Introduction

Restorative treatments aim to restore the lost dental structure with appropriate materials. The treatment of dental caries results in a restoration structure [1, 2]. In the foundation, composite and amalgam are the two types of material used. Indications for the material vary according to the location of the tooth, the forces loaded on it, and the para-functional habits and oral hygiene of the patient. Current developments in composite restorations have broadened the areas of use [3].

For the complete polymerization of composite resins hardened with light that is generally preferred during the restoration of cavities, it is necessary to use a certain thickness. The maximum thickness defined for this has been determined as 2mm [4]. Bulk-fill composites, which have similar content to conventional resin-based composites, have recently come into clinical use. These are materials in layers 4 or 5mm thickness that can be polymerized in a single step. Thus, although the treatment process is more rapid and simple, the contamination risk is overcome during the placement of the layers [5, 6].

Polymerization with a light source in a single session entails problems in greater thicknesses of bulk-fill composites, such as polymerization shrinkage stress and providing sufficient polymerization. To overcome similar problems in these composites, the organic matrix has been modified, the monomer size has been increased, and although there are differences between manufacturers, inorganic fillers have been added. High-branching methacrylate, aromatic UDMA, and hydroxyl free BisGMA have been added to the organic part, and ytterbium trifluoride, barium glass, and zirconium particles to the inorganic filler content [5]. However, composite elements such as BisGMA, UDMA, TEGDMA, and EBPDMA monomers are found in the organic structures in the base.

Bulk-fill composites are containing patented urethane dimethacrylate with photoactive groups, which aim to control polymerization kinetics (eg, Smart Dentin Replacement (SDR) technology). Ivocerin starter has been reported to have been added to accelerate and increase polymerization depth with Tetric Evo Ceram as an additional camphorquinone/amine starter. In other bulk-fill materials, no difference has been reported in respect of starter systems. A simple method used by all manufacturers to increase polymerization depth is the reduction of the amount of filler with an increase in translucency [7].

Bulk-fill composites can be classified according to viscosity as low and high viscosity. As materials with low viscosity have lower mechanical properties, the restoration must be finished using a posterior composite in the uppermost layer. Materials with high viscosity can be polymerized without the need for a different composite in the final layer [5, 8].

Evaluations of the physical and mechanical properties in newly-developed restorative materials such as decrease in the microhardness of a restorative material may lead to its breakdown or deterioration, can be determined in in-vitro studies by fixing the factors beyond the conditions studied. With in-vitro studies, an idea can be obtained about several properties of the material without it being used within the mouth. However, as the main aim of restorations is for use within the mouth, several different factors can affect, such as micro-organisms, chemical agents, and oral fluids, primarily saliva. Therefore, after sufficient in-vitro studies, materials must be processed in a series of in-vivo studies [9].

For a clinical study to be meaningful and to be able to provide standardization of follow-up, internationally accepted criteria must be used. The International Modified Ryge Criteria (USPHS-Modified United States Public Health Service), FDI (World Dental Federation) criteria and CDA (California Dental Association) criteria have been defined, and are widely used for the evaluation of restorations.

The evaluation of the clinical acceptability of many restorations is based on the degree of success of restorations with the USPHS criteria. Criteria such as color compatibility, edge discoloration, retention, anatomic form, edge compatibility, surface structure, secondary decay, and postoperative sensitivity, which are of clinical importance for dental restorations, have been designed for evaluation. According to the modified USPHS criteria, defined characteristics in the restoration are evaluated with Alpha, Bravo, Charlie scores according to the evaluation of the patient, radiographs, and visual examination with assistive manual instruments. These scores are defined as Alpha indicating the best score and Charlie the worst [10, 11].

The FDI criteria were published in 2007, defined as for the direct and indirect evaluation of restorations. The evaluation of restorations is classified under 3 main headings as aesthetic, functional, and biological criteria, and by separation into sub-groups within each group. The final points of the 3 main categories are determined by the scores of the sub-categories and considering the worst scores of the group. Scoring is applied from 1 to 5 during evaluation. In the evaluation of these criteria, scores 1, 2, and 3 indicate that the restoration is clinically sufficient, 4 points indicate that it is clinically insufficient but can be repaired, and a score of 5 indicates that it is completely clinically insufficient. Thus results are obtained as to whether the restoration is acceptable or unacceptable, and if it is unacceptable, whether or not it can be repaired. Those which can be repaired are defined as partially successful and those which can not be repaired as completely unsuccessful [12].

This study aimed to compare and evaluate the clinical characteristics of different bulk-fill composites with conventional composites used in the restoration of interface caries.

Materials and Methods

Patient selection

This study was planned as an in-vivo study within the framework of the defined criteria. Before the study, approval was granted by the Local Ethics Committee of the Dentistry Faculty of Dicle University (decision no: 2017/8). The study was conducted in the Restorative Dental Treatment Clinic of Dicle University. Informed consent was obtained from all the patients included in the study.

From a total of 120 posterior teeth with interface caries, 30 were selected at random to form the control group and the remaining 90 teeth with interface caries formed the study group.

Before treatment, radiographic and clinical evaluations were made of both groups. Group 1 (control group) was applied with a clinically accepted universal composite (Gradia Direct Posterior/Gradia -DP). Group 2 was applied with bulk-fill composite with Ivocerin starter added to camphorquinone (Tetric Evo Ceram Bulk-Fill/Ivoclar Vivadent). Group 3 was applied with a bulk-fill material placed in the cavity with a sonic method (SonicFill 2Bulk-Fill/Kerr). Group 4 was applied with a bulk-fill composite material with a camphorquinone starter (Filtek Bulk-Fill/3M ESPE). The selection of the restorative material to be applied to the teeth was determined randomly.

Inclusion criteria

The patients included in the study were those who provided informed consent, had good oral hygiene, were open to receiving information about dental caries and the benefits of restoration, agreed to attend follow-up examinations at certain intervals, had at least one interface caries, that the decay could be restored was confirmed clinically and radiographically, and had contact between the teeth and opposite teeth.

Clinical protocol

The vitality of the teeth to which the restoration was to be applied was evaluated using a digital vitalometer (Digitest II, Parkell Inc, USA). Local anaesthetic was applied before the procedure or as required during the procedure, taking into consideration the depth of the decay and the pain threshold of the patient. In the tooth with the decay, a cavity was opened with a diamond drill and fissure burr with the tooth surface underwater cooling with an aerator. The cavity was cleaned with a steel drill with a slowly rotating micromotor. This process was continued until there was no decay remaining. The cavity was then washed with water and dried with sterile cotton pellets. Cotton rolls and saliva absorbers were used to provide isolation. The depth of the opened cavity was evaluated when the procedure was finished, and in a deep cavity, calcium hydroxide was applied to the deepest point to form a superficial necrosis layer and repair dentin. The cavity layer above was covered with the material. A sectioned matrix band (Palodent V3/Dentsplay, USA) was applied to the cavity with a wedge of appropriate width, and after application of the bonding agent, the relevant composite material was applied to the cavity following the manufacturer’s instructions.

Group 1; After preparation of the teeth, the defined self-etch adhesive system (Clearfil S³ Bond- Kuraray, Sakazu, Kurashiki, Okayama, Japan) was applied to the cavity wall in accordance with the manufacturer’s instructions in the guide to the material, using a brush for 10 secs then after waiting 20 secs isolated from blood and saliva, it was dried for a further 5 secs with air spray and another thin layer of the bond was applied. Polymerization was applied with an LED light source at 400-550 nm wavelength for 10 secs. Using the incremental layering technique, Gradia Direct Posterior composite (GC Corp, Tokyo, Japan) was applied to the cavity in 2mm layers and each layer was polymerized with light for 20 secs.

Group 2; After opening the cavity and completing the adhesive process in the same manner as for Group 1, Filtek bulk-fill (Filtek Bulk-Fill/3M ESPE) single-use capsule material was placed in an application gun and was applied to the cavity in a single layer of 4-5mm. During placement, the tip of the single-use capsule was placed close to the deepest point, and care was taken when withdrawing. Thus it was aimed to avoid unwanted gaps in the composite.

Group 3; Tetric Evo Ceram Bulk-Fill composite (Ivoclar Vivadent Schaan, Liechtenstein) was applied to the prepared cavity in 4mm layers and was condensed and shaped with appropriate manual instruments. Then polymerization was applied with an LED light source at 400-550 nm wavelength for 20 secs to the occlusal, buccal and lingual surfaces.

Group 4; Sonic 2 Bulk-Fill was applied with an appropriately shaped handpiece adapted for the unit. The tips of the single-use composite were placed on the handpiece as defined in the instructions. Placement of the material, which has a level of application from 1 to 5 was achieved in all the cavities at level 3 at the standard rate at a thickness of 4-5mm. Then, polymerization was applied with an LED light source at 400-550 nm wavelength for 20 secs to the occlusal, buccal and lingual surfaces.

When polymerization was completed, the finishing and polishing procedures of the restorations were applied first with surface smoothing using fine-grained diamond burrs with yellow bands together with water cooling. Occlusion compatibility of the restorations was obtained and composite sandpaper was used on the interfaces. Then the polishing procedures were completed using Arkansas stone, yellow composite varnish rubbers, and polymax-impregnated varnish felt (TDV Dental), respectively. The edges of the restoration were checked very often with a fine-tipped probe. Following the procedures, oral hygiene education was given to patients by explaining dental care related to oral hygiene health and it was aimed to raise awareness in the patients.

Clinical evaluation

Patients were requested to attend the clinic for evaluations at 3, 6, 9, and 12 months after the application of the restoration. Evaluations of the restorations were made according to the FDI criteria together with the modified USPHS criteria. The teeth with the restorations were dried with pressurized air spray and isolated with cotton rolls, then examined with a mirror and probe. When necessary, radiographs were taken and the vitalometer device was used.

The scoring of the FDI criteria was as follows: 1=the restoration is excellent or there is no clinical deficiency, 2=excellent if sufficient characteristics can be obtained after a small change, 3=can be used clinically but there are 1 or more insufficient characteristics, 4=the restoration does not have sufficient characteristics but can be used clinically with repair, 5=completely insufficient clinical characteristics and there is an indication for change.

If there was the loss of retention in the restoration, it was only evaluated in respect of this criteria without examination of the other criteria, and it was not included in subsequent evaluations. For restorations scored as 4 points, evaluations were terminated after repairing. In localized defects, conditions that can be repaired include the addition of filling material to small openings and fractures, changing a part of the restoration, or when discolored areas are limited.

Statistical analysis

Data obtained in the study were analyzed statistically using IBM SPSS Statistics vn 22 software. In the evaluation of the FDI criteria, the Shapiro Wilk test, Friedman’s Two-Way ANOVA, and the Kruskal Wallis H-test were used. Pearson Chi-square analysis and the Wilcoxon test were used in the evaluation of the USPHS criteria. A value of p<0.05 was considered statistically significant.

Results and Discussion

All the patients attended the follow-up appointments, but 1 patient in Group 3 presented in the 5th month with complaints of severe night-time pain and was referred to the endodontics clinic with the indication for canal treatment. Therefore, the evaluation of Group 3 was completed with 29 restorations and the overall total was 119.

FDI criteria findings

The results obtained from the evaluations of the restorations with the FDI criteria were compared within and between the groups and analyzed statistically.

The statistically significant results of the inter-group comparisons in Table 1 and of the intra-group evaluations are shown in Table 2.

Table 1. The statistically significant results of the inter-group comparisons.

Table 2. The statistically significant results of the intra-group