Heat-polymerized Polymethyl Methacrylate Research Articles

Comparison of strength of milled and conventionally processed PMMA complete-arch implant-supported immediate interim fixed dental prostheses

Statement of problemA typical conversion process of a complete-arch immediate loading protocol entails preparing holes in a complete denture for connection to interim copings, which reduces the strength of the prosthesis. The excellent mechanical properties of milled polymethyl methacrylate (PMMA) disks may provide interim prostheses with improved strength. PurposeThe purpose of this in vitro study was to measure the flexural strength and failure load of simulated acrylic resin immediate implant-supported interim prostheses fabricated by conventional processing and computer-aided manufacturing. Material and methodsA master patient model was created with an acrylic resin base and 2 BioHorizons Internal 4.5-mm-diameter implants placed with a 21.5-mm span and multiunit abutments (MUA) tightened to place. Two groups with different prosthodontic designs were used: one represented the standard fixed prosthesis with support at each end (noncantilever, NC), and the other group represented the cantilever portion of the prosthesis (cantilever, C). Two connection designs of prosthesis blocks to MUA abutments were evaluated: one with typical holes in the prosthesis for capturing interim copings and one with a low-profile coping. For the heat-processed PMMA groups (HP/NC and HP/C), wax patterns were milled, and heat-polymerized denture base PMMA prostheses were processed. The milled PMMA groups (M/NC and M/C) were milled from a tooth-shaded PMMA disk for the prosthesis blocks. The milled low-profile groups (Mlp/NC and Mlp/C) had identical dimensions except that connection to the low-profile coping was designed with a cement space and a narrow diameter screw access hole and was milled from a PMMA disk. The failure load (N) of the cantilever prostheses was recorded, and for NC groups, the 3-point flexural strength formula (MPa) was calculated. The Weibull modulus, characteristic strength, and summary statistics were computed, and the groups were statistically analyzed with ANOVA and the post hoc Tukey test (α=.05). ResultsThe mean flexural strengths (MPa) were HP/NC=91.35 ±18.92; M/NC=143.94 ±36.79; Mlp/NC=117.06 ±13.86. Significant differences were found among groups (P<.001). Mean failure loads (N) and Weibull modulus (WM) of cantilever prosthesis strengths were for HP/C=512.66, WM=5.597; M/C=695.06, WM=4.875; Mlp/C=254.97, WM=1.797 (P<.001). ConclusionsImplant fixed interim structures milled from high-density PMMA blanks had a 35% higher flexural strength for both the standard prostheses and the cantilever prostheses than heat-processed denture base PMMA. The low-profile coping design was stronger than the heat-processed material, and the failure point was relocated from the lateral walls to the cervical margin area.

In Vitro Effect of Denture Cleansers on the Color Stability of Polyetheretherketone and Other Denture Base Polymers

The aim of this in vitro study was to compare the long-term effect of overnight use of denture cleansers with different chemical compositions on the color stability of denture base polymers (DBPs). The four DBPs evaluated were PEEK (PK group), thermoinjection-molded polyamide (PA group), auto-polymerized polymethylmethacrylate (PMMA) (AP group), and heat-polymerized resin PMMA (HP group). The cleaning agents used were Corega tablet (CT), Protefix tablet (PT), and 0.5% sodium hypochlorite (NaOCl) solution (SH). Distilled water (DW) served as a control. Forty-eight disc-shaped specimens (10mm × 2mm) were prepared from each DBP and randomly immersed in the different storage media (n=12 in each group). Color measurements of the specimens before and after immersion in the denture cleansers were made using a spectrophotometer (VITA Easyshade V). The color changes were measured and recorded in L* a* b*. After 120 d, the CIEDE2000 formula was used to calculate color changes (∆E00). For analysis of the data, a multivariate analysis of variance was used (p&lt;0.05). The results of the statistical analysis revealed significant color change differences in the DBPs immersed in the various denture cleansers (p&lt;0.05). Groups PA and PK showed the highest values for all solutions. AP-SH showed the highest ∆E00 value in group AP, no significant difference was found between other solutions. In group HP, there was no statistically significant difference between the average ∆E00 values of all solutions. Long-term daily use of the denture cleansers affected the color stability of all the DBPs, although the level of color change was acceptable. Laboratory and clinical studies on the color stability of PEEK are needed to confirm the results of this study.

Determining growth inhibition of Candida albicans biofilm on denture materials after application of an organoselenium-containing dental sealant

Statement of problemDenture stomatitis is a chronic inflammatory condition caused by the formation of Candida albicans biofilm on denture bases. It is associated with aggravating intraoral pain, itching, and burning sensations. It can also potentiate cardiovascular diseases and aspiration pneumonia. The problem has thus far eluded efficient, toxic-free, and cost-effective solutions. PurposeThe purpose of this in vitro study was to investigate the effectiveness of organoselenium to inhibit the formation of C. albicans biofilm on the surface of acrylic resin denture base materials when it is either incorporated into the acrylic resin material or coated on the denture surface as a light-polymerized surface sealant. Material and methodsSixty heat-polymerized polymethyl methacrylate disks were fabricated and assigned to 4 groups (n=15): disks coated with a light-polymerized organoselenium-containing enamel surface sealant (DenteShield), disks impregnated with 0.5% organoselenium (0.5% selenium), disks impregnated with 1% organoselenium (1% selenium), and disks without organoselenium (control). C. albicans biofilm was grown on each disk which had been placed in a well of the microtiter plate containing 1-mL brain heart infusion broth inoculated with C. albicans. The plates were incubated aerobically at 37 °C for 48 hours. A confocal laser scanning microscope was used to determine the biofilm thickness, biomass, and live/dead cell ratio. Biofilm morphology was examined with scanning electron microscopy, whereas microbial viability was quantified by the spread plate method. The data were analyzed by using ANOVA and Tukey-Kramer multiple comparisons (α=.05). ResultsThe microbial viability, biofilm thickness, biofilm biomass, and live/dead cell ratio were lower (P<.001) on disks in the test groups (DenteShield, 0.5% selenium, 1% selenium) when compared with the control group, with these variables being lowest in the 0.5% selenium and 1% selenium groups. The 0.5% selenium and 1% selenium groups did not differ significantly from each other in any of the variables (P>.05). Scanning electron microscope images showed inhibition of both biofilm growth and yeast to hyphae transition in the DenteShield, 0.5% selenium, and 1% selenium groups, with visible disruption of the biofilm morphology. ConclusionsThe present study demonstrated that organoselenium, whether incorporated into or coated on the surface of an acrylic resin denture base material, has the potential to inhibit Candida albicans biofilm growth on denture surfaces and as such can be clinically useful for the prevention of denture stomatitis.

Evaluation of flexural properties and dynamic mechanical analysis of glass fiber-reinforced polyamide resin.

The aim of this study was to evaluate flexural strength, elastic modulus and dynamic mechanical analysis (DMA) of heat-polymerized polymethyl methacrylate resin, polyamide resin and glass fiber-reinforced polyamide resin. Three groups were determined according to denture base materials as polymethyl methacrylate resin (H), polyamide resin (P) and glass fiber reinforced polyamide resin (R). Sixteen specimens for each denture base material were prepared with dimensions of 64x10x3.3 mm for three-point bending test. Two specimens for each denture base material were prepared with dimensions of 30x10x3 mm for DMA. Polymethyl methacrylate and polyamide specimens were prepared according to the manufacturer's recommendations. The silane was applied to glass fibers (4.5 mm length) 2% by weight of the polyamide resin, they were placed in polyamide resin cartilages and injected to the mold. The thermal aging procedure was applied to half of specimens of each material (n=8). Flexural strength and elastic modulus of the specimens were determined by three-point bending test at a speed of 5 mm/ min. DMA was performed to 1 specimen from each group to evaluate viscoelastic properties. Data were analyzed with one-way ANOVA, Tukey and Paired t tests. A statistically significant difference was found in flexural strength and elastic modulus values of denture base materials (p=0.00). The highest flexural strength and elastic modulus values were observed in polymethyl methacrylate group. There was no significant difference between polyamide and glass-fiber reinforced polyamide groups (p=0.497). No significant difference was determined in all threedenture base materials before and after aging procedure. The reinforcement with glass-fibers did not affect the flexural strength and elastic modulus of polyamide resin.

Effects of boron on the mechanical properties of polymethylmethacrylate denture base material.

The objective of this study was to determine whether the addition of different types of boron (Borax, Boric Acid and Colemanite) to polymethyl methacrylate denture base resin would improve flexural and impact strengths, and surface hardness of polymethyl methacrylate. Borax, Boric acid, Colemanite were added to heat polymerized polymethyl methacrylate specimens were prepared for flexural strength (65x10x2.5 mm), impact strength (50x6x4 mm), and hardness (20x6x4 mm) tests according to the manufacturers' instructions (n=10). To determine flexural strength of the specimens, they were loaded until failure on a universal testing machine using a three point bending test. Specimens were subjected to the Charpy impact test machine. Hardness of the specimens was measured with an analog shoremeter Shore D. The data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=0.05). The highest mean flexural strength value was seen in 3% Borax group and followed by 1% Colemanite group. In addition, the highest mean impact strength value was recorded in 1% Colemanite group, and differences between 1% Colemanite group and control group were found to be statistically significant (p=0,001). Furthermore, there was significant difference in hardness between control group and all other groups (p<0.001). The addition of 1% Colemanite to polymethyl methacrylate improved the mechanical properties of PMMA.

Bite Force in Elderly with Full Natural Dentition and Different Rehabilitation Prosthesis.

(1) Background: This study aimed to investigate maximum bite force (MBF) in elderly patients with natural full dentition (FD), patients rehabilitated with Traditional Complete Dentures (CD), with overdentures (IRO) and edentulous patients (ED). We also tested whether MBF changes are associated with gender, age of the patients and body mass index (BMI) as result of altered food; (2) Methods: Three hundred and sixty-eight geriatric patients were included. We studied two types of prostheses: (a) IRO with telescopic attachments. (b) CD (heat polymerized polymethyl methacrylate resin). The MBF was measured using a digital dynamometer with a bite fork; (3) Results: We found that MBF is higher in males than females, regardless of teeth presence or absence (p < 0.01). In patients with CD or IRO, there are no differences between males and females; prostheses improve MBF compared to edentulous patients (p < 0.0001) and this effect is greater with IRO prostheses (p < 0.0001); the chewing force of FD subjects remains greater (p < 0.0001); there are no differences among chewing strength based on different BMI categories, although FD subjects have a reduced incidence of obesity; there is a significant negative correlation between MBF and age (p = 0.038; R = 0.145), and no correlation between MBF and BMI; (4) Conclusions: This study showed that MBF improves more in patients using IRO prostheses, although not reaching the MBF of FD subjects. MBF does not correlate with BMI, although we found increased percentages of obesity in edentulous subjects or those with prostheses. Thus, old people wearing prostheses require special attention by a nutritionist to avoid risk of malnutrition.

Fungicidal and inhibitory efficacy of cinnamon and lemongrass essential oils on Candida albicans biofilm established on acrylic resin: An in vitro study

Statement of problemIt is unclear whether cinnamon and lemongrass essential oils can effectively reduce the Candida-biofilm frequently formed on dental devices made from heat-polymerized polymethyl methacrylate (PMMA) resin that contributes to the development of mild oropharyngeal as well as life-threatening candidiasis in patients wearing the devices. PurposeThe purpose of this in vitro study was to determine the efficacy of cinnamon and lemongrass essential oils in eradicating Candida albicans biofilm on heat-polymerized PMMA specimens and to determine whether they retard the formation of fungal biofilm. Material and methodsThe antifungal effect of cinnamon and lemongrass essential oils was determined by using agar disk diffusion and broth microdilution methods to obtain minimum inhibitory concentrations. The mature C albicans biofilm (48 hours) was pre-established on PMMA specimens before being individually treated with various concentrations (½, 1, 2, 4, 8, 16 times minimum inhibitory concentration) of each tested oil for different exposure times (1, 2, 4, 8, and 24 hours). In another experiment, fungal biofilm was established on the PMMA specimens that were primed individually with various concentrations of the tested oils for different times. The 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT)-reduction assay was used to quantitate biofilm viability in both experiments. Statistical analysis was performed by using the 1-sample Kolmogorov-Smirnov test and 2-way ANOVA followed by the Tukey multiple comparison test (α=.05). ResultsMinimum inhibitory concentration values of cinnamon and lemongrass essential oils against planktonic C albicans were 0.1 μL/mL (0.01% v/v) and 0.4 μL/mL (0.04% v/v). At 8 times the minimum inhibitory concentration, cinnamon oil (0.8 μL/mL or 0.08% v/v) and lemongrass oil (3.2 μL/mL or 0.32% v/v) eradicated the pre-established fungal biofilm by 99.0% in an exposure time of 1 hour. In contrast, high concentrations of 8 and 16 times the minimum inhibitory concentration of cinnamon oil (0.8 μL/mL or 0.08% v/v) and lemongrass oil (6.4 μL/mL or 0.64% v/v) coated on PMMA specimens for 24 hours were only able to inhibit the formation of fungal biofilm by approximately 70.0%. ConclusionsCinnamon and lemongrass essential oils can eliminate pre-established C albicans biofilm and restrain the formation of fungal biofilm on heat-polymerized PMMA specimens. Both effects of the tested essential oils depended on dose and exposure or priming time.

Bond strength of artificial teeth to thermoplastic denture base resin for injection molding.

This research was conducted to investigate the bond strength between artificial teeth and a thermoplastic denture base resin for injection molding with different surface preparations for use in flexible resin removable partial dentures. Composite resin denture teeth and acrylic denture resin teeth were bonded to three types of thermoplastic denture base resins for injection molding (polyamide, polyester, and polycarbonate) and a conventional heat-polymerized polymethyl methacrylate (PMMA) resin (control). The ridge lap surfaces of the artificial teeth were classified into four groups based on the type of ridge lap surface treatment applied (n=10): no treatment, ethyl acetate, small T-shaped tunnel, and large T-shaped tunnel. The specimens were tested for bond strength. The results showed that the ethyl acetate treatment was ineffective for enhancing the bond strength (p>0.05) between the artificial teeth and thermoplastic denture base resin for injection molding, whereas the T-shaped tunnel was quite effective in this regard (p<0.05).

Color stability of 3D-printed denture resins: effect of aging, mechanical brushing and immersion in staining medium

PURPOSEThis in-vitro study evaluated and compared the color stability of 3D-printed and conventional heat-polymerized acrylic resins following aging, mechanical brushing, and immersion in staining medium.MATERIALS AND METHODSForty disc-shaped specimens (10 mm in diameter and 3 mm thick) were prepared from two 3D-printed [DentaBASE (DB) and Denture 3D+ (D3D)] and one conventional polymethylmethacrylate (PMMA) denture materials. The specimens were thermo-cycled, subjected to mechanical brushing, and were immersed in either coffee, lemon juice, coke, or artificial saliva (AS) to simulate one and two years of oral use. Color measurements of the specimens were recorded by a spectrophotometer at baseline (T0), and after one (T1) and two years (T2) of simulation. The color changes (∆E) were determined and also quantified according to the National Bureau of Standards (NBS) units. Descriptive statistics, followed by factorial ANOVA and Bonferroni post-hoc test (α=.05), were applied for data analysis.RESULTSThe independent factors, namely material, staining medium, and immersion time, and interaction among these factors significantly influenced ∆E (P<.009). Irrespective of the materials, treatments, and time, the highest and the lowest mean ∆Es were observed for PMMA in lemon juice (4.58 ± 1.30) and DB in AS (0.41 ± 0.18), respectively. Regarding the material type, PMMA demonstrated the highest mean ∆E (2.31 ± 1.37), followed by D3D (1.67 ± 0.66), and DB (0.85 ± 0.52), and the difference in ∆E between the materials were statistically significant (P<.001). All the specimens demonstrated a decreased color changes at T2 compared to T1, and this difference in mean ∆E was statistically significant (P<.001).CONCLUSIONThe color changes of 3D-printed denture resins were low compared to conventional heat polymerized PMMA. All the tested materials, irrespective of the staining medium used, demonstrated a significant decrease in ∆E values over time.

Comparative evaluation of three types of denture base materials with saliva substitute before and after thermocycling: An in vitro study

Statement of problemXerostomia refers to the decrease in the quality and quantity of saliva. In denture wearers, xerostomia affects the retention of the denture because of lack of wettability of the denture base. However, which denture base resin materials are best wetted by artificial salivary substitutes is unclear. PurposeThe purpose of this in vitro study was to determine the wetting properties of 3 different commercially available denture base resin materials with artificial salivary substitute by using contact angle measurements and to compare these properties before and after thermocycling. Material and methodsA total 120 specimens were fabricated with 3 different denture base materials (n=40): heat-polymerized polymethylmethacrylate (DenTek), injection-molded nylon polyamide (Valplast), and microwave polymerized (VIPI WAVE). The advancing and receding contact angles were measured with a goniometer by using the WinDrop++ software program. The contact angle hysteresis was calculated from the advancing and receding contact angles values. The same specimens were subjected to thermocycling to measure the advancing and receding contact angles values. The comparative evaluation was carried out before and after thermocycling. ResultsThe mean ±standard deviation contact angles of the microwave-polymerized material were (62.40 ±1.21 degrees) advancing contact angle, (32.12 ±0.66 degrees) receding contact angle, and (30.28 ±1.40 degrees) contact angle of hysteresis. It was followed by the injection-molded nylon polyamide material, whose mean ±standard deviation contact angle values were (68.57 ±1.72 degrees) advancing contact angle, (43.02 ±1.39 degrees) receding contact angle, (26.27 ±2.05 degrees) contact angle hysteresis and high impact strength heat-polymerized polymethylmethacrylate material, whose mean ±standard deviation contact angle values were (69.81 ±0.16 degrees) advancing contact angle, (41.90 ±1.02 degrees) receding contact angle, and (27.91 ±0.97 degrees) contact angle hysteresis. The statistical analysis showed significant differences among contact angle values of the microwave-polymerized material as compared with the heat-polymerized polymethylmethacrylate and injection-molded nylon polyamide materials (P<.001). ConclusionsThe microwave-polymerized material showed better wettability with artificial saliva substitute than heat-polymerized polymethylmethacrylate and injection-molded nylon polyamide.

A novel economically viable solution for 3D printing-assisted cranioplast fabrication

Cranioplasty is a common neurosurgical procedure which makes use of autologous bone or alloplastic material for cranial defect reconstruction. Alloplastic reconstruction is routinely done in cases where viable autologous bone is not available due to various reasons. Hydroxyapatite implants, patient-specific titanium and PEEK are widely employed materials due to their biocompatibility, durability, and high adaptation accuracy. However, their high cost and limited availability make them a less viable option for the common man. Polymethyl methacrylate (PMMA) is one of the commonly used alloplastic material for cranioplasty. This note presents a novel, economic, patient-specific, 3D printing-assisted and heat polymerized PMMA cranioplast fabrication technique with an accuracy comparable to that of patient-specific titanium and PEEK cranioplast.

Impact of Surface Treatment with Different Repair Acrylic Resin on the Flexural Strength of Denture Base Resin: An In Vitro Study

The aim and objective of the present study was to assess the flexural strength of denture base resin based on surface treatment with different acrylic resin repair materials. Totally, 120 heat-polymerized polymethyl methacrylate denture base resin materials which are rectangular shaped with the size of 65 mm × 10 mm × 2.5 mm were fabricated. 150 μm-sized alumina used for surface treatment. All the 120 heat-cured, surface-treated acrylic denture base resin samples were randomly divided into three groups. Group I: glass-fiber-reinforced auto-polymerizing acrylic resin, group II: auto-polymerizing acrylic resin, and group III: light-cured acrylic resin. A universal testing machine was used to test the flexural strength of the repaired specimens. A highest mean flexural strength (88.96 ± 0.31) was demonstrated by group I, followed by group II (72.18 ± 1.86) and group III (66.30 ± 1.02). ANOVA demonstrated a statistically significant inter-group difference. On multiple comparisons, using Tukey's post hoc test a statistically significant difference between groups I and II and between groups I and III was found. After considering the limitations, the present study concluded that the highest flexural strength is shown by glass-fiber-reinforced auto-polymerizing acrylic resin than by auto-polymerizing acrylic resin and light-cured acrylic resin. Denture repair comprises of joining two fractured parts of a denture with a denture repair material. The success of denture repair depends on the adhesion phenomenon. The treatment of the surface can be accomplished using a suitable material which changes chemically and morphologically and thus promotes better adhesion.

A comparative study to evaluate the retention of conventional retention sleeve material versus retention.sil 600 in implant-retained overdentures: In vitro study

Purpose: The aim of this study was to assess and evaluate the retention of conventional retentive sleeve material versus retention.sil in implant-retained overdentures.Methodology: Custom-designed models of uniform dimensions were made from heat-polymerized polymethyl methacrylate resin. The model had two components which comprised a lower member (matrix) and an upper member (patrix). The lower member (matrix) was embedded with two ADIN implant analogs attachment (Adin Implant System Ltd. Israel) of 3.75 mm × 10 mm with prefabricated ball attachment at an interimplant distance of 20 mm. The upper member was prepared to receive two different retention sleeve materials, conventional retentive/plastic sleeve attachment (Adin Implant System Ltd. Israel), and retention.sil 600 (Bredent medical GmbH and Co. KG). Using a universal testing machine, each of the models was subjected to 100 pulls each to dislodge the upper member from the lower member, and the force values as indicated on the digital indicator were tabulated.Statistical Analysis Used: Statistical analysis comprised Kolmogorov–Smirnov test, Friedman test, Mann–Whitney test, and Wilcoxon signed-rank test.Results: The statistical model revealed that when subjected to vertically directed forces, the conventional retentive/plastic sleeve attachment (Adin Implant System Ltd. Israel) developed higher retentive force as compared to the retention.sil 600 (Bredent medical GmbH and Co. KG).Conclusions: The conventional retentive sleeve material maintains their retentive capacity longer than the retention.sil 600. Further research is required to increase the retentive force in retention.sil material, thereby increasing denture retention and stability.

Immediate Post-Operative Reconstruction of Calvarial Bone by Cranioplasty Prosthesis in Calvarial Bone Fibrous Dysplasia

Objectives: Immediate post-operative reconstruction of calvarial bone by cranioplasty prosthesis in calvarial bone fibrous dysplasia. An easy and economical method for reconstruction of the defect. Methods: Surgical excision of right parietal cranial space occupied lesion was performed followed by fabrication of immediate postoperative period cranioplasty prosthesis by using clear heat polymerized polymethylmethacrylate. Results: The cranial defect created during excision of calvarial bone fibrous dysplasia was immediately replaced by cranioplasty prosthesis which was fabricated in the immediate post-operative period using heat polymethylmethacrylate. Conclusions: Polymethylmethacrylate is a very reliable thermoplastic material that can be prefabricated or even placed immediately after post-operative period to produce a suitable prosthesis. Polymethylmethacrylate implants have been outmoded by computer-aided design and computer-aided manufacturing and newer 3-dimensional printed implants, but these newer methods are accompanied by higher expenses and timing issues.

Patient and Clinical Evaluation of Traditional Metal and Polyamide Removable Partial Dentures in an Elderly Cohort.

To evaluate several clinical and functional parameters by administration of specific questionnaires to an elderly patient's cohort wearing three different types of removable partial denture (RPD): VALPLAST-RPD (Polyamide VALPLAST), CoCr-RPD (cobalt-chromium alloy), and PMMA-RPD (heat polymerized polymethyl methacrylate). One hundred twenty patients (mean age 73 years) were included in this study. All patients were treated with a removable partial denture for the maxillary arch. After 1 year of use, patients and clinicians were asked to compile specific questionnaire on patient satisfaction, including aesthetic, functional, and clinical outcomes. It was also evaluated whether the localization of the missing teeth according to Kennedy classification may affect these parameters. Categorical data obtained from the questionnaires were analyzed by chi-squared test. VALPLAST-RPD was the most satisfactory aesthetically. Nevertheless, patients of VALPLAST-RPD group reported increased difficulty in cleaning the prosthesis, roughness perceived by the tongue, and increased retention loss (p < 0.001). Patients with PMMA-RPD claimed a higher level of encumbrance (p < 0.001) and increased speech difficulties (p = 0.002). Clinically, patients of VALPLAST-RPD and PMMA-RPD groups displayed redness of the mucosa area around abutment teeth (p < 0.001). Patients of VALPLAST-RPD group had four cases of artificial teeth loss and two cases of discoloration. The position of missing teeth did not significantly influence any parameter. Each RPD material utilized may present advantages and disadvantages in an elderly population. VALPLAST-RPD may be recommended to older patients with non-extensive edentulous areas supported by anterior and posterior teeth, and not subjected to strong chewing loads. The main advantages are aesthetic satisfaction and easiness to insert and remove it.

Adhesion potential of relining materials to polyamide and PMMA-based denture base materials: effect of surface conditioning methods

This study evaluated the bond strength of relining materials to different denture base materials polyamide and polymethylmethacrylate denture base materials after various surface conditioning methods. Denture base resin specimens (N = 128; n = 8 per group) (10 × 10 × 2.5 mm3) were fabricated out of injection-moulded thermoplastic polyamide resin (POL) (Deflex) and heat-polymerized polymethylmethacrylate (PMMA, Dura Dent) (HC). The specimens were randomly divided into 4 main groups according to different surface conditioning methods: (a) No conditioning, control (C), (b) grinding with green stone (G), (c) application of primer (V), (d) silica coating with Al2O3 particles coated with SiO2 (Rocatec) (R). Half of the specimens in each group received auto-polymerized hard relining resin (GC, GC Reline Hard) and the other half PMMA based relining resin (SC, Dura Dent). After thermocycling (×5000), the bonded specimens were tested under tensile forces (0.5 mm/min). Data (MPa) were analyzed using Mann–Whitney U and Kruskal–Wallis tests (alpha = 0.05). Bond strength of relining resins were significantly higher to PMMA than to POL, regardless of the conditioning method (p < 0.05). While R positively affected the bond strength results (p < 0.05) (4.99 ± 1.65–3.27 ± 1.31), application V or G did not show significant effect to POL-relining resin adhesion. After R conditioning, bond strength values were significantly higher in HC-GC group (7.48 ± 2.32) than POL-GC group (3.27 ± 1.31) (p < 0.05). Adhesion of auto-polymerized relining materials to thermoplastic polyamide or polymethylmethacrylate denture resins could be improved after surface conditioning with silica-coating.

Biofilm Formation of Respiratory Pathogens on Vanillin-Incorporated Denture Base Resin

The adherence of microorganisms to denture base materials and the consequent formation of biofilms on these surfaces are contributing factors to biofilm-related oral and systemic diseases. Aspiration pneumonia is a potentially life-threatening respiratory infection associated with the entry of foreign materials into the bronchi. Vanillin-incorporated polymethyl methacrylate (PMMA) resin has been developed for the use in dentistry and demonstrated to have antimicrobial activity. Objective: To evaluate antimicrobial property of vanillin-incorporated PMMA denture base resin on biofilm formation of respiratory pathogens. Materials and methods: The heat polymerized PMMA denture base resin samples (Siam Cement Group, Thailand) were prepared according to the percentage of vanillin incorporation (0%, 0.1% and 0.5% vanillin). Another group of commercial resin samples without vanillin (Triplex®, Ivoclar Vivadent, USA) was prepared in the same manner. All samples were coated with sterile unstimulated saliva collected from three healthy adult volunteers at 37 °C for 60 min. The respiratory pathogenic bacteria used in this study were Staphylococcus aureus ATCC 5638, Streptococcus pneumoniae ATCC 49619, and Pseudomonas aeruginosa ATCC 27853. They were prepared to a concentration of approximately 107 colony forming unit (CFU)/mL. The bacterial biofilm formation was done in 96-well plate and incubated at 37°C for 24-48 h. The amount of biofilm was quantified by Cell Counting Kit WST-8 (Dojindo Molecular Technologies, USA) at 420 nm. All tests were performed in triplicate on three separate occasions. One-way ANOVA and Turkey’s test were used for the statistical analysis. Results: The vanillin-incorporated resin groups (0.1% and 0.5% vanillin) had a significant reduction of S. aureus and P. aeruginosa biofilm mass compared with resins without vanillin (0% vanillin and commercial resin groups). No significant difference was observed in the S. pneumonia biofilm formation. Up to 80% and 33% reductions of biofilm mass were demonstrated on P. aeruginosa and S. aureus, respectively. Conclusion: The incorporation of vanillin to denture base PMMA resin could significantly inhibit biofilm formation of respiratory pathogens. Using this PMMA resin, denture base materials with antimicrobial property can be applied to reduce a risk of respiratory infection in denture wearing patients.

Evaluation and comparison of different polymerization techniques, curing cycles, and thicknesses of two denture base materials.

The study aimed to compare the effect of different materials, thicknesses, and polymerization methods and cycles, on the surface porosity of acrylic denture base resins. Conventional heat-polymerized polymethyl methacrylate (PMMA) and specially designed acrylic resin (Acron MC) were used to make 84 rectangular samples. They were divided into three groups to evaluate and compare the polymerization techniques, curing cycles, and thicknesses of the two denture base materials (28 samples each). Group A contained PMMA samples polymerized using water bath method (control group); Group B contained Acron MC samples polymerized by microwave method, and Group C contained PMMA samples polymerized by microwave method. Each group was further divided based on sample thickness and polymerization cycles. Each sample was scanned for surface porosity and area of each pore was measured using optical microscope. Data was analyzed using ANOVA, Bonferroni, and student t-tests. Unpaired student t-test was performed to compare the means of surface porosity with polymerization cycles and thicknesses among the groups. The power of study was kept at 80%. Group C showed highest mean % of porosity depending on method of polymerization, different polymerization cycles (short and long) and polymerization cycles within the group. Group B showed the highest mean % of porosity depending on thickness and thickness within the groups. Microwavable acrylic resin polymerized by microwave energy exhibited statistically insignificant increase in porosity when compared to conventional heat cured acrylic resin by water bath method. Conventional acrylic resin polymerized by microwave energy exhibited high statistically significant porosity irrespective of sample thickness. There was statistically insignificant increase in porosity depending on sample thickness irrespective of material and method of polymerization.

Comparative Evaluation of Water Sorption of Heat-Polymerized Polymethyl Methacrylate Denture Base Resin Reinforced with Different Concentrations of Silanized Titanium Dioxide Nanoparticles: An In vitro Study.

Statement of Problem:Polymethyl methacrylate (PMMA) is the most regularly used material in denture fabrication. Water sorption of denture base PMMA denture base resin has negative effects on physical properties, may lead to harmful tissue reactions in patients, and also has detrimental effects on color stability of the denture base.Purpose:The purpose of this study was to evaluate the effect on water sorption of heat-cured PMMA denture base material after incorporation of 1%, 3%, and 5% by weight of silanized titanium dioxide (TiO2) nanoparticles.Materials and Methods:For preparation of test samples, TiO2 nanoparticles (PCode: 700339, Sigma-Aldrich, USA) were coated with a layer of trimethoxysilylpropylmethacrylate (PCode: 440159, Sigma-Aldrich, USA) before sonicated in monomer (MMA) (DPI Heat Cure) with the percentages 1%, 3%, and 5% by weight; after sonication, it was mixed with PMMA powder using conventional denture fabrication procedure. Then, we prepared total 40 samples for study; 10 samples for each four groups, i.e. that is one control group and three experimental groups. The first group was prepared from PMMA without addition of TiO2 nanoparticles (control group), the second group with the addition of 1 wt% TiO2 nanoparticles, the third group with 3 wt% TiO2 nanoparticles, and the fourth one with 5 wt% TiO2 nanoparticles (experimental groups). Water sorption test was then conducted on each sample.Results:Each group was evaluated for water sorption test, and it was found that increasing the wt% of nanoparticles, there was a significant decrease in water sorption of denture base resin from 1.74 to 1.46 mean wt%. P value suggested that the difference of mean percent increase across all groups was statistically significant with P = 0.034.Conclusion:The maximum decrease in water sorption was observed in denture base resin incorporated with 5 wt% TiO2 nanoparticles.

GÜMÜŞ ZEOLİT İLAVE EDİLEN AKRİLİK REZİNLERİN EĞİLME DAYANIMLARININ İN-VİTRO DEĞERLENDİRİLMESİ

Amac: Bu calismanin amaci, antimikrobiyal ajan olarak farkli agirlik yuzdeleriyle ilave edilen gumus-zeolitin isiyla polymerize olan polimetilmetakrilat protez kaidesinin egilme dayanimina etkisinin isil islem oncesi ve sonrasi degerlendirilmesidir. Gerec ve Yontem: 64x10x3,3mm ebatlarinda standart test ornekleri gumus-zeolitin (Zeomic @ ) % 0, % 0,5, % 2 ve % 4 kuru agirlik yuzdelerinde isi ile polimerize olan akrilik tozuna ilave edilmesiyle hazirlanmistir. Her grup icin toplam 20 ornek hazirlanmistir. Kontrol grubu olarak gumus-zeolit ilave edilmeyen ornekler kullanilmistir (n=20). Bu gruplar daha sonra isil islem uygulanmayan ve uygulanan olmak uzere 2 alt gruba (n=10) daha ayrilmistir. Isil dongu uygulanan gruptaki ornekler 10000 donguluk isil dongu islemine (5 °C ve 55 °C’de, 30 sn aralikla) tabii tutulmuslardir. Egilme dayanimlarinin hesaplanmasinda universal test cihazinda 3 nokta egme testi yapilmistir. Verilerin istatistiksel analizi icin Minitab Release 15 yazilim programi ile ANOVA ve bagimli orneklem t-testi kullanilmistir. Anlamlilik p 0.05). Ayrica isil dongu islemi butun gruplarda egilme dayanimini istatistiksel olarak anlamli sekilde azaltmistir (p<0.05). Sonuc: Calismamizda gumus-zeolitin agirlik yuzdesinin artmasi ve isil dongu islemi uygulanmasi ile egilme dayaniminin azalmasina ragmen bulunan degerler ISO 20795-1:2013(E) no’lu standartta belirtilen 65 MPa’ dan daha yuksek bulunmustur. Anahtar Kelimeler: Akrilik, Egilme dayanimi, Gumus-zeolit, Isil dongu islemi IN-VITRO EVALUATION OF FLEXURAL STRENGTHS OF ACRYLIC RESINS INCORPORATED SILVER ZEOLITE ABSTRACT Aim: The aim of this study was to evaluate the effect of silver-zeolite on flexural strength, which was added into heat polymerized polymethylmethacrylate (PMMA) denture base resin with different percentages as antimicrobial agent before and after thermal cycling. Material and method: Standard test specimens in sizes of 64x10x3.3 mm were prepared by adding silver-zeolite (Zeomic @ ) into heat polymerized acrylic powder with 0 %, 0.5 %, 2 %, and 4 % dry weight percentages. A total of 20 samples were prepared for each group. A total of 20 samples without silver-zeolite served as the control group. These groups were then divided into 2 subgroups (n = 10), a not-thermal cycled and thermal cycled group. Samples in thermal cycled group were subjected to 10000 thermal cycling (5 °C-55 °C). Three-point FS of the specimens was tested in a universal testing machine and the flexural strength data (σ) was calculated (MPa). Statistical analysis of the data was performed using the Minitab Release 15 software program by ANOVA and paired t-test. Significance was set at p<0.05. Results: For both groups (non-thermal cycled and thermal cycled), the flexural strength of the control group (0% weight percentage) was significantly higher than the other three groups (0.5 %, 2 %, 4 %) (p<0.05). The differences between other 3 groups were also statistically significant (p<0.05). In addition, for all groups the flexural strength decreased statistically significantly with thermal cycling (p<0.05). Conclusion: Although an increase in the percentage of silver-zeolite and the application of thermal cycling reduced the flexural strength, our results are still higher than the 65 MPa which is specified in the standard ISO 20795-1: 2013 (E). Keywords: Acrylic, Flexural strength, Silver-zeolite, Thermal cycling