|Year : 2022 | Volume
| Issue : 3 | Page : 176-180
Evaluation of fracture resistance of maxillary premolars with class II mod cavities restored with fiber-reinforced composite and Cention N — An in vitro study
Leela Naga T. Pavani1, Krishnaveni M Marella2, Srividya Putta3, MK Ramya2
1 Conservative Dentistry and Endodontics, Consultant Endodontist, Bengaluru, Karnataka, India
2 Conservative Dentistry and Endodontics, KVG Dental College and Hospital, Sullia, Karnataka, India
3 Prosthodontics and Crown and Bridge, Consultant Prosthodontist, Bengaluru, Karnataka, India
|Date of Submission||04-May-2021|
|Date of Decision||21-May-2021|
|Date of Acceptance||15-Jun-2021|
|Date of Web Publication||26-Dec-2022|
Dr. Krishnaveni M Marella
Department of Conservative and Endodontic, KVG Dental College and Hospital, Sullia - 574 327, Karnataka
Source of Support: None, Conflict of Interest: None
Aim: The purpose of this in vitro study is to assess the influence of fiber-reinforced composite (FRC) and Cention N on the fracture resistance of maxillary premolars with class II mesio-occluso-distal (MOD) cavities.
Materials and Methods: Forty-five freshly extracted human maxillary premolar teeth were collected and embedded in an acrylic cylinder up to 2.0 mm below the cementoenamel junction (CEJ) using self-cure acrylic resin. MOD cavities were prepared with continuous water cooling using a high-speed handpiece and a diamond bur. Samples were then divided randomly into three experimental groups with 15 teeth each according to the respective composite: Group A: teeth were left intact; Group B: fiber-reinforced composite (FRC); and Group C: Cention N. All groups were stored in water at 37°C for 24 hours and thermocycled 500 times between 5°C and 55°C. All specimens were subjected to compressive axial loading in a universal testing machine using a steel bar which was placed centrally to the occlusal surface and applied in parallel to the long axis of the tooth until fracture occurred.
Statistical Analysis: One-way analysis of variance (ANOVA) and Tukey's post hoc test were used to analyze the results.
Results: In the present study, Cention N showed significantly high fracture resistance compared to fiber-reinforced composite.
Conclusion: Among the test specimens, Cention N showed significantly high fracture resistance.
Keywords: Cention N, fiber-reinforced composite (FRC), fracture resistance, Instron universal testing machine, mesio-occluso-distal cavity
|How to cite this article:|
Pavani LN, Marella KM, Putta S, Ramya M K. Evaluation of fracture resistance of maxillary premolars with class II mod cavities restored with fiber-reinforced composite and Cention N — An in vitro study. J NTR Univ Health Sci 2022;11:176-80
|How to cite this URL:|
Pavani LN, Marella KM, Putta S, Ramya M K. Evaluation of fracture resistance of maxillary premolars with class II mod cavities restored with fiber-reinforced composite and Cention N — An in vitro study. J NTR Univ Health Sci [serial online] 2022 [cited 2023 Mar 22];11:176-80. Available from: https://www.jdrntruhs.org/text.asp?2022/11/3/176/365022
| Introduction|| |
Together with dental caries and periodontal disease, tooth fracture is the most common cause of tooth loss. Dental restorations cause the loss of enamel continuity and increase the fracture susceptibility of teeth. Cusp fracture often occurs in teeth with restorations that cover more than one-third of the intercuspal distance. It was claimed by Mincik J et al. that mechanical resistance of the remaining dental tissues might get reduced by 20% due to occlusal cavity preparation and the resistance decreases by 63% when both the marginal ridges are deteriorated. The reinforcement of tooth structures is made possible with the advancements in the field of dental materials and bonding agents with their improved quality. The preservation of tooth structure under occlusal loading is important, and unlike amalgam, bonded composite restorations usually strengthen the tooth. Since their development, several improvements have been made to the physical and mechanical properties of resin composites and have permitted their successful use in posterior restorations.
More recently, a breakthrough in the field of restorative dentistry is everX Posterior, a fiber-reinforced composite equipped with short glass fibers which mimic the collagen fibers of dentine and therefore achieve a higher fracture toughness for restoration. Thus, everX Posterior, due to its specific material structure, provides new options in restorations of large cavities in the posterior area with its exceptional fracture toughness which prevent the occurrence of fractures in the filling.
Cention N is an “alkasite” restorative which is a new category of filling material, like compomer or ormocer and is essentially a subgroup of the composite resin. Although Cention N is similar to a standard amalgam or glass ionomer restoration in terms of bulk placement, possible use without an adhesive and self-curing properties, it also has a number of advantages over these materials.
Cention N offers tooth-colored esthetics together with high flexural strength. Thus, it redefines the basic filling, combining bulk placement, ion release, and durability in a dual-curing, esthetic product—satisfying the demands of both dentists and patients. Currently, there is mere literature comparing fiber-reinforced composite (FRC) and Cention N composite restorations in reinforcing weakened teeth. Hence, fiber-reinforced composite (FRC) and Cention N were compared to evaluate the fracture resistance in MOD cavities of posterior teeth.
| Materials and Methods|| |
Forty-five freshly extracted human maxillary premolar teeth were collected and stored in normal saline solution. Roots of the teeth are dipped in molten wax to a depth of 1 mm below CEJ to produce a 0.2- to 0.3-mm layer of wax approximately equal to the average thickness of the PDL.The teeth had their roots embedded in a cylindrical PVC ring (1.4 × 2.5 cm) using a self-cure acrylic resin (Rapid Repair, Dentsply) up to 1 mm below the cementoenamel junction (CEJ). Later wax spacer is removed, and polyvinyl siloxane impression material (Aquasil, Dentsply) was delivered into resin alveolus which will simulate periodontal ligament. MOD cavities were prepared on 45 premolar teeth.The preparations were ½ of the intercuspal width and 2.0 mm deep pulpally, and the proximal boxes were prepared at a width of ½ the total faciolingual dimensions, with an axial wall that was 2.0 mm wide and 1.5 mm deep.
Samples were then divided randomly into three experimental groups with 15 teeth each as follows:
Group A: Teeth were left intact (control);
Group B: Restored with fiber-reinforced composite (FRC);
Group C: Restored with Cention N.
In Group B, all the prepared cavity surfaces were dried with oil-free compressed air, etched with 37% phosphoric acid for 15 seconds, rinsed, and dried. Adper Single Bond 2 (3M ESPE) bonding agent was applied to the etched surface, gently dried, and cured for 20 seconds. The specimens were restored with the corresponding composite and cured for 20 seconds according to manufacturer's instructions. In Group C, all the prepared cavity surfaces were restored with Cention N, corresponding to a powder/liquid weight ratio of 4.6 to 1.
Thermocycling of the samples was performed (500 cycles) at 5°C ± 2°C–55°C ± 2°C with 30-s dwell time and 5-s transfer time. Then, the specimens were stored in an incubator at 37°C for 24 h.
All specimens were subjected to compressive axial loading in a universal testing machine using a steel bar which was placed centrally to the occlusal surface and applied in parallel to the long axis of the tooth until fracture occurred. Forces necessary to fracture each tooth were measured in Newtons (N). The data obtained were tabulated and subjected to statistical analysis.
The data presented as mean ± standard deviations were calculated using SPSS version 16.0 software. One-way ANOVA was applied to evaluate the fracture resistance values, and Tukey's post hoc test was applied for pairwise comparison among various groups. The level of significance was set at P < 0.05.
Ethical approval for this study (GPRDCH/IEC/2018/002) was provided by the Institutional Ethics Committee, G Pulla Reddy Dental College and Hospital, Kurnool on 1st December 2018.
| Results|| |
The results of the study with mean and standard deviations are shown in [Table 1]. One-way analysis of variance showed statistically significant differences among the mean fracture resistance values of Group A (1027.35), Group B (732.57), and Group C (947.56) where P < 0.001. The mean value of fracture resistance of teeth restored with Cention N (947.56) is higher when compared to fiber-reinforced composite (732.57). However, these values are less when compared to the control group (1027.35) [Chart 1].
Inter-group comparisons are shown in [Table 2] evaluated by Tukey's post hoc test. When Group A is compared with Group B and Group B with Group C, there is a statistically significant difference with P value 0.001. However, Group A is compared with Group C, P > 0.05, indicating that there was no significant difference between the groups.
| Discussion|| |
Premolars were selected in this study due to their anatomy, function, crown size, and crown/root ratio which make them more prone to fracture than other posterior teeth. Moreover, considering their location in the dental arch, they are subjected to both compressive and shear forces. Cuspal inclination of premolars renders them more susceptible to cusp fracture under occlusal force. They were also appropriate in evaluating the efficacy of materials to increase their fracture resistance. MOD cavities were designed in order to mimic a situation that may often be seen in clinical settings and are considered to be the worst in terms of fracture resistance. Hence, maxillary premolars with MOD cavities were selected to evaluate fracture resistance of the composite materials.
Thermocycling of the samples was performed as it simulates in vitro, thermal changes that occur in the oral cavity. A layer of light body elastomeric impression material, polyvinyl siloxane, was applied around the root surfaces before mounting of specimens in acrylic block to simulate the periodontal ligament.
In 2013, a new, short-fiber-reinforced restorative composite was introduced to the market (everX Posterior, GC Europe, Leuven), intended to offer a restorative material of enhanced durability for medium- to large-size class II cavities. The everX Posterior contains E-glass fibers impregnated within the nanohybrid composite. This premixed material is more convenient to use as it eliminates the need to place the glass fibers in the cavity which is a time-consuming and cumbersome procedure. Total inorganic and filler content is 74.2 wt%/53.6 vol%. The short E-glass fibers present in the everX Posterior prevent and arrest crack propagation that often starts from the surface of the restoration. During the premarket in vitro and clinical test phases, it proved to exhibit better mechanical and polymerization stress properties than conventional composite, thus holding the promise of a new biomimetic restorative material for the posterior region, a part of the oral cavity where the teeth are often exposed to excessive forces, leading to cracking and fracture.
Reinforcing effect of the fiber fillers is based on stress transfer from the polymer matrix to fibers. Random fiber orientation and the polymer matrix by the semi-IPN structure likely had a significant role in mechanical properties. In addition to the toughening mechanism by fibers, the linear polymer chains of PMMA in the cross-linked matrix of Bis-GMA–TEGDMA plasticize the polymer matrix to some extent and increase the fracture toughness of the composite resin. Hence, in the present study, everX Posterior was compared with Cention N.
Cention N is an “alkasite” restorative which is a new category of filling material, like compomer or ormocer, and is essentially a subgroup of the composite resin. This new category utilizes an alkaline filler, capable of releasing acid-neutralizing ions. Cention N is a radiopaque, self-curing filling material with light-curing option, which releases fluoride and calcium ions. It is suitable for use as a full volume replacement material in restorations for class I, II, and V cavities, which offers tooth-colored esthetics together with high flexural strength. Cention N can be optionally cured with light in the wavelength range of 400–500 nm.
A combination of UDMA (urethane dimethacrylate), DCP (tricyclodecane-dimethanol dimethacrylate), an aromatic aliphatic UDMA and PEG-400 DMA (polyethylene glycol 400 dimethacrylate), interconnects (cross-links) during polymerization, resulting in strong mechanical properties and good long-term stability. Cention N does not contain Bis-GMA, HEMA, or TEGDMA.
The most important and extensively investigated variable for physical performance in dental composite resins is filler loading. The fillers of Cention N were chosen not only to achieve strength but also to obtain the desired handling characteristics of the mixed material. In its mixed state (powder + liquid), Cention N contains 78.4 wt%/57.6 vol% inorganic filler, whereas FRC exhibits 74.2 wt%/53.6 vol% inorganic filler content. Kim and Watts reported that the threshold of filler loading for the highest fracture toughness values in resin composites was 55% by volume. This percent of filler loading is more important than weight percent. Previous studies found a positive correlation between filler loading and mechanical performance. The alkaline glass also releases hydroxide and calcium (OH- and Ca2+) ions which can further help prevent demineralization of the tooth substrate.,,,
Stress transfer from the polymer matrix to filler particles is one of the important factors that affects fracture toughness and flexural strength values. There may be a difference in the adhesion between filler particles and matrix among these resin composites. Besides the filler system, monomer structures of the resin matrix also influence the mechanical properties.
Clinical studies have confirmed that a flexural strength of ≥100 MPa is an important factor for long-lasting restorations. At ≥100 MPa, Cention N offers very good flexural strength for the stress-bearing posterior region (R&D, Ivoclar Vivadent AG, Schaan, Liechtenstein, 2016). Cention N is a tooth-colored filling material with a high translucency of approximately 11%. This allows Cention N to blend naturally with the surrounding tooth structure, while covering discolored dentin at the same time.
| Conclusion|| |
From the present study, it can be concluded that Cention N showed significantly high fracture resistance when compared to fiber-reinforced composite. Cention N, the alkasite restorative, is a strong, ion-releasing, esthetic, economical, and long-lasting basic filling material with good flexural strength for the stress-bearing posterior region as an alternative restorative material. However, it should be emphasized that clinical trials are necessary in order to evaluate the usefulness of Cention N in dental restorations.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]