|Year : 2019 | Volume
| Issue : 6 | Page : 833-841
Mechanical performance of a newly developed glass hybrid restorative in the restoration of large MO Class 2 cavities
ZB Kutuk, C Ozturk, FY Cakir, S Gurgan
Department of Restorative Dentistry, School of Dentistry, Hacettepe University, Ankara, Turkey
|Date of Acceptance||23-Feb-2019|
|Date of Web Publication||12-Jun-2019|
Dr. Z B Kutuk
Department of Restorative Dentistry, School of Dentistry, Hacettepe University, Ankara - 06100
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: To evaluate the mechanical properties of a glass hybrid (GH) restorative system (EQUIA Forte/GC) and compare it with a microhybrid composite (G-aenial Posterior/GC) by compressive strength (CS) and fracture resistance (FR) tests. Materials and Methods: Cylindrical specimens were subjected to a CS test (n = 12). There were about 48 mandibular molars were used for a FR test and divided into four groups: Group 1 (positive control), sound teeth; Group 2 (negative control), extended size Class 2 cavities prepared on the mesial surfaces of teeth; Group 3, extended size Class 2 cavities restored with a composite; and Group 4, extended size Class 2 cavities restored with GH. Specimens were subjected to loading until a fracture occurred. Data were analyzed statistically (α = 0.05). Results: The fracture modes were examined by scanning electron microscope (SEM). The CS values of the composite and GH were 278.20 ± 17.34 MPa and 164.62 ± 25.72 MPa, respectively (P < 0.05). No differences were observed between the FR of restored groups (P > 0.05). Conclusions: The GH exhibited sufficient mechanical properties as a restorative material, and could be preferred for extensive caries lesions on posterior teeth.
Keywords: Composite resin, compressive strength, fracture resistance, glass hybrid
|How to cite this article:|
Kutuk Z B, Ozturk C, Cakir F Y, Gurgan S. Mechanical performance of a newly developed glass hybrid restorative in the restoration of large MO Class 2 cavities. Niger J Clin Pract 2019;22:833-41
|How to cite this URL:|
Kutuk Z B, Ozturk C, Cakir F Y, Gurgan S. Mechanical performance of a newly developed glass hybrid restorative in the restoration of large MO Class 2 cavities. Niger J Clin Pract [serial online] 2019 [cited 2019 Jun 25];22:833-41. Available from: http://www.njcponline.com/text.asp?2019/22/6/833/260048
| Introduction|| |
The primary cause of tooth damage is dental caries or cavities. Conservatively, in recent years the treatment of primary or secondary caries has involved the use of composite resins for the placement of posterior permanent tooth restorations particularly because of its better esthetic properties and the general concerns about the limitations of amalgam.,
Since tooth tissue loss is an irreversible process, the least invasive technique should be considered as the first therapeutic choice. The life span of a restoration, known as service life or length of service, defines the longevity of the restored tooth unit and is multifactorial. It depends on the patient, operator (dentist), and material related properties.,,, The amount of residual tooth tissue is also of paramount importance.,,
The posterior direct tooth-colored restorative materials should have adequate strength to resist masticatory and occlusal forces. The compressive strength and fracture resistance are considered to be good indicators for simulating the masticatory forces encountered in the mouth. The compressive test aims to evaluate the material's resistance to vertical stresses as well as the occlusal forces during function, and would be a more important property for understanding the durability of posterior restorations which encounter higher masticatory loads. However, fracture resistance is also an essential factor that affects cracking of the restorations under heavy loading. The experimental and theoretical efforts have been made to relate the strength of a material to its fracture resistance in addition to the structural parameters.
Hybrid composite resins are considered to be the “gold standard,” and three-step or two-step agents are recommended as gold standard adhesives. The Academy of Operative Dentistry-European Section (AODES) also suggests the use of microhybrid or nanohybrid composite resins with a minimum of 60% filler load by volume to restore the lost tooth structure.
In contrast to composite resins, conventional glass ionomers (GIs), have traditionally been considered inferior restorative materials. While GIs traditionally have been tagged as temporary materials not suitable for permanent restorations, and have mainly been placed temporarily over residual lesions since their limited flexural strength does not allow for their use to permanently restore extended cavities, recent meta-analytical findings have emphasized that highly viscous GIs are not obviously inferior to the current gold standard (amalgam). Highly viscous GIs are constantly being enhanced to improve their clinical handling, and performance in order to be increasingly used in restorative dentistry as a permanent restorative. The recent advances in this material class, however, have widened the indication spectrum of GIs, and one very recent development was the introduction of glass hybrid (GH) (EQUIA Forte), which is a bulk-fill highly viscous GI reinforced with ultrafine, reactive glass particles forming a GH restorative, and has been promoted as amalgam alternative. This reinforced GI contains a second smaller and more reactive silicate particle and higher-molecular-weight acrylic acid molecules which supposedly increase matrix cross-linking. This, in turn, is thought to improve the material's flexural strength. Covering these restorations with a resin layer is supposed to further improve wear resistance and esthetic appearance. Although the long-term successful performance of restorative GI systems in the restoration of Class 1 and conservative (small size) Class 2 cavities was demonstrated by clinical studies,, it remains unclear if GH may truly be used to restore large size Class 2 cavities, since the fracture resistance of teeth restored with GH is unknown.
Therefore, the present in vitro study aimed to assess the compressive strength and fracture resistance of a GH restorative system and a microhybrid composite resin and to compare the mechanical performance of these materials in large Class 2 cavities on molar teeth. The first hypothesis was that the GH restorative material would have significantly lower compressive strength than the microhybrid composite resin, and the second hypothesis was that GH restorative material would not adequately ensure fracture resistance in large size Class 2 cavities of molar teeth.
| Materials and Methods|| |
The Human Research Ethics Committee of the university approved this study with process no: GO 17/406-06.
Materials selected for this study included a microhybrid composite resin (G-ænial Posterior/GP) and a GH restorative system (EQUIA Forte/EF). The GH restorative system was assessed with a nanofilled resin coating (EQUIA Forte Coat). Details of the materials used in this study are shown in [Table 1].
Compressive Strength Test: Specimens for compressive strength (CS) test were prepared using a customized Teflon mold 8 mm in height and 4 mm in diameter. The Teflon mold was placed on a glass plate, and the bottom surface was covered with a Mylar strip (S.S. White Limited, Middx, England).
A G-ænial Posterior composite resin was placed with 2 mm layers in a Teflon mold in four steps, and each layer was polymerized using a light emitting diode (LED) light device (1400 mW/cm2) (Starlight S, Mectron SpA, Carasco, Italy) for a 20s curing time. The upper surface of the last layer was covered with a Mylar strip to prevent the formation of an oxygen inhibition layer, and constant pressure was applied with a 1 mm thick microscope glass. Then, the pieces of the mold were carefully removed, and cylindrical specimens (4 mm Ø, 8 mm height, n = 12) were obtained.
EQUIA Forte specimens for CS test were prepared according to the manufacturer's instructions. The capsule was tapped on its side on a hard surface to loosen the powder; then, to activate the capsule, the plunger was pushed until it was flush with the main body, and the capsule was immediately placed into a capsule applier and the lever was clicked once. The capsule was mixed with an automixer (Coxo Medical Instrument Co., Ltd, Guangdong, China), and then applied to the Teflon mold. The upper surface was covered with a Mylar strip, and constant finger pressure was applied for the duration of the setting process (2 min, 30s). When the setting was completed, the EQUIA Forte Coat was applied to the top surfaces of the GH specimens using micro-tip applicators without air blowing and light cured for 20s.
The CS of tested materials were evaluated in ambient air (23 ± 1°C) according to ISO 9917-1:2007. The test was carried after 24h water storage at 37°C. The CS was determined by loading in using a universal mechanical testing machine (Universal Testing Machine, Mod Dental, Ankara, Turkey) at a crosshead speed of 1 mm/min until specimen failure. The fracture load was noted for each sample. The CS was calculated according to equation CS = 4 F/(π D2)
where CS is the compressive strength; F is the maximum applied load in Newton (N), and D is the diameter of the specimen in mm.
Fracture Resistance Test: There were about 48 extracted human lower first molars for periodontal or orthodontic reasons were selected according to their mesial-distal (mean ± SD = 11.27 ± 0.13 mm) and buccal-lingual width (mean ± SD = 10.11 ± 0.14 mm), with a maximum deviation of 0.2 mm from the means in each dimension set as the limit. Teeth were cleaned in 5.25% NaOCl for five min and examined for defects. The root surface of each tooth was coated with a layer of liquid latex separating material (Rubber-Sep, Kerr, Orange, CA) prior to embedding to mimic the periodontal ligament, and then the specimens were embedded in methacrylate resin (SC, Imicryl, Konya, Turkey) at 2.0 mm from the cementoenamel junction (CEJ) using a gauge to simulate the bone level.
The teeth were divided randomly into four groups (n = 12): Group 1: positive control, intact, unprepared, and unrestored teeth; Group 2: mesio-occlusal (MO) cavities, prepared and unrestored; Group 3: MO cavities prepared and restored with microhybrid composite resin (G-Premio Bond/G-ænial Posterior); and Group 4: MO cavities prepared and restored with GH restorative system (EQUIA Forte).
Standardized large size Class 2 MO cavities were prepared by the same trained operator to eliminate inter-operator differences under water cooling. A high-speed handpiece with a flat end cylinder diamond bur (10-4 mm, #835, Diatech, Coltène/Whaledent AG, Altstätten, Switzerland) was used to prepare cavities in Group 2, 3, and 4.
As recommended by the manufacturer of EQUIA Forte, the proximal cavity boundaries were placed 1.0-1.5 mm distance from the cusp peaks [Figure 1]. The isthmus width was larger than 1/3 of the intercuspal space, and the occlusal portion cavity depth was 2.5 mm. The axial wall in the mesial proximal box was prepared to a depth of 2 mm, and the gingival margin was placed 1.5 mm above the CEJ. The cavosurface margins were prepared at 90°, and all the internal lines and point angles were rounded. The depth and width of the cavities were checked using a scaled periodontal probe (instrument number 23/UNC 15; Hu Friedy, Chicago, IL, USA). The cavity design with dimensions is shown in [Figure 2].
|Figure 2: Standardized large size Class 2 MO cavity preparation and corresponding measurements. (a) General view of the cavity from occlusal side. (b) The gingival margin was placed 1.5 mm above to the CEJ. (c) The axial wall height was approx. 2.5 mm. (d) The occlusal portion cavity depth was 2.5 mm. (e) The axial wall in the mesial proximal box was prepared to a depth of 2 mm|
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The prepared cavities in Group 3 were rinsed with water and air-dried with an air/water syringe. After application of a contoured matrix band (Hawe Tofflemire Contoured Matrices, Kerr, Bioggio, Switzerland), the enamel surfaces were acid-etched selectively with 35% phosphoric acid gel (GLUMA Etch 35 Gel, Heraeus Kulzer, Hanau, Germany) for 15s, rinsed with water, and gently air-dried. The universal adhesive G-Premio Bond (GC Corp., Tokyo, Japan) was applied to the cavity walls for 10s and then spread with maximum compressed air for 5s. The adhesive layer was light-cured for 10s. Microhybrid composite resin (G-ænial Posterior) was placed in several consecutive 2 mm-thick oblique increments. Each increment was light cured from the occlusal surface for 20s. After removal of the matrix, the restorations were finished with a series of Soflex discs (Optidisc, Kerr, Bioggio, Switzerland).
The prepared cavities in Group 4 were rinsed with water and air-dried with an air/water syringe. After application of a contoured matrix band, the cavity surfaces were treated with 20% polyacrylic acid (Cavity Conditioner, GC Corp.) for 10s, rinsed with water, and air-dried. The GH restorative system was prepared the same as the CS test and applied to the cavities. The restorations were finished as in Group 3, and then the coating agent (EQUIA Forte Coat, GC Corp.) was applied using the micro-tip applicators without air blowing and light cured for 20s.
The specimens were stored in distilled water for 24h and thermo-cycled (Thermo-cycle Machine, Mod Dental) for 10.000 cycles at 5°C and 55°C with each cycle corresponding to a 20s bath at each temperature with a 5s dwell time. Afterwards, all prepared specimens were tested for fracture resistance, using a universal loading device (Universal Testing Machine, Mod Dental). Each test was performed at a cross-head speed of 1 mm/min, and load was applied using a 5 mm diameter stainless-steel ball-shaped stylus. The ball-shaped stylus should contact the inclined planes of the buccal and lingual cusps beyond the margins of the restorations. A Mylar strip was placed between the specimen and the stylus to avoid local stress concentration by dispersing the load. The peak load to fracture was recorded in N for each specimen, and the mean was calculated for each group.
The fracture types seen in the specimens were evaluated under a stereomicroscope (Leica MZ 16A, Leica Microsystems, Switzerland), and classified in two forms. The first classification was made according to repairability: (1) a restorable fracture above the CEJ means that, in case of fracture, the tooth can be re-restored by restoration; (2) a non-restorable fracture extends below the CEJ and the tooth is likely to be extracted. The second classification is based on the surface of the fracture: (1) adhesive + cohesive in restoration, the type of fracture in which the restoration breaks and separates from the dental tissue; (2) adhesive + cohesive in restoration + cohesive in the tooth, the type of fracture in which fracture of the tooth is seen when the restoration is broken and separated from the dental tissue; (3) cohesive in tooth, the type of fracture that can only be seen in the teeth; and (4) cohesive in restoration, the type of fracture that can only be seen in restoration.
Scanning Electron Microscope (SEM) (JSM-6400 Scanning Electron Microscope, Jeol Ltd, Tokyo, Japan) images were taken of selected specimens from each group, and their fracture types were investigated at 15×, 50×, and 200×. Surface characteristics of the tested materials in the study were also investigated under SEM at 250×, 500×, and 1000×.
All statistical calculations were performed using the SPSS software program (SPSS 20.0 for Windows/SPSS Inc., Chicago, IL, USA) at a α = 0.05 confidence interval. Since, the Kolmogorov-Simirnov test indicated that the compressive strength data did not follow normal distribution in any of the groups, the non-parametric Mann-Whitney U test was utilized for the comparison. The differences between the groups were evaluated by the Kruskal Wallis test, and pair-wise comparisons were performed using the Tukey HSD (honestly significant difference) test in the analysis of fracture resistance values.
| Results|| |
[Table 2] summarizes the CS values for the tested materials. According to the Mann-Whitney U test results following the Kolmogorov-Smirnov test, the CS values of the materials were found to be statistically different. The microhybrid composite resin (G-ænial Posterior) (278.20 ± 17.34 MPa) showed significantly higher mean CS values than the GH (EQUIA Forte) (164.62 ± 25.72 MPa) (P < 0.001).
The fracture resistance values for the four groups are presented in [Table 3]. There was a statistically significant difference among the groups according to the Kruskal-Wallis test (P < 0.05). The highest mean fracture resistance value was seen in the positive control group (977.99 ± 92.79 N). This value was significantly higher than the mean fracture resistance value of the negative control (418.48 ± 36.91 N) and the EQUIA Forte restored (841.88 ± 74.57 N) groups (P < 0.05). The lowest mean fracture resistance value was found in the negative control group (418.48 ± 36.91 N), which was statistically lower than the positive control group (977.99 ± 92.79 N) and G-ænial Posterior restored (961.87 ± 46.04 N) groups (P < 0.05).
Pair-wise comparison of the test groups with the Tukey HSD test are shown in [Table 4]. There is no statistically significant difference between the mean values of the fracture resistance of the groups restored using G-ænial Posterior and EQUIA Forte (P = 0.239).
|Table 4: Pair-wise comparison of the fracture resistance values of groups according to the Tukey HSD test|
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Fracture types and their percentage distributions of the specimens in the groups subjected to restoration after the fracture resistance test are given in [Figure 3]. Different fracture types of teeth restored with G-ænial Posterior and EQUIA Forte are shown in [Figure 4] and [Figure 5]. The most common type of fracture in both groups was adhesive + cohesive in the restoration fracture where the restoration was broken and separated from the tooth. All of the fracture types seen in the group restored with G-ænial Posterior were restorable, whereas two (16.66%) specimens in the group restored with EQUIA Forte exhibited non-restorable fractures. In [Figure 6] it provides representative SEM images of an adhesive + cohesive in a restoration fracture type of a specimen in the G-ænial Posterior restored group. SEM images of an adhesive + cohesive in a restoration fracture type of a specimen in the EQUIA Forte restored group is in [Figure 7]. The SEM observations of the tested materials for surface analysis are shown in [Figure 8]. The smooth surface appearance of the composite resin and glass fillers of the GH restorative material with different sizes were clearly seen.
|Figure 3: Percentage distributions of fracture types of the specimens according to 2 classified forms (repairability and fracture surface)|
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|Figure 4: Examples of different fracture types on teeth restored with G-ænial Posterior: (a) adhesive + cohesive in restoration, (b) adhesive + cohesive in restoration + cohesive in tooth (can be re-restored), (c) cohesive in tooth, (d) cohesive in restoration|
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|Figure 5: Examples of different fracture types on teeth restored with EQUIA Forte (a) adhesive + cohesive in restoration, (b) adhesive + cohesive in restoration + cohesive in tooth (can be re-restored), (c) adhesive + cohesive in restoration + cohesive in tooth (cannot be re-restored)|
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|Figure 6: SEM images of an 'adhesive + cohesive in restoration' fracture type of a specimen in tooth restored with G-ænial Posterior. (a) The photograph of the tooth before SEM evaluation, (b) 15×, (c) 50×, (d) 200×. (E: Enamel; D: Dentin; GP: G-ænial Posterior)|
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|Figure 7: SEM images of an 'adhesive + cohesive in restoration' fracture type of a specimen in tooth restored with EQUIA Forte. (a) The photograph of the tooth before SEM evaluation, (b) 15×, (c) 50×, (d) 200×. (D: Dentin; EF: EQUIA Forte)|
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|Figure 8: SEM images of the surface appearance of the materials at different magnifications; G-ænial Posterior: (a) 250×, (b) 500×, (c) 1000×; EQUIA Forte: (d) 250×, (e) 500×, (f) 1000×|
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| Discussion|| |
While treating deep and large caries lesions, dentists cope with managing the vitality of the pulp and restoring the resulting extended cavity. The present in vitro study investigated an alternative appropriate restorative material for these types of large cavities and assessed the suitability of a new restorative material, GH restorative, in terms of compressive strength, fracture resistance, and reparability properties.
The compressive strength of the microhybrid composite resin was found to be higher than the GH restorative system. Thus, the first hypothesis was accepted. These results suggested that the new GH restorative system (EQUIA Forte) needs to improve its compressive strength property. On the other hand, and perhaps more relevantly, the two materials did not differ significantly in their fracture resistance on molar teeth. Therefore, the second hypothesis was rejected.
The compressive strength test is one of the main methods to assess the ability of a material to withstand masticatory forces. Previous studies reported compressive strength values for composite resins that ranged from 250 to 390 MPa.,, This reported compressive strength for composite resin ensures sufficient strength to be used for restoring all cavity types. In this study, the composite resin exhibited significantly higher mean values of compressive strength than the GH restorative system. This may be explained by the different compositions of these materials. GI based restoratives consist of basic fluoroaluminosilicate glasses and acidic copolymers that chemically set by acid-base reactions. Water is the reaction medium into which cement-forming cations are leached and transported to react with polyacids. Water also serves to hydrate the cross-link matrix, increasing the cement strength. The final set glass ionomer structure contains a substantial amount of unreacted glass that acts as fillers for the set cement. New generations of GI restoratives have coating agents; however, we still advocate for improvement of their physicomechanical properties and clinical longevity., However, the results of the study indicated that the coating application could not be enough to increase the compressive strength of the GH restorative system as much as the composite resin.
The mean value of the compressive strength of the GH restorative system recorded in this study was closer to the GI based restorative materials that have been reported in the literature after 24 hours of setting time using standardized cylindrical specimens.,,,
In the present study, the specimens for the fracture resistance test were stored in distilled water for 24 h and thermo-cycled for 10.000 cycles at 5°C and 55°C to simulate a one-year aging period. There is a wide variation in temperature amplitude as well as in the number and duration of the elected cycles (500-5 million cycles) in several studies.,, Some authors reported degradation of the GI after the thermo-cycle while others did not find any degradation effects using such experimental simulation method.,,
A fracture is a complete or incomplete breakage in a material resulting from the application of extreme strength. Fracture resistance is a substantial attribute directly related to cracking. Theoretical and practical experiments have been made concerning the strength of a material in terms of its fracture resistance in addition to the constructional parameters. Depending on the stress status in direct restorative materials, fracture resistance can increase or decrease according to the strength changes.
This study showed that the extended sized cavities restored with the microhybrid composite resin strengthened the remaining tooth structure. There is no significant difference in the fracture resistance was found between teeth restored with the microhybrid composite resin and the unprepared teeth. This result could be attributed to the improved characteristics of posterior composite resins. It was also found that the cavity preparation weakened the teeth. On the basis of the application of loading, the microhybrid composite resin (G-ænial Posterior) increased the resistance to fracture similar to that of the intact, unprepared teeth. Moreover, restoring the extended sized cavities with the GH restorative system (EQUIA Forte) increased the fracture strength up to 66% of the mean value exhibited by the intact teeth and up to 67% of the mean value exhibited by the restored teeth with microhybrid composite resin (G-ænial Posterior).
The superior results for the fracture resistance of the GH restorative system in the present study may be due to the additions of certain components to the material. The coating agent (EQUIA Forte Coat) applied to the surface of the GH restorative system contains a nanofilled resin that may have contributed significantly to the increased resistance of the material to mechanical forces. Other studies have recommended that GI based restorative surfaces, before being contaminated with water, should be coated in order to optimize their mechanical strength., Additionally, the incorporation of ultrafine, highly reactive glass particles in the GH restorative system [Figure 8] could be the reason for having similar fracture resistance to the microhybrid composite resin.
In a recent study, Ong et al. compared the viscoelastic properties of the same GH restorative system with bulk-fill reinforced highly viscous GI cements and different composite resins. The authors reported that EQUIA Forte was significantly more rigid and deformed less than the other materials under functional stresses, supporting its indication for posterior restorations. A recent systematic review also reported a comparable failure rate between highly viscous GIs and amalgam in permanent posterior teeth. So, the results of this study were found to be compatible with these studies.
Although, composite resin is stronger than the GH restorative system tested in the present study, its fracture mode resulted within the material. This was in contrast to the GH restorative system that showed fracture lines within the material and the sacrificing of the surrounding enamel and/or dentin, which was not a characteristic of GI based restoratives. In a clinical situation, the former fracture mode is to be preferred to the latter, as it permits easier repair. A direct restoration should recover the stress/strain conditions of the original intact tooth.
The present study has a number of limitations. First, the cavities were prepared by the operator using high-speed hand instruments and standardized via measuring with a periodontal probe, which increases variability between samples and results in cavities that might be less undermining and extended than real-life deep cavities. Second, clinically, masticatory forces have a relatively permanent magnitude and are applied over a longer period of time. The variations in application speed, and direction cause a different pattern of fractures. In vitro studies are not an exact imitation of an ordinary chewing blow because they apply a continuously increasing force until the tooth fractures, but they represent an important source of information on the structural integrity of the tooth. Third, the thermo-cycle procedure was applied to fracture resistance specimens whereas compressive strength specimens were stored for 24 h in distilled water and not subjected to the thermo-cycle procedure as defined by ISO 9917-1:2007.,
The GH restorative system is obtained by the development of GIs that are accepted as materials for the future in restorative and minimally invasive dentistry. Recent studies suggest that these materials are promising as permanent restorative materials in large Class 2 restorations., These laboratory results cannot be directly extrapolated to the clinical situation, but they could give impressions regarding clinical performance of new restorative materials. However, the mechanical properties need to be further improved.
As a result, it may be preferable to use the GH restorative system, which stands out because of its favorable properties, such as its fast and easy application and compatibility with dental tissue, as an alternative to composite resins in the restoration of large caries lesions in posterior teeth.
| Conclusions|| |
Within the limitation of this in vitro study, the following conclusions may be drawn:
- the compressive strength of the GH restorative system (EQUIA Forte) was lower than the composite resin (G-ænial Posterior),
- the fracture resistance of the GH restorative system (EQUIA Forte) was comparable to the composite resin (G-ænial Posterior),
- the fracture resistance of the composite resin (G-ænial Posterior) was found to be similar to that of intact teeth,
- the most common fracture type was adhesive + cohesive in restoration in the teeth restored with composite resin (G-ænial Posterior) and the GH restorative system (EQUIA Forte), and
- a small number of non-restorable fractures occurred in teeth restored with the GH restorative system (EQUIA Forte) while restorable fractures occurred with respect to forces in all teeth restored with composite resin (G-ænial Posterior).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3], [Table 4]