Comparative evaluation of fracture resistance of various core buildup materials on endodontically treated teeth: An in vitro study

Greeshma Kumbaiah; Veena Hegde; Kishore Ginjupalli; Kavishma Sulaya; Jayaprakash K

doi:10.4103/jioh.jioh_288_21

ORIGINAL RESEARCH

Year : 2022 | Volume : 14 | Issue : 6 | Page : 597-602

Comparative evaluation of fracture resistance of various core buildup materials on endodontically treated teeth: An in vitro study

Greeshma Kumbaiah¹, Veena Hegde¹, Kishore Ginjupalli², Kavishma Sulaya¹, Jayaprakash K³
¹ Department of Prosthodontics and Crown & Bridge, Manipal College of Dental Sciences, Manipal, India
² Department of Dental Materials, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal, India
³ Department of Biomaterials, Yenepoya Dental College, Mangalore, Karnataka, India

Date of Submission	20-Oct-2021
Date of Acceptance	11-Oct-2022
Date of Web Publication	30-Dec-2022

Correspondence Address:
Dr. Veena Hegde
Department of Prosthodontics and Crown & Bridge, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal 576104, Karnataka
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jioh.jioh_288_21

Abstract

Aim: The present study aimed to evaluate and compare the fracture resistance of four different core build-up materials on endodontically treated teeth. Materials and Methods: In this in vitro study, sample size estimation was done using G*power software (version 3.1.9.2), an effect size of 0.66 was obtained at 95% confidence interval. 48 Teeth samples were decoronated 2 mm above the Cementoenamel junction. Root canal treatment done, followed by preparation of post space and fiberglass posts of 10 mm length was cemented with resin cement into the root canal and 4 mm above the prepared tooth. All the samples were randomly divided into 4 groups of 12 samples for four different core build up materials. All teeth were restored with a Nickel chromium crown of standard dimensions and cemented with glass ionomer cement. Fracture resistance measured by applying the load at an angle of 135° to the long axis of the tooth at a crosshead speed of 0.05 mm/min until failure. Analysis was performed using KRUSKAL-WALLIS to compare mean values and standard deviation of fracture resistance, followed by post – hoc MANN WHITNEY test for assessing the significant difference of fracture resistance between the four groups. Results: Resistance to fracture was greater in Luxacore Z group followed by Vitremer, Denfil and Filtek. However, no statistically significant differences in the fracture resistance were observed among the groups. Conclusion: The results indicate that Luxacore Z core build-up material exhibits superior fracture resistance. Resin modified glass ionomer cement had fracture resistance comparable to Luxacore.

Keywords: Nonvital, LuxaCore, Resin Cements, Tooth Cervix, fiberglass, Dental Pulp Cavity, Glass Ionomer Cements, Tooth, Vitremer

How to cite this article:
Kumbaiah G, Hegde V, Ginjupalli K, Sulaya K, Jayaprakash. Comparative evaluation of fracture resistance of various core buildup materials on endodontically treated teeth: An in vitro study. J Int Oral Health 2022;14:597-602

How to cite this URL:
Kumbaiah G, Hegde V, Ginjupalli K, Sulaya K, Jayaprakash. Comparative evaluation of fracture resistance of various core buildup materials on endodontically treated teeth: An in vitro study. J Int Oral Health [serial online] 2022 [cited 2023 Feb 1];14:597-602. Available from: https://www.jioh.org/text.asp?2022/14/6/597/366433

Introduction

Tooth that are grossly decayed, large failing restoration or fractured tooth requires full coverage to restore its original form and function. If there is pulpal involvement with sufficient tooth loss, it will require core build up to support the final restoration or additional support may be taken by placing post in the root to enhance the support for core build up.

A core restoration should provide sufficient strength and resistance during the crown preparation, impression recording and support permanent restoration in the long term. It must be strong enough to withstand the multidirectional forces of mastication. It should also have sufficient mechanical and physical properties, which will certainly affect its clinical service life. Various research investigations have reported that core build up with prefabricated glass fibre posts using a resin composite exhibits superior resistance to fracture.^[1]

The vertical band of the prepared tooth structure towards the gingiva called as “ferrule effect” is critical for long-term success of the post and core restorations. Primarily, it provides a resistance form that enhances the longevity of the tooth and provides retention.

Due to resemblance to the tooth structure in strength and resistance to the fracture, fibre reinforced composite post can be used as a core material. Resin composites with higher filler content and greater strength have been designed specifically for the building of the core and to enhance the ease of fabrication.^[2]

A core restoration should provide sufficient strength and resistance during the crown preparation, impression recording and support permanent restoration in the long term. It must be strong enough to withstand the multidirectional force of mastication. It should also have sufficient mechanical and physical properties, which will certainly affect its durability. Hence, the selection of core build-up materials is an important part of the clinical condition. Thus this study aimed to evaluate the fracture resistance of root canal treated teeth restored using four different core build-up materials.

Null hypothesis: There is significant difference among the selected core build up materials.

Materials and Methods

This in vitro study was conducted at the Department of Prosthodontics and Crown and Bridge, Manipal College of Dental Sciences, Manipal. The Kasturba Hospital Institutional Ethical Committee Clearance was obtained for the study with the ethical clearance number 714/2017. Sample size estimation was done using G*power software (version 3.1.9.2), an effect size of 0.66 was obtained at 95% confidence interval.

Specimen selection and root canal preparation

Total 48 extracted mandibular first premolars free of dental caries, cracks, any restorations, or any other defects were selected. Each tooth was marked 2 mm above the CEJ [Figure 1]. At this level, it was measured mesiodistally (5.6 ± 0.5 mm), labio-lingually (8.2 ± 0.5 mm), and the root length (14.5 ± 0.5 mm) using a digital Vernier calliper. Decoronation was made perpendicular to the axis of the root at 2 mm above CEJ using slow speed handpiece [Figure 1]. All teeth were root canal treated using a step-back technique using hand protaper(Dentsply Sirona, US) until F3 file. Up to 4 mm root length was sectionally obturated using eugenol-based root canal cement(Endoseal, India). To ensure complete setting of cement, all specimens were stored for 24hrs at 37°c.

Figure 1: Procedure

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Block preparation

For the simulation of the periodontal ligament around the root, a polyvinyl siloxane (Flexceed, GC, JAPAN) was used. 0.5 mm of the root portion below the CEJ level of each tooth was dipped in molten modelling wax (Renfert, hotty, Germany) at temperature 90°c [Figure 1]. This resulted in approximately 0.2 mm of uniform thickness of wax around the root. A silicone mould index (Aquasil, Putty, Dentsply Sirona, US) was prepared for the specimen positioning. The peeso drill was drilled into the canal and was supported by dental surveyor to suspend the tooth into the silicone mold [Figure 1]. Auto-polymerizing acrylic resin (Dentsply, US) was poured into the mold resulting in root with wax coating below the level of CEJ embedded in acrylic resin to the level of CEJ. Later dewaxing was done and the mold was filled with polyvinyl siloxane (Aquasil, Dentsply Sirona, US), tooth was positioned back in the mold in the same position resulting in 0.2 mm of polyvinyl siloxane.

Post space preparation and post cementation

Using a peeso reamer drill, a depth of 10 millimetres of post space was prepared, preserving the apical seal of 4 mm of intact gutta-percha [Figure 1]. The canals were prepared with peeso drills corresponding to post size no.2 (Reforpost, Angelus, Brazil). Each post was cemented with dual-polymerizing resin cement(Solocem, Coltene, Switzerland) as per the manufacturer’s instructions. Fibre post was cut at 14 mm length with a high-speed diamond rotary cutting instrument, resulting in a projection of 4 mm of the post above the prepared tooth and 10 mm of the post in the root [Figure 1]. Subsequently, all the samples were grouped randomly into four groups (n = 12).

Core build-up

The core build-up is done by building the core with a height of 4 mm labially, 2 mm lingually, with coronal post end completely covered [Figure 1]. This is followed by crown preparation with the circumferential 0.5-mm chamfer finish line at the CEJ line providing a ferrule effect of 2 mm. This resulted in height of the core 6 mm labially and 4 mm lingually including ferrule from CEJ. A mould is prepared with 1 mm thick clear bioplast(Biotec, US), which helps in standardizing the other core build-up. The composite core was built using either Luxacore Z (DMG, Germany), Vitremer (3M, US), Denfil or Filtek 250 XT(3M, US). All the materials were manipulated as per the manufacturer’s instructions and core was built-up incrementally and cured on each side for 20 seconds.

Crown restoration

The full veneer metal crowns were fabricated for each specimen by preparing a wax pattern using blue inlay casting wax (Dentaurum StarWax CB). The wax pattern thickness of the axial walls ranged from 1–1.5 mm, 1 mm on the occlusal surface, and 1.5 mm on the cusp. On the occlusal surface, a notch was prepared in the center to facilitate testing of fracture resistance. To standardize, putty index of the wax pattern was made using polyvinyl siloxane(Aquasil, Dentsply Sirona, US). Four notches were made on the buccal, lingual, mesial, and distal sides of the index to facilitate the flow of excess molten wax while fabricating wax patterns for the rest of the samples.

Wax patterns are sprued and invested in phosphate bonded investment (bellasun, begosol mixing liquid, bego), and casting procedure is carried out followed by sandblasting, finishing, and polishing of the crowns [Figure 1]. The finished crowns were cemented with type I glass ionomer cement (GC, Tokyo, Japan). All Specimens after cementation were stored for 24 hours at room temperature (37°c) before testing.

Fracture resistance testing

The fracture resistance test was performed using a universal testing machine (Instron model 3366) by loading the specimens at an angle of 135° to the long axis of the tooth by applying the load on the prepared occlusal notch at a crosshead speed of 0.5 mm/min until fracture [Figure 1]. Maximum load observed during the testing was considered as fracture resistance and is reported in Newtons.

Statistical analysis

The data were analysed using Kruskal-Wallis and significant differences among the groups was compared using Mann Whitney post-hoc test at 95% confidence interval.

Results

[Table 1] and the [Graph 1] shows fracture resistance among the materials. The normal distribution was tested using Kruskal-Wallis test. Resistance to fracture load was greater in the Luxacore Z group (418.71 ± 103.93) followed by Vitremer (368.35 ± 146.26), Denfil (317.87 ± 126.92) and Filtek 250 XT (311.39 ± 110.97). Post-Hoc (Mann-Whitney) test was used to analyse the differences between the groups and the results are shown in [Table 2]. Fracture resistance load results did not show significant statistical difference from each other (P value>0.05) where only mean values were taken into consideration. For all groups, the pattern of failure occurred at apical-facial direction continued from lingual margin of the crown.

Table 1: Comparison of mean fracture resistance among the groups using kruskal-wallis test

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Graph 1: Comparison of mean fracture resistance among the groups. Group 1-Vitremer, Group 2-Luxacore Z, Group 3-Denfil, Group 4-Filtek

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Table 2: Post-hoc (Mann Whitney) test

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Following graph shows fracture resistance among the materials. Fracture resistance load results did not show a significant statistical difference from each other (P value>0.05). Resistance to fracture load was greater in Luxacore Z group (418.71 ± 103.93) followed by Vitremer (368.35 ± 146.26), Denfil (317.87 ± 126.92) and Filtek 250 XT (311.39 ± 110.97). For all groups, the pattern of failure occurred at apical-facial direction continued from the lingual margin of the crown.

Discussion

The objective of the study was to evaluate and compare the fracture resistance of four commercially available core materials on endodontically treated teeth with glass fibre posts. Whenever there is a substantial loss of coronal tooth structure, it is necessary to increase the strength of the residual tooth structure by strengthening the abutment core around the fibre post.

In this study, premolars were considered as these are very susceptible to cusp fractures when compared to other posterior teeth when exposed to occlusal forces. During the process of mastication, premolars are subjected to a lot of detrimental forces such as shear and compressive forces. The samples were subjected to oblique loading as it the worst-case scenario in mechanical testing in terms of loading directions.^[3],[4]

When core build-up materials are tested for the fracture-related mechanical properties under stress, usually it has been evaluated by choosing the material parameter like fracture toughness^.[5]

The primary purpose of a post is to retain a core in a tooth with extensive loss of coronal tooth structure. The higher fracture resistance of the tooth is observed with the parallel post, as the stress distribution is uniform along the length of the post.^[6] Jayasenthil et al. studied the fracture resistance of four glass fibre post systems with different surface geometries and found that numerous taper designs of angelus fibre post showed the highest fracture resistance.^[7] Thus, the post selected in the present study was the Angelus Reforpost fibre glass post.

Juloski J et al^[8] in their literature review on the ferrule effect, indicated that the presence of a 1.5- to 2 mm ferrule has a positive effect on fracture resistance of endodontically treated teeth. Thus, in the present study, 2 mm ferrule height was prepared to represent the situation that can be retained with fibre glass posts, so that the impact of the core material used can be studied clearly.

The strength of core materials is one of the important properties in achieving long-standing restoration success particularly when the remaining structure of the tooth is reduced.^[9] One of the core build-up materials selected in the present study is Vitremer resin-modified glass ionomers, as glass ionomers are still popular as core build-up materials because, they are easy to handle, bond to the surface of the tooth, and release fluoride. The tooth can be prepared directly after the core build up with glass ionomer cement similar to composites.^[10] A study by Subash et al. assessed biodentin, hybrid composite resin, resin-modified glass ionomer cement as a core material tested for fracture resistance^[11] and observed that resin-modified glass ionomer exhibited an optimal fracture load of 612.07 N. In another study by Taha et al. fracture strength of root canal treated teeth restored with direct resin restoration was assessed and concluded that teeth with a glass ionomer core were not significantly weaker than intact teeth [560 ± 167N].^[12] Both the studies are in accordance with the present study where the resin-modified glass ionomer showed mean strength of 368.35 ± 146.26 N. The other three composite core build-up materials considered in the present study are Luxacore Z, Denfil, Filtek 250 XT. A study conducted by Tsiagali et al. concluded that teeth with more than half of coronal structure lost restored with amalgam showed better resistance to fracture than composite.^[13] Seung-Geun Ahn et al. conducted a study to compare the mechanical properties like flexural strength and modulus of elasticity of different post and core materials, found that the flexural strength of Luxacore is approximately 90% identical to amalgam.^[9] However, there was no significant difference among the experimental groups. Accordingly, the materials used for core buildup did not make any significant difference in fracture resistance of the Endodontically treated teeth as showed in a study by Alshahrani AS.^[14] Also in accordance with study by Izadi^[15] the current results revealed that the fracture resistance is independent of the type of core material used, and none of the tested core materials had any superiority over each other.

Thus, study proves against null hypothesis that there is no significant difference among the core build-up materials selected. A retrospective clinical study with an 8-year observation period has reported no significant difference between LuxaCore and a hybrid light-cure composite for core buildup.^[14] Buneet Kaur et al. concluded from a similar study that bulk fill composite had the least fracture resistance.^[16] A study conducted by Panitiwat P et al.^[17]and a review by Zarow M et al^[18] also concluded that fracture resistance improved with higher filler content in the composite core build up resin. Mergulhao VA et al. reported that bulk fill composite had fracture resistance similar to the sound teeth and also that conventional composite had the highest prevalence of unrepairable fracture.^[19] A review by Iaculi et al. stated that fiber post with direct composite had better fracture resistance.^[20] Contrary to this a study by Tangsripongkul et al. stated that teeth restored with fiber post and resin composite showed no improvement in fracture resistance.^[21] In accordance to our study Vyas R et al. stated that dual cure composite had better resistance when compared to other composites.^[22]

The results of the present study indicate that the use of Luxcore Z core build-up material exhibits superior fracture resistance. Since, resin modified glass ionomer cement had fracture resistance comparable to Luxacore, the same can be clinically used as an economical core material when there is no excessive loss of tooth.

Conclusion

The conclusion that can be derived from the study is there was no statistically significant difference found in the fracture resistance of the four core build-up material used. Filtek and Denfil core build up material showed similar fracture resistance values. The maximum fracture resistance was observed for Luxcore Z core build-up material. As Resin modified glass ionomer cement had resistance to fracture that is comparable to Luxacore, it can also be used as an economical core material where the loss of tooth structure is not excessive.

Limitation and scope

Limitation of present study is that it is an in vitro study which is difficult to generalise the result to clinical implication. All metal crowns were chosen for the research, study may vary relating to other aesthetic crown restoration. As only one type of post system is used in the study various other post system may be compared

Clinical implications

Variations in the selection of core build up materials does not significantly influence the fracture resistance of the tooth.

Acknowledgement

Nil.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Author contributions

Greeshma Kumbaiah was the primary investigator and conducted data extraction, Veena Hegde conceived the idea and literature search, Kishore Ginjupalli accomplished data extraction, Kavishma Sulaya revised the article. Jayaprakash K helped with the testing of the samples.

Ethical policy and institutional review board statement

The Kasturba Hospital Institutional Ethical Committee Clearance was obtained for the study with the ethical clearance number 714/2017.

Patient declaration of consent

Not applicable.

Data availability statement

Data analyzed in this study were a re-analysis of existing data, which are openly available at locations cited in the reference section.

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