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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 15  |  Issue : 1  |  Page : 1-6

Marginal fit of class II cavities restored with bulk-fill composites


Department of Conservative Dentistry, Faculty of Dentistry, Tanta University, Tanta, Egypt

Date of Submission08-Mar-2017
Date of Acceptance03-May-2017
Date of Web Publication4-Apr-2018

Correspondence Address:
Hend A Ibrahim
Department of Conservative Dentistry, Faculty of Dentistry, Tanta University, Tanta
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tdj.tdj_12_17

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  Abstract 

Purpose
To evaluate the marginal integrity of three types of bulk-fill composite resins in class II cavities.
Materials and methods
Simple class II cavities with parallel walls were prepared in 40 extracted human sound molars were selected. The overall dimensions and depth of the cavities were standardized as follow: 4 mm length occlusocervically, 4 mm width buccolingually and 2 mm depth axially. The teeth were randomly divided into four groups (n = 10 each): group 1: Tetric N-Bond Universal and Tetric EvoCeram Bulk Fill composite; group 2: Single Bond Universal and Filtek Bulk Fill posterior composite; group 3: Futurabond U and Admira Fusion X-Tra; group 4: Tetric N-Bond Universal and Tetric EvoCeram composite. All samples were thermocycled for 600 cycles. Impressions of the teeth were made using a polyvinyl siloxane then poured with epoxy resin. These replicas gold sputtered and examined under scanning electron microscopy.
Results
Group 3 recorded the lowest mean marginal gap length value, while group 4 recorded the highest mean marginal gap length value. One-way analysis of variance was used to compare the tested groups at a level of significance (P ≤ 0.001). For width of proximal gap the lowest mean marginal gap length value found in group 3, while the highest mean value of gap width proximally found in group 1. In width of cervical gap the lowest mean marginal gap length value was found in group 3, while the highest mean value of gap width cervically found in group 4. One-way analysis of variance test was used to compare the tested groups at a level of significance (P ≤ 0.05).
Conclusion
Admira Fusion X-Tra has good results compared to other used bulk fill and conventional composites.

Keywords: bulk-fill composites, marginal integrity, scanning electron microscope, thermocycling


How to cite this article:
Ibrahim HA, Shalaby ME, Abdalla AI. Marginal fit of class II cavities restored with bulk-fill composites. Tanta Dent J 2018;15:1-6

How to cite this URL:
Ibrahim HA, Shalaby ME, Abdalla AI. Marginal fit of class II cavities restored with bulk-fill composites. Tanta Dent J [serial online] 2018 [cited 2018 Aug 18];15:1-6. Available from: http://www.tmj.eg.net/text.asp?2018/15/1/1/229242


  Introduction Top


Today, composite resins are considered materials of choice in restorative dentistry because of the increasing demand for high-quality aesthetic results in every day practice. Despite the continuous evolution of these resins, problems such as polymerization shrinkage and marginal microleakage still occur [1]. Furthermore, with high-viscosity composite resin; it is difficult to obtain perfect adaptation to internal cavity surface and proper marginal seal of the cavity [2].

The polymerization shrinkage and its associated stresses still remain major drawback of dental composite. During polymerization the distance between groups of atoms/molecules decreases with resultant volume change that is known as shrinkage. The polymerization of resin-based composites generates stresses due to their contraction during the process. Shrinkage stresses occur when contraction is obstructed and the material is rigid enough to resist sufficient plastic flow to compensate for the original volume [3].

Polymerization shrinkage causes stresses at the interface between tooth and restoration as the elastic modulus of the composite increases during curing. This stress manifested as bond failure, cuspal flexure, enamel microcracking, microleakage and its sequences which lead to restoration failure [4].

Restoration placement techniques are major factor in the modification of shrinkage stresses. To avoid the clinical consequences of polymerization shrinkage, incremental filling techniques are preferred over the bulk filling method to obtain effective marginal seal by reducing the stresses developed within the tooth–restoration system [5],[6].

Resin composites have undergone continuous development through years as regards their various components, for example, the filler and the initiator, the so called 'bulk-fill composites' [7]. These materials are suitable for insertion in a 4-mm bulk placement due to their reduced polymerization stress and their high reactivity to light curing [8]. Recently, many products have been marketed as low-shrinkage stresses materials that have modified initiation systems, potentially allowing placement of these materials in one layer (bulk-fill) of up to 4 mm in thickness with adequate polymerization and short activation times. Also these materials are indicated for use as flowable base materials to be veneered with 2 mm of posterior hybrid composite or as a final filling that does not require veneering [8],[9].

The aim of the present study is to evaluate the marginal integrity of three types of bulk-fill composite resins in class II cavities. Marginal adaptation was assessed with observation of epoxy replicas under SEM, before and after thermomechanical loading. The null hypothesis tested was that there would be differences in marginal adaptation in cavities restored with conventional and different bulk-fill composites.


  Materials and Methods Top


Forty extracted human sound molars of an age ranging between 25 and 50 years were used in this study. These teeth were obtained from Oral Surgery Department in Tanta University. All patients are informed about the purpose of the study and using of their extracted teeth according to Ethics Committee of Faculty of Dentistry, Tanta University. The teeth were stored in 0.1% thymol solution [10] and were used within 1 month after extraction.

The teeth were fixed with sticky wax to the base of plastic cylinder. The cylinder was filled with self-curing acrylic resin so that only root was embedded within the self-curing acrylic resin. Simple class II cavities with parallel walls were prepared. The cavities were prepared using coarse diamond stone (size 10; OKO Dent, Tautenhain, Germany) with water spray and finished with fine-grained burs or stone. The cervical margin was established 1.5 mm above the cement–enamel junction. The overall dimensions and depth of the cavities were standardized as follow: 4 mm length occlusocervically, 4 mm width buccolingually and 2 mm depth axially. The cavity depth and length were judged with a permanent mark on the diamond stone and then verified using a periodontal probe.

The teeth were randomly divided into four groups: three experimental groups corresponding to the different bulk fill composites and a control group in which conventional composite was used (n = 10 each). The prepared cavities were treated with its corresponding adhesives and composites according to manufacturer's instructions as follow: group 1: Tetric N-Bond Universal and Tetric EvoCeram Bulk Fill composite (Ivoclar Vivadent AG, Schaan, Liechtenstein); group 2: Single Bond Universal and Filtek Bulk Fill posterior composite (3M ESPE, Maplewood, Minnesota, USA); group 3: Futurabond U and Admira Fusion X-Tra (VOCO GmbH, Cuxhaven, Germany); group 4: Tetric N-Bond Universal and Tetric EvoCeram composite (Ivoclar Vivadent AG) as control group.

Metallic matrix retainer and band used to restore the missing wall of the tooth. After composite placement, restorations were finished and polished with flexible disks (3M ESPE) and then all teeth were kept in water for 24 h. Ten samples in each group were thermocycled in a thermocycling apparatus (custom made apparatus at Conservative Dentistry Department, Faculty of Dentistry, Alexandria University) (by alternating immersion in water bath at 5–50°C with a dwell time of 2 min) for 600 thermal cycles.

Impressions of the teeth were made using a polyvinyl siloxane material (light body). The impressions were then poured with epoxy resin (Chemical Industries for Construction, Egypt). Then, gold sputtered to render the surface electrically conductive. These replicas were examined under SEM (JSM-5300 Scanning Microscope; JEOL, Peabody, Massachusetts, USA) at 30 kV power with different magnifications (×50, ×2000) to study restoration–tooth interface. Degree of marginal gap was determined as the ratio of the length of gaps to the total length of the margins for proximal and cervical margins, and then converted to a percentage and also width of gap. A statistical evaluation was performed using statistical package for the social sciences (SPSS, version 23; SPSS Inc., Chicago, Illinois, USA) with one-way analysis of variance and Tukey's test.


  Results Top


Length of marginal gap

The mean ± SD marginal gap length values (mm) of the data collected from all tested groups were tabulated in [Table 1]. It was found that the highest mean value of open margin was recorded for Tetric EvoCeram group, while the lowest mean marginal gap length value was recorded for Admira Fusion X-Tra group. Tukey's test was performed to find out which group is responsible for the recorded difference and found that the responsibility fall on Admira Fusion X-Tra group since a high statistical significant difference was recorded between group 3 (Admira Fusion X-Tra) and other groups (groups 1, 2, 4).
Table 1: Mean marginal gap length values in proximal cavity of the four tested groups

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The percentage of marginal gap in the different tested groups in all the samples was shown in [Table 2]. It was found that, the highest percent of open margin was recorded for Tetric EvoCeram group, while the lowest mean marginal gap length value was recorded for Admira Fusion X-Tra group. Representative SEM micrographs are shown in [Figure 1] and [Figure 2].
Table 2: Percentage of marginal gap in overall restorations in four tested groups

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Figure 1: SEM image of a restoration in (group 3) Admira Fusion X-Tra with no marginal gap formation in one proximal wall and cervical wall "white arrow" and marginal gap formation in other proximal wall "yellow arrow" (Mag. x50).

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Figure 2: SEM image of a restoration in (group 4) Tetric Evo Ceram with marginal gap formation in proximal and cervical walls "yellow arrow" (Mag. x50).

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Gap width

Width of proximal gap

The mean ± SD values of marginal gap width (μm) of the data collected from all tested groups were tabulated in [Table 3]. It was found that, the highest mean value of gap width proximally was recorded for Tetric EvoCeram Bulk Fill group, while the lowest mean marginal gap length value was recorded for Admira Fusion X-Tra group. Tukey's test found that a statistical significant difference was recorded between Admira Fusion X-Tra group and Tertic EvoCeram Bulk Fill group. Representative SEM micrographs are shown in [Figure 3] and [Figure 4].
Table 3: Mean values of width of proximal gap of the four tested groups

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Figure 3: SEM image of a restoration in (group 1) Tetric Evo Ceram Bulk Fill showing the width of the proximal gap (Mag. x2000).

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Figure 4: SEM image of a restoration in (group 3) Admira Fusion X-Tra showing the width of the proximal gap (Mag. x2000).

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Width of cervical gap

The mean ± SD values of marginal gap width (μm) of the data collected from all tested groups were tabulated in [Table 4]. It was found that, the highest mean value of gap width cervically was recorded for Tetric EvoCeram group, while the lowest mean marginal gap length value was recorded for Admira Fusion X-Tra group. Tukey's test found that Admira Fusion X-Tra group at par with Tetric EvoCeram group (P = 0.054), while there were no significant differences among the other tested groups. Representative SEM micrographs are shown in [Figure 5] and [Figure 6].
Table 4: Man values of width of cervical gap of the four tested groups

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Figure 5: SEM image of a restoration in (group 3) Admira Fusion X-Tra showing the width of the cervical gap (Mag. x2000).

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Figure 6: SEM image of a restoration in (group 4) Tetric Evo Ceram showing the width of the cervical gap (Mag. x2000).

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  Discussion Top


The materials tested in this study were chosen to represent a new category of bulk fill composites currently available on the market for restoring the teeth. The composition of these materials has been altered in various ways to allow for increased depth of curing while having less shrinkage and shrinkage stress than previous generations of composite materials [11].

Bulk-fill composites and the corresponding adhesive systems can be used to effectively seal cavity floors, which considerably help to prevent postoperative sensitivity in patients. Correctly used, bulk-fill composites will produce restoration margins that are just as tight as those of restorations placed with regular layering composites [12]. In a laboratory study on the marginal adaptation of class II restorations, the results of both low-viscosity and high-viscosity bulk-fill composites were comparable to those of conventional composites [10].

As mentioned before in the present in-vitro study, Admira Fusion X-Tra (group 3) exhibited satisfactory marginal adaptation and recorded statistically significant lowest value in both marginal gaps length and width (proximally and cervically) along the composite/enamel interface. Admira Fusion X-Tra is a purely Ormocer-based material. Due to introducing Ormocers as dental materials was their reduced polymerization shrinkage and wear when compared to regular red blood cells (RBCs) as well as in the very similar coefficient of thermal expansion compared to the natural tooth structure [13]. The used adhesive with group 3 Futurabond U which contains the highly functionalized SiO2 nanoparticles (Ø=20 nm) in Futurabond U facilitate a cross-link of the resin components and enhance its film-building properties. Nanoparticles reinforce the hybrid layer for long lasting high bond strength. This ensures a superior marginal integrity and protection against sensitivities.

This result was explained and agreed with Abdalla [14] who have evaluated whether the layer thickness of Admira Fusion X-Tra (4 mm, 2 mm) affects the quality of the restorations after 6 months in clinical study. He found in his explanation, after 6 months, no significant differences were observed between the two different restorative techniques. He concluded that Admira Fusion X-Tra can be applied in layers of up to 4 mm in the posterior region. Thanks to the low polymerization shrinkage of just 1.25% by volume and the very low-shrinkage stress of 3.9 MPa, the material is ideally suited to use in the bulk-fill technique.

There were no significant differences among other groups 1, 2, 4 (Tetric EvoCeram Bulk Fill, Filtek Bulk Fill and Tetric EvoCeram) in both marginal gaps length and width (proximally and cervically) along the composite/enamel interface. This came in agreement with Campos et al. [10] reported that applying simple layering techniques, bulk-fill materials do not allow better marginal adaptation than a standard composite. Also these results agree with Heintze et al. [15] who evaluate the marginal quality of composite resin restorations (Tetric EvoCeram) placed in extracted molars either in bulk (4 mm) or three increments. They found that there was no statistically significant difference between the resin restorations placed in bulk and those placed in three increments.

The findings in our study agree with Colak et al. [16] who found that Tetric EvoCeram (TBF) and Tetric EvoCeram Bulk-Fill systems exhibited statistically similar shear bond strength values. This may be because they exhibit very similar mechanical properties and consistency. On the other hand, Orłowski et al. [17] disagreed with our result who stated statistically significant better marginal integrity of flowable tested materials, SDR, SonicFill, and Filtek Bulk Fill (compared to the composite Tetric EvoCeram Bulk Fill), may be due to their flow consistency during application.

For the width of cervical gap, it found that group 3 (Admira Fusion X-Tra) at par with group 4 (Tetric EvoCeram), while there were no significant differences among the other tested groups. This result agrees with Al-Harbi et al. [18] who reported that Bulk-fill composites provide similar marginal performance to open-sandwich and incremental composites. Agarwal et al. [19] agree with our result who found that no significant differences in marginal and internal adaptation at the cervical tooth–restoration interface in cavities restored using either the bulk fill or the incremental fill technique.

Several in-vitro studies confirmed that bulk-fill RBCs may be applied in increments up to 4 mm thickness when adequate cured. Besides, an acceptable marginal adaptation is reported, which is similar to that of standard RBCs. In a similar vein, Furness et al. [20] tested a comparable proportion of gap-free tooth–restoration interfaces in either bulk-fill or conventional RBCs restorations. In contrast to these findings, identified Benetti et al. [21] some bulk-fill restoratives to produced larger gaps at the dentin margin of class II cavities, when compared to regular RBCs restorations.


  Conclusion Top


  • The use of bulk fill composites could decrease the marginal gap formation improving the continuity between the tooth structure and the restorative materials providing a more stable interface between tooth and these advanced restorative biomaterials
  • Admira Fusion X-Tra have good results compared to other used bulk fill and conventional composites.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Heintze SD, Monreal D, Peschke A. Marginal Quality of class II composite restorations placed in bulk compared to an incremental technique: evaluation with SEM and stereomicroscope. J Adhes Dent 2015; 17:147–154.  Back to cited text no. 15
    
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[PUBMED]  [Full text]  
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    Figures

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

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



 

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