Influence of polymerization method, curing process, and length of time of storage in water on the residual methyl methacrylate content in dental acrylic resins

Comparison of methods for the synthesis of silver nanoparticles stabilized in a solid polymethacrylate matrix

Silver nanoparticles were synthesized inside the small plates of transparent polymer medium by reduction of silver cations. The difference in morphology and sizes of nanoparticles synthesized by chemical, photochemical and thermal reduction was revealed, which depends both on the component ratio of the mixture and on the reduction time for the specific component ratio The polymethacrylate matrix itself acts as the stabilizing agent. A colorimetric sensor based on polymethacrylate matrix and silver nanoparticles was developed for the detection of hydrogen peroxide. The optical properties of the sensor were characterized by spectrophotometer using the surface plasmon resonance. A colorimetric sensor with nanoparticles undergoing to thermal reduction showed a quick result for the determination of hydrogen peroxide in the range 0.2-4.4 mM with a detection limit 0.1 mM.

Effects of various beverages on characteristics of provisional restoration materials

OBJECTIVE

To investigate the effect of common beverages on four currently used provisional restoration materials: Protemp®4, Integrity®, polymethyl methacrylate (PMMA) block, and acrylic resin. Flowable resin composite is included as a control group.

MATERIALS AND METHODS

Each material was formed into disks of 10-mm diameter and 4-mm thickness (N = 40) by loading the material into acrylic molds. The exposed surface in the mold was covered using a glass slide to prevent an oxygen inhibition layer, and polymerization then proceeded. The solidified disks were placed in distilled water for 24 h. These samples (n = 8) were then immersed for 14 days in one of four different beverages: water, orange juice, cola, and coffee. Changes in color dimension, hardness, and roughness were observed and then analyzed using two-way repeated analysis of variance.

RESULTS

The provisional materials had more obvious changes in all three color dimensions than the flowable resin composite. Integrity showed the biggest changes, followed by acrylic resin and PMMA block, whereas Protemp had the smallest changes. The hardness of all the materials significantly decreased after immersion in any of the beverages for 14 days. There were no changes in surface roughness when the materials were immersed in distilled water. The surface roughness of the PMMA block significantly decreased in orange juice whereas that of Integrity and acrylic resin significantly increased in cola.

CONCLUSION

Different kinds of provisional materials had different degrees of staining due to their composition. Moisture had a significant influence on the hardness of materials, and the acidity of cola significantly roughened the surface of the provisional materials.

Evaluation of polymethyl-methacrylate and acetal denture base resins processed by two different techniques before and after nano-chlorohexidine surface treatment

BACKGROUND

Flexible denture base polymers have gained popularity in modern dentistry however, their biofilm formation tendency, adversely affecting the oral tissue heath, remains a concern. Consequently, this study aimed to evaluate surface roughness and biofilm formation tendency of two types of denture base resins manufactured with two techniques before and after surface coating with chlorohexidine (CHX) NPs.

MATERIALS AND METHODS

Acetal (AC) and Polymethyl-methacrylate (PMMA) resins manufactured by conventional and CAD/CAM methods were shaped into disk (10 X 10 X 1 mm). They were dipped for 8 h and 24 h in colloidal suspension prepared by mixing aqueous solution of CHX digluconate and hexa-metaphosphate (0.01 M). Surface roughness, optical density (OD) of microbial growth media and biofilm formation tendency were evaluated directly after coating. Elutes concentrations of released CHX were evaluated for 19 days using spectrophotometer. Three-way ANOVA and Tukey's post-hoc statistical analysis were used to assess the outcomes.

RESULTS

AC CAD/CAM groups showed statistically significant higher roughness before and after coating (54.703 ± 4.32 and 77.58 ± 6.07 nm, respectively). All groups showed significant reduction in OD and biofilm formation tendency after surface coating even after 19 days of CHX NPs release.

CONCLUSIONS

Biofilm formation tendency was highly relevant to surface roughness of tested resins before coating. After CHX NPs coating all tested groups showed significant impact on microbial growth and reduction in biofilm formation tendency with no relation to surface roughness. Significant antimicrobial effect remained even after 19 days of NPs release and specimens storage.

Recent Advances in 3D Printing of Polymers for Application in Prosthodontics

Contemporary mass media frequently depict 3D printing as a technology with widespread utilization in the creation of dental prosthetics. This paper endeavors to provide an evidence-based assessment of the current scope of 3D printing's integration within dental laboratories and practices. Its primary objective is to offer a systematic evaluation of the existing applications of 3D-printing technology within the realm of dental prosthetic restorations. Furthermore, this article delves into potential prospects, while also critically examining the sustained relevance of conventional dental laboratory services and manufacturing procedures. The central focus of this article is to expound upon the extent to which 3D printing is presently harnessed for crafting dental prosthetic appliances. By presenting verifiable data and factual insights, this article aspires to elucidate the actual implementation of 3D printing in prosthetic dentistry and its seamless integration into dental practices. The aim of this narrative review is twofold: firstly, to provide an informed and unbiased evaluation of the role that 3D printing currently plays within dental laboratories and practices; and secondly, to instigate contemplation on the transformative potential of this technology, both in terms of its contemporary impact and its future implications, while maintaining a balanced consideration of traditional dental approaches.

Evaluation of different decontamination procedures on bond strength to sound and caries affected dentin using "no-wait" universal adhesive

BACKGROUND

Current study aimed to evaluate the effect of different decontamination procedures on micro-shear bond strength (μSBS) of sound (SoD) and caries-affected dentin (CAD) of two universal adhesives after blood-saliva contamination.

METHODS

One hundred and eighty bovine anterior teeth were prepared and allocated into the respective groups according to tested dentin substrates [SoD, CAD], universal adhesives [Clearfil Bond Universal Quick (UBQ), All-Bond-Universal (ABU)], adhesive contamination stage [none, contamination before and after adhesives light-curing], and according to decontamination procedures [no decontamination, water rinsing, adhesive rebond, Ethylenediaminetetraacetic acid (ETDA) and chlorhexidine (CHX) application]. Universal adhesives were applied according to manufacturer instructions in self-etch (SE) bonding mode. Four composite microrods were built for each tooth. Specimens were kept in distilled water for 24 hours at 37°C before testing μSBS. Four-way ANOVA and Tukey HSD tests were used for data analysis.

RESULTS

A statistically significant difference between contamination stages of both universal adhesives at different decontamination procedures for SoD and CAD. Highest μSBS was recorded for UBQ control group at SoD, while the least was recorded for light-cured ABU upon water rinsing decontamination procedure of CAD.

CONCLUSIONS

Proper cavity isolation is mandatory to avoid possible contamination which can dramatically affect μSBS. CHX is a potent cavity decontaminant that can restore different dentin substrates bond strength. EDTA presents a promising substitute. UBQ adhesive showed better bonding performance than ABU to both dentin substrates. Application of regular cavity decontamination approaches is highly advised in daily practice to avoid possible detrimental effect of accidental cavity contamination.

Understanding the Mechanical, Surface, and Color Behavior of Oral Bioactive Prosthetic Polymers under Biodegradation Processes

Changes in the properties of resin-based polymers exposed to the oral environment can emerge when chlorhexidine (CHX) is incorporated to develop bioactive systems for treating denture stomatitis. Three reline resins loaded with CHX were prepared: 2.5 wt% in Kooliner (K), 5 wt% in Ufi Gel Hard (UFI), and Probase Cold (PC). A total of 60 specimens were submitted to physical aging (1000 cycles of thermal fluctuations, 5-55 °C) or chemical aging (28 days of pH fluctuations in artificial saliva, 6 h at pH = 3, 18 h at pH = 7). Knoop microhardness (30 s, 98 mN), 3-point flexural strength (5 mm/min), and surface energy were tested. Color changes (ΔE) were determined using the CIELab system. Data were submitted to non-parametric tests (α = 0.05). After aging, bioactive K and UFI specimens were not different from the controls (resins without CHX) in mechanical and surface properties. Thermally aged CHX-loaded PC specimens showed decreased microhardness and flexural strength but not under adequate levels for function. The color change was observed in all CHX-loaded specimens that underwent chemical aging. The long-term use of CHX bioactive systems based on reline resins generally does not impair removable dentures' proper mechanical and aesthetic functions.

Effect of microwave polymerization on the thermomechanical and surface properties of ocular prosthetic acrylic resins

BACKGROUND

Polymerization conditions affect the physical-mechanical properties of acrylic resins used for craniofacial prostheses.

OBJECTIVE

The aim of this study was to evaluate the effect of microwave polymerization on the thermomechanical properties and surface morphology of ocular prostheses fabricated with polymethyl methacrylate (PMMA).

METHODS

PMMA discs were polymerized with microwave energy and with conventional heat polymerization (CHP) method. Ocular prostheses were fabricated to determine whether there were changes according to the polymerization method. The surface morphology and roughness were observed under SEM and AFM. The Vickers Hardness number (VHN) and flexural strength were measured. Thermal properties were evaluated with TGA/DSC, and chemical composition with FTIR.

RESULTS

The PMMA acrylic resin polymerized with microwave energy showed a smooth surface with some relief areas. In the internal surface of the ocular prosthesis with microwave energy the PMMA is more compact. The mean roughness values were higher and statistically significant with CHP (P < 0.05), while the surface hardness and flexural strength were higher with microwave energy (P < 0.05).

CONCLUSION

There were no changes in the calorimetry with either method, TGA showed an exothermic peak around 120 °C with CHP method. PMMA polymerized with microwave energy improved the mechanical and surface properties of the ocular prostheses.

The effect of cooling procedures on monomer elution from heat-cured polymethyl methacrylate denture base materials

OBJECTIVE

To evaluate the amount of methyl methacrylate (MMA) released in water from heat-cured polymethyl methacrylate (PMMA) denture base materials subjected to different cooling procedures.

METHODOLOGY

Disk-shaped specimens (Ø:17 mm, h:2 mm) were fabricated from Paladon 65 (PA), ProBase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) denture materials using five different cooling procedures (n=3/procedure): A) Bench-cooling for 10 min and then under running water for 15 min; B) Cooling in water-bath until room temperature; C) Cooling under running water for 15 min; D) Bench-cooling, and E) Bench-cooling for 30 min and under running water for 15 min. A, B, D, E procedures were proposed by the manufacturers, while the C was selected as the fastest one. Control specimens (n=3/material) were fabricated using a long polymerization cycle and bench-cooling. After deflasking, the specimens were ground, polished and stored in individual containers with 10 ml of distilled water for seven days (37oC). The amount of water-eluted MMA was measured per container using isocratic ultra-fast liquid chromatography (UFLC). Data were analyzed using Student's and Welch's t-test (α=0.05).

RESULTS

MMA values below the lower quantification limit (LoQ=5.9 ppm) were registered in B, C, E (PA); E (PB) and B, D, E (QC) procedures, whereas values below the detection limit (LoD=1.96 ppm) were registered in A, D (PA); A, B, C, D (PB); C, D, E (VE) and in all specimens of the control group. A, B (VE) and A, C (QC) procedures yielded values ranging from 6.4 to 13.2 ppm with insignificant differences in material and procedure factors (p>0.05).

CONCLUSIONS

The cooling procedures may affect the monomer elution from denture base materials. The Ε procedure may be considered a universal cooling procedure compared to the ones proposed by the manufacturers, with the lowest residual monomer elution in water.

Autopolymerizing acrylic repair resin containing low concentration of dimethylaminohexadecyl methacrylate to combat saliva-derived bacteria

Biofilm accumulation on the polymethyl methacrylate (PMMA) restorations negatively affect the prognosis of the provisional restorations or the following treatment. This study developed a novel antibacterial PMMA resin containing low concentration of dimethylaminohexadecyl methacrylate (DMAHDM). Four resins were tested: (1) PMMA resin (Control), (2) 1.25% DMAHDM, (3) 2.5% DMAHDM, (4) 5% DMAHDM. Adding 1.25% DMAHDM into the PMMA resin did not influence the mechanical properties, degree of conversion, monomer releasing, and color stability of the specimens (p > 0.05). The incorporation of DMAHDM into PMMA resin could greatly prevent saliva-derived biofilms adhesion compared with the control group (p < 0.05). The metabolism level of saliva-derived biofilms on the 1.25%, 2.5%, and 5% DMAHDM resins were reduced by 20%, 54%, and 62%, respectively. And the mechanism of DMAHDM disturbing the integrity of bacterial cell walls was confirmed by flow cytometric analysis. Adding 1.25% and 2.5% DMAHDM did not compromise cytocompatibility of the modified resin (p > 0.05). Therefore, novel PMMA resin containing low concentration DMAHDM is promising as a future antimicrobial provisional restoration material for preventing microbial-induced complications in clinical settings. Graphical abstract.

Cytotoxicity of 3D‐printed, milled, and conventional oral splint resins to L929 cells and human gingival fibroblasts

Objectives

Evidence on the biocompatibility of three‐dimensional (3D)‐printed and milled resins for oral splints is limited. This in vitro study assessed the influence of the manufacturing method on the cytotoxicity of oral splint resins on L929 cells and human gingival fibroblasts (GF1).

Materials and Methods

Standardized specimens of four 3D‐printed, two‐milled, one‐thermoformed, and one‐pressed splint resin were incubated with L929 and GF1 cells for 24 h. Immunofluorescence and WST‐8 assay were performed to evaluate cytotoxic effects. One‐way analysis of variance and Tukey's multiple comparison test were applied with the variables “splint resin” and “manufacturing method” (p < .05).

Results

Immunofluorescence showed attachment of L929 and GF1 cells to the splint resins. Irrespective of the manufacturing method, the WST‐8 assay revealed significant differences between splint resins for the viability of L929 and GF1 cells. L929 cells generally showed lower viability rates than GF1 cells. The evaluation of cell viability by the manufacturing method showed no significant differences between 3D printing, milling, and conventional methods.

Conclusions

The cytotoxic effects of 3D‐printed, milled, and conventional oral splint resins were similar, indicating minor influence of the manufacturing method on biocompatibility. Cytotoxicity of the resins was below a critical threshold in GF1 cells. The chemical composition might be more crucial than the manufacturing method for the biocompatibility of splint resins.

Effect of post-curing light exposure time on the physico-mechanical properties and cytotoxicity of 3D-printed denture base material

OBJECTIVE

This study investigated the effect of post curing light exposure time on the physico-mechanical properties and cytotoxicity of a 3D-printed PMMA-based denture material in comparison to a conventional heat-cured alternative as a control.

METHODS

3D-printed specimens were fabricated followed by post-curing for 0, 5, 10 or 20 min at 200 W and light wavelength range of 390-540 nm. Heat-cured specimens were fabricated using a standard protocol. Specimens were placed in artificial saliva at 37 ℃ for 48 h (immediate groups) and 6 months (aged group), then evaluated flexural strength/modulus, fracture toughness, microhardness, and degree of conversion. Water sorption and solubility was assessed after 28 days. Flexural strength, flexural modulus, and fracture toughness were tested through three-point bending tests, while the surface hardness was tested using Vickers's test. Fractured specimens were viewed by scanning electron microscope (SEM). Cytotoxicity in term of cell viability was evaluated using human oral fibroblasts.

RESULTS

Flexural strength/modulus, fracture toughness and surface hardness significantly improved with the increase in light curing time up to 20 min. The same pattern of improvement was found with degree of conversion, water sorption, solubility, and cell viability. There was no significant difference (p < 0.01) between heat-cured material and 3D specimens post-cured for 20 min in term of flexural strength/modulus, surface hardness, and degree of conversion at the two-storage time points.

SIGNIFICANCE

Generally, the physico-mechanical properties of the 3D-printed denture base material improve as post curing time increases up to 20 min which exhibited comparable performance as the conventional heat-cured control.

Effect of processing methods on the cytotoxicity of methyl methacrylate-based ocular prostheses: An in vitro study

The study evaluated the influence of cycles and methods of an ocular prosthesis resin on cytotoxicity toward human conjunctival cells. Resins were polymerized by water bath (WB, 74 °C or 100 °C for 30 min to 9 h), microwave (MW, 1200 W, 3 to 14 min and 30 s at 0 to 720 W), or autopolymerization (AP, room temperature for 20 min ± 60 °C for 30 min). Degree of conversion (DC), cytotoxicity, level of inflammatory mediators, gene expression of different markers, and apoptosis were evaluated. Data were submitted to ANOVA and Tukey test (p < 0.05). WB with longer processing time at higher temperature had highest DC (85.6%) and higher TGF β1-gene expression (1.39); long cycle low power MW showed lowest DC (69.6%), lower cell proliferation (85.4%, MTT), and large IL-2 release (39,297 ng/mL). AP with additional processing time showed lower cell proliferation (75.3%, Alamar Blue), and AP polymerized at room temperature showed higher CASP 9-gene expression (1.21). AP methods showed higher IL-6 release (>277 pg/mL). Short cycle medium power MW had higher IL-23 release (534.2 pg/mL). MW (long and short cycles) and AP polymerizations have triggered a more intense inflammatory response. Among methods recommended by the manufacturer, WB showed high DC and less cytotoxicity.

Impact of polymerization and storage on the degree of conversion and mechanical properties of veneering resin composites

To investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (E_IT), and flexural strength (FS) of veneering resin composites (SR Nexco Paste (NP), Ceramage Incisal (CI), Gradia Plus (GP); n=60/group) cured with different polymerization devices (bre.Lux Power Unit, Labolight DUO, Otoflash G171, LC-3DPrint Box, PCU LED; n=12/subgroup) after storage. Otoflash G171 and Labolight DUO showed increased DC/HM/E_IT. CI presented the lowest DC and highest HM/E_IT. NP showed the highest DC and lowest HM/E_IT. Within Otoflash G171, Laboligth DUO and PCU LED, highest FS was observed for CI. Storage did not affect DC/HM/E_IT for specimens cured with Otoflash G171 or Labolight DUO. With storage not showing an influence on the tested parameters for polymerization devices that otherwise presented superior results, increased storage time cannot be recommended. For the tested resin composites, this study observed a high/low degree of conversion to coincide with respectively low/high amounts of fillers/mechanical properties.

Prosthodontic Applications of Polymethyl Methacrylate (PMMA): An Update

A wide range of polymers are commonly used for various applications in prosthodontics. Polymethyl methacrylate (PMMA) is commonly used for prosthetic dental applications, including the fabrication of artificial teeth, denture bases, dentures, obturators, orthodontic retainers, temporary or provisional crowns, and for the repair of dental prostheses. Additional dental applications of PMMA include occlusal splints, printed or milled casts, dies for treatment planning, and the embedding of tooth specimens for research purposes. The unique properties of PMMA, such as its low density, aesthetics, cost-effectiveness, ease of manipulation, and tailorable physical and mechanical properties, make it a suitable and popular biomaterial for these dental applications. To further improve the properties (thermal properties, water sorption, solubility, impact strength, flexural strength) of PMMA, several chemical modifications and mechanical reinforcement techniques using various types of fibers, nanoparticles, and nanotubes have been reported recently. The present article comprehensively reviews various aspects and properties of PMMA biomaterials, mainly for prosthodontic applications. In addition, recent updates and modifications to enhance the physical and mechanical properties of PMMA are also discussed.

Evaluation of a novel fixed-space maintainer made of light-cured acrylic resin: an in vitro study

To evaluate a fixed-space maintainer made of light-cure acrylic resin (LCAR) for its flexural and shear bond strength using different bonding systems to the enamel. 45 extracted primary teeth were selected. They were randomly divided into three equal groups (n = 15) along with the type of adhesive system (Tetric Flow, Transbond XT, and Fuji Ortho LC) used for bonding (LCAR) to the tooth surface. Surfaces were treated; LCAR was attached to the treated surfaces using a split Teflon mold. For flexural strength testing, ten bars of LCAR were made using another Teflon-split mold. Shear bond strength and mean flexural strength values were evaluated by a universal testing machine. The highest values of bond strength were recorded for Transbond XT, followed by Tetric Flow, while the lowest values were for Fuji Ortho LC. Various groups had a significant difference as investigated by ANOVA. ARI scores showed no significant difference in debond sites. Mean value and standard deviation of flexural strength for LCAR were 82.83  ± 5.2. LCAR has superior mechanical properties and could be an alternative to currently-in-use space maintainer though in vivo and in vitro trials are needed to progress the ultimate design of LCAR.

Thermal, structural and morphological characterization of dental polymers for clinical applications

PURPOSE

Polymers are used in dentistry on a daily basis due to their mechanical, functional and aesthetic properties. However, such biomaterials are subject to deterioration in the oral environment. Thus, this study aimed to evaluate the structural properties of five commonly used dental polymers to determine their best clinical indications.

METHODS

Four hundred-fifty samples of five dental polymers (polyethylenterephthalat - glycol modified (PG), polymethyl methacrylate (PA), ethylene vinyl acetate(E), polycarbonate (PC), polyetheretherketone (PK) were prepared to investigate their thermal, structural and chemical characteristics using energy dispersive spectroscopy (EDS), Fourier transform infrared analysis(FTIR), scanning electron microscopy (SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), X-ray diffraction(XRD), and Shore D hardness test. Data were analyzed using one-way ANOVA, Tukey's HSD, and Levene's tests (α=0.05).

RESULTS

PK (87.2) and PA (82.4) displayed the highest hardness values and smooth surfaces, as observed with SEM (p<0.001). Silica was detected in PK, PA, and E by EDS and XRD. The highest glass transition temperature was recorded for PC (145.00±2.00°C) and PK (143.00±1.87°C), while the lowest value was measured for E (50.00±2.12°C)(p<0.001).The highest mass loss was detected for PG (91.40±1.40%) by TGA.

CONCLUSIONS

PA and PK polymers can be used for stress-containing treatments due to their mechanical properties. These two materials are also advantageous in terms of plaque accumulation as these polymers reveal smoother surfaces than other groups. Insufficient physical and thermal properties require the use of E with caution and only in limited clinical indications.

Impact of fabrication procedures on residual monomer elution of conventional polymethyl methacrylate (PMMA)-a measurement approach by UV/Vis spectrophotometry

OBJECTIVES

To analyse the residual monomer (MMA) elution of polymethyl methacrylate (PMMA) in distilled water after diverse fabrication methods and aging procedures.

MATERIALS AND METHODS

PMMA specimens (N = 192, PalaXpress; Kulzer, Hanau, Germany) were manufactured (pouring, n = 96/injection, n = 96) and polymerized in water (55°C) without pressure (n = 48) and with 2 bar pressure (n = 48). Specimens were grinded (n = 24) or polished (n = 24) and aged for 12 h in distilled water/37°C (n = 12) or at air/20°C (n = 12) and stored afterwards in distilled water at 37°C. MMA elution was evaluated after 1, 2, 3, 4, 5, 6, 7, 10, 15 days (UV/Vis spectrophotometry). Data were analysed with Kolmogorov-Smirnov, Mann-Whitney-U and Cohen-d test using SPSS (α < 0.5).

RESULTS

The pouring procedure resulted in significantly higher MMA elution than the injection procedure up to 5 days. Polymerization with a pressure of 2 bar reduced the MMA elution significantly for poured specimens. Polishing reduced the MMA elution in comparison to grinding.

CONCLUSIONS

The fabrication procedure (pouring/injection) showed the strongest correlation to the MMA elution (r = 0.500), followed by polishing (r = 0.243), the pressure during polymerization (r = 0.109) and the storage medium (r = 0.053).

CLINICAL RELEVANCE

Higher MMA elution may increase the risk of chemical irritations, allergic reactions and hypersensitivities of the oral mucosa. Technicians and dentists should be aware about the elution differences dependent on the fabrication procedure.

Evaluation of the physical and antifungal effects of chlorhexidine diacetate incorporated into polymethyl methacrylate

This study aimed to evaluate the physical properties and antifungal activities of polymethyl methacrylate (PMMA) acrylic resins after the incorporation of chlorhexidine diacetate salt (CDA).

A silver nanoparticle-poly(methyl methacrylate) based colorimetric sensor for the detection of hydrogen peroxide

A colorimetric sensor based on nanoparticles was developed for the detection of hydrogen peroxide. Nanoparticles were made using small sheets of poly(methyl methacrylate) (PMMA) and silver nitrate. The optical properties of the solution were characterized by spectrophotometer using the localized surface plasmon resonance (LSPR) phenomenon. The shape and size of the nanoparticles were obtained using a transmission electron microscope (TEM). Silver-poly(methyl methacrylate) nanoparticles solution (AgNP-PMMA) proved to be particularly sensitive to hydrogen peroxide compared to other analytes. This sensor provided a quick, practical and easy tool to detect hydrogen peroxide.

Effect of Pressure, Post-Pressing Time, and Polymerization Cycle on the Degree of Conversion of Thermoactivated Acrylic Resin

Herein, the effect of different post-pressing times and pressure in two cycles of polymerization on the degree of conversion (DC) of thermally activated acrylic resin (TRRA) is analyzed to optimize the polymerization of this material. After post-pressing for 0, 6, or 12 h, polymerization was performed with or without a pressure of 60 psi (0.41 MPa) in a short (4 h) or a long (11 h) cycle, totaling 12 groups. To determine the DC, PMMA specimens were analyzed by Fourier transform infrared spectroscopy. The influence of each factor alone on the DC was studied by experimental planning. The statistical tests used were three-way ANOVA, t-test, Tukey's test, and Levene's test, with a margin of error of 5%. Two groups prepared with post-pressing times of 12 h had the lowest DC (p < 0.001). Post-pressing times of 0 and 6 h did not yield statistically different results. Pressure increased the DC in only one group (long cycle +12 h, p=0.001). The short cycle resulted in a higher DC than the long cycle in 2 groups (with pressure +0 h, p=0.002; without pressure +6 h, p=0.015), while the long cycle yielded a statistically higher DC in only one group (with pressure +12 h, p < 0.001). The polymerization showed satisfactory DC in all 12 groups. Small differences found among the specimens indicate that the pressure, post-pressing time, and polymerization cycles herein were not influential factors for the DC of PMMA.

Comparative evaluation of the amount of the residual monomer in conventional and deep-frozen heat cure polymethylmethacrylate acrylic resin: An in vitro study

Statement of Problem:

Heat cure acrylic resin material with reduced monomer content is generally recommended for clinical usage as it leads to improved mechanical, physical, and biocompatibility properties.

Aims and Objective:

The purpose of the present study was to evaluate and compare the amount of the residual monomer in the conventional and three different groups of deep-frozen heat cure polymethylmethacrylate (PMMA) acrylic resin.

Materials and Methods:

Totally 40 Specimens of heat cure PMMA acrylic resin (DPI India) (10 conventional heat cure and 30 deep frozen) were made using two disc-shaped stainless steel molds and invested into type II dental stone using compression molding technique. Each group contained 10 specimens (n = 10). Group 1: Control group of conventional polished PMMA specimen stored in water for 24 h at +37°C (10 specimens), Group 2: Deep frozen unpolished PMMA (10 specimens), Group 3: Deep frozen polished PMMA (10 specimens), and Group 4: Deep frozen polished PMMA specimen stored in water for 24 h at +37°C (10 specimens). Amount of the residual monomer content in all the specimens was measured using high-performance liquid chromatography. Data were analyzed using One-Way Analysis of Variance and multiple comparison Tukey's post hoc test (α = 0.05).

Results:

Least residual monomer content was found in Group 4 (0.12 wt%) followed by Group 3 (0.19 wt%), Group 2 (0.23 wt%), and Group 1 (0.26 wt%). Statistically significant difference (P < 0.05) was found in residual monomer content for all the four groups tested. Post hoc test for intergroup comparison also showed a significant difference between groups.

Conclusion:

The amount of the residual monomer was found to be least in deep-frozen polished PMMA specimen stored in water for 24 h at +37°C (Group 4). Thus, it can be concluded that deep freezing, polishing, and storing in water can reduce the residual monomer content.

Allergic effects of the residual monomer used in denture base acrylic resins

Denture base resins are extensively used in dentistry for a variety of purposes. These materials can be classified as chemical, heat, light, and microwave polymerization materials depending upon the factor which starts the polymerization reaction. Their applications include use during denture base construction, relining existing dentures, and for fabrication of orthodontic removable appliances. There have been increased concerns regarding the safe clinical application of these materials as their biodegradation in the oral environment leads to harmful effects. Along with local side effects, the materials have certain occupational hazards, and numerous studies can be found in the literature mentioning those. The purpose of this article is to outline the cytotoxic consequences of denture base acrylic resins and clinical recommendations for their use.

Investigation of flexural strength and cytotoxicity of acrylic resin copolymers by using different polymerization methods

PURPOSE

The aim of this study was to appraise the some mechanical properties of polymethyl methacrylate based denture base resin polymerized by copolymerization mechanism, and to investigate the cytotoxic effect of these copolymer resins.

MATERIALS AND METHODS

2-hydroxyethyl methacrylate (HEMA) and isobutyl methacrylate (IBMA) were added to monomers of conventional heat polymerized and injection-molded poly methyl methacrylate (PMMA) resin contents of 2%, 3%, and 5% by volume and polymerization was carried out. Three-point bending test was performed to detect flexural strength and the elasticity modulus of the resins. To determine the statistical differences between the study groups, the Kruskall-Wallis test was performed. Then pairwise comparisons were performed between significant groups by Mann-Whitney U test. Agar-overlay test was performed to determine cytotoxic effect of copolymer resins. Chemical analysis was determined by FTIR spectrum.

RESULTS

Synthesis of the copolymer was approved by FTIR spectroscopy. Within the conventional heat-polymerized group maximum transverse strength had been seen in the HEMA 2% concentration; however, when the concentration ratio increased, the strength decreased. In the injection-molded group, maximum transverse strength had been seen in the IBMA 2% concentration; also as the concentration ratio increased, the strength decreased. Only IBMA showed no cytotoxic effect at low concentrations when both two polymerization methods applied while HEMA showed cytotoxic effect in the injection-molded resins.

CONCLUSION

Within the limitations of this study, it may be concluded that IBMA and HEMA may be used in low concentration and at high temperature to obtain non-cytotoxic and durable copolymer structure.

The effect of repeated microwave irradiation on the dimensional stability of a specific acrylic denture resin

PURPOSE

To determine the dimensional stability of a poly(methyl methacrylate) (PMMA) acrylic resin when subjected to multiple sessions of repeated microwave irradiation at power settings of 700 and 420 W.

MATERIALS AND METHODS

Twenty standardized denture bases were fabricated using a PMMA resin. Points of measurement were marked on each denture base with a standardized template, and the distances between points were recorded using a digital microscope. The denture bases were randomly placed into two experimental groups of 10 bases each. Individual denture bases were placed into a glass beaker containing 200 ml of room temperature deionized water and then exposed to either 700 or 420 W of microwave radiation for 3 minutes. The denture bases were allowed to cool to room temperature, and measurements between points were recorded. This process was carried out for two microwave periods with measurements being completed after each period. The data were then analyzed for any significant changes in distances between points using a Student's t-test.

RESULTS

All denture bases experienced 1.0 to 2.0 mm or approximately 3% linear dimensional change after each period of microwaving. Results were significant with all t-tests having values of p < 0.05.

CONCLUSION

This report showed that the denture bases deformed significantly under experimental conditions at either 700 W for 3 minutes in 200 ml of water or 420 W for 3 minutes in 200 ml of water.

Effect of different solutions on color stability of acrylic resin-based dentures

The aim of this study was to evaluate the effect of thermocycling and immersion in mouthwash or beverage solutions on the color stability of four different acrylic resin-based dentures (Onda Cryl, OC; QC20, QC; Classico, CL; and Lucitone, LU). The factors evaluated were type of acrylic resin, immersion time, and solution (mouthwash or beverage). A total of 224 denture samples were fabricated. For each type of resin, eight samples were immersed in mouthwashes (Plax-Colgate, PC; Listerine, LI; and Oral-B, OB), beverages (coffee, CP; cola, C; and wine, W), and artificial saliva (AS; control). The color change (DE) was evaluated before (baseline) and after thermocycling (T1), and after immersion in solution for 1 h (T2), 3 h (T3), 24 h (T4), 48 h (T5), and 96 h (T6). The CIE Lab system was used to determine the color changes. The thermocycling test was performed for 5000 cycles. Data were submitted to three-way repeated-measures analysis of variance and Tukey's test (p<0.05). When the samples were immersed in each mouthwash, all assessed factors, associated or not, significantly influenced the color change values, except there was no association between the mouthwash and acrylic resin. Similarly, when the samples were immersed in each beverage, all studied factors influenced the color change values. In general, regardless of the solution, LU exhibited the greatest DE values in the period from T1 to T5; and QC presented the greatest DE values at T6. Thus, thermocycling and immersion in the various solutions influenced the color stability of acrylic resins and QC showed the greatest color alteration.

Effect of thermal cycling on denture base and autopolymerizing reline resins

Objective:

This study evaluated the fracture toughness (FT) of denture base and autopolymerizing reline resins, with and without thermocycling (T).

Material and Methods:

Specimens of each material (denture base acrylic resin - Lucitone 550 - L; autopolymerizing reline resins - Ufi Gel Hard-UH, Tokuyama Rebase II-TR, New Truliner- NT and Kooliner-K), were produced, notched and divided into two groups (n=10): CG (control group of autopolymerizing reline resins and L): FT tests were performed after polymerization; TG (thermocycled group): FT tests were performed after T (5ºC and 55ºC for 5,000 cycles).

Results:

Results (MPa.m^(1/2)) were analyzed by two-way ANOVA and Tukey's test (p=0.05). L exhibited the highest FT mean values in both groups (CG - 2.33; TG - 2.17). For the CG groups, NT showed the highest FT (1.64) among the autopolymerizing reline resins, and K the lowest (1.04). After T, when the autopolymerizing reline resins were compared, a statistically significant difference in FT was found only between the NT (1.46) and TR (1.00).

Conclusions:

Thermocycling increased the FT of K and did not influence the FT of L, UH, TR and NT.

Influence of acrylic resin polymerization methods on residual monomer release

AIM

The aim of this study was to quantify and compare the amount of methyl methacrylate (MMA) monomer released from three different denture base acrylic material processed by different polymerization methods and storage conditions.

MATERIALS AND METHODS

Microwave-cured, conventional heat and injection-technique acrylic polymerized materials were stored in neutral (pH = 7) and acidic (pH = 4.5) artificial saliva for 24 hours at the room temperature, separately. The residual MMA content was determined by high performance liquid chromatography (HPLC).

RESULTS

The MMA leaching from resins showed that microwave-cured material has lower residual MMA leach compared both conventional and injection-technique on neutral saliva storage conditions.

CONCLUSION

The all data's exhibited higher MMA release into an acidic saliva environment than neutral artificial saliva and there were no significant differences between the materials groups on acidic saliva storage conditions.

CLINICAL SIGNIFICANCE

Microwave polymerization method might has some advantages on reducing release of MMA concentration and may contributory effect upon polymerization reaction on neutral pH storage condition, therefore methods of polymerization should be considered as amount of monomer release.

Effect of autoclave postpolymerization treatments on the fracture toughness of autopolymerizing dental acrylic resins

INTRODUCTION

Microwave and water bath postpolymerization have been suggested as methods to improve the mechanical properties of heat and autopolymerizing acrylic resins. However, the effects of autoclave heating on the fracture properties of autopolymerizing acrylic resins have not been investigated.

PURPOSE

The aim of this study was to assess the effectiveness of various autoclave postpolymerization methods on the fracture properties of 3 different autopolymerizing acrylic resins.

METHODS

Forty-two specimens of 3 different autopolymerizing acrylic resins (Orthocryl, Paladent RR and Futurajet) were fabricated (40x8x4mm), and each group was further divided into 6 subgroups (n=7). Control group specimens remained as processed (Group 1). The first test group was postpolymerized in a cassette autoclave at 135°C for 6 minutes and the other groups were postpolymerized in a conventional autoclave at 130°C using different time settings (5, 10, 20 or 30 minutes). Fracture toughness was then measured with a three-point bending test. Data were analyzed by ANOVA followed by the Duncan test (α=0.05).

RESULTS

The fracture toughness of Orthocryl and Paladent-RR acrylic resins significantly increased following conventional autoclave postpolymerization at 130°C for 10 minutes (P<.05). However, the fracture toughness of autoclave postpolymerized Futurajet was not significantly different than its control specimens (P<.05). The fracture toughness of Futurajet was significantly less than Paladent RR and Orthocryl specimens when autoclaved at 130°C for 10 minutes.

CONCLUSIONS

Within the limitations of this study, it can be suggested that autoclave postpolymerization is an effective method for increasing the fracture toughness of tested autoploymerized acrylic resins.

Effect of monomer content in the monomer-polymer ratio on complete denture teeth displacement

The purpose of the study was to verify the linear displacement of teeth in maxillary complete dentures influenced by different monomer-polymer ratios - according to the manufacturer's instructions, with 25% excess or 25% less monomer content - in the conventional and microwaved polymerization techniques. Wax base plates and wax planes were made on edentulous maxillary stone casts according to traditional method. The set was assembled in semi-adjustable articulator with a lower toothed stone cast as guide to mounting of the maxillary artificial teeth. Impressions were taken from this tooth arrangement with silicone and the mold was used to standardize the mounting of the teeth of all dentures. Referential points were made on the artificial teeth for linear measurements with optical microscope before processing of the dentures and after deflasking. Denture bases were conventionally packed with acrylic resin according to the monomer-polymer ratio protocol. Tooth displacement data were submitted to ANOVA and Tukey test (α=0.05). There were no statistically significant differences (p>0.05) between the group with monomer content recommended by the manufacturer and groups with 25% more and 25% less monomer, in both conventional and microwaved polymerizations. Excess or less monomer in the monomer-polymer ratio and polymerization types did not change the linear distance between teeth.

Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

OBJECTIVES

Residual methyl methacrylate (MMA) may leach from the acrylic resin denture bases and have adverse effects on the oral mucosa. This in vitro study evaluated and correlated the effect of the leaching residual MMA concentrations ([MMA]r) on in vitro cytotoxicity of L-929 fibroblasts.

MATERIAL AND METHODS

A total of 144 heat-polymerized acrylic resin specimens were fabricated using 4 different polymerization cycles: (1) at 74ºC for 9 h, (2) at 74ºC for 9 h and terminal boiling (at 100ºC) for 30 min, (3) at 74ºC for 9 h and terminal boiling for 3 h, (4) at 74ºC for 30 min and terminal boiling for 30 min. Specimens were eluted in a complete cell culture medium at 37ºC for 1, 2, 5 and 7 days. [MMA]r in eluates was measured using high-performance liquid chromatography. In vitro cytotoxicity of eluates on L-929 fibroblasts was evaluated by means of cell proliferation using a tetrazolium salt XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) assay. Differences in [MMA]r of eluates and cell proliferation values between polymerization cycles were statistically analyzed by Kruskal-Wallis, Friedman and Dunn's multiple comparison tests. The correlation between [MMA]r of eluates and cell proliferation was analyzed by Pearson's correlation test (p<0.05).

RESULTS

[MMA]r was significantly (p<0.001) higher in eluates of specimens polymerized with cycle without terminal boiling after elution of 1 and 2 days. Cell proliferation values for all cycles were significantly (p<0.01) lower in eluates of 1 day than those of 2 days. The correlation between [MMA]r and cell proliferation values was negative after all elution periods, showing significance (p<0.05) for elution of 1 and 2 days. MMA continued to leach from acrylic resin throughout 7 days and leaching concentrations markedly reduced after elution of 1 and 2 days.

CONCLUSION

Due to reduction of leaching residual MMA concentrations, use of terminal boiling in the polymerization process for at least 30 min and water storage of the heat-polymerized denture bases for at least 1 to 2 days before denture delivery is clinically recommended for minimizing the residual MMA and possible cytotoxic effects.

Shear Bond Strength of Provisional Restoration Materials Repaired with Light-cured Resins

Specific repair resins should be chosen for certain provisional materials, since optimal bond strength can be achieved only when the repair resin has similar chemical components to those of the resin matrix (either methacrylate or bis-acryl) for the provisional restoration.