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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 14  |  Issue : 4  |  Page : 216-219

Fracture resistance of premolars teeth restored by silorane, nanohybrid and two types of fiber-reinforced composite: an in-vitro study


Department of Operative Dentistry, Faculty of Dentistry, Al Azhar University, Cairo, Egypt

Date of Submission16-Sep-2017
Date of Acceptance15-Nov-2017
Date of Web Publication21-Dec-2017

Correspondence Address:
Mostafa S Mohamed Ata
Department of Operative Dentistry, Faculty of Dentistry, Al Azhar University, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tdj.tdj_46_17

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  Abstract 

Objective
The objective was to evaluate and compare the fracture resistance of human maxillary premolars teeth restored with low shrinkage microhybrid composite Silorane-based; Filtek P90 LS, conventional methacrylate-based nanohybrid composite; Ceram X Mono, and two types of fiber-reinforced composites (FRCs); Alert and XENIUS base, micro glass fibers and short glass fibers, respectively in mesio-occluso-distal cavities.
Materials and methods
A total of 45 human maxillary premolars were selected. Standardized mesio-occluso-distal cavities were prepared in all teeth. Five prepared teeth received no treatment and served as controls (group 1). A total of 40 teeth were randomly divided into four experimental groups (n = 10); group 2: low shrinkage Silorane-based composite, group 3: nanohybrid resin composite, group 4: microfibers reinforced resin composite, and group 5: short fibers reinforced resin composite. Restorations were done for all groups. After being stored 24 h at 37°C, fracture resistance was measured in a universal Instron testing machine by using a 4 mm diameter steel sphere which was applied on tooth buccal and lingual cusps at a cross-head speed of 2 mm/min until fracture occurred.
Statistical analysis
One-way analysis of variance and Tukey's post-hoc test.
Results
Highest mean fracture resistance was observed with FRC, nanohybrid, Silorane and lastly with control respectively. Statistically Significant difference was revealed by analysis of variance (P ≤ 0.0001) and Tukey's post-hoc test (P ≤ 0.0001).
Conclusion
Among the experimental groups, FRC showed the highest fracture resistance.

Keywords: fiber composite, fracture resistance, silorane


How to cite this article:
Mohamed Ata MS. Fracture resistance of premolars teeth restored by silorane, nanohybrid and two types of fiber-reinforced composite: an in-vitro study. Tanta Dent J 2017;14:216-9

How to cite this URL:
Mohamed Ata MS. Fracture resistance of premolars teeth restored by silorane, nanohybrid and two types of fiber-reinforced composite: an in-vitro study. Tanta Dent J [serial online] 2017 [cited 2018 May 24];14:216-9. Available from: http://www.tmj.eg.net/text.asp?2017/14/4/216/221382


  Introduction Top


Following the preparation of wide mesio-occluso-distal (MOD) cavities, there is a decrease in the fracture resistance of the teeth. An ideal restoration for a tooth is able to maintain the esthetics, function, preserve the remaining tooth structure, and prevent the microleakage. There would be situations where both marginal ridges are involved in caries and cannot be restored with amalgam restoration as tooth need to be reinforced using resin composite. To preserve the remaining tooth structure, a material with high strength and acceptable clinical performance desirable. The introduction of composites and dentinal adhesives has been a significant contribution to the fracture resistance of teeth because it can reinforce the dental structure as a result of bonding to the tooth [1]. A restored tooth tends to transfer stresses differently than an intact tooth. Moreover, adhesive restorations better transmit and distribute functional stresses across the bonding interface and have the potential to reinforce weakened tooth structure [2]. Polymerization of composites can cause deformation on the surrounded tooth structure resulting in microcracks which predispose the tooth to fracture [3]. In contrast to incremental technique, if the preparation is bulk-filled with a single composite increment, the resulting high C-factor can further increase shrinkage stress. Fracture resistance is one of the most important characteristics of dental materials. It depends on material resistance to crack propagation from its internal defects [4]. These cracks can result in microscopic fractures of the restoration margins or bulk fracture of the filling. Reinforcing with short fibers has been revealed to control the polymerization shrinkage stress and microleakage compared with conventional composite resins [5]. Placement of fiber-reinforced resin composite in MOD wide cavities is a more promising technique than the older ones.


  Materials and Methods Top


Materials

The extracted teeth used in this research were obtained from the human tooth bank of the Faculty of Dental Medicin, Al- Azahr Univerisity with the requiremints of the local ethical committee. All patients were informed about using their extracted teeth in this study and signed.

  • Filtek P90 LS: low shrinkage silorane-based microhybrid composite (3M ESPE St. Paul, Min, USA)
  • Ceram X Mono: methacrylate-based nanohybrid composite (Dentsply Caulk, Milford, DE, USA)
  • Alert: microfiber reinforced composite (FRC), (Jeneric / Pentron, Wallingford, CT, USA)
  • XENIUS base: short FRC (Stick Tech Ltd, Turku, Finland).


Methods

Cavity preparation

In this in-vitro study, 45 recently extracted intact maxillary premolars, without caries, restoration, cracks, and fracture were collected and placed in 10% formalin solution for disinfection (24 h before use). For all specimens, class II MOD cavities were prepared in all the specimens using an airotor handpiece with a long straight fissure diamond point in order to obtain a uniform smear layer. Dimensions of the MOD cavities were standardized using standard diameter size of fissure diamond point and graduated periodontal probe so preparing cavities with a 2 ± 0.2 mm pulpal depth, 1.5 ± 0.2 mm gingival width, 2 ± 0.2 mm axial height, parallel proximal walls with 3 ± 0.2 mm buccolingual width and occlusal isthmus width one-third of the intercuspal distance. Dimensions of the cavity were measured with the help of Vernier digital calipers.

For better harmony among the cavities, a single periodontal probe was used as a guide, and no bevel was performed except for the axiopulpal line-angles. A bur was used to cut four teeth. All the cavities were prepared by a single operator.

Restoration procedure

Following cavity preparation, each tooth was placed in acrylic mold for proper handling then all teeth were stored in distilled water for 24 h before use. Five prepared teeth received no treatment and served as controls. A total of 40 teeth were randomly divided into four groups with 10 teeth each and restored according to manufacturer's instructions.

A Tofflemire Matrix band Retainer was tightened around the tooth and held by finger pressure against the gingival margin of the cavity, so that the preparation could not be overfilled at the gingival margin. This also allowed the light to be directed only in the apical direction while curing the composite.

For group 2 (low shrinkage group), teeth were matriced as mentioned above and all the teeth were self-etched with Filtek P90 LS Adhesive Primer, which was applied in thin layer and light cured for 10 s using the light-emitting diode light curing unit. Next, Filtek P90 LS adhesive bonding agent was applied and gently air dried. A second layer was applied, gently air dried and light cured for 10 s, light curing was done with Optilux 500 with a light intensity of 500 mW/cm 2. Filtek P90 LS (A3 Shade) composite was then placed in increments of 2 mm, which was judged with the William's graduated periodontal probe. Each increment was light cured for 40 s.

For groups 3, 4, and 5 teeth were matriced as mentioned above and all the teeth were total-etched with 37% phosphoric acid etching gel for 15 s and the etchant was rinsed off with water for 5 s and then air dried for 2 s. A layer of Adper Single Bond bonding agent was applied onto the cavity surface, gently air dried, and light cured for 20 s. A second layer was then applied, gently air dried, and light cured for 20 s. The teeth were then restored with conventional nanohybrid composite (group 3), Alert (group 4), and Xenius base (group 5) using incremental layering technique. After removal of the matrix, all the restorations were light cured from mesial and distal aspect for 40 s, and finishing and polishing of the restorations were done.

The specimens were stored in 37°C distilled water. A compressive force at a strain rate of 2 mm/min was applied using universal Instron testing machine by a 4 mm diameter steel sphere, which was parallel to the long axis of the teeth and centered over the teeth until it just contacted the occlusal surface of the restoration. Forces necessary to fracture each tooth were measured in Newton (N). The data obtained were tabulated and subjected to statistical analysis as shown in [Table 1].
Table 1: Fracture resistance (mean±SD) of control group, silorane, nanohybrid, microfiber, and short fiber-reinforced resin composite

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  Results Top


Highest mean fracture resistance was observed with FRC, nanohybrid, silorane, and lastly with control respectively (as shown in [Table 1]). One-way analysis of variance test revealed statistically significant difference (P < 0.0001) between all the groups. Intergroup multiple comparisons were done by Tukey's post-hoc test which also revealed statistically significant difference (P < 0.0001) between all the groups.


  Discussion Top


The objective of this study was to evaluate the fracture resistance of teeth restored with low shrinkage silorane-based composite resin, conventional nanohybrid composite, and newer FRC resin in maxillary premolars. Maxillary premolars were chosen as they are more prone to fracture due the anatomical shape with steep cuspal inclines, leads to cuspal separation during mastication and greater incidence of fracture than mandibular premolars. MOD cavities were prepared in the teeth as these are considered to be the worst in terms of fracture resistance.

Recently, short FRC (XENIUS) base was introduced as a restorative composite resin. It is intended to be used as filling material in high stress-bearing areas especially in large cavities of vital and nonvital posterior teeth. It consists of a combination of a resin matrix, randomly oriented E-glass fibers, and inorganic particulate fillers. The resin matrix contains bis-GMA, TEGDMA, and PMMA forming a matrix called semi-Interpenetrating Polymer Network (semi-IPN) (net-polymethyl methacrylate)-inter-net-poly (bis-glycidyl-A-dimethacrylate) which provides good bonding properties and improves toughness of the polymer matrix.

Results of this study showed statistical significance and higher fracture resistance was exhibited by FRC (group 4 and group 5). The E-glass fibers present in the material prevent the crack propagation that often starts from the surface of the restoration due to repetitive cyclic fatigue, in contrast to conventional composites and prevent the crack to go below the gingival margin [6]. Nanohybrid composite showed higher fracture resistance than silorane composite.

Luthria et al. [7] have shown that reinforcement of fibers imparts strength and toughness to composite resins. Glass fibers are known to be resistant to tension and are able to stop the propagation of fractures in the composite mass and also keep the buccal and lingual cusps together through splinting mechanism, recovering the fracture resistance due to their high tensile strength, density, and percentage of elongation allowing them to withstand high stresses without fracturing.

Results of this study were in agreement with the study by Kolbeck et al. [8], who reported that, glass fibers performed better than polyethylene fibers due to pre-impregnation with light cured composite which ensures a good bond with the composite resin. In addition, glass fibers have very high tensile strength, density, and percentage of elongation allowing them to withstand high stresses without fracturing [2]. These findings also were in agreement with a study by Soares et al.[9], which showed that fracture toughness of polymer-based materials was improved when they were reinforced with glass FRC.

Soares et al. [9] found a positive correlation between filler loading and mechanical performance. They reported that the threshold of filler loading for the highest fracture toughness values in resin composites was 55% by volume. This percent of filler loading is more important than weight percent. In their study, composite Venus bulk fill had the lowest filler loading that is 38% by volume showed better mechanical values than composite Filtek bulk fill in their study, which has filler loading of 42% by volume. Composite Tetric EvoCeram bulk fill, containing filler load of 60% by volume demonstrated the significantly lower fracture toughness and flexural strength values. In other words, their study demonstrated the absence of a direct relationship between volumetric content of inorganic particles and fracture resistance parameters (fracture toughness and flexural strength). Stress transfer from the polymer matrix to filler particles is one of the important factors effects on fracture resistance values. There may be difference in the adhesion between filler particles and matrix among these resin composites. Beside the filler system, monomer structures of the resin matrix also influence the mechanical properties.

A study of Garoushi et al. [10] showed how short fiber fillers could stop the crack propagation and provided increase in fracture resistance of composite resin. In order for a fiber to act as an effective reinforcement for polymers, stress transfer from the polymer matrix to the fibers is essential. This is achieved by having a fiber length equal to or greater than the critical fiber length. XENIUS base had fiber length between 1 and 2 mm, thus exceeding the critical fiber length. It is therefore not surprising that short fiber inclusion with semi-IPN resin matrix revealed substantial improvements in mechanical properties. On other hand, FRC, Alert had fiber length in micrometer scale (20–60 m) which explained the difference in fracture resistance values between the two materials. Reinforcing effect of the fiber fillers is based on stress transfer from polymer matrix to fibers but also behavior of individual fiber as a crack stopper [11]. Alert showed high values of mechanical parameters, which seems to be a result of high filler load level.

Silorane is a microhybrid composite with larger size and less percentage of filler particles as compared to that of nanohybrid group, which leads to early crack propagation and decreased fracture resistance. The low-shrinking Filtek P90 LS restorative is based on the new ring-opening silorane chemistry. The name 'silorane' derives from its chemical building blocks siloxanes and oxiranes. The combination of these two chemical building blocks provides the biocompatible, hydrophobic, and low-shrinking silorane-base of Filtek P90 LS Low Shrink posterior restorative. It polymerizes by cationic ring-opening polymerization. It consists of quartz-modified with silane layer and yttrium fluoride fillers of microhybrid type of 75 vol% [12],[13].

Nanohybrid composite resin (group 3) showed an acceptable fracture resistance. The high filler loading enables nanocomposites to demonstrate good physical and mechanical properties and reinforce the tooth structure well. Single bottle total etch system gave evidence of better bond strength than the newer self-etch systems. The presence of the adhesive layer under the restoration acts as a stress buffer [14],[15]. A study by Ausiello et al. [16], has shown that an optimal adhesive layer thickness leads to maximum stress release while preserving interface integrity. The acceptable fracture resistance of group 3 (nanohybrid composites) can be attributed to the increase in strain capacity of the adhesive resin and the improved physical and mechanical properties of nanocomposites [16].

Despite this result in fracture resistance, all the experimental groups' demonstrated results much higher than the average normal biting force of human maxillary premolars (100–300 N). Many differences exist between fractures occurring clinically and those induced by a machine. Forces generated intraorally during function vary in magnitude, speed of application, and direction, whereas the forces applied to the teeth in this study were at a constant direction and speed and they increased continuously until fracture occurred.


  Conclusion Top


  • Short glass FRC resin (XENIUS base) revealed improvements in fracture resistance values compared with the commercial restorative composites. This could suggest better performance of the new FRC in high stress-bearing application areas.
  • Further in-vivo studies should be done to test the reinforcement effect of fibers in clinical situations.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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De Freitas CR, Miranda MI, de Andrade MF, Flores VH, Vaz LG, Guimarães C. Resistance to maxillary premolar fractures after restoration of class II preparations with resin composite or ceromer. Quintessence Int 2002; 33:589–594.  Back to cited text no. 2
    
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El-Mowafy O, El-Badrawy W, Eltanty A, Abbasi K, Habib N. Gingival microleakage of class II resin composite restorations with fiber inserts. Oper Dent 2007; 32:298–305.  Back to cited text no. 4
    
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Luthria A, Srirekha A, Hegde J, Karale R, Tyagi S, Bhaskaran S. The reinforcement effect of polyethylene fibre and composite impregnated glass fibre on fracture resistance of endodontically treated teeth: an in vitro study. J Conserv Dent 2012; 15:372–376.  Back to cited text no. 7
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Kolbeck C, Rosentritt M, Lang R, Handel G. In vitro study of fracture strength and marginal adaptation of polyethylene-fibre-reinforced-composite versus glass-fibre-reinforced-composite fixed partial dentures. J Oral Rehabil 2002; 29:668–674.  Back to cited text no. 8
    
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Soares S, Queiroz E, Araújo T, Campos R, Araújo C, Soares C. Fracture resistance and stress distribution in endodontically treated maxillary premolars restored with composite resin. J Prosthodont 2008; 17:114–119.  Back to cited text no. 9
    
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Garoushi S, Tanner J, Vallittu PK, Lassila L. Preliminary clinical evaluation of short fiber-reinforced composite resin in posterior teeth: 12-months report. Open Dent J 2012; 6:41–45.  Back to cited text no. 10
    
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