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ORIGINAL ARTICLE
Year : 2020  |  Volume : 23  |  Issue : 3  |  Page : 349-354

Comparative evaluation of fracture toughness and marginal adaptation of two restorative materials in nonendodontically and endodontically treated teeth: An in vitro study


1 Department of Restorative Dental Science, College of Dentistry, Jazan University, Jazan, Kingdom of Saudi Arabia
2 Department of Conservative Dentistry and Endodontics, KLE Society's Institute of Dental Science, Bangalore, Karnataka, India

Date of Submission09-Aug-2019
Date of Acceptance09-Dec-2019
Date of Web Publication5-Mar-2020

Correspondence Address:
Dr. S Bhandi
Department of Restorative Dental Science, College of Dentistry, Jazan University, Jazan
Kingdom of Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_424_19

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   Abstract 


Objective: To evaluate and compare the fracture resistance and marginal adaptation of Zirconomer and bulk fill posterior restorative material (Surefil SDR) in nonendodontically and endodontically treated teeth. Materials and Methods: The sample consisted of 52 caries-free extracted human premolars which were individually mounted in polyvinyl chloride (PVC) ring filled with acrylic resin up to 1.0 mm below the cementoenamel junction. The teeth were then divided into four groups according to the restorative material used as group I: Zirconomer + Operative only, Group II: Zirconomer + Endodontic treatment, Group III: SDR + Operative, and Group IV: SDR + Endodontic treatment. Fracture strength was tested using a universal testing machine and was expressed in Newtons. The marginal gap was measured at its maximum using a scanning electron microscope and expressed in micrometers. One-way analysis of variance followed by Tukey's post hoc test was used to compare the mean fracture resistance (N) and marginal adaptation (μm) between the four groups. Statistical significance was determined at α = 0.05. Results: Group 3 exhibited significantly highest mean fracture resistance than Group 1 (P < 0.001), Group 2 (P < 0.001), and Group 4 (P < 0.001). Group 4 had significantly higher mean fracture resistance than Group 1 (P = 0.008) and Group 2 (P < 0.001). Group 1 exhibited significantly highest mean marginal gap than Group 3 (P < 0.001) and Group 4 (P < 0.001). Group 2 had a significantly higher mean marginal gap than Group 3 (P < 0.001) and Group 4 (P < 0.001). Conclusion: The fracture resistance and marginal adaptation of Zirconomer are significantly lower than Surefil SDR in both nonendodontically and endodontically treated teeth.

Keywords: Endodontically treated teeth, fracture resistance, marginal adaptation Surefil SDR, Zirconomer


How to cite this article:
Mashyakhy M, Jabali A, Karale R, Parthiban G, Sajeev S, Bhandi S. Comparative evaluation of fracture toughness and marginal adaptation of two restorative materials in nonendodontically and endodontically treated teeth: An in vitro study. Niger J Clin Pract 2020;23:349-54

How to cite this URL:
Mashyakhy M, Jabali A, Karale R, Parthiban G, Sajeev S, Bhandi S. Comparative evaluation of fracture toughness and marginal adaptation of two restorative materials in nonendodontically and endodontically treated teeth: An in vitro study. Niger J Clin Pract [serial online] 2020 [cited 2020 Apr 7];23:349-54. Available from: http://www.njcponline.com/text.asp?2020/23/3/349/280032




   Introduction Top


The restoration of endodontically treated teeth should not only strive to achieve a functional and esthetic harmony but also provide adequate marginal seal and strength to the remaining tooth structure.[1],[2],[3] Due to the extensive and deep cavity preparation necessary for caries removal, endodontic treatment deems the tooth weak and highly prone to cuspal deflection and fractures.[4],[5],[6] The amount of residual coronal dentin and the support provided by the restoration are crucial in the prognosis and long-term success of the treatment of endodontically treated teeth.[7],[8],[9],[10] Despite the best efforts of the clinician, polymerization shrinkage leads to marginal gaps and the resulting microleakage is further detrimental to the prognosis of the tooth. Furthermore, the present composite resins suffer from the problem of inadequate polymerization resulting in restoration with poor strength. In addition, incomplete polymerization causes elution of the monomer which may lead to poor marginal adaptation, gap formation, microleakage, and secondary caries. All these factors are a threat to the pulpal integrity and cause restoration failure.[1],[11],[12]

Over the years, various techniques and material advancements have been tried to minimize the adverse effects caused due to polymerization shrinkage.[1],[13],[14] Recently, a new type of resin composite has been developed by certain manufacturers known as the “bulk fill” materials, which offer the advantage of enhanced curing, reduced shrinkage, and improved physical properties. For aesthetic restorations in posterior teeth, bulk fill flowable resin composites are used along with traditional composites thereby offering lower polymerization shrinkage, flowability for easy placement, better marginal adaptation, and reduced microleakage. In addition, they have a low modulus of elasticity which can reduce the stress generated on the cavity walls, and hence providing support to the tooth structure.[15],[16]

Glass ionomer cement (GIC) possesses many ideal properties such as adhesion to the tooth structure, modulus of thermal expansion similar to dentin, fluoride release, lack of exothermic polymerization, and biocompatibility to oral tissues. All these aforementioned properties have made it an indispensable dental restorative material. However, one of the major drawbacks of GIC is its weak mechanical properties such as brittleness, low strength, and poor fracture toughness.[17]

A new material, zirconia-reinforced GI (Zirconomer, Shofu Inc., Japan), was recently introduced, to overcome the limitations of conventional GICs. It contains zirconium oxide, glass powder, tartaric acid (1%–10%), polyacrylic acid (20%–50%), and deionized water as its liquid. The filler zirconium oxide strives to possess excellent strength, durability, and sustained fluoride release, thereby combining and retaining the benefits of both amalgam and conventional GICs.[17],[18],[19]

Hence, the objective of this study was to evaluate and compare the fracture resistance and marginal adaptation of Zirconomer and bulk fill posterior restorative material (Surefil SDR) in nonendodontically and endodontically treated teeth. The null hypothesis was that there is no difference in the fracture resistance and marginal adaptation of Zirconomer and bulk fill posterior restorative material (Surefil SDR) in nonendodontically and endodontically treated teeth.


   Materials and Methods Top


Study design

An experimentalin vitro study was conducted to evaluate and compare the fracture resistance and marginal adaptation of Zirconomer and bulk fill posterior restorative material (Surefil SDR) in nonendodontically and endodontically treated teeth.

The sample size was calculated based on the results of a previous study.[20]

Source of the data

Fifty-two orthodontically extracted human premolars were used in the study. Only teeth which were completely formed, caries-free, unrestored, and free of other defects were included in the study. The teeth were disinfected in 0.1% thymol, stored in distilled water, and used within 3 months after extraction. All teeth were individually mounted in polyvinyl chloride (PVC) ring filled with acrylic resin up to 1.0 mm below the cementoenamel junction. Teeth were then divided into four groups according to the restorative material used (n = 13):

Group I – Zirconomer + Operative only (cavity preparation with #245 bur followed by Zirconomer filling)

Group II – Zirconomer + Endo (Protaper F2/F3, with AH plus sealer + Zirconomer post endo restoration)

Group III – SDR + Operative only (cavity preparation with #245 bur, followed by Surefill SDR of 4 mm and 1–1.5 mm of occlusal Spectrum TPH)

Group IV – SDR + Endo (Protaper F2/F3, with AH plus sealer followed by Surefill SDR and 1–1.5 mm of occlusal Spectrum TPH)

Cavity preparation

Standardized class II mesio occluso distal (MOD) cavities were prepared in all teeth. Class II MOD cavities were made with 5-mm cavity depth, 2.5-mm-wide, proximal box, an axial wall of 1 mm, and a gingival seat width of 2 mm.

Root canal treatment

In Groups 2 and 4, access opening was done with endo access burs.

The root canals were prepared using Protaper F2/F3. Irrigation during cleaning and shaping was performed using a 2.5% NaOCl solution. After instrumentation, all teeth were obturated with gutta-percha and AH plus sealer.

Operative procedure

In Groups 1 and 3, the MOD cavities were treated with two-step etch-and-rinse adhesive and bonding agent was applied according to the manufacturer's instructions, and they were light-cured with an LED light for 20 s. After adhesive application, a metal matrix band was placed and the teeth were restored with a Surefil SDR flow resin composite Pennsylvania, United States (Dentsply). The flowable composite Surefil SDR was applied in a 3.5- to 4-mm layer and then was light-cured. Subsequently, the conventional composite was placed in a 1- to 1.5-mm-thick horizontal layer (Spectrum TPH 3; Dentsply). Light curing was done for 20 s each with the light source in contact with the coronal edge of the matrix band.

Groups 1 and 2 cavities were restored with Zirconomer filling material, using a matrix band. After 24 h, the proximal margins of all restored teeth were finished with soflex disks. All bonding and restorative procedures were conducted in controlled temperature and humidity.

The specimens were stored at 37°C in water in the dark for 2 months and then subjected to repeated thermal stress. Thermocycling was carried out 600 times in flushing water with temperature changing from 5°C to 50°C and back. The dwell time at each temperature was 2 min.

Fracture resistance

All restored teeth (n = 13 teeth per group) were mounted in a universal testing machine and subjected to a compressive axial load applied to the center of the occlusal surface and parallel to the long axis of the tooth and the slopes of the cusps, using a round-end steel device (8.0 mm in diameter). The compressive force was applied until the specimen fractured. The load required to fracture the specimens was expressed in Newtons.

Marginal adaptation

The fractured fragments were subjected for analysis in a scanning electron microscope. The gap was measured at its maximum and expressed in micrometers [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d.
Figure 1: (a-d) SEM images of the marginal gap

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Statistical analysis

The data were entered in Microsoft Office, Excel worksheets, and analyzed using software IBM SPSS v. 20.0 (IBM Statistics, SPSS, Chicago, IL, USA). The normality of the data was assessed using Shapiro–Wilk test, while Levene's test for equality of error variances was used to analyze the homogeneity of error variances. Descriptive statistics were calculated. One-way analysis of variance (ANOVA) followed by Tukey's post hoc test were used to compare the mean fracture resistance (N) and marginal adaptation (μm) between four groups. Statistical significance was determined at α = 0.05.


   Results Top


This study consisted of four study groups with a sample size of 13 per group. The mean fracture resistance of Group 1 was 431.29 ± 196.06 N, Group 2 was 320.25 ± 170.98 N, Group 3 was 804.96 ± 167.47 N, and Group 4 was 682.65 ± 221.14 N. The difference between the mean fracture resistance (N) between four groups was statistically significant at P < 0.001 [Table 1].
Table 1: Comparison of mean fracture resistance (N) between four groups using one-way ANOVA test

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[Table 2] presents the results of Tukey's multiple comparison post hoc test, which revealed that Group 3 exhibited significantly highest mean fracture resistance when compared with Group 1 (P < 0.001), Group 2 (P < 0.001), and Group 4 (P < 0.001), followed by Group 4 with significantly higher mean fracture resistance when compared with Group 1 (P = 0.008) and Group 2 (P < 0.001). However, the mean fracture resistance did not significantly differ between Group 1 and Group 2 (P = 0.45) and also between Group 3 and Group 4 (P = 0.37).
Table 2: Multiple comparisons of mean difference in fracture resistance (N) between four groups using Tukey's HSD post hoc analysis

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The mean marginal gap of Group 1 was 41.598 ± 6.057, Group 2 was 37.088 ± 6.074, Group 3 was 14.034 ± 6.168, and Group 4 was 9.723 ± 4.275. The difference between the mean marginal adaptation (μm) between four groups was statistically significant at P < 0.001 [Table 3].
Table 3: Comparison of mean marginal gap (μm) between four groups using one.way ANOVA test

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[Table 4] depicts the results of Tukey's multiple comparison post hoc test, which revealed that Group 1 exhibited significantly highest mean marginal gap when compared with Group 3 (P < 0.001) and Group 4 (P < 0.001), followed by Group 2 with significantly higher mean marginal gap when compared with Group 3 (P < 0.001) and Group 4 (P < 0.001). However, the mean marginal adaptation did not significantly differ between Group 1 and Group 2 (P = 0.196) and also between Group 3 and Group 4 (P = 0.230).
Table 4: Multiple comparisons of mean difference in marginal gap (μm) between four groups using Tukey's HSD post hoc analysis

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   Discussion Top


This study was conducted to evaluate and compare the fracture resistance and marginal adaptation of Zirconomer and Surefil SDR in nonendodontically and endodontically treated teeth. The results of the study revealed that Surefil SDR had significantly higher fracture resistance and lower marginal gap when compared with the Zirconomer; hence, the null hypothesis was rejected. In addition, there was no statistically significant difference observed between the nonendodontically and endodontic teeth for the same material.

Fracture of restorations is a significant concern in the success and longevity of clinical restorative dentistry. This fracture may be the culmination of crack propagation in the restoration that was initiated by a flaw that was not detected or managed. The fracture may also be a result of heavy masticatory loads.[21] In this study, the Surefill SDR exhibited significantly higher fracture resistance than the Zirconomer. However, there was no difference between the nonendodontically and the endodontically treated teeth for each material.

Sud et al. compared the fracture resistance of maxillary premolars with MOD cavities restored with Zirconomer, amalgam, composite, GIC, resin-modified GIC, and miracle mix. As in this study, the teeth restored with composite showed the highest fracture resistance when compared with Zirconomer.[20] Patil and Hambire conducted a study to examine the mechanical properties of Composite, Giomer, Ketac molar, and Zirconomer and reported Zirconomer to be the weakest.[22] Mohanty and Ramesh reported that the compressive strength of Zirconomer was significantly lesser than Surefil SDR and similar to that of dental amalgam.[23]

Marginal gaps are primarily due to the shrinkage that resin composites undergo during polymerization. The adverse effect of microleakage includes pulpal irritation, marginal discoloration, and secondary caries.[24] However, despite improvements in the formulation of new bonding agents with enhanced marginal adaptation and bond strengths, as well as clinical techniques designed to reduce the effects of shrinkage, a perfect marginal seal is still not achievable.

Patel et al. evaluated and compared the sealing properties of amalgam, composite, and white amalgam (Zirconomer) and concluded that even though newer materials such as Zirconomer are being marketed aggressively, amalgam still proves to be one of the best restorative materials for posterior restoration. Despite being the more modern material, the Zirconomer had highest microleakage when compared with composite and amalgam.[25] Similar results have been reported by various other authors.[26],[27] In a study conducted by Prabhakar et al., it was observed that the marginal adaptation of Zirconomer was inferior compared with conventional GICs.[28] This could be attributed to the relatively larger size of the filler particles in Zirconomer which prevents proper adaptation of the restoration to the tooth surface.[19]

Zirconomer is a new class of glass ionomer restorative material that professes to combine the strength and longevity of amalgam with micromechanical bonding and fluoride release associated with GICs without the threats associated with the use of mercury. This is achieved by the addition of zirconia as a filler particle in the glass component of Zirconomer, thereby enhancing the mechanical properties of the material. It has been marketed as ideal for permanent posterior restorations in high caries-risk patients and cases where, previously, amalgam was the restorative material of choice.[19],[20],[25]

Despite the promises made by the manufacturers of Zirconomer, this study found that the mechanical properties, that is, fracture resistance and marginal adaptation, are inferior to that of Surefil SDR. Hence, it is advisable for the clinicians to understand the mechanical properties of Zirconomer before routinely recommending it for posterior restoration. Studies have shown that the addition of ceramic additives improves the mechanical properties, especially the compressive strength of the GIC.[29] Thus, future studies could investigate the effects of additives in improving other vital properties of the cement including fracture resistance and marginal adaptation.


   Conclusion Top


It can be concluded from this study that the fracture resistance and marginal adaptation of Zirconomer are significantly lower than Surefil SDR in both nonendodontically and endodontically treated teeth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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[PUBMED]  [Full text]  
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Gupta AA, Mulay S, Mahajan P, Raj AT. Assessing the effect of ceramic additives on the physical, rheological and mechanical properties of conventional glass ionomer luting cement – An in-vitro study. Heliyon 2019;5:e02094.  Back to cited text no. 29
    


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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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