Influence of inorganic nanoparticles on dental materials' mechanical properties. A narrative review.

Inorganic nanoparticles have been widely incorporated in conventional dental materials to help in improving their properties. The literature has shown that incorporating nanoparticles in dental materials in different specialties could have a positive effect on reinforcing the mechanical properties of those materials; however, there was no consensus on the effectiveness of using nanoparticles in enhancing the mechanical properties of dental materials, due to the variety of the properties of nanoparticles itself and their effect on the mechanical properties. This article attempted to analytically review all the studies that assessed the effect of different types of inorganic nanoparticles on the most commonly used dental materials in dental specialties such as polymethyl methacrylate, glass ionomer cement, resin composite, resin adhesive, orthodontic adhesive, and endodontic sealer. The results had shown that those inorganic nanoparticles demonstrated positive potential in improving those mechanical properties in most of the dental materials studied. That potential was attributed to the ultra-small sizes and unique physical and chemical qualities that those inorganic nanoparticles possess, together with the significant surface area to volume ratio. It was concluded from this comprehensive analysis that while a definitive recommendation cannot be provided due to the variety of nanoparticle types, shapes, and incorporated dental material, the consensus suggests using nanoparticles in low concentrations less than 1% by weight along with a silane coupling agent to minimize agglomeration issues and benefit from their properties.

Cytotoxic effects of dose dependent inorganic magnesium oxide nanoparticles on the reproductive organs of rats.

INTRODUCTION: Magnesium oxide nanoparticles (MgO NPs) have a variety of applications that have contributed to their elevated popularity, however, the safety and toxic effects on humans are also of concern with these increased applications. There is insufficient data regarding the effect of MgO NPs on reproductive organs, which are crucial aspects to the body's vital physiological functions. The present study was undertaken in male and female rats to assess the reproductive toxicological potential of two doses (low versus high) of MgO NPs on testicular and ovarian tissues. The toxicity was evaluated using histological, hormonal, and oxidative parameters. MATERIAL AND METHODS: In this work, magnesium oxide nanoparticles (MgO NPs) were synthesized by the sol-gel route and were characterized by X ray diffraction analysis (XRD) and Fourier transform infra-red spectroscopy (FTIR). Forty-eight adult Wister albino rats were used in this experiment which were divided into groups of male and female, and then further into control, low dose MgO NPs, and high dose MgO NPs. The low dose used was 131.5 mg/kg b.w. (1/10 LD50) while the high dose used was 263 mg/kg b.w. (1/5 LD50). All doses were given orally by gastric tube. After 4 weeks, blood samples were collected to investigate the level of sex hormones and both ovarian and testicular tissues were examined for variable oxidative parameters and histopathological changes by light microscopy. RESULTS: The obtained findings showed that high dose of MgO NPs produced considerable changes in sex hormones and stress parameters in both male and female rats in comparison to the low dose and control groups. Histomorphometric analysis demonstrated the presence of histopathological alterations in the testicular and ovarian tissues. CONCLUSION: The results of this study showed dose-dependent adverse effects of MgO NPs on the testis and ovary both functionally and histopathologically as compared to the control rats.

Effect of non-rigid connector on the stress distribution of tooth-implant supported fixed prostheses using different implant length and diameter: A comparative 3D finite element study.

PURPOSE: To investigate the significance of the connector type on stress dissemination within the tooth-implant-supported fixed dental prostheses in the mandibular posterior region with different combinations of implant diameter and length by means of finite element analysis (FEA). MATERIALS AND METHODS: Six models of different designs for tooth-implant fixed dental prosthesis (FDPs) were simulated and divided into two main groups. Implant lengths were 10, 11.5, and 13 mm while implant diameters were 3.7, 4.7, and 5.7 mm. The main difference between the groups was the connector type. Models were evaluated using 3D FEA (Solidworks Premium 2018 × 64 Edition). Group A tooth-implant FDPs (5.7 mm × 10 mm) had a mesial and distal rigid connector while group B tooth-implant FDPs (3.7 mm × 10 mm, 3.7 mm × 11.5 mm, 3.7 mm × 13 mm, 4.7 mm × 10 mm and 5.7 mm × 10 mm) had a mesial non-rigid connector in their design between the pontic and the tooth. Models were analyzed to determine the magnitude of von Misses Stresses at six specific zones (fixed dental prosthesis, bone around distal implant, bone around tooth, cementum, periodontal ligament, implant) under vertical occlusal loading of 100 N after meshing and assigning the material properties. RESULTS: Stress values around the supporting bone were significantly higher in Group B (tooth-implant FDP with non-rigid connection) when compared to Group A (tooth-implant FDP with rigid connection). Also, the stresses measured at the FDP level showed that the rigid connection group (5.7 mm × 10 mm) exhibited 26% lower stress values when compared to the non-rigid group (5.7 mm × 10 mm). CONCLUSIONS: Implant-tooth FDPs with rigid connector design using the combination of implant diameter and length (5.7 mm × 10 mm) demonstrated a better design modality thus predicting a higher success rate and more longevity than using the non-rigid connection option.

Noninvasive Adaptation Appraisal of Antimicrobial Nano-Filled Composite.

OBJECTIVE: The aim of this research was to assess the effect of incorporating zein-coated magnesium oxide (zMgO) nanofillers to resin-based composite on the internal adaptation of the restorations using cross-polarisation optical coherence tomography (CP-OCT). METHODS: Thirty noncarious human molar teeth were used. Class V cavities (3 × 5 mm) were prepared on the buccal and lingual surfaces of each tooth. Clearfil SE Bond 2 was applied to all the cavities and then the teeth were divided into 3 groups (n = 10) as follows: group 1-restored with N-Flow composite; group 2 and group 3-restored with N-Flow composite mixed with different zMgO nanoparticle concentrations (0.3% and 0.5% by weight, respectively) and then light cured using an LED curing device. Specimens were examined for interfacial adaptation examination under CP-OCT. Characterisation of the dental composite incorporating zMgO was done by Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Results were analysed with Kruskall-Wallis test followed by Mann-Whitney U test, at a significance level of P < .05. RESULTS: XRD spectra exhibited the sharp peaks of zMgO in the composite enhanced with zMgO nanoparticles. FESEM analysis showed a uniform distribution of the zMgO nanoparticles in the composite and FTIR illustrated no change in the spectra. The gap percentage along the cavity floor was significantly lower in groups 2 and 3 in comparison to group 1 (P < .05). Also there was a significant difference in gap percentages between groups 2 and 3 (P < .05), with group 3 showing the lowest gap percentage. CONCLUSIONS: The incorporation of 0.3% and 0.5% zMgO nanoparticles in flowable composite assists in improving the internal adaptation of the composite to the tooth surface.

The Effect of Implant Length and Diameter on Stress Distribution of Tooth-Implant and Implant Supported Fixed Prostheses: An In Vitro Finite Element Analysis Study.

The aim of this study is to evaluate the effectiveness of the implant diameter and length on force dissemination of tooth-implant and implant retained fixed restorations. A finite analysis model was used via a 3D simulation of a unilateral mandibular Kennedy Class I arch. Through thresholding the resultant assembly, a region of interest was selected from the computed tomography (CT) scan. Details of the diameter (D) and length (L) of implant were introduced. Ds used were 3.7, 4.7, and 5.7, while Ls used were 10, 11.5, and 13. The constant was the use of rigid connectors in both designs (implant-implant and implant-tooth fixed partial dentures [FPDs]) and the mesial implant (D 3.7 and L 11.5). Stress in cancellous bone around mesial abutment, which is the second premolar in tooth-implant FPD and mesial implant in the implant-implant FPD, revealed that the stress was significantly lower in tooth-implant FPD when compared with implant-implant FPD (21.1 ± 0.00 vs 46.1 ± 0.00, P < .001). Stress distribution in the bone around any implant depends on several factors such as diameter, length, and tooth-implant vs implant-implant support. The implant diameter was more significant for improved stress distribution than implant length. A moderate increase in the length of the implant consequently reduced stress.

Appraisal of empathy among dental interns and postgraduate students at King Abdulaziz University: A cross-sectional study.

PURPOSE/OBJECTIVES: Empathetic communication of dentists with their patients is a primary characteristic of their health care. This study aims to evaluate dental students' empathy levels during the transitional period of internship and postgraduate studies of different specialties at one of the oldest dental schools in Saudi Arabia and explore how this empathy was affected by gender, age, and study duration. METHODS: In this study, the self-reported empathy level among the participants was assessed using the Jefferson scale of empathy-student version (JSE-HPS). This survey includes a 20-question Likert scale formulated to measure clinical empathy in health care professionals. The JSE-HPS was distributed to all registered dental interns and postgraduate students during the academic year 2019-20 in King Abdulaziz University Faculty of Dentistry (KAUFD), Jeddah, Saudi Arabia. RESULTS: Mean total score of empathy of the participants was (101.07 ± 14.8) with a response rate of 89%. A statistically significant higher empathy score appeared among dental postgraduate students in general (p = 0.04) and specifically among the females (p = 0.04) and those with postgraduate programs for more than four years, (p = 0.02). Dental postgraduate students scored significantly higher in the parameters of standing in patients' shoes (p = 0.02). CONCLUSION: Gender, academic level, and duration of postgraduates' studies influenced empathy more than the age of the dental graduates in KAUFD. Our recommendation is to integrate empathy into the dental curriculum emphasizing interactive communication skills and early patient contact.

Assessment of the dose-dependent biochemical and cytotoxicity of zein-coated MgO nanowires in male and female albino rats.

Introduction: Recently, zein-coated MgO nanowires were synthesized, which could be promising as an effective antimicrobial compounds that can be combined in the preparation of a diversity of new dental formulations. However, there is a deficiency of information concerning their toxicological profile regarding the human health.Objective: This in vivo study aimed to explore the hepato- and nephrotoxicity of low versus high doses of zein-coated MgO nanowires in rats.Materials and Methods: A 21-day recurrent dose toxicity research was carried out. Wistar rats were divided into 2 main groups, males and females (n = 18). Each group was further subdivided into 3 subgroups: control, MgO-zein nanowires low dose, MgO-zein nanowires high dose. The low dose used was 100 mg/kg while the high dose used was 200 mg/kg.Results: The results showed that MgO-zein nanowires at both doses did not affect the electrolytes levels compared to the control levels. Also, they did not produce any significant alteration in liver function markers in both rats' genders. MgO-zein nanowires at both doses did not produce any effective alteration in serum creatinine in treated rats of both genders. Moreover, very minimal histological alterations were observed in both doses of MgO-zein nanowires in liver and kidney of both genders.Conclusion: Based on the observed safety of zein-coated MgO nanowires, it can be utilized as an effective antimicrobial compound that can be combined in the preparation of a diversity of new dental formulations.KEY MESSAGESMgO NPs are globally used in multiple fields including the therapeutic field.Zein has wide pharmaceutical applications especially coating the tablet over sugar.There are no cytotoxic studies that investigate MgO-zein nanowires safety until now.

In vitro Investigation of the Antimicrobial Activity of Mouth Washes Incorporating Zein-Coated Magnesium Oxide Nanoparticles.

PURPOSE: This in vitro study was undertaken to investigate the antimicrobial effect of distinctive oral mouth washes after the addition of zein-coated (Magnesium oxide) MgO nanoparticles on exemplary of some oral microorganisms. MATERIALS AND METHODS: Three hundred and twelve samples were used in this study. A set of five concentrations of MgO nanoparticles with zein and without zein-coating were incorporated into three oral mouth washes: Listerine zero, Listerine total control and Oral B in the mass percentages of 0.3%, 0.5%, 1%, 2%, 5% and 10%, in addition to controls with no MgO nanoparticles. The antimicrobial effect of three mouth washes with variable concentrations of MgO was tested against the following organisms: Staphylococcus aureus, Streptococcus mutans, Enterococcus faecalis and Candida albicans using the disc diffusion test (DDT) and direct contact test (DCT). Data were analyzed using one-way ANOVA statistical test. RESULTS: The tested mouthwashes with zein-coated MgO nanoparticles showed significant differences of antimicrobial activity on S. mutans, S. aureus, E. faecalis, and C. albicans in the disc diffusion test. While in the DCT, all tested mouthwashes with MgO nanoparticles with and without zein coating showed antimicrobial activity on all tested microorganisms. CONCLUSION: Zein-coated MgO nanoparticles may be considered as a potential antimicrobial agent when added to oral mouthwashes. Future analysis, including in vivo studies, is required in order to incorporate zein/MgO nanoparticles into oral mouthwashes that may improve its antibacterial property.

Effect of Two Implant-supported Partial Overdenture Attachment Design on the Periodontal Health.

OBJECTIVE: This study aimed to evaluate and compare the effect of locator attachment and ball and socket (BS) attachment on the peri-implant and periabutment supporting structures on clinical pocket depth and gingival index in cases of limited interarch spaces in mandibular Kennedy class I implant-supported removable partial overdentures. MATERIALS AND METHODS: A comparative clinical trial was conducted among twenty partially edentulous patients aged 30-60 years. The study participants were randomly divided into two study groups based on the attachment system used: group I - locator attachment, and group II - BS attachment. Two implants were positioned in the 1st or 2nd molar area following the two-stage surgical protocol. Evaluation of the peri-implant and periabutment supporting structures was done at the time of overdenture insertion and after 6, 12, and 18 months by measuring the pocket depth and gingival index. Inter- and intragroup comparisons were done using independent-samples t test and paired-sample t test respectively. p < 0.05 was considered statistically significant. RESULTS: It was observed that there was a statistically significant increase in the pocket depth around the implant as well as the abutment in both groups at 6, 12, and 18 months when compared to baseline. Intergroup comparison for pocket depth and gingival index revealed nonsignificant results. However, the values were higher in the BS group. CONCLUSION: The locator attachment group had lower, though statistically not significant, pocket depth and gingival index scores around both the dental implant and the natural abutment as compared with the BS attachment. CLINICAL SIGNIFICANCE: Gingival health surrounding dental implant attachments is very crucial for the long-term success of dental implant, this could help the clinician to select the proper design for implant attachment underneath the over denture prosthesis.

Stress Analysis for Different Designs of Implant-borne and Tooth-implant Fixed Partial Dentures in Mandibular Posterior Region.

AIM: The utilization of fixed partial dentures (FPD) ceramic frameworks for replacing the missing posterior teeth is observed to have reported high failure rates. For this reason, 3-units FPD are designed and used extensively in the clinical practices, particularly for posterior mandibular region. The current study however, aims to carry out an evaluation of different stress patterns that are induced in a 3-units FPD within posterior part of mandible using finite element analysis (FEA). MATERIALS AND METHODS: Different modalities of the implant-supported FPDs such as type of connector, length and diameter of implants were taken into account. A three-dimensional (3D) model simulation of a mandibular Kennedy class II removal partial denture (RPD) was designed from a computerized tomography (CT) input with digital imaging communication on medicine (DICOM) format. In addition, occlusal load of 100 N was also used for central fossae of first premolar, first molar and second molar of the 3-units' reconstruction for each model. The magnitude of von Mises stress including minimum stress, maximum stress and average stress were also evaluated for each loading condition. RESULTS: The findings of the current study showed evidence that tooth-implant design with a nonrigid connector has significantly increased the average stress. Furthermore, it was observed that rigid connector has considerably minimized the stress within the tooth-implant-supported FPD. CONCLUSION: The study concluded that stress designs significantly influence the stress distribution around the bone. CLINICAL SIGNIFICANCE: This study gives some guidance and criteria for the selection of the type of fixed implant prosthesis in the posterior mandibular region.

Marginal and internal adaptation of ceramic crown restorations fabricated with CAD/CAM technology and the heat-press technique.

STATEMENT OF PROBLEM: The accuracy of chairside computer-aided design and computer-aided manufacturing (CAD/CAM) restorations is questionable, and the effect of the die spacer settings is not well stated in the literature. PURPOSE: The purpose of the study was to evaluate the marginal and internal adaptation of E4D crowns fabricated with different spacer thicknesses and to compare these crowns with those fabricated with the heat-press technique. MATERIAL AND METHODS: The E4D system was used to fabricate 30 crowns for the first 3 groups, with different spacer thickness settings: 30 µm, 60 µm, and 100 µm. In the fourth group, 10 lithium disilicate crowns were fabricated with the heat-press technique. The occlusal gap, axial gap, vertical marginal gap, and absolute marginal discrepancy were evaluated by x-ray microtomography. Statistical significance was assessed with the Kruskal-Wallis test (α=.05). For post hoc analyses, the Mann-Whitney U test was used alongside the Bonferroni correction for multiple comparisons (α=.008). RESULTS: Within the CAD/CAM groups, the 30-µm spacer thickness resulted in the lowest median axial gap (90.04 µm), whereas the 60-µm spacer thickness resulted in the lowest median occlusal gap (152.39 µm). The median marginal gap values of the CAD/CAM-60 group (49.35 µm) and CAD/CAM-100 group (46.65 µm) were lower than those of the CAD/CAM-30 group (55.18 µm). No significant differences among the CAD/CAM groups were observed for absolute marginal discrepancy. The heat-press group had significantly different values than those of the CAD/CAM groups. CONCLUSION: The spacer thickness and fabrication technique affected the adaptation of ceramic crowns. The heat-press group yielded the best marginal and internal crown adaptation results. The 30- or 60-µm spacer settings are recommended for the E4D CAD/CAM system.