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ORIGINAL ARTICLE
Year : 2019  |  Volume : 22  |  Issue : 6  |  Page : 782-789

The influence of restorative material and glass fiber posts on fracture strength of endodontically treated premolars after extensive structure loss


1 Department of Restorative Dentistry, Faculty of Dentistry, Hacettepe University, Altindag, Ankara, Turkey
2 Department of Endodontics, Faculty of Dentistry, Hacettepe University, Altindag, Ankara, Turkey

Date of Acceptance25-Feb-2019
Date of Web Publication12-Jun-2019

Correspondence Address:
Dr. F D Oz
Department of Restorative Dentistry, Faculty of Dentistry, Hacettepe University, Altindag - 06100, Ankara
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_11_19

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   Abstract 


Objective: The aim of this in vitro study was to investigate the fracture strength and cuspal deflection of endodontically treated premolars restored using different composite resins along with or without fiber post application. Materials and Method: Eighty intact premolars were randomly divided into eight groups (n = 10); CO group: intact teeth (control), OPR group: mesio-occlusal-distal-palatal (MODP) preparation (OPR) + endodontic treatment (ET), TC group: MODP preparation + ET + Tetric N-Ceram, TB group: MODP preparation + ET + Tetric EvoCeram Bulk Fill, SO group: MODP preparation + ET + SonicFill 2, TC-P group: MODP preparation + ET + Hahnenkratt glass fiber post + Tetric N-Ceram, TB-P group: MODP preparation + ET + Hahnenkratt glass fiber + Tetric EvoCeram Bulk Fill, and SO-P Group: MODP preparation + ET + Hahnenkratt glass fiber post + SonicFill 2. After thermocycling, specimens were subjected to a compressive load until fracture. Data were analyzed using analysis of variance and Tukey tests (P < 0.05). Results: The mean fracture strength of groups which received post treatment showed similar fracture strength values [TC-P (931.6 ± 97.9), TB-P (882.0 ± 59.7), SO-P (862.0 ± 143.0) (P > 0.05)] and was significantly higher than OPR (530.6 ± 41.7), TC (841.2 ± 93.1), TB (774.5 ± 101.8), and SO (735.0 ± 178.01) groups (P < 0.05). No significant difference was detected among groups considering cuspal deflection (P > 0.05). The fiber post insertion resulted in more unfavorable fractures. Conclusion: Endodontically treated teeth restored with fiber post and bulk-fill or conventional composite resins demonstrated fracture strength values similar to intact teeth.

Keywords: Bulk-fill, composite resin, fiber post, fracture strength


How to cite this article:
Oz F D, Attar N, Sungur D D. The influence of restorative material and glass fiber posts on fracture strength of endodontically treated premolars after extensive structure loss. Niger J Clin Pract 2019;22:782-9

How to cite this URL:
Oz F D, Attar N, Sungur D D. The influence of restorative material and glass fiber posts on fracture strength of endodontically treated premolars after extensive structure loss. Niger J Clin Pract [serial online] 2019 [cited 2019 Jun 24];22:782-9. Available from: http://www.njcponline.com/text.asp?2019/22/6/782/260027




   Introduction Top


The restoration of teeth with endodontic treatment (ET) is a challenge, because of the fragility of tooth structure after caries removal, cavity preparation, and root canal shaping. These etiological factors are mentioned as the reason of increased fracture risk and decreased longevity of the restorations.[1] It is reported that ETs reduce 38% flexural strength of teeth after procedures.[2] The coronal restoration is required to solve the lost functional problem and serve to protect the ET from microleakage and penetration of microorganisms.[3] Large coronal tooth structure loss requires the placement of endodontic post. The use of prefabricated fiber-reinforced composite posts instead of cast posts increased in dental practice due to their aesthetic color, easy application, short clinical time, and simpler removability.[4] Appropriate endodontic post should fit in the canal accurately, be biocompatible with dentin structure, and distribute masticatory forces. The composite in the fiber posts allow them to have compatible elastic modulus with dentin and a reduced probability of root fracture.

Several restorative materials can be used for endodontically treated teeth such as amalgam, glass ionomer, and composite resins. The good aesthetic and efficient adhesion of composite resins which might eliminate the need for extensive cavity preparation make them the first choice for restoration.[5] However, polymerization shrinkage and its associated stresses lead to adaptation problems at the interface and cuspal deflection.[6] Different methods such as incremental placement technique are proposed to eliminate these problems. The incremental technique is widely used, but it appears to be time-consuming and increases contamination risk and air entrapment between increments.[7] Thicker increments with an adequate curing to maintain optimum mechanical properties might solve these problems. To simplify the clinical application of composite resins, modifications were made on the organic matrix and bulk-fill composite resins were introduced.[8] Bulk-fill composite resins were introduced to place composite resins with 4 or 5 mm increments and still obtain adequate light polymerization.[9] They can be applied with a single increment in deep cavities such as endodontically treated premolars. Some studies[10],[11] mentioned that bulk-fill composite resins presented good marginal adaptation and low polymerization shrinkage. The first bulk-fill approach was Smart Dentin Replacement (SDR) composite, a high translucent composite which has to be used in combination with a universal composite. A polymerization modulator has been added and embedded in the resin and marketed as a stress decreasing flowable bulk-fill material.[12] Tetric EvoCeram Bulk Fill composite contains new initiator (Ivocerin; Ivoclar Vivadent, Schaan, Liechtenstein) which, along with the camphorquinone/amine present in the composites, allows suitable polymerization, even in higher increments and still the presence of prepolymerized particles of Tetric EvoCeram Bulk Fill can decrease polymerization shrinkage.[13] A clinical study[14] showed acceptable results for bulk-fill composites similar to conventional layering technique including lower fracture rates. However, a clinical report considering endodontically treated teeth restored with bulk-fill composites is not present. An in vitro study[15] reported that endodontically treated teeth (mesio-occlusal-distal cavities) restored with a low-shrinkage composite showed similar fracture strength values to intact teeth.

The aim of this study was to evaluate the fracture strength of endodontically treated teeth after restoration with different types of composite resins and fiber post application. The null hypotheses were that (1) the tested composites would show similar cuspal deflection values at restored teeth after restoration, (2) the tested universal composite and bulk-fill composites would exhibit similar fracture strengths at teeth with extensive structure loss, and (3) fiber post insertion would not affect the fracture strengths of large mesio-occlusal-distal-palatal (MODP) restorations.


   Materials and Method Top


Eighty extracted single-rooted human maxillary premolars were used in this study (Hacettepe University Ethical Committee Approval No. GO 18/308-39). Teeth were examined under magnifying glasses (Hires 2.5; Orascoptic, CA, USA) to detect any preexisting defects. Intact, no caries, unrestored teeth were included. The calculus, plaque, and the remaining tissue were removed with scaling instruments and pumice using a rubber cup. An electronic digital calliper (Absolute Digimatic; Mitutoyo, Tokyo, Japan) was used for crown measurements, and teeth with similar mesiodistal and buccolingual sizes were chosen (buccolingual width: 8.81–10.55 mm; mesiodistal width: 6.45–8.72 mm). The teeth were stored in 0.1% thymol for 1 week at room temperature and transferred to distilled water at 4°C until specimen preparation. A radiograph was taken and inspected for all included teeth to determine whether they were all similar and single-rooted.

Cavity preparation and ET

Standardized MODP cavities were prepared with diamond burs (Diatech, Heerbrugg, Germany) that were replaced after every third cavity preparation. The gingival floor was 1.0 mm above the cemento-enamel junction (CEJ). The palatinal cusps were reduced by 2 mm according to the anatomic shape and the approximal box was two-thirds of the buccal palatal width. The cavosurface margins were prepared at 90°, and all internal line angles were rounded. All cavity preparations were checked with a periodontal probe to ensure correct dimensions.

Endodontic access cavities were prepared using a high-speed handpiece. The pulp chamber roof was penetrated with a cylindrical diamond bur (Diatech Dental; Coltene/Whaledent, Altstatten, Switzerland) on a high-speed handpiece with water spray cooling. Then the cavities were extended with a diamond tapering cylindrical bur. Afterward, root canal shaping was conducted with K-files (#10) (MANI, Inc, Tochigi, Japan). The working length was determined by inserting K-files until they can be seen at the apical foramen and subtracting 0.5 mm from this length. The root canals were prepared using ProTaper rotary files (Dentsply Maillefer, Ballaigues, Switzerland) up to F3 (#30), in conjunction with 2 mL of 2.5% NaOCl irrigation between each file. Prepared root canals were rinsed with 17% EDTA (Pulpdent, Watertown, MA, USA) for 1 minute, followed by a final rinse with 5 mL of distilled water and were then dried using paper points. The roots were filled with ProTaper F3 gutta-percha and AH Plus (Dentsply DeTrey, Konstanz, Germany) epoxy resin-based root canal sealer using single-cone technique. Excessive coronal gutta-percha was removed, and the endodontic access cavities were sealed with a thin layer of resin-modified glass ionomer cement (Riva Light Cure; SDI, Victoria, Australia). Samples were stored in 100% humidity for 7 days to allow the sealer to set.

The post space was prepared using Peeso reamers up to size 5 leaving apical 4 mm of gutta-percha obturation in the apical area. The post space was irrigated with 3% sodium hypochlorite followed by saline solution and dried using paper points.

Cuspal deflection measurements

Before preparations and between measurements, the teeth were stored in an incubator (37°C). The cuspal measurements were taken between two same points which were marked before. Ten measurements at different time intervals (5 min, 24 h, 1 week, and 2 weeks after preparation) using a digital micrometer gauge (Absolute Digimatic) were taken and recorded. The mean value was considered the result of that specimen. After restorative procedures, the cuspal measurements were taken again, calculated, and recorded as mentioned before. The difference between “initial” and “after restorative procedures” was noted as cuspal deflection values.

Test groups

Teeth were randomly assigned into eight groups (n = 10); CO group: intact teeth (control), OPR group: MODP preparation + ET, TC group: MODP preparation + ET + Tetric N-Ceram (Ivoclar Vivadent) composite resin restoration, TB group: MODP preparation + ET + Tetric EvoCeram Bulk Fill (Ivoclar Vivadent,) composite resin restoration, SO group: MODP preparation + ET + SonicFill 2 (Kerr, Orange, CA, USA) composite resin restoration, TC-P group: MODP preparation + ET + glass fiber post (Hahnenkratt, Königsbach-Stein, Stuttgart, Germany) + Tetric N-Ceram (Ivoclar Vivadent) composite resin restoration, TB-P group: MODP preparation + ET + glass fiber post (Hahnenkratt) + Tetric EvoCeram Bulk Fill (Ivoclar Vivadent) composite resin restoration, and SO-P group: MODP preparation + ET + glass fiber post (Hahnenkratt) + SonicFill 2 (Kerr) composite resin restoration.

The fiber posts were cemented with a dual-cure resin cement (Duo-Link; Bisco, Schaumburg, IL, USA) according to the manufacturer's instructions [Table 1]. Before cementations, silane (Monobond; Ivoclar Vivadent) was applied to each fiber post for 60 s.
Table 1: Materials used in the study

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A 0.3-mm-thick periodontal ligament was simulated to the external root surface of each tooth using a vinyl polysiloxane impression (Virtual Light Body; Ivoclar Vivadent) material. Then, the root of all teeth were embedded in an autopolymerizing acrylic resin (Meliodent; Heraeus Kulzer, Hanau, Germany) up to 1 mm below the CEJ, with the long axis of the tooth perpendicular to the base of acryl.

For all restored groups, a universal metal matrix band/retainer (Tofflemire) was placed at the prepared teeth and supported externally by low-fusing compound to maintain adaptation of the band to the cavity margins. The materials used in this study are listed in [Table 1]. The adhesive systems and composite resins were placed according to the manufacturers' instructions [Table 1]. The palatal part of all restorations was 2 mm and was measured before fracture strength testing.

All specimens were stored in distilled water at 37°C for 24 h and then subjected to thermocycling at 5000 cycles in water baths between 5°C and 55°C. Dwell time of each temperature was 20 s, and the transfer time from one bath to the other was 5 s.

Fracture strength measurements and failure mode evaluations

The specimens were subjected to compressive loading in a universal testing machine (LR50K; Lloyd Instruments, Fareham, UK) at a crosshead speed of 0.5 mm/min. A steel sphere (5 mm in diameter) was seated perpendicularly to the long axis of the tooth and was in contact with the occlusal surface of the tooth. A thin plastic tape was placed on the surface of the ball to ensure a stable contact between the steel ball and tooth structure. The load required to fracture the specimen was recorded in newtons. After fracture strength measurements, fracture patterns were evaluated under a stereomicroscope. The results were analyzed by one-way analysis of variance followed by Tukey's honestly significant difference test (P < 0.05). The statistical analyses were carried out at the 5% significance level using IBM SPSS version 22.0 software (SPSS, Chicago, IL, USA).

Scanning electron microscope microphotographs were taken to analyze the composite resins' filler particles [Figure 1], the fiber post [Figure 2], and fracture patterns [Figure 3], [Figure 4], [Figure 5], [Figure 6] after fracture load tests.
Figure 1: SEM evaluations of composite resins used in the study. (a) Tetric NCeram (TC) and (b) Tetric EvoCeram Bulk Fill (TB), (c) SonicFill 2 (SO)

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Figure 2: SEM microphotographs of the fiber post

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Figure 3: SEM microphotographs of a repairable sample with post treatment

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Figure 4: SEM microphotographs of a nonrepairable sample without post treatment

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Figure 5: SEM microphotographs of a repairable sample with post treatment

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Figure 6: SEM microphotographs of a nonrepairable sample with post treatment

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   Results Top


The cuspal deflection values are given in [Table 2]. No significant difference was detected among groups (P > 0.05). The mean fracture strength and standard deviations are given in [Table 3]. The intact teeth (control) demonstrated the highest fracture strength (1047.3 ± 105.6) which was significantly higher than OPR (530.6 ± 41.7), TC (841.2 ± 93.1), TB (774.5 ± 101.8), and SO (735.0 ± 178.01) groups (P < 0.05). The OPR group showed significantly lower fracture strength (530.6 ± 41.7) than all the other groups (P < 0.05). The groups which did not receive post treatment demonstrated no significant differences among each other (TC, TB, and SO). Post inserted groups showed similar fracture strength values [TC-P (931.6 ± 97.9), TB-P (882.0 ± 59.7), SO-P (862.0 ± 143.0) (P > 0.05)]. In addition, the post-inserted groups (TC-P, TB-P, and SO-P) were found to exhibit similar fracture strength values with the control group.
Table 2:Mean cusp deflection values of tested groups

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Table 3:Mean compressive strength values of tested groups

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Fracture patterns were categorized according to five groups mentioned in [Table 4], and representative photographs are shown in [Figure 7]. The TC group mostly exhibited severe (mode V) (60%) and nonrepairable fractures (60%); however, TB and SO groups showed 20% severe (mode V) and 20% nonrepairable fractures. The post-inserted groups mostly demonstrated severe (mode V) (TC-P: 90%, TB-P: 70%, SO-P: 60%) and nonrepairable fractures (TC-P: 90%, TB-P: 70%, SO-P: 60%).
Table 4: Frequency (%) of failure modes among the experimental groups (n=10)

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Figure 7: Representative photographs of fracture modes: (a) mode III, (b) mode IV, (c) mode V, (d) repairable, and (e) nonrepairable

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   Discussion Top


Polymerization shrinkage is a factor that might cause problems such as fractures, stress, gap formation, and microleakage resulting in secondary caries.[16] Polymerization shrinkage levels are affected by the composition and filler content of resin composites.[17] A higher filler percentage could reduce the polymerization shrinkage. Prager et al.[18] reported that the filler content has a direct effect on cusp deflection, high filler percentages exhibited higher cusp deflection values, and composite resins with similar filler percentages showed similar cuspal deflection values. On the other hand, they also mentioned that high filler percentage has an opposite effect on volumetric shrinkage, since higher filler loadings produced lower volumetric shrinkage percentages. The filler contents were similar in this study, hence no significant difference considering cuspal deflection among different composite resins at large cavity preparations was detected and the first hypothesis was accepted. Other factors that might affect the shrinkage are the curing and placement techniques. Various polymerization techniques (such as soft-start techniques, continuous light polymerization, intermittent light polymerization)[19] and incremental placement technique have been proposed to minimize polymerization shrinkage. The incremental technique has been highly recommended to reduce the negative effects of shrinkage. In the past decade, bulk-fill composites were introduced as an innovative approach to apply direct composite restorations with 4–5 mm increments causing low polymerization shrinkage stress with only a single increment placement. Tetric N-Ceram, Tetric EvoCeram Bulk Fill, and SonicFill2 were placed with 2-, 4-, and 5-mm increments, respectively. A recent in vitro study[20] showed that some low-viscosity bulk-fill composite resins generate less shrinkage stress compared with other conventional composite resins, but Tetric N-Ceram and Tetric EvoCeram Bulk Fill exhibit similar stress values. Low-shrinkage silorane-based composite might be effective in reducing cuspal deflection and could be a promising method for better fracture strength.[6] Behery et al.[21] reported that silorane-based composite resulted in lower cuspal deflection compared with Tetric EvoCeram Bulk Fill composite restorative. The cuspal deflection measurement technique of this study was similar to our study. Differently, Elsharkasi et al.[22] compared the cuspal deflection of teeth restored with Tetric EvoCeram Bulk Fill and SonicFill to a conventional composite (x-trafil-VOCO) and showed that bulk-fill composite resins exhibit smaller cuspal deflection values. However, the present investigation demonstrated no difference between an incrementally placed composite and bulk-fill composites. Hence, the first hypothesis was accepted. In addition, SonicFill 2 is applied using a sound-activated handpiece in the cavity in 5-mm increments. Although the application and increment millimeters are different, the bulk-fill composite resins showed similar results in this study (P > 0.05).

The second hypothesis was accepted. The possible explanation could be that the incrementally placed composite was cured more efficiently which provides greater fracture toughness and improves the strength compared with bulk-fill composites.

Tooth structure preservation is mainly the most important factor during ET and selection of post diameter. The amount of remaining tooth structure is shown to significantly influence the stress distribution and mode of failure in the tooth restoration system.[23] The tooth restored with wide diameter posts and less remaining radicular dentin diameter exhibits least resistance to fracture.[24] Hence, all fiber posts were in the same size in this study to exclude this factor. Similar to our study, Miao et al.[25] also reported that teeth restored using fiber post exhibit similar fracture strength values to intact teeth. An in vitro study[26] demonstrated that fracture strength for unrestored teeth with MOD preparation was 50% weaker than that of unaltered premolar teeth. Besides, cusp fractures might be observed more often at endodontically treated MOD cavity preparations.[27] Especially, teeth with palatal cusp fracture are recommended to be restored after post placement to ensure stability of the restoration. Even though metal posts are widely used at posterior teeth with extensive tooth loss, they may cause discoloration and root fracture.[28] The long-term survival of endodontically treated teeth still remains a problem, and many attempts were made to improve their fracture strength using different post systems. In addition, the main goals are to provide reduction in root fracture possibility and protect the remaining cusp structure. Kivanc et al.[29] showed that restoring teeth with palatal cusp loss with fiber posts and composite resin exhibited higher fracture strength compared with teeth restored with only composite resin. Also, another in vitro investigation[30] pointed out that endodontically treated maxillary premolars demonstrate better fracture strength values and force distribution with polyethylene fibers (Ribbond) and fiber post application. In accordance with these results, this study found that fiber posts provided superior fracture strength for endodontically treated premolar teeth with MODP preparations. Hence, the third hypothesis is rejected. The fracture strength of large MODP restorations is affected by the choice of restorative techniques. The highest unrepairable fractures (90%) were observed at Tetric N-Ceram with post insertion. This might be attributed to the high fracture strength values of this group. Also, the loading force distribution to the weakened root might be undesirable. Similar to this study, an in vitro study[25] showed that endodontically treated maxillary premolars exhibit higher unfavorable fractures with composite restorations after post insertion. Conversely, some studies[30],[31],[32] reported that fiber posts at endodontically treated teeth resulted in more favorable fracture mode above CEJ.


   Conclusion Top


Within the limitations of this in vitro study, it is concluded that the use of fiber post provided higher fracture strength for premolars with large structure loss with ET. The bulk-fill and conventional composite resins show similar cuspal deflection and fracture strength values. However, long-term clinical studies are required to support these results.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

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



 

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