Journal of Oral Research and Review

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 12  |  Issue : 1  |  Page : 28--33

Evaluation of the fracture resistance of three different core materials used for Nayyar dowel-core technique in restoring endodontically treated teeth: An in vitro study


Kakollu Sudha, Thota Murali Mohan, Bhupathi Sravanthi Yadav, Ediga Sandhya Rani, Kalagotla Aparna, Kasireddy Jyothsna 
 Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Vijayawada, Andhra Pradesh, India

Correspondence Address:
Bhupathi Sravanthi Yadav
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Vijayawada, Andhra Pradesh
India

Abstract

Background: Endodontically treated teeth have increased susceptibility to fracture. To promote the fracture resistance, reinforcing the endodontically treated teeth is of utmost importance. An ideal restoration or core is necessary to build up the coronal portion of the tooth to an ideal anatomic form before the full coverage placement. Aims: Compare the fracture resistance of Nayyar Cores of amalgam, Zirconomer, and Para Core with natural teeth . Methods: This study compared the fracture resistance of coronal-radicular restorations made from three different restorative materials. Sixty human mandibular molars were selected, 45 of which were decoronated and root treated – 15 of these molars restored with amalgam, 15 with Zirconomer, and 15 using Para Core. The 15 natural teeth used as a control group. All the teeth were mounted in acrylic and subjected to compressive loading to failure on a universal testing machine. The force required to fracture each core specimen was recorded. Results: The data of the study were statistically analyzed by ANOVA test and Tukey post hoc test. The results of the study showed that natural teeth as having the highest fracture resistance values, followed by Para Core, amalgam, and Zirconomer. The differences among all groups were significant. Conclusion: Within the limitations of this study, natural teeth showed higher fracture resistance to that of the Para Core, amalgam, and Zirconomer. Among the 3 Nayyar cores, Para Core has higher fracture resistance.



How to cite this article:
Sudha K, Mohan TM, Yadav BS, Rani ES, Aparna K, Jyothsna K. Evaluation of the fracture resistance of three different core materials used for Nayyar dowel-core technique in restoring endodontically treated teeth: An in vitro study.J Oral Res Rev 2020;12:28-33


How to cite this URL:
Sudha K, Mohan TM, Yadav BS, Rani ES, Aparna K, Jyothsna K. Evaluation of the fracture resistance of three different core materials used for Nayyar dowel-core technique in restoring endodontically treated teeth: An in vitro study. J Oral Res Rev [serial online] 2020 [cited 2020 Apr 10 ];12:28-33
Available from: http://www.jorr.org/text.asp?2020/12/1/28/276711


Full Text



 Introduction



Endodontic treatment mainly performed on teeth that are significantly affected by caries, repeated restorations, and fractures. Moreover, they are further weakened by the endodontic procedures designed to provide optimal access. Loss of inherent dentinal fluid may also affect an alteration in tooth properties. It is therefore accepted that endodontically treated teeth are weaker, increased susceptibility to fracture, and tend to have a lower lifetime prognosis.

The quality of root canal treatment and prosthodontic reconstruction are the two key factors that determine the longevity of the endodontically treated teeth.[1] Hence, the proper root canal treatment and reconstruction of these endodontically treated teeth are of utmost importance.

The strength of the endodontically treated tooth can be enhanced with intracoronal support as well as an extra coronal cast restoration. A foundation restoration or core can be used to build a severely broken down tooth to restore the bulk of the coronal portion of the tooth to an ideal anatomic form before the full coverage crown is placed.[2]

Many procedures, techniques, and various materials have been suggested for core build-up. Nayyar et al. proposed a method using an amalgam dowel core. In this technique, the remaining pulp chamber and the prepared canals by extending amalgam into the canals provide retention for the amalgam core. This technique involves the removal of obturated gutta-percha to the depth of 2–4 mm from canal orifice and restoring with amalgam.[1]

Several dental materials have been used as an alternative for amalgam for core build-up procedures. Most of these materials were not specifically developed for this purpose, but as a consequence of their properties, have found application in core build-up procedures.

The optimal properties of core build-up material are adequate strength, must be biocompatible, exhibit a high level of resistance to bacterial leakage, and be dimensionally stable in the presence of oral fluids.[1]

This study focuses on the evaluation of the occlusal fracture resistance strength of the three different core materials using the Nayyar technique.

Aim and objective

Compare the fracture resistance of Nayyar Cores of amalgam, Zirconomer, and Para Core with natural teeth.

 Methods



For the present study, 60 extracted mandibular molars used. Forty-five samples were decoronated at 2 mm above the level of cementoenamel junction (CEJ).

Working length determined, proper cleaning and shaping, and obturation was done. Gutta-percha from these root samples was removed till a depth of 3 mm from the coronal orifice with the use of a heated hand plugger. Then all the samples were randomly divided into groups as follows.

Group 1: Natural teeth (n = 15)Group 2: Amalgam (Tytin FC fast-set silver amalgam (Kerr/Sybron, Orange, CA, USA) [Figure 1] (n = 15). The samples were mounted on a custom-made wax block, and matrix band was placed around the tooth and impression compound was placed around the banded sample to secure it firmly, as shown in [Figure 2]. The amalgam was triturated according to the manufacturer's guidelines using an amalgamator. Condensation was then commenced immediately, with the amalgam packed first into the root canal space, then built to a height of 4 mm above the CEJ. After removal of the matrix band, the occlusal surface of the core was carved to an anatomic formGroup 3: Zirconomer (Shofu, USA) [Figure 3] (n = 15) samples were banded as same as in Group 2. Zirconomer hand-mixed at specific powder to liquid ratio of 2:1 using glass slab and plastic spatula. The core material was initially placed into the root canals before incremental placement of subsequent material. The core was built to a height of 4 mm above the CEJ. When the cement mixture loses luster matrix band was removed, and occlusal surface of the core was carved to an anatomic formGroup 4: Para Core (Coltene Whaledent, USA) [Figure 4] (n = 15) samples were banded as same as in Group 2. The surface was treated with ParaBond nonrinse conditioner, scrubbed for 30 s, air dry for 2 s, followed by application of premixed adhesive A and adhesive B on the conditioned surface for 30 s and air drying for 2 s and left for self-curing for 2 min before core build-up. The core material was initially placed into the root canals before incremental placement of subsequent material. The core was built to a height of 4 mm above the CEJ. Initially, light-cured for 10 s per surface to initiate polymerization and to achieve final set, left for 4 min for auto-polymerization using blue light. The optimum consistency of the material allows it to be shaped into the approximate shape of a core during application. After removal of the matrix band, the occlusal surface of the core was carved to an anatomic form.

Samples were stored in distilled water for 24 h. All the samples were mounted with self-cure acrylic resin to a depth of 2 mm apical to the CEJ. Then, the teeth were then loaded to failure in a Howden universal testing machine using a 4.5 mm diameter stainless steel rod, which was placed in the midline fissure at a crosshead speed of 0.5 mm/min. Then, the force (N) at which teeth were fractured was recorded for each specimen.{Figure 1}{Figure 2}{Figure 3}{Figure 4}

 Results



SPSS (version 16) and Microsoft Excel software were used to carry out the statistical analysis of data. Mean and standard deviations were calculated. A comparison between the groups was made using the ANOVA test, and the pairwise comparison was made using the Tukey posthoc test [Table 1]. P < 0.05 was considered statistically significant. Results demonstrated that natural teeth, amalgam, Zirconomer, and Para Core has fracture resistance values as 3150.22, 1395.87, 404.34, 2446.04 N/mm2, respectively. Decreasing order for the fracture resistance values is Natural teeth >Para Core >amalgam >Zirconomer.{Table 1}

Natural teeth have significant statistical differences (P[3]

According to Peroz et al., restoration of endodontically treated teeth was done depending upon the number of walls remaining after access cavity preparation. A core is indicated in cases of Class II where two remaining walls are present and Class III, where three remaining walls are present.[4]

A foundation restoration or core is used to build a badly broken down tooth to restore the bulk of the coronal portion of the tooth to an ideal anatomic form before the full coverage crown is placed. It should provide the patient with a long-lasting restoration with adequate function. Building up the tooth to an ideal contour simplifies the subsequent tooth preparation. As the core becomes an integral part of the structure of the tooth, it should provide strength to resist the intraoral compressive and tensile forces.[2]

Compressive and tensile stresses of core materials are thought to be important because cores usually replace a large bulk of tooth structure and must resist multidirectional masticatory forces for many years.[2]

A core is usually required to replace a large bulk of tooth structure.[3] Nayyar et al. suggested a technique using an amalgam dowel core. In this technique, retention for the amalgam core is derived from the remaining pulp chamber and the prepared canals by extending amalgam to these areas. This technique involves the removal of obturated gutta-percha to the depth of 2–4 mm from the canal orifice and restoring it with amalgam.[1] Using this technique, Nayyar and others reported 400 successful restorations when cast crowns were placed as the final restoration.[5]

Criteria of Nayyar cores

The size of the remaining pulp chamber should be of sufficient width and depth to provide for adequate bulk and retentionAdequate dentin thickness in the area of the pulp chamber is required for rigidity and strength.[3]

This procedure should be restricted to teeth with <4 mm of pulp chamber height.[6]

The restoration of endodontically treated teeth offers many challenges for the restorative dentist because of high failure rates, and this led to the development of a magnitude of restorative alternatives for endodontically treated teeth.[7]

The most commonly used core build-up material is amalgam, which has many advantages; those include high compressive strength and dimensional stability in the oral environment. Amalgam has been used successfully as a final restorative material to replace tooth tissue in bulk in root canal treated posterior teeth. However, this material has disadvantages, which include – poor color stability, low initial strength, lack of adequate inherent bond to the tooth structure, and a high coefficient of thermal diffusivity.[5]

Alternatives to amalgam, several dental materials have been used for core build-up procedures. Most of these materials were not specifically developed for this purpose, but as a consequence of their properties, have found application in core build-up procedures. Improvements in composites and the development of enamel–dentine bonding systems have stimulated trends toward more conservative techniques, which afford increased opportunities to preserve the vitality of badly broken permanent molar teeth in their restoration. New formulations of glass polyalkenoate (ionomer) cements have resulted in an increasing range of applications for such materials in posterior teeth.[8]

In this study, Zirconomer and Para Core materials were taken for comparison with amalgam. Zirconomer is developed to exhibit the strength, i.e., consistent with amalgam, through a rigorous manufacturing technique. The glass component of this high-strength glass ionomer (GI) undergoes finely controlled micronization to achieve optimum particle size and characteristics. The polyalkenoic acid and the glass components have been specially processed to impart superior mechanical and handling qualities to this high-strength. It contains zirconium oxide, glass powder, tartaric acid (1%–10%), polyacrylic acid (20%–50%), and deionized water as its liquid.[9]

The accessible zirconia powders have different grain sizes and different additives, such as yttrium oxide and alumina, which can be distributed homogeneously throughout the whole material.

Excellent resistance to abrasion and erosion is by continuous formation of aluminum salt bridges, which has improved the strength of the cement. The micro-sized yttria-stabilized zirconia – GI cement (GIC) powders revealed a bimodal particle distribution, and this ensured a high packing density of GIC, giving high mechanical properties to Zirconomer.[10]

It has the property of transformational toughening, which is the ability to stop the growth of cracks, and it gives zirconia its unique mechanical properties.[11]

Para Core is a fiber-reinforced, dual-core, and radiopaque core build-up material.

Which exhibits a stackable with the nonslumping type of consistency, and it is formulated to cut similar to that of dentinIt incorporates glass particles which impart high strength, and the material showed excellent physical properties. A dual-cure material that will ensure a complete cure.[12]

In this study, fracture resistance was taken as a parameter for the comparison of different Nayyar cores because, according to Cohen, fracture resistance of the endodontically treated teeth decreases because of the alteration changes in the composition, dentin structure, and macro tooth structure.

According to Cohen, when posterior teeth are largely intact, a coronal-radicular foundation restoration may be used. Moreover, the advantage of this procedure is that a single, homogeneous material is used for the entire restoration, rather than the dual phases of a conventional preformed post and core.

Para Core has shown higher fracture resistance due to the macroscopic size of the unidirectional fiber bundles, which reinforces and improves the mechanical properties of the resin. The presence of fiber affects the fracture process, which results in interruption of the crack growth progression and thus enhances the fracture toughness. Moreover, it also has the property of adherence to tooth substance through the use of dentin adhesive systems.[2]

Zirconomer has lower fracture resistance compared to that of the amalgam, and these results are contradictory to the study conducted by Dr. Kamath and Salam.[13]

Zirconomer has less fracture resistance, which may be due to its self-curing nature and has a similar chemical nature of GIs, resulting in more dissolution in water.[7]

This finding goes in a good agreement with the previous work by Patel et al.[14] who found almost similar outcomes when they tested the dye penetration of Zirconomer in human molar teeth. This could be explained because of the chemical structure of Zirconomer, which comprises ceramic particles (zirconia) as fillers. It is possible that the zirconia fillers would cause interference in the chelating reaction between the carboxylic group (-COOH) of poly-acrylic acid and the calcium ions (Ca2+) of tooth apatite.

A recent study by Asafarlal[15] showed that the microleakage value of Zirconomer was higher compared to the other GICs. This was believed to be owing to the large size of the filler particles of zirconia, which leads to poor adaptation at the tooth-restoration interface.

 Conclusion



Within the limitations of this study, Natural teeth have a higher fracture resistance than Nayyar cores. Among the Nayyar cores, Para Core showed higher fracture resistance, and Zirconomer has lower fracture resistance. Hence, Para Core can be used as an alternate core build-up material in place of amalgam.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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