One way ANOVA and Independent t test were performed to assess the microhardness. P value < 0.05 was considered statistically significant.

RESULTS

Table 1 & Graph 1: The table and graph shows the mean, standard deviation and comparison of microhardness of the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid). In Group I, the mean and standard deviation showed the value of 55.90 ± 3.58, while in group II, the mean and standard deviation showed the value of 64.75 ± 3.45. In Group III, the mean and standard deviation showed the value of 75.05 ± 9.85. On intergroup comparison a statistically significant difference was found in the microhardness among the three groups (p value < 0.001).

Table 1

                 One way Anova, sig. 2 tailed, p<0.05

*= Statistically significant difference with p<0.05      Std. Deviation = SD, Std. Error = SE

  Graph 1: Comparison of mean value of microhardness of the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid)

Table 2 & Graph 2: The table and graph shows mean, standard deviation and comparison of pre immersion micro hardness in both the immersion mediums (Artificial saliva & Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid). In Group I, the mean and standard deviation showed the value of 56.01 ± 3.44 and 55.80 ± 3.91, in group II, the mean and standard deviation showed the value of 64.09 ± 3.87 and 65.40 ± 3.06 while in group III, the mean and standard deviation showed the value of 73.63 ± 12.96 and 76.47 ± 5.81 in artificial saliva & mouthrinse respectively. On comparison no statistically significant difference was found in the pre immersion microhardness among all the three groups (Group I: p value of 0.127, Group II: p value of 0.137 & Group III: p value of 0.745).

Table 2

           Independent t test, sig 2 tailed, p<0.05 Std. Deviation = SD, Std. Error = SE

Graph 2: Comparison of pre immersion micro hardness in both the immersion mediums (Artificial saliva & Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid)

Table 3 & Graph 3: The table and graph shows mean, standard deviation and comparison of post immersion micro hardness in both the immersion mediums (Artificial saliva & Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid). In Group I, the mean and standard deviation showed the value of 53.99 ± 5.56 and 52.51 ± 2.19, in group II, the mean and standard deviation showed the value of 48.53 ± 4.71 and 48.71 ± 3.49 while in group III, the mean and standard deviation showed the value of 66.01 ± 8.47 and 70.18 ± 6.72 in artificial saliva & mouthrinse respectively. On comparison no statistically significant difference was found in the pre immersion microhardness among all the three groups (Group I: p value of 0.47, Group II: p value of 0.09 & Group III: p value of 0.82).

Table 3

Independent t test, sig 2 tailed, p<0.05                                Std. Deviation = SD, Std. Error = SE

Graph 3: Comparison of post immersion micro hardness in both the immersion mediums (Artificial saliva & Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid)

Table 4 & Graph 4: The table and graph shows the comparison of pre and post immersion microhardness in terms of immersion medium (Artificial saliva) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid). On comparison no statistically significant difference was found in group I (p value of 0.413) while a statistically significant difference was found in group II and group III (p value of < 0.001 & 0.007 respectively).

Table 4

Paired t test, sig 2 tailed, p<0.05                                      Std. Deviation = SD, Std. Error = SE

*= Statistically significant difference with p<0.05

Graph 4: Comparison of pre and post immersion microhardness in terms of immersion medium (Artificial saliva) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid)

Table 5 & Graph 5: The table and graph shows the comparison of pre and post immersion microhardness in terms of immersion medium (Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid). On comparison no statistically significant difference was found in group I (p value of 0.051) while a statistically significant difference was found in group II and group III (p value of < 0.001 & 0.041 respectively).

Table 5

Paired t test, sig 2 tailed, p<0.05                                      Std. Deviation = SD, Std. Error = SE

*= Statistically significant difference with p<0.05

Graph 5: Comparison of pre and post immersion microhardness in terms of immersion medium (Mouthrinse) among all the three groups (Reveal HD Bulk fill, Filtek Z350 XT Nanohybrid, P 60 Microhybrid)

Figure 1: Armamentarium used in the study

Specimens used in the study Figure 2: Specimens for microhardness test (6mm × 2mm)

Procedure for microhardness evaluation

Figure 3: Teflon mould (6mm × 2mm)

Figure 4: Restorative material placed in mould

Figure 5: Restorative material pressed with slide on top

               Figure 6: Prepared specimen

Figure 7: Specimens stored in distilled water

Figure 8: Division of groups specimens

Figure 9: Specimen placed in microhardness tester for microhardness evaluation

DISCUSSION

Today, caries is increasingly recognized as an infectious disease process. Because of this, clinicians now prefer to treat it like a medical illness than just drilling and filling. Treatment focuses on control measures and remineralization methods of initial lesions. Effective control of caries requires interception of key disease factors, particularly cariogenic bacterial plaque. Since the mechanical plaque control alone is often inadequate, chemo prophylactic agents such as Chlorhexidine and fluoride containing mouth rinses serve as useful adjuncts in caries control.32 In clinical dentistry, restorative composites are widely used because of their adhesion ability to dental structures and aesthetic quality. The enhanced mechanical properties of these materials have led to a universal application and versatility, being indicated for both anterior and posterior teeth. Despite effective polymerization, composites exhibit instability and can interact with the oral environment. In the oral cavity, these materials are able to absorb water and release chemical substances. The process of sorption and solubility may initiate various physical and chemical processes that can adversely affect the structure integrity and function of the polymeric material.33 In recent years, the popularity of tooth colored restorative materials has promoted a rapidly increasing use of resins to meet the cosmetic expectations of the patients. The longevity and durability of the esthetic restorative materials in the oral environment are important factors for the proper selection of the material. The use of antimicrobial mouth rinses is an approach to limiting the accumulation of dental plaque with a primary objective of controlling the development and progression of periodontal disease and dental caries.22 Today, mouthrinses are the part of people’s routine oral hygiene. They are commonly used even without professional prescription. Long term use of mouthrinses can lower the longevity of restoration and may affect the oral tissues.24 Various internal and external factors influence the longevity, durability, and degradation of dental composite resins. Failure of resin restoration may occur due to change in the mechanical and chemical properties of the composite resin material. Both of them are inter-dependent on each other. Mechanical properties may be altered as the resin is exposed to unwanted compressive and tensile forces while chemical properties of resin is altered by the internal environment of oral cavity, food or other materials used; which further affects the mechanical properties.27 Hardness is the resistance of material to indentation, and it correlates well to material’s strength and rigidity, while the microhardness is nondestructive laboratorial test specifically located, that supplies fundamental data about the material.15 Hardness is critical parameter of the restorative materials, as it contributes to the long term durability in the oral environment. So reduction in the hardness of a material may result in premature failure of a restoration requiring its replacement.22 Hiora K herbal mouthrinse is newly introduced in market and its effect on composite resin materials is not known. Also literature on the effect of mouthrinses on newly introduced composite resin material is limited. Hence the aim of this in vitro study was to evaluate the effect of commercially available herbal mouthrinse on microhardness of various composite restorative materials. The results of the present study demonstrated that the mean microhardness of group III (P60 Microhybrid) was found to be highest followed by group II (Filtek Z350 XT Nanohybrid) and group I (Reveal HD Bulk fill). The three composite restorative materials tested here differed statistically in terms of compressive strength with a p-value of <0.05. The result was in accordance with a previous studies done by George et al., 26 and Yesilyurt et al.34 This could be attributed to the fact that 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. In the present study there was a statistically significant reduction observed in post immersion microhardness in group II (Filtek Z 350 XT Nanohybrid) and group III (P60 Microhybrid) compared to the baseline values in both the immersion mediums. The results were in accordance with the previous studies done by Dieb et al., 13 and Jyothi KN et al.6 This may be because of the acidic pH of the mouthrinses which would have caused acid erosion of the resin composite by acid etching and leaching the principle matrix forming cations. However contrasting results were found in previous studies performed by Gurdal P et al., 35 and Rios et al.36 where there was no statistically significant effect of mouthrinse found on microhardness of the tested composite restorative resin materials. Every study is formed with few strengths and limitations side by side. The strength of the present study includes the use of evaluation of newly introduced herbal mouthrinse Hiora K for the first time as per our knowledge on microhardness of various restorative composite resin materials.

The limitation of this study is that the in vivo oral conditions are different from in vitro experimental conditions. Several other factors need to be taken into consideration, such as saliva which may dilute or buffer the mouth rinse, salivary pellicle that might have a protective effect, food habits, beverages, temperature changes and change in pH, oral care products, which may isolate and interfere with the physical and mechanical properties of the materials, influencing the durability of the restorative treatment. Therefore, further studies are necessary to determine the effects of mouthrinses in vivo..

CONCLUSION

Based on the observations and results obtained from the present study it could be concluded that: There was a statistically significant difference observed between Group I (Reveal HD Bulk fill), Group II (Filtek Z350 XT Nanohybrid) and Group III (P 60 Microhybrid) in terms of microhardness. Group III (P 60 Microhybrid) showed higher microhardness followed by Group II (Filtek Z350 XT Nanohybrid) and Group I (Reveal HD Bulk fill). There was a statistically significant reduction observed in the post immersion microhardness in group II (Filtek Z 350 XT Nanohybrid) and group III (P60 Microhybrid) compared to the baseline values in both the immersion mediums. Group I (Reveal HD Bulk fill) did not show any statistically significant reduction in post immersion microhardness compared to baseline values in both the immersion mediums. As per the results and statistical evaluation outcome, Hiora K (alcohol free) mouthrinse did show statistically significant reduction in microhardness in two of the tested composite restorative materials. Alcohol content is not the only factor in mouth rinses that can degrade materials. Also changes in microhardness of composite resins may be material dependent. Hence further in vivo studies are recommended to substantiate the results of this present study.

REFERENCES

1. 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.
2. Khan AA, Siddiqui AZ, Mohsin SF, Al-Kheraif AA. Influence of mouth rinses on the surface hardness of dental resin nano-composite. Pak J Med Sci 2015;31(6):1485-1489.
3. 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 Journal of Oral Sciences 2014 Jul 1;1(2):105.
4. Miranda DD, Bertoldo CE, Aguiar FH, Lima DA, Lovadino JR. Effects of mouthwashes on Knoop hardness and surface roughness of dental composites after different immersion times. Brazilian oral research 2011 Apr;25(2):168-73.
5. Gorka K, Kamal V, Kumar A, Mandal S, Kumar A, Kumar M. Comparative Evaluation of Erosive Potential of a Chemical and Herbal Mouthwash on the Surface Roughness of Resin-modified Glass Ionomer Restorative Materials: An in vitro Study. Int J Prev Clin Dent Res 2016;3(1):30-34.
6. Jyothi KN, Crasta S, Venugopal P. Effect of five commercial mouth rinses on the microhardness of a nanofilled resin composite restorative material: An in vitro study. Journal of conservative dentistry: JCD. 2012 Jul;15(3):214.
7. Karabulut B, Can-Karabulut DC, Güleç S, Doğan CM. Effect of a novel commercial potassium-oxalate containing tooth-desensitizing mouthrinse on the microhardness of resin composite restorative materials with different monomer compositions. Journal of clinical and experimental dentistry. 2016 Dec;8(5):e491.
8. https://www.tabletwise.net/himalaya-hiora-mouthwash.
9. Gürgan S, Önen A, Köprülü H. In vitro effects of alcohol-containing and alcohol-free mouthrinses on microhardness of some restorative materials. Journal of oral rehabilitation 1997 Mar;24(3):244-6.
10. Yap AU, Tan BW, Tay LC, Chang KM, Loy TK, Mok BY. Effect of mouthrinses on microhardness and wear of composite and compomer restoratives. Operative dentistry 2003 Nov 1;28(6):740-6.
11. Badra VV, Faraoni JJ, Ramos RP, Palma-Dibb RG. Influence of different beverages on the microhardness and surface roughness of resin composites. Oper Dent 2005 Mar 1;30(2):213-9.
12. Cavalcanti AN, Mitsui FH, Ambrosano GM, Mathias P, Marchi GM. Effect of different mouthrinses on Knoop hardness of a restorative composite. American journal of dentistry 2005 Dec 1;18(6):338-40.
13. Diab M, Zaazou MH, Mubarak EH, Olaa MI. Effect of five commercial mouthrinses on the microhardness and color stability of two resin composite restorative materials. Aust J Basic Appl Sci 2007;1(4):667-74.
14. Yanikoglu N, Duymus ZY, Yilmaz B. Effects of different solutions on the surface hardness of composite resin materials. Dental materials journal 2009;28(3):344-51.
15. Al-Hyali NA, AL-Azzawi HJ. Effect of three types of mouth rinses and human saliva on microhardness of packable and nanocomposite resins (In vitro study). Journal of baghdad college of dentistry. 2011;23.
16. Festuccia MS, Garcia LD, Cruvinel DR, Pires-De-Souza FD. Color stability, surface roughness and microhardness of composites submitted to mouthrinsing action. Journal of Applied Oral Science 2012 Apr;20(2):200-5.
17. Munawar AH, Febrida R, Nurdin D. Influence of alcohol-containing mouthwash and alcohol-free mouthwash towards the hybrid composite restoration materials surface hardness. Padjadjaran Journal of Dentistry 2013;25(3).
18. Ahmad A, Abidi SY, Abbasi ZA, Shaikh AA, Meo AA. EFFECT OF DIFFERENT CHLORHEXIDINE BASED MOUTHWASHES ON HARDNESS OF RESIN BASED DENTAL COMPOSITES. AN IN-VITRO STUDY. Cell.;336:0349844.
19. Ozer S, Sen Tunc E, Tuloglu N, Bayrak S. Solubility of two resin composites in different mouthrinses. BioMed research international 2014 Jan 1;2014.
20. Lepri CP, Ribeiro MV, Dibb A, Palma-Dibb RG. Influence of mounthrinse solutions on the color stability and microhardness of a composite resin. Int J Esthet Dent 2014 Jan 1;9(2):238-46.
21. de Moraes Porto IC, das Neves LE, de Souza CK, Parolia A, Barbosa dos Santos N. A comparative effect of mouthwashes with different alcohol concentrations on surface hardness, sorption and solubility of composite resins. Oral health and dental management 2014 Jun 1;13(2):502-6.
22. Das S, Sowmya K. An evaluation of the effect of alcohol and non-alcohol based mouth rinses on the microhardness of two esthetic restorative materials–An in vitro study. Int J Appl Dent Sci 2015;1:27-31.
23. Goyal A, George JV, Mathew S, Singh R, Ramesh P. Effect of four commercial mouth rinses on the microhardness and solubility of a supra nanocomposite and a microhybrid composite: An in vitro study. Sch. J. Dent. Sci 2016; 3(10):272-277.
24. Kochhar R, Dewan R, Soi S, Punjabi M. An evaluation and comparison of the effect of five mouthrinses on the microhardness of esthetic hybrid composite restorative material-an in vitro study. Journal of Dental Specialities. 2017 May 15;5(1):66-9.
25. Beverley Themudo and Annapoorna, B. M. “Effect of toothbrush mouthrinse cycling on surface roughness and microhardness of nanohybrid composite resin and giomer”, International Journal of Current Research 2017;9(07): 54745-54750.
26. Dalmia S, Aher G, Gulve M, Samuel R, Kolhe S. Comparative Evaluation of The Effect of Chlorhexidine Based Mouthwash and Herbal Mouthwash on The Microhardness Of Two Different Composite Resins An In Vitro Study. International Journal of Advanced Research. 2018;6(3):306-11.
27. Shah Y, Chudasama K, Shah K, Chokshi S, Sanghvi Z, Patel P. EFFECT OF FOUR COMMERCIAL MOUTHRINSES ON THE MICROHARDNESS OF NANOHYBRID COMPOSITE RESTORATIVE MATERIAL-AN IN VITRO STUDY. Co-Editor. 2019 Jan 1:16.
28. Thirunavakarasu R, Nasim I. Effect of mouthwashes on different composite resin-An in vitro study. Drug Invention Today. 2019 Nov 1;11(11).
29. Rajasekhar R, James B, Johny MK, Jacob J. Evaluation of the effect of two commercially available non-alcoholic mouth rinses on the microhardness of composite material-An invitro study. Dental Journal 2019;1(1).
30. Surendra K, Prasad SD, Kumar CS, Reddy SM, Babu KC. EFFECT OF ALCOHOL CONTAINING AND ALCOHOL-FREE MOUTHWASHES ON THE MICROHARDNESS OF NANO COMPOSITES-AN INVITRO STUDY. Intl. J. Clin. Diag. Res. 2019;7(4):I
31. Altwaim B, Salama F, Alogayyel S. Effect of Probiotic Mouthrinses on Surface Microhardness of Esthetic Restorative Materials. The Journal of Contemporary Dental Practice. 2020 May 1;21(5):543-8.
32. Kanan SM, Mohammed AK. The effect of mouth rinses on surface micro hardness of two esthetic restorative materials. Iraqi National Journal of Nursing Specialties 2012;25(1):101-8.
33. Leal JP, da Silva JD, Leal RF, Oliveira-Júnior CD, Prado VL, Vale GC. Effect of mouthwashes on solubility and sorption of restorative composites. International journal of dentistry 2017 Jun 8.
34. Yesilyurt C, Yoldas O, Altintas SH, Kusgoz A. Effects of food-simulating liquids on the mechanical properties of a silorane-based dental composite. Dental materials journal 2009;28(3):362-7.
35. Gürdal P, Akdeniz BG, Hakan Sen B. The effects of mouthrinses on microhardness and colour stability of aesthetic restorative materials. Journal of oral rehabilitation 2002 Sep;29(9):895-901.
36. Rios D, Honório HM, Francisconi LF, Magalhães AC, Machado MA, Buzalaf MA. In situ effect of an erosive challenge on different restorative materials and on enamel adjacent to these materials. Journal of dentistry 2008 Feb 1;36(2):152-7..