Comparison of fiber-reinforced composite and nanohybrid resin impregnated with glass fibers as postendodontic restoration in molars - A clinical study.

Background: Restoration of endodontically treated teeth is one of the most challenging part of operative dentistry. The introduction of fiber-reinforced composite has provided a considerable opportunity to modify material's behavior and to enhance the response of existing materials. Aim: The aim of the study is to comparatively evaluate the efficacy of fiber-reinforced composite resins and nanohybrid resin impregnated with glass fibers as postendodontic restoration in molars. Materials and
Methods: Fifty patients with deep occlusal carious lesion requiring root canal treatment were selected and treated. For postendodontic restoration, it was divided into Group A (Interlig) and Group B (ever-X posterior) which were eventually restored according to the manufacturer's instructions. Patients were recalled for evaluation at 3-, 6-, 12-month interval. The restorations were evaluated according to modified United States Public Health Service Criteria. Statistical Analysis: Chi-square test was used for intergroup comparison.
Results: A statistically significant difference was noted in terms of fracture of tooth and ever-X posteriors proved to be a superior material and no statistically significant difference observed for marginal discoloration, marginal integrity, fracture of core-build up and secondary caries at the evaluation period of 1 year.
Conclusion: Ever-X posteriors performed better than Interlig group as postendodontic restoration after 1 year of evaluation. Copyright:

INTRODUCTION

Restoration of endodontically treated teeth is one of the most challenging part of the operative dentistry.[1] Fracture susceptibility of root canal treated teeth is more than teeth with vital pulp because of extensive loss of tooth structure.[23] Hence, intracoronal reinforcement of such teeth in posterior region is of great significance in providing fracture resistance.[4]

The gold standard for postendodontic restorations is a full coverage restoration, but there are situations where the tooth is partially erupted, or it needs to be kept for long-term follow-up. In such instances, to prevent the fracture of root canal-treated teeth, a simple, quick, high strength, direct, and cost-effective restorative procedure is desirable.[5]

With the advancement in adhesive technology, it has become possible to create conservative and highly aesthetic restoration with direct bonding to the teeth using resin composite restoration.[6] The polymerization shrinkage induces stresses that may cause the composite to pull away from the cavity margins, resulting in adhesive failure and marginal gap formation.[7] Further, although nanohybrid composite has high strength, it has a comparatively low fracture resistance in high stress-bearing areas such as cusp and marginal ridges.[8] To overcome this problem, various fiber reinforcement systems are used to increase durability and damage tolerance of resin-bonded composite materials.[910]

It is hypothesized that the fibers offer load paths for carrying stresses with directionality of properties such as strength and modulus. They also resist crack formation by acting as a stiff band. Furthermore, the resistance to microcracking is increased and shrinkage as well as creep is decreased.[11]

Glass fibers (Interlig) having a higher modulus of elasticity will result in less elastic deformation during load application, and the compressive and tensile force will be transferred to the material located beneath the fibers, thus having a modifying effect on the interfacial stresses developed along the etched enamel resin boundary.[12] Moreover, glass fibers have also demonstrated their ability to withstand tensile stress and stop crack propagation in composite material.

Ever X posterior, a premixed fiber-reinforced composite by GC consisting of E-glass fibers impregnated inside the nanohybrid composite is fabricated to be used as dentine replacement, in combination with conventional composite as enamel replacement. A substructure is created by the short fibers of ever X posterior, reinforcing composite restoration in large cavities. Furthermore, it is also known to have the classical advantageous features such as stoppage and prevention of crack propagation, fracture toughness equivalent to dentine, polymerization shrinkage reduction, and achievement of reliable bond to conventional composite and tooth structure. Hence, the present study aims to compare the clinical efficacy of endodontically treated teeth restored with conventional nanohybrid composite impregnated with glass fibers, at occlusal third and newer fiber-reinforced composite resin (ever X posterior) in molars.

The null hypothesis for this study was that there will be no difference in clinical performance of fiber-reinforced composite resins and nanohybrid resin impregnated with glass fibers at 3-month, 6-month, and 1-year interval.

MATERIALS AND METHODS

The study was conducted in the Department of Conservative Dentistry and Endodontic after obtaining Institutional Ethical clearance (SVIEC/ON/Dent/BNPG-15/D16031). Fifty patients with a minimum of one deep occlusal carious lesion requiring root canal treatment were included in the study, and written informed consent was obtained. Thus, a total of 50 restorations were performed. The sample size estimation was done using SPSS 18.0 software (statistical package for social sciences, (Armonk, NY, USA: IBM Corp)). The minimum sample required in each group was 20 with total sample size of 40 achieving 80% power of the study. Anticipating the loss to follow-up, 20% increase in the actual number of samples was done.

Selection criteria

Patients aged 18–60 years with primary endodontically treated molar with one surface defect and only those patients ready to sign the consent letter were included in the study. The tooth in which root canal therapy needed to be kept for observation for a longer duration and the tooth where the evaluation of the healing of periapical lesion was needed before proceeding with full coverage restoration were also included. Patients with poor oral hygiene, severe or chronic periodontitis, heavy bruxism and other parafunctional habits, malocclusion, fractured or visibly cracked teeth, tooth with open apex, resorptive defect, calcified canals, and serving as an abutment were excluded.

A total of 50 blinded subjects were assigned to the groups randomly using computer generated random number table. Allocation sequence was concealed from researchers who were part of the study to reduce bias. Operator enrolled the participants and assigned them for intervention according to the allocated group.

Group A: Interlig (E-Glass Fibers mixed with nanohybrid composite)

Group B: Ever-X posterior (Premixed Glass fiber-reinforced composite).

All the teeth were treated by principal investigator. Immediately after the obturation of root canal system using AH plus sealer and Gutta percha, the postendodontic restorations were placed as per the allotted group.

After shade selection, bonding agent was applied in the cavity with the help of applicator tip and light cured for 10 s. After this, flowable composite (Wave MV, SDI, Baywater, Australia) was placed on the floor of pulp chamber followed by nanohybrid composite (Solare-X, GC Corporation, Tokyo, Japan) with the help of the Teflon coated instrument by incremental layering technique (2 mm thick layers).

For Interlig Group (Angelus) (Group A), a piece of glass fiber was then adapted on the occlusal one third using flowable composite in buccopalatal/lingual direction. The combination was then light cured for 30 s using a Blue phase light cure unit (Vivadent, Schaan, and Lichtenstein). The exposed fiber surface was then covered with nanohybrid composite and light cured for 30 s.

For Ever-X Posterior Group (GC Corporation, Europe) (Group B), ever-X posterior was placed on the occlusal one third using a flowable composite and the combination was light cured for 30 s using a Blue phase light cure unit. A layer of nanohybrid was placed on top of this fiber-reinforced composite to cover it followed by curing for 30 s.

Subsequently, finishing and polishing of the restorations in both the groups were done using Shofu finishing and polishing kit (Shofu INC, Japan). Patients were then instructed to maintain proper oral hygiene. All the restorations were clinically evaluated after 3 months, 6 months, and 1 year by a blinded investigator other than the operator who placed the restoration, using modified United States Public Health Service (USPHS) criteria as first described by Cvar and Ryge for marginal discoloration, marginal integrity, fracture of core build up, fracture of tooth and secondary caries. Both the patient and the investigator were unaware of the materials used in this double-blinded study. All evaluations were carried out under dental operating light using flat-surface mouth mirrors and dental explorers.

The results obtained were tabulated and sent for statistical analysis wherein P value and Chi-square value were calculated and P value for the statistical significance was taken as <0.05 and <0.001 as highly significant.

RESULTS

Out of the 50 patients treated, 30 were male, while 20 were female, ranging in age from 18 to 60 years with a mean age of 40 years. The follow-up considered in the study was at 3 months, 6 months, and 1 year. At all three time intervals, 10 out of 50 patients did not turn up for the follow-up. Thus, the dropout percentage was 20%. After making allowance for the dropouts, a total of 40 restorations in 40 patients were considered. Intergroup comparison was done using modified USPHS criteria, and P value for the statistical significance was taken as <0.05.

Table 1 shows the comparative data for marginal discoloration, marginal integrity, fracture of core build up and retention, tooth fracture, and secondary caries between Interlig (Group A) and ever-X Posterior (Group B) groups at different evaluation periods, respectively. There was no statistically significant difference in terms of marginal discoloration, fracture of core build up and retention as well as secondary caries at any interval of time. However, in terms of marginal integrity, a clinically significant difference was very well evident showing Group B to be superior than Group A.

Table 1

Evaluation of materials using modified USPHS* criteria at all the time periods

Category	Material	Time Period
		3 months				6 months				1 year
		A(%)	B(%)	C(%)	D(%)	A(%)	B(%)	C(%)	D(%)	A(%)	B(%)	C(%)	D(%)
Marginal Dis-coloration	Group A	15 (75)	5 (25)	0 (0)	0 (0)	10 (50)	11 (55)	8 (40)	9 (45)	5 (26.3)	10 (52.6)	2 (10.52)	2 (10.52)
	Group B	15 (75)	5 (25)	0 (0)	0 (0)	1 (5)	1 (5)	0 (0)	0 (0)	9 (45)	10 (50)	1 (5)	0 (0)
		P: 1				P: 0.55				P: 0.32
Marginal Integrity	Group A	15 (75)	4 (20)	1 (5)	0 (0)	9 (45)	8 (40)	2 (10)	1 (5)	7 (36.84)	6 (31.57)	2 (10.52)	4 (21.05)
	Group B	16 (80)	4 (20)	0 (0)	0 (0)	14 (70)	6 (30)	0 (0)	0 (0)	11 (55)	7 (35)	1 (5)	1 (5)
		P: 1.032				P: 4.373				P: 3.076
Fracture of core build-up and retention	Group A	20 (100)	0 (0)			20 (100)	0 (0)			19 (100)	0 (0)
	Group B	20 (100)	0 (0)			20 (100)	0 (0)			20 (100)	0 (0)
		P: 1				P: 1				P: 1
Tooth Fracture	Group A	20 (100)	0 (0)			19 (95)	1 (5)			13 (68.42)	6 (31.57)
	Group B	20 (100)	0 (0)			20 (100)	0 (0)			19 (95)	1 (5)
		P: 0				P: 1.026				P: 4.674
Secondary Caries	Group A	20 (100)	0 (0)			19 (95)	1 (5)			16 (84.21)	3 (15.78)
	Group B	20 (100)	0 (0)			20 (100)	0 (0)			19 (95)	1 (5)
		P: 1				P: 0.55				P: 0.32

*USPHS – United States Public Health Service

The result of the current study in terms of tooth fracture showed that at the interval of 3 months, there was absolutely no fracture in any of the two groups. At the interval of 6 months, only 1 sample had undergone fracture in Group A and no fracture of sample was evident in Group B whereas about 6 samples in Group A and 1 sample in Group B was reported with a tooth fracture at the interval of 12 months. A statistically significant difference was noted in terms of fracture of tooth and Ever-X posteriors proved to be a superior material at the evaluation period of 1 year.

DISCUSSION

The introduction of fiber-reinforced composite (FRC) has provided a considerable opportunity to modify material's behavior and to enhance the response of existing materials. It is highlighted that the E-glass fibers made of alumina-borosilicate glass undergo stress-modifying effect by absorbing and distributing the forces to the tooth which is said to happen due to the monoblock created between the dentine and the restorative material.[1314]

In the current study, incremental placement technique was used along with the flow of composite at the floor of the pulp chamber which acts as an ”elastic buffer” or ”stress breaker,” thereby helping to relieve contraction stresses and improve marginal integrity.[15] This layer further reduces the thermo-elastic mismatch between the components.[1116]

Various researchers such as Eapen et al., Kimarh et al., and Ellakwa et al. in their studies on influence of fiber position on flexural properties and strain energy of a FRC proved previously that the resistance to fracture of teeth increased significantly when the fibers were placed on the occlusal surface of the restoration from buccal to lingual direction. In addition, placement of fibers on the occlusal surface helps to keep the buccal and lingual cusps together, resulting in higher fracture resistance.[17181920] Hence, in the present study, the same location of the fiber was followed which was later covered by the conventional nanohybrid composite on top of it.

Neither of the composite restoration filled with Interlig or ever-X posteriors were completely lost. However, the study showed a statistically significant difference in terms of fracture of tooth at the evaluation period of 1 year and ever-X posteriors proved to be a superior material. This may be due to the better mechanical property of ever-X posteriors as they consist of short randomly arranged E-glass Fibers incorporated in resin matrix containing barium glass fillers which provides an isotropic reinforcement effect in multiple directions instead of just one or two directions.[1217] Furthermore, 3 mm of critical length of fiber in FRC substructure is known to have a beneficial effect on fracture resistance by deflecting the path of fracture away from the roots.[417] Second, the strong adhesion between the resin and the silanated fibers in ever-X Posteriors minimizes the shrinkage in horizontal direction after placement, maintaining the marginal integrity of the restoration. Furthermore, the synergistic effect of the ever-X posterior and nanohybrid composite helps to create a bilayered restoration that can withstand double the load of a restoration made from conventional composite alone.[17]

The inferior performance of the Interlig group in terms of fracture of tooth may be attributed to the discontinuous phase generated with the continuous polymer resin matrix due to the mixing of E-glass Fibers separately to the nanohybrid composite at the time of restoration. Second, there is a high chance of void formation which is known to create huge oxygen-inhibited areas within the FRC complex and hence lowers the flexural resistance of the Interlig-Fibers.[1721] Furthermore, the 3-mm length of E-glass Fibers when placed bi-directionally provides the orthotropic reinforcement in just two directions. Furthermore, the glass fibers being rigid are difficult to adapt closely to the teeth, which may result in uneven thickness of the composite material, thus resulting in decreased functionality of the reinforced composite in clinical conditions.[1722] Finally, the placement of fibers is a cumbersome, technique-sensitive, and time-consuming procedure.[5]

The result showed no statistically significant difference between the two groups in terms of marginal discoloration, marginal integrity, fracture of core-build up and retention, and secondary caries; however, a clinically significant difference was very well evident showing ever-X posteriors to be superior to Interlig group in terms of marginal integrity.

The result is in accordance with the study conducted by Moezizadeh et al.[3] in which the effects of fiber and its orientation on fracture resistance of composite restorations in root-filled teeth were evaluated.

Limitations of the present study include short follow-up period. Further studies involving restoration of both the marginal ridges in badly mutilated teeth are required with long-term follow-up period.

CONCLUSION

Within the limitations of this study, it can be concluded that although there was no statistically significant difference noted in terms of marginal discoloration, marginal integrity, fracture of core build up, and secondary caries at any interval of time among the two groups, there was a statistically significant difference in terms of fracture of teeth at 12-month evaluation time showing ever-X posterior to be better than Interlig E-Glass Fiber group as postendodontic restorative material. Hence, ever-X posterior group can be successfully used to restore endodontically treated tooth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.