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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 5  |  Page : 124-128  

Comparative evaluation of the surface hardness of different esthetic restorative materials: An in vitro study


1 Department of Conservative Dentistry and Endodontics, Noorul Islam College of Dental Sciences, Trivandrum, Kerala, India
2 Department of Conservative Dentistry and Endodontics, Rajas Dental College & Hospital, Kavalkinaru, Tamil Nadu, India
3 Department of Conservative Dentistry and Endodontics, St. Joesph Dental College and Hospital, Eluru, Andhra Pradesh, India

Date of Submission25-Jan-2020
Date of Decision04-Feb-2020
Date of Acceptance02-Mar-2020
Date of Web Publication28-Aug-2020

Correspondence Address:
Anoop Samuel
Department of Conservative Dentistry and Endodontics, Noorul Islam College of Dental Sciences, Aralumoodu, Neyyattinkara, Trivandrum 695123, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jpbs.JPBS_40_20

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   Abstract 

Aim: The aim of this study was to evaluate the surface hardness of a newly developed fiber-reinforced composite and bulkfill composites. Materials and Methods: Fiber-reinforced composite and other commercially available bulkfill composites were used. Fifteen cylindrical specimens (5 mm × 5 mm) were made from each material in metal template. Molds were filled in one increment for both bulkfill composites and fiber-reinforced composite and cured using Ivoclar blue phase light-curing unit at a wavelength of 850 mW/cm2. A dark container was used to store specimens to keep dry at room temperature for 24 h before testing. Vickers hardness number (VHN) on the top and bottom surfaces of each specimen was measured by a microhardness tester. Data for VHN were analyzed by using analysis of variance (ANOVA) and pair-wise Newman–Keuls test. Results: No significant difference was observed in Vickers hardness test. The mean value of VHN on the top and bottom surfaces showed significant difference from each other. Fiber-reinforced composite showed the highest VHN as compared with other materials. Conclusion: Fiber-reinforced composite has the highest Vickers hardness ratio indicating highest degree of conversion and better clinical performance.

Keywords: Depth of cure, incremental fill composite, resin composite, surface hardness


How to cite this article:
Samuel A, Raju R, Sreejith K B, Kalathil BM, Nenavath D, Chaitra V S. Comparative evaluation of the surface hardness of different esthetic restorative materials: An in vitro study. J Pharm Bioall Sci 2020;12, Suppl S1:124-8

How to cite this URL:
Samuel A, Raju R, Sreejith K B, Kalathil BM, Nenavath D, Chaitra V S. Comparative evaluation of the surface hardness of different esthetic restorative materials: An in vitro study. J Pharm Bioall Sci [serial online] 2020 [cited 2020 Sep 19];12, Suppl S1:124-8. Available from: http://www.jpbsonline.org/text.asp?2020/12/5/124/292867




   Introduction Top


In 1990s, amalgam is being widely used as a universal filling material and composite restorations introduced as a new era of minimally invasive dentistry. Dental composites have some mechanical properties as compared to tooth of enamel and provide a long shelf life period.[1] Different types of composites, including conventional, microfilled, hybrid, flowable, packable, and nanofilled, have been introduced. Insufficient depth of cure is one of the major disadvantages of resin-based composite material; because of this reason, composite restorations in large cavities, especially class II restorations[2] material, are added in layers of maximum 2 mm thickness and cured, that is, incremental placement technique.

Recently, bulkfill composites were introduced for posterior bulk fill placement. The bulkfill composite material can be placed in 4 mm thickness bulk and can be cured in one step rather than multiple steps as incremental placing technique.[3] Different properties of bulkfill composite resins were examined by many studies; properties such as microleakage, polymerization shrinkage, and degree of conversion were studied extensively. All of such studies indicated that bulkfill composite resins have no significant difference in properties as compared to conventional dental composite resins.[4],[5],[6]

Degree of conversion is the major factor that influences physical and mechanical properties of dental composites. The degree of conversion in dental composite restoration is influenced by different factors. These factors include power density and wavelength of curing light, irradiation time, tip size of light source, contents of organic matrix, inorganic filler quantity and distribution, type of photoinitiator used, and color of the composite resins.

Variations in composition of material and its viscosity whether flowable or nonflowable are the factors that affect the physical and mechanical properties of different available bulkfill composites. Fiber-reinforced composite restorations contain fibers aimed at enhancing their physical properties. In composite matrix, the fibers are ideally bonded to the resin via an adhesive interface.

Different types of laboratory investigations have been introduced to evaluate dental composite resins; flexural strength and flexural modulus tests are used as an indicator for material durability under stress. These tests can also be used to correlate with the clinical longevity of composite restorations. Fracture toughness test is an alternative method to examine the material’s ability under stress without fracture and crack propagation inside the material before failure.[7] Also, Vickers hardness assay can be used for testing surface hardness and the mode of failure of the material. The longevity strength and the sustainability of composite restoration especially in stress-bearing area depend on the surface hardness of the material.

Thus, the aim of study was to evaluate the surface hardness of the fiber-reinforced composite and two different bulkfill composite restoration materials. The null hypothesis was that there is no significant difference in clinical performance of fiber-reinforced composite and other bulkfill composites.


   Materials and Methods Top


The bulkfill dental composite materials used for this study were as follows: Filtek Bulk Fill (FB, 3M ESPE, St. Paul, Minnesota), Tetric EvoCeram Bulk Fill (TECB, Ivoclar Vivadent AG, Schaan, Liechtenstein), and a fiber-reinforced bulkfill dental composite resin, EverX Posterior (EXP, GC Europe NV, Leuven, Belgium).

A total of 45 samples were prepared [Figure 1]. They were divided into three experimental groups (n = 15). Metal template was prepared; it had inner diameter of 8 mm and thickness of 2 mm. Metal templates were placed on Mylar strips (Primo Dental Products MS500 Mylar Matrix Strips, 4′′ Long × 3/8′′ Wide) placed on a glass slab [Figure 2] and were filled in one increment [Figure 3] After that Filtek Bulk Fill (FB, 3M ESPE) was filled in 15 samples and other 15 samples were prepared with Tetric EvoCeram Bulk Fill (TECB). Other 15 samples were prepared using fiber-reinforced bulkfill dental composite resin, EverX Posterior (EXP, GC Europe NV) [Figure 4]. On the upper surface, a Mylar strip was placed and the material was flattened with a glass slide. Glass slab was removed after removal of excess material, and cured using light-emitting diode (LED) [Figure 5] (Cromalux Mega-Physik, Rastatt, Germany; 850 mW/cm2) for 40s and the light cure tip kept at a distance of 1 mm. The specimens were then removed from the molds after which finishing and polishing done in the mold [Figure 6]. The top surface was marked with an indelible marker [Figure 7]. All samples were kept dry at room temperature in lightproof containers for 24 h.
Figure 1: Metal template

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Figure 2: Metal template restored with composite

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Figure 3: Glass slab and Mylar strip to remove excess material

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Figure 4: Prepared samples

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Figure 5: Curing of composite

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Figure 6: Finishing and polishing

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Figure 7: Indenter

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Vickers hardness test was done using a 50-g load and dwell time was 15s. In each sample, three indentations were made on both the top and the bottom surfaces. The formula to calculate the Vickers hardness ratio of the top and bottom surfaces is as follows:

Vickers hardness ratio = bottom VHN mean value × 100

Top VHN mean value.

Statistical analysis

The statistical analysis of data was performed by using a two-way analysis of variance (ANOVA) test, Bonferroni test, and Student’s t test. All the data collected were analyzed using Statistical Package for the Social Sciences (SPSS) software program, version 14.0 (SPSS, Chicago, IL, USA).


   Results Top


The test was conducted on three experimental groups. [Table 1] shows the Vickers hardness mean value of top and bottom surfaces. Group I fiber-reinforced composite showed greater hardness as compared to Group II (Tetric EvoCeram Bulk Fill composite) with a P value 0.001 (both top and bottom surfaces). P Value was highly statistically significant.
Table 1: Descriptive statistics and comparative analysis of top and bottom surface hardness values

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[Table 2] shows the intergroup comparison on top and bottom surfaces of the depth of cure. The difference in top and bottom surface hardness was statistically significant in both the groups. The difference in mean depth of cure was not statistically significant between Groups I and II.
Table 2: Descriptive statistics and comparative analysis of depth of cure

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   Discussion Top


Surface hardness shows abrasion resistance that prevents the materials from the creation of permanent deformities, increasing the scratch and abrasion resistance seen if the microhardness is high. So the material efficiently prevents from various forces.[8],[9] Greater depth of cure and lower polymerization-induced shrinkage stress are the features of bulkfill composite materials; it is due to technology such as “polymerization modulators,” which allows certain amount of flexibility and optimized network structure during polymerization. Recently introduced are bulkfill composites for class I and class III restorations.

These composite resins have excellent handling characteristics and can be placed in 4 mm increments with minimal polymerization stress. According to various studies, silver amalgam and gold alloys have been used with clinical success for a century, especially as a posterior restorative material because of their good mechanical properties.

Recently, bulkfill composite materials have been introduced due to the high esthetic properties of composite resins. The main mechanical property of composite resin is compressive strength. Low-compressive strength in a restorative material tends to lead the tooth failure, fracture, and periodontal problems or extraction of the broken tooth.[10],[11] Vickers hardness ratio is related to the depth of cure (80%) and the degree of polymerization. A high degree of polymerization is an important factor for achieving superior physical and mechanical properties. Marginal microleakage, discoloration, and decreased bonding strength of resin composite restorations[12] are caused by inadequate polymerization.

In this study, hardness and depth-of-cure values in fiber-reinforced composites were higher than the other two composite samples when cured with LED light. A metal template was used because the material does not stick to the mold and can be easily molded after polymerization. A bulk insertion technique was adopted in this study and a maximum of 2 mm thickness.[13]

The result of this study depends on different factors, such as composition of organic matrix, amount and type of filler particles, and also on degree of conversion. Several studies have suggested that microfilled composites are challenging to cure because the small filler particles cause light to scatter, thus decreasing the effectiveness of the curing light. The result obtained in this study is that the fiber-reinforced composite tested may be used as a restorative material in stress-bearing areas. The outcomes examined with this study should be followed by long-term clinical studies to assure the performance of the material under routine clinical conditions.


   Conclusion Top


In this study, superior fracture resistance, high flexural strength, modulus, and higher microhardness values were reported by fiber-reinforced composite everX Posterior compared to other bulkfill composite resins.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Magro ED, Sinhoreti MAC, Correr LAB, Consani RLX, Sicoli EA, Mendonca MJ, et al. Effect of different modes of light modulation on the bond strength and knoop hardness of a dental composite. Bray Dent J 2008;19:334-40.  Back to cited text no. 1
    
2.
Versluis A, Douglas WH, Cross M, Sakaguchi RL Does an incremental filling technique reduce polymerization shrinkage stresses? J Dent Res 1996;75:871-8.  Back to cited text no. 2
    
3.
Furness A, Tadros MY, Looney SW, Rueggeberg FA Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. J Dent 2014;42:439-49.  Back to cited text no. 3
    
4.
El-Safty S, Silikas N, Watts DC Creep deformation of restorative resin-composites intended for bulk-fill placement. Dent Mater 2012;28:928-35.  Back to cited text no. 4
    
5.
Alshali RZ, Silikas N, Satterthwaite JD Degree of conversion of bulk-fill compared to conventional resin-composites at two time intervals. Dent Mater 2013;29:e213-7.  Back to cited text no. 5
    
6.
Ende VA, Munck DJ, Landuyt VKL, Poitevin A, Peumans M, Van Meerbeek B Bulk-filling of high C-factor posterior cavities: effect on adhesion to cavity bottom dentin. Dent Mater 2013;29:269-77.  Back to cited text no. 6
    
7.
Abouelleil H, Pradelle N, Villat C, Attikn N, Colon P, Grosgogeat B Comparison of mechanical properties of a new fiber reinforced composite and bulk filling composites. Restor Dent Endod 2015;40:262-70.  Back to cited text no. 7
    
8.
Jendresen MD Clinical behavior of 21st-century adhesives and composites. Quintessence Int 1993;24:659-62.  Back to cited text no. 8
    
9.
Manhart J, Kunzelmann KH, Chen HY, Hickel R Mechanical properties of new composite restorative materials. J Biomed Mater Res 2000;53:353-61.  Back to cited text no. 9
    
10.
Jung M, Eichelberger K, Klimek J Surface geometry of four nanofiller and one hybrid composite after one-step and multiple-step polishing. Oper Dent 2007;32:347-55.  Back to cited text no. 10
    
11.
Papadogiannis Y, Lakes RS, Palaghias G, Helvatjoglu-Antoniades M, Papadogiannis D Fatigue of packable dental composites. Dent Mater 2007;23:235-42.  Back to cited text no. 11
    
12.
Aguiar FHB, Georgtto MH, Soares GP, Catelan A, Dos Santos PH, Ambrosano GHB, et al. Effect of different light curing modes on degree of conversion, staining susceptibility and stain’s retention using different beverages in a nano filled composite resin. J Esthe Restor Dent 2011;23: 115-21.  Back to cited text no. 12
    
13.
Yap AU Effectiveness of polymerization in composite restoratives claiming bulk placement: impact of cavity depth and exposure time. Oper Dent 2000;25:113-20.  Back to cited text no. 13
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2]



 

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