Denture Liners: A Systematic Review Relative to Adhesion and Mechanical Properties

Assessment of occlusion changes during laboratory phase of relining: An in vitro study

AIM

Assessment of occlusion changes during laboratory phase of relining is essential to evaluate the occlusal discrepancies that could get incorporated in the denture with the use of different relining materials. Since the long term stability and functional success of the denture is heavily influenced by occlusion, an In-vitro study to assess these changes after relining is warranted. The aim of the study is to evaluate the changes in occlusion during laboratory phase of relining procedure.

SETTINGS AND DESIGN

This is an in vitro study with a total of 30 specimen.

MATERIALS AND METHODOLOGY

A total of 30 maxillary standardized dentures were fabricated after mounting on a semi adjustable articulator. These samples will be divided into three groups based on the relining material used (Autopolymerizing resin, Heat-cure resin, Tissue conditioner). The vertical dimension, Centric contact points and eccentric contact points were measured before and after relining.

STATISTICAL ANALYSIS USED

The variables were tested to see if they had a normal distribution using the Shapiro-Wilk test. Parametric distribution was seen for ECP leading to further comparison using one way analysis of variance (ANOVA). Non-parametric distribution was found while testing the VD, CCP leading to adoption of Kruskal-wallis test for comparison of groups. Dunn Bonferroni test was done for VD since results were significant.

RESULTS

The results of this in-vitro study showed statistically significant difference with respect to change in vertical dimension in all groups pre and post relining (P = 0.005). The centric contact points showed lesser variation in position when comparing the pre to the post relining phase with the use of autopolymerising resins, whereas heat cure resins and tissue conditioners showed statistically significant difference in the centric point contacts post relining. No statistically significant changes were seen in eccentric occlusion post relining in all groups. Tissue conditioners showed minimum mean changes in eccentric contacts.

CONCLUSION

Within the limitations of this study, the use of autopolymerising resins depicted the most stable results with respect to occlusion, for relining of dentures.

Comparative analysis of cytotoxicity effects of two denture hard lining materials on human gingival fibroblasts: an in vitro study

Background

The objective of this study was to compare the cytotoxicity of TDV and Rebase II denture hard liners on human gingival fibroblasts, aiming to address issues associated with incomplete polymerization and free monomers that affect material properties.

Methods

Seventy-two specimens (24 each of TDV, Rebase II, and controls) were prepared under aseptic conditions according to factory instructions. Cytotoxicity was determined using the MTT test with methyl tetrazolium salt added to the cell culture medium. A two-way ANOVA and a post-hoc Tukey test was used to evaluate the results of incubation before mitochondrial activity was measured using Multiscan spectrophotometry (570 nm).

Results

There were significant differences in cell viability between the groups after 24 hours (P < 0.001), with TDV having higher viability than Rebase II. The difference between Rebase II and TDV, however, was not significant at 48 and 96 hours (P > 0.131). At 24 hours, Rebase II exhibited significantly lower viability than TDV liner, with a significant difference between the two groups (P = 0.001).

Conclusion

Due to the maximum monomer release in the early hours of incubation, the amount of cytotoxicity decreased with increasing incubation time.

The Effect of Exposure to Candida Albicans Suspension on the Properties of Silicone Dental Soft Lining Material

While functioning in the oral cavity, denture soft linings (SL) are exposed to contact with the microbiota. Dentures can offer perfect conditions for the multiplication of pathogenic yeast-like fungi, resulting in rapid colonisation of the surface of the materials used. In vitro experiments have also shown that yeast may penetrate SL. This may lead to changes in their initially beneficial functional properties. The aim of this work was to investigate the effect of three months of exposure to a Candida albicans suspension on the mechanical properties of SL material and its bond strength to the denture base polymer, and to additionally verify previous reports of penetration using a different methodology. Specimens of the SL material used were incubated for 30, 60 and 90 days in a suspension of Candida albicans strain (ATCC 10231). Their shore A hardness, tensile strength, and bond strength to acrylic resin were tested. The colonization of the surface and penetration on fractured specimens were analysed with scanning electron and inverted fluorescence microscopes. Exposure to yeast did not affect the mechanical properties. The surfaces of the samples were colonised, especially in crystallized structures of the medium; however, the penetration of hyphae and blastospores into the material was not observed.

Influence of hydrothermal aging on the shear bond strength of 3D printed denture-base resin to different relining materials

OBJECTIVES

This study evaluated the repairability of three-dimensional printed (3DP) denture bases based on different conventional relining materials and aging.

MATERIAL AND METHODS

The groups for surface characterization (surface-roughness and contact-angle measurements) were divided based on the denture base and surface treatment. Shear bond strength test and failure-mode analysis were conducted by a combination of three variables: denture base, relining materials, and hydrothermal aging (HA). The initial characterization involved quantifying the surface roughness (n = 10) and contact angle (n = 10) of denture base specimens with and without sandblasting (SB) treatment. Four relining materials (Kooliner [K], Vertex Self-Curing [V], Tokuyama Rebase II (Normal) [T], and Ufi Gel Hard [U]) were applied to 3DP, heat-cured (HC), and self-cured (SC) denture-base resin specimens. Shear bond strength (n = 15) and failure-mode analyses (n = 15) were performed before and after HA, along with evaluations of the fractured surfaces (n = 4). Statistical analyses were performed using a two-way analysis of variance (ANOVA) for surface characterization, and a three-way ANOVA was conducted for shear bond strength.

RESULTS

The surface roughness peaked in HC groups and increased after SB. The 3DP group displayed significantly lower contact angles, which increased after treatment, similar to the surface roughness. The shear bond strength was significantly lower for 3DP and HC denture bases than for SC denture bases, and peaked for U at 10.65 ± 1.88 MPa (mean ± SD). HA decreased the shear bond strength relative to untreated samples. Furthermore, 3DP, HC, and SC mainly showed mixed or cohesive failures with V, T, and U. K, on the other hand, trended toward adhesive failures when bonded with HC and SC.

CONCLUSION

This study has validated the repairability of 3DP dentures through relining them with common materials used in clinical practice. The repairability of the 3DP denture base was on par with that of conventional materials, but it decreased after aging. Notably, U, which had a postadhesive application, proved to be the most effective material for repairing 3DP dentures.

Different Polymers for the Base of Removable Dentures? Part II: A Narrative Review of the Dynamics of Microbial Plaque Formation on Dentures

This review focuses on the current disparities and gaps in research on the characteristics of the oral ecosystem of denture wearers, making a unique contribution to the literature on this topic. We aimed to synthesize the literature on the state of current knowledge concerning the biological behavior of the different polymers used in prosthetics. Whichever polymer is used in the composition of the prosthetic base (poly methyl methacrylate acrylic (PMMA), polyamide (PA), or polyether ether ketone (PEEK)), the simple presence of a removable prosthesis in the oral cavity can disturb the balance of the oral microbiota. This phenomenon is aggravated by poor oral hygiene, resulting in an increased microbial load coupled with the reduced salivation that is associated with older patients. In 15-70% of patients, this imbalance leads to the appearance of inflammation under the prosthesis (denture stomatitis, DS). DS is dependent on the equilibrium-as well as on the reciprocal, fragile, and constantly dynamic conditions-between the host and the microbiome in the oral cavity. Several local and general parameters contribute to this balance. Locally, the formation of microbial plaque on dentures (DMP) depends on the phenomena of adhesion, aggregation, and accumulation of microorganisms. To limit DMP, apart from oral and lifestyle hygiene, the prosthesis must be polished and regularly immersed in a disinfectant bath. It can also be covered with an insulating coating. In the long term, relining and maintenance of the prosthesis must also be established to control microbial proliferation. On the other hand, several general conditions specific to the host (aging; heredity; allergies; diseases such as diabetes mellitus or cardiovascular, respiratory, or digestive diseases; and immunodeficiencies) can make the management of DS difficult. Thus, the second part of this review addresses the complexity of the management of DMP depending on the polymer used. The methodology followed in this review comprised the formulation of a search strategy, definition of the inclusion and exclusion criteria, and selection of studies for analysis. The PubMed database was searched independently for pertinent studies. A total of 213 titles were retrieved from the electronic databases, and after applying the exclusion criteria, we selected 84 articles on the possible microbial interactions between the prosthesis and the oral environment, with a particular emphasis on Candida albicans.

The Impact of the Addition of Vitamins on a Silicone Lining Material to the Oral Mucosa Tissue-Evaluation of the Biocompatibility, Hydrolytic Stability and Histopathological Effect

Background and Objectives: One's quality of life depends on overall health, and in particular, oral health, which has been and continues to become a public health issue through frequent manifestations in various forms, from simple oral stomatitis (inflammations of the oral cavity) to the complicated oral health pathologies requiring medical interventions and treatments (caries, pulp necrosis and periodontitis). The aim of this study focused on the preparation and evaluation of vitamins (vitamin A, B1 and B6) incorporated into several silicone-based lining materials as a new alternative to therapeutically loaded materials designed as oral cavity lining materials in prosthodontics. Materials and Methods: Silicone-based liners containing vitamins were prepared by mixing them in solution and becoming crosslinked, and then they were characterized using Fourier-transform infrared (FT-IR) spectroscopy to confirm the incorporation of the vitamins into the silicone network; scanning electron microscopy (SEM) to evidence the morphology of the liner materials; dynamic vapor sorption (DVS) to evaluate their internal hydrophobicity, swelling in environments similar to biological fluids and mechanical test to demonstrate tensile strength; MTT to confirm their biocompatibility on normal cell cultures (fibroblast) and mucoadhesivity; and histopathological tests on porcine oral mucosa to highlight their potential utility as soft lining materials with improved efficiency. Results: FT-IR analysis confirmed the structural peculiarities of the prepared lining materials and the successful incorporation of vitamins into the silicone matrix. The surface roughness of the materials was lower than 0.2 μm, while in cross-section, the lining materials showed a compact morphology. It was found that the presence of vitamins induced a decrease in the main mechanical parameters (strength and elongation at break, Young's modulus) and hydrophobicity, which varied from one vitamin to another. A swelling degree higher than 8% was found in PBS 6.8 (artificial saliva) and water. Hydrolytic stability studies in an artificial saliva medium showed the release of low concentrations of silicone and vitamin fragments in the first 24 h, which increased the swelling behavior of the materials, diffusion and solubility of the vitamins. The microscopic images of fibroblast cells incubated with vitamin liners revealed very good biocompatibility. Also, the silicone liners incorporating the vitamins showed good mucoadhesive properties. The appearance of some pathological disorders with autolysis processes was more pronounced in the case of vitamin A liners. Conclusions: The addition of the vitamins was shown to have a beneficial effect that was mainly manifested as increased biocompatibility, hydrolytic stability and mucoadhesiveness with the mucosa of the oral cavity and less of an effect on the mechanical strength. The obtained lining materials showed good resistance in simulated biological media but caused a pronounced autolysis phenomenon, as revealed by histopathological examination, showing that these materials may have broad implications in the treatment of oral diseases.

Comparative Evaluation of Hardness and Energy Absorption of Some Commercially Available Chairside Silicone-Based Soft Denture Liners and a Heat-Cured Soft Denture Liner

Aim

To investigate the hardness and energy absorption of four commercially available chairside types of silicone materials and compare their properties with heat-cured silicone material.

Materials

The chairside materials investigated were GC reline soft, mucopren soft, sofreliner soft and elite soft relining. The heat-cured polymer silicone material was Molloplast B. All soft lining materials were processed according to manufacturers' instructions. Two properties were investigated. Ten specimens for each test were prepared for each soft liner except for the water absorption and solubility test, for which only five specimens were prepared. The specimens of energy absorption (10 × 10 × 3 mm) were tested using a Lloyd instruments testing machine. Hardness specimens (38 × 38 × 3) were tested using a shore A durometer and were divided into two subgroups; dry and wet storage.

Results

The specimens of energy absorption (10 × 10 × 3 mm) were tested using a Lloyd instruments testing machine. Sofreliner soft was significantly softer than Molloplast B. GC reline soft was significantly harder than molloplast B. At high loads, sofreliner soft and elite soft relining was significantly more resilient than molloplast B. Mucopren soft was significantly stiffer than Molloplast B. At low loads, all materials showed similarities in stiffness and resilience; the difference between them was insignificant. After one month of immersion, GC reline and mucopren significantly increased hardness values.

Conclusion

In all conditions and at all four-time points, the hardness values for GC Reline soft were the greatest, and hardness values for Sofreliner Soft were the least. Some chairside soft denture lining materials could have similar significant properties to molloplast-B, such as sofreliner soft and elite.

Effect of Ionic Liquids on Mechanical, Physical, and Antifungal Properties and Biocompatibility of a Soft Denture Lining Material

This study aims to evaluate the effect of ionic liquids and their structure on the mechanical (tensile bond strength (TBS) and Shore A hardness), mass change, and antifungal properties of soft denture lining material. Butyl pyridinium chloride (BPCL) and octyl pyridinium chloride (OPCL) were synthesized, characterized, and mixed in concentrations ranging from 0.65-10% w/w with a soft denture liner (Molloplast-B) and were divided into seven groups (C, BPCL1-3, and OPCL1-3). The TBS of bar-shaped specimens was calculated on a Universal Testing Machine. For Shore A hardness, disc-shaped specimens were analyzed using a durometer. The mass change (%) of specimens was calculated by the weight loss method. The antifungal potential of ionic liquids and test specimens was measured using agar well and disc diffusion methods (p ≤ 0.05). The alamarBlue assay was performed to assess the biocompatibility of the samples. The mean TBS values of Molloplast-B samples were significantly lower (p ≤ 0.05) for all groups except for OPCL1. Compared with the control, the mean shore A hardness values were significantly higher (p ≤ 0.05) for samples in groups BPCL 2 and 3. After 6 weeks, the OPCL samples showed a significantly lower (p ≤ 0.05) mass change as compared to the control. Agar well diffusion methods demonstrated a maximum zone of inhibition for 2.5% OPCL (20.5 ± 0.05 mm) after 24 h. Disc diffusion methods showed no zones of inhibition. The biocompatibility of the ionic liquid-modified sample was comparable to that of the control. The addition of ionic liquids in Molloplast-B improved the liner's surface texture, increased its hardness, and decreased its % mass change and tensile strength. Ionic liquids exhibited potent antifungal activity.

Effect of Adding Silver-Doped Carbon Nanotube Fillers to Heat-Cured Acrylic Denture Base on Impact Strength, Microhardness, and Antimicrobial Activity: A Preliminary Study

Poly (methyl methacrylate) (PMMA), is an acrylic polymer substance that is mostly used for denture base applications. The purpose of this laboratory study was to investigate the effect of adding 0.05 wt.% Ag-doped carbon nanotubes (CNT) to PMMA-based (PMMA and MMA) denture base material on the impact strength, microhardness, and antimicrobial activity. A total of 60 heat-cured acrylic resin specimens were prepared. The specimens were randomly divided into two main groups (n = 30/group), according to the powder used: (a) control group, using heat-cured PMMA; (b) treatment group, using a powder prepared by blending 0.05 wt.% silver-doped CNT nanoparticles with heat-cured PMMA. The impact strength, microhardness and anticandidal activity for each group were assessed via the Charpy, Vickers and agar diffusion tests, respectively (n = 10/test for each subgroup). Data were analyzed using independent-sample t-tests (p ≤ 0.05). The results of the impact strength test revealed that the treated heat-cured PMMA-MMA with Ag-doped CNT (2.2 kJ/mm²) was significantly higher than that of the control heat-cured PMMA (1.6 kJ/mm²). Similarly, the Vickers microhardness of the treatment group (52.7 VHN) was significantly higher than that of the control group (19.4 VHN). Regarding the agar diffusion test, after 24 h of incubation, the treated heat-cured PMMA with the Ag-doped CNT exhibited significantly higher anticandidal activity than that of the control group. Therefore, Ag-doped carbon nanotubes could be considered as promising fillers for the dental heat-cured acrylic resin to improve the resistance of the resultant denture against sudden fractures, scratching, and candida invasion.

Polyphosphazene-Based Biomaterials for Biomedical Applications

Recently, synthetic polymers have attracted great interest in the field of biomedical science. Among these, polyphosphazenes (PPZs) are regarded as one of the most promising materials, due to their structural flexibility and biodegradability compared to other materials. PPZs have been developed through numerous studies. In particular, multi-functionalized PPZs have been proven to be potential biomaterials in various forms, such as nanoparticles (NPs) and hydrogels, through the introduction of various functional groups. Thus, PPZs have been applied for the delivery of therapeutic molecules (low molecular weight drugs, genes and proteins), bioimaging, phototherapy, bone regeneration, dental liners, modifiers and medical devices. The main goal of the present review is to highlight the recent and the most notable existing PPZ-based biomaterials for aforementioned applications, with future perspectives in mind.

Development of Phantoms for Multimodal Magnetic Resonance Imaging and Magnetic Particle Imaging

Phantoms are crucial for the development of imaging techniques based on magnetic nanoparticles (MNP). They serve as test objects to simulate application scenarios but are also used for quality assurance and interlaboratory comparisons. Magnetic particle imaging (MPI) is excellent for specifically detecting magnetic nanoparticles (MNP) without any background signals. To obtain information about the surrounding soft tissue, MPI is often used in combination with magnetic resonance imaging (MRI). For such application scenarios, this poses a challenge for phantom fabrication, as they need to accommodate MNP as well as provide MR visibility. Recently, layer-by-layer fabrication of parts using Additive Manufacturing (AM) has emerged as a powerful tool for creating complex and patient-specific phantoms, but these are characterized by poor MR visibility of the AM material. We present the systematic screening of AM materials as candidates for multimodal MRI/MPI imaging. Of all investigated materials, silicone (Dreve, Biotec) exhibited the best properties with sufficient MR-signal performance and the lowest absorption of MNP at the interface of AM materials. With the help of AM and the selection of appropriate materials, we have been able to produce suitable MRI/MPI phantoms.

Influence of Incorporating 5% Weight Titanium Oxide Nanoparticles on Flexural Strength, Micro-Hardness, Surface Roughness and Water Sorption of Dental Self-Cured Acrylic Resin

Background: Polymethyl methacrylate (PMMA) is used in fabricating acrylic denture bases. Repairing a fractured acrylic denture base can be done by self-cured PMMA, yet this is still a weak point after repair. The aim of this study was to evaluate the effect of incorporating 5% weight titanium oxide nanoparticles (TiO₂) to self-cured PMMA on flexural strength, surface micro-hardness, roughness, and water sorption. Methods: A total of 160 acrylic–resin specimens were used in this study. They were divided in two main groups; (a) control group, prepared by mixing self-cured PMMA powder to its liquid monomer, (b) treated group, prepared by blending 5% weight TiO₂ nanoparticles to self-cured PMMA powder then this blend was mixed with the liquid monomer. Flexure strength, surface micro-hardness, roughness, and water sorption were evaluated. Data were analyzed using independent sample t-tests (p ≤ 0.05). Results: There was a significant increase in the flexural strength of PMMA of the treated group after the addition of TiO₂ (137.6 MPa) compared with the control (75.4 MPa) (p ≤ 0.001). No significant difference between the two groups in terms of micro-hardness (p = 0.385) and surface roughness (p = 0.269). Water sorption showed a significant reduction in the treated group (p ≤ 0.001). Conclusions: Addition of 5% weight TiO₂ nanoparticles to the self-cured acrylic resin improved its flexural strength and reduced its water-sorption without impairing the surface micro-hardness and roughness.

Effect of different mouthwashes on the shear bond strength and surface roughness of intraoral and heat-cured soft liners

Background

The present study aimed to determine the effect of mouthwashes on the shear bond strength (SBS) and surface roughness (SR) of soft liners.

Materials and Methods

In this in vitro study, a total of 72 samples were prepared to evaluate the SBS (n = 36 for each liner). An autopolymerized (Mollosil Plus) and a heat-polymerized liner (Molloplast B) were injected in between two blocks of heat-processed acrylic resin (Triplex). The samples in each liner group were subdivided into three subgroups. Control group samples were totally stored in distilled water. In test groups, samples were immersed in chlorhexidine (CHX) or mouthwash containing ginger extract for 30 min daily. After 20 days, the SBSs were evaluated using a universal testing machine. To evaluate the SR, 30 disk-shaped samples (15mm*10mm) were prepared for each type of liners and stored in the similar solutions; distilled water, CHX and ginger mouthwash (n=10). SR was measured at 1 day and after 90 days with a profilometer. One-way ANOVA, independent t-test, and paired t-test were used to analyze data. P < 0.05 was considered statistically significant.

Results

The SBS in Molloplast B liner was significantly higher than Mollosil regardless of type of solution (P < 0.001). In both liners, the mean SBS was not statistically different between the three groups of solutions. Changes in SR were not statistically significant after 90 days, except for the Mollosil group, immersed in ginger extract solution which was increased (P = 0.04).

Conclusion

SBS of either group of liners did not change in both mouthwashes; However, SBS of heat-polymerized liner was higher than autopolymerized in all groups. Ginger extract-containing mouthwash increased SR of autopolymerized liner used in this study; whereas, there were no significant changes in the heat-cured liner. According to this study, CHX can be used for the disinfection of prosthesis lined with either type of liners.

Denture cleanliness and hygiene: an overview

Dentures are an excellent treatment modality for partial and edentate patients; however, improper denture care and hygiene can result in both decreased longevity of the prosthesis and increased risk of developing dental caries, periodontal disease and oral candidosis. Previously, it has been shown that patients and dental professionals are unaware of the different materials and methods available for optimum denture care and hygiene. This article provides an overview of the key legislation and main commercially available methods for denture cleanliness and hygiene, and serves as a basis for providing tailored denture hygiene for denture wearers.

Patients typically demonstrate poor levels of denture hygiene which impacts oral health.

Denture hygiene instructions comprise mechanical and chemical methods; both should be tailored to the denture wearer.

Denture base and denture teeth materials had different compatibility with different denture cleaning methods.

Soft Denture liner and microbial disinfection with contemporary and conventional agents

AIM

The present study aimed to assess the effect of PDT, herbal and chemical disinfectants on the dental pathogen adherence to soft denture liner colonized with E. coli, C. Albicans, S.aureus, and S. mutans.

MATERIAL AND METHODS

A total of 20 samples of soft-lined removable acrylic complete dentures were fabricated and subjected to the American Type Culture Collection (ATCC) for the inoculation of E.coli, C.albicans, S.mutans and S.aureus in an in-vitro setup. The samples were then randomly divided into four groups and immersed in group 1: 5 µm of Rose Bengal (RB), group 2: Neem extract, group 3: Tea tree oil (TTO), and group 4: 0.12% CHX solutions respectively. Statistical analysis was accomplished by the SPSS 10 statistical software for Windows at a significance level p< 0.05. Two-way ANOVA and Tukey's multiple comparison test were used to analyze the data and compare the means and standard deviation values of CFU/mL (log10) for exposed E. coli, C. albicans, S aureus, and S. mutans.

RESULTS

Intragroup comparison indicated E.coli and C.albicans did not unveil a decrease in reduction CFU/mL (log10) when SDL irradiated with RB 5 µm. Whereas, CFU/mL (log10) values of S.aureus; 2.62±0.68 CFU/mL and S.mutans: 3.41±0.13 CFU/mL plunged significantly (p<0.05). Likewise, S. aureus and S. mutans CFU/mL (log10) strain values display reduction when treated with all four disinfectants while the count of C.albicans unveiled a significant plunge with CHX, TTO and neem extract except RB (p<0.05) CONCLUSION: 0.12% CHX and TTO have enhanced antimicrobial efficacy in reducing adhered bacterial colonies of E.coli, C.albicans, S.aureus, and S.mutans (CFU)/mL on a denture soft liner.

Investigating Tensile Bonding and Other Properties of Yttrium Oxide Nanoparticles Impregnated Heat-Cured Soft-Denture Lining Composite In Vitro

Aims

This study was conducted to assess the effect of the addition of yttrium oxide (Y₂O₃) nanoparticles on the tensile bond strength, tear strength, shore A hardness, and surface roughness of soft-denture lining material.

Materials and Methods

Y₂O₃ NPs with 1.5 and 2 wt.% were added into acrylic-based heat-cured soft-denture liner. A total of 120 specimens were prepared and divided into four groups according to the test to be performed (tensile bond strength, tear strength, surface hardness, and surface roughness).

Results

There was a highly significant increase in tensile bond strength between the soft liner and the acrylic denture base, tear strength, and hardness at both concentrations as compared to the control group, whereas there was a nonsignificant difference between 1.5wt% of Y₂O₃ nanoparticles and the control group, and between 1.5wt% and 2wt% of Y₂O₃ nanoparticles. But there was a significant difference between 2wt% of Y₂O₃ nanoparticles and the control group.

Conclusion

The Y₂O₃ nanoparticles impregnated in soft-lining materials increased the mechanical properties of both tensile bonding strength and tear strength. Also, there was a significant increase in hardness but there was no change in surface roughness of acrylic-based denture soft-lining materials.

Soft Denture Liner Adhesion to Conventional and CAD/CAM Processed Poly(Methyl Methacrylate) Acrylic Denture Resins-An In-Vitro Study

This study aimed to evaluate the airborne-particle abrasion surface treatment effects on the tensile bond strength (TBS) between resilient denture liner and CAD/CAM or conventional heat polymerized poly (methyl methacrylate) (PMMA) acrylic denture resins. A total of 48 dumbbell-shaped specimens (70 mm in total length, and 12 mm and 7 mm in diameter at the thickest and thinnest section, respectively) were prepared from CAD/CAM and conventional acrylic resins. Before relining with denture liner, 12 specimens from each material were surface-treated by 110 µm Al₂O₃ airborne-particle abrasion, and the remaining specimens served as control (no treatment). Following relining, all the specimens were aged by thermal cycling (1000 cycles, 5–55 °C). The TBS of denture liner to acrylic denture resins was tested in a universal testing apparatus at a 5 mm/min crosshead speed. The debonded surfaces were visually examined for the failure modes. ANOVA and multiple comparisons posthoc analysis tests were applied to determine the significant difference in TBS between the study groups (α = 0.05). A significant difference in TBS was observed between the control and surface treated groups (p < 0.001) for both acrylic resins materials. However, there was no statistically significant difference in bond strength between the acrylic resins materials (p = 0.739). Surface treatment with airborne-particle abrasion demonstrated increased TBS of the soft denture liners to acrylic resins. The TBS of conventional and CAD/CAM acrylic resins to soft denture liners were not considerably different.

Analysis of the Hardness of Soft Relining Materials for Removable Dentures

The main functional feature of elastomeric soft linings materials is the ability to discharge loads in the tissues of the mucosa. As a result, there are fewer injuries to the mucosa and chewing ability increases. In addition, these prostheses are more comfortable in the patient’s opinion. To obtain the equal distribution of forces on the muco-bone basis and to reduce the traumatizing effect of the denture plate for patients using full dentures, soft lining materials can be used. Aim of the study: the aim of the work was a comparative laboratory study of ten materials used for soft lining of acrylic complete dentures. Methodology: Materials based on acrylates (Vertex Soft, Villacryl Soft, Flexacryl Soft) and on silicones (Sofreliner Tough Medium, Sofreliner Tough Medium, Ufi Gel SC, GC Reline Soft, Elite Soft Relining, Molloplast) were compared. Laboratory tests include tests of changes in Shore’a A hardness of soft lining material. The tests were conducted taking into account 90 day term aging in the distilled water environment based on the methodology presented in the European Standard ISO 10139-2. Results: For most silicone materials, only small changes in hardness were found in the range of 0.7 (Ufi Gel SC) to 3.3 (Sofreliner Tough Medium) on the Shore A scale. The exception was GC Reline Soft, for which a marked increase in hardness was noted. All materials based on acrylates were characterized by successive increase in hardness over time. However, in the case of the Vertex Soft material, the increase in hardness was relatively small (5.5 ShA).

Quality of Life, Satisfaction, Occlusal Force, and Halitosis after Direct and Indirect Relining of Inferior Complete Dentures

Objective  The aim of this study was to compare the direct relining technique with the indirect relining technique in relation to quality of life, satisfaction with the relining, occlusal force, and halitosis of users of acrylic complete dentures.

Materials and Methods  Twenty bimaxillary edentulous individuals were selected. They had to use the same pair of complete dentures for a minimum of 1 year and a maximum of 5 years. The subjects were randomly divided in groups of direct relining and indirect relining of the inferior denture ( n = 10). Both groups received the same silicone-based relining. The clinical tests verified the quality of life (Oral Health Impact Profile in edentulous individuals), the satisfaction with the relining, the occlusal force, and halitosis. The tests (halitosis and occlusal force) were performed initially (before the relining), immediately after the relining, and 30, 60, 90, and 180 days after the relining. The questionnaires (quality of life and satisfaction with the relining) were performed initially (before the relining), and 30, 60, 90, and 180 days after the relining.

Statistical Analysis  Analysis of variance and the Tukey test were used ( p < 0.05).

Results  There was no statistical difference comparing the two techniques in all the evaluations ( p < 0.05). There was a significant statistical difference for the factor of time in all clinical tests for each relining technique ( p < 0.05). The quality of life and satisfaction with the relining increased significantly 30 days after the relining when compared with the initial time point, for both techniques ( p < 0.05). The occlusal force increased significantly after 90 and 180 days when compared with the initial time point, for both techniques ( p < 0.05). Halitosis decreased significantly immediately after the relining when compared with the initial time point, for both techniques ( p < 0.05).

Conclusion  Independent of the relining technique used, there was an increase in the quality of life, satisfaction with the relining, and occlusal force, as well as a reduction in the level of halitosis. Both techniques generated similar results and therefore can be options in clinical practice.

An in vitro evaluation of tensile bond strength of soft liners bonded to different denture base resins

Background

Clinically, adhesion failure is the most critical problem because of the failure of the optimal bond between denture base and the soft liner.

Objectives

This study was performed to assess the tensile bond strength of two temporary soft liners to different denture base resins.

Materials and Methods

Forty-eight blocks with 16 samples each of heat-cured denture base resin of three different types were fabricated from custom-made stainless steel die after de-waxing mold space. Surface roughening of each acrylic resin specimens which bonds with soft liners was done by abrading the surface and to this temporary soft liners (Perma soft denture liner and Pro soft denture liner) were bonded. The universal testing machine was used to test the tensile strength of bonded space. The results were statistically analyzed using the Statistical Software IBM SPSS Statistics for Windows, version 20.0. (Armonk, NY, USA: IBM Corp.) using the Chi-square test, Post hoc Tukey's HSD, and two way ANOVA tests.

Results

It was observed that Perma soft was prevalent over Pro-soft denture liner on the basis of tensile bond strength with all three different types of denture base resins. Trevalon HI and acrylic composite exhibited better bond strength results with both Perma soft and GC Pro-soft denture liner as compared to other types of denture base resins.

Conclusion

Perma soft had a better bond strength compared to Pro-soft denture liner in bonding modified denture base and conventional resins.

Photodynamic antimicrobial chemotherapy through photosensitizers loaded poly-l-glycolic acid on Candida albicans in denture lining material: Release, biological and hardness study

AIM

The aim of this in-vitro study was to formulate poly-l-glycolic acid nanoparticles loaded with methylene blue (PLGA-MB) and to characterize their physicochemical features, photosensitizer-release kinetics and antimicrobial efficacy against Candida albicans (C. albicans) after incorporating in polymethyl methacrylate (PMMA) denture lining materials.

MATERIAL AND METHODS

MB-PLGA nanoparticles were synthesized according to the modified nanoprecipitation method. The morphological characterization of the nanoparticles was studied under scanning and transmission electron microscope. Particle size, surface charge, polydispersity index (PDI) and MB release were evaluated. The effect of 660 nm semiconductor AlGaInP diode laser on C. albicans was studied in vitro. The PMMA was weighed and PLGA free and PLGA-MB were added in the lining material according to the weight percentage as 2.0 wt.% and 5.0 wt.% and tested for the diameter of the inhibition zones of C. albicans growth and shore A hardness.

RESULTS

Homogenous spherical nanoparticles with round morphology with size ranging between 60-80 nm were observed while PLGA-MB were seen to have irregular structure within the nanoparticle under TEM. PLGA-Free was larger in size than the loaded PLGA (∼62 nm) that evidenced reduction in size by adding the MB photosensitizer. PDI recordings reduced from 0.198 for the PLGA-Free nanoparticles to 0.164 for the PLGA-MB nanoparticles. The entrapment efficiency of MB inside PLGA showed an average percentage of ∼75 % uptake that resulted in the overall loading of ∼15 %. An overall inhibition of 78 %, 41 % and 28 % of C. albicans growth was seen with a concentration of 0.1, 0.5 and 1.0 μg/mL, respectively. The application of PLGA nanoparticles loaded with MB evidenced >75 % of C. albicans. MB incorporation did not lead to a clinically relevant change on shore A hardness.

CONCLUSION

PLGA loaded with MB is believed to have promising target therapy against C. albicans in denture soft lining materials in terms of PACT in vitro. The synergistic association between PLGA and MB proved enhanced antifungal activity. PLGA-MB could be an important tool in nanobiotechnology and photodynamic therapy for novel formulations with higher antimicrobial efficacy and improved drug delivery from denture soft lining materials.

Mechanical and Surface Properties of Resilient Denture Liners Modified with Chitosan Salts

Chitosan (CS) and its derivatives show antibacterial and antifungal properties and could help treat and prevent denture stomatitis (DS). Mechanical and surface properties of resilient denture liners were evaluated when modified with CS salts. CS-hydrochloride (CS-HCl) and CS-glutamate (CS-G) were added to resilient denture liners Ufi Gel P and Coe-Soft at four different concentrations (0.1%, 0.2%, 0.4%, 1% w/w) from which specimens were produced, as well as a control group of each material with no added CS salt. Ten specimens per group (Ø 35 mm, height 6 mm) were manufactured. They were stored in distilled water at 37 °C for a total of 30 days (d). Shore A hardness (SHA) and surface roughness (Ra) were evaluated after 24 h (T1), 7 d (T2), 14 d (T3) and 30 d (T4). Kruskal-Wallis and U-test (Bonferroni-Holm adjusted) were used for statistical analysis (p ≤ 0.05). Ra increased significantly once CS salts were added. SHA increased significantly for some groups, but all specimens fulfilled requirements set by ISO 10139-2:2016. Modification with CS salts does not influence the mechanical properties of the modified resilient denture liners in a clinically relevant manner. Despite the increased roughness, the concept is suitable for further studies. Especially antimicrobial/antibiofilm studies are needed.