|Year : 2022 | Volume
| Issue : 6 | Page : 566-573
Comparative evaluation of compressive strength and fracture resistance of posterior restorative materials alkasite and newer glass ionomers with amalgam: An in vitro study
Gurmeen Kaur1, Chitharanjan Shetty2, Mithra N Hegde2
1 Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Dental College and Hospital, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
2 Department of Conservative Dentistry and Endodontics, AB Shetty Memorial Institute of Dental Sciences, Mangalore, Karnataka, India
|Date of Submission||29-Apr-2022|
|Date of Acceptance||10-Oct-2022|
|Date of Web Publication||30-Dec-2022|
Dr. Gurmeen Kaur
Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Dental College and Hospital, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
Aim: The conventional restorative materials amalgam and glass ionomer have multifarious drawbacks leading to introduction of newer materials with superior biomechanical attributes. The present study aimed to assess and compare the compressive strength of ceramic-reinforced glass ionomer cement, zirconia-reinforced glass ionomer cement, high strength glass ionomer posterior restorative material, alkasite restorative material, and amalgam when used as posterior restorative materials. Materials and Methods: Five restorative materials were evaluated: modified glass ionomer cements including ceramic-reinforced, zirconia-reinforced, and high strength glass ionomer; alkasite restorative material; and dental amalgam. Fifty cylindrical specimens were fabricated using test materials (n = 10 for each group). Class II cavities prepared on 50 intact permanent molars were restored with test materials. After thermocycling and 24 h of storing, the specimens in artificial saliva, compressive strength, and fracture resistance were tested. Data were analyzed statistically. One-way analysis of variance and post hoc Tukey test were used for intergroup comparison. Pearson’s correlation was used for correlating the maximum load by cylindrical and tooth specimens. Results: A significantly high compressive strength was displayed by specimens of group 4, followed by group 5, group 3, group 1, and least by group 2. The highest fracture resistance was displayed by teeth restored with the test materials in group 4, group 1, group 5, group 2, and least by group 3. Conclusion: Within the limitations of the present study, alkasite restorative material (Cention N) showed the highest compressive strength in cylindrical and highest fracture resistance in tooth specimens.
Keywords: Compressive Strength, Dental Amalgam, Glass Ionomer Cements, In Vitro, Zirconia
|How to cite this article:|
Kaur G, Shetty C, Hegde MN. Comparative evaluation of compressive strength and fracture resistance of posterior restorative materials alkasite and newer glass ionomers with amalgam: An in vitro study. J Int Oral Health 2022;14:566-73
|How to cite this URL:|
Kaur G, Shetty C, Hegde MN. Comparative evaluation of compressive strength and fracture resistance of posterior restorative materials alkasite and newer glass ionomers with amalgam: An in vitro study. J Int Oral Health [serial online] 2022 [cited 2023 Feb 1];14:566-73. Available from: https://www.jioh.org/text.asp?2022/14/6/566/366440
| Introduction|| |
The selection of posterior restorative material depends upon various factors such as caries extent, patient’s age, and esthetic and functional requisites of the restoration. Because of the concentration of stresses at the axio-pulpal line angle of a class II cavity, the failure of restoration chiefly occurs in the isthmus region. Hence, materials with higher compressive strength are advocated in cases such as class II cavity restoration where it is imperiled under heavy forces.
Amalgam, with its long-term clinical history, has been an efficacious restorative material for posterior restorations owing to its durability, wear resistance, self-sealing property, and technique insensitivity. Glass ionomer cements (GIC) bond to tooth structure chemically and release fluoride. Composite resins are esthetic and may reinforce tooth structure.
The “basic filling materials” have varied shortcomings such as the low flexural strength of glass ionomers, their high surface wear and porosity, intrinsic metallic grey color of amalgam, its incapability to bond with a tooth, and apprehensions regarding mercury content. By weight, dental amalgam consists of about 50% elemental mercury. The Minamata Convention on Mercury, 2013, proposes measures to downscale the use of dental amalgam and addresses a multipronged approach for phasing down its use.
Gradual diminish in its use has been inevitable, bringing in the exigency for adhesive dental materials that are cost-effective, fluoride-releasing, and user-friendly and offer both strength and good esthetics.
Ceramic-reinforced GIC complies with the caliber of GIC and amalgam. It incorporates a particulate ceramic component that imparts wear and erosion resistance and elevates the strength of the cement without abdicating appearance. Zirconia-reinforced GIC comprises zirconium oxide (powder) and polyacrylic acid with deionized water (liquid). It is fortified by zirconia fillers that accentuate the structural integrity, and the homogenization of glass particles imparts superior mechanical properties and durability to the material.
High strength posterior restorative GIC contains strontium that forms strontium-hydroxyapatite and strontium-fluoroapatite within the tooth structure. When the material is placed in a calcium-containing environment (saliva), it results in calcium ion diffusing into glass ionomer surface conferring a surface strengthening effect.
Alkasite restorative material is a composite with alkaline monomer, consisting of a combination of aromatic-aliphatic-urethane dimethacrylate, dicalcium phosphate, and polyethylene glycol-400 dimethacrylate, which interconnect during polymerization. This interconnection results in superior mechanical properties and endurance. It contains isofiller and inorganic fillers barium-aluminum-silicate and ytterbium trifluoride that bestow adequate strength and desired handling characteristics to the mixed material.
The current study aims at estimating and comparing the compressive strength and fracture resistance of ceramic-reinforced GIC (Amalgomer CR, Advanced Health Care Ltd., Tonbridge, UK), zirconia-reinforced GIC (Zirconomer, Shofu Inc., Kyoto, Japan), high strength glass ionomer posterior restorative material (GC gold label HS posterior extra [type IX], GC Corporation, Tokyo, Japan), alkasite restorative material (Cention N, Ivoclar Vivadent, Liechtenstein), and amalgam (Dental Products of India Ltd. Alloy) in the form of cylindrical specimens and restored class II cavities.
| Materials and Methods|| |
The present in vitro study was conducted in the Department of Conservative Dentistry and Endodontics, A.B. Shetty Memorial Institute of Dental Sciences, Deralakatte, NITTE Deemed to be University, Mangalore. The testing of the specimens was done in Konkan Speciality Polyproducts Pvt. Ltd., Scientific Services Group, Baikampady, Mangalore.
Ethical approval and informed consent
Ethical clearance was attained from the Ethics Committee of the institutional review board (ABSM/EC/71/2018) on October 25, 2018. The study complied with the Declaration of Helsinki guidelines. Waiver for informed consent was obtained, and the confidentiality of the participant information was ensured, and no identifying information related to the study participants is disclosed in the publication arising from the study.
The sample size was determined as reported in a previous study. The Power Analysis and Sample Size software PASS 15 was used. Sample size was n = 10 for each group.
Teeth included were intact permanent molar teeth, without any anatomical defect. All molars had similar dimensions at the cemento enamel junction level.
Carious, fractured, restored teeth, teeth with developmental anomalies, and deciduous teeth were excluded from the study.
Preparation of cylindrical specimens
Cylindrical specimens were fabricated in a metallic mold of 6 mm height and 4 mm diameter, according to ISO standardization 9917-1:2007 for powder/liquid acid-base dental cements and 4049:2009 for polymer-based materials. Ten samples were made from each of five materials. Covered by Mylar matrix strip, the mold was positioned onto a glass slab. The materials to be tested were proportioned and manipulated as per manufacturer’s directions and dispensed slowly in the molds till marginally overfilled in a way that no air bubble was enclosed. A second Mylar matrix strip was positioned on the mold and was covered with another glass slab. Extra material was extruded by pressing for 30 s, and a smooth end surface was obtained. After 1 h, samples were withdrawn from the mold, and any surplus material was gently grinded [Figure 1]A.
|Figure 1: Methodology: (A) 50 cylindrical specimens; (B) class II cavity preparation; (C) class II restoration; (D) class II restorations in 50 molars; (E) universal testing machine (Zwick Roell, Z020); (F) cylindrical specimens subjected to compressive load; (G) ball indenter; (H) tooth specimens subjected to compressive load|
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- Group C1: cylindrical specimens of ceramic-reinforced GIC;
- Group C2: cylindrical specimens of zirconia-reinforced GIC;
- Group C3: cylindrical specimens of high strength glass ionomer (GI) posterior restorative material;
- Group C4: cylindrical specimens of alkasite;
- Group C5: cylindrical specimens of silver amalgam.
Preparation of tooth specimens
Fifty intact permanent molars freshly extracted for periodontal reasons were collected from the Department of Oral and Maxillofacial Surgery, A.B. Shetty Memorial Institute of Dental Sciences, Deralakatte, NITTE Deemed to be University, Mangalore, and disinfected.
Teeth were embedded onto self-cure acrylic resin blocks, with the crown topmost and long axis perpendicular and resin being 1.0 mm beneath the cementoenamel junction.
Mesio-occlusal class II cavities were prepared by a single operator on all molars with standardized dimensions of 2 ± 0.2 mm pulpal depth, 2 ± 0.2 mm gingival width, and 3 ± 0.2 mm buccolingual width using #245 carbide bur (SS White Dental) at high speed under water cooling [Figure 1B]. Two observers blindly verified the prepared cavities using a calibrated periodontal probe. The prepared teeth were categorized into five groups by random allocation (n = 10 for each group) and filled with the restorative materials [[Figure 1]C and D].
- Group T1: tooth specimens restored with ceramic-reinforced GIC;
- Group T2: tooth specimens restored with zirconia-reinforced GIC;
- Group T3: tooth specimens restored with high strength GI posterior restorative material;
- Group T4: tooth specimens restored with alkasite;
- Group T5: tooth specimens restored with silver amalgam.
All specimens were thermocycled in temperature varying from 5°C to 55°C for 20 s in each for 500 cycles and were submerged in artificial saliva for 24 h at a room temperature.
Compressive strength of the cylindrical samples and fracture resistance of the restored tooth specimens were evaluated by means of Universal Testing Machine (Zwick-Roell Z020, Zwick, Ulm, Germany) [[Figure 1]E]. Along the longitudinal axis of the cylindrical samples, the compressive load was freighted at a speed of 0.5 mm/min [Figure 1F]. For each cylindrical specimen, the maximum force at which failure occurred was noted, and the compressive strength (MPa) was determined by the equation:
, where p = maximum force (N); d = average diameter of specimen (mm).
For fracture resistance evaluation, vertical compressive load on tooth specimens was applied with a stainless steel ball measuring 2.5 mm in diameter, with a crosshead speed of 0.5 mm/min, in the isthmus region [[Figure 1]G and H]. The load at which the restorations fractured was recorded.
Obtained data was analyzed using one-way analysis of variance (ANOVA). Post hoc analysis was performed by Tukey-Kramer test for intergroup comparison for statistically significant results found by ANOVA. The analyses were conducted at a significance level of P < 0.05. For correlating the maximum load by cylindrical and tooth specimens, Pearson’s correlation was used. All analyses were performed using Excel 365 (Microsoft Office) and SPSS software, version 23.
| Results|| |
The mean compressive strength of cylindrical specimens of C4 alkasite material (150.07 ± 22.22 MPa) was the highest, followed by C5 silver amalgam (90.56 ± 15.23 MPa), C3 high strength GI posterior restorative material (42.75 ± 7.84 MPa), C1 ceramic-reinforced GIC (27.11 ± 6.6 MPa), and least strength was observed in C2 zirconia-reinforced GIC (23.33 ± 4.08 MPa). This comparison is significant with statistics of 114.64 and a P value of <0.001 [Table 1]; [Graph 1]A and B.
|Table 1: Comparison of compressive strength and maximum compressive load between the five groups of cylindrical specimens—one-way ANOVA test|
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|Graph 1: (A) Comparison of compressive strength of cylindrical specimens; (B) and (C) comparison of maximum compressive load (Fmax) on cylindrical specimens and tooth specimens, respectively; (D)–(H) linear regression between Fmax for cylindrical and tooth specimens of groups 1–5, respectively|
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Teeth in group T4 filled with alkasite showed the highest fracture resistance (636.6 ± 141.68 N), followed by T1 ceramic-reinforced GIC (488.4 ± 145.43 N), T5 silver amalgam (423.8 ± 182.15 N), T2 zirconia-reinforced GIC (420 ± 90.19 N), and least by T3 high strength GI posterior restorative material (418.8 ± 147.44 N). This comparison is significant with statistics of 4.204 and a P value of 0.006 [Table 2]; [Graph 1 C].
|Table 2: Comparison of maximum compressive load between the five groups of tooth specimens—one-way ANOVA test|
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On comparison of the compressive strengths of the five groups of cylindrical specimens, the post hoc analysis shows that differences between groups C1 and C4 (P < 0.001); C1 and C5 (P < 0.001); C2 and C3 (P = 0.014); C2 and C4 (P < 0.001); C2 and C5 (P < 0.001); C3 and C4 (P < 0.001); C3 and C5 (P < 0.001); and C4 and C5 (P < 0.001) were statistically significant [Table 3].
Pearson’s correlation test was used to correlate the measure between maximum compressive load supported by cylindrical specimens made of particular restorative material and tooth specimens restored with the same [Table 4]; [Graph 1] D–H:
|Table 4: Pearson’s correlation between maximum compressive load supported by cylindrical and tooth specimens|
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- Group 1: moderate positive correlation, not significant (P = 0.414);
- Group 2: poor negative correlation, not significant (P = 0.935);
- Group 3: poor positive correlation, not significant (P = 0.668);
- Group 4: poor negative correlation, not significant (P = 0.683);
- Group 5: very good positive correlation, statistically significant (P = 0.04).
| Discussion|| |
For restoring posterior teeth, the choice of material is based upon the strength of the material and the area of application such that it resists intraoral forces in functional and parafunctional movements of the jaw. Low compressive strength of the material compared to the tooth will lead to the fracture of restoration under occlusal load, whereas very high compressive strength will lead to the failure of tooth structure. Hence, its compressive strength should be equivalent to that of the tooth for harmonious relationship with surrounding tissues.
Over decades, dental amalgam has been the preferred restorative material for class I, class II restorations, and in large load-bearing fillings in posterior teeth in the adult dentition. Anusavice reported that even after 10 years of placement, approximately 90% of amalgam restorations were still functional. Under simulated chewing conditions, the average fatigue life for amalgam was produced after more than one million cycles. Hence, amalgam is used for the direct posterior restoration attributable to its unparalleled mechanical properties and extensive function.
The objective of the present in vitro study was to estimate and compare the compressive strength of the newer modifications of GIC that are ceramic-reinforced, zirconia-reinforced, high strength posterior glass ionomer, and alkasite cement with amalgam.
It was found that the compressive strength of alkasite restorative material (Cention N) was significantly higher than amalgam, regardless of cylindrical specimens or class II restoration. Similarly, Kumar and Ajitha found that the compressive strength of alkasite restorative material is equivalent and sometimes superior to that of high copper amalgam and can be used for restoring stress-bearing posterior teeth. Kaur et al. found that alkasite Cention N is a better substitute to GIC type IX for restoring posterior teeth. Chowdhury et al. found that alkasite had greater fracture resistance as compared to dental amalgam and composite. Verma et al. found that cylindrical specimens of alkasite had significantly higher compressive strength than GIC type IX, whereas Mishra et al. found that cylindrical amalgam specimens performed better than GIC and alkasite in terms of compressive strength and that alkasite had significantly higher compressive strength than GIC.
Cention N, an alkasite, releases hydroxide ions to neutralize acid attacks. It possesses a polymer structure that is exceptionally crosslinked and a patented isofiller that helps relieve shrinkage stress and reduces the force of shrinkage due to chemical bonds between matrix and fillers by silane coupling agent. The reduced volumetric shrinkage allows for bulk increment placement of the material and an increase in its compressive strength. Hence, Cention N has been designed for comprehensive and definitive replacement of posterior tooth structure.
Mallya et al. found a statistically significant difference between Cention N, GIC, and dental amalgam, where GIC (Fuji IX) exhibited the poorest mechanical properties.
In the present study, compressive strength of silver amalgam cylindrical specimen, as well as class II restoration, was superior to GIC but inferior to composite based material. Cho et al. attributed this to the coefficient of elasticity of amalgam that it is thrice as rigid as composites. A very good positive correlation was found between the load-bearing capacity of the cylindrical and tooth specimen of amalgam. This could be because teeth filled with a restorative material with greater rigidity than dentin have a higher resistance to disintegration.
Amalgomer CR displayed higher compressive strength than GIC type IX. This can be attributed to the reinforcement of quartz filler content by ceramic particles that partly react with the matrix to create bonds and enhance the gross strength of the restoration. This could also explain the moderate positive correlation between the maximum compressive loads taken by cylindrical and tooth specimens of Amalgomer CR.
The results are contradictory to the study by Ayad et al. where they found that ceramic-reinforced glass ionomer had higher compressive strength compared with high copper amalgam. Results of the present study also contradict those of Chalissery et al. and Dheeraj et al., where compressive strengths of amalgam and Zirconomer were similar.
Type IX GIC specimens show significantly higher compressive strength than Zirconomer. This is in accordance with Gudugunta et al. and contradicts the findings of Bhatia8 and Mohanty and Ramesh.
For tooth specimens with restored class II cavities, the present study does not show any statistically significant difference between the fracture resistance of teeth filled with Amalgomer CR, Zirconomer, GIC, and amalgam. Similar outcomes were reported by Sud et al., Kamath and Salam. The fracture resistance of Zirconomer could be attributed to the reinforcement of structural integrity by an addition of zirconia filler particles. Gudugunta et al. found that amalgam and composite have greater compressive strength when compared with Zirconomer. And after 24 h, all the three materials showed compressive strength over 300 MPa and can be used as posterior restorative materials as per the limit set by ISO.
The overall values observed in the present study seem to be lower than most other studies. This could be an effect of thermocycling or storage in artificial saliva, which drastically reduces the strength of materials, as suggested by Wang et al. Though the values are low, the values for amalgam and the glass ionomer-based cements are in a similar range. Hence, the assessed materials may be used as an alternative to amalgam.
In the present study, in vitro models were tested in the form of cylindrical specimens and class II cavities restored with the test materials in the permanent molar teeth. It is important to conduct preliminary and safety tests in vitro before performing clinical trials in patients, which would dispense conclusive evidence for the clinical application of the restorative materials. The projection of in vitro findings to the clinical circumstances must be done with caution, keeping the limits of in vitro studies in mind.
| Conclusions|| |
In the present in vitro study, alkasite restorative material (Cention N) exhibited better compressive strength and fracture resistance and can be used for restoring posterior teeth. It seems to be a superior alternative to amalgam and GIC. However, further clinical studies with long follow-up period are indispensable to correlate its execution and qualitatively evaluate the survival of restorations.
We express our gratitude to the Department of Conservative Dentistry and Endodontics, AB Shetty Memorial Institute of Dental Sciences, Mangalore for their support for the research.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
Dr Gurmeen Kaur: research concept and design, collection and/or assembly of data, data analysis and interpretation, writing the article. Dr Chitharanjan Shetty: research concept and design, critical revision and final approval of the article. Dr Mithra N. Hegde: Revision and final approval of the article.
Ethical policy and Institutional Review board statement
This study was approved by Institutional Ethical Committee ABSMIDS, Nitte Deemed to be University, Mangalore (certificate number: ABSM/EC/71/2018, dated 25th October 2018).
Patient declaration of consent
Data availability statement
Data are available itself in the article.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]