Journal of Oral and Maxillofacial Radiology

: 2014  |  Volume : 2  |  Issue : 1  |  Page : 21--25

Comparison of radiopacities of different flowable resin composites

Derya Yildirim1, Rabia Banu Ermis2, Ozlem Gormez1, Gul Yildiz2,  
1 Department of Dentomaxillofacial Radiology, Suleyman Demirel University, Isparta, Turkey
2 Department of Restorative Dentistry, Suleyman Demirel University, Isparta, Turkey

Correspondence Address:
Derya Yildirim
Department of Dentomaxillofacial Radiology, Faculty of Dentistry, Suleyman Demirel University, Dogu Kampus Cunur - 32260, Isparta


Objectives: Radiopacity can facilitate diagnostic observations adjacent to flowable resin composites. The aim of this study was to evaluate the radiopacity of the current low viscosity flowable resin composites and to compare them with human dental tissues. Materials and Methods: Five specimens of seven flowable light cured composite materials with a thickness of 2 mm were prepared and radiographed alongside an aluminum stepwedge, human enamel and dentin. Three standart occlusal radiographs for each material were taken with exposure time of 0.32 seconds and focus-film distance of 40 cm. Films were processed in an automatic device, and digitized using a desktop scanner. Mean gray values of the materials, stepwedge, enamel and dentine were measured using Image J software. The data were analyzed using the Duncan multiple range test. Results: The mean gray values of flowable resin composites ranged from 26.61 ± 1.45 to 38.38 ± 1.47. The radiopacity values of the materials evaluated were in decreasing order: G-aenial Flo, Filtek Ultimate Flowable, Flowline, Estelite Flow Quick, Leaddent Flow, Supraflow, Bright Light Flow. All flowable resin composites, except Bright Light Flow, demonstrated significantly greater radiopacity values than 2 mm of the aluminum scale and dentin (P < 0.05). The radiopacity of only one flowable composite, G-aenial Flo, was found to be significantly higher from enamel (P < 0.05). Conclusions: All investigated materials presented radiopacity values above the minimum recommended by the international organization for standardization.

How to cite this article:
Yildirim D, Ermis RB, Gormez O, Yildiz G. Comparison of radiopacities of different flowable resin composites.J Oral Maxillofac Radiol 2014;2:21-25

How to cite this URL:
Yildirim D, Ermis RB, Gormez O, Yildiz G. Comparison of radiopacities of different flowable resin composites. J Oral Maxillofac Radiol [serial online] 2014 [cited 2020 Apr 3 ];2:21-25
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Flowable composite resins (FCRs) are light-cured, low viscosity restorative materials which have become popular since 1995. Hybrid composite with reduced filler level and a narrower particle size distiribution enables this resin composite to flow readily, spread uniformly and adapt intimately to prepared tooth surfaces. [1],[2] Because of their greater ease of adaptation, the clinicians prefer to use flowable composites as base or liner under the resin composite restorations. The materials are also recommended for cervical lesions, restorations in deciduous teeth and in the proximal boxes of Class II restorations. They may also be used to seal pits and fissures in a manner similar to the use of fissure sealents. [1],[2],[3],[4]

Radiopacity is an essential property of all dental restorative materials in order to assess restorations for marginal defects and overhangs, and to evaluate the proximal contour and integrity of the restoration at subsequent recall appointments. [5],[6] Radiopacity of dental materials enables the clinician to make the radiographic diagnosis of secondary caries. The detection of caries under a nonradiopaque restorative material is almost impossible, and would allow the caries process to continue undetected. [2],[6],[7],[8],[9] In case of accidental ingestion or traumatic impaction, radiopacity provides the determination of dental devices or fragments lodged in soft tissues. Also, the location of radiopaque restorative materials that were accidentaly aspired or inhaled can be easily made. [2],[10],[11] Radiopacity of dental materials is usually determined in comparison with the radiopacity of enamel, dentin and aluminum (Al). [6],[11] Most studies revealed that, for optimum contrast, a restorative material with a radiopacity slightly greater than, or equal to, enamel is ideal for detection of secondary caries in radiographs. [2],[3],[5],[11],[12] On the other hand, the radiopacity of dental materials has been standardized by The International Standars Organization (ISO). According to ISO 4049, if a manufacturer claims their product to be radiopaque, its radiopacity must be equal to or greater than that of Al with the same thickness. [13]

Studies evaluating the radiopacity of dental materials are continuing because of the new materials that come on to the market. There are several studies on the radiopacity of composites in the literature; however, few studies regarding the radiopacity of FCRs are available. The aim of this study, therefore, was to evaluate the radiopacity of seven commercially available low-viscosity light-cured FCRs and to compare them with the human dental tissues.

 Materials and Methods

Radiopacity of seven low-viscosity light-cured FCRs with a filler content by weight between 55% and 78.5% was investigated in this study. Information provided by the manufacturers' is summarized in [Table 1].{Table 1}

A teflon ring mold with an internal diameter of 5 mm and a depth of 2 mm was placed on a glass slab. Each material was packed into the mould until it was overfilled and then covered with another glass slab. The samples were then light cured for 40 seconds using the exit window of a quartz-tungsten halogen unit (600 mW/cm 2 , Demetron LC, Kerr, Orange, CA, USA) that was placed against the glass slab. Before preparation of the specimens of each group, the light output was checked by a radiometer (Demetron, Danbury, CT, USA). Five samples were made of each FCR material. Specimens with porosities were excluded from the study and replaced to provide five homogeneous specimens of each material.

To obtain enamel and dentin specimens, three freshly extracted non-carious human third molars were mounted in gypsum blocks and then the teeth were sectioned mesiodistally by using a low-speed diamond saw (Microcut125, Metkon, Bursa, Türkiye). The tooth slices involving each enamel and dentin substrate were ground flat with carbide paper and the specimens 2.0 mm in thickness were obtained. The specimens were stored in the incubator at 37°C and in 100% humidity for 24 hours. The tooth slices were kept in distilled water until use.

An aluminium stepwedge (6063 alloy, 98% purity) with six 2-mm thick incremental steps was used as a standard for comparison of radiopacity of the test materials. All the specimens were placed directly on a 57 × 76 mm Ultra-speed occlusal radiographic film (Eastman Kodak Co, Rochester, NY, USA), together with an Al stepwedge and three tooth slices of both enamel and dentin, which were used for comparison [Figure 1]. A 2-mm thick lead sheet was placed under the film in order to prevent back-scattered radiation. All specimens were placed at a 40 cm focus-film distance for 0.32 s in a dental X-ray unit (PlanmecaIntra, Helsinki, Finland) with 2 mm Al equivalent total filtration at 63 Kv, 8 mA. This procedure was repeated in order to obtain three different radiographic sets of the same specimens. The X-ray unit was kept in the same position throughout the experiment. All the radiographs were processed at once in an automatic processor (Dürr XR 24 Beitigheim, Germany) at 28°C for 4.3 minutes with fresh solutions.{Figure 1}

The radiographs [Figure 1] were digitized using a desktop scanner with a transparent adapter (Epson Perfection V700, Japan) at 16-bit gray value and 300 dpi resolution and saved in TIFF format. On each radiographic image, a 20 × 20 pixel region of interest (ROI) was selected on the center of each test material, on dentin and enamel of each tooth specimen and on each step of the stepwedge. The image was enlarged in order to accurately define the enamel and dentin layers. Mean gray values (MGV) of the each test material, stepwedge and enamel and dentine on three digitized radiographs were measured using ImageJ 1.46r software. The mean of three MGVs was accepted as the MGV of test materials.

The mean MGVs and standard deviation of the five identical disc of materials and three human dentine and enamel samples were calculated. The data were analyzed by Duncan's multiple range test using the statistical analysis system (SAS, Cary, NC, USA). A probability of P < 0.05 was considered significant. The radiopacity value of enamel and dentin was considered as the control value.


The means and standard deviations for the MGVs of the restorative materials and enamel and dentin are presented in [Table 2] and [Figure 2]. The MGVs of the FRCs varied among the tested flowable restorative materials (P < 0.05) and ranged from 26.61 ± 1.45 to 38.38 ± 1.47.{Table 2}

All the FRCs tested had radiopacity values greater than the radiopacity of dentine and 2 mm Al (P > 0.05), except for Bright Light Flow that showed MGV similar to the dentin substrate and 2 mm Al (P > 0.05). G-aenial Flo had the highest MGV (38.38 ± 1.47) which was significantly higher than those of human enamel and the other tested materials [P < 0.05, [Table 2], [Figure 2]. G-aenial Flo demonstrated similar MGV to the 4 mm Al (P > 0.05).{Figure 2}

Only one material, Filtek Ultimate Flowable (31.88 ± 1.45), showed MGV similar to enamel (P > 0.05). MGVs of Flowline (31.41 ± 1.60), Estelite Flow Quick (31.30 ± 1.99), Leaddent Flow (31.20 ± 1.32) and Supraflow (28.13 ± 0.95) were lower than the MGV of enamel (P < 0.05), which presented no statistically significant difference among them (P > 0.05, [Table 2]).


The radiopacity determination of dental materials on radiographs were evaluated either by optic densitometry or digital image analysis. [14],[15],[16],[17],[18] Optical density is a logarithmic measure of the ratio of transmitted to incient light through the film image while digital image analysis provides direct record of radiographic density as determined by pixel shade, which is automatically recorded by computer software as a value ranged in 0-255. [19],[20],[21] Digital images can be obtained with either direct or indirect methods and evaluated with the aid of specific software programs. [14] Digital radiographic systems have the advantages of immediate image capture without the need for processing step, image manipulation and enhancement available in software. However, image manipulation such as changes in image resolution might lead to erroneous interpretation due to image degradation. Wenzel et al. [22] evaluated the conventional intraoral radiographs and two digital systems according to investigate the possibility of differentiating the radiopacity of dental filling materials and reported that the digital systems were less reliable than conventional films in this discrimination. Gürdal and Akdeniz [14] compared the radiographic densitometry and indirect digital image analysis for establishing the radiopacity of resin-based restorative materials and showed that the two methods were produced similar results and reported that the digital image analyses is a suitable alternative to transmission densitometry. In our study, FRCs were evaluated on digitized conventional radiographs and according to standardize the radiography procedure focus-to-film distance was set up, such variations about the room temperature and differences in developing solutions were eliminated.

The desirable radiopacity of resin composites is still a controversial issue. Materials with radiopacity lower than enamel might be misinterpreted as secondary caries on radiographic images. [23] When the radiopacity is too high it may obscure details of adjacent anatomy and excessive radiopacity may hide the diagnosis of caries adjacent to the restoration. [6],[12],[24],[25] In connection with a high radiopacity near a less radiopaque area can cause the mach band effect, which produces a visual illusion that enhances the contrast between a light and a darker area, making the dark borderline area darker. [26] Some authors suggested that radiopacity of a material that will be used as a base or liner equal to or slightly greater than enamel is more appropriate to enable secondary caries detection. [11],[12] The clinician expects that a restorative material to be easily identified from dentin radiographically to differentiate the dentin-resin interface and not to misinterpret as decalcified dentin. [27],[28] In this study only one test material, Bright Light Flow (filler content of 56% by weight), showed similar radiopacity with dentin and 2 mm of the aluminum scale while all the other evaluated materials demonstrated significantly higher radiopacities than those of dentin and 2 mm of the aluminum scale (P > 0.05). All the evaluated FRCs fulfill the requirements of ISO 4049 about radiopacity of materials. Among the test materials, only G-aenial Flo had a higher radiopacity than enamel whereas Filtek Ultimate Flowable demonstrated similar radiopacity to enamel, which is stated by various authors as a required feature of a resin composite. [2],[3],[5],[11],[12]

The radiopacity of resin composites depend on the percentage and type of fillers. [5],[6],[9],[29] When the tested FRC materials were evaluated in regard to the percentages of filler content, Supraflow (55%) and Bright Light Flow (56%) that have the lowest filler loading by weight demonstrated the lowest radiopacity. On the other hand, among the materials Filtek Ultimate Flowable (78.5%) that have the highest filler loading by weight demonstrated similar radiopacity to the materials with lower filler loading, Flowline (60%), Estelite Flow Quick (71%), Leaddent Flow (63%) and Supraflow (55%).

Chemical materials composed of fillers with high atomic numbers, such as zinc (Zn, atomic number:30), strontium (Sr, atomic number:38), zirconium (Zr, atomic number:40), barium (Ba, atomic number: 56) and lanthanum (La, atomic number: 57) appear more radiopaque, whereas materials containing fillers such as quartz, lithium-aluminum glasses and silica (silicone dioxide) appear radiolucent so these fillers must be blended with other fillers to produce a radiopaque composite. [1],[6],[20],[30] Zirconia was introduced into dentistry in the end of the 1990s and its usage in dentistry is increasing as a result of its excellent strength, superior fracture resistance and suitable optical properties. [31] Zirconia is currently being used as a material for composites, extracoronal attachments, crowns, veneers, frameworks, dowels, implants, abutments, endodontic posts and orthodontic brackets. [31],[32] The radiopacity of such restorative materials like ceramics [31],[33] and core materials [34] were evaluated by several studies and it was reported that the zirconia containing materials demonstrated the highest radiopacity. Toyooka et al. [35] evaluated the radiopacity of resin composite materials and according to chemical analyses of fillers. The authors suggested that the radiopacity of the composite resin was linearly proportional to the amount of the radiopaque oxide in the filler and zirconium dioxide was radiopacifier equal to or even stronger than bariumoxide.

In this study, the radiopacity of zirconia containing materials Estelite Flow Quick (filler content of 71% by weight) and Filtek Ultimate Flowable (filler content of 78.5% by weight) demonstrated similar radiopacity with barium or glass filler containing FRCs, Flowline (filler content of 60% by weight), Leaddent Flow (filler content of 71% by weight) and Supraflow (filler content of 55% by weight). In the current study, G-aenial Flo presented the highest radiopacity among the tested flowable composites. In a previous study, [23] it was reported that G-aenial Flo showed higher radiopacity than enamel and dentin as similarly found in the current study. Aluminum glass and strontium glass (filler content of 69% by weight) containing material, G-aenial Flo, presented more gray values than the barium glass or zirconia containing FCRs. Despite the various filler types and filler loading of evaluated FRCs, the materials Filtek Ultimate Flowable, Flowline, Estelite Flow Quick, Leaddent Flow and Supraflow demonstrated similar radiopacity in the current study. In relation to this result of the study, the proportional amount of radiopaque glass to silica in the filler composition might be more important than the percentage of filler loading that influences radiopacity.

In conclusion, the FCRs assessed in this study presented different radiopacity values. All investigated materials presented radiopacity values above the minimum recommended by the international organization for standardization. Future studies that evaluate the radiopacity of dental restorative materials according to type, percentage, proportional amount of the radiopaque element in the filler should be undertaken in order to evaluate new restorative material compositions in the market.


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