Conventional Heat-polymerized Acrylic Resin Research Articles

Impact of Polymerization Technique and ZrO2 Nanoparticle Addition on the Fracture Load of Interim Implant-Supported Fixed Cantilevered Prostheses in Comparison to CAD/CAM Material.

ZrO2 nanoparticles (ZNPs) have excellent physical properties. This study investigated the fracture load of implant-supported, fixed cantilevered prosthesis materials, reinforced with ZNPs and various polymerization techniques, compared with conventional and CAD/CAM materials. Sixty specimens were made from two CAD/CAM; milled (MIL) (Ceramill TEMP); and 3D-printed (NextDent Denture 3D+). Conventional heat-polymerized acrylic resin was used to fabricate the other specimens, which were grouped according to their polymerization technique: conventionally (HP) and autoclave-polymerized (AP); conventionally cured and reinforced with 5 wt% ZNPs (HPZNP); and autoclave reinforced with 5 wt% ZNPs (APZNP). The specimens were thermocycled (5000 cycles/30 s dwell time). Each specimen was subjected to static vertical loading (1 mm/min) using a universal Instron testing machine until fracture. Scanning electron microscopy was used for fracture surface analyses. The ANOVA showed significant fracture load differences between all the tested groups (p = 0.001). The Tukey post hoc tests indicated a significant difference in fracture load between all tested groups (p ˂ 0.001) except HP vs. HPZNP and AP vs. MIL. APZNP had the lowest mean fracture load value (380.7 ± 52.8 N), while MIL had the highest (926.6 ± 82.8 N). The CAD/CAM materials exhibited the highest fracture load values, indicating that they could be used in long-term interim prostheses. Autoclave polymerization improved fracture load performance, whereas ZrO2 nanoparticles decreased the fracture load performance of cantilevered prostheses.

Comparison of shear bond strength of CAD/CAM and conventional heat-polymerized acrylic resin denture bases to auto-polymerized and heat-polymerized acrylic resins after aging

BackgroundThe aim of this study was to investigate the shear bond strength of CAD/CAM and conventional heat polymerized acrylic resin denture bases bonded to self-cured and heat-cured acrylic resins after aging. Material and MethodsA total of 40 cubic specimens were fabricated from conventional heat-polymerized and CAD/CAM denture base resins. Denture base resin specimens in each group were divided into two subgroups (n=10) in which they were bonded to either a heat-cured (HC) or a self-cured (SC) reline resin. Subsequently, the specimens were subjected to thermocycling. Then the shear bond strength (SBS) of specimens was measured using the universal testing machine. After testing, modes of failure were examined using light microscopy. The results were submitted to statistical analysis. ResultsMann-Whitney test showed that in each group of denture base materials, specimens bonded to HC reline resin had significantly higher SBS than those bonded to SC reline resin (P<0.001). Conventional denture base bonded to HC resin exhibited the highest value of SBS. There was no statistically significant differences between the SBS of HC reline resin bonded to conventional and CAD/CAM with regards to SBS (P=0.218). However, the SBS of SC reline resin was significantly higher when bonded to CAD/CAM compared to conventional denture base resin (P<0.001). ConclusionsHeat-cured reline resin showed higher shear bond strength to both CAD/CAM and conventional heat-polymerized denture resin in comparison to self-cured reline resin. Although there was no difference between the bond strength of heat-cured reline resin to CAD/CAM and conventional denture base, self-cured reline material produced stronger bond with CAD/CAM denture base. Key words:CAD/CAM, shear bond strength, reline, denture base resin.

Pressure transmission area and maximum pressure transmission of different thermoplastic resin denture base materials under impact load

PurposesThe purposes of the present study were to examine the pressure transmission area and maximum pressure transmission of thermoplastic resin denture base materials under an impact load, and to evaluate the modulus of elasticity and nanohardness of thermoplastic resin denture base. MethodsThree injection-molded thermoplastic resin denture base materials [polycarbonate (Basis PC), ethylene propylene (Duraflex), and polyamide (Valplast)] and one conventional heat-polymerized acrylic resin (PMMA, SR Triplex Hot) denture base, all with a mandibular first molar acrylic resin denture tooth set in were evaluated (n=6). Pressure transmission area and maximum pressure transmission of the specimens under an impact load were observed by using pressure-sensitive sheets. The modulus of elasticity and nanohardness of each denture base (n=10) were measured on 15×15×15×3mm3 specimen by using an ultramicroindentation system. The pressure transmission area, modulus of elasticity, and nanohardness data were statistically analyzed with 1-way ANOVA, followed by Tamhane or Tukey HSD post hoc test (α=.05). The maximum pressure transmission data were statistically analyzed with Kruskal–Wallis H test, followed by Mann–Whitney U test (α=.05). ResultsPolymethyl methacrylate showed significantly larger pressure transmission area and higher maximum pressure transmission than the other groups (P<.001). Significant differences were found in modulus of elasticity and nanohardness among the four types of denture bases (P<.001). ConclusionsPressure transmission area and maximum pressure transmission varied among the thermoplastic resin denture base materials. Differences in the modulus of elasticity and nanohardness of each type of denture base were demonstrated.

Cumulative effect of microwave sterilization on the physical properties of microwave polymerized and conventional heat-polymerized acrylic resin.

Aims:To evaluate and compare the flexural strength and impact strength of conventional and microwave cured denture base resins before and after repeated sterilization using microwave energy to consider microwave curing as an alternative to the conventional method of sterilization.Materials and Methods:The conventional heat cure acrylic resin (DPI heat cure material) Group A and microwave-polymerized acrylic resin (Vipi Wave Acrylic resin) Group B were used to fabricate 100 acrylic resins samples using a standard metal die of (86 mm × 11 mm × 3 mm) dimensions. The criterion was flexural strength and impact strength testing which had Group A and Group B samples; 50 samples for flexural strength and 50 samples for impact strength measurement. For each criterion, five control samples were taken for Group A and Group B. The samples were stored in water before experimenting. The test samples were subject to four cycles of microwave sterilization; followed by flexural strength testing with a 3-point flexural test in universal testing machine (UNITEK 94100) and impact strength testing with impact testing machine (ENKAY Pr09/E1/16).Results:The physical properties had significant changes for conventionally cured denture base resins, whereas no changes found for microwave-cured resins after repeated sterilization cycles.

Color stability, water sorption and cytotoxicity of thermoplastic acrylic resin for non metal clasp denture.

PURPOSEThe aim of this study was to compare the color stability, water sorption and cytotoxicity of thermoplastic acrylic resin for the non-metal clasp dentures to those of thermoplastic polyamide and conventional heat-polymerized denture base resins.MATERIALS AND METHODSThree types of denture base resin, which are conventional heat-polymerized acrylic resin (Paladent 20), thermoplastic polyamide resin (Bio Tone), thermoplastic acrylic resin (Acrytone) were used as materials for this study. One hundred five specimens were fabricated. For the color stability test, specimens were immersed in the coffee and green tee for 1 and 8 weeks. Color change was measured by spectrometer. Water sorption was tested after 1 and 8 weeks immersion in the water. For the test of cytotoxicity, cell viability assay was measured and cell attachment was analyzed by FE-SEM.RESULTSAll types of denture base resin showed color changes after 1 and 8 weeks immersion. However, there was no significant difference between denture base resins. All specimens showed significant color changes in the coffee than green tee. In water sorption test, thermoplastic acrylic resin showed lower values than conventional heat-polymerized acrylic resin and thermoplastic polyamide resin. Three types of denture base showed low cytotoxicity in cell viability assay. Thermoplastic acrylic resin showed the similar cell attachment but more stable attachment than conventional heat-polymerized acrylic resin.CONCLUSIONThermoplastic acrylic resin for the non-metal clasp denture showed acceptable color stability, water sorption and cytotoxicity. To verify the long stability in the mouth, additional in vitro studies are needed.

Evaluation of adhesion of reline resins to the thermoplastic denture base resin for non-metal clasp denture

This study aimed to evaluate the tensile and transverse bond strength of chairside reline resins (Tokuyama Rebase II, Mild Rebaron LC) to a thermoplastic acrylic resin (Acrytone) used for non metal clasp denture. The results were compared with those of a conventional heat polymerized acrylic resin (Paladent 20) and a thermoplastic polyamide resin (Biotone). The failure sites were examined by scanning electron microscopy to evaluate the mode of failure. As results, the bond strength of reline resins to a thermoplastic acrylic resin was similar to the value of a conventional heat polymerized acrylic resin. However, thermoplastic polyamide resin showed the lowest value. The results of this study indicated that a thermoplastic acrylic resin for non metal clasps denture allows chairside reline and repair. It was also found that the light-polymerized reline resin had better bond strength than the autopolymerizing reline resin in relining for a conventional heat polymerized acrylic resin and a thermoplastic acrylic resin.

Comparative evaluation of surface porosities in conventional heat polymerized acrylic resin cured by water bath and microwave energy with microwavable acrylic resin cured by microwave energy

Background:Conventional heat cure poly methyl methacrylate (PMMA) is the most commonly used denture base resin despite having some short comings. Lengthy polymerization time being one of them and in order to overcome this fact microwave curing method was recommended. Unavailability of specially designed microwavable acrylic resin made it unpopular. Therefore, in this study, conventional heat cure PMMA was polymerized by microwave energy.Aim and Objectives:This study was designed to evaluate the surface porosities in PMMA cured by conventional water bath and microwave energy and compare it with microwavable acrylic resin cured by microwave energy.Materials and Methods:Wax samples were obtained by pouring molten wax into a metal mold of 25 mm × 12 mm × 3 mm dimensions. These samples were divided into three groups namely C, CM, and M. Group C denotes conventional heat cure PMMA cured by water bath method, CM denotes conventional heat cure PMMA cured by microwave energy, M denotes specially designed microwavable acrylic denture base resin cured by microwave energy. After polymerization, each sample was scanned in three pre-marked areas for surface porosities using the optical microscope. As per the literature available, this instrument is being used for the first time to measure the porosity in acrylic resin. It is a reliable method of measuring area of surface pores. Portion of the sample being scanned is displayed on the computer and with the help of software area of each pore was measured and data were analyzed.Results:Conventional heat cure PMMA samples cured by microwave energy showed maximum porosities than the samples cured by conventional water bath method and microwavable acrylic resin cured by microwave energy. Higher percentage of porosities was statistically significant, but well within the range to be clinically acceptable.Conclusion:Within the limitations of this in-vitro study, conventional heat cure PMMA can be cured by microwave energy without compromising on its property such as surface porosity.

Adherence of Candida albicans to Flexi-ble Denture Base Material

Assessment of Candida albicans adherence to flexible denture base material (Valplast) and con-ventional heat polymerized acrylic resin in the presence and absence of saliva. Materials and Me-thods: A total of 28 square specimens (10 mm x10 mm x3mm) were constructed from Valplast and acrylic denture base materials according to manufacturers' instructions and kept without finishing or polishing. C. albicans was isolated from patients with denture stomatitis. Fourteen specimens (7 of each material) were not coated with human saliva (control), deposited in yeast suspension (107 ) yeast cells/ml, incubated for 1hr at room temperature and washed with phosphate buffer saline and then stained with crystal violet. The remaining 14 specimens (7 of each material) were coated with saliva and treated as previously described. Adherent yeast cells in 84 fields of view (0.25mm2/field) of mate-rials were enumerated. The results were expressed as yeast cells/mm2 of material. Results: In compari-son between the two denture base materials, Candida adherence to acrylic resin (170 yeast cells/mm2) is greater than Valplast (126 yeast cells/mm2). Both saliva uncoated and coated acrylic samples have higher means of Candida adherence (208, 132 cells/mm2) than saliva uncoated and coated Valplast samples (175, 77 cells/mm2) respectively. High significant reduction in yeast counts was seen in both materials after saliva coating. Conclusions: Great reductions in yeast counts were determined in Val-plast material specially in saliva coated specimens when compared with acrylic resin.

Effects of aluminum oxide addition on the flexural strength, surface hardness, and roughness of heat-polymerized acrylic resin

Background/purposeAcrylic dentures frequently fracture during service due to their poor strength characteristics. The aim of this study was to evaluate the effects of adding 0.5–5 wt% aluminum oxide (Al2O3) powder on the flexural strength, surface hardness, and roughness of a conventional heat-polymerized acrylic resin. Materials and methodsIn total, 50 specimens were prepared for each test. Specimens were divided into five groups (n = 10) coded A to E. Group A was the control group (without adding Al2O3). Specimens in the other four groups (B–E) were reinforced with Al2O3 at loadings of 0.5, 1, 2.5 and 5 wt%. Flexural strength was assessed with a three-point bending test using a universal testing machine. Hardness testing was conducted using a Vickers hardness tester. A surface-roughness test was performed with a profilometer. ResultsData analyses using analysis of variance and Tukey'shonest significant difference tests showed that adding 2.5 wt% Al2O3 significantly increased the flexural strength compared to the control group (P = 0.000). The Vickers hardness significantly increased (P < 0.05) after incorporation of 2.5 and 5 wt% Al2O3. No significant difference (P > 0.05) was detected in surface-roughness levels between the reinforced and control groups. ConclusionReinforcement of the conventional heat-cured acrylic resin with 2.5 wt% Al2O3 powder significantly increased its flexural strength and hardness with no adverse effects on the surface roughness.

The Effect of Polymerization Cycles on Color Stability of Microwave‐Processed Denture Base Resin

This study evaluated the effect of different microwave polymerization cycles on the color changes of a microwave-processed denture base resin after accelerated aging and immersion in beverages. Specimens of light pink acrylic resin were divided into three groups according to polymerization cycle: (A) 500 W for 3 minutes, (B) 90 W for 13 minutes + 500 W for 90 seconds, and (C) 320 W for 3 minutes + 0 W for 4 minutes + 720 W for 3 minutes. Control groups were a heat-processed acrylic resin (T) and a chemically activated denture repair resin (Q). Eight specimens per group were aged in an artificial aging chamber and evaluated at 20, 192, and 384 hours. Another series of 40 specimens per group were immersed in water, coffee, tea, cola, or red wine and evaluated at 1, 12, and 36 days. Color was measured by a spectrophotometer before and after aging or immersion. Color changes (DeltaE) were analyzed by ANOVA/Bonferroni t-test (alpha = 0.05). Mean DeltaE (+/- SD) after 384 hours of accelerated aging were (A) 2.51 +/- 0.50; (B) 3.16 +/- 1.09; (C) 2.89 +/- 1.06; (T) 2.64 +/- 0.34; and (Q) 9.03 +/- 0.40. Group Q had a significantly higher DeltaE than the other groups. Color changes of immersed specimens were significantly influenced by solutions and time, but the five groups showed similar values. Mean DeltaE at 36 days were (water) 1.4 +/- 0.8; (coffee) 1.3 +/- 0.6; (tea) 1.7 +/- 0.5; (cola) 1.4 +/- 0.7; and (red wine) 10.2 +/- 2.7. Results were similar among the five test groups. Color changes of the microwave-polymerized denture base resin tested were not affected by different polymerization cycles after accelerated aging or immersion in beverages. These changes were similar to the conventional heat-polymerized acrylic resin test, but lower than the repair resin after accelerated aging.