Biocompatibility of dental casting alloys: a review

Cytotoxicity and genotoxicity of orthodontic bands after aging: an in-vitro study

BACKGROUND

This investigation sought to evaluate cytotoxic and genotoxic effects of two different types of orthodontic bands after aging in acidic and neutral artificial saliva using human gingival fibroblast-like (HGF1-PI 1) cell lines.

METHODS

Two commercial brands of orthodontic molar bands (American orthodontic (AO) and 3 S-dental bands), commonly used by orthodontists, were tested. These bands were divided into four groups to examine the effects of aging following thermocycling, and pH variations (pH = 4.5 and pH = 7.4). Cytotoxicity was assessed using the MTT assay. Comet assay was used to evaluate genotoxicity.

RESULTS

Our results demonstrated that AO molar bands exhibited significant cytotoxic effect on gingiva cells following incubation in acidic condition compared to untreated control (P = 0.04), however no effect was observed at neutral condition. In contrast, 3 S-dental molar bands showed no significant differences at both conditions compared to control group. Regarding genotoxicity, DNA damage was evident for both brands at pH = 4.5, however, AO molar bands demonstrated longer comet tails compared to 3 S-dental molar bands. AO molar bands was also showed relatively DNA destruction at pH 7.4, while no genotoxicity was for 3 S-dental molar bands.

CONCLUSION

The results collectively showed that AO molar bands exhibited cytotoxicity only at acidic pH, while 3 S-dental molar bands showed no cytotoxic effects at either acidic or neutral conditions. Additionally, AO molar bands demonstrated greater genotoxicity than 3 S-dental molar bands at both pH levels. These data represented acceptable biocompatibility for both bands in neutral conditions. However, AO bands seem to become toxic for gingiva cells in acidic milieu.

Bond strength of 4META-MMA-TBB resin to a CAD/CAM composite resin block and analysis of acetone-insoluble cured resin residues at adhesive interfaces

This study investigated the adhesion of 4META-MMA-TBB resin to CAD/CAM composite resin blocks. CAD/CAM composite resin blocks were subjected to alumina blasting, ceramic primer treatment, or both, and then bonded with 4META-MMA-TBB resin. The tensile bond strength of 4META-MMA-TBB resin to blocks without surface treatment was approximately 20 MPa, but with surface treatment, it significantly improved to approximately 40 MPa. Cohesive failure was observed in some blocks with surface treatment with both alumina blasting and ceramic primer. As a result of Soxhlet extraction of the adhesive interface with acetone solvent and FT-IR spectrum analysis, it was found that PMMA remained on the block surface when surface treatment with both alumina blasting and ceramic primer were performed. These results demonstrated that the bond strength of 4META-MMA-TBB resin is significantly improved when both alumina blasting and ceramic primer are applied as surface pretreatment to the CAD/CAM composite resin block.

Marginal bone loss and soft tissue health around two-implant mandibular overdenture retained with milled versus selective laser melted cobalt chromium bar: a randomized clinical trial

BACKGROUND

To assess marginal bone loss and soft tissue health around two-implant mandibular overdenture retained with milled versus selective laser-melted cobalt chromium (Co-Cr) bars.

METHOD

This research was set to be a parallel, triple-blinded, randomised controlled trial. Twenty completely edentulous patients received new conventional complete dentures according to conventional techniques. Two implants were placed at mandibular canine areas bilaterally, and patients were randomly allocated into two equal groups: the milled Co-Cr bar group and the selective laser melted (SLM) Co-Cr bar group. Marginal bone loss (MBL), modified plaque index (mPI), modified gingival index (mGI), and probing depth (PD) were evaluated at 0-month (baseline), 6-month, and 12-month follow-up visits. Repeated measures ANOVA test and Bonferroni's post-hoc test were used for parametric data as PD, while for non-parametric data as MBL, mGI, and mPI, Mann-Whitney U test and Friedman's test were used. A P-value ≤ 0.05 was set as the statistical level of significance. The study protocol was approved by the Faculty Research Ethics Committee at Minia University (636 4/10/2022). Registration for the clinical trial was made retrospectively on clinicaltrials.gov with ID NCT06401200 at 04/30/2024.

RESULTS

The follow-up period (one year) was completed without a dropout. Regarding MBL, no statistically significant difference was found between the two groups throughout the study. However, the milled group showed significantly increased MBL from 0- to 6-month follow up period. In both groups, mPI increased significantly from 0- to 6-months post-loading. On the other hand, no statistically significant difference between the two groups was found regarding mPI and mGI throughout the study follow-up periods. The PD was significantly lower in the milled compared to the SLM group at the 6- and 12-month follow up period.

CONCLUSION

Two-implant mandibular overdenture retained with milled or SLM Co-Cr bar can provide an acceptable treatment option for completely edentulous patients regarding marginal bone loss and soft tissue outcomes.

Preparation and antibacterial evaluation of silver-doped zirconia for enhanced dental restoration performance

Because of its superior strength, esthetic properties, and excellent biocompatibility, zirconia is preferred for dental prosthetic such as crowns and bridges. However, zirconia crowns and bridges are susceptible to secondary caries owing to margin leakage. Silver is a well-known antibacterial agent, making it a desirable additive to zirconia crowns and bridges for secondary caries prevention. This study focuses on imparting zirconia composite with antibacterial properties to enhance its protective capacity in dental restorations. We used the sol-gel method to dope Ag into zirconia. Silver-doped zirconia powders were prepared at Zr:Ag molar ratios of 100:0,100:0.1, 100:0.5, 100:1, 100:3, and 100:5 (respective samples denoted as Ag-0, Ag-0.1, Ag-0.5, Ag-1, Ag-3, and Ag-5) and were subjected to firing at various temperatures (400 °C-1000 °C). We performed x-ray diffraction to investigate the crystal phase of these powders and x-ray fluorescence and field emission scanning electron microscopy to analyze their elemental composition and surface morphology, respectively. Moreover, we performed spectrophotometry to determine theL*a*b* color values, conducted dissolution tests, and quantified the Ag content through inductively coupled plasma optical emission spectroscopy. In addition, we studied the antibacterial activity of the samples. Analyses of the samples fired at ⩽600 °C revealed a predominantly white to grayish-white coloration and a tetragonal crystal phase. Firing at ⩾700 °C resulted in gray or dark gray coloration and a monoclinic crystal phase. The Ag content decreased after firing at 900 °C or 1000 °C. Ag-0.5 and above exhibited antibacterial activity against bothEscherichia coliandStaphylococcus aureus. Therefore, the minimum effective silver-doped zirconia sample was found to be Ag-0.5. This study allows the exploration of the antimicrobial potential of silver-doped zirconia materials in dental applications such as prosthdontical lining materials, promoting the development of innovative restorations with protective capacity against secondary caries.

Estimating Ni, Cr, Co, and Mo release from 3 dental casting alloys in saliva and blood at 6 and 12 months by using inductively coupled plasma mass spectroscopy

STATEMENT OF PROBLEM

The leaching of elements from long-term definitive prostheses, with saliva acting as an electrolyte, poses a biological concern. The approximate concentration in the biological samples that are considered clinically toxic ranges from 1 to 5000 nmol/L for Cr and Co, 1 to 200 nmol/L for Ni, and 1 to 20 nmol/L for Mo. While in vitro studies are available regarding the leaching of elements in artificial saliva, solutions containing protein, solutions of different pH, and different culture media, the in vivo effects of leaching in the biological sample with increasing time are unknown.

PURPOSE

The purpose of this clinical study was to quantify the Ni, Co, Cr, and Mo metals in saliva and blood before and after restoration with prostheses made from 3 different brands of dental casting alloy at 6 and 12 months.

MATERIAL AND METHODS

Three popular brands of Ni-Cr alloy with different compositions were evaluated. A total of 150 participants requiring a definitive prosthesis were enrolled and divided into 3 groups (n=50). Heavy metal levels from saliva and blood were measured by using the inductively coupled plasma mass spectroscopy method before cementation of the prosthesis and after 6 and 12 months.

RESULTS

The presence of Ni in saliva was in the range of 10.34 to 12.12 μg/L, Cr was 1.04 to 1.22 μg/L, and Mo was 1.04 to 1.08 μg/L over a period of 6 and 12 months after cementation of the metal prosthesis. The presence of Ni in blood was in the range of 6.35 to 14.45 μg/L and that of Cr was 9.09 to 16.16 μg/L over a period of 6 and 12 months after cementation. Co levels were not detected from any brands in saliva or blood, and Mo was detected only in the saliva samples.

CONCLUSIONS

Increased levels of Ni and Cr in saliva and blood from all 3 brands of base metal alloy at 6 and 12 months were observed at higher than threshold values.

A Comparison of the Structure and Selected Mechanical Properties of Cr/Co Alloys Obtained by Casting and Selective Laser Melting

Selective laser melting (SLM) technologies are becoming increasingly popular. The aim of the work is to compare the metallographic structure, hardness, and selected strength properties of alloys obtained by casting and by SLM, with a particular emphasis on fatigue strength. Twenty Cr/Co alloy bars were made by casting or SLM, and samples of appropriate dimensions were prepared for individual tests. The microstructures of the samples were tested by metallography, and then tested for hardness, impact strength, tensile strength, bending strength, and fatigue strength; they were also subjected to fracture after bending, tensile, fatigue, and impact tests, with the resulting fractures examined by scanning electron microscopy (SEM). Primary dendrites and small amounts of gas bubbles were present in the cast samples ground lengthwise. The SEM samples were more finer grained and uniform. Compared to the casting samples, the SLM samples demonstrated higher hardness, lower mean impact strength and higher tensile strength. The casting samples also displayed lower mean elongation values. The casting samples demonstrated slightly higher fatigue strength. The fractures of the casting samples showed an interdendritic character with clearly visible dendrites at the fracture, while those of the SLM samples were also intergranular, but finer grained. SLM generally results in better strength properties, while casting obtains slightly greater fatigue strength.

Soldering in Dentistry: An Updated Technical Review

INTRODUCTION

The need to permanently join two or more pieces of metal using heat is a frequent condition in various fields of medicine such as dentistry. Welding, brazing and soldering are permanent joining techniques between different metals that require in-depth background knowledge in order to obtain predictable results.

AIM

This review examines the different methods of joining metals using heat and their fields of application.

DISCUSSION

It is possible to create permanent metal joints in various phases of the creation of final products that will be used on the patient. In several cases, welds are also made directly by the manufacturer during industrial processing. In dentistry, dental laboratories perform complex welds mainly on dental prostheses and orthodontic appliances during the production process. It is also possible to obtain intraoral welding carried out by the clinician inside the patient's oral cavity. Welding can be carried out using combustible gases, electric current, infrared light and laser light through different technical procedures which must be chosen according to the specific needs and the metals to be joined.

CONCLUSIONS

It is useful for the dentist and dental technician to know the different welding methods, including those carried out in the factory by the manufacturer, to better understand the physical properties and mechanical resistance of the components marketed for the construction of prostheses and orthodontic appliances. The enormous variety of conditions in which those who practice welding can find themselves therefore presupposes in-depth knowledge in this field in order to apply the most suitable technique.

Oral galvanism related to dental implants

BACKGROUND

A range of different chemical interactions can generate an unexpected electronic current in a process called galvanism. Oral galvanism (OG) can also be generated by different chemical actions from diverse intraoral rehabilitated metals, including gold, copper, mercury, titanium, and titanium alloy. The main aim of this manuscript is to review OG, particularly focusing on titanium implants and related metallic materials. We searched the MEDLINE (PubMed), Embase, Scopus, and Google Scholar databases for relevant literature published through December 2019. The keywords included "galvanic current", "galvanism", "galvanic corrosion", "oral galvanism", combined with "oral", "oral cavity", "implant", and "saliva."

RESULTS

Out of 343 articles, 126 articles that met the inclusion criteria were reviewed. We examined and summarized research on OG through a division into four categories: definition and symptoms, diagnosis with testing methods, galvanic corrosion, and oral precancerous lesions with OG.

CONCLUSIONS

Patients with OG have high oral energy and current, and although this phenomenon may be due to the patient's mental illness, OG due to amalgam or mercury occurs. It is evident that the difference in electron potential caused by different elemental components such as titanium alloy and pure titanium, which are essential for manufacturing the implant fixture and the abutment, and chrome and nickel, which are essential for manufacturing the upper crown, causes OG. Since the oral cavity is equipped with an environment in which electric current can be transmitted easily due to saliva, it is imperative that clinicians review the systemic and local effects of salivation.

Polymeric Denture Base Materials: A Review

An ideal denture base must have good physical and mechanical properties, biocompatibility, and esthetic properties. Various polymeric materials have been used to construct denture bases. Polymethyl methacrylate (PMMA) is the most used biomaterial for dentures fabrication due to its favorable properties, which include ease of processing and pigmenting, sufficient mechanical properties, economy, and low toxicity. This article aimed to comprehensively review the current knowledge about denture base materials (DBMs) types, properties, modifications, applications, and construction methods. We searched for articles about denture base materials in PubMed, Scopus, and Embase. Journals covering topics including dental materials, prosthodontics, and restorative dentistry were also combed through. Denture base material variations, types, qualities, applications, and fabrication research published in English were considered. Although PMMA has several benefits and gained popularity as a denture base material, it has certain limitations and cannot be classified as an ideal biomaterial for fabricating dental prostheses. Accordingly, several studies have been performed to enhance the physical and mechanical properties of PMMA by chemical modifications and mechanical reinforcement using fibers, nanofillers, and hybrid materials. This review aimed to update the current knowledge about DBMs' types, properties, applications, and recent developments. There is a need for specific research to improve their biological properties due to patient and dental staff adverse reactions to possibly harmful substances produced during their manufacturing and use.

Cytotoxicity of Metal Ions Released from NiTi and Stainless Steel Orthodontic Appliances, Part 1: Surface Morphology and Ion Release Variations

Despite numerous studies on ion release from orthodontic appliances, no clear conclusions can be drawn due to complex interrelations of multiple factors. Therefore, as the first part of a comprehensive investigation of cytotoxicity of eluted ions, the objective of this study was to analyze four parts of a fixed orthodontic appliance. Specifically, NiTi archwires and stainless steel (SS) brackets, bands, and ligatures were immersed in artificial saliva and studied for morphological and chemical changes after 3-, 7-, and 14-day immersion, using the SEM/EDX technique. Ion release profiles were analyzed for all eluted ions using inductively coupled plasma mass spectrometry (ICP-MS). The results demonstrated dissimilar surface morphologies among parts of the fixed appliance, due to variations in manufacturing processes. The onset of pitting corrosion was observed for the SS brackets and bands in the as-received state. Protective oxide layers were not observed on any of the parts, but adherent layers developed on SS brackets and ligatures during immersion. Salt precipitation, mainly KCl, was also observed. ICP-MS proved to be more sensitive than SEM/EDX and exhibited results undetected by SEM/EDX. Ion release was an order-of-magnitude higher for SS bands compared to other parts, which was attributed to manufacturing procedure (welding). Ion release did not correlate with surface roughness.

Metal Ions Release from Welded Co-Cr Dental Alloys

Cobalt-chromium alloys (Co-Cr) are widely used in dentistry due to their excellent mechanical properties and corrosion resistance. Since prosthetic materials must be permanently stable in the oral cavity, it is very important to determine the release of ions from alloys in the oral cavity. In dentistry today, metals and alloys are mainly joined by laser and tungsten inert gas (TIG) welding. Therefore, in this work, the release of metal ions from six different Co-Cr alloys joined by these two welding methods was quantified to determine the effects of the welding method on an ion release. Static immersion tests, atomic absorption spectrometry and statistical analysis were performed for this purpose. The results showed that laser-welded alloys release a lower amount of metal ions compared to TIG-welded alloys.

Surface Characteristics and Adhesion of Veneering Composite Resin to PAEK-Based Substructure Restorative Materials

PURPOSE

To evaluate and compare the shear bond strength (SBS) of composite veneering material to polyetherketoneketone (PEKK), polyetheretherketone (PEEK), zirconia (YZ), and nickel-chromium alloy (NiCr) substructure restorative materials.

MATERIALS AND METHODS

Forty samples (12 × 2 mm) were prepared from four materials: PEKK, PEEK, zirconia, and NiCr alloy (n = 10). The Vickers hardness was evaluated before preparing the surface for bonding by shot-blasting using 110 μm Al₂ O₃ particles. The surface roughness (Ra) of each sample was determined using a noncontact optical profilometer. The veneering resin was bonded onto each sample following primer application. The prepared samples were then subjected to an SBS test using a universal testing machine at 0.5 mm/min crosshead speed. Failure modes and surface topography following debonding were assessed. The data were statistically analyzed using ANOVA and Tukey's post-hoc comparison test (p < 0.05).  RESULTS: The highest and lowest mean surface roughness was observed in PEEK (3.45 ±0.13 μm) and NiCr (1.87 ±0.07 μm) materials, respectively. A significant difference in roughness values was observed between the materials except for NiCr and YZ (p = 0.547). Concerning SBS, PEEK and NiCr exhibited the highest (16.23 ±0.96 MPa) and lowest (10.1 ±0.63 MPa) values. The mean difference in SBS indicated a statistically significant difference between the material groups (p < 0.01).

CONCLUSIONS

PEKK materials demonstrated significantly lower SBS than PEEK and significantly higher SBS values than conventional zirconia and alloy materials. A positive and significant correlation between mean roughness and SBS was observed, but the causality could be either intrinsic to the material or the roughness.

Promoted mechanical properties and functionalities via Ta-tailored Ti-Au-Cr shape memory alloys towards biomedical applications

In view of the urgent demands of shape memory alloys (SMAs) for biomedical applications due to the world population aging issue, the mechanical properties and functionalities of the biocompatible Ti-Au-Cr-based SMAs, which are tailored by Ta additions, have been developed in this study. The quaternary SMAs were successfully manufactured by physical metallurgy techniques and their mechanical properties and functionalities were examined. In the continuous tensile tests, it was found that the correlation between the yielding strength and phase stability followed a typical trend of mechanical behavior of SMAs, showing the lowest yielding strength at the metastable β-parent phase. Functional mappings between the alloy strength and elongation revealed that compared to the Ta-free specimen, the ductility was promoted 50% while the strength remained intact through the 4 at.% introduction of Ta. Slight shape recovery was observed in the cyclic loading-unloading tensile tests during the unloading process and the highest shape recovery was found in the Ti-4 at.% Au-5 at.% Cr-4 at.% Ta specimen. This indicates that the 4 at.% Ta tailored Ti-Au-Cr SMAs could be a promising material for biomedical applications.

Toxicity of Orthodontic Brackets Examined by Single Cell Tracking

Subtle toxic effects may be masked in traditional assays that average or summate the response of thousands of cells. We overcome this by using the recent method of single cell tracking in time-lapse recordings. This follows the fate and behavior of individual cells and their progeny and provides unambiguous results for multiple simultaneous biological responses. Further, single cell tracking permits correlation between progeny relationships and cell behavior that is not otherwise possible, including disruption by toxins and toxicants of similarity between paired sister cells. Notably, single cell tracking seems not to have been previously used to study biomaterials toxicity. The culture medium was pre-conditioned by 79 days incubation with orthodontic brackets from seven separate commercial sources. Metal levels were determined by Inductively Coupled Plasma Mass Spectrometry. Metal levels varied amongst conditioned media, with elevated Cr, Mn, Ni, and Cu and often Mo, Pb, Zn, Pd, and Ag were occasionally found. The effect on human dermal fibroblasts was determined by single cell tracking. All bracket-conditioned media reduced cell division (p < 0.05), while some reduced cell migration (p < 0.05). Most bracket-conditioned media increased the rate of asynchronous sister cell division (p < 0.05), a seemingly novel measure for toxicity. No clear effect on cell morphology was seen. We conclude that orthodontic brackets have cytotoxic effects, and that single cell tracking is effective for the study of subtle biomaterials cytotoxicity.

Strength of Polyether Ether Ketone Composite as a Major Connector Material for Removable Partial Dentures

PEEK composite was tested mechanically as a maxillary removable partial denture (RPD) framework material instead of cast cobalt chromium alloy. Methods: Partial edentulous upper jaw cast was scanned using structured-light 3D scanner, palatal strap (PS) designs for RPD were designed by a designing dental laboratory software. CAD/CAM machine fabricated PSs patterns using their designs’ STL software files. PSs were made from poly-ether-ether ketone (PEEK) reinforced by ceramic fillers using thermal injection press technique and Co-Cr alloy using centrifugal casting, each material group was subdivided into two subgroups according to storage conditions (stored and non-stored subgroups), storage took place in deionized water for about 180 days at 37.5 ± 2 o C. All specimens were subjected to fracture resistance test using universal testing machine then maximum compression load (MCL) result values were subjected to statistical analysis. PEEK composite specimens were scanned by field emission microscope (FEM) and energy dispersive spectroscopy. Storage water of PEEK composite was analyzed using atomic absorption spectroscopy (AAS). Results: In either stored or non-stored subgroups of PEEK composite straps they showed significant lower mean MCL values than corresponding alloy subgroups (p=0.0001). FEM scanning showed fillers agglomerations in non-stored PEEK composite and their nearly absence from stored PEEK composite specimens. AAS detected Al element in PEEK composite storage water. Conclusion: Mechanically thermally injected ceramic reinforced PEEK composite could not replace cast Co-Cr alloy as PSs material for maxillary RPD. Biocompatibility concerns raised in this study due to suspected Al leaching and ceramic fillers dissolution from PEEK composite matrix.

Fatigue Resistance of Cast-on Implant Abutment Fabricated with Three Different Alloys

OBJECTIVES

 This study aimed to evaluate fatigue resistance of cast-on implant abutment using three alloys.

MATERIALS AND METHODS

 Forty specimens of implant-supported crowns were prepared; Group 1 (TA) stock titanium abutments, Group 2 (GS) abutment cast with 40% gold alloy, Group 3 (GP) abutment cast with palladium alloy, and Group 4 (CN) abutment cast with nickel-chromium alloy. Specimens were cyclic loaded at 20 Hz, starting from 200 N (5,000 cycles), followed by stepwise loading of 400, 600, 800, 1,000, 1,200, 1,400, 1,600, and 1,800 N (30,000 cycles/step). Specimens were loaded until failure or reached 245,000 cycles.

STATISTICAL ANALYSIS

 The withstand cycles were analyzed using one-way analysis of variance and Weibull survival analysis. Fracture surfaces were examined using scanning electron microscopy.

RESULTS

 The results of withstand cycles were TA (189,883 ± 22,734), GS (195,028 ± 22,371), GP (187,662 ± 22,555), and CN (200,350 ± 30,851). The statistical analysis showed no significant difference between the groups (p = 0.673).

CONCLUSION

 Although CN has higher Weibull characteristic strength which means greater durability, its lower Weibull modulus demonstrated less structural reliability. Consistent failures at implant fixture level were also found in CN group.

On a high photocatalytic activity of high-noble alloys Au-Ag/TiO2 catalysts during oxygen evolution reaction of water oxidation

The analysis via density functional theory was employed to understand high photocatalytic activity found on the Au-Ag high-noble alloys catalysts supported on rutile TiO2 during the oxygen evolution of water oxidation reaction (OER). It was indicated that the most thermodynamically stable location of the Au-Ag bimetal-support interface is the bridging row oxygen vacancy site. On the active region of the Au-Ag catalyst, the Au site is the most active for OER catalyzing the reaction with an overpotential of 0.60 V. Whereas the photocatalytic activity of other active sites follows the trend of Au > Ag > Ti. This finding evident from the projected density of states revealed the formation of the trap state that reduces the band gap of the catalyst promoting activity. In addition, the Bader charge analysis revealed the electron relocation from Ag to Au to be the reason behind the activity of the bimetallic that exceeds its monometallic counterparts.

Fixed Prosthetic Restorations and Periodontal Health: A Narrative Review

Periodontal health plays an important role in the longevity of prosthodontic restorations. The issues of comparative assessment of prosthetic constructions are complicated and not fully understood. The aim of this article is to review and present the current knowledge regarding the various technical, clinical, and molecular aspects of different prosthetic biomaterials and highlight the interactions between periodontal health and prosthetic restorations. Articles on periodontal health and fixed dental prostheses were searched using the keywords “zirconium”, “CAD/CAM”, “dental ceramics”, “metal–ceramics”, “margin fit”, “crown”, “fixed dental prostheses”, “periodontium”, and “margin gap” in PubMed/Medline, Scopus, Google Scholar, and Science Direct. Further search criteria included being published in English, and between January 1981 and September 2021. Then, relevant articles were selected, included, and critically analyzed in this review. The margin of discrepancy results in the enhanced accumulation of dental biofilm, microleakage, hypersensitivity, margin discoloration, increased gingival crevicular fluid flow (GCF), recurrent caries, pulp infection and, lastly, periodontal lesion and bone loss, which can lead to the failure of prosthetic treatment. Before starting prosthetic treatment, the condition of the periodontal tissues should be assessed for their oral hygiene status, and gingival and periodontal conditions. Zirconium-based restorations made from computer-aided design and computer-aided manufacturing (CAD/CAM) technology provide better results, in terms of marginal fit, inflammation reduction, maintenance, and the restoration of periodontal health and oral hygiene, compared to constructions made by conventional methods, and from other alloys. Compared to subgingival margins, supragingival margins offer better oral hygiene, which can be maintained and does not lead to secondary caries or periodontal disease.

Comparison of Bond Strength in the Different Class of Resin Cements to Cast and CAD/CAM Co-Cr Alloys

Objectives

Despite the widespread use of resin cements in cementing dental restorations, their bond strength to CAD/CAM base metal alloys is not widely studied. This study aimed to evaluate the microshear bond strength (μSBS) between cobalt-chrome (Co-Cr) alloys fabricated using casting or CAD/CAM methods with three types of resin cements.

Materials and Methods

Fifty Co-Cr blocks were prepared with CAD/CAM or casting technique. Specimens were divided using primer or not and bonded to three types of resin cements: Panavia F2, RelyX Unicem, and Duo-Link. The differences between the mean μSBS values were analyzed using the two-way ANOVA test and Tukey analysis (α = 0.05). The mode of failure was evaluated using a stereomicroscope. In addition, the specimens were examined by scanning electron microscopy (SEM) based on two received signals: backscattered electrons (SEB) and secondary electrons (SEs). One intact alloy specimen in each group was analyzed by energy-dispersive X-ray spectroscopy (EDX).

Results

Most of the specimens in the no-primer group were prematurely debonded. Statistical analyses showed that the interaction between the alloy substrate and cement type was significant (p=0.001). The bond strength of Panavia F2 was significantly higher than Duo-Link in the CAD/CAM group (p=0.001). SEM evaluation confirmed the difference in grain structures, while EDX showed no remarkable difference in the chemical composition of the alloy substrates.

Conclusion

Alloy fabrication technique may influence the bond strength of resin cements. In the CAD/CAM group, cement containing MDP molecules exhibited higher strength than the etch-and-rinse one.

Investigations of Effects of Intermetallic Compound on the Mechanical Properties and Shape Memory Effect of Ti-Au-Ta Biomaterials

Owing to the world population aging, biomedical materials, such as shape memory alloys (SMAs) have attracted much attention. The biocompatible Ti-Au-Ta SMAs, which also possess high X-ray contrast for the applications like guidewire utilized in surgery, were studied in this work. The alloys were successfully prepared by physical metallurgy techniques and the phase constituents, microstructures, chemical compositions, shape memory effect (SME), and superelasticity (SE) of the Ti-Au-Ta SMAs were also examined. The functionalities, such as SME, were revealed by the introduction of the third element Ta; in addition, obvious improvements of the alloy performances of the ternary Ti-Au-Ta alloys were confirmed while compared with that of the binary Ti-Au alloy. The Ti₃Au intermetallic compound was both found crystallographically and metallographically in the Ti-4 at.% Au-30 at.% Ta alloy. The strength of the alloy was promoted by the precipitates of the Ti₃Au intermetallic compound. The effects of the Ti₃Au precipitates on the mechanical properties, SME, and SE were also investigated in this work. Slight shape recovery was found in the Ti-4 at.% Au-20 at.% Ta alloy during unloading of an externally applied stress.

Risk Assessment of Oxidative Stress Induced by Metal Ions Released from Fixed Orthodontic Appliances during Treatment and Indications for Supportive Antioxidant Therapy: A Narrative Review

The treatment with fixed orthodontic appliances could have an important role in the induction of oxidative stress and associated negative consequences. Because of the simultaneous effects of corrosion, deformation, friction, and mechanical stress on fixed orthodontic appliances during treatment, degradation of orthodontic brackets and archwires occurs, causing higher concentrations of metal ions in the oral cavity. Corroded appliances cause the release of metal ions, which may lead to the increased values of reactive oxygen species (ROS) due to metal-catalyzed free radical reactions. Chromium, iron, nickel, cobalt, titanium, and molybdenum all belong to the group of transition metals that can be subjected to redox reactions to form ROS. The estimation of health risk due to the amount of heavy metals released and the level of selected parameters of oxidative stress generated for the time of treatment with fixed orthodontic appliances is presented. Approaches to avoid oxidative stress and recommendations for the preventive use of topical or systemic antioxidants during orthodontic treatment are discussed.

Enhancement of mechanical properties and shape memory effect of Ti-Cr-based alloys via Au and Cu modifications

The requirements for biomedical materials have been raised greatly due to the rapidly aging global population. Shape memory alloys (SMAs) are indeed promising materials for biomedical applications due to their controllable shape deformation via the manipulation of temperature and/or stress. This study investigated the enhancement of the fundamental mechanical properties and the shape memory effect (SME) in the Ti-Cr-based alloys via the modification of Au and Cu. The quaternary Ti-Cr-Au-Cu alloys were successfully manufactured by physical metallurgy methods and their phase constitutions, mechanical properties, SME, and superelastic (SE) behaviors have been investigated in this study. Cold-workability, which was enhanced by the introduction of the Au element, was elaborated by the phase constitutions of the alloys. The β-parent phase was stabilized to around body temperature by the introduction of the β-stabilizers of Cr, Au, and Cu, and the functionalities of the specimens were revealed at the operating temperature. Perfect SME at the shape recovery rate of 100% was practiced by the substitution of Au by Cu and the mechanical properties, such as strength and ductility, were also enhanced. Functional mappings of the fundamental mechanical properties, which could be a helpful tool for the investigations of the quaternary Ti-Cr-Au-Cu alloys, were constructed in this work.

A 3D Finite Element Analysis Model of Single Implant-Supported Prosthesis under Dynamic Impact Loading for Evaluation of Stress in the Crown, Abutment and Cortical Bone Using Different Rehabilitation Materials

In the literature, many researchers investigated static loading effects on an implant. However, dynamic loading under impact loading has not been investigated formally using numerical methods. This study aims to evaluate, with 3D finite element analysis (3D FEA), the stress transferred (maximum peak and variation in time) from a dynamic impact force applied to a single implant-supported prosthesis made from different materials. A 3D implant-supported prosthesis model was created on a digital model of a mandible section using CAD and reverse engineering. By setting different mechanical properties, six implant-supported prostheses made from different materials were simulated: metal (MET), metal-ceramic (MCER), metal-composite (MCOM), carbon fiber-composite (FCOM), PEEK-composite (PKCOM), and carbon fiber-ceramic (FCCER). Three-dimensional FEA was conducted to simulate the collision of 8.62 g implant-supported prosthesis models with a rigid plate at a speed of 1 m/s after a displacement of 0.01 mm. The stress peak transferred to the crown, titanium abutment, and cortical bone, and the stress variation in time, were assessed.

Effects of Copper Surface Oxidation and Reduction on Shear-Bond Strength Using Functional Monomers

This study was conducted to clarify the influence of the copper surface oxidation and reduction on the shear-bond strength with functional monomers. Unheated copper specimens (UH; n = 88) were wet-ground. Three-quarters of the UH were then heated (HT). Two-thirds of the HT was then immersed in a hydrochloric acid solution (AC). Half of the AC was then reheated (RH). Each group was further divided into two groups (n = 11), which were primed by either 6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate (MTU-6) or 10-methacryloyloxydecyl dihydrogen phosphate (MDP). The shear-bond strength tests were used for bonding with an acrylic resin. The surface roughness values and chemical states of the four groups were analyzed using a confocal scanning laser microscope and X-ray photoelectron spectroscopy (XPS). The shear-bond strengths of HT and RH were the lowest in the MTU-6-primed groups. The result of AC was significantly lower than others in the MDP-primed groups. The XPS results showed that the surfaces of UH and AC consisted of Cu₂O and Cu. The surface changed to CuO upon heating. The presence or absence of copper-oxide films showed the opposite trends in the effectiveness of MTU-6 and MDP to improve bond strength. The results could elucidate the effects of functional monomers on copper-oxide films.

Characteristics of Periodontal Tissues in Prosthetic Treatment with Fixed Dental Prostheses

The objective of the present study was to investigate the effects of various types of fixed prostheses on periodontal tissues and explore the association of gingival biotype and gum recession in relation to prosthesis types. The study participants (N = 95) were divided into three groups based on the type of dental prosthesis: Group-I: cobalt-chrome (Co-Cr) ceramic prosthesis fabricated by the conventional method (n = 35); Group-II: consisted of patients with Co-Cr ceramic prostheses fabricated by a computer-aided design and computer aided manufacturing (CAD/CAM) technique (n = 30); and Group-III: zirconia-based prostheses fabricated by the CAD/CAM technique (n = 30). Following the use of prostheses, periodontal examinations were performed using the Community Periodontal Index (CPI) and Modified Approximal Plaque Index (MAPI). In addition, the gingival biotype was examined using a probe transparency method. The Statistical Package for the Social Sciences (SPSS), Version 20 (IBM Company, Chicago, IL, USA), was used to analyze the results, and the significance level was set at p = 0.05. It showed the MAPI results after the use of prosthetic rehabilitation for 12 months of periodontitis in 87.9% ± 15.4 of patients in Group-I, in 80.6% ± 17.97 in those in Group-II, and in 62.5% ± 21.4 in those in Group-III (p < 0.01). The CPI index results indicated a high prevalence of periodontal disease in all groups. The number of people with healthy periodontium constituted 17.1% of patients in Group-I, 24.2% in Group-II, and 37.1% in Group-III. Our study concluded that prosthetic treatment with periodontal diseases showed better outcomes while using dental prostheses fabricated by the CAD/CAM technique compared to the conventionally fabricated dental prostheses. The thin gingival biotype is more often associated with gingival recession than the thick biotype.

Characteristics of Periodontal Tissues in Prosthetic Treatment with Fixed Dental Prostheses

The objective of the present study was to investigate the effects of various types of fixed prostheses on periodontal tissues and explore the association of gingival biotype and gum recession in relation to prosthesis types. The study participants (N = 95) were divided into three groups based on the type of dental prosthesis: Group-I: cobalt-chrome (Co-Cr) ceramic prosthesis fabricated by the conventional method (n = 35); Group-II: consisted of patients with Co-Cr ceramic prostheses fabricated by a computer-aided design and computer aided manufacturing (CAD/CAM) technique (n = 30); and Group-III: zirconia-based prostheses fabricated by the CAD/CAM technique (n = 30). Following the use of prostheses, periodontal examinations were performed using the Community Periodontal Index (CPI) and Modified Approximal Plaque Index (MAPI). In addition, the gingival biotype was examined using a probe transparency method. The Statistical Package for the Social Sciences (SPSS), Version 20 (IBM Company, Chicago, IL, USA), was used to analyze the results, and the significance level was set at p = 0.05. It showed the MAPI results after the use of prosthetic rehabilitation for 12 months of periodontitis in 87.9% ± 15.4 of patients in Group-I, in 80.6% ± 17.97 in those in Group-II, and in 62.5% ± 21.4 in those in Group-III (p < 0.01). The CPI index results indicated a high prevalence of periodontal disease in all groups. The number of people with healthy periodontium constituted 17.1% of patients in Group-I, 24.2% in Group-II, and 37.1% in Group-III. Our study concluded that prosthetic treatment with periodontal diseases showed better outcomes while using dental prostheses fabricated by the CAD/CAM technique compared to the conventionally fabricated dental prostheses. The thin gingival biotype is more often associated with gingival recession than the thick biotype.

ICP-MS measurements of elemental release from two palladium alloys into a corrosion testing medium for different solution volumes and agitation conditions

STATEMENT OF PROBLEM

The in vivo release of Pd from palladium alloys into the oral environment and sensitivity reactions by patients has been of concern. However, little information is available about the variation in elemental release from different palladium alloys.

PURPOSE

The purpose of this in vitro study was to compare the elemental release into a corrosion-testing medium from a high-palladium alloy (Freedom Plus, 78Pd-8Cu-5Ga-6In-2Au) and a Pd-Ag alloy (Super Star, 60Pd-28Ag-6In-5Sn) under different conditions.

MATERIAL AND METHODS

Alloys were cast into Ø12×1-mm-thick disks, subjected to simulated porcelain-firing heat treatment, polished, and ultrasonically cleaned in ethanol. Three specimens of each alloy were immersed for 700 hours in a solution for in vitro corrosion testing (ISO Standard 10271) that was maintained at 37 °C. Two solution volumes (125 mL and 250 mL) were used, and the solutions were subjected to either no agitation or agitation. Elemental compositions of the solutions were analyzed by using inductively coupled plasma-mass spectroscopy (ICP-MS). Concentrations of released elements from each alloy for the 2 solution volumes and agitation conditions were compared by using the restricted maximum likelihood estimation method with a 4-way repeated-measures ANOVA, the Satterwhite degrees of freedom method, a lognormal response distribution, and the covariance structure of compound symmetry.

RESULTS

For the 4 combinations of solution volume and agitation conditions, the mean amount of palladium released was 3 orders of magnitude less for the Pd-Ag alloy (0.009 to 0.017 μg/cm² of alloy surface) compared with the Pd-Cu-Ga alloy (17.9 to 28.7 μg/cm²). Larger mean amounts of Sn, Ga, Ag, and In (0.29 to 0.39, 0.57 to 0.83, 0.71 to 1.08, and 0.91 to 1.25 μg/cm², respectively) compared with Pd were released from the Pd-Ag alloy. Smaller amounts of Cu, Ga, and In (4.8 to 9.9, 5.9 to 12.8, and 4.2 to 9.5 μg/cm², respectively) compared with Pd were released from the Pd-Cu-Ga alloy. The Ru released was much lower for the Pd-Ag alloy (0.002 μg/cm²) than the Pd-Cu-Ga alloy (0.032 to 0.053 μg/cm²). Statistically significant differences (P<.001) in elemental release were found for the factors of alloy and element and the alloy×element interaction. Significant differences were found for the solution volume (P=.022), solution volume×element interaction (P=.022), and alloy×solution volume×element interaction (P=.004). No significant effect was found for agitation condition.

CONCLUSIONS

The relative amounts of released elements from each alloy were not proportional to the relative amounts in the composition. The amounts of Pd and Ga released from the Pd-Cu-Ga alloy were consistent with the breakdown of a Pd₂Ga microstructural phase and perhaps some dissolution of the palladium solid solution matrix. Precipitates, rather than the palladium solid solution matrix, appeared to undergo greater dissolution in the Pd-Ag alloy. The Pd-Ag alloy should have lower risk of adverse biological reactions than the Pd-Cu-Ga alloy.

Comparison of Cell Viability and Chemical Composition of Six Latest Generation Orthodontic Wires

Orthodontic wires are made of alloys containing different metals, including nickel. It is important to evaluate their biocompatibility prior to use, owing to their long-term use in patients. This in vitro study compared the cytotoxicity and chemical composition of six latest orthodontic wires: Fantasia®, Tanzo®, FLI®, NT3®, DuoForce®, and Gummetal®. The before-use group consisted of wires that were not used in the mouth, and the after-use group consisted of wires that were used in the mouth for two months. The wires were placed in contact with human gingival fibroblasts (HGF) for 72 h, and cytotoxicity was determined using the resazurin test. The chemical composition and surface characterisation were evaluated by spectrometry and scanning electron microscopy. The groups were compared using ANOVA and Kruskal–Wallis test. Only the FLI® wires produced a 36% reduction in HGF viability (p < 0.05) and presented greater irregularities and loss of polymer structure. After-use wires showed a significant reduction in the percentage of nickel and the appearance of new elements (oxygen and carbon). Therefore, it can be concluded that no toxic ion release was noticed in this study. Rhodium-coated wires were more stable than PTFE-coated wires, and only the FLI® wires showed a slight cytotoxic effect.

In-Situ XRD Study of Phase Transformation Kinetics in a Co-Cr-W-Alloy Manufactured by Laser Powder-Bed Fusion

The additive manufacturing process of laser powder-bed fusion (L-PBF) is an increasingly popular approach for patient-specific production of dental frameworks made from Co-Cr alloys. Macroscopically, frameworks produced in this way exhibit high anisotropy especially in Young’s modulus, and are missing standardized requirements. Microscopically, pronounced texture and high residual stresses are characteristic. To reduce resulting detrimental effects, the as-built (AB) parts are heat treated. Dependent on the treatment temperature, effects like the transformation of the γ-phase matrix in the AB condition to ϵ-phase, precipitation, stress relief, and grain growth were observed. While the existence of these processes was established in the past, little is known about their kinetics. To fill this gap, these effects were studied with in-situ X-ray diffraction (XRD) methods in isothermal heat treatments (HTs) at four different sample surface temperatures TS reaching from 650∘C to 900∘C. Furthermore, room temperature ex situ XRD and SEM/EDS measurements completed the analysis. An evaluation of the datasets, with single peak fitting and QXRD methods, yielded the following results. In the HTs below a certain threshold, a γ-to-ϵ transformation was observed in the sample bulk and close to the sample surface. In the latter case, evidence for a partially strain-induced transformation related to oxide formation was present. Above this threshold and possibly slightly below, σ- and Laves-phase precipitated. Additionally, peak profile evolutions hinted at a drop of inter- and intragranular stresses within the first 30 to 60 min. Therefore, an HT of about 30 to 60 min slightly above the threshold is proposed as optimal for reducing residual stresses while retaining a predominantly single-phased microstructure, possibly superior in corrosion properties and likewise in bio-compatibility.

Periodontal clinico-morphological changes in patients wearing old nickel-chromium and copper alloys bridges

Elderly population frequently presents more than one prosthetic restoration realized from different types of dental alloys which, in time, suffer various alterations in the oral environment. Metallic ions are released in saliva due to its electrolytic qualities, interacting with the contact tissues. Studies regarding cytotoxicity of dental alloys are providing contradictory results. Besides biocompatibility, the microbial factor is also greatly influencing the long-term success of the prosthetic rehabilitation. This study's aim was to assess the response of the gingival tissue to nickel-chromium (Ni-Cr) and copper (Cu)-based dental casting alloys from fixed dentures present in many patients from Romania. Gingival samples were taken from 124 patients wearing fixed dental restorations made from these two types of alloys from injured areas surrounding the abutment teeth; histological specimens were prepared, fixed in 10% neutral buffered formalin, paraffin-embedded and stained with Hematoxylin-Eosin (HE). Histological analysis showed the existence of a chronic inflammatory infiltrate in the gingival chorion, necrosis areas, and vascular congestion. Various morphological alterations appeared, depending on the intensity of the inflammation and the immune response. The surface epithelium suffered a hyperplasic reaction, either limited to acanthosis or involving the whole epithelium, the release of the Cu(2+) and Ni(2+) ions from the dental alloys used in bridges and crowns being responsible for inducing gingival hyperplasia and a chronic inflammation in the areas situated around the abutment teeth. The immunohistochemical study allowed us to observe an increased number of positive cluster of differentiation 3 (CD3) T-lymphocytes in periodontium, proving that the cellular immune response is rapid and intense.

Ion Release from Dental Implants, Prosthetic Abutments and Crowns under Physiological and Acidic Conditions

Ion release from dental implants and prosthetic restoration can affect osteointegration and implant viability over a long period of time. Therefore, the aim of this study was to study the ion release from implants and crowns, with and without intermediate anodized abutments, in two different media, simulating clinical conditions. The implants, intermediate prosthetic abutments and Cr–Co crowns were divided into two groups depending on the media: Hanks’ solution and 1% lactic acid, simulating body fluids and microbiologically conditioned fluids, respectively. The study followed the ISO 10271:2011 and 10993-15:2000 standards modified to simulate the replacement of fluids in the oral environment. The ions’ release was measured by inductively coupled plasma mass spectroscopy (ICP-EOS), and only aluminum, chromium, cobalt, titanium and vanadium were identified. Ion concentration was higher in lactic acid than in Hanks’ solution at all time points (p < 0.05). Only vanadium showed a very low ion release in lactic acid, with no statistically significant differences from the ion release in Hanks’ solution (p = 0.524). Both anodized abutments and the immersion medium influenced the release of ions and affected the corrosion of these structures. The presence of an intermediate anodized abutment also affected ion release, as the level of ions was lower in groups with this component.

The effects of recasting on the cytotoxicity of dental base metal casting alloys

Aim and Objectives

In dentistry, base metal casting alloys are extensively used for the fabrication of inlays, onlays, crowns, bridges, partial dentures, etc. During the casting of these alloys, excess amount of material used than needed will be collected as sprue buttons at the end, which is either added to the fresh alloy during casting and reused or disposed of.

Materials and Methods

The aim of the present in vitro experimental study was to investigate the effect of the complete recasting of four commercially available cobalt-chromium (Co-Cr) and nickel-chromium (Ni-Cr) base metal casting alloys on their cytotoxicity. During the study, four groups of alloys were subjected to complete recasting up to twenty times without the addition of new alloy. The cytotoxicity assessment of the selected alloys after recasting (Co-Cr and Ni-Cr alloys) was carried out using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Results

The results indicated that Co-Cr alloys exhibit superior cell viability compared to Ni-Cr alloys, and cytotoxic potential of the alloys increased with repeated casting and led to increased cell death. The recasting of alloys in the present study did not show high cytotoxicity even after the 20^th recasting.

Conclusion

From the results of the present study, it can be concluded that the alloys generated as a waste in the dental laboratory can be safely reused up to five times or at least once before they can be disposed, which reduces the cost of the treatment and also helps in conserving the natural resources.

Mechanical Properties and Metal-Ceramic Bond Strength of Co-Cr Alloy Manufactured by Selective Laser Melting

Cobalt–chromium (Co-Cr) metal is one of the widely used biomaterials in the fabrication of dental prosthesis. The purpose of this study was to investigate whether there are differences in the properties of metals and bond strength with ceramics depending on the manufacturing methods of Co-Cr alloy. Co-Cr alloy specimens were prepared in three different ways: casting, milling, and selective laser melting (SLM). The mechanical properties (elastic modulus, yield strength, and flexural strength) of the alloys were investigated by flexure method in three-point bending mode, and microstructures of the specimens were analyzed. After application of the veneering ceramic through the three-point bending test, bond strength of the Metal-Ceramic was investigated. The cracked surfaces were observed by means of energy dispersive X-ray (EDX) spectroscopy and scanning electron microscopy (SEM) with backscattered electron (BSE) images. In mechanical properties, the elastic modulus was highest for the casting group, and the yield strength and flexural strength were lowest for the milling group. The SLM group showed finer homogeneous crystalline-microstructure, and a layered structure was observed at the fractured surface. After the ceramic bond strength test, all groups showed a mixed failure pattern. The casting group showed the highest bond strengths, whereas there was no significant difference between the other two groups. However, all groups have met the standard of bond strength according to international standards organization (ISO) with the appropriate passing rate. The results of this study indicate that the SLM manufacturing method may have the potential to replace traditional techniques for fabricating dental prosthesis.

Assessment of occupational exposure to fine particulate matter in dental prosthesis laboratories in Kocaeli, Turkey

Dental prosthesis laboratories (DPLs) are among the workplaces where predominantly manual production takes place. In such working environments, during the manual manufacturing process, which involves fine smoothing and polishing of dental prostheses, fine particulate matter is released into the ambient air. In this study, the particulate matter (PM) concentrations and elemental content of the fine particles in the working ambient air were identified in six DPLs in Kocaeli, Turkey. PM_2.5 mass concentrations, measured in all the DPLs, ranged between 80.8 and 1645 μg/m³ (mean 414 ± 406). As a result of the analyses performed with an ICP-MS device (Perkin Elmer Elan®DRC-e), trace elements of Be, Cd, Hg, and, notably, Co, Cr, Mo, and Ni were found. The researchers calculated the excess lifetime cancer risks and total hazard indexes. The average total cancer risk for all the DPLs was 8 × 10^-3, which is higher than the acceptable limit of 1.0 × 10^-6, and the total hazard index was 187, which is greater than the acceptable limit of 1.0. Considering these high-level risks, the study concluded that there is a need for new production methods, and strict application of occupational health and safety measures, to reduce the fine particle exposure of the workers in the laboratories. In addition, there are prescribed limit values for particulate matter only for respirable particles in working environments. The establishment of limit values, especially for PM_2.5 concentrations, is important for the protection of the health of the employees.

Electrochemical Synthesis of Polypyrrole and Polypyrrole-Indomethacin Coatings on NiCr Alloys Involving Deep Eutectic Solvents

There is an increased interest in the use of the deep eutectic solvents (DESs) as electrolytic media for electrochemical synthesis of conducting polymers, which could influence their characteristics. Moreover, the polypyrrole layers represent an attractive route for pharmaceutical drug release. The paper presents several experimental results regarding the electrodeposition of polypyrrole and of polypyrrole-indomethacin coatings on nickel-chromium NiCr alloy substrates widely used in dentistry, involving DES-based electrolytes, namely eutectic mixtures of choline chloride and malonic acid. This type of electrolyte also allowed an enhanced dissolution of indomethacin as compared to aqueous ones. The electropolymerization process has been investigated by cyclic voltammetry and chronoamperometry. The obtained indomethacin containing polymeric coatings have been thoroughly characterized involving scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, contact angle measurements in simulated body fluid (SBF) and indomethacin release studies. Adherent and uniform polypyrrole-indomethacin layers have been obtained on NiCr alloy substrates. The release tests showed that the polypyrrole coatings containing indomethacin may deliver the drug molecules for longer periods of at least 17 days. The maximum released amount was around 99.6% suggesting these layers may act as an active reservoir for indomethacin. Kinetics analysis based on the Korsmeyer–Peppas model suggested the diffusion of the drug out of the polymer layer as the most probable mechanism governing the release.

Functional, compositional, and regulatory analyses of imported and non-imported single dental crowns

The aims of the study were to investigate functional and esthetic properties, the composition of the alloy, and the content of hazardous elements of single dental crowns with metal skeleton and fired porcelain. Epoxy models made from full mouth impressions taken of a patient with a crown preparation of the right maxillary first permanent molar were used for production of identical polyether impressions, which were distributed to dentists in Norway. The dentists sent the impressions to their regular dental laboratories. All 55 crowns collected were anonymized and examined. Of the crowns received, 35 were made in Norway, 12 were imported, and 8 were of unknown origin. The evaluation of functional properties revealed that 50% of the Norwegian, 42% of the imported, and 25% of the unknown-origin crowns were considered unacceptable. The composition of the alloy was not in accordance with that stated by the manufacturer for 17%, 13% and 20% of the crowns, where this information was provided. The lead content of the alloy exceeded the limit set by the ISO 22674: 2016 for 18% of the crowns in total. The statement that shall follow the work according to EU-regulations was not complete for approximately 75% of the works received.

Ion release from three different dental alloys - effect of dynamic loading and toxicity of released elements

Objective

The aims of this in vitro study were to assess if dynamic loading increases the metal ion release of selected dental alloys and to evaluate the cytotoxicity of the released metal ions.

Materials and methods

One Pd–Ag alloy (Aurolite 2B) and two Co–Cr alloys (Wirobond 280 and d.Sign 30) were investigated. Two different corrosion immersion tests were used: a standardized static test (ISO 22674: 2016) and an experimental dynamic test. Both tests involved immersion of the specimens in a lactic acidic solution (pH = 2.3). Inductively coupled plasma mass spectrometry was used to identify and quantify released elements. A human monocyte cell-line (THP-1) was exposed to serially diluted solutions containing the selected metal ions. Cell viability was measured using the methyl-thiazolyl-tetrazolium assay.

Results

According to the threshold defined in ISO 22674, only low concentrations of released elements were observed for both corrosion tests. No increase in metal ion release from the dynamic test compared with the static test was observed. Of the released elements, only Zn(II) and Co(II) showed a cytotoxic effect on THP-1 cells at 250 µM and higher concentrations. No increased viability loss was observed when adding other released elements to the exposure mixture.

Conclusions

The tested alloys showed low levels of metal ion release from both static and dynamic corrosion testing. Dynamic loading did not increase the metal ion release compared to the static corrosion test. Concentrations of 250 µM and above of Zn(II) and Co(II) showed a cytotoxic effect on THP-1 cells.

Evaluation of corrosion resistance of Co-Cr alloys fabricated with different metal laser sintering systems

PURPOSE

The aim of this study was to evaluate the corrosion resistance of the specimens produced by five different commercial metal laser sintering (MLS) systems with their recommended Co-Cr alloy powders.

MATERIALS AND METHODS

The MLS machines and the alloy powders used were, ProX 100-ST2724G (St-Pro), Mysint 100-EOS SP2 (SP2-Mys), EOSINT 270-EOS SP2 (SP2-EOS), SLM 100-Starbond CoS (SB-SLM), and MLab Cusing-Remanium® Star (RS-MLab), respectively. Eight specimens from each group were prepared. Open circuit potential (Eocp) and electrochemical impedance spectroscopy (EIS) measurements of polished surfaces of the specimens were conducted in a three-electrode cell using a potentiostat-galvanostat in Fusayama-Meyer artificial saliva (AS). Specimens from each group were immersed in AS and de-ionized water for seven days. Eocp, charge transfer resistance (Rct) values, and released ions (µg/cm2 × 7d) in different solutions were determined. The specimen surfaces were observed with SEM/EDS. Results were analyzed statistically.

RESULTS

Eocp values have shifted to potentials that are more positive over time. Steady-state Eocp values were from high to low as follows, SB-SLM, SP2-Mys, SP2-EOS, RS-MLab, and ST-Pro, respectively. After 60 mins, RS-MLab specimens had the highest Rct value, followed by SP2-Mys, SB-SLM, SP2-EOS, and ST-Pro. In all groups, ion release was higher in AS than that in de-ionized water.

CONCLUSION

There were small differences among the corrosion resistances of the Co-Cr alloy specimens produced with MLS systems; meanwhile, the corrosion resistances were quite high for all specimens.

Evaluation of human osteoblast metabolic activity in modified titanium-conditioned medium

To evaluate human osteoblast metabolic activity cultured in medium conditioned with commercially pure titanium after surface treatments with alumina or ceramic grit-blasting followed by acid etching. Commercially available, pure Grade 4 titanium disks were used and subjected to seven different surface modifications: (1) machined (MA)-used as the control group; (2) blasted with Al₂O₃ (Al₂O₃); (3) blasted with sintered ceramic (HAS); (4) blasted with non-sintered ceramics (HA); (5) blasted with Al₂O₃ and etched with HCl/H₂SO₄ (Al₂O₃ DE); (6) blasted with sintered ceramic and etched with HCl/H₂SO₄ (HAS DE), and (7) blasted with non-sintered ceramic and etched with HCl/H₂SO₄ (HA DE). A samples roughness evaluation test was carried out with an interference microscope, and energy-dispersive X-ray spectroscopy was performed to evaluate the presence of aluminum, phosphorus, and calcium deposited during the titanium surface treatment along with carbon contaminants acquired by the surface during processing. A culture medium conditioned with the respective samples was prepared in five dilutions, and its effect on human osteoblast cell viability was evaluated using the relative viability of cells. Human osteoblast metabolic activity was found to be the most intensive for the Al₂O₃ DE sample. The lowest activity was observed for the HAS DE. The material's cytocompatibility depended on both the surface roughness and its chemical composition. Etching had a dual effect on cell activity, depending on the chemical composition of the titanium surface after blasting.

Electrochemical Performance of Fe40Al-X (X = Cr, Ti, Co, Ni) Alloys Exposed to Artificial Saliva

Fe–Al intermetallic compounds have been considered excellent candidates as alternative alloys for various applications in corrosive environments compared to other Fe-based alloys. Their excellent corrosion resistance is due to the development of an Al-based passive layer. The performance of the passive layer can be improved by adding a third alloy element. Therefore, in this study the electrochemical performance of the Fe40Al intermetallic alloy modified by the addition of a third alloy element (Cr, Ti, Co, Ni) is evaluated. The corrosion resistance of intermetallic alloys has been evaluated by electrochemical tests (potentiodynamic polarization curves, and measurements of open circuit potential, linear polarization and electrochemical impedance) in artificial saliva. The performance of intermetallic alloys was compared with that of Ti. The results obtained showed that the addition of Ni and Ti substantially improves the corrosion resistance of the base intermetallic. The corrosion resistance shown is comparable or greater than that shown by Ti. However, the addition of Co reduces the corrosion resistance of the base intermetallic.

Effect of core materials for core fabrication for dental implants on in-vitro cytocompatibility of MC3T3-E1 cells

Background

Despite the wide use of dental materials for CAD/CAM system in prosthetic treatment, the effect of the materials, which are used as dental implants core fabricated, on cells involved in dental implant osseointegration is uncertain. This study aimed to investigate and compare the effect of single core materials used for dental implants fabricated by the dental prostheses fabrication process and the CAD/CAM milling method on MC3T3-E1 cells.

Methods

The materials used for prostheses restoration in this experiment were Porcelain Fused Gold (P.F.G), Lithium disilicate glass ceramic (LiSi₂), Zirconia (ZrO₂), Nickel-Chromium (Ni-Cr) and Cobalt-Chromium (Co-Cr). MC3T3-E1 cells were cultured and used, the cell adhesion and morphology were observed and analyzed using confocal laser scanning microscopy (CLSM). Methoxyphenyl tetrazolium salt (MTS) and alkaline phosphatase (ALP) assay were used to observe the cell proliferation and differentiation.

Results

CLSM revealed irregular cell adhesion and morphology and the filopodia did not spread in the Ni-Cr specimen group. Significantly high cell proliferation was observed in the ZrO₂ specimen group. The LiSi₂ specimen group presented significantly high cell differentiation. Intergroup comparison of cell proliferation and differentiation between the Ni-Cr specimen group and all other specimen groups showed significant differences (p < .05).

Conclusion

Cell proliferation and differentiation were observed from the cores, which were fabricated with all specimen groups on cytocompatibility except the Ni-Cr specimen group.

Metal nanoparticles-induced activation of NLRP3 inflammasome in human oral keratinocytes is a possible mechanism of oral lichenoid lesions

The NLRP3 inflammasome has been implicated in the pathogenesis of various inflammatory diseases and is activated by particulate stimulants. Oral epithelial keratinocytes are frequently exposed to metal nanoparticles. In this study, we examined the effects of gold, silver, and palladium nanoparticles, which are frequently used for dental metal alloys on cell proliferation, cytotoxicity, autophagy, lysosomal functions, and NLRP3 inflammasome activation using the immortalized human oral keratinocyte cell line RT-7. The metal nanoparticles were agglomerated in the membrane vesicles in RT-7 cells and suppressed cell proliferation and increased lactate dehydrogenase activity as well as the proportion of apoptotic cells. Silver and palladium nanoparticles induced autophagy and lysosomal dysfunctions and all metal nanoparticles tested triggered the secretion of IL-1β through caspase-1 activation. Furthermore, the epithelium obtained from patients with oral lichenoid lesions (OLLs) had robust NLRP3, ASC, caspase-1, and IL-1β-positive keratinocytes and cDNA microarray showed significant elevation in the mRNA levels of NLRP3. These results suggest that internalized metal nanoparticles in oral mucosal epithelial cells activate the NLRP3 inflammasome through the induction of lysosomal damage and autophagy dysfunction. This process may be involved in the pathogenesis of OLL and suggest its potential as an alternative target for OLL therapy.

Wire Electrodes Embedded in Artificial Conduit for Long-term Monitoring of the Peripheral Nerve Signal

Massive efforts to develop neural interfaces have been made for controlling prosthetic limbs according to the will of the patient, with the ultimate goal being long-term implantation. One of the major struggles is that the electrode’s performance degrades over time due to scar formation. Herein, we have developed peripheral nerve electrodes with a cone-shaped flexible artificial conduit capable of protecting wire electrodes from scar formation. The wire electrodes, which are composed of biocompatible alloy materials, were embedded in the conduit where the inside was filled with collagen to allow the damaged nerves to regenerate into the conduit and interface with the wire electrodes. After implanting the wire electrodes into the sciatic nerve of a rat, we successfully recorded the peripheral neural signals while providing mechanical stimulation. Remarkably, we observed the external stimuli-induced nerve signals at 19 weeks after implantation. This is possibly due to axon regeneration inside our platform. To verify the tissue response of our electrodes to the sciatic nerve, we performed immunohistochemistry (IHC) and observed axon regeneration without scar tissue forming inside the conduit. Thus, our strategy has proven that our neural interface can play a significant role in the long-term monitoring of the peripheral nerve signal.

Genotoxic effects in oral mucosal cells caused by the use of orthodontic fixed appliances in patients after short and long periods of treatment

OBJECTIVE

This study aimed to evaluate the genotoxic effects in the oral epithelial cells of patients undergoing fixed orthodontic treatment and to compare these to a control group without treatment. The null hypothesis to be tested is that corrective orthodontic treatment at different periods does not cause genotoxic effects in patients.

MATERIAL AND METHODS

An observational cross-sectional study including 74 patients enrolled in corrective orthodontic treatment and 21 control patients, between 11 and 35 years of age, of both genders, participated in the research. Patients undergoing treatment were divided into four treatment groups differentiated by treatment periods: G1, n = 21 (1 month to 12 months); G2, n = 21 (13 to 24 months); G3, n = 23 (25 to 48 months); and G4, n = 9 (over 48 months). Cells were collected by scraping the internal side of the cheek and subsequently placed in tubes containing 0.9% sodium chloride solution. The sample underwent evaluation for genotoxic effects by means of the micronucleus test (MNT). Bivariate analyses were performed using parametric tests (t test or ANOVA) and nonparametric tests (Chi-square test, Kruskal-Wallis test, Dunn post-test). The adopted level of significance was 5%.

RESULTS

Statistically significant differences for any of the genotoxic abnormalities (binucleated, trinucleated, karyolysis, piknosis, nuclear buds) were not found except for karyolysis, which was higher in the control group than in G4 (p < 0.05).

CONCLUSIONS

This study did not demonstrate evidence of genotoxic effects even after long periods of corrective orthodontic treatment.

CLINICAL RELEVANCE

This study explores genotoxic effects in fixed orthodontic patients.

Different Materials Used as Denture Retainers and Their Colour Stability

BACKGROUND:

Retainers are of great importance for the longevity of the prosthetic removable partial denture during various functions especially the esthetic one. The key of successful clasp selection is to select a direct retainer that will control tipping and torquing forces on the abutment teeth, provide retention against reasonable dislodging forces and are compatible with both tooth and tissue contour together with the aesthetic desire of the patient.

AIM:

This study aims to compare different clasp material to enhance the choice of the clasp based on the aesthetic point of view.

METHODS:

The colour evaluation of the tested materials had been evaluated by computer aided technique with digital camera with 3 Mega Pixels of resolution.

RESULTS:

In the current research, the technique of colour evaluation was carried out to compare different clasp materials to enhance the choice of the clasp based on the aesthetic point of view. Most commonly, Removable Partial Denture (RPD) retainers are fabricated identically from the metal framework’s alloy as Cobalt Chromium (CoCr) alloy although it is unaesthetic. This esthetic problem has been overcome by other methods and by utilising different materials, these included covering the retainers with tooth-coloured acrylic resin, as well as the introduction of esthetic materials as; Thermoplastic Acetal, Versacryl, and Thermopress.

CONCLUSION:

It has been concluded that the non-metallic Acetal resin clasp shows superior physical properties regarding colour stability.

Potential Causes of Titanium Particle and Ion Release in Implant Dentistry: A Systematic Review

Implant surface characteristics, as well as physical and mechanical properties, are responsible for the positive interaction between the dental implant, the bone and the surrounding soft tissues. Unfortunately, the dental implant surface does not remain unaltered and changes over time during the life of the implant. If changes occur at the implant surface, mucositis and peri-implantitis processes could be initiated; implant osseointegration might be disrupted and bone resorption phenomena (osteolysis) may lead to implant loss. This systematic review compiled the information related to the potential sources of titanium particle and ions in implant dentistry. Research questions were structured in the Population, Intervention, Comparison, Outcome (PICO) framework. PICO questionnaires were developed and an exhaustive search was performed for all the relevant studies published between 1980 and 2018 involving titanium particles and ions related to implant dentistry procedures. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed for the selection and inclusion of the manuscripts in this review. Titanium particle and ions are released during the implant bed preparation, during the implant insertion and during the implant decontamination. In addition, the implant surfaces and restorations are exposed to the saliva, bacteria and chemicals that can potentially dissolve the titanium oxide layer and, therefore, corrosion cycles can be initiated. Mechanical factors, the micro-gap and fluorides can also influence the proportion of metal particles and ions released from implants and restorations.