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 Table of Contents  
ORIGINAL RESEARCH
Year : 2022  |  Volume : 13  |  Issue : 4  |  Page : 149-153

Fracture Resistance of Teeth Restored with Newer Methacrylate-Based Dental Composite Materials: An In Vitro Study


1 MIDAC Dental Centre, Kozhikode, Kerala, India
2 Department of Conservative Dentistry and Endodontics, A. B. Shetty Memorial Institute of Dental Sciences, Nitte University Deralakatte, Mangaluru, Karnataka, India

Date of Submission13-May-2021
Date of Decision16-Nov-2021
Date of Acceptance08-Nov-2022
Date of Web Publication12-Dec-2022

Correspondence Address:
Mithra N Hegde
Department of Conservative Dentistry and Endodontics, A. B. Shetty Memorial Institute of Dental Sciences, Nitte University Deralakatte, Mangaluru, Karnataka – 575018
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/denthyp.denthyp_69_21

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  Abstract 


Introduction: Composite have evolved significantly due to the increase in the demand for a more esthetic and conservative approach in dentistry. Modifications have been made on the filler particle size and loading, followed by alterations in the resin matrix substance. Methacrylate-based composite with the addition of nanoparticles to the filler has been introduced in the market, providing improved esthetics and lower polymerization shrinkage. The present study was done to compare the fracture resistance of teeth restored using two newer methacrylate-based composite materials, along with the flexural strength of the composites. Methods: Sixty mandibular premolars were divided into two control groups of 10 teeth each and two experimental groups of 20 teeth. Group I − intact teeth with no preparations (n = 10), Group II − prepared but unrestored teeth (n = 10), Group III − teeth prepared and restored with a stackable nanohybrid methacrylate-based composite material (IPS Empress DirectTM), and Group IV − teeth prepared and restored with a packable submicron methacrylate-based composite material (Brilliant EverglowTM), respectively. The teeth were embedded in resin-filled PVC rings, and a compressive loading test was carried out for all groups at a cross-head speed of 0.5 mm/min. The flexural strengths of the two composite materials were also analyzed using three-point bending test using Universal Testing Machine. The statistical significance (P < 0.05) of the differences between the experimental groups was analyzed by ANOVA and Tukey post hoc test. Results: The mean fracture resistance was highest in Group IV (1877.37 ± 494.79) followed by Group III (1763.69 ± 392.51), Group I (1607.08 ± 283.48), and Group II having the least (1442.08 ± 373.66). The mean fracture resistance overall differed significantly between the four groups (P = 0.048). Tukey test showed fracture resistance differed significantly between Group II and Group IV (P = 0.042) and no significance among other groups. Conclusion: Fracture resistance was highest in the group restored with the packable submicron hybrid composite material. The packable submicron methacrylate-based composite material also showed higher flexural strength than stackable nanohybrid composite material.

Keywords: Composites, fracture resistance, flexural strength, universal testing machine


How to cite this article:
Narayanan S, Hegde MN, Thirunarayanan S, Dsouza TS. Fracture Resistance of Teeth Restored with Newer Methacrylate-Based Dental Composite Materials: An In Vitro Study. Dent Hypotheses 2022;13:149-53

How to cite this URL:
Narayanan S, Hegde MN, Thirunarayanan S, Dsouza TS. Fracture Resistance of Teeth Restored with Newer Methacrylate-Based Dental Composite Materials: An In Vitro Study. Dent Hypotheses [serial online] 2022 [cited 2023 Feb 6];13:149-53. Available from: http://www.dentalhypotheses.com/text.asp?2022/13/4/149/363437




  Introduction Top


Esthetic dentistry is a rapidly evolving discipline. The demand for esthetic restorations is increasing day-by-day and restorations of posterior with resin-based composite materials are gaining a lot of popularity. The newer composites and adhesive systems are rapidly developing to replace silver amalgam restoration and protect the remaining tooth structure.[1]

Debilitation of the teeth following mesio-occluso-distal (MOD) preparations and reinforcing the residual tissues by restorations have been focused on in various studies.[2],[3] MOD preparations usually bring about a significant reduction in tooth strength because of the loss of marginal ridges and microfractures caused by applied occlusal forces.[4],[5]

Transfer of stress tends to be different in a restored tooth compared to an intact tooth. Adhesive restorations are more effective in relaying and diffusing functional stresses over the bonding interface, with the added capability of sustaining weakened tooth form.[6],[7],[8] On exertion of extreme force, the fracture would emanate, which can be either complete or incomplete. Experimental and theoretical efforts are made to check the fracture resistance of the material and correlate it with the hardness and stability of the material.[9] The fracture resistance of a composite material may depend on the specific failure mode of heterogeneous materials.[10]

Composite restorations are suitable for use in both anterior and posterior teeth. Despite the excellent properties of resin composites, one main drawback of composites is the comparably high fragility and low fracture strength in stress-bearing posterior restorations.[11]

Methacrylate-based material, especially PolymethylMetha Acrylate (PMMA), gained popularity for various dental applications due to its unique properties, including its low density, esthetics, cost-effectiveness, ease of manipulation, and tailorable physical and mechanical properties.[12] PMMA-based biocomposites with the addition of epoxy resins, polyamide, or butadiene styrene have been reported to improve the impact strength of PMMA.[13] The only drawback of methacrylate-based composite is the increased polymerization shrinkage. With the innovative improvements, newer materials with low-polymerization shrinkage have been introduced.[14]

This study intended to compare and assess fracture resistance of restored teeth using two newer methacrylate-based composite restorations.


  Materials and Methods Top


Following local ethical approval, the present in vitro study was carried out in the Department of Conservative Dentistry and Endodontics, AB Shetty Memorial Institute of Dental Sciences, Mangalore. The sample size was calculated as 60, based on 80% power, 5% level of significance, effect size of 0.45 using G Power software (http://www.gpower.hhu.de/). Sixty non-carious permanent maxillary premolars were selected and groups were separated as follows.

Group I − Intact teeth with no preparations (n = 10)

Group II − Prepared but unrestored teeth (n = 10)

Group III − Teeth prepared and restored with a stackable nanohybrid methacrylate-based composite material (IPS Empress DirectTM)

Group IV − Teeth prepared and restored with a packable submicron methacrylate-based composite material (Brilliant EverglowTM)

Class II MOD preparations were performed on 50 premolar teeth with a tungsten carbide bur. The preparations were ¼ of the inter-cuspal width and 2 mm deep pulpally, and the proximal boxes, with an axial wall that is 2 mm wide and 2 mm deep. All the teeth were embedded in cylindrical PVC (Polyvinyl chloride) rings of 2 and 2.5 cm width, filled with self-cure acrylic resin.

Light curing was carried out for 30 seconds. Tofflemire metal matrices were used to re-establish the proximal surface of the restorations.

Fracture resistance test

All the teeth were subjected to compressive loading in a Universal Testing Machine. It was done using an 8-mm metal sphere with a crosshead speed of 0.5 mm/min, which was placed centrally to the occlusal surface and applied in parallel to the long axis of the tooth and the slopes of the cusps (rather than the restoration). Fracture resistance was calculated in Newton units.

Flexural test

For flexural strength testing, rectangular specimens were prepared in stainless steel mould with internal dimensions of 25mm × 2 mm × 2 mm according to ISO 4049 standards for resin composites. Two groups were formed, each having 10 composite specimens and named as Group A and Group B. In group A, 10 samples were prepared on the mould by directly filling with stackable nanohybrid methacrylate-based composite and photo polymerized for 40 seconds. In group B, another 10 samples were prepared on the mould by directly filling with packable submicron methacrylate-based composite and photo polymerized for 40 seconds. After filling the mould to excess, the material surface was covered with a mylar strip and a glass slide was compressed to extrude excess material. A ll specimens were photo polymerized using LED light.

Statistical analysis

The data were analyzed using SPSS 22 (IBM Corp, Armonk, NY). The statistical significance (P < 0.05) of the differences between the experimental groups was analyzed by ANOVA and Tukey post hoc tests.


  Results Top


The mean fracture resistance was highest in Group IV (1877.37 ± 494.79), followed by Group III (1763.69 ± 392.51), Group I (1607.08 ± 283.48), and Group II was least (1442.08 ± 373.66). The mean fracture resistance overall differed significantly between the four groups (P = 0.048). [Table 1]
Table 1 Comparison of fracture resistance between the four groups

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Tukey test for the intergroup comparison shows fracture resistance differs significantly between Group II and Group IV (P = 0.042). There is no statistical significant difference between Group I and II (P = 0.808), Group I and III (P = 0.762), Group I and IV (P = 0.339), Group II and III (P = 0.197), Group III and IV (P = 0.820). [Table 2] and [Table 3].
Table 2 Post hoc testsTukey HSD multiple comparisons

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Table 3 Comparison of Flexural strength (MPa) between two groups

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  Discussion Top


In the current study, teeth restored, Brilliant EverglowTM, a packable sub-micron hybrid methacrylate-based composite marketed by ColteneInc and IPS Empress DirectTM is a stackable nanohybrid methacrylate-based composite marketed by Ivoclar Vivadent were compared for their fracture resistance.

Among the groups, packable sub-micron hybrid composite showed the highest fracture resistance compared to nanohybrid composite and control groups. This was statistically significant between sub-micron hybrid composite and unrestored teeth. The lowest fracture resistance was observed in the negative control group as removing the tooth structure languish the tooth, and it was not followed by a restoration which further weakened the tooth structure. Soares et al.[15] claimed that if the tooth is not restored, it causes a wedge-like effect between buccal and palatal cusps, causing fracture of the teeth. Composite restoration enhances the fracture resistance because of its high modulus of elasticity. The resin composite’s overall chemical structure and properties vary significantly depending on their constituents, chemistry, and interaction with each other. Such variables may alter the material’s susceptibility to the oral environment, leading to variations in degradation and fracture.[16] This result could be associated with factors like heavily filled composites having higher fracture toughness, the molecular weight of the principal organic resin, cohesive bonding of the bonding agent.

Several studies have been conducted by Soares et al.,[15] Kikuti et al.,[17] and Steel et al.,[18] to determine the fracture resistance of sound teeth. Several parameters determine fracture resistance such as, morphological variations of tooth present, method of sample preservation, type of loading, its speed, and several application designs.

Lloyd and Iannetta[19] proposed that stress intensification factor (Kc) is seen to increase on the addition of filler particles. However, once a threshold level is reached, further increase of filler particle will decline the strength, thereby decreasing the stress factor. The current study is in accordance with this investigation, wherein nanohybrid composite has lesser filler concentration by weight (75%) than sub-micron hybrid composite (79%).

In a study done by Htang et al.,[20] fracture resistance was observed in the different filler contacting groups. It was found that the filler content lower than the threshold value and the one higher than the threshold value both had low fatigue fracture resistance. Too high or too low filer content compromised the fracture resistance. The key to determine the fracture resistance is the distance between the filler particle, for appropriate and even distribution of stress.[21] In highly filled composites, the cracks which are formed due to the stress formation are because of quartz particles which are fragile in nature. This could support the result of the present study wherein fracture resistance was seen to be lower in nanohybrid methacrylate-based composite material, which has lesser filler concentration and more inter-particulate distance.

The results of the study concluded that all of the experimental groups achieved satisfactory results, except for Group II, which presented the lowest mean values of fracture resistance. Reel and Mitchell,[22] who concluded that in the teeth restored with composite, there was fortification rendered by the material.Direct composite resin restoration can resist the fracture of the tooth in a nominal mesiooccluso distal cavity preparation to fracture resistance values of a sound tooth. However, the composition of the restorative material has an important influence on the fracture resistance for more extensive preparations. With this current research, the nanoparticle resin showed significantly lower fracture resistance values compared to nanohybrid composite resins. However, large cavities restored with nanohybrid resins demonstrated fracture resistance values statistically similar to the medium-sized restorations.[23]

The flexural strength of the two composite materials were carried out using the three-point bending test and the sub-micron hybrid methacrylate-based composite material showed slightly higher flexural strength compared to the nanohybrid methacrylate-based composite material, even though it was not statistically significant. In this study, it was found that flexural strength was not based alone on the resin matrix but other factors also governed it. It was also found that it was independent of modulus of elasticity which was in contrast to the study done by Rodrigues. Junior who concluded that the filler content significantly interfered in the flexural strength and modulus of elasticity of the composites tested.[24]


  Conclusion Top


Within the limitations of the study, the sub-micron hybrid composite was found to have highest fracture resistance among all the groups. For intergroup comparison, unrestored prepared teeth had least fracture resistance and sub-micron hybrid composite proved highest resistance to fracture, followed by nanohybrid composite and intact teeth. The sub-micron hybrid composite showed higher flexural strength compared to the nanohybrid, but was not statistically significant.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors report no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3]



 

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