Statement of the Problem: Bulk fill composites have been introduced over the recent years in order to accelerate the process of tooth restoration by inserting composite in bulk up to 4mm thickness.
Purpose: This in vitro study aims to evaluate the effect of occlusal loading on the gingival microleakage of bulk fill composites compared with a conventional composite.
Materials and Method: In this experimental study, box only class II cavities with gingival margins placed 1mm below the cemento-enamel junction were prepared on the mesial and distal surfaces of 36 maxillary premolars (72 cavities). The samples were divided into three groups and restored as follows: Group 1 (Tetric N-Ceram, incremental filling), Group 2 (X-tra fill, bulk filling), Group 3 (Tetric N-Ceram Bulk Fill, bulk filling). All restorations were thermocycled for 2000 cycles (5-50̊C), and then half of the samples were subjected to 200,000 cycles of loading. All the specimens were immersed in 0.5% basic fuchsin for 48 hours, and then, sectioned and evaluated for microleakage with a stereomicroscope. Data were analyzed using Kruskal-Wallis, and Mann-Whitney U-tests. P Results: There were no significant differences among the gingival microleakage of three composites in both unloaded and loaded groups. Also, no statistically significant difference was found between the microleakage of unloaded and loaded groups in all materials.
Conclusion: Occlusal loading did not affect the gingival microleakage of bulk fill composites, and the microleakage of class II cavities restored with the bulk filling technique was similar to that of restored with the incremental technique.
Although resin composites have been considered as the first choice for the direct restorations, their polymerization shrinkage has remained as a critical problem [ 1 - 2 ]. The volumetric shrinkage of composites is variable between 2% to 5%. The tensile stress of the composite shrinkage can cause debonding of the tooth-composite interface, which consequently, leads to postoperative sensitivity, enamel cracks, secondary caries, and microleakage [ 3 - 4 ].
Microleakage is one of the important factors, which affects the success rate of composite restorations and refers to the transfer of bacteria, liquids, and molecules between the prepared surface of tooth and restorative material [ 5 ]. It has been considered as a main challenge for the restorations of class II cavities with the direct composite, especially when the gingival margin is in the dentin [ 5 ]. The incremental technique is one of the methods for decreasing the polymerization shrinkage and increasing the marginal seal, but this method is time-consuming and there is a possibility of formation of bubbles among the restoration layers [ 1 - 2 , 6 ].
In order to accelerate the process of composite placement, new composites called bulk fill composites, have been introduced which can be inserted as a bulk to the depth of 4 mm according to the claim of their manufactures [ 7 ]. The main advantages of the bulk fill composites are their increased curing depth, which results from their higher translucency, and their lower polymerization shrinkage, due to the changes occurred in the content of filler such as the presence of iso-fillers or their resin matrix such as the presence of plasticizers or the polymerization modulator in the matrices [ 8 ].
Bulk fill composites have two consistencies; flowable and paste type. The flowable bulk fill composites are required to be covered with a final capping layer of the conventional composite, due to their low surface hardness and elastic modulus, but conventional bulk fill composites do not need this final coating [ 9 ].
The increased curing depth of bulk fill composites is due to their high level of translucency, the high volume of urethane dimethacrylate (UDMA) monomer, instead of bisphenole A glycidyl dimethacrylate (Bis-GMA) (UDMA indicated higher final degree of conversion than Bis-GMA). Moreover, it can be due to the presence of especial photoinitiator such as Ivocerin in Tetric N-Ceram Bulk Fill, the similar refractive indices of Bis-GMA monomer and Silica filler particles, the reduction in filler content, and increased dimension of filler particles (which decreases the matrix-filler interface. Thus, light scattering is decreased and allowing better light penetration) [ 10 ]. Bulk fill composites can be inserted into the depth of 4 mm in one layer. Therefore, working with them is easy and requires less time [ 11 ].
In the oral environment, restorations are under thermal and mechanical stresses and weakening of the adhesive resin caused these stresses are an important issue in operative dentistry [ 12 ]. In fact, the reaction of composite restorations to hydrolytic degradation and occlusal loading will define its resistance to fatigue and tooth-restoration interface breakdown [ 13 ]. Some studies indicated increased microleakage of composite restoration under the occlusal loading [ 12 , 14 ], while, the others reported that occlusal loading did not affect the marginal adaptation of composite restoration [ 15 - 16 ]. The aim of this study was to evaluate the effect of occlusal loading on the gingival microleakage of bulk fill composites (Tetric N-Ceram Bulk Fill and X-tra fill) compared to a conventional composite (Tetric N-Ceram), by the method of dye penetration and scanning electron microscopy (SEM) evaluation in class II cavities.
Materials and Method
The samples of this experimental in vitro study consisted of 36 extracted maxillary premolar teeth. They were extracted for orthodontic treatments and had intact surfaces, without caries and decalcification. The teeth were disinfected in the 0.5% Chloramine-T solution for one week and then, were kept in the normal saline solution.
A total of 72 standard cavities of class II (box only) with the buccolingual width of 4mm, the depth of 1.5 mm and the occlusal-gingival length of 1 mm under cemento-enamel junction were prepared on the mesial and distal surfaces of all teeth, using a water-cooled high speed hand-piece and the fissure diamond bur (Tizkavan, Tehran, Iran). By cutting five cavities, the bur was changed. The materials used in the present study and their chemical compositions were mentioned in Table 1. First, the metal matrix band was fixed using a Tofflemire holder. Then, all the cavities were etched with 37% phosphoric acid gel (Total Etch, Ivoclar Vivadent) for 15 seconds, washed thoroughly, and the excess moisture of each cavity was removed with a small cotton pellet. Subsequently, two layers of Tetric N-Bond (Ivoclar Vivadent) were applied 10 seconds by micro brush on the walls of cavities, gently air dried, then light cured for 20 seconds with a light emitting diode (LED) curing unit (DEMI, Kerr, USA) at 800 mW/cm² intensity. Afterward, the samples were divided into one of the following groups randomly.
|Tetric N-Bond||Phosphoric acid acrylate, HEMA, Bis-GMA, UDMA, ethanol, film-forming agent, catalysts, and stabilizers||Ivoclar Vivadent, Schann, Liechtenstein||V37028|
|X-tra fill||Bis-GMA, UDMA, TEGDMA, Fillers: 86% wt, 70% vol, Ba-B-Al-Si glass||Voco Cuxhaven, Germany||1633494|
|Tetric N-Ceram||UDMA, ethoxylated Bis-EMA, Bis-GMA (18.8 wt%), barium glass filler, ytterbium trifluoride, mixed oxide (63.5 wt%), polymer (17.0 wt%), additives, catalysts, stabilizers, and pigments (0.7 wt%)||Ivoclar Vivadent, Schann, Liechtenstein||V23282|
|Tetric N-Ceram Bulk Fill||Dimethacrylates 21.0% (Bis-GMA, Bis-EMA, UDMA) Polymer Filler 17.0% (Barium glass filler, Ytterbium trifluoride) Mixed oxide 61.0% Additive, Initiators, Stabilizers, pigments, 1.0%||Ivoclar Vivadent, Schann, Liechtenstein||V19409|
|HEMA: 2-hydroxyethyl methacrylate, UDMA: urethane dimethacrylate, Bis-GMA: bisphenol A glycidyl dimethacrylate, TEGDMA: triethylene glycol dimethacrylate, Bis EMA: ethoxylated bisphenol A glycol dimethacrylate.|
In the group 1, the cavities were restored with Tetric N-Ceram composite (Ivoclar Vivadent) incrementally (with 2mm thickness in each layer) and each layer was cured for 20 seconds.
In the group 2, the cavities were restored with X-tra fill composite (Voco, Germany) as bulk (a 4mm thick increment was placed into the cavity and cured for 20 seconds, followed by the next increment to entirely fill the cavity and cured for 20 seconds).
In the group 3, the cavities were restored with Tetric N-Ceram Bulk Fill (Ivoclar Vivadent) as bulk (a 4mm_thick increment was placed into the cavity and cured for 20 seconds, followed by the next increment to fill the cavity entirely and cured for 20 seconds).
In all groups, after removing the matrix strip, the restorations were cured from the buccal and palatal aspects for 20 seconds on each side, and then all the restorations were finished and polished by diamond finishing burs and polishing disks (Soflex, 3M, ESPE, USA). After keeping them in an incubator at 370C for 24 hours, the samples were subjected to 2000 thermal cycles in water bath between 5-500C (dwell time: 30 seconds in every bath and transfer time: 20 seconds) (Baradaran Pouya, Iran). Then in each group, half of the samples were kept in an incubator at 37 0C and the other half of the samples were mounted up to 1mm apical to cervical margins of restorations in self-curing acrylic resin (Acropars, Iran). Then they were subjected to 200,000 cycles of loading with a force of 60 N, frequency of 2 He-rtz and displacement of 1mm by using a chewing simulator machine (Germany, SD Mekantronik) (Figure 1).
Before sectioning the samples, an impression (precise, Coltene, Switzerland) was taken off the surface of 12 restorations, two samples in each subgroup, and the positive epoxy resin replica was gained from each sample. Each replica was placed on a metallic stub and sputter coated with a thin layer of gold and was evaluated with a SEM microscope (TESCAN-Vega3, Czech Republic) with 1000X magnification. Then, interfacial gaps were measured (Figure 2). The whole length of all gaps was shown as a percentage of all lengths of the restoration margins.
All surfaces of the teeth except the parts that have been filled and 1 mm around the margins were sealed with two layers of nail polish. Then, the teeth were immersed in the 0.5% basic fuchsin solution for 48 hours. Samples were washed with distilled water, dried, and embedded in self-curing acrylic resin. In the next step, the teeth were sectioned longitudinally in the mesio-distal direction through the center of restorations using a cutting machine with low- speed diamond disk (Presi, Mecantome, T201A, France) under continuous water irrigation. After that, the samples were assessed using a stereomicroscope (Nikon, 30DS, SMZ 800, Tokyo, Japan) with a magnification of 40X (Figure 3). The degree of dye penetration was scored as (0) for absence of dye penetration, (1) for dye penetration up to 1/2 of the gingival wall, (2) when dye penetration was more than 1/2 of the gingival wall but does not reach the axial wall, and (3) when dye penetration was present along the axial wall.
The statistical analyses were done by using Kruskal-Wallis and Mann-Whitney U tests. The p Value of <0.05 was considered as the significant level.
The results of the gingival microleakage of restored samples with different composites are shown in Table 2 and Figure 4. There were no significant differences among the gingival microleakage of three composites in both unloaded and loaded groups (p > 0.05). Moreover, there was no significant difference between the bulk filling and incremental filling technique. Furthermore, no statistically significant difference was found between the gingival microleakage of unloaded and loaded groups in all composites (p> 0.05). Table 3 shows the inter-facial gaps observed under SEM.
|Score 0||Score 1||Score 2||Score 3|
|Tetric N-Ceram Bulk Fill||Unloaded||5||5||2||0|
|Filling Materials||Loading Status||The mean percentage of interfacial gaps of two specimens of each group (%)|
|Tetric N-Ceram Bulk Fill||Unloaded||1.06|
The important factor, which determines the preservation of composite restoration is the marginal seal and lack of leakage [ 7 ].
The present study indicated that there were no significant differences among the gingival microleakage of three kinds of composites in both loaded and unloaded groups. In addition, there was no significant difference between bulk filling and incremental filling method, which is in agreement with the findings of some studies [ 17 - 18 ]. Heintze et al. [ 17 ] evaluated the quality of gingival margins of class II composite restorations, which placed in bulk or three increments, and showed that there was no significant difference between two techniques. Furness et al. [ 18 ] restored the cavities of class I with bulk fill (SDR, Quixx, Sonic Fill, Tetric EvoCeram) and a conventional composite, Filtek Supreme, and indicated that there was no significant difference between the marginal integrity of two composite placement methods.
Kim et al. [ 19 ] found that the flowable bulk fill composites indicated better performance in terms of composite-tooth interfacial de-bonding than the conventional flowable composites, due to their lower polymerization shrinkage and elastic modulus. In the bulk fill composites, their lower polymerization shrinkage and elastic modulus decreased the amount of microleakage [ 20 ]. It is believed that the occlusal loads and the thermal changes lead to the gap in the interface of teeth-restoration [ 21 - 22 ]. In this study, 200000 cycles of loading were applied to mimic one year of service in vivo [ 23 ]. The results of the present study showed that the microleakage of gingival margins of three composites was not affected by cyclic loading. This finding is consistent with the previous studies [ 15 - 16 ]; However, some studies indicated the increase of microleakage of composite restorations under the cyclic loading [ 14 , 24 ].
Campos et al. [ 25 ] evaluated the marginal integrity of bulk fill composites (Surefill SDR, Sonic Fill, Venus Bulk Fill, and Tetric Evo-Ceram) in the class II cavities after 240000 cycles of loading and showed that occlusal loading did not affect the marginal adaptation of bulk composites and only Venus composite showed increased gingival microleakage after loading.
Shahidi et al. [ 24 ] evaluated the effect of 1,000,000 cycles of loading on marginal adaptation of class II cavities restored with Surefil SDR, Ceram X, Sonic Fill, Tetric, and Extra-low shrinkage composites. They reported that the effect of occlusal loading on the gingival marginal adaptation of all groups except for Tetric was statistically significant, which was not in agreement with the current study results. Jung et al. [ 14 ] reported that after applying the 600,000 cycles of loading, the microleakage was significantly increased in the gingival margins of restored class II cavities by bulk fill composites (SDR, Sonic Fill, Venus bulk fill, Tetric N-Ceram Bulk Fill), which is not in accordance with the result of this study. Such different results may be explained by the differences in the number of cycles of loading (1,000,000 and 600,000 instead of 200,000). The higher number of cycles may have a more destructive and damaging effect on marginal adaptation [ 24 ]. The gap formation in composite restorations is the result of different parameters such as the restorative materials stiffness, the degree of conversion and the polymerization shrinkage of composites [ 26 ]. The sufficient cure and degree of conversion of composites is one of the criteria, which affect the marginal adaptation, and inadequate polymerization of composites might lead to marginal microleakage [ 27 ]. The previous studies have reported the sufficient degree of conversion of X-tra fill and Tetric N-Ceram composites at the depth of 4mm [ 14 , 27 ]. In a study conducted by Abed et al. [ 27 ], X-tra fill showed significantly the highest degree of conversion. Jung et al. [ 14 ] also reported the higher bottom/top surface hardness ratio of Tetric N-Ceram Bulk Fill (82%), than the other evaluated composites, which is due to the presence of the special initiator (Ivocerin). It is a germanium-based photoinitiation and has a higher absorption spectrum compare to camphorquinone [ 14 ]. The sealing ability of restorative materials also depends on the type of material and adhesive systems [ 28 ]. It has been shown that the properties of resin composite affect the resistance to marginal degradation more than the marginal adhesion [ 29 ]. Considering the role of composite, elastic modulus and the amount of polymerization shrinkage are the main factors affect the marginal integrity of composite restorations [ 30 ].
Low shrinkage composites provide lower shrinkage stresses during curing. Thus, they are able to withstand fatigue at the tooth-restoration interface better than the other resin composites [ 3 ]. Kleverlan et al. [ 31 ] reported a strong linear correlation between polymerization shrinkage stress and gap formation. Jung et al. [ 14 ] also indicated that after loading correlation between marginal integrity and linear polymerization shrinkage was higher than preloading, which is due to the weakness of the bonding between tooth and composite through the loading process. Therefore, better adaptation would result in lower polymerization shrinkage [ 14 ].
Bulk fill composites show less polymerization shrinkage, due to the use of stress-reducing resin technology. This technology is based on the changes in the chemistry of monomers [ 32 ]. Manufacture companies changed the Bis-GMA monomer, which resulted in the production of monomers with lower viscosity such as Bis-GMA without the hydroxyl group, aliphatic urethane dimethacrylate, partially aromatic UDMA, and methacrylate with several branches. These changes decreased the polymerization shrinkage of bulk fill composites [ 32 ]. Likewise, in the bulk fill composites, the reaction of polymerization occurs more slowly, which decreases the shrinkage stress without compromising the degree of conversion [ 30 ].
The other possible explanation refers to the use of composites with nanofiller content in this study (Tetric N-Ceram Bulk and Tetric N-Ceram). Cyclic forces decrease the performance of bonding, due to fatigue at the adhesive interface. Some investigations indicated that nano-composites had a higher fatigue limit, due to their
Based on the limitations of this study, occlusal loading did not increase the gingival microleakage of bulk fill composites. In addition, the microleakage of class II cavities restored with the bulk filling technique was similar to that of restored with incremental technique.
- Joseph A, Santhosh L, Hegde J, Panchajanya S, George R. Microleakage evaluation of Silorane-based composite and methacrylate-based composite in class II box preparations using two different layering techniques: an in vitro study. Indian J Dent Res. 2013; 24:148.
- Klautau EB, Carneiro KK, Lobato MF, Machado SMM, Silva e Souza MH. Low shrinkage composite resins: influence on sealing ability in unfavorable C-factor cavities. Braz Oral Res. 2011; 25: 5-12.
- Yamazaki PCV, Bedran-Russo AKB, Pereira PNR, Wsift EJ. Microleakage evaluation of a new low-shrinkage composite restorative material. Oper Dent. 2006; 31: 670-676.
- Tavangar M, Tayefeh Davalloo R, Darabi F, Karambin M, Kazemi R. A Comparative Evaluation of Microleakage of Two Low-Shrinkage Composites with a Conventional Resin Composite: An In Vitro Assessment. J Dent Shiraz. 2016; 17:55-61.
- Bagis YH, Baltacioglu IH, Kahyaogullari S. Comparing microleakage and the layering methods of silorane-based resin composite in wide Class II MOD cavities. Oper Dent. 2009; 34:578-585.
- Usha H, Kumari A, Mehta D, Kaiwar A, Jain N. Comparing microleakage and layering methods of silorane-based resin composite in class V cavities using confocal microscopy: An in vitro study. J Conserv Dent. 2011; 14: 164-168.
- Orłowski M, Tarczydło B, Chałas R. Evaluation of marginal integrity of four bulk-fill dental composite materials: In vitro study. Sci World J. 2015; 2015: 701262.
- Leprince JG, Palin WM, Vanacker J, Sabbagh J, Devaux J, Leloup G. Physico-mechanical characteristics of commercially available bulk-fill composites. J Dent. 2014; 42: 993-1000.
- Tarle Z, Attin T, Marovic D, Andermatt L, Ristic M, Taubock TT. Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites. Clin Oral Investig. 2015; 19:831-840.
- Zorzin J, Maier E, Harre S, Fey T, Belli R, Lohbauer U, et al. Bulk-fill resin composites: Polymerization properties and extended light curing. Dent Mater. 2015; 31:293-301.
- Olegário IC, Hesse D, Bönecker M, Imparato JCP, Braga MM, Mendes FM, et al. Effectiveness of conventional treatment using bulk-fill composite resin versus Atraumatic Restorative Treatments in primary and permanent dentition: a pragmatic randomized clinical trial. BMC Oral Health. 2017; 17: 34-41.
- Bedran-de-Castro AKB, Pereira PNR, Pimenta LAF, Thompson JY. Effect of thermal and mechanical load cycling on microtensile bond strength of a total-etch adhesive system. Oper Dent. 2004; 29: 150-156.
- Eirich FR. Degradation of dental polymers. J Polym Sci. 2003; 25: 303-304.
- Jung JH, Park SH. Comparison of polymerization shrinkage, physical properties and marginal daptation of fowable and restorative bulk fill resin-based composites. Oper Dent. 2017; 42: 375-386.
- Li H, Burrow MF, Tyas MJ. The effect of load cycling on the nanoleakage of dentin bonding systems. Dent Mater. 2002; 18:111-119.
- Felipe L, Schneider J. Microleakage evaluation of composite restorations submitted to load cycling. Cienc Odontol Bras. 2004; 7:27-33.
- Heintze SD, Monreal D, Peschke A. Marginal Quality of Class II Composite Restorations Placed in Bulk Compared to an Incremental Technique: Evaluation with SEM and Stereomicroscope. J Adhes Dent. 2015; 17: 147-154.
- Furness A, Tadros MY, Looney SW, Rueggeberg FA. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. J Dent. 2014; 42: 439-449.
- Kim RJY, Kim YJ, Choi NS, Lee IB. Polymerization shrinkage, modulus and shrinkage stress related to tooth-restoration interfacial debonding in bulk-fill composites. J Dent. 2015; 43: 430-439.
- Bavaria SR, Shah NC, Shah RP, Makati DJ. A comparative evaluation of microleakage of two different bulk fill composites with ever X posterior composite for class II restorations by dye extraction method- An in Vitro Study. IOSR J Dent Med Sci. 2017; 16:72-77.
- Peutzfeldt A, Asmussen E. Determinants of in vitro gap formation of resin composites. J Dent. 2004; 32: 109-115.
- Skalecka-Sadel A, Grzebieluch W. The marginal sealing of class II composite resin restoration located in enamel- Evaluation in vitro. Dent Med Probl. 2012; 49: 502-509.
- Heintze SD. How to qualify and validate wear simulation devices and methods. Dent Mater. 2006; 22:712-734.
- Shahidi C, Krejci I, Dietschi D. In Vitro evaluation of marginal adaptation of direct class II composite restorations made of different “‘Low-Shrinkage’” systems. Oper Dent. 2017; 42:273-283.
- Campos EA, Ardu S, Lefever D, Jassé FF, Bortolotto T, Krejci I. Marginal adaptation of class II cavities restored with bulk-fill composites. J Dent. 2014; 42:575-581.
- Benetti AR, Havndrup-Pedersen C, Honore D, Pedersen MK, Pallesen U. Bulk-fill resin composites: polymerization contraction, depth of cure, and gap formation. Oper Dent. 2015; 40:190-200.
- Abed YA, Sabry HA, Alrobeigy NA. ScienceDirect Degree of conversion and surface hardness of bulk-fill composite versus incremental-fill composite. Tanta Dent J. 2015; 12:71-80.
- Papadogiannis D, Tolidis K, Gerasimou P, Lakes R, Papadogiannis Y. Viscoelastic properties, creep behavior and degree of conversion of bulk fill composite resins. Dent Mater. 2015; 31:1533-1541.
- Ferracane JL, Condon JR. In vitro evaluation of the marginal degradation of dental composites under simulated occlusal loading. Dent Mater. 1999; 15:262-267.
- Webber FBM, Marin GC, Saram P, Lolli LF, Marson FC. Bulk-Fill Resin-Based Composites: Microleakage of Class II Restorations. J Surg Clin Dent. 2014; 2: 15-19.
- Kleverlaan CJ, Feilzer AJ. Polymerization shrinkage and contraction stress of dental resin composites. Dent Mater. 2005; 21:1150-1157.
- Garcia D, Yaman P, Dennison J, Neiva GF. Polymerization Shrinkage and Depth of Cure of Bulk Fill Flowable Composite Resins. Oper Dent. 2014; 39: 441-448.
- Krifka S, Federlin M, Hiller K-A, Schmalz G. Microleakage of silorane- and methacrylate-based class V composite restorations. Clin Oral Investig. 2012; 16: 1117-1124.
- Gogna R, Jagadis S, Shashikal K. A comparative in vitro study of microleakage by a radioactive isotope and compressive strength of three nanofilled composite resin restorations. J Conserv Dent. 2011; 14: 128-131.
- Draughn RA. Compressive Fatigue Limits of Composite Restorative Materials. J Dent Res. 1979; 58:1093-1096.