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Comparative evaluation of mechanical properties of three different direct posterior restorative materials: An in vitro study


1 Department of Conservative Dentistry and Endodontics, Dr. D.Y. Patil Dental College and Hospital, Dr. D.Y. Patil Vidyapeeth (Deemed to be University), Pimpri, Pune, Maharashtra, India
2 Graduate student, Department Of Endodontics, University of Detroit Mercy, Michigan, USA
3 Department of Oral Pathology and Microbiology, Dr. D.Y. Patil Dental College and Hospital, Dr. D.Y. Patil Vidyapeeth (Deemed to be University), Pimpri, Pune, Maharashtra, India

Date of Submission06-May-2021
Date of Decision28-May-2021
Date of Acceptance28-May-2021

Correspondence Address:
Karan Bhargava,
Department of Conservative and Endodontics, Dr. D.Y. Patil Dental College and Hospital, Dr. D.Y. Patil Vidyapeeth (Deemed to be University), Sant Tukaram Nagar, Pimpri, Pune - 411 018, Maharashtra
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjdrdypu.mjdrdypu_329_21

  Abstract 


Aim: The aim of this study was to evaluate and compare the compressive strength, Vickers microhardness number, and wear resistance of amalgam (DPI), Filtek Z350 nanohybrid (3M ESPE), and Zirconomer (Shofu) restorative materials after 24 h and 3 months. Methodology: The restorative materials were divided into Zirconomer (Group I), Filtek Z350 (Group II), and amalgam (Group III). These materials were placed in cylindrical molds to prepare the specimens. The specimens were stored in distilled water at 37°C. The specimens were tested at 24 h and 3 months for compressive strength, wear resistance, and microhardness. Results: Group I showed significantly less maximum load (N) and compression strength (MPa) when compared with Group III (control) and Group II (P < 0.01). There was no significant difference in microhardness between the three groups. Group I showed significantly more wear (weight loss [g]) and wear (weight loss [%]) when compared with Group III (control) and Group II. Conclusion: The study concludes that amalgam and nanohybrid composite performed better than Zirconomer at the end of 24 h and 3 months.

Keywords: Amalgam, composite, compressive strength, Vickers microhardness, wear resistance, Zirconomer



How to cite this URL:
Somani S, Shetty R, Bhargava K, Bhawalkar A, Kumar T, Newase P, Sarode G. Comparative evaluation of mechanical properties of three different direct posterior restorative materials: An in vitro study. Med J DY Patil Vidyapeeth [Epub ahead of print] [cited 2022 Dec 7]. Available from: https://www.mjdrdypv.org/preprintarticle.asp?id=338911




  Introduction Top


The ultimate goal of dental restorative materials is to mimic the biological, functional, and esthetic properties of healthy tooth structure. Dental amalgam and gold alloys, which have a long record of clinical success, have been used as dental restorative materials for more than 100 years, especially in posterior teeth, because their mechanical properties match those of natural teeth; however, these metallic materials are not esthetic.[1]

With the decline in popularity of amalgam in recent years, there is a need for an equally strong yet safer replacement.[2] In the last few decades, the increasing demand for esthetic dentistry has led to the development of resin composite materials for direct restorations with improved physical and mechanical properties, esthetics, and durability.[3]

Resin composites have gone through generations of traditional macrofilled composites, microfilled, hybrid, microhybrid, and nanocomposites. Composite resin posterior restorations are influenced by mechanical properties, such as fracture toughness, compressive strength, flexural strength, wear resistance, and diametric tensile strength. Composite resins have better mechanical properties, such as compressive strength, than other restorations such as conventional or resin-modified glass ionomers, suggesting a longer clinical life in regions submitted to occlusal loads. No single composite material is able to meet the functional needs of both posterior Class I and Class II restorations. Nanocomposites have improved mechanical properties, but still, this material lacks some important properties such as anticariogenicity and microleakage.[4]

Glass ionomers were introduced in the early 1970s (Wilson and Kent 1972). Glass ionomer possesses certain properties that make them useful as restorative filling material. This includes low coefficient of thermal expansion which is similar to tooth, chemical bonding to both enamel and dentin, and release of fluoride ions to adjacent tooth structure. They are, however, susceptible to fracture and exhibit lower wear resistance.[5]

Because of low tensile strength and brittleness of unreinforced cement, attempts were made to improve cement strength. In 1977, the addition of amalgam alloy powder to glass-ionomer powder (admix) was proposed to provide radiopacity and increased strength.[6] Since the end of the 1980s, more developed glass-ionomer cement (GIC) were introduced such as resin-modified GIC (RM-GIC) have become available, to overcome the disadvantages such as moisture sensitivity and poor mechanical strength.

Hence, to overcome the drawbacks of composites and to get benefited from the properties of both GIC and composites, Zirconomers (zirconia-reinforced GIC) were introduced in the market.

Zirconomer defines a new class of restorative glass ionomer that promises the strength and durability of amalgam with the protective benefits of glass ionomer while completely eliminating the hazard of mercury. The inclusion of zirconia fillers in the glass component of Zirconomer reinforces the structural integrity of the restoration and imparts superior mechanical properties for the restoration of posterior load-bearing areas where the conventional restorative of choice is amalgam. A combination of outstanding strength, durability, and sustained fluoride protection deems it ideal for permanent posterior restoration in patients with high caries incidence as well as cases where strong structural cores and bases are required.[2]

For any material to be successful in an oral environment, it should have standard physical and mechanical properties. Hence, this study was taken up to evaluate and compare the compressive strength, wear resistance, and hardness of Zirconomer, amalgam, and composite restorative materials.


  Methodology Top


Sample preparation

  • The restorative materials were divided into the following groups


    • Zirconomer (Shofu) (Group I)
    • Filtek Z350 (3M ESPE) (Group II)
    • Amalgam (D.P.I) (Group III) (Control).


  • Cylindrical specimens were prepared in molds using glass tubing of 3 mm diameter and 6 mm thickness for compressive strength and 1 cm diameter and 2 mm thickness for wear resistance and Vickers microhardness
  • All the samples were slightly overfilled and compressed with glass plates
  • For the light curable composites, the procedure was similar to those for amalgam and Zirconomer, except that the specimens were exposed to a light-emitting diode light source for (20 s)
  • The extracted teeth were mounted in acrylic blocks
  • All the samples were stored in distilled water at 37°C.


Compressive strength test

Ten samples (n = 10) of each material were placed in a universal testing machine at a crosshead speed of 0.05 mm/min. Testing of samples was done at 24 h and 3 months.

Vickers microhardness test

Vickers diamond indenter was used as a standard hardness tester for specimen indentation (n = 10) per group; a load of 150 g applied for 20 s was used to make indentation of each material. Testing of sample was done at 24 h and 3 months.

Two-body wear resistance

  • Ten extracted teeth and ten material discs (n = 10) per group were taken
  • Teeth were mounted on one side and material discs were mounted on the other side of the equipment, and a rotating wheel of 350 rpm for 5000 cycles was placed on the surface of the material disc. Thus, the counter body was sliding on the material specimen. The reduction of surface was measured in micrograms in the weighing machine. Testing of sample was done at 24 h and 3 months.


Statistical analysis

Statistical analysis was done by descriptive statistics as mean and standard deviation (SD). Student's paired “t” test and unpaired “t” test were used to compare all experimental groups and control groups. Probability P < 0.05 was considered statistically significant. Statistical analysis software SYSTAT version 12 (Cranes Software is a Global Scientific and Engineering Software Products and Solutions Company located in Bengaluru, Karnataka , India) was used to analyze the data.

Ethics

The study protocol was approved by the Institute Ethics Committee of Dr. D. Y. Patil Vidyapeeth, Pune, letter number DYPDCH/27/2021, dated May 18, 2021.


  Results Top


Compressive strength

The mean and SD value of compressive strength for Group I was 51.543 ± 23.776, Group II was 88.687 ± 32.965, and Group III (control) was 91.79 ± 26.51 after 24 h. After 3 months, the values were as follows: Group I 46.497 ± 20.32533, Group II 84.287 ± 26.59433, and Group III 99.389 ± 16.65558. There was a highly significant difference between Group I and Group III (control) (P < 0.01) and between Group I and Group II (P < 0.01). There was no significant difference between Group II and Group III (control).

Microhardness

The mean and SD value after 24 h of Group I was 104.46 ± 5.41, Group II was 106.01 ± 20.59, and Group III (control) was 108.50 ± 6.47. After 3 months, the value for Group I was 101.891 ± 5.217459, Group II was 108.258 ± 19.11159, and Group III was 112.96 ± 12.56814. There was no significant difference between mean values of microhardness between Group I and Group III (P > 0.05), between Group I and Group II (P > 0.05), and between Group I and Group III (P > 0.05).

Wear resistance

The amount of wear weight loss of Group I was 1.49, Group II was 0.98, and Group III was 0 after 24 h. The values were 1.59, 0.78, and 0.5 for Groups I, II, and III, respectively, after 3 months. There was a highly significant difference between mean values of wear (weight loss [g]) and wear (weight loss [%]) between Group I and Group III (P < 0.01), between Group I and Group II (P < 0.01), and between Group II and Group III (P < 0.01).


  Discussion Top


The selection of an appropriate restorative material has become a difficult task because of the wide variety of materials available on the market. Although the mechanical properties of the material do not necessarily represent their actual clinical performance, they are used to guide the effects of changes in their composition or processing on these properties. The tests might help the clinician make a more informed decision by comparing between formulations and brands.[7]

For any material to be successful in the oral environment, it should have standard physical and mechanical properties. Restorations on posterior teeth are constantly subjected to functional loading. Mechanical properties of a material describe its response to these physical and chemical challenges.[8]

The results of the wear test show that the mean value and SD values of initial weight (g) and weight after test (g) between Group I, Group II, and Group III after 24 h and 3 months (positive control) are highly significant. The highest wear resistance was found with amalgam followed by composite and Zirconomer.

Modern dental amalgam encompasses a number of broad classes of materials, with variants in phase content, making them the most metallurgically complex biomaterial. The older generation dental amalgam did have a limited life span, because they contained the gamma-2 phase that caused progressive weakening of the amalgam through corrosion.[9]

By the elimination of gamma-2 phase and introduction of newer amalgam with higher copper content, there are several clinical studies that have demonstrated that high copper amalgam can provide satisfactory wear resistance for more than 12 years. Due to several studies demonstrating the high wear resistance of amalgam in the oral environment, it was taken as a control in this study.[10],[11],[12],[13],[14]

The results in regard to wear resistance obtained in this study were in accordance with the previous studies which showed the superior performance of amalgam. In this study, amalgam showed the least wear loss at 24 h and 3 months.

According to various previous researches carried out on the wear resistance of early dental composites, it was concluded that increased filler loading increases the wear performance of material. Hence, the current concept is based on nanotechnology which says to minimize the size of the filler particles and to increase the filler loading to satisfy all the requirements of dental composites.[15]

The advent of composite resins brought about several advantages such as tooth reinforcement and improved bonding.[16]

Some in vitro study results say that under three-body abrasive wear test conditions, the addition of inorganic fillers can improve the wear resistance of dental composites.[15],[17],[18],[19],[20],[21]

In the present study, Filtek Z350 nanocomposite shows the lower two-body wear loss for 24 h and 3 months than Zirconomer. This might be because it has been noted that the addition of high levels of filler particles into the resin matrix has an adverse effect on wear resistance under two-body wear conditions. During the wear process, the wear surface is acted on by a combination of normal loading and frictional shearing forces.[22]

The main aim of introducing Zirconomer in the market was to improve the mechanical properties of GIC by applying nanotechnology that has been made available so that it can be used as permanent posterior restoration under high stress-bearing areas of occlusion. More recently, nanotechnologies have been applied to the RM glass ionomers in the form of nanoparticles (nanomers) and nanoclusters in fluoroaluminosilicate glass.[22]

The results obtained in this study showed that Zirconomer has the highest wear loss for 24 h and 3 months. It might be due to the improper bonding of zirconia particles with glass-ionomer matrix, which has led to the highest wear loss of zirconia filler particles during two-body wear tests.[23]

Amalgam showed the highest compressive strength at 24 h and 3 months. Filtek Z350 showed lower compressive strength to amalgam. This observation is in accordance with the results discussed by Ruddell et al., who stated that there can be drop-in mechanical properties due to microcracking present in some nanoparticles which was introduced during impregnation procedures resulting in inbuilt flaws.[24]

Zirconomer showed the least compressive strength at 24 h and 3 months. It can be due to the lower compressive strength of GIC or improper bonding of zirconia particles with glass-ionomer matrix and factors such as integrity of the interface between the glass particles and the polymer matrix, the particle size, and the number and size of voids which have an important role in determining the compressive strength.[23]

Amalgam showed the highest Vickers microhardness, followed by Filtek Z350 and Zirconomer. However, there was no significant difference between the values. These results are in accordance with previous studies regarding the Vickers hardness number of amalgam.[10],[11],[12],[13],[14]

Jayashankara et al. evaluated the fracture resistance of various composite fillings in teeth, and the results of their study were similar to our study.[25]

Zirconomer showed the least wear resistance, compressive strength as well as Vickers microhardness values compared to amalgam and Filtek Z350 within the limitations of this study.


  Conclusion Top


This study evaluated and compared mechanical properties of three different posterior restorative materials, namely Zirconomer, Filtek Z350, and amalgam. Zirconomer showed the lowest compressive strength, lowest microhardness, and lowest wear resistance of the three tested restorative materials.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Khatib MM, Sarvesha B, Mahajan V. Evaluation of compressive load required to fracture premolar restored with different restorative materials – An in vitro. Int J Med Dent Sci 2016;5:1236-40.  Back to cited text no. 16
    
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Torii Y, Itou K, Itota T, Hama K, Konishi N, Nagamine M, et al. Influence of filler content and gap dimension on wear resistance of resin composite luting cements around a CAD/CAM ceramic inlay restoration. Dent Mater J 1999;18:453-61.  Back to cited text no. 20
    
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Jayashankar CM, Jameela.V.A, Sharath Kumar P, Anil Kumar S, Girish S.A, Ahmed M, et al. An in vitro comparitive evaluation of fracture resistance of dental amalgam, nano composite filtek-Z350 AND CENTION-N in Class II cavities. Int J Curr Adv Res 2020;9:20896-900.  Back to cited text no. 25
    




 

 
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