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Table of Contents   
ORIGINAL ARTICLE  
Year : 2023  |  Volume : 26  |  Issue : 1  |  Page : 83-87
A comparative study on microleakage of two low shrinkage composite materials in Class II cavities: A stereomicroscopic analysis


Department of Conservative Dentistry and Endodontics, Bapuji Dental College and Hospital, Davangere, Karnataka, India

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Date of Submission05-Aug-2022
Date of Decision11-Sep-2022
Date of Acceptance03-Oct-2022
Date of Web Publication08-Dec-2022
 

   Abstract 

Aim: To compare the microleakage of Filtek bulk fill posterior and Beautifil II LS composites in Class II cavities using stereomicroscope.
Materials and Methods: A total of 34 extracted teeth were randomly divided into two groups. Teeth were prepared and mounted on a plaster block. In each tooth, Class II cavities were prepared, following which the cavities were etched and bonded. In Group I, 17 teeth were restored with Filtek bulk fill posterior composite in bulk fill technique and in Group II, 17 teeth were restored with Beautifil II LS following manufacture's instructions. The samples were then thermocycled and then the tooth were immersed in 1% methylene blue for 24 h and were divided into two halves mesiodistally using a diamond disc at low speed. Then, all the sections were observed under a stereomicroscope at ×10 magnification.
Results: Mann–Whitney U-test displayed a statistically significant higher mean rank among Filtek bulk fill group (mean rank = 23.09) when compared to Beautifil II LS composite group (mean rank = 11.91).
Conclusion: The study concluded that in Class II restorations, Beautifil II LS showed significantly less microleakage than Filtek bulk fill posterior.

Keywords: Beautifil II LS; Filtek bulk fill posterior; microleakage; stereomicroscope

How to cite this article:
Jacob G, Goud K M. A comparative study on microleakage of two low shrinkage composite materials in Class II cavities: A stereomicroscopic analysis. J Conserv Dent 2023;26:83-7

How to cite this URL:
Jacob G, Goud K M. A comparative study on microleakage of two low shrinkage composite materials in Class II cavities: A stereomicroscopic analysis. J Conserv Dent [serial online] 2023 [cited 2023 Feb 6];26:83-7. Available from: https://www.jcd.org.in/text.asp?2023/26/1/83/362922

   Introduction Top


A healthy mouth is essential for a sustainable quality of life. There have been more changes and developments in dentistry over the past decade than in the previous 100 years, and the pace is accelerating. In the era of using minimally invasive procedures rather than using extension for prevention as a treatment guideline, emphasis is now placed on restriction with conviction.[1]

Currently, with the advent of adhesive dentistry and increased demand for esthetic restorations, composite resins are the most widely used direct restorative materials for restoration of dental cavities, coronal fractures, tooth wear, and congenital defects of teeth.[2] In composite resins, despite good physical properties, polymerization shrinkage and its related stress remains the biggest challenge. Polymerization shrinkage causes microcracks in composite, debonding of material from cavity walls with subsequent gap formation, marginal microleakage, and postoperative sensitivity.[3]

Microleakage is defined as passage of bacteria, liquids, molecules, and ions through the cavity wall and restorative material, which is not clinically detectable.[2] It is considered as a major factor negatively influencing the longevity of restorations causing hypersensitivity, secondary caries, and pulpal injury. Thus, a uniform interface between restorative material and tooth is required to seal margins. Obtaining such an interface is challenging in Class II restorations especially at gingival margins as they are at a higher risk of microleakage due to close location to gingival crevice.[4] Therefore, it is necessary to overcome the polymerization shrinkage and associated microleakage of composites to obtain marginal integrity and thereby to increase the longevity of restoration.

Various methods have been advocated to reduce the polymerization shrinkage and subsequent microleakage, such as the incremental placement technique, soft start polymerization, and application of stress absorbing intermediate layer.[5] On the contrary, recently certain changes have been made in the composite matrix such as addition of modified fillers and monomers to reduce polymerization shrinkage and to enhance its properties.[6]

Bulk fill type of composite resins has been introduced in the market with a view to simplify the procedure of introducing the material into cavity and its polymerization. It can be used as a dentin replacement beneath conventional resin composite or as a single filling material.[7] Bulk fill composites possess specific characteristics including enhanced followability to achieve consistent adaptation to cavity preparation. Improved depth of cure off at least 4 mm eliminates the need for layering.[6]

Filtek bulk fill posterior (3M ESPE) is a nanocomposite which contains two novel methacrylate monomers, namely aromatic urethane dimethacrylate (AUDMA) and addition fragmentation monomer (AFM) which in combination act to reduce polymerization stress and associated shrinkage.[8] AUDMA is a high-molecular-weight monomer which decreases the number of reactive groups in the resin, thereby reducing the volumetric shrinkage. AFM is the second unique monomer which contains a third reactive site that cleaves through a fragmentation process during polymerization. This process provides a mechanism for the relaxation of the developing network and subsequent stress relief.[8]

Beautifil II LS (SHOFU) is a recently introduced bioactive universal hybrid composite which through the addition of a new steric repulsion structure (SRS) monomer and SPR-G technology is formulated to reduce polymerization shrinkage and microleakage. The manufacturers claim low volumetric shrinkage of 0.85% for these composites compared to 2%–5% for conventional composites.[9]

Till now, there are no studies which compared the microleakage between Filtek bulk fill posterior and Beautifil II LS composites in Class II cavities.

Thus, the aim of the study is to evaluate and compare the microleakage between Filtek bulk fill posterior and Beautifil II LS composites in Class II cavities using stereomicroscope.


   Materials and Methods Top


The present in vitro study was carried out in the Department of Conservative Dentistry and Endoodntics, Bapuji Dental College and Hospital, under the following reference no. BDC Exam/548/2021-22. It was performed on Intact noncarious freshly extracted human maxillary premolars (extracted for orthodontic or periodontal reasons) without caries, cracks, fractures, and attrition.

Methodology

  • For the proposed study, 34 extracted noncarious permanent human maxillary premolars fulfilling the absolute inclusion and exclusion criteria was used as samples
  • After cleaning debris and residual tissue tags, the specimens were stored in 0.1% thymol until use for disinfection[10]
  • Each specimen was mounted with adjacent tooth in plaster blocks.[2] In each tooth, standardized Class II proximal box cavities of depth – 4 mm, buccolingual length – 3 mm, and width of gingival floor from enamel – 1.5 mm was prepared using no. 835-014, flat-end cylinder diamond points under water and air cooling conditions. A new diamond point was utilized for every five cavities.[8] The dimensions of the cavities were measured using William's graduated periodontal probe. Matrix application was done by using tofflemire matrices and wedges[2],[9]
  • All the prepared cavity surfaces were dried with oil-free compressed air. The cavities were etched with 37% phosphoric acid etching gel. The phosphoric acid etchant was applied to the enamel first, and then to the dentin for 15 s, rinsed with water for 15 s, and dried without overdrying.[10] Adper single bond 2, bonding agent was applied to the etched surface and gently dried and cured following manufacturer's instructions.[2],[9] Teeth were then randomly divided into two groups of (20) each
  • Group 1: Teeth restored with Filtek bulk fill posterior
  • Group 2: Teeth restored with Beautifil II LS
  • In Group 1, specimens were restored with Filtek bulk fill posterior in an increment of 4 mm and in Group 2, samples were restored with Beautifil II LS in increments of 2 mm and cured following manufacturer's recommendations using Bluedent LED curing light with an output of 800–1200 Mw/cm2. After restoration, all margins of the restoration were finished with Sof Lex discs
  • The specimens were stored at 100% relative humidity at 37°C for 24 h and submitted to 500 thermocycles at 5°C and 55°C with a dwell time of 30 s at each temperature.[2] In the following step, samples were covered with two layers of nail varnish on all tooth surfaces except the resin composite restoration and 1 mm area around it.[2],[8] The specimens were then immersed in 1% methylene blue solution for 24 h at 37°C[10]
  • After dye exposure, the teeth were rinsed thoroughly under running water and then bisected longitudinally in mesiodistal direction parallel to the long axis of teeth[8],[10]
  • The samples were examined under a stereomicroscope with ×20 magnification.[8],[10] Cervical microleakage scoring was done by following the ISO score system (ISO/TS 11405: 2003) as follows[10]
  • Score 0 = No dye penetration
  • Score 1 = Dye penetration into ½ of the cervical floor
  • Score 2 = Dye penetration more than ½ of the gingival floor without reaching the axial wall
  • Score 3 = Dye penetration into cervical and axial wall.


Statistical analysis

The data obtained from the samples were subjected to statistical analysis using the SPSS software (SPSS Software Version 28). The Mann–Whitney U-test was used to compare significant differences between two independent groups when the dependent variable is either ordinal or continuous, but not normally distributed. Data on micro-leakage were represented in ordinal scores in this study.


   Results Top


Mann–Whitney U-test displayed a statistically significant higher mean rank among Filtek bulk fill composite group (mean rank = 23.09) when compared to Beautifil II LS composite group (mean rank = 11.91) [Table 1] and [Figure 1]. This indicates that the Filtek bulk fill composite group shows higher micro-leakage than Beautifil II LS composite group. The stereomicroscopic images of both the groups are depicted in [Figure 2] and [Figure 3].
Table 1: Comparison of level of micro-leakage between Filtek bulk fill and Beautifil II LS composites

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Figure 1: Comparison of Level of microleakage between Filtek Bulk Fill and Beautifil II LS composites

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Figure 2: Stereomicroscopic images of Group 1 – Filtek Bulk fill

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Figure 3: Stereomicroscopic images of Group 2 – BeautiFil II LS

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   Discussion Top


Marginal integrity is an important factor which determines the longevity of any restoration.[10] This integrity is compromised, when microleakage occurs resulting from polymerization shrinkage. Microleakage is defined as passage of bacteria, liquids, molecules, and ions through the cavity wall and restorative material, which is not clinically detectable. It may cause hypersensitivity, recurrent caries, and pulpal pathoses. Besides pulpal irritation and secondary caries, microleakage also results in marginal discoloration.[11]

Despite having good physical and mechanical properties, the major shortcoming of resin composites are polymerization shrinkage and associated stress and is the most common cause for failure of direct composite restorations. Polymerization shrinkage is dependent on several factors such as boundary conditions, the material's formulation (filler content, monomeric chemistry, monomeric structure, filler/matrix interactions, additives, etc.), amount of material in the polymerization reaction, the tooth and restoration geometry, the placement technique, and the curing protocol.[6],[11]

Several methods are proposed in the literature to reduce the polymerization shrinkage. From the material aspect, this includes increasing the filler content, modification of polymer matrix by using ring opening silorane molecules, and addition of new monomers. Other methods include the incremental layering technique, soft start polymerization, use of stress absorbing layer with low elastic modulus liners, and preheating of composites.[5],[12]

In the present study, microleakage was assessed in Class II cavities, as obtaining a uniform interface between restorative material and tooth which is required to seal margins is challenging in Class II cavities especially at gingival margins as they are at a higher risk of microleakage due to close location to gingival crevice.[4] In order to standardize the type of sample, only maxillary premolars were used in the study. As the magnitude of polymerization shrinkage depends on configuration C factor, in the present study, all the cavities prepared were of same dimension, i.e., standardized Class II proximal box cavities of depth –4 mm, buccolingual length –3 mm, and width of gingival floor from enamel –1.5 mm. To ensure standardization, all cavities were prepared by the same operator and the dimensions were checked during and after cavity preparation using a periodontal probe. In order to obtain proximal contact and contour, tofflemire matrix and wedges were used.[6]

Another factor which determines the polymerization shrinkage is the distance between resin surface and light curing tip. Therefore, for achieving optimal degree of conversion, the light curing tip was positioned at 1 mm and at 90° from the composite surface and to achieve standardization, the light curing mode was same for all specimens.[6],[13]

One of the techniques employed to reduce polymerization shrinkage is the incremental placement technique, where composites are placed and cured in 2-mm increments.[5] Recently, bulk fill composites were introduced which can be placed and cured as a single increment of 4–5 mm.[8] Bulk fill composites have higher filler content and thus have increased mechanical properties. Due to an enhanced translucency and incorporation of a photoactive group in the methacrylate resin, polymerization kinetics are claimed to be better controlled.[14] However, there is inconclusive evidence in the literature regarding the microleakage between incremental and bulk fill placement techniques.

Materials selected for the study were Filtek bulk fill posterior which is cured in 4-mm increment and Beautifil II LS, a low-shrinkage composite cured in two 2-mm increments following the manufacturer's recommendations.

In the present study, after restoration, all the specimens were subjected to thermocycling. Thermocycling process has been introduced as an artificial aging methodology and to simulate the oral conditions, thereby evaluating the influence of thermal stresses on the bond strength of dental materials.[15],[16]

In the present study, microleakage test was carried out using dye penetration with 1% methylene blue as it is a simple, inexpensive method and methylene blue provides easy visualization of prepared cavity in digital images and excellent contrast with the surrounding environment.[17],[18] The extent of microleakage was assessed using a stereomicroscope as it is a simple and effective method which enables observers to view objects in three dimensions while offering live observation of samples in monitors and provides exceptional range of options regarding resolution and magnification and enhanced visibility from illumination options.[2],[3],[18]

In the present study, microleakage was seen in both the groups; however, microleakage values were higher in filtek bulk fill group compared to those of Beautifil II LS, and this difference was statistically significant. This is in accordance with the previous studies done by Alqudaihi et al. and Al-Gailani et al.[19],[20] The lowest microleakage observed with Beautifil II LS composites can be explained by the addition of a novel SRS molecule which is designed to minimize polymerization shrinkage through molecular steric repulsion resulting in a sturdy and stable restoration microstructure. The balance of the multi-filler phase and innovative SRS monomer also creates a none stick, moderately firm, sculptable paste that is easy to adapt, without any slump, which may reduce the handling-associated problems. Also, the bioactive S-PRG fillers incorporated in giomer exhibit acid-neutralizing ability to maintain an acid-neutral and fluoride-rich environment, as claimed by the manufacturer and these might be the reasons for this result.[20]


   Conclusion Top


Within the limitations of this in vitro study and based on the results, it can be concluded that the low-shrinkage Beautifil II LS composites had significantly lower microleakage compared to Filtek bulk fill posterior in Class II cavities; therefore, it can be successfully used with increased longevity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Correspondence Address:
Dr. Gifty Jacob
Department of Conservative Dentistry and Endodontics, Bapuji Dental College and Hospital, Davangere, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcd.jcd_444_22

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