Durability of peel bond of resilient denture liners to acrylic denture base resin

PurposeThe purpose of this study was to determine the durability of the peel bond of commercial resilient denture liners to a denture base resin using a thermal cycling test.MethodsEight commercial resilient denture liners (five silicone and three acrylic) were used in the study. The samples were exposed to thermal cycles between 5 °C and 55 °C for 1 min for 0, 1,250, 2,500, 5,000 and 10,000 cycles. The test samples were placed under tension until failure in a materials testing machine using a crosshead speed of 20 mm/min. The modes of debonding were characterized as tear, peel or snap. Statistical analysis was performed using one-way and two-way analysis of variance and Student–Newman–Keuls multiple comparison tests (α = .05).ResultsA significant difference was found between different resilient denture liners for peel bond strength at 0 cycles. No extreme influence on the peel bond strength was observed under any of the thermal cycles. The snap mode of debonding was observed in most samples of all materials for all cycles.ConclusionAll resilient denture liners tested had a sufficiently strong bond to the denture base resin. Within the limitations of this study, the results show that all of the materials were acceptable for clinical use, having met the accepted adequate bond strength for resilient denture liners of 0.45 MPa.     

Effect of oral antiseptic agents on phospholipase and proteinase enzymes of Candida albicans

ObjectiveCandida-associated denture stomatitis is the most prevalent form of oral candida infections among the denture wearers. Generally, antiseptic oral rinses used in the treatment of these infections are considered as an adjunct or alternative antifungal treatment. Studies have suggested that the intraoral concentrations of antiseptics decrease substantially to the sub-therapeutic levels on account of the dynamics of the oral cavity. This condition yields the question about the minimum antiseptic concentration that effect the character or pathogenesis of Candida during treatment. The extracellular phospholipase and proteinase enzymes of Candida albicans are regarded to have a crucial role in the pathogenesis of human fungal infections. Therefore, the aim of this study was to investigate the effect of different sub-therapeutic concentrations of chlorhexidine gluconate, hexetidine and triclosan on the production of these enzymes by C. albicans strains isolated from 20 patients with denture stomatitis.MethodsPhospholipase test was done by using Sabouraud dextrose agar with egg yolk, proteinase test was done by using bovine serum albumin agar.MethodsPhospholipase test was done by using Sabouraud dextrose agar with egg yolk, proteinase test was done by using bovine serum albumin agar.ResultsExoenzyme production of 20 strains which were brief exposured to sub-therapeutic concentrations of three antiseptic agents decreased significantly compared with the strains that were not exposured with antiseptic values (p < 0.05). There was significant difference between the sub-therapeutic concentrations of each of three antiseptics (p < 0.05). When the same concentrations of each antiseptic was compared, there were no significant differences between enzymatic activities (p > 0.05).ConclusionsThe results of this study show that sub-therapeutic levels of each antiseptic may modulate candidal exoenzyme production, consequently suppressing pathogenicity of C. albicans.     

Effect of storage in artificial saliva and thermal cycling on Knoop hardness of resin denture teeth

PurposeThis study aimed to evaluate the effect of different storage periods in artificial saliva and thermal cycling on Knoop hardness of 8 commercial brands of resin denture teeth.MethodsEigth different brands of resin denture teeth were evaluated (Artplus group, Biolux group, Biotone IPN group, Myerson group, SR Orthosit group, Trilux group, Trubyte Biotone group, and Vipi Dent Plus group). Twenty-four teeth of each brand had their occlusal surfaces ground flat and were embedded in autopolymerized acrylic resin. After polishing, the teeth were submitted to different conditions: (1) immersion in distilled water at 37 ± 2 °C for 48 ± 2 h (control); (2) storage in artificial saliva at 37 ± 2 °C for 15, 30 and 60 days, and (3) thermal cycling between 5 and 55 °C with 30-s dwell times for 5000 cycles. Knoop hardness test was performed after each condition. Data were analyzed with two-way ANOVA and Tukey's test (α = .05).ResultsIn general, SR Orthosit group presented the highest statistically significant Knoop hardness value while Myerson group exhibited the smallest statistically significant mean (P < .05) in the control period, after thermal cycling, and after all storage periods. The Knoop hardness means obtained before thermal cycling procedure (20.34 ± 4.45 KHN) were statistically higher than those reached after thermal cycling (19.77 ± 4.13 KHN). All brands of resin denture teeth were significantly softened after storage period in artificial saliva.ConclusionStorage in saliva and thermal cycling significantly reduced the Knoop hardness of the resin denture teeth. SR Orthosit denture teeth showed the highest Knoop hardness values regardless the condition tested.     

The effect of antifungal agents on surface properties of poly(methyl methacrylate) and its relation to adherence of Candida albicans

PurposeCandida-associated denture stomatitis is the most prevalent form of oral candidosis affecting 65% of denture wearers. Failure of therapy and recurrence of infection are not uncommon and the continuous use of antifungal agents may affect the surface properties of the denture material and may contribute to Candida adhesion. This study aimed to investigate surface properties of poly(methyl methacrylate) PMMA denture material before and after exposure to antifungal agents and its relation to in vitro adhesion of Candida albicans.MethodsFour groups of acrylic specimens (20 mm × 20 mm × 2.5 mm) were prepared (25 specimens in each group). Specimens were immersed in nystatin (group 1), fluconazole (group 2), distilled water (group 3) and group 4 was not exposed. Specimens were tested for surface roughness, contact angle, surface hardness and in vitro Candida adherence to PMMA.ResultsThe results showed that nystatin had no statistically significant effect on surface hardness (P > 0.05), but had a statistically significant effect on surface roughness, contact angle, and Candida adhesion to PMMA (P < 0.05). On the other hand, fluconazole had no statistically significant effect on surface hardness or roughness (P > 0.05), but had a statistically significant effect on contact angle, and Candida adhesion to PMMA (P < 0.05). Distilled water had no statistically significant effect on surface hardness, roughness, contact angle, or Candida adhesion to PMMA (P > 0.05).ConclusionsExposure of PMMA to nystatin may induce changes in roughness, wettability while exposure to fluconazole may affect surface free energy and therefore may increase Candida adhesion to it.     

Effect of denture adhesives on oral moisture: A multicenter randomized controlled trial

PurposeThe purpose of this study was to investigate the effect of denture adhesives on oral moisture in a 10-center parallel randomized clinical trial.MethodsTwo hundred edentulous subjects wearing complete dentures were allocated into three groups: cream-type adhesive, powder-type adhesive and control groups. The adhesives (and saline solution in the control group) were applied to the mucosal surface of the dentures for 4 days, and baseline data and data after the intervention for eight meals over 4 days were obtained. For the main outcome, oral moisture was measured with a moisture checking device. Secondary outcomes were denture satisfaction, masticatory performance, denture retention, and occlusal force. In addition to between-group and within-group comparisons of oral moisture, investigations for secondary outcomes were undertaken in subgroups classified according to the degree of oral moisture at baseline (normal subgroup and dry mouth subgroup). Intention-to-treat analysis was also performed.ResultsBetween-group and within-group comparisons of oral moisture showed no significant differences. The cream-type and powder-type denture adhesives were significantly effective in the dry mouth group for denture satisfaction ratings of ability to masticate, stability, retention, and comfort of mandibular dentures (p < 0.05). The masticatory performance and retentive force of the dry mouth denture adhesive using groups were significantly improved after intervention (p < 0.05).ConclusionsThe oral moisture of complete denture wearers was not influenced by the use of denture adhesives. Our findings showed that denture adhesives improved subjective denture satisfaction, masticatory performance, and retention for complete denture patients with oral dryness.     

Microbiological and clinical assessment of the abutment and non-abutment teeth of partial removable denture wearers

ObjectiveThe aim of this study was assessing the changes in both clinical and microbiological parameters of healthy individuals after rehabilitation with removable partial denture (RPD).Design11 women received unilateral or bilateral free-end saddle RPD in the mandibular arch. Clinical and microbiological parameters of abutment, non-abutment, and antagonist teeth were assessed at baseline (RPD installation) and after 7, 30, 90, and 180 days of function. The Checkerboard DNA–DNA hybridization technique was used to identify and quantify up to 43 different microbial species from subgingival biofilm samples. Probing depth, gingival recession, and bleeding on probing were also investigated over time.ResultsThe total and individual microbial genome counts were shown significantly increased after 180 days with no significant differences between abutment, non-abutment, or antagonist teeth. Streptococcus spp., Aggregatibacter actinomycetemcomitans, and other species associated to periodontitis (Peptostreptococcus anaerobius, Prevotella nigrescens, and Tannerella forsythia), as well as opportunistic Candida spp., were recovered in moderate counts. Abutment teeth presented higher values of gingival recession when compared with non-abutment or antagonist teeth, irrespectively time of sampling (p < 0.05). No significant differences were found between groups regarding bleeding on probing or probing depth over time.ConclusionsOverall, the microbial counts significantly increased after 6 months of denture loading for both abutment and non-abutment teeth with no significant differences regarding the microbial profile over time. Bleeding on probing and probing depth showed no significant difference between groups over time whereas gingival recession increased in the abutment teeth.     

Influence of different flask systems on tooth displacement and framework misfit in mandibular fixed implant-supported complete dentures

PurposeTo evaluate the influence of different metallic flask systems for acrylic resin denture processing on tooth displacement and framework misfit of mandibular fixed implant-supported complete dentures.MethodsStandard mandibular implant-supported complete dentures in five implants were waxed and randomly assigned to three groups: G1 – conventional flask, G2 – double flask, and G3 – occlusion flask. Framework misfit in all the implants and the linear distances between teeth (I-I – incisor-to-incisor; P-P – premolar-to-premolar; M-M – molar-to-molar; RI-RM – right-incisor-to-right-molar; and LI-LM – left-incisor-to-left-molar) were measured before and after denture processing using an optical microscope. Dentures were processed by hot water curing cycle (9 h/74 °C). Collected data were analyzed by paired Student's t-test and one-way ANOVA (α = 0.05).ResultsAll the measured distances presented changes in tooth displacement after denture processing. However, the M-M distance for G1 (p = 0.003) and the P-P (p = 0.042) and LI-LM (p = 0.044) distances for G3 showed statistically significant differences. Differences between the flask systems were not statistically significant. Statistically significant differences in the framework misfit due to denture processing were found for all the implants and groups, with the exception of right median implant for G2 and right distal implant for G3. A comparison of the flask systems found statistically significant differences in which G1 presented an increase in the misfit values and G2 and G3 a decrease.ConclusionsDifferent flask systems did not cause significant changes in tooth displacement. Frameworks misfit values were influenced by the different flask systems. The conventional flask presented an increase in the framework misfit, while the experimental flasks showed a decrease.     

The influence of vertical dimension of occlusion changes on the electroencephalograms of complete denture wearers

PurposeThe present study was conducted to identify how changes in the vertical dimension of occlusion (VDO) affect the sensory perception and activity of the brain in complete denture wearers using an electroencephalogram (EEG).MethodsSubjects were 21 individuals wearing complete dentures who regularly visited the Division of Prosthodontics at Tsurumi University Dental Hospital for checkups (12 males and 9 females, average age: 76.6). Based on their original dentures, two duplicate dentures with different VDO (−3 mm and +5 mm) were fabricated. EEG activity and occlusal force were measured before and after gum chewing with each denture in all subjects. Negative indicator scores for psychological conditions and stable neuronal activity (Dα) were calculated using EEG data. Statistical analysis was performed using the Wilcoxon test to compare changes in the sensory perception, activity of the brain, and occlusal force (α = 0.05).ResultsAfter gum chewing with the +5-mm denture, a significant increase was observed in the negative indicator score (p < 0.05). No significant difference was found in the Dα values before and after gum chewing with any of the dentures (p > 0.05). A significant decrease was observed in the occlusal force between the original denture and the −3-mm denture (p < 0.05).ConclusionPsychological condition and occlusal force were influenced by immediate changes in the VDO of the complete denture.     

Effect of experimental photopolymerized coatings on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion

ObjectiveThis study investigated the effect of experimental photopolymerized coatings, containing zwitterionic or hydrophilic monomers, on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion.MethodsAcrylic specimens were prepared with rough and smooth surfaces and were either left untreated (control) or coated with one of the following experimental coatings: 2-hydroxyethyl methacrylate (HE); 3-hydroxypropyl methacrylate (HP); and 2-trimethylammonium ethyl methacrylate chloride (T); and sulfobetaine methacrylate (S). The concentrations of these constituent monomers were 25%, 30% or 35%. Half of the specimens in each group (control and experimentals) were coated with saliva and the other half remained uncoated. The surface free energy of all specimens was measured, regardless of the experimental condition. C. albicans adhesion was evaluated for all specimens, both saliva conditioned and unconditioned. The adhesion test was performed by incubating specimens in C. albicans suspensions (1 × 10⁷ cell/mL) at 37 °C for 90 min. The number of adhered yeasts were evaluated by XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-5-[{phenylamino}carbonyl]-2H-tetrazolium-hydroxide) method.ResultsFor rough surfaces, coatings S (30 or 35%) and HP (30%) resulted in lower absorbance values compared to control. These coatings exhibited more hydrophilic surfaces than the control group. Roughness increased the adhesion only in the control group, and saliva did not influence the adhesion. The photoelectron spectroscopy analysis (XPS) confirmed the chemical changes of the experimental specimens, particularly for HP and S coatings.ConclusionsS and HP coatings reduced significantly the adhesion of C. albicans to the acrylic resin and could be considered as a potential preventive treatment for denture stomatitis.     

Effect of denture cleansers on physical properties of heat-polymerized acrylic resin

PurposeThis study aimed to measure the color change, surface roughness and flexural strength of heat-polymerized acrylic resin after its immersion in denture cleansers, simulating a 180-day use.MethodsThirty disk-shaped (15 mm × 4 mm) and 30 rectangular samples (65 mm × 10 mm × 3.3 mm) were prepared from heat-polymerized acrylic resin and immersed in Corega Tabs, Bony Plus, and distilled water. Color measurements (ΔE) were determined by a portable colorimeter. A surface analyzer was used to measure the roughness before and after immersion (ΔRa). The flexural strength (S) was measured using a 3-point bending test. The ΔE values were submitted to statistical analysis by the Kruskal–Wallis test, followed by Dunn's Multiple Comparisons test. The ΔRa and S values were submitted to statistical analysis by ANOVA, followed by a Student–Newman–Keuls test (α = .05).ResultsThe color changes were significantly higher for the Corega Tabs than for the control group. The mean ΔE values quantified by the National Bureau of Standards (NBS) were classified as Trace (0.0–0.5). The Bony Plus group had significantly higher surface roughness than the other groups. Corega Tabs and Bony Plus groups presented lower flexural strength than the control group.ConclusionsAlthough the color changes after the immersion in denture cleansers were clinically insignificant, the Corega Tabs group showed higher color differences. The Bony Plus group showed significantly increased surface roughness. Both effervescent tablets Corega Tabs and Bony Plus significantly diminished the flexural strength of the acrylic resin.     

Shear bond strength between light polymerized hard reline resin and denture base resin subjected to long term water immersion

Statement of the problemThe effect of long-term water immersion on the shear bond strength between denture base resin and Triad visible-light-polymerized (VLP) direct hard reline resin is not known.PurposeThe aim of this study was to investigate the bonding characteristics of Triad VLP direct hard reline resin to heat-polymerized denture base resin subjected to long-term water immersion.Material and methodsNinety circular disks, 15 mm in diameter and 3 mm thick, of denture base resin were polymerized from a gypsum mold. Sixty specimens were subjected to water immersion and 30 were stored at ambient room temperature for 4 months. Thirty water-immersed specimens were dried with gauze (group 1), while the other 30 water-immersed specimens were dried with a hair dryer (group 2). The dry specimens (n = 30) represented the control group (group 3). All specimens were air abraded and painted with bonding agent before packing Triad VLP direct hard-reline resin. Specimens in each group were subjected to thermal cycling for 50,000 cycles between 4 °C and 60 °C water baths with 1-min dwell time at each temperature. The bond strength at which the bond failed under stress was recorded using a universal testing machine. One-way ANOVA and Tukey post hoc comparison were applied to find significant differences between groups (α = 0.05).ResultsSignificant differences in mean shear bond strength among the specimens existed because of variable water content in the denture base resin (P < 0.05). Group 3 (dry) was higher than group 2 (desiccated), and the lowest was group 1 (saturated).ConclusionThe shear bond strength of Triad VLP direct hard reline resin to denture base resin depended on the water content in the denture base resin. The dry denture base resin demonstrated superior bond strength compared with the desiccated and water-saturated denture base resins.     

The effect of subinhibitory concentrations of gentian violet on the germ tube formation by Candida albicans and its adherence to oral epithelial cells

ObjectiveThis study investigated the effect of subinhibitory concentrations of gentian violet on the germ tube formation by Candida albicans and its adherence ability to oral epithelial cells.MethodsThirty strains of C. albicans isolated from denture wearers, normal healthy individuals and HIV positive patients were used in the study. The antifungal property (Minimum Fungicidal Concentration) of gentian violet was determined at various time intervals using a microdilution technique. The effect of subinhibitory concentrations of gentian violet on the adherence ability (0.000244%) and on germ tube formation ((0.000244%, 0.000122%, 0.000061% and 0.000031%) was determined. In both experiments, water was used as a control. The test results were compared using the Kruskal-Wallis test.ResultsAt 60 min a high concentration (0.0078%) of gentian violet was required to completely kill C. albicans. Subinhibitory concentrations of gentian violet significantly reduced the adherence ability of C. albicans by 57% (p < 0.01) and equally inhibited germ tube formation (p < 0.01) compared with the controls. The inhibition was concentration dependent, with up to 98% reduction at a concentration of 0.000244%. Germ tube reduction was significantly higher in the isolates from the HIV positive patients than in the isolates from denture wearers.ConclusionAt high concentrations, gentian violet killed C. albicans, whereas at subinhibitory concentrations it reduced its virulence by preventing the adherence ability and germ tube formation. This suggests that the beneficial effects of gentian violet would last beyond the fungicidal concentrations in the treatment of candidiasis.     

Differences in comminution progress during mastication in healthy dentate and denture-wearing elderly people

PurposeThis study aimed to investigate the effect of removable denture prostheses on the comminution progress in elderly people.MethodsTwenty-two denture wearers of Eichner’s classification B and C (75.1 ± 5.3 years old) and 20 young fully dentate subjects (27.6 ± 1.9 years old) participated in the masticatory examination, which used a combined test food from 5 daily food materials. Full masticatory cycles lasting until subjects needed to swallow and the half number of the cycles were adopted as masticatory conditions. Digital images of food particles under wet conditions were obtained for each bolus, and particles were analyzed by calculating the homogeneity and particle size indices.ResultsThe characteristic properties of the food particles were observed using a homogeneity index in the elderly denture group for half masticatory strokes. Their homogeneity index was significantly higher than that of the young dentate group. By contrast, no significant difference was observed in the indices for particles immediately before swallowing between two groups.ConclusionsThe comminuted particle size before swallowing in healthy denture wearers was not significantly different from that in the natural dentate group. The comminution of the first-half process in denture wearers was typical and could be one possible focus for meal property specifications in future studies.     

Investigation on how renewal of complete dentures impact on dietary and nutrient adequacy in edentulous patients

PurposeThe aim of this study is to investigate changes of diet and nutrient adequacy between complete denture wearers with their existing dentures and those with new dentures.MethodsAfter obtained their written informed consent 30 patients who visited Nihon University School of Dentistry at Matsudo Affiliated Hospital from March 2004 to November 2005 were asked to record their 3 consecutive day's meals and to take a picture of them. Furthermore, foods which they can eat with their dentures were examined the questionnaire developed by Hirai. Referring to the obtained records and pictures, one dietitian interviewed to confirm the exact intakes of meals. In addition, the masticatory ability was calculated using the questionnaire. The nutrient adequacy and masticatory score determined at the time of the first and second survey were examined by repeated-measures ANOVA. A p-value less than 0.05 was considered statistically significant.ResultThe total intake of energy and nutrients was almost over 100% in both the groups. However, no statistically significant difference was obtained. The masticatory score with the existing and new denture were 66.1 ± 18.5 and 58.3 ± 19.9, respectively. The score increased significantly in the new denture group when compared with that of the existing denture group.ConclusionThe self-evaluation of the masticatory function improved after the switch from the old to new dentures.     

Influence of a Brazilian wild green propolis on the enamel mineral loss and Streptococcus mutans’ count in dental biofilm

ObjectiveThis study investigated the anti-demineralizing and antibacterial effects of a propolis ethanolic extract (EEP) against Streptococcus mutans dental biofilm.DesignBlocks of sound bovine enamel (n = 24) were fixed on polystyrene plates. S. mutans inoculum (ATCC 25175) and culture media were added (48 h–37 °C) to form biofilm. Blocks with biofilm received daily treatment (30 μL/1 min), for 5 days, as following: G1 (EEP 33.3%); G2 (chlorhexidine digluconate 0.12%); G3 (ethanol 80%); and G4 (Milli-Q water). G5 and G6 were blocks without biofilm that received only EEP and Milli-Q water, respectively. Final surface hardness was evaluated and the percentage of hardness loss (%HL) was calculated. The EEP extract pH and total solids were determined. S. mutans count was expressed by log₁₀ scale of Colony-Forming Units (CFU/mL). One way ANOVA was used to compare results which differed at a 95% significance level.ResultsG2 presented the lowest average %HL value (68.44% ± 12.98) (p = 0.010), while G4 presented the highest (90.49% ± 5.38%HL) (p = 0.007). G1 showed %HL (84.41% ± 2.77) similar to G3 (87.80% ± 6.89) (p = 0.477). Groups G5 and G6 presented %HL = 16.11% ± 7.92 and 20.55% ± 10.65; respectively (p = 0.952). G1 and G4 differed as regards to S. mutans count: 7.26 ± 0.08 and 8.29 ± 0.17 CFU/mL, respectively (p = 0.001). The lowest bacterial count was observed in chlorhexidine group (G2 = 6.79 ± 0.10 CFU/mL) (p = 0.043). There was no difference between S. mutans count of G3 and G4 (p = 0.435). The EEP showed pH 4.8 and total soluble solids content = 25.9 Brix.ConclusionThe EEP seems to be a potent antibacterial substance against S. mutans dental biofilm, but presented no inhibitory action on the de-remineralization of caries process.     

Evaluation of the Candida albicans removal and mechanical properties of denture acrylics cleaned by a low-cost powered toothbrush

PurposeTo investigate the effects of using a low-cost powered toothbrush for cleaning on dental prostheses made of heat polymerized poly(methyl methacrylate), PMMA.MethodsHeat cured PMMA specimens beam with the dimensions of 45.0 mm × 6.5 mm × 4.5 mm were fabricated. The specimens were kept in water storage at 37 °C constant temperature for 0, 1, 7, 15, 30 and 60 days and randomly assigned for testing or control. Test specimens underwent brushing by using a powered toothbrush at an applied force of 2.00 N for 22 min with water as medium. Surface roughness measurement (R_a), flexural strength and efficacy of brushing to remove coated Candida albicans biofilm were investigated.ResultsThe results of the mean surface roughness value and the flexural strength were analysed by using two-way ANOVA and Tukey post hoc test at 5% significance level. In general, the specimens showed no significant changes in flexural strength after brushing. However, the flexural strength and the surface roughness value were significantly lower in specimens group after 7 days in water storage compared to the control. SEM micrographs of post-brushed specimens revealed satisfactory removal of C. albicans biofilm.ConclusionA low-cost powered toothbrush together with a liquid medium successfully removed C. albicans biofilm on dental acrylic PMMA-based prostheses, without compromising the mechanical properties.     

Antibacterial response of oral microcosm biofilm to nano-zinc oxide in adhesive resin

ObjectiveVarious nanoparticles are currently under investigation to impart biointeractivity for dental materials. This study aimed to: (1) formulate an experimental dental adhesive containing ZnO nanoparticles; (2) evaluate its chemical and mechanical properties; and (3) assess the antibacterial response against oral microcosm biofilm.MethodsNanosized ZnO was chemically and morphologically evaluated. ZnO was incorporated at 0 (G_CTRL), 2.5 (G_2.5%), 5 (G_5%) and 7.5 (G_5%) wt.% in an experimental dental adhesive. The adhesives were evaluated for the degree of conversion (DC), flexural strength (FS), and elastic modulus (E). The antibacterial activity was evaluated using a 48 h-microcosm biofilm model after the formation of acquired pellicle on samples’ surfaces. Colony-forming units (CFU), metabolic activity, and live/dead staining were assessed.ResultsNanosized ZnO presented characteristic peaks of Zn-O bonds, and the particles were arranged in agglomerates. The DC ranged from 62.21 (±1.05) % for G_Ctrl to 46.15 (±1.23) % for G_7.5% (p < 0.05). G_7.5% showed lower FS compared to all groups (p < 0.05). Despite achieving higher E (p < 0.05), G_2.5% did not show differences for G_Ctrl regarding the FS (p > 0.05). G_7.5% had lower CFU/mL compared to G_Ctrl for mutans streptococci (p < 0.05) and total microorganisms (p < 0.05), besides presenting lower metabolic activity (p < 0.05) and higher dead bacteria via biofilm staining.SignificanceThe dental adhesives' physicochemical properties were similar to commercial adhesives and in compliance with ISO recommendations. G_7.5% restricted the growth of oral microcosm biofilm without impairing the physicochemical performance.     

Evaluation of antibiofilm and mechanical properties of new nanocomposites based on acrylic resins and silver vanadate nanoparticles

ObjectiveThe purpose of this study was evaluate, for the first time, the impact of incorporation of nanostructured silver vanadate (β-AgVO₃) in antibiofilm and mechanical properties of dental acrylic resins (poly(methyl methacrylate), PMMA).DesignThe β-AgVO₃ was synthesized and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and microanalysis (SEM/EDS). Resins specimens were prepared with 0–10% wt.% β-AgVO₃ and characterized by SEM, XRD and optical microscopy_. The antibiofim activity of the samples against Candida albicans and Streptococcus mutans was investigated by XTT reduction test, colony-forming units (CFUs), and confocal laser scanning microscopy (CLSM). The flexural strength, hardness, and surface roughness of the samples containing β-AgVO₃ were compared with the pure PMMA matrix.ResultsThe incorporation of 10% β-AgVO₃ significantly reduced the metabolic activity of C. albicans and S. mutans (p < 0.05). There was a reduction in microbial load (CFU/mL) of microorganisms for the different concentrations used (p < 0.05), which was confirmed by confocal microscopy. The addition of β-AgVO₃ did not change the mechanical properties of hardness and surface roughness of the resins (p > 0.05). However, flexural strength decreased with the addition of amounts greater than 1% (p < 0.05).Conclusionsβ-AgVO₃ additions in dental acrylic resin may have an impact on inhibition of biofilm of main microorganisms associated with dental prostheses. However, the viability of clinical use should be evaluated in function of changed promoted in some mechanical properties.     

Microhardness of resin composite materials light-cured through fiber reinforced composite

ObjectivesTo compare polymerization efficiency of resin composite basing materials when light-cured through resin composite and fiber reinforced composite (FRC) by testing microhardness.MethodsSimulated indirect restorations were prepared by application of resin composite (Clearfil AP-X) or FRC (EverStick) to nylon rings with 1.5 mm thickness and 8 mm diameter, followed by light-curing. Resin composite basing material (Clearfil Majesty Flow or Clearfil AP-X) was applied to identical rings and light-cured through the simulated indirect restorations with exposure times of 20, 40, or 60 s. Light-curing though a ring without resin material (=no indirect restoration) served as control. For each combination of basing material and indirect restoration 10 specimens were prepared for each exposure time. Top and bottom surface Vickers microhardness numbers (VHNs) of basing materials were recorded after 24 h.ResultsAfter 60 s exposure time, VHNs with indirect FRC were not different from control VHNs, while VHNs with indirect resin composite were significantly lower (p < 0.001). Linear regression analysis revealed that resin composite basing material used had the greatest effect on top and bottom VHNs (p < 0.001). The presence of an indirect restoration resulted in decreased VHNs (p < 0.001), with resin composite resulting in lower VHNs when compared to FRC. Moreover, a longer exposure time resulted in increased VHNs (p < 0.001).SignificanceResults suggest that polymerization of resin composite basing materials is more effective when light-curing through an FRC than through a resin composite indirect restoration. Prolonging of exposure time, however, is necessary when compared to light-curing without presence of indirect restoration material.     

Self-cured resin modified by quaternary ammonium methacrylates and chlorhexidine: Cytotoxicity,antimicrobial, physical,and mechanical properties

ObjectiveTo evaluate the addition of dimethylaminohexadecyl methacrylate (DMAHDM) and chlorhexidine diacetate on cytotoxicity, antimicrobial activity, physical, and mechanical properties of a self-cured resin.Methods132 disk-shaped and 48 rectangular specimens were divided into four experimental groups as described: Control Group (CG – no addition), dCHX (1%), DMAHDM (5%), and DMAHDM + dCHX (5% + 1%). The biofilm viability, flexural strength (FS - ISO 20795-1:2013), surface roughness (SR), and color stability (ΔE) were analyzed after being stored for 4 weeks in distilled water and immersed for 72 h in coffee. Cytotoxicity was measured after 24 h, 3, and 7 days of elution using an MTT test on L929 cells (ISO 10993-5:2009). SR and ΔE were measured by a contact profilometer and a spectrophotometer using the CIELab parameter. Data were submitted to ANOVA and Bonferroni’s/Tukey’s tests (p ≤ 0.05).ResultsSignificant antimicrobial activity against Streptococcus mutans and Candida albicans was detected in all groups when compared to the CG (p < 0.05). Only the dCHX group, in 24 h of elution, demonstrated no cytotoxicity effects. There was a statistical difference for FS on the tested groups (p < 0.05). No differences were detected in the initial roughness’ measurements among the groups (p > 0.05). However, after storage and immersion in coffee, the groups containing DMAHDM presented with rougher surfaces and significantly lower color stability compared to the control (p < 0.05).SignificanceThe addition of dCHX and DMAHDM in self-cured resin presented antimicrobial properties; however, cytotoxicity, physical, and mechanical properties were compromised.