Development of new radiopaque glass fiber posts

Materials Science and Engineering C 59 (2016) 855–862

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Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec

Development of new radiopaque glass fiber posts Gabriel Furtos a,⁎, Bogdan Baldea b, Laura Silaghi-Dumitrescu a a b

Raluca Ripan Institute of Research in Chemistry, Babes-Bolyai University, Cluj-Napoca, Romania Dep. of Prosthodontics, Faculty of Dental Medicine, Timisoara, Romania

a r t i c l e

i n f o

Article history: Received 27 September 2014 Received in revised form 7 October 2015 Accepted 29 October 2015 Available online 31 October 2015 Keywords: Radiopacity Fiber reinforced post X-ray

a b s t r a c t The aim of this study was to analyze the radiopacity and filler content of three experimental glass fiber posts (EGFP) in comparison with other glass/carbon fibers and metal posts from the dental market. Three EGFP were obtained by pultrusion of glass fibers in a polymer matrix based on 2,2-bis[4-(2-hydroxy-3methacryloyloxypropoxy)-phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) monomers. Using intraoral sensor disks 27 posts, as well as mesiodistal sections of human molar and aluminum step wedges were radiographed for evaluation of radiopacity. The percentage compositions of fillers by weight and volume were investigated by combustion analysis. Two EGFP showed radiopacity higher than enamel. The commercial endodontic posts showed radiopacity as follows: higher than enamel, between enamel and dentin, and lower than dentin. The results showed statistically significant differences (p b 0.05) when evaluated with one-way ANOVA statistical analysis. According to combustion analyses, the filler content of the tested posts ranges between 58.84 wt.% and 86.02 wt.%. The filler content of the tested EGFP ranged between 68.91 wt.% and 79.04 wt.%. EGFP could be an alternative to commercial glass fiber posts. Future glass fiber posts are recommended to present higher radiopacity than dentin and perhaps ideally similar to or higher than that of enamel, for improved clinical detection. The posts with a lower radiopacity than dentin should be considered insufficiently radiopaque. The radiopacity of some glass fiber posts is not greatly influenced by the amount of filler. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Endodontically treated teeth with insufficient coronal dental tissue need posts and a core in order to support the final prosthetic restoration. Some studies showed that posts do not strengthen teeth, and that they are used only to support the retention of a core that does not have sufficient coronal dentin to support occlusal function [1]. Furthermore, the preparation of a post space may increase the risk of root fracture and treatment failure [2]. Factors such as mechanical properties, design, translucency, and radiopacity are very important in selecting a post. The success of the procedure depends on the properties of the post but also on other indirect factors such as cement, core material, crown and the quality of the endodontic treatment. As an esthetic alternative to metal and carbon fiber post, transparent quartz fiber posts with light conductive properties were introduced [3]. While metallic and ceramic posts were radiopaque, the carbon fiber posts introduced in 1990 [4] and the glass fiber posts (GFP) showed insufficient or missing radiopacity [5]. The radiopacity is as important as the recognition of faulty proximal contours, detection of secondary

⁎ Corresponding author at: Dep. of Dental Materials, Raluca Ripan Institute of Research in Chemistry, Babes-Bolyai University, 30 Fantanele Street, 400294 Cluj-Napoca, Romania. E-mail address: [email protected] (G. Furtos).

http://dx.doi.org/10.1016/j.msec.2015.10.091 0928-4931/© 2015 Elsevier B.V. All rights reserved.

caries [6], voids, marginal adaptation, and interfacial gaps on the radiograph [6,7]. A radiopaque post provides an easy evaluation at the interface with the root canal space [8] and helps the clinician in establishing a correct diagnostic of the technical failures, loss of retention, root fractures, post fracture or periapical lesion [9]. Carbon fiber posts could be clinically and radiographically unremarkable [10]. The main components of GFP are glass fibers and polymers which are practically radiolucent. All glass fibers contain amorphous silicon dioxide as the main component. AR glass fibers with ZrO2 content could be an alternative to various other glass fibers (E-, R-, or S-) used in dentistry [11–13]. Addition of radiopaque compounds could improve radiopacity — depending on the type of compounds and their quantities [14,15]. For fixation of the post, a radiopaque dental cement is applied to the root canal walls. Unfortunately, in most cases a radiopaque dental cement did not provide sufficient radiopacity [14] for easy radiographic evaluation of post/core assembly; most likely, this was because the cement was applied in a too thin layer around a GFP [16]. Also, an optimal radiopacity of GFP can provide advantages when using new techniques of 3D visualization of tooth and oral structures by cone-beam computerized tomography (CBCT) [17]. Considering that there are many GFP on the commercial market, an evaluation in the same radiographic condition using a reference human dentin and enamel will help clinicians. Today, using a GFP with improved radiopacity, good mechanical properties, translucency and adhesion to dental cement, could be an

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G. Furtos et al. / Materials Science and Engineering C 59 (2016) 855–862

ideal clinical decision. Improving the interfacial adhesion strength between the fiber and the epoxy resin matrix, as well as the mechanical properties was possible using a coupling agent or argon plasma [18]. Replacing the epoxy resin with methacrylate systems similar to the resin matrix for dental restorative treatments, could represent an advantage for adhesion to the dental cement. Using a polymer matrix based on 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (bis-GMA), triethyleneglycol dimethacrylate (TEGDMA) for obtaining new GFP could create a favorable outcome due to the close chemical compatibility of GFP with the dental cement. The aim of this study was to investigate the radiopacity and the influence of the filler content of experimental glass fiber posts (EGFP) based on alkaline resistant (AR) glass fibers for improving the radiopacity. These new EGFP were compared to “wired” glass fiber posts (WGFP); “wired” carbon fiber posts (WCFP); carbon fiber posts (CFP) and metal posts (MP). Post materials were also investigated for the percentage of fillers by weight and volume. The null hypotheses were: (1) that there is no difference in radiopacity of posts, human enamel or dentin and (2) that the percentage of fillers by weight and volume could be correlated with the radiopacity of each composite material. 2. Materials and methods 2.1. Materials The reagent grade chemicals ZrO2 powder (Aldrich Chemical, Milwaukee, WI, USA), 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (bis-GMA, Aldrich Chemical, Milwaukee, WI, USA), triethyleneglycol dimethacrylate (TEGDMA, Sigma Chemical, St. Louis, MO, USA). Camphorquinone (CQ) and N,N-dimethylaminoethyl methacrylate (DMAEMA) constituted the photoinitiator system and were supplied by Merck–Schuchardt, Germany. Silane A-174 (γ-methacryloxypropyl-1-trimethoxysilane) was purchased from Aldrich Chemical, Milwaukee, WI, USA, and used as an adhesion promoter for glass fibers. All materials were used as received without any further purification. 2.1.1. Glass fibers Unidirectional alkaline resistant (AR) glass fibers bundles were treated with γ-methacryloxypropyl-1-trimethoxysilane (silane A174) — 1 wt.% silane A-174 to the amount of glass fibers. The silane

solution was prepared by dissolving silane A-174 in ethanol–water 90/10 vol.% acidified to pH 3.8, and maintained at this level using glacial acetic acid. The glass fiber roving was maintained in this solution for 1 h. After that, the silane layer was dried and cured at 110 °C for 2 h. The A174 silane is currently used as a coupling agent in dentistry and contains an ester functional group on one end, able to react with the OH-groups of the glass fiber surface after hydrolysis of the methoxy groups from the silane. At the other the A-174 silane features a methacrylate group able to make a new\\C\\C\\covalent bond with methacrylate groups from monomers when the polymerization reaction starts. Thus, the fillers will be compatible with the resin before curing and able to be connected to the polymer matrix after curing.

2.1.2. Obtaining the experimental glass fiber posts An experimental organic matrix was obtained from bis-GMA (60 wt.%) and TEGDMA (40 wt.%) in which the light-curing initiating system was dissolved, consisting of DMAEMA (1 wt.%) and CQ (0.5 wt.%). The light-curing monomer mixtures (L0) were mixed with the inorganic fillers (ZrO2 powder, 20 wt.% and 50 wt.%) for obtaining the light-cured resin composites (L20 and L50). Three experimental glass fiber posts were obtained as previously described [19], by pultrusion of unidirectional glass fibers with L0, L20 and L50. EGFP 1 was obtained by applying 0.80 g of light-curing resin (L0) to 20 cm length of the glass fiber roving, followed by pultrusion of transparent glass tubes of 20 cm length and inside diameter of 1.51 mm. The design for obtaining the EGFP is depicted schematically in Fig. 1. EGFP 2 and 3 were obtained by applying 1.02 g L20 and 1.65 g L50 to the same length of the glass fiber roving with pultrusion in the same transparent glass tube. The glass fiber roving mixed with excess of light-cured resin composites were guided to enter and pass through the transparent glass tube. Under this force, the fibers undergo a rearrangement and the fibers with ZrO2 and resin are organized into a compact shape, while air bubbles and excess resin are squeezed out at the entering of the tube. When the glass fiber roving with light-curing resin composites were pultruded until the end of tube, visible light was applied from an Optilux 501 halogen curing light (Kerr/Demetron, λmax 400–505 nm, intensity N 690 mW/cm2) [19]. The dental curing light guide tip had an 8 mm diameter and was applied on the length of the glass tube mold containing the post, for light-curing 60 s/one section. After curing, the glass fiber posts were pultruded out from the glass mold. The resulting EGFP 1, 2 and 3 can be seen in Fig. 2.

Fig. 1. Schematic design of the obtaining experimental glass fiber posts.


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Fig. 2. Endodontic posts used for study: 1–18 GFP; 19–20 WGFP; 21 WCFP; 22–23 CFP; 24–26 EGFP; 27 MP.

2.1.3. Endodontic post used for study Twenty-four commercial endodontic post materials and three EGFP were investigated in this study (Table 1 and Fig. 2), comparing their radiopacity with those of human enamel and dentin.

Density values used for experimental glass fibers obtained were 2.7 g/cm3; because the glass fiber posts consists mainly of glass fibers, the fraction of fillers by vol.% was calculated using only the density of glass fibers.

2.2. Methods

2.2.2. Endodontic post specimen preparation for radiopacity test The endodontic posts in this study were embedded in polymethylmethacrylate (PMMA) and were sectioned using a diamond saw (Isomet 1000, Buehler, Lake Bluff, IL). The resulted slices were polished using # 800 and 1200 carbide paper, to a thickness of 1 mm (± 0.01). The diameters and heights of the samples were measured using an electronic digital caliper (Vogel, Germany), with an accuracy level of ± 0.01 mm. For the current study, two freshly extracted human molars and one premolar tooth extracted for orthodontic purposes were selected, which on visual examination were free of caries, hypoplastic defects or cracks. These teeth were stored in buffered formal saline for 24 h post-extraction, and then in water at room temperature (23 ± 1 °C). They were subsequently embedded in acrylic resin, and 1 mm (± 0.01) mesiodistal sections from each tooth were obtained using a rotary cutting machine. In addition to these samples, pure aluminum samples with thicknesses of 1 to 10 mm were also prepared. A recently extracted non-carious human maxillary premolars, with one straight root canal and fully developed apices, extracted for periodontal reasons, were selected for this study. The tooth was cleaned of

2.2.1. Percentage of fillers by weight and volume The filler (inorganic filler or glass fibers) content of the test specimens (n = 10) was measured by combustion analysis in a furnace. The test specimens were dried in a desiccator at room temperature for one day before and after combustion, and weighed to an accuracy of 0.0001 g. The combustion of the samples was performed at 650 °C, for one hour. The weight percentage of the fillers was determined by calculating the difference of weight of the crucible before and after ashing in air. The fillers weight percentage was then converted to a volume percentage using the following formula from Eq. (1) Fraction of fillers vol:% ¼

w f =d f 100 w f =d f þ wr =dr

ð1Þ

where: wf and wr are the weight fractions of fillers and resin, respectively, and df and dr are the density of the fibers and resin, respectively. Values of 2.55 g/cm3 and 1.238 g/cm3 were used for the densities of the E glass fibers and resin [20], in order to evaluate commercial GFP. Table 1 Endodontic posts used for study. No.

Material

Manufacturer

Batch

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

FRC Postec Plus Danville Ice Post Danville Ice Light Aestheti-Plus DT White Post Light Post DT Light Post UniCore Post RelyX™ Fiber Post Glassix ParaPost Fiber Lux ParaPost TaperLux ParaPost FiberWhite Fibrapost Fibrapost+ Fibrapost Lux Mirafit White Saremco Posts Non-Stop Fiber Reforpost Glass Fiber Core post - Glass fiber post Core post - Carbon fiber post Reforpost Carbon Fiber Mirafit Carbon Experimental glass fiber post 1 (EGFP 1) Experimental glass fiber post 2 (EGFP 2) Experimental glass fiber post 3 (EGFP 3) ParaPost XP

Ivoclar Vivadent Danville Materials Inc. Danville Materials Inc. RTD RTD RTD RTD Ultradent 3M ESPE NORDIN S.A. Coltene Whaledent Coltene Whaledent Coltene Whaledent PDSA PDSA PDSA Hager & Werken Saremco Dental AG Angelus DenMat DenMat Angelus Hager & Werken

K22326 13654 10724 3SQ0410A 2007020023 70780712 066030710 B2X7Z 094320810 08039 MT65701 MT68102 MT65845 1785 AM 5124 FA 2742 FA 06069/234 2049 AM 26092 G314010097 H104010065 2850 02287/455

Coltene Whaledent

81492D

Type of post

Size

Ø (mm)

GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP GFP WGFP WGFP WCFP CFP CFP EGFP 1 EGFP 2 EGFP 3 MP

3 Blue Blue 3 1 3 3 4 3 4 6 6 6 4 4 4

2/1 mm 1.6 1.6 2.1/1.4 1.4/1 2.1/1.4 2.1/1.4 1.5/1.75 1.90/0.90 1.5 1.50/0.60 1.50/0.60 1.50/0.60 1.90/1.47 1.90/1.47 1.90/1.47 1.5 1.46/0.78 1.5 1.4 1.4 1.1 1.5 1.5 1.5 1.5 1.5

Black 3

6

Note: GFP: glass fiber post; WGFP: “wired” glass fiber post; WCFP: “wired” carbon fiber post; CFP: carbon fiber post; EGFP: experimental glass fiber post; MP: titanium post.

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Fig. 3. Radiographs of endodontic posts before section.

soft tissue and calculus and sectioned 2-mm occlusally at the cementoenamel junction (CEJ) with a diamond bur under water-cooling, which exposed the pulp chamber. After that, the tooth was endodontically treated and AH Plus sealer (Dentsply Maillefer) was applied in a thin layer. Gutta-percha was injected to full working length with a 27gauge needle from the Obtura III System (Obtura Spartan, Fenton, MO, USA). A 9-mm deep post space was prepared with a cylindrically drill from ParaPost Fiber Lux kit (black) of 1.5 mm diameter to match the size of the corresponding experimental post (1.5 mm in diameter). The canals were rinsed with 17% EDTA solution for 1 min using the EndoVac system, then with deionized water until they appeared completely free of debris or residual filling material under the dental operating microscope (OPMI Pico, Germany) and dried with paper points (Dentsply Maillefer, Switzerland). Cementation of EGFP 1, 2 and 3 in the root canal was performed with the self-adhesive resin cement RelyX U200 (RXU2) (3M ESPE, Seefeld, Germany). A free portion of the fiber post, extruding 5 mm from the build-up material, was left to confirm the direction of the post in the root canal.

2.2.3. Radiograph images The slices with endodontic post sections (n = 6), the teeth slices and the aluminum step wedges were placed on an intraoral sensor (XIOS Plus, Sirona) and radiographed using a dental X-ray machine (Intraoral X-Ray Soredex, Minray) at 70 kV, 7 mA, 0.04 s with a targetsensor at the distance of 30 cm. The mean gray value of each aluminum step wedge and selected materials were measured by outlining a region of interest using the equal-density area tool of the Image J software (version 1.37 V, Wayne Rasband, National Institutes of Health, Bethesda, MD, USA). The regions were selected by avoiding areas containing air bubbles inside the material, and the average gray value was recorded for each sample. For each radiograph image the calibration curve generated by the gray-scale values as a function of the aluminum thickness was calculated. The radiopacity values of the samples were expressed in terms of the equivalent thickness of aluminum per 1 mm unit thickness of material. Digital periapical radiographs of tooth with EGFP 1, 2

and 3 were taken using the same radiographic procedure used for post sections. 2.2.4. Statistical analyses Data were statistically analyzed by one-way analysis of variance (ANOVA) and by Tukey's test with the level of significance set at 0.05 in order to determine the significant differences between the mean values of the tested materials. 3. Results 3.1. Radiopacity Radiographs of all the posts tested before sectioning are shown in Fig. 3. Visible differences in the radiopacity are noted and may be linked to the different composition as well as variable diameters of the samples. The endodontic post sections were compared radiographically with dentin, enamel and aluminum step wedges (Figs. 4 and 5). Fig. 6 shows radiograph of teeth with EGFP 1, 2 and 3. The mean results of radiopacity (Fig. 7) for commercial and experimental post showed values from − 0.02 mmAl for Aestheti-Plus (RTD) to 6.97 mmAl for ParaPost XP (Coltene Whaledent). The radiopacity values of the tested endodontic posts were statistically different (p b 0.05). EGFP 2 and 3 showed higher radiopacity than commercial glass fiber posts. EGFP 1 presented radiopacity value between human dentin and enamel. However, the radiopacity values of some tested posts were statistically different from those of human enamel or dentin. Our study reflects that not all glass fiber posts on the market have an adequate radiopacity. The correct radiopacity enables the radiographic visualization and verification, enhancing the diagnostic decision and reducing the unwarranted retreatment of teeth. Two WGFP and one WCFP post were investigated, and an obvious difference between composites and wire was observed. Due to difficulties in distinguishing the post on radiographs, the radiopacity of Reforpost Carbon Fiber (Angelus) could not be evaluated.

Fig. 4. Radiographs of 1–14, 17–23, 27, EGFP 1–3 endodontic post sections, human dentin and enamel sections.


Fig. 5. Radiograph of 1–23 and 27 endodontic post sections.

3.2. Percentage of fillers by weight and volume Combustion analyses reveal that the filler content of the tested posts ranges between 58.84 wt.% (41.70 vol.%) for ParaPost FiberWhite (Coltene Whaledent) to 86.02 wt.% (60.64 vol.%) for Danville Ice Post (Danville Materials Inc.) (Figs. 8 and 9). The three materials with highest filler content were “wired” glass/carbon fiber posts, and this could be explained by the metal (wires) part used. Our experimental posts showed filler content of 49.64 wt.% (52.58 vol.%) for EGFP 1 just with glass fibers; 73.51 wt.% (58.12 vol.%) for EGFP 2 and 79.40 wt.% (65.84 vol.%) for EGFP 3. Figs. 8 and 9 show the relationship between percentage of filler by weight and volume for glass fiber posts and radiopacity (WGFP and WCFP not included, as they contain metal wires which make them too different from the other samples).

4. Discussion The radiopacity analysis of the post materials using 1 mm-thick sample slices, with the possibility to investigate more samples on the same radiograph, provides for an accurate method for this purpose (Figs. 4 and 5). Investigation of the radiopacity along the length of the post (Fig. 3) could provide confusing results because the cylindrical shape of the post cannot provide a large surface of even thickness for investigation, as well as because of the different diameter or size of different brands of posts. The hypothesis that there is no difference in radiopacity between different endodontic posts and human enamel and dentin was rejected. ParaPost XP (Coltene Whaledent) (Fig. 2) is a metallic (titanium alloy) post that showed the highest radiopacity value (Figs. 3, 4 and 7). This was used also as reference for metal posts from the market. A higher radiopacity than that of the metal should be

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avoided. Higher radiopacity values may induce “shadows” on radiographs that may obscure and leave undiagnosed adjacent caries or defects [6,7,20,21]. Today one of the demands for an ideal post is to have mechanical properties closer to dentin. Introduction of glass fiber reinforced composites post on the market is considered a new trend because of their translucency [22,23]. Glass fiber posts are considered as an esthetic alternative to metal posts, with the ability to protect the root by transferring less stress to the dentin walls, and having a modulus of elasticity similar to that of the dentin [24,25]. ParaPost XP (Coltene Whaledent), EGFP 2 and 3, FRC Postec Plus (Ivoclar Vivadent), Fibrapost Lux (PDSA), UniCore Post (Ultradent), DT Light Post (RTD), RelyX™ Fiber Post (3M ESPE), Danville Ice Light (Danville Materials Inc.), Glassix (NORDIN S.A), Light Post (RTD), ParaPost TaperLux, ParaPost Fiber Lux (Coltene Whaledent) and Danville Ice Post (Danville Materials Inc.) had radiopacity value higher than that of the enamel (Fig. 7). These materials can be seen very well in root canals in comparison to dentin and enamel. Another glass fiber post group, EGFP 1, Fibrapost + (PDSA) and ParaPost FiberWhite (Coltene Whaledent), had radiopacity values higher than dentin and slightly lower than enamel. All these posts can be seen in root canal, but for a better visualization we recommend a radiopacity slightly higher than that of enamel. Fibrapost (PDSA), Hager & Werken, Mirafit Carbon (Hager & Werken), Saremco Posts Non-Stop Fiber (Saremco Dental AG), Aestheti-Plus, DT White Post (RTD), Glass Fiber (Angelus), Core post–Glass fiber post, Core post–Carbon fiber post (DenMat) had radiopacity lower than 1 mm of Al and dentin and could be considered insufficiently radiopaque, especially if the posts will not be cemented with a highly radiopaque cement. Radiopaque cement can provide important information for the clinicians about the presence of the post into the root canal and also about the topography of the root canal space were the post is located. In the case of Reforpost Glass Fiber (Angelus), Core post–Glass fiber post, Core post–Carbon fiber post (DenMat), the producers chose to embed into the core of the post a metal wire to improve radiopacity and for better detection. Our study shows that the composites used to embed this wire had radiopacity lower than dentin while the second component of these posts, the metal wire, had greater radiopacity than enamel. This may be a disadvantage for radiographic detection of the interface between the post and the surrounding medium. Reforpost Carbon Fiber (Angelus) and Mirafit Carbon (Hager & Werken) (Figs. 3 and 5, posts 22 and 23) had the lowest radiopacity values and may be radiographically undetectable. Unfortunately, carbon fiber reinforced posts, like metallic posts, are considered non-esthetical because of the black color and lack of the radiopacity. Using highly radiopaque luting cement may be a solution for better visualization on radiographs of glass fiber posts with low radiopacity values. The thickness of the layer of such cements (usually low) may be a key issue from that point of view, and further work in this direction is needed.

Fig. 6. Radiograph of tooth with EGFP 1, 2 and 3.

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Fig. 7. Radiopacity of endodontical posts (horizontal bars blue and red indicate means values not statistically significantly different from each other compared using the Tukey test, p N 0.05). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The radiopacity of the dental materials is highly influenced by the amount of elements with high atomic numbers in the composition of the material [7,26]. Examples of “effective atomic numbers” for some media are: air (7.6), water, muscle (7.4), fat (5.9–6.3), bone (11.6– 13.8), Zn (30), Sr (38), Zr (40), Ba (56), Iodine (53) [27]. Excess heavy metal oxide in fillers may be disadvantageous for the translucency of

the materials; also, barium or strontium ions can disrupt aluminosilicate networks [28] and increase the solubility and degradation of dental composites [28,29]. In our work, the reason for using AR glass fibers to obtain EGFP was that they have a better potential to improve radiopacity by their ZrO2 content (15–20%) [30,31] than other E-, Ror S-glass fibers without radiopaque elements [11–13] used in dentistry

Fig. 8. The relationship between radiopacity and percentage of filler by weight (a) and percentage of filler by volume (b) for glass fiber posts.


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Fig. 9. The percentage of filler by weight and percentage of filler by volume for glass fiber posts.

[13] and orthopedic fields [32]. A translucent GFP (Aestheti-Plus, LightPost (RTD)) was prepared from quartz glass fibers [33] in order to obtain a good translucence, a better light transmission and also for obtaining esthetic restorations. Quartz glass fibers have more than 99.9% SiO2 in their composition. GFP will not be radiopaque without addition of radiopaque fillers, because SiO2 is not radiopaque. The low radiopacity value of the quartz glass fiber posts obtained in this study is in agreement with other results from literature [5]. This study reflects an EGFP 1 with just 49.64 wt.% AR glass fibers without other radiopaque fillers that can provide a radiopacity of 1.77 mmAl. This radiopacity value was more than that of dentin and was in agreement with ISO4049 that requires a minimum radiopacity of 1 mmAl [34]. The evaluation of the radiopacity of EGFP cemented in the root canal showed a good visualization and evaluation in comparison with tooth structure (Fig. 6). EGFP 1 looks more transparent than EGFP 2 and 3 (Fig. 6). This could be explained by using the ZrO2 filler in EGFP 2 and 3. Translucent fiber posts have been reported to improve the depth of cure of photo-activated resin based luting cement [35–36]. The second null hypothesis, that the percentage of fillers by weight and volume could be correlated to radiopacity, was rejected. At r2wt. = 0.0265 (Fig. 9a) and r2vol. = 0.0063 (Fig. 9b) there is no relationship between the percentage of filler by weight and volume used in glass fiber posts, and the radiopacity. The regression of EGFP 1, 2 and 3 showed a strong correlation between the percentage of fillers by weight and volume vs. radiopacity: r2wt. = 0.9962 and r2vol. = 0.9988. This correlation in case of EGFP 1, 2 and 3 could be explained by the fact that the same chemical compounds were used as raw materials. The low regression value of all GFP from the study (Fig. 9a and b) could be explained by different chemical compositions and densities of inorganic and organic components. One may conclude that in radiopaque glass fiber posts the most important influence on is from the high atomic number elements, and the quantity of these elements in the composition of materials. While the composition of the commercial products is largely unknown, in our study the combustion analyses reveal that the filler content of the tested posts ranges between 58.84 wt.% (41.70 vol.%) to 86.02 wt.% (60.64 vol.%) (Figs. 8 and 9). The first three materials with highest filler content were “wired” glass/carbon fiber posts, and this can be explained as due to the use of the metal wire. Our EGFP showed filler contents between 79.04 wt.% (62.67 vol.%) for EGFP 3; 73.51 wt.% (55.23 vol.%) for EGFP 2 and 68.91 wt.% (49.64 vol.%) for EGFP 1 (containing only glass fibers) (Figs. 8 and 9). All these three EGFP had the same quantity of AR fibers, implying that the improvement in radiopacity beyond EGFP 1 could be attributed to the addition of 10.16 wt.% ZrO2 in EGFP 3 and 4.60 wt.% ZrO2 in EGFP 2. One may also conclude from this study that using AR glass fibers (49.64 wt.%) without radiopaque filler it is possible to obtain a radiopacity of the glass fiber posts between those of human dentin and enamel. Addition of ZrO2 in EGFP 2 and 3 increases the radiopacity beyond that of enamel, and offers a good clinical radiopacity evaluation. AR glass fibers also offer advantages in mechanical properties, as their tensile strength of 3241 MPa and modulus of 73.1 GPa are close to the values seen in E-glass fibers (3445 MPa and 72.4 GPa, respectively) [37]. EGFP showed a good mechanical behavior, with fracture loads

from 68.02 to 115.97 N and with the force load at upper yield values from 38.70 to 70.46 N, close to other GFP on the dental market [19]. 5. Conclusions Within the limitations of this study, we may conclude that using materials with adequate radiopacity in clinical practice is essential for evaluation of the different interfaces between restorative materials. Future glass fiber posts are recommended to have higher radiopacity values than dentin and perhaps ideally similar to or higher than that of enamel, in order to improve the radiographic detection. Posts with lower radiopacity than dentin should be avoided because these could not be visualized on radiographs unless used with highly radiopaque cement. AR glass fibers have a great potential for obtaining radiopaque posts with acceptable clinical radiopacity characteristics. These results encourage us to pursue further investigations of EGFP based on AR glass fibers for clinical application. Conflict of interest The authors declare that they have no conflicts of interest. Acknowledgments The authors are grateful to Coltene Whaledent, DenMat, Danville Materials Inc., Edwards Dental, Ivoclar Vivadent, Hager & Werken. PDSA, RTD, Saremco Dental AG, Ultradent, and 3M ESPE for the donation of the materials. The authors thank the COST Action MP1301 for COST meeting support. This work was supported by two grants of the Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project numbers 165/2012 and 115/2014. References [1] G. Heydecke, F. Butz, J.R. Strub, Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study, J. Dent. 29 (2001) 427–433. [2] J.A. Sorensen, J.T. Martinoff, Endodontically treated teeth as abutments, J. Prosthet. Dent. 53 (1985) 631–636. [3] C. Parisi, L.F. Valandro, L. Ciocca, M.R. Gatto, P. Baldissara, Clinical outcomes and success rates of quartz fiber post restorations: a retrospective study, J. Prosthet. Dent. 114 (2015) 367–372. [4] B. Duret, M. Reynaud, F. Duret, Un nouvau concept de reconstitution coronoradiculaire: Le Composiposte (1), Chir. Dent. Fr. 540 (1990) 131–141. [5] W.J. Finger, W.M. Ahlstrand, U.B. Fritz, Radiopacity of fiber-reinforced resin posts, Am. J. Dent. 15 (2002) 81–84. [6] I. Espelid, A.B. Tveit, R.L. Erickson, S.C. Keck, E.A. Glasspoole, Radiopacity of restorations and detection of secondary caries, Dent. Mater. 7 (1991) 114–117. [7] H. Toyooka, M. Taira, K. Wakasa, M. Yamaki, M. Fujita, T. Wada, Radiopacity of 12 visible-light-cured dental composite resins, J. Oral Rehabil. 20 (1993) 615–622. [8] E. Rodrigues, L.M. Salzedas, A.C. Delbem, D. Pedrini, Evaluation of the radiopacity of esthetic root canal posts, J. Esthet. Restor. Dent. 26 (2014) 131–138. [9] M. Ghavamnasiri, F. Maleknejad, H. Ameri, M.J. Moghaddas, F. Farzaneh, J.E. Chasteen, A retrospective clinical evaluation of success rate in endodontic-treated premolars restored with composite resin and fiber reinforced composite posts, J. Conserv. Dent. 14 (2011) 378–382.

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