Clinical performance of Class I nanohybrid composite restorations with resin-modified glass-ionomer liner and flowable composite liner: A randomized clinical trial.

BACKGROUND: Liners play a vital role in minimizing polymerization shrinkage stress by elastic bonding concept and increase the longevity and favorable outcome for composite restorations. AIMS: The aim of this study was to evaluate the clinical performance of nanohybrid composite restorations using resin-modified glass-ionomer and flowable composite liners. SETTINGS AND
DESIGN: A single-centered, double-blinded randomized clinical trial, with split-mouth design and equal allocation ratio that was conducted in the Department of Conservative Dentistry and Endodontics.
MATERIALS AND METHODS: In forty patients, a total of eighty Class I restorations were placed with resin-modified glass-ionomer cement (RMGIC) liner (FUJI II LC, GC America) in one group and flowable composite liner (smart dentin replacement/SDR, Dentsply Caulk, Milford, DE, USA) in another group. All restorations were clinically evaluated by two examiners, immediately (baseline), 3, 6, and 12 months using US Public Health Service modified criteria. STATISTICAL ANALYSIS USED: Statistical analysis was performed using McNemar's test (P < 0.05).
RESULTS: There was no significant difference in the color match, marginal discoloration, surface roughness, and marginal adaptation. Restorations with RMGIC liner group show 20% Bravo scores on anatomic form at 12 months but are still clinically acceptable.
CONCLUSION: Nanohybrid composite restorations with RMGIC (Fuji II LC) and flowable composite liner (SDR) demonstrated clinically acceptable performance after 12 months.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Increasing demands for esthetic restorations make composite as an alternative in direct posterior restorations.[1] Composite materials allow “minimum invasive technique” and further reinforce remaining tooth structure. Clinical reliability and longevity of composite restorations in stress-bearing posterior teeth area depend only when these materials sustain polymerization stress. However, polymerization shrinkage poses a problem leading to volumetric reduction within the material at the restoration-tooth interference.[23]

Polymerization stress results in postoperative sensitivity, marginal staining, microleakage, gap formation, thus imposes its limitations in the application of direct restorations.[4] Many techniques and newer materials have been introduced to reduce polymerization stress such as incremental layering technique, soft-start polymerization, and use of low modulus of elasticity liner as an intermediary layer between restoration and tooth structure.[56]

When the remaining dentin thickness is <2 mm, liners are usually applied for pulp protection. Glass-ionomer and flowable composite liners are commonly used between tooth structure and composite restoration. This technique is commonly known as sandwich technique.[78]

Recently introduced nanofilled composites have nanosized filler particles to increase weight percentage of composites. Nanofilled composites have certain advantages such as reduced polymerization shrinkage, increased fracture and wear resistance, and high polish and polish retention in stress-bearing areas. Tetric N-Ceram is one such nanohybrid composite which was introduced a few years back.[910]

Smart dentin replacement (SDR) material is a recently introduced flowable composite which can be used as liner in Class I and Class II restorations. SDR resin provides an approximate 20% reduction in volumetric shrinkage and almost an 80% reduction in polymerization stress compared to a traditional resin system.[11]

GC Fuji II LC material, a resin-modified glass ionomer, can be used as a liner under the restorations, to reduce to some extent, the polymerization shrinkage stress of composite restorations. Basically, these liners either flowable composite or resin-modified glass ionomer provide better adaptation and act as a flexible stress-absorbing layer between restoration and tooth.[12]

Randomized clinical trials are considered as a gold standard test for measuring the long-term performance of the materials in patients.[5] Thus, the aim of this randomized clinical trial is to check the clinical performance of nanohybrid composite (Tetric N-Ceram) either with flowable composite liner (SDR) or with resin-modified glass-ionomer liner (GC Fuji II LC).

The null hypothesis of this study is that there is no difference in clinical performance of Tetric N-Ceram at 12-month period whether it is used with SDR/GC FUJI II LC liner.

MATERIALS AND METHODS

Subjects

This study was approved by the Ethical Committee (RC. No. NDC/PG-2013-14/EC/2014) and was conducted in the Department of Conservative Dentistry and Endodontics. This randomized clinical trial has been registered in the Clinical Trial Registry of India (CTRI/2015/02/005539).

Based on proportions detected by two independent groups, sample size estimation was calculated using a priori by G*Power 3.1.9.2 software (Faul et al. 2007). The minimum sample size of each group was calculated, following these input conditions: Power of 0.9 and P ≤ 0.05. To compensate for participants dropouts during follow-up, the sample size was set at forty restorations per group.

Therefore, forty patients with the following inclusion criteria were enrolled, patients with:

Age group between 18 and 40 years who require at least two Class I restorations

Good oral hygiene

Normal occlusion

Occlusal caries with the International Caries Detection and Assessment System score 4.

The exclusion of patients was based on the following criteria:

Subjects with fewer than twenty teeth

History of existing tooth sensitivity

Bruxism

Known allergy to resin-based materials

Pregnancy or breast-feeding

Chronic use of anti-inflammatory, analgesic, and psychotropic drugs.

Randomization

As it is a split-mouth design, the same patient received both liners. At the beginning of the procedure, a block of four numbers was chosen randomly from random number table. In the four-number table, if the first number that was chosen was even, then flowable composite liner was placed in the first tooth based on the order of the tooth and the other tooth received resin-modified glass-ionomer cement (RMGIC) liner. If the number was odd, then RMGIC liner was given to the first tooth and the other tooth received SDR liner. Finally, both the teeth were restored with nanohybrid composite.

Operative procedure

All operative procedures were performed by the same operator. Before restorative procedures, periapical radiographs of the teeth to be restored were taken. Vitality tests were done using electrical pulp tester. After shade selection, the operative field was isolated with a rubber dam. Cavity design was restricted to eliminate carious lesion using #245 carbide bur (Diatech, Coltène/Whaledent) under constant cooling. Application of SDR liner (Dentsply Caulk, Milford, DE, USA), RMGIC liner (GC Fuji II LC, GC Corporation, Tokyo, Japan), and Tetric N-Ceram (Ivoclar Vivadent, Schaan, Liechtenstein) composite was placed according to manufacturer's instructions. Details of the materials used are summarized in Table 1. The composite material was applied using the oblique layering technique, with each layer not exceeding 2 mm. Each layer was cured for 20 s using the LED curing light unit (Bluephase c8; Ivoclar Vivadent AG, Schaan, Liechtenstein) with a light intensity of 800 mW/cm2. The restorations were contoured using a superfine diamond bur (Diatech, Coltène/Whaledent) under an air-water coolant, and finally finishing and polishing of the restorations were done using Soflex discs.

Table 1

Materials used in this study

Outcome evaluations

In the present study, the primary outcome measure was the clinical performance of the restorations which includes functional and esthetic aspects. The secondary outcome measures were measured using modified US Public Health Service criteria for retention, color match, marginal discoloration, anatomic form, secondary caries, surface roughness, marginal adaptation, and postoperative sensitivity by two different evaluators.[13] Both the evaluators did not know which liner was used in each tooth, thus provided the blinding of the evaluator. The evaluation was done at baseline, 3-, 6-, and 12-month period. The criteria of the evaluation for each outcome are detailed in Table 2. Any discrepancy between the evaluators in rating was discussed, and the consensus was reached.

Table 2

US Public Health Service Modified Ryge Direct Evaluation Criteria Rating System

Statistical analysis

Statistical analyses were carried out between each outcome in between the groups at 3-, 6-, and 12-month time period using McNemar's test. Significant P value was set at ά <0.05.

RESULTS

Totally, forty patients were recruited in the study with two restorations in each patient using two different liners which comprised eighty restorations. Of these, forty patients at 6-month follow-up, there was one dropout, and at 12-month time period, three dropouts were seen. The dropouts were mainly because of the relocation of the patients. Flow diagram of the trial participants is shown in Figure 1.

Figure 1

Consort flow diagram

In this present study, at 3-month time period, 40 restorations were evaluated in each group, whereas at 6 months, it was 39 restorations in each group and 37 restorations were evaluated at 12-month time period in each group. At 3-, 6-month time period, there was no significant difference in any of the secondary outcome measures in either of the group [Table 3]. After 1 year interval, there was a difference in scoring for surface roughness, marginal discoloration, marginal adaptation, and anatomic form. More ά ratings were recorded for these secondary outcomes in flowable composite liner group. Even though ά ratings were more, there was no statistically significant difference between the two groups and restorations are clinically acceptable.

Table 3

Summary of the clinical findings of restorations using US Public Health Service criteria at the end of 1 year

DISCUSSION

In the present study, the dropout ratio was only 5%, it does not affect the results of the present study. Many in vitro studies have shown that the flowable composite liners and RMGIC liners act as a stress-absorbing layer to decrease polymerization shrinkage stress. The concept of stress absorption varies with flowable composite liner and RMGIC liner.[141516]

In the literature, clinical trials of Lopes et al.,[17] Banomyong et al.,[18] Loguercio et al.,[19] and Burrow and Tyas[20] have evaluated the clinical performance of posterior composites at different time periods. In these studies, they have tested different types of posterior composites with different types of adhesive techniques and tested composites such as Prodigy condensable composite, Filtek Supreme XT, Filtek Z 250, and Filtek Supreme XT, and stated that there is no difference in the clinical performance of composites in the posterior restorations.

The present randomized clinical trial was designed according to the guidelines of consolidated standards of reporting clinical trials (CONSORT guidelines). The aim of this clinical trial was to test the clinical performance of nanohybrid composite with single adhesive technique but with varying liners. During recent years, nanohybrid composite is gaining popularity because of their advantages such as reduced polymerization shrinkage, fracture and wear resistance, and high polish and polish retention in stress-bearing areas.[21]

The results of the present study have also shown that the clinical performance of the composite in relation to retention, color match, marginal adaptation, anatomic form, surface roughness, secondary caries, marginal discoloration, and postoperative sensitivity has no significant difference with SDR liner/GC Fuji II LC liner.

A randomized clinical trial by Banomyong et al.[18] and Ernst et al.[22] have stated that there is no difference in the clinical performance of composite with or without RMGIC liner/flowable composite liner.

In the present study, we have employed the study design with two different liners to test the clinical performance of composite, rather than with or without liner as the liners act as stress-absorbing layer to decrease polymerization shrinkage stress. Even our results have shown that there is no difference in the clinical performance of the restoration with RMGIC liner and flowable composite liner. The secondary outcomes such as marginal discoloration, surface roughness, marginal adaptation and anatomic form, and percentage of alpha ratings were more for the flowable composite liner. The more alpha ratings for these outcomes in flowable composite liner group do not have any significant difference in the results. The other secondary outcomes were retention, color match, postoperative sensitivity, and secondary caries; there was no difference in the alpha ratings of either of the groups.

A study by Burrow and Tyas[20] has stated that there is no significant difference in postoperative sensitivity of a composite restoration with or without RMGIC liner.

There was only a change in scoring with Bravo scores for surface roughness (5.4%), marginal adaptation (2.7%), anatomic form (5.4%), and marginal discoloration (2.7%) in RMGIC liner group, but this was not a statistically significant difference. All the restorations were clinically admissible.

CONCLUSION

Within the limitation of this study, it was concluded that the secondary outcomes such as retention, secondary caries, postoperative sensitivity, marginal adaptation, marginal discoloration, color match, anatomic form, and surface roughness were clinically acceptable for Tetric N-Ceram restorations with flowable composite liner and RMGIC liner.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.