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Background and aims. The aim of this study was to compare flexural strength of specimens processed by conventional and injection-molding techniques.
Materials and methods. Conventional pressure-packed PMMA was used for conventional pressure-packed and injection-molded PMMA was used for injection-molding techniques. After processing, 15 specimens w...
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... resin polymers have been introduced as denture base materials and the majority of denture bases are fabricated using polymethylmethacrylate (PMMA). These materials have optimal physical properties and excellent esthetics with relatively low 1 toxicity compared to other plastic denture bases. Compression molding with heat activation in a water bath for resin polymerization is the conventional me- 2 thod to process dentures. However, shrinkage and dimensional change of denture bases during resin polymerization is unavoidable and has been well do- cumented. Mechanical behavior of the denture base, including flexural strength, depends on the type of 3 the material and even on processing techniques. Therefore, acrylic resins and processing methods have been modified to improve physical and chemical properties of denture bases. One example is the introduction of injection-molding technique. 4 In 1942, Pryor introduced the injection-molding technique to overcome the adverse effects of com- 5 pression molding. Grunewald et al investigated Pryor’s technique and reported no significant advantages over the conventional method. Several injec- tion-molded denture base materials and processing techniques are now available, with each claimed to 6,7 produce denture bases with better properties. Ivocolar acrylic resins are one of the important resins 1 among complete denture materials. Therefore, in this study, Ivocolar acrylic resins were used as a con- trol (SR-Ivocap Triplex Hot) and experimental groups (SR-Ivocap High Impact), which had the most similarities in chemical structures according to manufactures’ claims. Previous studies have compared injection and conventional molding methods by use of acrylic resins with different systems and brands with principal differences in chemical struc- 8-10 tures. As a result, in the current study we tried to use the materials with the most similarity. Other drawbacks and shortcomings of previous studies were the fact that they evaluated flexural strength by production of specimens with various shapes (dentures and denture-shaped specimens). In the present study, rectangular specimens were examined and thus, variables such as shape, size and thickness of the samples were controlled. The aim of this study was to compare the flexural strength of rectangular resin specimens cured by conventional processing method versus SR-Ivocap injection-molding system. In this study, flexural strength of conventional pressure-packed PMMA (SR-Ivocap Triplex Hot, Ivoclar Vivadent, Liechtenstein) was compared to those of injection-molded PMMA base material (SR-Ivocap High Impact, Ivoclar Vivadent, Liechtenstein). Three rectangular stainless steel plates were fabricated (Figure 1) to prepare 15 acrylic resin specimens (Figure 2) with a nominal size of 50×20×4 mm, for conventional and injection-molding methods. Two layers of wax (Cavex, Netherlands) were placed on stainless steel plates and flasked. To em- bed the flasks, type III dental stone (Herodent; Vigodent, Petropolis, RJ, Brazil) was used and mixed according to manufacturer's instructions (100 g of powder with 30 mL of water). The liquid-to-powder ratio of SR Triplex Hot resin was 10 mL of liquid to 23 g of powder. The acrylic resin was mixed according to manufacturer’s rec- ommendations and packed in the flask. Conventional PMMA specimens were fabricated using a conventional flasking and pressure-pack technique. Polymerization of the resin was carried out in boiling water under a pressure of 100 N for 45 minutes. After polymerization, the curing flasks were bench- cooled to room temperature, and the specimens were deflasked. The surfaces were finished using 800-, 400- and 200-grit sandpapers (Norton; Saint-Gobain Abrasivos, Brasil). For the injection-molded technique, the specimens were flasked according to manufacturer’s instructions using the Ivocap flask. Premeasured SR-Ivocap capsules of resin and monomer (20 g powder, 30 mL monomer) were mixed in Cap vibrator (Ivoclar AG) for 5 minutes before injecting into the flask. For curing process of the SR-Ivocap system, hydraulic pressure of 6 atm at 100°C was maintained for 35 minutes. A 10-minute cooling process using running water with a pressure of 6 atm was used before de fl asking the denture. Finally, there was a further l0-minute cooling period, but without any extra pressure. Then the specimens were dedeflasked and the surfaces were finished using 800-, 400- and 200-grit sandpapers (Norton; Saint-Gobain Abrasivos, Brasil). All the specimens were stored in distilled water at room temperature for 10 days before flexural strength test. The tests were carried out immediately after retrieving the specimens from distilled water without drying the specimens. For flexural test, a universal testing machine (Model STM-50, Santam, Tehran, Iran) was used (Figure 3). The distance between the specimen supports was 40 mm and the loading force was applied to the specimens at a crosshead speed of 5 mm/min until the specimens fractured. The diameter of loading and supporting plunger was 20 mm. The maximum load exerted on the specimens was recorded, and the flexural strength was calculated 11 according to the following formula: 2 F=3WL/2bd [F: flexural strength; W: load at fracture; L: distance between supporting points (40 mm); b: width of specimens (mm); d: specimen thickness (mm)] Flexural strength was calculated in MPa. Following data collection, statistical analysis was carried out by SPSS (SPSS Inc., Chicago, IL, USA) using t-test. Statistical significance was defined at P<0.05. A summary of the flexural strength in conventional pressure-packed and injection-molded SR-Ivocap is shown in Table 1. Flexural strength of injection- polymerized acrylic resin specimens was higher than that of the conventional method. T-test showed that the difference was statistically significant (P=0.006). This study evaluated the flexural strength of rectangular specimens produced using injection-molding and compression-molding techniques with thermally activated PMMA resin. Conventional method is the most applicable method for curing acrylic resin due to its simplicity and relatively good accuracy and in various studies this method has been considered the gold standard for comparison with the other techniques. 2 Among denture processing methods, injection molding has always been interesting for re- searchers because of compensation of polymerization shrinkage due to the pressure exerted by injec- 1 tion of the acrylic resin. 12 Wolfaardt reported that many different factors af- fected physical properties of acrylic resin dentures. 13 14 Factors such as size and shape, denture thickness, 15 different types of denture base materials, and pres- 16 ence of teeth can influence the physical and mechanical characteristics of bases during denture processing. Many studies have evaluated the physical properties of denture bases by production of different specimens with various shapes. Therefore, it is better to use specimens with simple shapes for comparison of properties instead of dentures and denture- shaped specimens. In the present study, rectangular specimens were examined and thus, variables such as shape, size, and thickness of the samples were controlled. By this approach, the physical properties were directly related to acrylic resin itself. Similar to the present study, Salim 17 and Baydas 18 used rectangular acrylic resin plates for their evaluation. In con- trast, complete denture bases were utilized in sepa- 19 20 rate research studies by Jackson, Nogueira, Ab- 21 22 by and Venus. In most studies, only the molding technique has been considered as variables that affect the physical and mechanical properties of dentures and less atten- tion has been focused on the effect of different types of acrylic resins used for molding. Differences in acrylic resin brands may be considered another vari- able in addition to molding technique, affecting the mechanical properties. In such studies, in addition to the method of molding, the type of the resin was also different in each group. Therefore, the results could not merely be attributed to the type of the molding process itself. 23-26 As a result, in the present study, denture base resins with the same composition were used (produced by Ivocolar Vivadent/Liechtenstein), which were processed by two different techniques. Therefore, comparisons were made only between the molding techniques and the effect of material type was eliminated. The denture base may fracture due to different rea- sons such as improper fitting, anatomical notches, and lack of adequate design. The fracture takes place due to flexure fatigue when the denture base is loaded and the maximum mechanical capacity of the 27 material is exceeded. The flexural strength is one of most important mechanical properties of resin materials and it has been reported that acrylic resins with incomplete polymerization have lower mechanical properties compared to those with complete 28-30 polymerization. Thus, by measuring the flexural strength, the quality of polymerization might be evaluated to some extent in addition to determination of 29 denture base resistance to force and trauma. Three-point flexural test, adopted by international standards for polymer materials, including ISO 1567:1999 Dentistry-Denture base polymers, is the most common technique of measuring flexural prop- 31 erties of denture bases. In this study, a loading force was applied to specimens at a crosshead speed 32 of 5 mm/min based on a study by Barbosa. Ac- cording to ISO 1565, flexural strength of acrylic resin, processed and cured with any method, should be 33 no less than 65 MPa. The results of this study demonstrated that the mean flexural strength of the two curing methods tested in the current work was ...
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Citations
... 13 Fracture resistance shows the ability of the prosthesis to withstand different masticatory forces. 14, 15 Cristache et al 16 suggested adding nanocomposite material incorporated with titanium oxides in 3D-printed complete dentures, this increases the clinical performance of the 3D-printed dentures and might increase the fracture resistance of the dentures as well. Also, it is suggested to increase the denture base thicknesses to compensate for the lower fracture resistance. ...
... Therefore, high flexural strength is necessary to prevent sudden failure [15]. As per the American Dental Association Standard No. 139, and in accordance with the International Organization for Standardization (ISO) guidelines 20795-1 for denture-base polymers, a flexural strength test is commonly used to assess material resistance [16][17][18]. ...
Background
This study compared the impact of thermal cycling on the flexural strength of denture-base materials produced through conventional and digital methods, using both subtractive and additive approaches.
Methods
In total, 60 rectangular specimens were fabricated with specific dimensions for flexural strength tests. The dimensions were set according to the International Organization for Standardization (ISO) guideline 20795-1:2013 as 64 × 10 × 3.3 ± 0.2 mm. Specimens from each material group were divided into two subgroups (thermal cycled or nonthermal cycled, n = 10/group). We used distinct methods to produce three different denture-base materials: Ivobase (IB), which is a computer-aided-design/computer-aided-manufacturing-type milled pre-polymerized polymethyl methacrylate resin disc; Formlabs (FL), a 3D-printed denture-base resin; and Meliodent (MD), a conventional heat-polymerized acrylic. Flexural strength tests were performed on half of the samples without a thermal-cycle procedure, and the other half were tested after a thermal cycle. The data were analyzed using a two-way analysis of variance and a post hoc Tukey test (α = 0.05).
Results
Based on the results of flexural-strength testing, the ranking was as follows: FL > IB > MD. The effect of thermal aging was statistically significant for the FL and IB bases, but not for the MD base.
Conclusions
Digitally produced denture bases exhibited superior flexural strength compared with conventionally manufactured bases. Although thermal cycling reduced flexural strength in all groups, the decrease was not statistically significant in the heat-polymerized acrylic group.
... The denture base subjected to flexural testing at different aging times simulates the ability to succeed intraorally under high functional loads during mastication and parafunction over time, 5 with flexural strength being one of the main determinants of the mechanical properties of acrylic resin, in which its high strength is directly linked to a high degree of monomer conversion. 15,25 According to the ISO 20795-1:2013 standard, 12 acrylic resins must not reach values < 65 MPa. The conventional, microwave-processed, and milled resins exhibited values > 65 MPa at all aging times, even with a significant decrease in milling after 24 months of aging (P < .05). ...
Purpose:
The purpose of this study was to investigate the mechanical properties of acrylic resins at different aging times for denture bases manufactured using the conventional method, microwave processing, milling, and 3D printing.
Materials and methods:
A total of 160 rectangular samples (64 Å~ 10 Å~ 3.3 ± 0.03 mm) were prepared, divided among the four main resin groups, and subdivided into four analysis times (T0, T1, T2, and T3), resulting in 10 samples per subgroup. The samples were stored in distilled water at 37° ± 2°C for 24 hours (T0), then subjected to thermocycling at temperatures of 5° ± 1°C and 55° ± 1°C in different numbers of cycles: 5,000 (T1); 10,000 (T2); and 20,000 (T3). The mechanical properties evaluated were surface microhardness, flexural strength, and modulus of elasticity. Statistical differences between resin groups and aging time were evaluated using two-way analysis of variance (P < .05).
Results:
The 3D-printed resin showed the significantly lowest values of microhardness, flexural strength, and modulus of elasticity compared to other resins (P < .001).
Conclusions:
The CAD/CAM-milled denture resin showed mechanical properties similar to those of traditional resins (conventional and microwave-processed). The 3D-printing resin did not show adequate mechanical properties for long-term clinical use. Despite this, new studies are developing better properties of this resin for long-term use.
... The molecular backbone characteristics of the co-monomers involved will determine the hydrophilicity, mobility, and kinetic parameters. When acrylic resin strengths are compared, those with a lower degree of conversion exhibit inferior mechanical properties [38]. The higher flexural strength values of CAD-CAM specimens may be attributed to a higher degree of conversion [15]. ...
Unlabelled:
PMMA (Polymethylmethacrylate) is the material of choice to fabricate denture bases. Recently, with the introduction of CAD-CAM and 3D printers in dentistry, new materials have been proposed for complete denture manufacturing.
Aim:
This study compared the flexural strength of different resins fabricated using different technologies (conventional, CAD-CAM-milled, and 3D-printed) and polymerization techniques.
Methods:
A total of 11 different resins were tested: six PMMA conventional (Acrypol R, Acrypol LL, Acrypol HI, Acrypol Fast, Acryself and Acryslef P), two milled obtained from UDMA PMMA disks (Ivotion disk and Aadva disk, control groups), two 3D-printed PMMA resins (NextDent Denture 3D+, and SprintRayEU Denture Base), and one 3D-printed composite resin (GC Temp Print). Flexural strength was measured using a universal testing machine. One-way ANOVA and Bonferroni post hoc tests were performed; the p-value was set at 0.05 to consider statistically significant differences among the groups. Spearman test was used to evaluate the correlation between polymerization technique and the flexural strength of 3D-printed resins.
Results:
CAD-CAM-milled specimens showed the highest flexural strength (107.87 MPa for UDMA) followed by 3D-printed composite resins (102.96 MPa). Furthermore, 3D-printed resins polymerized for 40 min with the BB cure unit showed no statistically significant differences with conventional resin groups. Moreover, in all the 3D-printed specimens, a high correlation between polymerization technique and flexural strength was found.
Conclusions:
In terms of flexural strength, the polymerization technique is a determinant for both acrylic and composite resins. Temp Print can be a potential alternative to fabricating removable dentures and showed promising results when used in combination with pink color resin powder.
... Another research investigation, [207], was dedicated to investigating the effect of bioactive glass particle addition on the acrylic resins commonly used in dentistry. Acrylic resins are usually used in prosthetic dentistry owing to their long-term durability and easy preparation technics [208], as well as their acceptable biocompatibility [209]. However, their bioactivity could be improved even more by adding bioactive particles into their structure, such as different bioglasses in different ratios. ...
Bioactive glasses (BGs) are especially useful materials in soft and bone tissue engineering and even in dentistry. They can be the solution to many medical problems, and they have a huge role in the healing processes of bone fractures. Interestingly, they can also promote skin regeneration and wound healing. Bioactive glasses are able to attach to the bone tissues and form an apatite layer which further initiates the biomineralization process. The formed intermediate apatite layer makes a connection between the hard tissue and the bioactive glass material which results in faster healing without any complications or side effects. This review paper summarizes the most recent advancement in the preparation of diverse types of BGs, such as silicate-, borate- and phosphate-based bioactive glasses. We discuss their physical, chemical, and mechanical properties detailing how they affect their biological performances. In order to get a deeper insight into the state-of-the-art in this area, we also consider their medical applications, such as bone regeneration, wound care, and dental/bone implant coatings.
... The denture base was able to succeed simulation intraorally to high functional loads during parafunction and mastication when subjected to a 3-point bend test. 6,7,8 The 3-point flexural test is commonly used for measuring flexural properties. The acrylic denture base resins should have at least 65 MPa Fs according to the ISO standards. ...
Background: The present study was conducted for assessing and comparing flexural strength of two types of denture base resins. Materials & methods: 100 acrylic specimens in all were created. Used were stainless steel dies. To complete the flasking process, dental plaster was applied to the metal dies. For the purpose of making room in the mould for the acrylic specimen, the stainless-steel dies were extracted. The following research groups were created by randomly selecting all of the specimens: Conventional denture base resins fall under Group 1, and glass reinforced denture base resins go under Group 2. The universal testing apparatus was used to determine the samples' flexural strength. Results: Mean flexural strength of group 1 specimens was 118.6 MPa. Mean flexural strength of group 2 specimens was 156.3 MPa. While comparing the mean flexural strength between group 1 and group 2, significant results were obtained. Conclusion: Glass reinforced denture base resins demonstrated higher flexural strength in comparison to conventional denture base resin.
... [17][18][19][20][21] As most of the denture fractures were either caused by flexural stresses or impact failure, evaluation of flexural and impact strength should be considered as unique parameters in evaluating the mechanical properties of the denture base material. [22][23][24][25] Denture base material's residual monomer content and mechanical properties are also affected by different processing techniques by which the dentures are processed. 26,27 Therefore the aim of the study was to compare and evaluate the flexural and impact strength of Polymethylmethacrylate (PMMA) denture base material processed by CAD-CAM, Compression-molded and Injection-molded specimens. ...
Background: One of the chief limitations of Polymethylmethacrylate denture base material is its inadequate mechanical property. Different processing methods of Polymethylmethacrylate have varying influences on the mechanical properties of denture base material. Aim: The aim of our in-vitro study was to comparatively evaluate the flexural and impact strength values between CAD-CAM, Compression-molded and Injection- molded Polymethylmethacrylate specimens. Materials and methods: A total of 66 acrylic rectangular specimens of ISO Standardization (64 x10 x3.3mm) were fabricated. This study was conducted between three groups: Group I (n=22)-CAD-CAM Milled specimens (Ruthinium, India), Group II (n=22)- Compression-molded specimens (Dental Products of India, Chennai), Group III (n=22)- Injection-molded specimens (SR- Ivocap High Impact, Ivoclar Vivadent). Flexural strength was evaluated using four-point bend test and Impact strength by IZOD Impact tester. Kruskal Wallis unpaired test was used to compare the mean values between groups and Mann Whitney U test was used to carry out pair wise comparison. Results: Flexural strength of CAD-CAM samples were found to be statistically highest followed by injection molded specimens. Conversely, Impact strength of injection- molded specimens were highest followed by CAD-CAM specimens. Flexural as well as impact strength values were found to be least among compression-molded specimens. Conclusion: CAD-CAM specimens exhibited higher flexural strength whereas Injection-molded specimens had the highest impact strength.
... 20 Milled materials have been reported to have better mechanical properties than conventionally fabricated PMMA and 3D-printed materials. [20][21][22][23][24] However, these studies compared a limited number of the available 3D-printed materials. Numerous 3D-printed materials have been developed since the advancement in 3D-printing technology, and their mechanical properties should be assessed to provide appropriate information for dental practitioners. ...
... ±0.82 MPa; ADH=91.37 ±4.35 MPa; DSL=102.3 ±1.03 MPa) was found to be significantly higher than L199 (66.27 ±4.02 MPa) (P<.05) ( Fig. 2A). This outcome was consistent with previous studies, [21][22][23][24][25][26] which reported that milled denture base materials had significantly higher flexural strength than conventionally fabricated denture base materials. Billets of milled denture base materials are fabricated from PMMA, which are polymerized under controlled conditions, providing more polymerization than conventionally fabricated denture base materials and a higher degree of conversion. ...
... Flexural strength is affected by the degree of polymerization achieved; hence, billets of milled denture base materials have higher flexural strength compared with those processed conventionally. 22,23 The flexural strength value was significantly (P<.05) different among the various types of milled denture base materials, which was consistent with previous studies, 20,24,26 possibly because of the different components and manufacturing techniques used in the fabrication of PMMA billets. Three types of novel 3D-printed resin materials were included in the current study. ...
Statement of problem:
Novel 3-dimensionally printed resin and milled polymethyl methacrylate materials have been marketed for computer-aided design and computer-aided manufacturing (CAD-CAM) denture base fabrication. However, information on the flexural strength of digitally fabricated denture base material is limited, and little is known about how they are affected by a hard-reline procedure.
Purpose:
The purpose of this in vitro study was to assess the flexural strength of 6 digitally manufactured denture base materials and to assess the effect of a hard-reline procedure on their flexural strength.
Material and methods:
A total of 140 strips of denture base material were fabricated from a conventional heat-polymerized polymethyl methacrylate (L199), 3 brands of milled polymethyl methacrylate (IBC, DSL, and ADH), and 3 brands of 3D-printed resin (DFD, ADB, and DrFD) (n=20). Ten specimens in each group did not receive any treatment, and 10 were relined with a hard-reline material (ProBase Cold Trial Kit). Specimens were then subjected to a 3-point flexural strength test using a universal testing machine at a crosshead speed of 5.0 mm/min. A 1-way ANOVA test followed by the Tukey multiple comparison test was used to detect the difference in flexural strength and the strain at fracture of the different types of denture base materials (α=.05). The comparison of flexural strength between with and without hard-reline was analyzed using an unpaired t test (α=.05).
Results:
All materials, with or without the hard-reline, met the International Organization for Standardization (ISO) 20 795-1:2013 standard for flexural strength (65 MPa). The milled materials (DSL>IBC≈ADH) showed higher flexural strength than the 3D-printed or conventional materials (DrFD>DFD≈ADB≈L199) without a hard-reline. No statistical difference in flexural strength was found among the hard-relined denture base materials (P=.164). All 3 milled materials showed reduced flexural strength after relining, while the relined conventional (L199) and 3D-printed materials (DFD and ADB) showed notably higher flexural strength; printed DrFD showed no significant difference (P=.066). In terms of strain at fracture, the milled materials displayed higher values than those of the conventional or 3D-printed materials (P<.05).
Conclusions:
All digitally fabricated denture base materials were within acceptable limits for clinical use, even after hard relining. Flexural strength was highly dependent on the type of material. Hard relining affected the flexural strength of most of the digitally fabricated denture base materials.
... The loading that occurs on the denture in the mouth during the masticatory process is represented by this flexural strength. 11,15 Flexural strength is of particular importance among the different physical attributes that might be impacted by cleansers since denture base resins can fail clinically owing to flexural fatigue. 16,17 Several studies investigated the effect of chemical and herbal cleansers on the flexural strength of conventional heat cured denture base materials. ...
... The loading that occurs on the denture in the mouth during the masticatory process is represented by this flexural strength. 11,15 Flexural strength is of particular importance among the different physical attributes that might be impacted by cleansers since denture base resins can fail clinically owing to flexural fatigue. 16,17 Several studies investigated the effect of chemical and herbal cleansers on the flexural strength of conventional heat cured denture base materials. ...
Statement of problem: Polymethyl-methacrylate is still a widely used material for complete and partial denture fabrication. Candida biofilm adherence to PMMA denture base has been studied, and ways to control its adherence by using different ways of cleaning, natural and chemical herbal cleanser-based methods have been introduced as an alternative to chemical methods. Using any type of cleanser may affect the flexure strength of denture bases. Purpose: This study aimed to compare the effect of herbal extract cleanser and chemical cleanser on the flexure strength of three different denture base materials: heat polymerized acrylic resin, thermoplastic polyamide (Nylon), and thermoplastic monomer-free microcrystalline polymer (Karadent). Materials and methods: A total of 90 samples were divided into three equal groups (Heat cured processed acrylic resin, Karadent, Nylon) Samples were immersed in the cleansing solution and distilled water as a control group for 15 days. Results: Flexure strength was measured using a universal testing machine, and the results were collected, tabulated, and statistically analyzed using ANOVA. There was a significant difference between thyme-immersed specimens and specimens immersed in sodium hypochlorite (NaoCl). The Karadent specimens showed the least flexure strength measures among the three groups. Conclusion: immersing in different cleanser affected the flexure strength of denture base materials, using thyme as a cleanser has less effect on denture base flexure strength in comparison to NaoCl.
