The dynamic viscoelasticity and plasticizer leachability of tissue conditioners

Effect of Food-Simulating Liquids on the Leachability of Plasticizers from Dental Tissue Conditioners

OBJECTIVE

 Tissue conditioners are composed of poly(ethyl methacrylate) (PEMA) powder and plasticizer/ethanol mix liquid. Butyl phthalyl butyl glycolate (BPBG) plasticizer is commonly used in tissue conditioners, but the main concern with phthalate plasticizer is its leachability and biocompatibility, especially the estrogenic activity and cytotoxicity of phthalate. Therefore, acetyl tributyl citrate (ATBC) plasticizer has been introduced and formulated as plasticizer in tissue conditioner; however its leachability characteristics are still unknown. Furthermore, the effect of foodsimulating liquids toward leachability of BPBG and ATBC plasticizers has not been documented. The objective of this study was to compare the effect of food-simulating liquids on the leachability of plasticizers and hardness of two experimental tissue conditioners containing BPBG and ATBC plasticizers.

MATERIALS AND METHODS

 Ten experimental materials were prepared using PEMA polymer powder with 95% plasticizer (BPBG and ATBC) and 5% ethanol by volume, using powder to liquid ratio of 1.67:1, and the thickness was controlled at 3 mm. Shore A hardness value was measured after immersion in distilled water, artificial saliva, 25% ethanol/water mix, 3% citric acid, and coconut oil at 37°C. Measurements were taken at 2 hours and 1, 2, 3, 4, 7, 10, 14, 21, 28, 42, 56, and 84 days. Six readings were taken for each sample and hardness change was calculated and statistically analyzed using Wilcoxon signed-rank test.

RESULTS

 Increase in hardness value was noted for both plasticizers over time with the highest increase was when immersed in coconut oil. Shore A hardness value was significantly higher in ATBC after 84 days of immersion in all food-simulating liquids. The increase in hardness is due to plasticizer/ethanol leaching; however, as ethanol content was the same (5%), the hardness change is attributed to the leaching of plasticizers.

CONCLUSION

 Leaching of both plasticizers was highest in coconut oil indicating that tissue conditioners may have a shorter intraoral lifetime in patients eating high-fat diet.

Synthesis, characterization, and evaluation of the antifungal properties of tissue conditioner incorporated with essential oils-loaded chitosan nanoparticles

Purpose

This study aims to investigate new tissue conditioner (TC) formulations involving chitosan nanoparticles (CSNPs) and essential oils (EO) for their antifungal potential, release kinetics, and hardness.

Materials and methods

CSNPs were synthesized, and the separate solutions of CSNP were prepared with two types of EO, i.e., Oregano oil and Lemongrass. The EO was loaded separately in two concentrations (200 μL and 250 μL). The blank and EO-loaded CSNPs were screened against Candida albicans (C. albicans), and their minimum inhibitory concentration was established. GC Reline^™ (GC corporation, USA) TC was considered a control group, whereby the four experimental groups were prepared by mixing CSNPs/EO solutions with TC powder. The antifungal effectiveness (C. albicans) and release kinetics behavior (1–6 h, 24 h, 48 h, and 72 h) was investigated. The Shore A hardness of control and experimental groups was evaluated in dry and wet modes (deionized water and artificial saliva). For statistical analysis, SPSS version 22 was used to do a one-way ANOVA post-hoc Tukey’s test.

Results

Compared to the control group, TCs containing blank CSNPs and CSNPs loaded with EO showed 3 and 5 log reductions in C. albicans growth, respectively. A significantly high antifungal effect was observed with TC containing lemongrass essential oil (200 μL). The continuous release of EO was detected for the first 6 hours, whereas completely stopped after 48 hours. Mean hardness values were highest for dry samples and lowest for samples stored in artificial saliva. The statistically significant difference within and between the study groups was observed in mean and cumulative essential oils release and hardness values of TCs over observed time intervals irrespective of storage media.

Conclusion

TCs containing essential-oil-loaded CSNPs seem a promising alternative treatment of denture-induced stomatitis, however, a further biological analysis should be taken.

Characterization and Physical and Biological Properties of Tissue Conditioner Incorporated with Carum copticum L

Aim

One of the main problems in dentistry is the injury caused by the long-term application of an ill-fitting denture. The existence of multiple microorganisms along with the susceptibility of the tissue conditioners to colonize them can lead to denture stomatitis. This study is aimed at developing a tissue conditioner incorporated with Carum copticum L. (C. copticum L.) for the effective treatment of these injuries.

Materials and Methods

The Carum copticum L. essential oil composition was determined by gas chromatography-mass (GC-mass) spectrometry. The antimicrobial activity of the essential oil against the standard strains of bacterial and fungal species was determined by broth microdilution methods as suggested by the Clinical and Laboratory Standards Institute (CLSI). The physical and chemical properties of the prepared tissue conditioner were investigated by viscoelasticity, FTIR assays, and the release study performed. Furthermore, the antibiofilm activity of the Carum copticum L. essential oil-loaded tissue conditioner was evaluated by using the XTT reduction assay and scanning electron microscopy (SEM).

Results

The main component of the essential oil is thymol, which possesses high antimicrobial activity. The broth microdilution assay showed that the essential oil has broad activity as the minimum inhibitory concentration was in the range of 32-128 μg mL^-1. The viscoelasticity test showed that the essential oil significantly diminished the viscoelastic modulus on the first day. The FTIR test showed that Carum copticum L. essential oil was preserved as an independent component in the tissue conditioner. The release study showed that the essential oil was released in 3 days following a sustained release and with an ultimate cumulative release of 81%. Finally, the Carum copticum L. essential oil exhibited significant activity in the inhibition of microbial biofilm formation in a dose-dependent manner. Indeed, the lowest and highest amounts of biofilm formation on the tissue conditioner disks are exhibited in the Streptococcus salivarius and Candida albicans by up to 22.4% and 71.4% at the 64 μg mL^-1 concentration of C. copticum L. with a statistically significant difference (P < 0.05).

Conclusion

The obtained results showed that the Carum copticum L. essential oil-loaded tissue conditioner possessed suitable physical, biological, and release properties for use as a novel treatment for denture stomatitis.

The Dynamic Viscoelasticity of Dental Soft Polymer Material Containing Citrate Ester-Based Plasticizers

The aim of this study was to investigate the dynamic viscoelasticity of dental soft polymer material containing citrate ester-based plasticizers. Three kinds of citrate ester-based plasticizer (Citroflex^® C-2: TEC, Citroflex^® A-2: ATEC, and Citroflex^® A-4: ATBC), with the combination of 5 wt% ethyl alcohol, were used as the liquid phase. The dynamic viscoelastic properties of nine ethyl methacrylate polymers: (A, B, C, D, E, F, G, H, and I) were immersed in 37 °C distilled water for 0, 1, 3, 7, 14 and 30 days, respectively. The dynamic viscoelastic properties were measured at 37 °C with an automatic dynamic mechanical analyzer. The shear storage modulus (G′), shear loss modulus (G″), and loss tangent (tan δ) were determined at 1 Hz. These parameters were statistically analyzed by two-way and one-way ANOVA and Tukey’s multiple comparison test at a predetermined significance level of 0.05. A significant difference was found among the materials in terms of the dynamic viscoelasticity. The materials containing citrate ester-based plasticizer ATBC showed the most stable dynamic viscoelasticity. Considering the limitations of this study, the results suggest that the inclusion of citrate ester-based plasticizer can improve the durability of dental soft polymer materials.

Evaluation of viscoelastic properties, hardness, and glass transition temperature of soft denture liners and tissue conditioner

Soft denture liners and tissue conditioners are widely used for the denture patients to cushion masticatory force and condition abused tissues, respectively. This study assessed methods for the evaluation of the viscoelasticity and glass transition temperature (T_g) of the silicone permanent soft liner, acrylic permanent soft liner, and tissue conditioner. Three rheological parameters of storage modulus (E'), loss modulus (E''), and loss tangent ([Formula: see text]), T_g, and hardness were determined using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and the Shore A0 hardness test. Five specimens were measured for each material. The time-temperature superposition principle was applied to produce master curves of E', E'', and [Formula: see text] for the tested materials at a reference temperature of 37 °C. The acrylic permanent soft liner and tissue conditioner exhibited viscoelastic behavior and sensitivity to frequency, especially at lower frequencies. The silicone permanent soft liner showed elastic behavior and was frequency-independent. T_g for the acrylic permanent soft liner was higher than that for the tissue conditioner, which in turn was higher than that for the silicone permanent soft liner for both DMA and DSC. In DMA, a higher frequency led to higher T_g values. A positive linear relationship was found between Shore A0 hardness and E' values, but not E'' and [Formula: see text] values. Shore hardness reflects elasticity, but not viscosity. The results of the present study can be used to improve methods for evaluating the viscoelasticity and T_g of soft denture liners and tissue conditioners.

Determining acceptable limits for water sorption and solubility of interim denture resilient liners

STATEMENT OF PROBLEM

Specifications for determining acceptable limits of water sorption (WS) and solubility for interim denture resilient liners are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the WS and solubility of interim resilient materials throughout their lifespans.

MATERIAL AND METHODS

Specimens (n=10) of 7 tissue conditioners, Coe-Comfort (CC), Softone (ST), Rite-Line (RL), Dura Conditioner (DC), Hydrocast (HC), Dentusoft (DS), and Visco-gel (VG) and 2 interim resilient liners, Trusoft (TS) and Coe-Soft (CS), were submitted to desorption until weight stabilization. Next, they were immersed in distilled water at 37°C for 3, 5, 7, or 14 days and then weighed, dried, and reweighed. Data (%) were analyzed using 2-way ANOVA and the Tukey honestly significant difference (HSD) test (α=.05).

RESULTS

VG demonstrated the highest WS (12.06 ±0.93%-16.62 ±0.87%) and solubility (20.30 ±4.26%-23.59 ±2.24%; P<.05) percentages. Low WS values were presented by CC (2.23 ±0.53%-2.99 ±0.49%; P<.05). The WS showed no significant changes for CC, CS, and TS over 14 days (P>.05). SL presented intermediate solubility values (4.09 ±1.60%-8.80 ±1.15%), and the other materials showed values lower than 3.35 ±0.70%. CC, DC, DS, HC, RL, TS, and CS showed no changes in solubility throughout the 14-day trial.

CONCLUSIONS

Over the lifespan of a tissue conditioner (7 days), CC, RL, DC, HC, DS, CS, and TS presented suitable in vitro performance. Among the tested materials, CC, CS, and TS were considered best suited for denture relining for up to 14 days.

The effect of crude drugs on the angiogenic property and dynamic viscoelasticity of PEMA-based soft polymer materials

This study aimed to determine the effect of crude drugs on the dynamic viscoelasticity and angiogenic property of soft polymer materials, in vitro. Two kinds of polyethyl methacrylates, and crude drugs (Astragalus membranaceus Bunge [HQ] and Salvia miltiorrhiza Bunge [DS]) were used in their powdered forms. And, acetyl tributyl citrate and ethyl alcohol were used in the liquid form. The dynamic viscoelasticity of each specimen was measured after 0, 1, 3, 7, 14 and 28 days of immersion in distilled water. The CellPlayer angiogenesis PrimeKit assay was used to test angiogenesis. Significant differences in dynamic viscoelasticity were observed among the materials. Specimens containing 1 wt% HQ showed higher angiogenic activity than those containing 5 wt% and 10 wt% HQ, and DS. Our results suggest that the addition of low amounts of crude drugs to soft polymer materials may promote angiogenesis in human tissues.

Theoretical Considerations and a Mathematical Model for the Analysis of the Biomechanical Response of Human Keratinized Oral Mucosa

Removable complete and partial dentures are supported by the residual alveolar ridges consisting of mucosa, submucosa, periosteum, and bone. An understanding of the biomechanical behavior of the oral mucosa is essential in order to improve the denture-bearing foundations for complete and partially edentulous patients. The purpose of this paper was to examine the biomechanical behavior of the soft tissues supporting a removable denture and develop a model for that reason. Keratinized oral mucosa blocks with their underlying bone were harvested from the maxillary palatal area adjacent to the edentulous ridges of a cadaver. The compressive response of the oral mucosa was tested by using atomic force microscopy. The specimens were first scanned in order their topography to be obtained. The mechanical properties of the specimens were tested using a single crystal silicon pyramidal tip, which traversed toward the keratinized oral mucosa specimens. Loading-unloading cycles were registered and four mathematical models were tested using MATLAB to note which one approximates the force-displacement curve as close as possible: a. spherical, b. conical, c. third order polynomial, d. Murphy (fourth order polynomial, non-linear Hertzian based). The third order polynomial model showed the best accuracy in representing the force-displacement data of the tested specimens. A model was developed in order to analyze the biomechanical behavior of the human oral keratinized mucosa and obtain information about its mechanical properties.

Dual-Purpose Bioreactors to Monitor Noninvasive Physical and Biochemical Markers of Kidney and Liver Scaffold Recellularization

Analysis of perfusion-based bioreactors for organ engineering and a detailed evaluation of physical and biochemical parameters that measure dynamic changes within maturing cell-laden scaffolds are critical components of ex vivo tissue development that remain understudied topics in the tissue and organ engineering literature. Intricately designed bioreactors that house developing tissue are critical to properly recapitulate the in vivo environment, deliver nutrients within perfused media, and monitor physiological parameters of tissue development. Herein, we provide an in-depth description and analysis of two dual-purpose perfusion bioreactors that improve upon current bioreactor designs and enable comparative analyses of ex vivo scaffold recellularization strategies and cell growth performance during long-term maintenance culture of engineered kidney or liver tissues. Both bioreactors are effective at maximizing cell seeding of small-animal organ scaffolds and maintaining cell survival in extended culture. We further demonstrate noninvasive monitoring capabilities for tracking dynamic changes within scaffolds as the native cellular component is removed during decellularization and model human cells are introduced into the scaffold during recellularization and proliferate in maintenance culture. We found that hydrodynamic pressure drop (ΔP) across the retained scaffold vasculature is a noninvasive measurement of scaffold integrity. We further show that ΔP, and thus resistance to fluid flow through the scaffold, decreases with cell loss during decellularization and correspondingly increases to near normal values for whole organs following recellularization of the kidney or liver scaffolds. Perfused media may be further sampled in real time to measure soluble biomarkers (e.g., resazurin, albumin, or kidney injury molecule-1) that indicate degree of cellular metabolic activity, synthetic function, or engraftment into the scaffold. Cell growth within bioreactors is validated for primary and immortalized cells, and the design of each bioreactor is scalable to accommodate any three-dimensional scaffold (e.g., synthetic or naturally derived matrix) that contains conduits for nutrient perfusion to deliver media to growing cells and monitor noninvasive parameters during scaffold repopulation, broadening the applicability of these bioreactor systems.

Effects of soft denture liners on L929 fibroblasts, HaCaT keratinocytes, and RAW 264.7 macrophages

The effects of six soft liners (Ufi Gel P (UG), Sofreliner S (SR), Durabase Soft (D), Trusoft (T), Coe Comfort (CC), and Softone (ST)) on L929, HaCat, and RAW 264.7 cells were investigated. Eluates (24 and 48 h) from the materials were applied on the cells and the viability, type of cell death, and morphology were evaluated. Cells were also seeded on the specimens' surfaces (direct contact) and incubated (24 or 48 h), and viability was analyzed. Controls were cells in culture medium without eluates or specimens. For cell viability, no significant differences were found among materials or between extraction periods, and the liners were noncytotoxic or slightly cytotoxic. Morphology of RAW 264.7 cells was altered by the 24 h eluates from CC and D and the 48 h eluates from SR, CC, and D. The 24 and 48 h eluates from all materials (except T) increased the percentages of L929 necrotic cells. For direct contact tests, the lowest cytotoxicity was observed for UG and SR. Although eluates did not reduce viability, morphology alterations and increase in necrosis were seen. Moreover, in the direct contact, effects on viability were more pronounced, particularly for D, T, CC and ST. Thus, the use of UG and SR might reduce the risk of adverse effects.