Microbiological, physicomechanical, and surface evaluation of an experimental self-curing acrylic resin containing halloysite nanotubes doped with chlorhexidine.

OBJECTIVE: The objective was to synthesize halloysite nanotubes loaded with chlorhexidine (HNT/CHX) and evaluate the antimicrobial activity, microhardness, color change, and surface characteristics of an experimental self-curing acrylic resin containing varying concentrations of the synthesized nanomaterial. METHODS: The characterization of HNT/CHX was carried out by calculating incorporation efficiency, morphological and compositional, chemical and thermal evaluations. SAR disks were made containing 0 %, 3 %, 5 %, and 10 % of HNT/CHX. Specimens (n = 3) were immersed in distilled water and spectral measurements were carried out using UV/Vis spectroscopy to evaluate the release of CHX for up to 50 days. The antimicrobial activity of the composite against Candida albicans and Streptococcus mutans was evaluated by disk-diffusion test. Microhardness, color analyses (ΔE), and surface roughness (Ra) (n = 9) were performed before and after 30 days of immersion. Data were analyzed using ANOVA/Bonferroni. {Results.} The incorporation efficiency of CHX into HNT was of 8.15 %. All test groups showed controlled and cumulative CHX release up to 30 or 50 days. Significant antimicrobial activity was verified against both microorganisms (p < 0.001). After the 30-day immersion period, the 10 % HNT/CHX group showed a significant increase in hardness (p < 0.05) and a progressive color change (p < 0.001). At T0, the 5 % and 10 % groups exhibited Ra values similar to the control group (p > 0.05), while at T30, all groups showed similar roughness values (p > 0.05). {Significance.} The modification of a SAR with HNT/CHX provides antimicrobial effect and controlled release of CHX, however, the immediate surface roughness in the 3 % group was compromised when compared to the control group.

Effect of sanitizing solutions on cobalt-chromium alloys for dental prostheses: A systematic review of in vitro studies.

STATEMENT OF PROBLEM: Given the wide use of cobalt-chromium (Co-Cr) alloys, especially for removable partial dentures, and the importance of chemical solutions to complement the cleaning of dental prostheses, safe disinfection products should be identified for the regular decontamination of Co-Cr dental prostheses. PURPOSE: The purpose of this systematic review of in vitro studies was to determine the effects on the properties of Co-Cr dental alloys of the various chemical agents used to clean dental prostheses. MATERIAL AND METHODS: In vitro studies were included based on a literature search conducted in March 2022 in the Medline/PubMed, SCOPUS, Web of Science, Virtual Health Library, and Embase databases. Independent reviewers performed the search, selection, extraction, and analysis of the data. The review was performed based on the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. The quality of the included articles was evaluated by using parameters adapted from the Consolidated Standards of Reporting Trials (CONSORT) guidelines, and the risk of bias analysis was performed based on previous studies. RESULTS: Among the 15 included studies, the chemical agents evaluated were alkaline peroxides and hypochlorites, mouthwashes containing cetylpyridinium chloride and chlorhexidine, diluted acids, and enzymes. Some peroxides produced increased ion release, surface roughness, and mass loss of the alloys. The hypochlorites were responsible for the greatest surface corrosion, yielding dark stains, rough regions, and depressions. Acetic and peracetic acids and mouthwashes containing chlorhexidine and cetylpyridinium did not produce significant changes in Co-Cr alloys. Most studies presented moderate risk of bias. CONCLUSIONS: According to the included studies, mouth rinses containing cetylpyridinium chloride or chlorhexidine and solutions with acetic and peracetic acid could be safely used to chemically sanitize Co-Cr prostheses. Alkaline peroxides should be used with caution, and alkaline hypochlorite solutions should be avoided.

Effect of a continuous mechanical polishing protocol on the color stainability, microhardness, mass, and surface roughness of denture base acrylic resin.

STATEMENT OF PROBLEM: The acrylic resin used in dental prostheses, which is subject to changes in its properties caused by hygiene chemicals, brushing, and colored beverages, can benefit from mechanical polishing methods. However, studies evaluating whether such procedures can be performed continuously without damaging the prosthetic materials are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of a continuous mechanical polishing protocol on the color stainability, surface roughness, microhardness, and mass of a denture base acrylic resin. MATERIAL AND METHODS: The polishing protocol was tested in specimens submitted to one of the following conditions: immersion in coffee (CF) (n=20); toothbrushing (Br, 35 600 cycles in a brushing simulation machine) (n=20); and immersion in 1% sodium hypochlorite (HYP) (n=20). For each condition, half of the specimens were polished (aluminum oxide paste and felt wheel attached to an electric motor, 3000 rpm) at simulated biweekly intervals. Two groups (n=10) of specimens were immersed in distilled water and used as the control for the immersion groups. Thus, the present study consisted of a total of 8 groups (n=80). Before and after simulated periods of 12 and 24 months, surface roughness was evaluated by using a contact profilometer; a spectrophotometer was used to calculate color changes (ΔE00); and a Knoop microdurometer and a precision balance were used to assess microhardness and mass changes. Data were compared by using 2-way mixed ANOVA. The Tukey HSD and Student t tests were used for post hoc analysis (α=.05). RESULTS: The polishing influenced surface roughness (Br, CF, HYP: P<.001) and color stainability (Br: P=.008; CF: P<.001). Significant increase in roughness was observed for the Br and HYP groups, and the polishing significantly reduced roughness under all experimental conditions. In general, the polishing did not affect the microhardness and caused minimum wear of the acrylic resin. ΔE00 values were above the clinical perceptibility threshold (ΔE00>1.30) for the Br group, exceeding the clinical acceptability threshold for the CF group (ΔE00= 2.51). Polishing reduced ΔE00 in these groups, making values similar to those found in the groups immersed in distilled water. The color in the HYP group was not influenced by polishing. CONCLUSIONS: In general, the tested polishing protocol reduced the deleterious effects of brushing and contact with 1% sodium hypochlorite and coffee, reducing surface roughness and color change without affecting microhardness and mass in any clinically relevant way.

Effect of a continuous mechanical polishing protocol and toothbrushing on the surface roughness of acrylic resin teeth.

PURPOSE: To evaluate in vitro the effect of a continuous mechanical polishing protocol, performed in different periods, on the surface roughness of acrylic resin teeth subjected to toothbrushing (Br). METHODS: Artificial acrylic teeth (n=30) were randomly divided into three groups according to the polishing protocol and toothbrushing (Br): Br; Br+Pol15 (Br associated with a biweekly polishing); Br+Pol30 (monthly polishing). Br group was subjected to a total of 89,000 brushing cycles. Polishing was performed by applying aluminum oxide paste to the specimens with a felt wheel coupled to an electric motor (5 seconds, 3,000 rpm) after each 741 and 1482 brushing cycles for Br+Pol15 and Br+Pol30 groups, respectively. A contact profilometer and an analytical balance were used to measure surface roughness and mass changes before (T0) and after 1, 2, 3, and 5 years (T4) of simulated toothbrushing. Scanning electron microscopy (SEM) images were obtained. Differences among groups were tested by means of two-way ANOVA/Bonferroni tests (P= 0.05). RESULTS: Toothbrushing gradually increased surface roughness [T0 - 0.16 (0.01); T4 - 0.30 (0.10); P< 0.001]. The tested polishing promoted a significant roughness reduction (P< 0.001) for both biweekly [T4 - 0.09 (0.01) ] and monthly [T4 - 0.13 (0.02) ] regimes, and it did not influence the mass alterations caused by toothbrushing. SEM showed a smoother aspect of the material surface subjected to biweekly polishing with less defects caused by brushing abrasiveness. CLINICAL SIGNIFICANCE: In order to reduce the effects of various deleterious factors on the properties of acrylic resin for removable prostheses during their period of use, a frequent mechanical polishing protocol could increase clinical performance and extend the lifespan of these appliances. Furthermore, a polishing protocol by means of a simple technique could be employed by patients in a home environment.

Is a two-step impression mandatory for complete denture fabrication on the severely resorbed mandible? A randomized trial on mastication, patient satisfaction and adjustments.

OBJECTIVES: To compare one- vs two-step impression procedures for the provision of conventional complete dentures (CCDs) for edentulous individuals with severe mandibular resorption, in terms of (1) masticatory performance and ability; (2) satisfaction with mandibular CCDs; and (3) post-delivery adjustments. METHODS: Fifty-two patients requiring maxillary + mandibular CCDs were randomly divided into two parallel arms according to the impression method of the mandibular ridge: (SI) single impression with stock trays (irreversible hydrocolloid); (TI) two-step impression in custom trays, with border molding (impression compound) followed by the impression itself (polyether). Mastication performance was evaluated by a colorimetric test, whereas patients answered questions on masticatory ability and satisfaction with mandibular CCDs (100-mm visual analogue scale). The number of post-delivery sessions for adjustments were also quantified. Outcomes were assessed at 3 and 6 months after delivery. RESULTS: The masticatory performance was similar for both groups, regardless of time (3 months, P = 0.62; 6 months, P = 0.61). No significant difference was found for patient-reported (P > 0.05), i.e. masticatory ability (general ease of chewing and quality of grinding food; ability to chew specific foods), general satisfaction with the mandibular CCD (general satisfaction, comfort, aesthetics, ability to speak and to perform correct cleaning, retention and stability). Both methods resulted in a similar number of post-delivery adjustment sessions [SI: 3.8 (1.7); TI: 3.2 (1.4); P = 0.09]. CONCLUSIONS: Compared to a traditional approach, CCDs obtained from a single impression achieve similar masticatory performance/ability and patient satisfaction, even in patients with severely reabsorbed mandibular ridge. Both methods demand the same amount of post-delivery adjustment. CLINICAL SIGNIFICANCE: A simplified impression technique which eliminates the secondary impression can provide CCDs of good clinical quality, which influences the OHRQoL, and satisfaction in the same extent they would by a two-step procedure, even for patients with severely reabsorbed mandibular ridges (ClinicalTrials.gov: NCT02339194).

Is a two-step impression mandatory for complete denture fabrication on the severely resorbed mandible? A randomized trial on patient perception and denture quality.

OBJECTIVES: To evaluate the effectiveness of CCDs produced by two impression procedures for the mandibular ridge, in patients with severe mandibular atrophy. METHODS: Fifty-two completely edentulous patients with severely resorbed mandibles were randomly allocated into two groups according to the impression procedure of the mandibular ridge: SI - single impression (stock tray and irreversible hydrocolloid); TI - two-step impression (custom tray, border molding with compound, and polyether). Assessments of oral health related quality of life (OHRQoL, primary outcome) and denture satisfaction were performed by using validated questionnaires. Denture quality was evaluated by means of functional tests. RESULTS: Regardless of the technique, participants reported better OHRQoL (P < 0.001) in both follow-up periods (3 and 6 months after denture delivery), and groups resulted in similar OHIP-EDENT scores in its different domains (P > 0.05). Between-group differences were insignificant for general satisfaction (3 months, P = 0.699, 6 months, P = 0.392), as well as for aspects such as esthetics, comfort, mastication, speech, and prosthesis retention (P > 0.05). Overall clinical quality of the CCDs (P = 0.383) was similar between-group, as well as in specific aspects - interocclusal distance, occlusion, articulation, retention of the maxillary denture, and stability of both maxillary and mandibular dentures (P > 0.05). CONCLUSIONS: Mandibular CCDs based on a single impression technique showed quality levels comparable to those generated by a two-step impression, both from the patient and clinician perspective. CLINICAL SIGNIFICANCE: A simplified impression technique which eliminates the secondary impression can provide CCDs of good clinical quality, which influences the OHRQoL, and satisfaction in the same extent they would by a two-step procedure, even for patients with severely reabsorbed mandibular ridges. (ClinicalTrials.gov: NCT02339194).

Effect of beverage solutions and toothbrushing on the surface roughness, microhardness, and color stainability of a vitreous CAD-CAM lithium disilicate ceramic.

STATEMENT OF PROBLEM: Computer-aided design and computer-aided manufacturing (CAD-CAM) has enhanced the physicomechanical stability of ceramics. However, various factors in the oral cavity may impair the longevity of restorations by negatively affecting their properties. Appropriate surface treatments such as glaze application or mechanical polishing are necessary to diminish these effects. PURPOSE: The purpose of this in vitro study was to evaluate the influence of common beverages and toothbrushing on the surface roughness, microhardness, and color stainability of a vitreous CAD-CAM lithium disilicate ceramic with a glazed or mechanically polished surface. MATERIAL AND METHODS: Specimens (N=160) were divided into 2 groups according to the surface treatment method: polishing with abrasive disks or glaze application. Each group was subdivided (n=8) according to the immersion solution and toothbrushing: distilled water and distilled water plus brushing; coffee and coffee plus brushing; black tea and black tea plus brushing; red wine and red wine plus brushing; and cola and cola plus brushing. Before and after simulating a 5-year period of immersion and toothbrushing, a contact profilometer and a Vickers microhardness tester were used to measure the surface roughness and microhardness. CIELab parameters were assessed by using a portable spectrophotometer, and color differences were calculated by using the CIEDE2000 formula (ΔE00). Data were compared by using 3-way ANOVA/Bonferroni test for post hoc analysis (α=.05). RESULTS: Surface roughness increased irrespective of solution (P=.763), being influenced by surface treatment (P<.001), with the glazed groups presenting higher values. Microhardness decrease was influenced by solutions (P<.038) and surface treatment (P<.001), and glazing was associated with lower values. Irrespective of the surface treatment, color stainability was influenced by solutions (P<.001), with ΔE00 values for red wine being above the perceptibility threshold (ΔE00>1.30). No influence of toothbrushing was found for any parameter (P>.05). CONCLUSIONS: Despite its excellent mechanical properties, CAD-CAM lithium disilicate ceramic degraded after exposure to commonly consumed beverages. Irrespective of surface treatment, beverages decreased microhardness and caused color changes. Surface roughness increased, showing higher variation for glazed groups. Toothbrushing was unable to potentiate or diminish the observed effects. In general, the results showed that proper mechanical polishing can produce a surface with desirable properties.

Efficacy of a propolis solution for cleaning complete dentures.

PURPOSE: The efficacy of a propolis solution against denture biofilm was evaluated by means of an in vitro assessment and a cross-over randomized clinical trial. METHODS: Acrylic resin specimens were contaminated by Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Candida albicans, Candida glabrata, Candida parapsilosis, immersed in a (A) propolis solution, (B) saline or (C) alkaline peroxide, applied onto Petri plates with culture medium and after incubation the number of colonies was counted. For the clinical trial, 30 complete denture wearers were randomly assigned to groups (A) propolis solution, and (B) saline, following one of the sequences (I)A/B or (II) B/A. After each intervention, biofilm was quantified by means of digital photos taken from the intaglio surface and a microbiological quantification of Candida spp. and mutans streptococci was conducted. RESULTS: Both propolis solution and alkaline peroxide reduced the microbial counts for S. mutans and C. albicans with significant and greater effect for group C (P< 0.05). However, no difference was found clinically between the interventions. The propolis solution showed an intermediate antimicrobial effect against S. mutans and C. albicans. Also, it did not exert an immediate effect on denture biofilm. CLINICAL SIGNIFICANCE: A commercially available propolis-based cleanser solution was evaluated in vitro and clinically for the treatment of denture stomatitis. Although an immediate effect on denture biofilm was not observed after a single application, It showed antimicrobial effect against S. mutans and C. albicans.

Domestic use of a disclosing solution for denture hygiene: a randomised trial.

OBJECTIVES: The purpose of this study was to investigate the effect of the domestic use of a disclosing agent for denture hygiene. MATERIALS AND METHODS: Completely edentulous participants wearing maxillary dentures were randomly assigned to one of the three intervention groups: (1) Follow-up only (control; n = 12); (2) Oral and denture hygiene instructions (n = 10); (3) Instructions associated with the home use of a disclosing agent (1% neutral red; n = 10). Biofilm coverage area (%) over internal and external surfaces of the maxillary denture was assessed at baseline and after 14 and 90 days. Data were evaluated by generalised estimating equations based on score tests (alpha = 0.05). RESULTS: The participants presented low changes for areas of biofilm coverage (14 days (%): internal: GI = 1.4 +/- 0.9; GII = 1.5 +/- 1.3; GIII = -0.4 +/- 0.9; external: GI = 1.4 +/- 1.5; GII = 1.5 +/- 1.4; GIII = -0.4 +/- 0.9; 90 days (%): internal: GI = 2.0 +/- 0.9; GII = 2.2 +/- 1.4; GIII = 0.3 +/- 1.0; external: GI = 2.1 +/- 1.4; GII = 2.2 +/- 1.5; GIII = 0.3 +/- 0.9). Changes were similar for the three groups (p = 0.293) and were not influenced by the test time (p = 0.218). CONCLUSION: It can be concluded that the home use of a disclosing agent for denture hygiene does not improve the removal of the biofilm, particularly for patients with adequate oral hygiene habits.

Physical properties of a denture base acrylic resins after incorporation of anionic chargesde radicais aniônicos / Propriedades físicas de uma resina acrílica para base de prótese após a incorporação

This study evaluated the influence of methacrylic acid (MA) incorporation on hardness, roughness, and flexural strength of a denture base acrylic resin. Thirty-two circular and 40 rectangular specimens were divided into four groups, according to the concentration of MA substituted into the monomer component of a heat-polymerized acrylic resin, as follows: 0% (Control), 10%, 20% and 50% (v/v). The following properties were assessed: Vickers hardness, surface roughness, and flexural strength. Variables were analyzed by ANOVA/Tukey’s test (α=.05). For the four incorporated MA concentrations (0%, 10%, 20% and 50%), the following results were obtained for hardness (19.0±1.4A, 19.6±1.3A, 19.6±0.9A, 14.2±0.6B VHN), surface roughness (0.26±0.05A, 0.17±0.01AB, 0.18±0.03AB, 0.13±0.03B μm) and flexural strengh (96.3±8.3A, 98.8±6.2A, 102.4±8.6A, 106.3±13.7A MPa). The incorporation of MA may cause slight changes in the structure of the tested material, as evidenced by the hardness test. However, the values for surface roughness reduced as MA concentration increased, suggesting that MA addition may improve the acrylic resin texture.

Este estudo avaliou a influência da incorporação do ácido metacrílico (AM) sobre a dureza, rugosidade e resistência flexural de uma resina acrílica para base de próteses removíveis. Trinta e dois espécimes circulares e 40 retangulares foram divididos em quatro grupos, conforme a concentração de AM substituído no componente monomérico de uma resina acrílica termopolimerizável: 0% (Controle), 10%, 20% e 50% (v/v). As seguintes propriedades foram avaliadas: dureza Vickers, rugosidade superficial e resistência flexural. As variáveis foram analisadas por meio de ANOVA seguida pelo teste de Tukey (α=0,05). Para as concentrações de AM incorporadas (0%, 10%, 20% e 50%), os seguintes resultados foram obtidos para a dureza (19,0±1,4A, 19,6±1,3A, 19,6±0,9A, 14,2±0,6B VHN), rugosidade superficial (0,26±0,05A, 0,17±0,01AB, 0,18±0,03AB, 0,13±0,03B μm) e resistência flexural (96,3±8,3A, 98,8±6,2A, 102,4±8,6A, 106,3±13,7A MPa). A incorporação do AM pode causar mudanças discretas nas propriedades estruturais do material testado, como evidenciado pelo teste de dureza. No entanto, os valores de rugosidade diminuíram em proporção ao acréscimo de AM, sugerindo que essa incorporação pode melhorar a textura da resina acrílica para base protética.