Flexural strength, biocompatibility, and antimicrobial activity of a polymethyl methacrylate denture resin enhanced with graphene and silver nanoparticles.

OBJECTIVE: The study evaluates the effect of adding graphene-Ag nanoparticles (G-AgNp) to a PMMA auto-polymerizing resin, with focus on antibacterial activity, cytotoxicity, monomer release, and mechanical properties. MATERIALS AND METHODS: Auto-polymerizing acrylic resin (M) was loaded with 1 wt% G-AgNp (P1) and 2 wt% G-AgNp (P2). Methyl methacrylate monomer release (MMA) was measured after immersion of the samples in chloroform and cell medium respectively. Cell viability was assessed on dysplastic oral keratinocytes (DOK) and dental pulp stem cells. Oxidative stress and inflammatory response following exposure of dysplastic oral keratinocytes to the experimental resins was evaluated. Antibacterial activity against Staphylococcus aureus, Streptococcus mutans and Escherichia coli and also flexural strength of the resins were assessed. RESULTS: Residual monomer: For samples immersed in chloroform, MMA concentration reached high levels, 10.27 µg/g for sample P1; MMA increased at higher G-AgNp loading; 0.63 µg/g MMA was found in medium for P1, and less for sample P2. Cell viability: Both cell lines displayed a viability decrease, but remained above 75%, compared to controls, when exposed to undiluted samples. Inflammation: proinflammatory molecule TNF-α decreased when DOK cultures were exposed to G-AgNp samples. MDA levels indicated increased oxidative stress damage in cells treated with PMMA, confirmed by the antioxidant mechanism activation, while samples containing G-AgNp induced an antioxidant effect. All tested samples showed antibacterial properties against Gram-positive bacteria. Samples containing G-AgNp also exhibited bactericide action on E. coli. Mechanical properties: both samples containing G-AgNp improved flexural strength compared to the sample resin, measured through elastic strength parameters. CONCLUSIONS: PMMA resin loaded with G-AgNp presents promising antibacterial activity associated with minimal toxicity to human cells, in vitro, as well as improved flexural properties. CLINICAL RELEVANCE: These encouraging results obtained in vitro support further in vivo investigation, to thoroughly check whether the PMMA loaded with graphene-silver nanoparticles constitute an improvement over current denture materials.

Comparative Assessment of the Functional Parameters for Metal-Ceramic and All-Ceramic Teeth Restorations in Prosthetic Dentistry-A Literature Review.

The metal-ceramic fixed partial prosthesis is the golden standard for posterior tooth restorations. Following the demands of patients and clinicians for metal-free restorations, all-ceramic materials were developed as they offer an adequate alternative with better optical qualities and good mechanical properties. This study aims to carry out a bibliographic review to assess the survival rate and the biological and technical complications of all-ceramic and metal-ceramic fixed partial dentures. An electronic search for articles in the English language literature was performed using PubMed (MEDLINE). This literature review focused on research studies between 2010 and 2020 that performed clinical studies on tooth-supported fixed partial dentures with a mean follow-up of at least 3 years. All the studies, which analyzed the survival and complications of tooth-supported fixed partial dentures, were included. Thus, 14 studies reporting on 756 all-ceramic and 160 metal-ceramic fixed partial dentures met the inclusion criteria. A comparative analysis was carried out based on all the data existing in the studies included in this review. The metal-ceramic fixed partial dentures showed survival rates of 95% to 100% at 3-, 5-, and 10-year follow-up periods. Zirconia fixed partial dentures were reported to have survival rates of 81% to 100% at 3-, 5-, 9-, 10-year follow-up evaluations. The reinforced glass-ceramic fixed partial dentures showed survival rates of 70% to 93.35% at 5 years, while the alumina FPDs showed a survival rate of 68% at 3 years follow-up. The incidence of caries and loss of vitality were reported as higher for all-ceramic prostheses as compared to the metal-ceramic ones. A significant framework fracture was reported for glass-infiltrated alumina fixed partial dentures in comparison to metal-ceramic fixed partial dentures. All-ceramic and metal-ceramic restorations showed similar survival rates after 3 years, although all-ceramic restorations have problems with technical complications such as chipping, which can lead to framework fractures over time.

A survey on dental students' perception regarding online learning during the COVID-19 pandemic.

Background and aims: This study aimed to assess the students' opinion about the efficiency of online teaching and also about the methods and features to be implemented even after this pandemic period would pass. Methods: A questionnaire was formulated in order to evaluate the students' perception about the teaching methods used by the Faculty of Dentistry, which was distributed through email. Results: The answers of 208 students were analyzed. There were 157 women and 51 men, 119 were from Cluj County, while 89 were from other Romanian counties; 102 of the students were in the 4th year of study, while 62 were still in the preclinical years (1st, 2nd, 3rd), and the rest of 44 of the subjects, were in the 5th or 6th year of study. 85.8% of the respondents were satisfied with the traditional lectures, 51.7% considered that online lectures were more useful than the traditional. 187 (88.6%) of the students were satisfied with the traditional practical activities, while 37 (16.1%) believed that online activities were more useful to them, 111 (52.6%), believed that they were able to communicate better with the teacher during the online lectures. Conclusions: Overall positive responses were reported regarding the acceptability and usability of online learning. The students viewed online learning helpful as a supplement to their learning rather than a replacement for traditional teaching methods.

Oral Hygiene Habits of Complete Denture Wearers in Central Transylvania, Romania.

PURPOSE: To identify the oral hygiene habits and denture hygiene status (e.g. sociodemographic characteristics, general health status) of complete denture wearers in Central Transylvania, Romania. MATERIALS AND METHODS: This descriptive cross-sectional study was based on an original self-administered questionnaire. It included 162 patients who experienced complete tooth loss in one or both jaws and wore polymethylmethacrylate acrylic (PMMA) complete dentures. The exclusion criteria were partial dentures, dentures fabricated from materials other than PMMA, and the patient being unable to provide all the required information. The questionnaire solicited information regarding sociodemographic status, general health and oral hygiene-related habits. The dentures were clinically evaluated in order to assess denture hygiene. RESULTS: Most respondents were completely edentulous (38.0% wore maxillary dentures, 10.6% mandibular dentures, while 51.6% had both), with an average age above 60, all wearing dentures. The clinical evaluation of the dentures revealed that 12.3% exhibited optimal hygiene status, 40.1% good, 32.7% unsatisfactory and 14.8% bad, with more women than men having well-cleaned dentures. Cleaning frequency was found to be 2-3 times per day for 54.3% of the patients, with 93.2% of the subjects using a toothbrush and 76.5% using toothpaste. Most of the participants felt at ease with the cleaning procedures. Only 30.9% of the respondents reported denture removal overnight. The results showed that the hygiene of the patients' dentures was not correlated with their answers regarding oral hygiene habits. CONCLUSIONS: Competent oral health and denture hygiene promotion should be established, especially regarding nocturnal denture removal, denture hygiene methods, instruments and cleaning frequency.

Association of Graphene Silver Polymethyl Methacrylate (PMMA) with Photodynamic Therapy for Inactivation of Halitosis Responsible Bacteria in Denture Wearers.

(1) Background: Poor hygiene and denture presence in the oral cavity are factors that favor bacterial accumulation, the cause of halitosis and of various oral and general diseases. Aim: This study aimed to evaluate the possibility of inactivating bacteria associated with halitosis in acrylic denture wearers using polymethyl methacrylate resin enhanced with graphene silver nanoparticles and the effect of the resin association with extra oral photodynamic therapy. (2) Methods: Graphene silver nanoparticles in 1 and 2 wt% were added to a commercial acrylic resin powder. Three study groups containing samples from the three different materials were established. The first group was not exposed to the light treatment, and the other two were exposed to red light (laser and light emitting diode) after photosensitizer placement on the disk's surface. Samples were incubated with Porphyromonas gingivalis and Enterococcus faecalis. (3) Results: For both bacterial strains, inhibition zones were obtained, showing significant differences for the light-treated samples. (4) Conclusions: Denture resins with antibacterial properties associated with extra oral photodynamic therapy exhibited enhanced antibacterial effects. The procedure could be used as a safer and more efficient alternative technique against halitosis and oral infections in denture wearers.

The Influence of Graphene in Improvement of Physico-Mechanical Properties in PMMA Denture Base Resins.

The clinical performances of dental materials depend on their mechanical profiles, determining their long-term deformation and wear resistance. This paper describes a study on the mechanical properties, water absorption and morphological properties of a polymethyl methacrylate (PMMA) resin enriched with graphene-silver nanoparticles (Gr-Ag). Two different concentrations-1 and 2 wt.%-of Gr-Ag were loaded into the PMMA material. For the mechanical characterization, the compression behavior, flexural strength and tensile strength were evaluated. Optical microscopy in polarized light and scanning electron microscopy were used for filler analysis. The filler addition led to an improvement in all mechanical properties, with slight changes being derived from the filler content variation. Gr-Ag use led to an increase in the applied maximum loads. Moreover, 1 wt.% Gr-Ag determined an increase of 174% in the modulus of rupture, which indicates high flexibility.

Morpho-histological assessment of the periodontal support structures under the action of excessive occlusal forces and under the influence of nicotine.

Smoking and occlusal trauma are two factors that can interfere with bone homeostasis. The aim of this study was to evaluate the histocellular changes occurring in the periodontal ligament and alveolar bone during the action of excessive occlusal forces, and to assess the influence of nicotine on the alveolar bone loss in teeth subjected to occlusal trauma. MATERIALS AND METHODS: Fifty-six Wistar rats were randomized into seven groups (n=8). Animals were exposed to nicotine and occlusal trauma for 7, 14 and 30 days. Three groups were exposed to occlusal trauma alone, another three groups were exposed to occlusal trauma and nicotine, and one group was not exposed to any treatment. RESULTS: Periodontal lesions induced in the first stage (7-14 days) manifested by a moderate increase of the periodontal space, a multiplication, thickening and elongation of periodontal fibers, as well as their condensation in the middle area of the periradicular space. Regarding bone changes induced by occlusal trauma, groups 5 and 7 (occlusal trauma and nicotine administration) had higher bone losses compared to groups 1, 2, 3, 4 and 6. This study demonstrated that nicotine significantly affected the alveolar bone. CONCLUSIONS: The induced occlusal trauma caused obvious tissue damage. At the same time, it was found that nicotine enhanced alveolar bone resorption, increased tooth mobility and induced an exacerbation of inflammatory processes.