Release of methyl methacrylate from heat-cured and autopolymerized resins: cytotoxicity testing related to residual monomer

The Influence of Contemporary Denture Base Fabrication Methods on Residual Monomer Content, Flexural Strength and Microhardness

(1) Background: Digital technologies are available for denture base fabrication, but there is a lack of scientific data on the mechanical and chemical properties of the materials produced in this way. Therefore, the aim of this study was to investigate the residual monomer content, flexural strength and microhardness of denture base materials as well as correlations between investigated parameters. (2) Methods: Seven denture base materials were used: one conventional heat cured polymethyl methacrylate, one polyamide, three subtractive manufactured materials and two additive manufactured materials. High-performance liquid chromatography was used to determine residual monomer content and the test was carried out in accordance with the specification ISO No. 20795-1:2013. Flexural strength was also determined according to the specification ISO No. 20795-1:2013. The Vickers method was used to investigate microhardness. A one-way ANOVA with a Bonferroni post-hoc test was used for the statistical analysis. The Pearson correlation test was used for the correlation analysis. (3) Results: There was a statistically significant difference between the values of residual monomer content of the different denture base materials (p < 0.05). Anaxdent pink blank showed the highest value of 3.2% mass fraction, while Polident pink CAD-CAM showed the lowest value of 0.05% mass fraction. The difference between the flexural strength values of the different denture base materials was statistically significant (p < 0.05), with values ranging from 62.57 megapascals (MPa) to 103.33 MPa. The difference between the microhardness values for the different denture base materials was statistically significant (p < 0.05), and the values obtained ranged from 10.61 to 22.86 Vickers hardness number (VHN). A correlation was found between some results for the material properties investigated (p < 0.05). (4) Conclusions: The selection of contemporary digital denture base manufacturing techniques may affect residual monomer content, flexural strength and microhardness but is not the only criterion for achieving favourable properties.

Water temperature for fabrication of autopolymerizing polymethyl methacrylate (PMMA) interim fixed restoration affects cytotoxicity and residual methyl methacrylate (MMA)

Background/purpose

Clinically, dentists are suggested to immerse autopolymerizing interim fixed restorations in hot water during fabrication. However, this suggestion, without including the best temperature, mostly comes from clinical experience instead of scientific evidence. This in vitro study evaluated the effect of water temperature on the cytotoxicity of interim partial fixed dental prostheses (FDPs) and examined its correlation with residual MMA.

Materials and methods

Tempron was chosen as the autopolymerizing polymethyl methacrylate material. Tempron was mixed and then soaked in water at different temperatures, except control group (Controlair) was not being soaking in water. The specimens were incubated with conditioned medium. The concentration of residual MMA was determined by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The cell viability of human gingival fibroblasts (HGFs) was evaluated by MTT assay.

Results

The 60 °C and 80 °C groups exhibited significantly higher cell viabilities than those of the other groups (P < 0.05) at 48 and 72 h. The concentration of residual MMA was highly correlated with this outcome: the higher the concentration of residual MMA detected in the eluates, the poorer the cell viability was; the longer the incubation time was, the stronger the correlation was between the concentration of residual MMA and the cell viability.

Conclusion

Autopolymerizing PMMA interim FDPs that are polymerized in water up to at least 60 °C could reduce cell toxicity. Higher water temperature could certainly decrease the amount of residual MMA, which is closely correlated with the outcome of cell viability.

Cytotoxicity of dental self-curing resin for a temporary crown: an in vitro study

BACKGROUND

Residual monomer tests using high-performance liquid chromatography and cytotoxicity tests were performed to analyze the effect on the oral mucosa of a self-curing resin for provisional crown production.

METHODS

A cytotoxicity test was performed to confirm whether leaked residual monomers directly affected oral mucosal cells. The cytotoxicity of the liquid and solid resin polymers was measured using a water-soluble tetrazolium (WST) test and microplate reader.

RESULTS

In the WST assay using a microplate reader, 73.4% of the cells survived at a concentration of 0.2% liquid resin polymer. The cytotoxicity of the liquid resin polymer was low at ≤0.2%. For the solid resins, when 100% of the eluate was used from each specimen, the average cell viability was 91.3% for the solid resin polymer and 100% for the hand-mixed self-curing resin, which is higher than the cell viability standard of 70%. The cytotoxicity of the solid resin polymer was low.

CONCLUSION

Because the polymerization process of the self-curing resin may have harmful effects on the oral mucosa during the second and third stages, the solid resin should be manufactured indirectly using a dental model.

Polymeric Denture Base Materials: A Review

An ideal denture base must have good physical and mechanical properties, biocompatibility, and esthetic properties. Various polymeric materials have been used to construct denture bases. Polymethyl methacrylate (PMMA) is the most used biomaterial for dentures fabrication due to its favorable properties, which include ease of processing and pigmenting, sufficient mechanical properties, economy, and low toxicity. This article aimed to comprehensively review the current knowledge about denture base materials (DBMs) types, properties, modifications, applications, and construction methods. We searched for articles about denture base materials in PubMed, Scopus, and Embase. Journals covering topics including dental materials, prosthodontics, and restorative dentistry were also combed through. Denture base material variations, types, qualities, applications, and fabrication research published in English were considered. Although PMMA has several benefits and gained popularity as a denture base material, it has certain limitations and cannot be classified as an ideal biomaterial for fabricating dental prostheses. Accordingly, several studies have been performed to enhance the physical and mechanical properties of PMMA by chemical modifications and mechanical reinforcement using fibers, nanofillers, and hybrid materials. This review aimed to update the current knowledge about DBMs' types, properties, applications, and recent developments. There is a need for specific research to improve their biological properties due to patient and dental staff adverse reactions to possibly harmful substances produced during their manufacturing and use.

Material extrusion of thermoplastic acrylic for intraoral devices: Technical feasibility and evaluation

With global demand for 3D printed medical devices on the rise, the search for safer, inexpensive, and sustainable methods is timely. Herein, we assessed the practicality of the material extrusion process for acrylic denture bases of which successful outcomes can be extended to implant surgical guides, orthodontic splints, impression trays, record bases and obturators for cleft palates or other maxillary defects. Representative materials comprising denture prototypes and test samples were designed and built with in-house polymethylmethacrylate filaments using varying print directions (PDs), layer heights (LHs) and reinforcements (RFs) with short glass fiber. The study undertook a comprehensive evaluation of the materials to determine their flexural, fracture, and thermal properties. Additional analyses for tensile and compressive properties, chemical composition, residual monomer, and surface roughness (Ra) were completed for parts with optimum parameters. Micrographic analysis of the acrylic composites revealed adequate fiber-matrix compatibility and predictably, their mechanical properties improved simultaneously with RFs and decreased LHs. Fiber reinforcement also improved the overall thermal conductivity of the materials. Ra, on the other hand, improved visibly with decreased RFs and LHs and the prototypes were effortlessly polished and characterized with veneering composites to mimic gingival tissues. In terms of chemical stability, the residual methyl methacrylate monomer contents are well below standards threshold for biological reactions. Notably, 5 vol% acrylic composites built with 0.05 mm LH in 0° on z-axis produced optimum properties that are superior to those of conventional acrylic, milled acrylic and 3D printed photopolymers. Finite element modeling successfully replicated the tensile properties of the prototypes. It may well be argued that the material extrusion process is cost-effective; however, the speed of manufacturing could be longer than that of established methods. Although the mean Ra is within an acceptable range, mandatory manual finishing and aesthetic pigmentation are required for long-term intraoral use. At a proof-of-concept level, it is evident that the material extrusion process can be applied to build inexpensive, safe, and robust thermoplastic acrylic devices. The broad outcomes of this novel study are equally worthy of academic reflection, and further translation to the clinic.

Obturator Manufacturing for Oronasal Fistula after Cleft Palate Repair: A Review from Handicraft to the Application of Digital Techniques

An oronasal fistula (ONF) is an abnormal structure between the oral and nasal cavities, which is a common complication of cleft palate repair due to the failure of wound healing. When some patients with ONF are unsuitable for secondary surgical repair, the obturator treatment becomes a potential method. The objectives of the obturator treatment should be summarized as filling the ONF comfortably and cosmetically restoring the dentition with partial function. The anatomy of patients with cleft palate is complex, which may lead to a more complex structure of the ONF. Thus, the manufacturing process of the obturator for these patients is more difficult. For performing the design and fabrication process rapidly and precisely, digital techniques can help, but limitations still exist. In this review, literature searches were conducted through Medline via PubMed, Wiley Online Library, Science Direct, and Web of Science, and 122 articles were selected. The purpose of this review was to introduce the development of the obturator for treating patients with ONF after cleft palate repair, from the initial achievement of the obstruction of the ONF to later problems such as fixation, velopharyngeal insufficiency, and infection, as well as the application of digital technologies in obturator manufacturing.

Automated Parallel Dialysis for Purification of Polymers

The implementation of a dialysis method for the simultaneous purification of different polymer materials in a commercially available automated parallel synthesizer (APS) is discussed. The efficiency of this "unattended" automated parallel dialysis (APD) method was investigated by means of proton nuclear magnetic resonance (¹H-NMR) measurements, which confirmed that the method enables the removal of up to 99% of the unreacted monomer derived from the synthesis of the corresponding polymers in the APS. Size-exclusion chromatography (SEC) revealed that the molar mass and molar mass distribution of the investigated polymers did not undergo significant changes after the application of the APD method. The method discussed herein can be regarded as a good alternative to the "unattended" and reliable purification of polymer libraries prepared in APS. This method may be useful for overcoming current limitations of high-throughput/-output (HT/O) synthesis of polymer libraries, where purification of the generated materials currently represents a significant constraint for establishing fully automated experimental workflows necessary to advance towards a full digitalization of research and development of new polymers for diverse applications.

Influence of postwashing process on the elution of residual monomers, degree of conversion, and mechanical properties of a 3D printed crown and bridge materials

OBJECTIVES

This study aimed to determine the effects of the postwashing method and time on the mechanical properties and biocompatibility of three-dimensional (3D) printed crown and bridge resin.

METHODS

DLP (digital light processing)-printed specimens produced from Nextdent crown & bridge (C&B) resins were washed separately using an ultrasonic bath and rotary washer with TPM (tripropylene glycol monomethyl ether) for 3 min, 6 min, 10 min, 20 min, and 1 h. Postcuring was applied for 30 min to each specimen after the washing process. The flexural strength, Vickers hardness, water sorption and solubility, degree of conversion (DC), elution of residual monomers, and biocompatibility of the specimens were evaluated.

RESULTS

The ultrasonic bath showed greater washing efficacy by reducing the residual HEMA (2-hydroxyethyl methacrylate) from 2.0634 ppm to 0.1456 ppm and reducing the residual TEGDMA (triethylene glycol dimethacrylate) from 1.4862 ppm to 0.1484 ppm. With prolonged washing, the flexural strength significantly decreased from 129.67 ± 6.66 MPa (mean±standard deviation) to 103.17 ± 7.20 MPa, while the Vickers hardness increased slightly for the first 6 min and then decreased thereafter significantly. The DC was 87.78 ± 1.34% after 3 min and then gradually decreased with extended washing time. The cytotoxicity significantly decreases with the increment of the washing time.

SIGNIFICANCE

The washing effect on the elution of residual monomers was better for an ultrasonic bath than for a rotary washer. Extending the washing time reduces the mechanical properties and cytotoxicity of the Nextdent C&B resin.

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.

Plasticizers and Salt Concentrations Effects on Polymer Gel Electrolytes Based on Poly (Methyl Methacrylate) for Electrochemical Applications

This work describes the electrochemical properties of a type of PMMA-based gel polymer electrolytes (GPEs). The gel polymer electrolyte systems at a concentration of (20:80) % w/w were prepared from poly (methyl methacrylate), lithium perchlorate LiClO₄ and single plasticizer propylene carbonate (PMMA-Li-PC) and a mixture of plasticizers made by propylene carbonate and ethylene carbonate in molar ratio 1:1, (PMMA-Li-PC-EC). Different salt concentrations (0.1 M, 0.5 M, 1 M, 2 M) were studied. The effect of different plasticizers (single and mixed) on the properties of gel polymer electrolytes were considered. The variation of conductivity versus salt concentration, thermal properties using DSC and TGA, anodic stability and FTIR spectroscopy were used in this study. The maximum ionic conductivity of σ = 0.031 S/cm were obtained for PMMA-Li-PC-EC with a salt concentration equal to 1 M. Ion-pairing phenomena and all ion associations were observed between lithium cations, plasticizers and host polymers through FTIR spectroscopy. The anodic stability of the PMMA-based gel polymer electrolytes was recorded up to 4 V. The glass temperatures of these electrolytes were estimated. We found they were dependent on the plasticization effect of plasticizers on the polymer chains and the increase of the salt concentration. Unexpectedly, it was determined that an unreacted PMMA monomer was present in the system, which appears to enhance ion conduction. The presence and possibly the addition of a monomer may be a technique for increasing ion conduction in other gel systems that warrants further study.

Effect of Candida albicans Suspension on the Mechanical Properties of Denture Base Acrylic Resin

Yeast-like fungi such as Candida albicans (C. albicans) are the primary pathogenic microorganism in the oral cavity of denture wearers. The research available so far, conducted according to a protocol based on the exposure of specimens to a C. albicans suspension and their cutting with water cooling, shows that hard polymethyl methacrylate (PMMA) prosthetic materials are not only surface colonized, but also penetrated by microorganisms in a short time. This justifies the hypothesis that exposure to a suspension of the C. albicans strain causes the changes in mechanical properties due to surface colonization and/or penetration of the samples. In the current study, the chosen mechanical properties (flexural strength, flexural modulus, tensile strength, impact strength, ball indentation hardness, and surface Vickers hardness at 300 g load) of the PMMA denture base material Vertex RS (Vertex-Dental, The Netherlands) exposed for 30, 60, and 90 days to a suspension of C. albicans were investigated. The potential penetration of yeast was examined on the fractured surfaces (interior of specimens) to eliminate the risk of the contamination of samples during cutting. There was no influence on the flexural strength, flexural modulus, tensile strength, impact strength, or ball indentation hardness, but a significant decrease in surface hardness was registered. Microscopic observations did not confirm the penetration of C. albicans. On the surface, blastospores and pseudohyphae were observed in crystallized structures and in traces after grinding, which indicates that in clinical conditions, it is not penetration but the deterioration of surface quality, which may lead to the formation of microareas that are difficult to disinfect, causing rapid recolonization.

Probing the role of methyl methacrylate release from spacer materials in induced membrane bone healing

In the induced membrane (IM) technique for bone reconstruction, a poly(methyl methacrylate) (PMMA) spacer is implanted to induce formation of a foreign body membrane around the defect site. Membrane development is essential for later bone grafting success, yet the mechanism by which the IM promotes bone regeneration remains unknown, as are the ways that spacer composition plays a role in the membrane's healing potential. This study investigated the impact of leached methyl methacrylate (MMA)-the major monomeric component of PMMA-on IM development. In vitro cell culture found that MMA elution did not impact endothelial cell or mesenchymal stem cell proliferation. For in vivo analysis, we advanced a streamlined rat femoral model to efficiently study the influence of spacer properties on IM characteristics. Comparison of membrane formation around polycaprolactone (PCL), MMA-eluting PCL (high-dose PCL-MMA and low-dose PCL-MMA), and surgical PMMA revealed robust membranes enveloped all groups after 4 weeks in vivo, with elevated expression of osteogenic bone morphogenetic protein-2 and angiogenic vascular endothelial growth factor compared with the surrounding muscle and bone tissues. Growth factor quantitation in IM tissue found no statistically significant difference between groups. New bone growth, vascularization, and CD163+ macrophage populations surrounding the polymer implants were also quantified; and blood vessel formation around high-dose PCL-MMA was found to be significantly decreased compared with PCL alone. To the best of our knowledge, these findings represent the first time that results have been obtained about the characteristics of membranes formed around PCL in the IM setting.

Elution behavior of a 3D-printed, milled and conventional resin-based occlusal splint material

OBJECTIVE

The elution of unpolymerized (co-)monomers and additives from methacrylic resin-based materials like polymethyl methacrylate (PMMA) can cause adverse side effects, such as mutagenicity, teratogenicity, genotoxicity, cytotoxicity and estrogenic activity. The aim of this study was to quantify the release and the cytotoxicity of residual (co-)monomers and additives from PMMA-based splint materials under consideration of real splint sizes. Three different materials used for additive (3D printing), subtractive (milling) and conventional (powder and liquid) manufacturing were examined.

METHODS

The splint materials SHERAprint-ortho plus (additive), SHERAeco-disc PM20 (subtractive) and SHERAORTHOMER (conventional) were analysed. 16 (n = 4) sample discs of each material (6 mm diameter and 2 mm height) were polished on the circular and one cross-section area and then eluted in both distilled water and methanol. The discs were incubated at 37 °C for 24 h or 72 h and subsequently analysed by gas chromatography/mass spectrometry (GC/MS) for specifying and quantifying released compounds. XTT-based cell viability assays with human gingival fibroblasts (HGFs) were performed for Tetrahydrofurfuryl methacrylate (THFMA), 1,4-Butylene glycol dimethacrylate (BDDMA) and Tripropylenglycol diacrylate (TPGDA). In order to project the disc size to actual splint sizes in a worst-case scenario, lower and upper jaw occlusal splints were designed and volumes and surfaces were measured.

RESULTS

For SHERAeco-disc PM20 and for SHERAORTHOMER no elution was determined in water. SHERAprint-ortho plus eluted the highest THFMA concentration of 7.47 μmol/l ±2,77 μmol/l after 72 h in water. Six (co-)monomers and five additives were detected in the methanol eluates of all three materials tested. The XTT-based cell viability assays resulted in a EC₅₀ of 3006 ± 408 μmol/l for THFMA, 2569.5 ± 308 μmol/l for BDDMA and 596.7 ± 88 μmol/l for TPGDA.

SIGNIFICANCE

With the solvent methanol, released components from the investigated splint materials exceeded cytotoxic concentrations in HGFs calculated for a worst-case scenario in splint size. In the water eluates only the methacrylate THFMA could be determined from SHERAprint-ortho plus in concentrations below cytotoxic levels in HGFs.

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.

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.

Cytotoxicity of long-term denture base materials

Introduction:

The aim of this study was to evaluate the cytotoxic effect of various denture base materials following four different aging periods.

Methods:

In total, 48 disc-shaped specimens per each group were prepared: Group I: acrylic resin polymerized in cool water and heated up to 100°C over 45 min and boiled for 15 min; Group II: acrylic resin polymerized under pressure in 40°C–45°C water bath for 10 min; Group III: autopolymerized hard relining resin Cold Liner Rebase; Group IV: autopolymerized hard relining resin Truliner; Group V: soft relining resin DentuSil. Then the specimens were stored in water for 24 h or 15 days, or thermocycled 2500 times or 10,000 times. Cytotoxicity was evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using L929 cells after 72-h cell incubation. Cell viability percentages were counted and statistical analyses were performed. The results were also evaluated according to ISO standard 10993-5.

Results:

All materials showed similar cell viability percentages following 24-h water storage and 2500 and 10,000 thermal cycles. Following 15-day water storage, a statistically significant difference was observed between the materials. Comparisons of the aging periods for each material showed statistically significant differences. Groups III and IV showed moderately cytotoxic effect following 15-day water storage. The remaining groups showed slightly cytotoxic or non-cytotoxic effect.

Discussion:

Polymerizing acrylic resins under pressure can be an alternative to conventional polymerizing to ensure a faster denture repair while providing similar cell viability values. Heat-cured acrylic resins provide higher cell viability than hard chairside lining materials in a 15-day period.

Percutaneous Endoscopic Retrieval of Intraspinal Cement Leakage: Technical Note

OBJECTIVE

We sought to preliminarily explore the efficacy and safety of percutaneous endoscopic spinal surgery for epidural cement leakage. We report a case series of patients who underwent percutaneous retrieval of leaked epidural cement and achieved spinal decompression under endoscopy.

METHODS

Five patients with neurologic impairment due to epidural cement leakage after percutaneous vertebroplasty were treated with percutaneous endoscopic spinal decompression. Computed tomography reconstruction and 3-dimensional imaging were used to evaluate the extruded material. During follow-up at 3, 6, and 12 months postoperatively, all patients were advised to undergo plain radiograph and computed tomography examinations.

RESULTS

The leaked epidural cement was successfully removed in all patients under percutaneous endoscopy through a unilateral or bilateral approach. At the 12-month follow-up, the visual analog scale score of all patients improved. In addition, the neurologic function of each patient improved to at least 1 grade level, as evaluated using the American Spinal Injury Association. According to the modified MacNab criteria, 2 patients had excellent recovery, whereas the other 3 patients had good recovery.

CONCLUSIONS

We described a novel and minimally invasive procedure to ameliorate intractable epidural cement extrusion. As an alternative to conventional laminectomy, percutaneous endoscopic retrieval achieved the targeted decompression without damaging the posterior lamina. Moreover, the whole operation was performed under regional anesthesia accompanied with dexmedetomidine sedation, allowed real-time neural function evaluation, and had lower risks of anesthesia-related complications, compared with general anesthesia.

Bacterial Colonization and Tissue Compatibility of Denture Base Resins

Currently, there is minimal clinical data regarding biofilm composition on the surface of denture bases and the clinical tissue compatibility. Therefore, the aim of this experimental study was to compare the bacterial colonization and the tissue compatibility of a hypoallergenic polyamide with a frequently used PMMA resin tested intraorally in a randomized split-mouth design. Test specimens made of polyamide (n = 10) and PMMA (n = 10) were attached over a molar band appliance in oral cavity of 10 subjects. A cytological smear test was done from palatal mucosa at baseline and after four weeks. The monolayers were inspected for micronuclei. After four weeks in situ, the appliance was removed. The test specimens were immediately cultivated on non-selective and selective nutrient media. All growing colonies were identified using VITEK-MS. The anonymized results were analyzed descriptively. A total of 110 different bacterial species could be isolated, including putative pathogens. An average of 17.8 different bacterial species grew on the PMMA specimens, and 17.3 on the polyamide specimens. The highest number of different bacterial species was n = 24, found on a PMMA specimen. On the two specimens, a similar bacterial distribution was observed. Micronuclei, as a marker for genotoxic potential of dental materials, were not detected. This study indicates that the composition of bacterial biofilm developed on these resins after four weeks is not influenced by the type of resin itself. The two materials showed no cytological differences. This investigation suggests that polyamide and PMMA are suitable for clinical use as denture base material.

Evaluation of the maladaptation of the test base in acrylic resin regarding the technique of preparation, place of measurement and storage time

Abstract Introduction The most used material for the preparation of the baseplates is the acrylic resin, but it can present distortions. Objective To evaluate preparation technique, region and storage time that presents less maladaptation of the base when made with self-cured acrylic resin. Material and method Models were created in gypsum type III simulating edentulous maxilla, as divided into 3 groups (n = 10): GC (control group) thermopolymerizable acrylic resin; G1 - manual adaptation technique and G2 - drip technique. For the measurements, silicone by condensation of light consistency that was interposed between base and model was used. With a hydraulic press, 50 kg pressure was applied leading the base of the model. The obtained mold was measured in the palate, canine and molar regions with a digital caliper at the following times: immediately after the base polymerization, at 24, 48, 72, 96 hours and one week. The results were submitted to statistical analysis. Result G1 presented maladaptation of 0.43 mm ± 0.10, while G2 obtained 0.39 mm ± 0.11. The lowest maladaptation occurred in the CG. The palate region presented greater maladaptation (0.52 ± 0.07) and the canine region, the lowest (CD = 0.27 mm ± 0.07 and CE = 0.27 ± 0.09); There was no statistically significant difference for storage times. Conclusion G2 presented lower values than G1, with no statistically significant difference. The palate region presented greater maladaptation, followed by molars and canines. The bases continued to maladaptation the model after the immediate polymerization, with no statistically significant difference.

Biocompatibility, bone healing, and safety evaluation in rabbits with an IlluminOss bone stabilization system

Bone healing, biocompatibility, and safety employing the IlluminOss System (IS), comprised of an inflatable balloon filled with photopolymerizable liquid monomer, was evaluated in New Zealand white rabbits. Successful bone healing and callus remodeling over 6 months was demonstrated radiologically and histologically with IS implants in fenestrated femoral cortices. Biocompatibility was demonstrated with IS implants in brushed, flushed femoral intramedullary spaces, eliciting no adverse, local, or systemic responses and with similar biocompatibility to K-wires in contralateral femurs up to 1 year post-implant. Lastly simulated clinical failures demonstrated the safety of IS implants up to 1 year in the presence of liquid or polymerized polymer within the intramedullary space. Polymerized material displayed cortical bone and vasculature effects comparable to mechanical disruption of the endosteum. In the clinically unlikely scenario with no remediation or polymerization, a high dose monomer injection resulted in marked necrosis of cortical bone, as well as associated vasculature, endosteum, and bone marrow. Overall, when polymerized and hardened within bone intramedullary spaces, this light curable monomer system may provide a safe and effective method for fracture stabilization. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2181-2190, 2017.

Synthesis and characterization of divinyl-fumarate poly-ε-caprolactone for scaffolds with controlled architectures

A vinyl-terminated polycaprolactone has been developed for tissue engineering applications using a one-step synthesis and functionalization method based on ring opening polymerization (ROP) of ε-Caprolactone, with hydroxyl ethyl vinyl ether (HEVE) acting both as the initiator of ROP and as photo-curable functional group. The proposed method employs a catalyst based on aluminium, instead of the most popular Tin(II) 2-ethylhexanoate, to reduce the cytotoxicity. Following the synthesis of the vinyl-terminated polycaprolactone, its reaction with fumaryl chloride (FuCl) results in a divinyl-fumarate polycaprolactone (VPCLF). The polymers obtained were thoroughly characterized using Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) techniques. The polymer has been successfully employed, in combination with N-vinyl pyrrolidone (NVP), to fabricate films and computer-designed porous scaffolds by micro-stereolithography (μ-SL) with gyroid and diamond architectures. Characterization of the networks indicated the influence of NVP content on the network properties. Human mesenchymal stem cells adhered and spread onto VPCLF/NVP networks showing good biological properties and no cytotoxic effect. Copyright © 2016 John Wiley & Sons, Ltd.

Cytotoxicity of Eluates from a Gamma-Ray-Polymerized Poly(Methyl Methacrylate)

The purpose of this study was to evaluate the cytotoxicity of gamma-ray-polymerized poly(methyl methacrylate) (PMMA). A total of 32 disk-shaped PMMA specimens were polymerized by gamma-irradiation with 1 Mrad for 4 h (Group 1), 2 Mrad for 8 h (Group 2), 3 Mrad for 12 h (Group 3), and thermally polymerized (Group 4). Four- and 6-day eluates of the specimens were prepared in Eagle’s Minimal Essential Medium (EMEM) without Fetal Calf Serum (FCS). The eluates and EMEM supplemented by 20% FCS were placed into Vero (green African monkey kidney) cell cultures, and incubated at 37 C for 24, 48, and 72 h. EMEM kept at 37 C for 4 and 6 days was also tested up to 72 h, and served as controls. After each incubation period, the number of viable cells were counted and stained at the termination of the experiments for histological evaluation. The number of viable cells for Group 1 was slightly lower than that of other groups after 24 h. The time-dependent increase in cells exposed to Group 3 eluates was comparable with the control group. There was a dose-dependent effect on cell response for gamma-ray-polymerized specimens. The number of viable cells and the morphological appearance of cells in all groups were similar. Eluates from PMMA polymerized by low doses of gammaray with reduced polymerization periods have early inhibitory effects on cell response. Higher doses of gamma-irradiation lead to better cellular response, and therefore, may be future candidates for polymerization of PMMA.

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.

Comparative effect of different polymerization techniques on residual monomer and hardness properties of PMMA-based denture resins

PURPOSE

The aim of this study was to compare the residual monomer and microhardness of poly(methyl methacrylate) (PMMA)-based denture resins processed by using autoclave and conventional water bath techniques.

METHODS

To determine the amount of residual methyl methacrylate (MMA) monomer, disk-shaped specimens (n=5) were prepared from 3 different acrylic resins (Meliodent, Paladent and Qc-20). Control groups were polymerized in water bath for 30 minutes at 100°C. The study groups were prepared in an autoclave device for 60°C/30 min followed 130°C/10 min and the other group for 60°C/30 min followed by 130°C/20 min. According to standard calibration curves, ultraviolet spectrophotometry at 230 nm was used to determine the residual monomer. For the Vickers hardness measurements, disk-shaped specimens (n=5) were prepared for each test group. Hardness measurements were performed with a Vickers hardness tester under a 4.91-N press load for a 30 seconds, after immersion in distilled water at 37ºC for 48 hours. The data were analyzed by ANOVA and Tukey HSD test (p<0.05).

RESULTS

Autoclave polymerization produced a significant decrease in the amount of residual monomers for all resin groups (p<0.05). This procedure also showed a significant increase in hardness for all resin groups (p<0.05). For the 3 resin groups, no significant differences were found between autoclave polymerization for 10 minutes and for 20 minutes (p>0.05).

CONCLUSIONS

The autoclave polymerization technique exhibited significantly lower residual monomer content and greater hardness than conventional heat polymerization.

High performance liquid chromatographic determination of residual monomer released from heat-cured acrylic resin. An in vivo study

PURPOSE

Heat-polymerized acrylic resins are used in dentistry for complete denture fabrication. Despite the polymerization method, conversion of monomer into polymer is often incomplete with free or unreacted residual monomer remaining in the polymerized resin. The aim of this study was to determine the amount of residual monomeric methyl methacrylate (MMA) leaching in the saliva of patients wearing complete dentures in their postinsertion period.

MATERIALS AND METHODS

Thirty edentulous participants as first-time complete denture wearers (age 60 to 65 years) were selected. All the prostheses were fabricated using a similar standard technique with a heat-cured acrylic resin denture base material. Saliva samples were collected at time intervals of 1 hour, 1 day, and 3 days postdenture insertion. Participants were asked to discharge saliva every 30 seconds into a pre-weighed screw-capped container for a 5-minute period. MMA levels were measured using high performance liquid chromatography. Data were analyzed by ANOVA and Tukey-HSD.

RESULTS

The maximum concentration of monomer released into saliva peaked 1 day after insertion of the complete dentures. The mean (SD) MMA content was 0.04 ± 0.01 (μg/ml) 1 hour after insertion, and 0.3 ± 0.09 (μg/ml), and 0.05 ± 0.01 (μg/ml) on the first and third days postinsertion, respectively.

CONCLUSIONS

Although the released monomeric MMA was not at toxic levels, it could potentially sensitize complete denture patients or elicit an allergic reaction. The risk of the residual material as a primary irritant for a sensitizing reaction could be minimized by immersion of the denture in water for 24 hours before insertion.

In vitro cytotoxicity of self-curing acrylic resins of different colors

Objective

The aim of this study was to assess the in vitro cytotoxicity of acrylic resins of different colors over time.

Methods

Specimens were divided into 4 groups (n = 6) according to the color of the acrylic resin (Orto Class, Clássico, Campinas, São Paulo, Brazil): Group 1: clear acrylic resin; group 2: pink acrylic resin; group 3: blue acrylic resin and group 4: green acrylic resin. All specimens were fabricated according to the mass manipulation technique and submitted to mechanical polishing protocol. The control was performed with an amalgam specimen (C+), a glass specimen (C-) and cell control (CC). Specimens were immersed in Minimum Eagle's Medium (MEM) and incubated for 24 h at 37ºC. The extracts from the experimental material were filtered and mixed with L929 fibroblast. Cytotoxicity was evaluated at 4 different times, 24, 48, 72 and 168 h. After contact, cells were incubated for 24 h and added to 100 µ of 0.01% neutral red dye. The cells were incubated for 3 h for pigment incorporation and fixed. Cells viability was determined by a spectroscopic (BioTek, Winooski, Vermont, USA) with a 492-nm wavelength λ=492 nm).

Results

There were no statistical differences between the experimental groups and the CC and C- groups.

Conclusion

Clear, pink, blue and green self-curing acrylic resins fabricated by means of the mass manipulation technique and mechanically polished are not cytotoxic. Neither the pigment added to the self-curing acrylic resin nor the factor of time influenced the cytotoxicity of the material.

Histopathological changes by the use of soft reline materials: a rat model study

Aim

To assess the histopathological changes of rat palatal mucosa exposed to soft reline materials.

Methods

Forty-five adult female Wistar rats with controlled living conditions and fed ad libitum were employed. Palatal appliances of heat-polymerized acrylic resin Lucitone 550 were manufactured and worn by forty animals during 14 days. Five animals did not use the appliances (G1) and were used to control the appliance influence. One experimental group (n = 10) used the appliances without any relining material (G2) to control the material effect. Three experimental groups (n = 10) received the following soft reline materials below appliances: Dentusoft (G3), Dentuflex (G4), and Trusoft (G5). Appliances from half of each experimental group(n = 5) was immersed in water bath at 55°C for 10 min before use. Animals were slaughtered and the palates were fixed in 10% buffered formalin. Hematoxylin and eosin stained sections of 5 µm were analyzed by computerized planimetry. Cellular compartment, keratin and total epithelial thickness, and basement membrane length were measured to histopathological description.Analysis of variance and Tukey post-hoc test were used to data examination(α = 0.05).

Results

For heat-treatment groups, G4 showed less elongated ridges at the basal layer interface (p = 0.037) than G2. When comparing the conditions with and without heat-treatment, only G2 showed a significant decrease in the cellular compartment, keratin layer and total epithelium thickness (p<0.05).

Conclusion

The post-polymerization for Lucitone 550 was an effective method to reduce the changes in the rat palatal mucosa. The soft reline materials tested did not cause significant histopathological changes in the rat palatal mucosa.

Effect of different adhesives combined with two resin composite cements on shear bond strength to polymeric CAD/CAM materials

This study tested the impact of different adhesives and resin composite cements on shear bond strength (SBS) to polymethyl methacrylate (PMMA)- and composite-based CAD/CAM materials. SBS specimens were fabricated and divided into five main groups (n=30/group) subject to conditioning: 1. Monobond Plus/Heliobond (MH), 2. Visio.link (VL), 3. Ambarino P60 (AM), 4. exp. VP connect (VP), and 5. no conditioning-control group (CG). All cemented specimens using a. Clearfil SA Cement and b. Variolink II were stored in distilled water for 24 h at 37 °C. Additionally, one half of the specimens were thermocycled for 5,000 cycles (5 °C/55 °C, dwell time 20 s). SBS was measured; data were analyzed using descriptive statistics, four- and one-way ANOVA, unpaired two-sample t-test and Chi(2)-test. CAD/CAM materials without additional adhesives showed no bond to resin composite cements. Highest SBS showed VL with Variolink II on composite-based material, before and after thermocycling.

The effect of mechanical and chemical polishing techniques on the surface roughness of heat-polymerized and visible light-polymerized acrylic denture base resins

OBJECTIVE

The purpose of this study was to compare the effects of mechanical polishing (MP) and chemical polishing (CP) on the average surface roughness (Ra) of heat-cured (HC) and light-cured (LC) denture base acrylic resins.

METHODS

A total of 120 specimens (30 × 15 × 3 mm) were prepared from one HC and one LC acrylic resin. To remove nodules and gross surface irregularities, all specimens were finished with a lathe-mounted small acrylic bur and 360-grit sandpaper. Ten finished specimens of each acrylic resin were randomly assigned to each of six polishing techniques: Resilit High-luster Polishing Liquid (RHPL), Universal Polishing Paste, Abraso-star K50, pumice, Jet Seal Liquid, or Acrypoint. MP was performed with an automatic polishing machine for 2 min, under 50 rpm and 500 g of load. CP was performed by immersing the HC and LC specimens in preheated methyl methacrylate at 75 ± 1 °C for 10 s. The surface roughness of the acrylic resin specimens was measured with a contact profilometer. The Ra values were analyzed by two-way analysis of variance, post hoc Scheffe's test, and paired t-test (p ⩽ 0.05). Polished and tested acrylic resin surfaces were evaluated by scanning electron microscopy.

RESULTS

MP was more effective than CP. The smoothest surface was obtained with the use of the RHPL on the LC (0.05 ± 0.01 μm) or HC (0.07 ± 0.01 μm) acrylic resin. Two-way ANOVA showed a statistically significant difference between MP and CP.

CONCLUSIONS

MP produced the smoothest surface of denture base acrylic resin. The mean surface roughness values after MP and CP were not influenced by the type of acrylic resin.

In vitro evaluation of long-term cytotoxic response of injection-molded polyamide and polymethyle metacrylate denture base materials on primary fibroblast cell culture

OBJECTIVE

This study investigated the long-term cytotoxic response of thermoplastic polyamide and conventional polymethyle metacrylate (PMMA) denture base materials.

MATERIALS AND METHODS

Twenty discs were prepared for each polyamide, heat and cold cured PMMA denture base resins (totally 60) and divided into four sub-groups (n = 5). Cytotoxicity was assessed with the direct cell contact method using cell viability and neutral red (NR) uptake assay. Each sub-group was tested at initial and after being aged for 24 h, 1 week and 8 weeks with artificial saliva according to ISO 10993 standards.

RESULTS

There were no significantly difference among the materials and control groups after initial, 24 h and 1 week testing. In 24 h testing, only Deflex was more toxic according to the Control group (p < 0.05). After 8 weeks of aging with artificial saliva, all materials were significantly cytotoxic when compared to the control group. QC20 was more toxic than Deflex and SC Cold Cure (p < 0.05). There were significant differences between the 8 week aging group and the initial, 24 h and 1 week testing for all materials (p < 0.05).

CONCLUSIONS

Cytotoxicity of all tested denture base materials increased significantly after the long-term aging. Therefore, long-term aging may be useful to determine a dental material's toxicity. Polyamide denture base material had a similar toxicity profile with conventional heat- and cold-cured PMMA.

Effect of biofilm formation, and biocorrosion on denture base fractures

PURPOSE

The aim of this study was to investigate the destructive effects of biofilm formation and/or biocorrosive activity of 6 different oral microorganisms.

MATERIALS AND METHODS

Three different heat polymerized acrylic resins (Ivocap Plus, Lucitone 550, QC 20) were used to prepare three different types of samples. Type "A" samples with "V" type notch was used to measure the fracture strength, "B" type to evaluate the surfaces with scanning electron microscopy and "C" type for quantitative biofilm assay. Development and calculation of biofilm covered surfaces on denture base materials were accomplished by SEM and quantitative biofilm assay. According to normality assumptions ANOVA or Kruskal-Wallis was selected for statistical analysis (α=0.05).

RESULTS

Significant differences were obtained among the adhesion potential of 6 different microorganisms and there were significant differences among their adhesion onto 3 different denture base materials. Compared to the control groups after contamination with the microorganisms, the three point bending test values of denture base materials decreased significantly (P<.05); microorganisms diffused at least 52% of the denture base surface. The highest median quantitative biofilm value within all the denture base materials was obtained with P. aeruginosa on Lucitone 550. The type of denture base material did not alter the diffusion potential of the microorganisms significantly (P>.05).

CONCLUSION

All the tested microorganisms had destructive effect over the structure and composition of the denture base materials.

Dendrimer/methyl methacrylate co-polymers: residual methyl methacrylate and degree of conversion

Dendrimer/methyl methacrylate co-polymers were studied for use in dental composites. The aim was to determine the effects of methyl methacrylate concentration in the resin mixture and polymerization method on the degree of conversion and residual monomer content of the copolymers. Two dendrimers were studied, D12 with 12 reactive methacrylate groups and D24 with 24 reactive groups. The concentration of methyl methacrylate varied from 20 wt% to 50 wt% of monomers. Camphorquinone (CQ) was used as the light-activation initiator and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) as the activator, both in the quantity of 3.0 wt%. Three polymerization methods were used: photo-polymerization, photo-polymerized immediately followed by post-polymerization at 120 degrees C for 15 min, and photo-polymerization followed by postpolymerization after 7 days. The degree of conversion was determined using FT-IR. Residual monomers were extracted with tetrahydrofuran and methanol and analyzed with HPLC. The highest degrees of conversion were 65 and 62%, and the lowest residual monomer contents 1.0 and 1.5% for D12 and D24, respectively. These were measured after heat-induced post-polymerization. For D12, increasing the proportion of methyl methacrylate decreased the degree of conversion and increased the residual monomer content after photo-polymerization. Post-polymerization enhanced the polymerization of the dendrimer co-polymers in respect of degree of conversion and residual monomer content. The present study suggested that the tested dendrimer/methyl methacrylate copolymers require heat-induced polymerization to reach the generally accepted levels of degree of conversion and residual monomers.

Real-time cell analysis of the cytotoxicity of the components of orthodontic acrylic materials on gingival fibroblasts

INTRODUCTION

The aim of this study was to evaluate the cytotoxicity of 3 orthodontic acrylic materials and 2 manipulation methods.

METHODS

The orthodontic acrylic materials Orthocryl EQ (Dentaurum, Ispringen, Germany), Orthoplast (Vertex Dental, Zeist, The Netherlands), and O-80 (Imicryl, Konya, Turkey) were prepared with 2 polymerization methods (doughing and spray on). Totally, 60 cylinders (5 × 2 mm), fabricated by using a different acrylic and method, were divided into 6 groups. Gingival fibroblasts were isolated from gingival connective tissue of systemically healthy subjects. Materials were incubated in Dulbecco's modified eagle's medium culture medium (Biological Industries, Beit Haemek, Israel) for 72 hours according to ISO 10993-5 standards (surface area to volume ratio of the specimen to cell-culture medium: 3 cm(2)/mL). Gingival fibroblasts were maintained with Dulbecco's modified eagle medium containing 10% fetal bovine serum. A real-time cell analyzer (RT-CES, xCELLigence; Roche Applied Science, Mannheim, Germany, and ACEA Biosciences, San Diego, Calif) was used to evaluate cell survival. After seeding 200 μL of the cell suspensions into the wells (20,000 cells/well) of the E-plate 96, gingival fibroblasts were treated with bioactive components released by the acrylic materials (1/1 and 1/2 dilutions) and monitored every 15 minutes for 121 hours. For the proliferation experiments, the statistical analyses used were 1-way analysis of variance (ANOVA) and Tukey-Kramer multiple comparisons tests.

RESULTS

There was no significant difference between the cell indexes of the control and study groups for the 1/1 and 1/2 dilutions at 21 and 32 hours. When evaluated at 68 hours, all 1/2 dilutions of acrylic materials showed statistically insignificant differences (P >0.05) except for Orthoplast (P <0.05). But all acrylic materials were different from the control group in the 1/1 dilutions (P <0.001). At 121 hours, all test groups were significantly different from the untreated control group (P <0.001).

CONCLUSIONS

The results indicate that the long cycle increased the cytotoxicity of the tested materials, and there was no significant difference between the spray-on and doughing methods on cytotoxicity.

Synthesis and biological evaluation of PMMA/MMT nanocomposite as denture base material

Inorganic-polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Poly (methylmethacrylate) (PMMA)/montmorillonite (MMT) nanocomposites were prepared by in situ suspension polymerization with dodecylamine used as MMT-modifier. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the structures of the nanocomposites. Cytotoxicity test, hemolysis test, acute systemic toxicity test, oral mucous membrane irritation test, guinea-pig maximization test and mouse bone-marrow micronucleus test were used to evaluate the biocompatibility of PMMA/MMT nanocomposites. The results indicated that an exfoliated nanocomposite was achieved, and the resulting nanocomposites exhibited excellent biocompatibility as denture base material and had potential application in dental materials.