Comparative evaluation of the compressive, tensile, and flexural strengths of paracore®, flourocore®2+, and multicore® resin-based core build-up materials - An in vitro study.

Aims: The study was aimed to evaluate and compare the compressive, diametral tensile, and flexural strengths of three different commercial resin based core materials and to single out the best resin-based core build-up material with respect to their physical properties among ParaCore® (Coltene Whaledent, USA), FlouroCore® 2+ (Dentsply International, USA), MultiCore® (Ivoclar Vivadent, Liechtenstein) with Miracle Mix® (GC America) core used as control. Materials and
Methods: One hundred and twenty samples were prepared, of which forty samples (10 of each material) were prepared in cylindrical stainless steel molds (height 6 mm, diameter 4 mm) for compressive strength measurements. Other forty samples (10 of each material) were prepared in cylindrical molds (diameter 6 mm, height 2 mm) for diametral tensile strength measurements. Forty samples (10 of each material) were prepared in stainless steel molds cuboidal in shape (length 25 mm, thickness 2 mm, and width 2 mm) for flexural strength measurements. The samples were tested on a Universal testing machine (Instron Machine 3366, made in the USA). Statistical Analysis Used: One-way analysis of variance was performed to determine any statistically significant differences (P < 0.05) among the resin-based core build-up materials with respect to their three respective strengths. Further, the statistical comparison was made among the four materials using Student's t-test at a significance level of 5%.
Results: Based on the results obtained it can be summarized that the ParaCore is the strongest material among all the four materials, followed by MultiCore, FlouroCore2+, and Miracle Mix. The Miracle mix is the weakest among all the materials owing to its inferior strength values.
Conclusion: The results of the present study imply that, in consideration of their superior strength values, resin-based core build-up materials, ParaCore, MultiCore, and FlouroCore2+ should be a preferred for use as core build-up material over Miracle Mix in specific clinical situations, in the same order of preference. Copyright:

INTRODUCTION

Teeth undergoing endodontic treatment are usually structurally compromised as regards the coronal tooth structure.[1] A core helps in the restoration of this badly mutilated tooth so that a full coverage prosthesis can be placed. Furthermore, it simplifies tooth preparation.[2] As the core helps restore a tooth functionally, it should have adequate strength to resist the various masticatory forces.[3]

A variety of dental materials have been used to build up the core, namely amalgam, composites, glass ionomer cements, and silver-reinforced GI (SRGI). Although most of these were not developed for this specific purpose, they were employed for core-build-ups owing to their various individual properties.[245678] Furthermore, noteworthy is the fact that, despite some disadvantages of SRGI, the wide use of GI-based core-build-up materials by clinicians has been reported in large surveys.[910] Newer commercially available formulations that have different combinations of materials have been introduced lately.[1112] These alternatives are available as flowable resin core build-up materials. Although they are tooth colored, there are concerns about their mechanical properties because the filler content had to be decreased to improve the flowability.[13]

Literature assessing the compressive strength (CS), diametral tensile strength (DTS), and flexural strength (FS) of newer resin-based core build-up materials is limited. Hence, the purpose of the present study was to evaluate the CS, DTS, and FS of three different commercial resin based core materials and to find out the best resin-based core build-up material with respect to their physical properties among ParaCore® (Coltene, Whaledent), FlouroCore®2+ (Dentsply), MultiCore® (Ivoclar Vivadent) with Miracle Mix® (GC America) core used as control.

MATERIALS AND METHODS

The study was reviewed by Institute Review Board (Reference no. 16/EC-03). The materials used in the study were ParaCore® (Coltene Whaledent, USA), FlouroCore® 2+ (Dentsply International, USA), MultiCore® (Ivoclar Vivadent, Liechtenstein) with Miracle Mix® (GC America) [Table 1].[14] This study was conducted on the material samples made according to the American Dental Association specification No. 27.[15] Similar material samples were made for such measurements in a study conducted by Agrawal and Mala.[16]

Table 1

Materials used in the study

Core material	Description	Composition	Manufact-urer
ParaCore®	Fiber-reinforced, dual core, radiopaque core build-up material	Para core contains: methacrylate (Bis-GMA, UDMA, TEGDMA. TMPTMA), sodium fluoride, barium glass, amorphous silica	Coltène Whaledent Group, Mahwah, NJ, USA
MultiCore®	Dual-curing, fluoride-containing, radiopaque composite for core build-ups	Bis-GMA, urethane dimethacrylate, and triethylene glycol dimethacrylate (29 weight%) - barium glass, ytterbiumtride Ba-Al-fluorosilicate glass and highly dispersed silicon dioxide (70 weight %) - catalysts, stabilizers and pigments	Ivoclar Vivadent Inc., Schaan, Leichtenstein
FlouroCore 2+®	FluoroCore® material uses a biocompatible urethane resin and is supplied in two shades, blue and tooth colored	UDMA - di and tri functional methacrylates - barium boron fluoroalumino silicate glass camphorquinone, photoinitiator, photoaccelerators, aluminum oxide, silicon dioxide, benzoyl peroxide	DENSPLY Caulk
Miracle Mix®	Miracle mix is a silver alloy-glass ionomer cement indicated as a core build-up material	Powder: Alumino-fluoro-silicate glass (amorphous) Alloy: Silver metal (56%), tin metal (29%), copper metal (15%) Liquid: Polyacrylic acid	GC America

Bis-GMA: Bisphenol A-glycidyl methacrylate, UDMA: Urethane dimethacrylate, TEGDMA: Triethylene glycol dimethacrylate, TMPTMA: Trimethylolpropane trimethacrylate

The samples were divided into three experimental groups, CS, DTS, FS (according to the type of strength being evaluated). Each group was further divided into four sub groups 1 to 4, (according to the resin-based core build-up materials being used).

Out of the total of 120 samples, forty samples (ten for each product) were be prepared in cylindrical stainless steel molds (6 mm in height, 3 mm in diameter) for CS measurements. Another forty samples (10 for each product) were prepared in cylindrical molds (6 mm in diameter, 2 mm in height) for DTS measurements. Forty samples (10 of each product) were prepared in cuboidal stainless steel molds (25 mm in length, 2 mm in thickness, 2 mm in width) for FS measurements.

All materials were manipulated according to the manufacturers’ instructions. The resin-based composites were cured in their molds with the same curing unit. The samples were then left to set in the molds at room temperature for 10 min. The miracle mix samples were left in mold for 5 min for achieving the final set. All the specimens were stored at 37°C in 100% humidity, and all properties were measured at the end of 24 h. The dimensions of the samples will be measured using Vernier calipers.

The samples were mounted on custom made jigs (corresponding to the size of the samples) between the disks of the blotting paper on the platens of the Universal testing machine (Instron Machine 3366, made in the USA) at a crosshead speed of 0.5/min for CS and DTS tests and 0.1 mm/min for FS tests [Figure 1].

Figure 1

Test setups: (a) Compressive strength test set up,(b) Diametral tensile strength test set up, (c) Flexural strength set up

Statistical analysis

The mean value with its standard deviation was calculated for each core material. One-way analysis of variance was performed to determine statistically significant differences (P < 0.05) among the resin-based core build-up materials with respect to their three respective strengths. Further, the statistical comparison was made among the four materials using Student's t-test at a significance level of 5%.

RESULTS

The results of the study showed highly significant differences (0.000) between CS, DTS, and FS values of the four materials. ParaCore showed the maximum CS followed by MultiCore, FlouroCore2+, and Miracle Mix. The lowest values were exhibited by Miracle Mix with the highly significant differences in values (P = 0.000).

The DTS values were significantly highest for FlouroCore2+ (P = 0.000, P ≤ 0.05 when compared to ParaCore), followed by Para Core, MultiCore, and Miracle Mix. However, the values for ParaCore and MultiCore were comparable with no significant difference (P > 0.05).

Paracore showed the highest FS values, followed by MultiCore and FlouroCore2+, and Miracle Mix. However, the difference between the values for ParaCore and MultiCore was nonsignificant (P > 0.05) [Graph 1].

Graph 1

Relative comparison of the four materials for the three strengths

DISCUSSION

CS is regarded as a critical indication of success because high CS is necessary to combat masticatory and parafunctional forces.[4] Tensile strength is significant because restorations are subject to many tensile stresses due to oblique and transverse loading.[4] High FS implies that the material has less tendency to craze and is resistant to erosion as well as defects.[2]

In the present study, ParaCore exhibited the highest compressive and Flexural strengths. This is because the macroscopic size of the unidirectional fiber bundles, reinforce the resin and improve its mechanical properties. Furthermore, the fibers interrupt crack growth progression, thereby enhancing fracture toughness.

The differences in the DTS and FS values of the resin-based core build-up materials can be attributed to the composition of the monomer used. The organic matrix of the majority of composite materials is based on Bis-GMA resin which is an aromatic dimethacrylate ester with a high rigidity and viscosity. To improve fluidity and enhance filler dispersion, a lower-molecular-weight polymer, triethylene glycol dimethacrylate (TEGDMA) is often added. However, it increases the polymerization contraction. Moreover, it has been stated that replacing Bis-GMA with TEGDMA increases the DTS and decreases the FS.[17] To address these issues, Bis-GMA is replaced with Urethane dimethacrylate (UDMA).

UDMA monomer has a similar molecular weight like Bis-GMA, but it is less viscous, so it assures a better polymerization.[18] and also improves the mechanical properties, like FS and diametral tensile strength.[19] This explains the results shown by FlouroCore 2+ as the monomers used are only UDMA and Urethane modified Bis-GMA dimethacrylate resins. One can also add that MultiCore has an organic matrix based on Bis-GMA but also contains TEGDMA and UDMA. This is a possible explanation of the results for MultiCore.

However, in ParaCore, the composition of the matrix is altered by the addition of TMPTMA. Trimethylolpropane trimethacrylate (TMPTMA) is a water-insoluble, low viscosity trifunctional methacrylate monomer that can act as a crosslinking agent in polymeric matrixes. Various studies investigating the effect of the addition of TMPTMA into the resin matrix have shown an increase in the physical properties of the composites.[202122]

Another significant finding is that Miracle Mix showed the lowest values. These values were, however consistent with the findings of Levartovsky et al.,[2] Saygili and Mahmali[23] and Beyls et al.[24] The possible explanation is the lack of interfacial bonding between the silver alloy fillers and the polyacrylate matrix of the cement.[25]

CONCLUSION

Based on the results obtained and respecting the limitations of this in vitro study, it was inferred that the ParaCore is the strongest material among all the four materials, followed by MultiCore and FlouroCore 2+. Moreover, Miracle Mix that appears to be used widely as a core build-up material with a good clinical success rate, it is not particularly suitable for this application. Resin-based core build-up materials should be used as alternatives.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.