Dental Magnetic Attachments Research Articles

Influence of Coating Material Thickness on the Attraction Force of Dental Magnetic Attachment: An In Vitro Study.

This study aimed to determine the influence of coating material thickness on the attraction force of dental magnetic attachment (DMA). An in vitro experimental design was implemented using DMA as samples coated with different material types including polytetrafluoroethylene (PTFE) and glass ionomer varnish. DMA consists of keeper and assembly. The coating material was applied to DMA in two ways, on the assembly only and both the keeper and assembly. The thickness of each coated DMA was measured with a digital micrometer, and analysis was subsequently conducted with a universal testing machine to evaluate potential alterations in magnetic attraction force. Comparison was made between the attraction force of both the coated and uncoated DMA serving as a control specimen. The thickness of the coating material applied to both the keeper and assembly was 25 μm, while PTFE and varnish coating on the assembly alone was estimated as 12 and 10 μm, respectively. The magnetic attraction force of the uncoated DMA was 613.63 gf. Following coating, the magnetic attraction force decreased by 34.02-79.45 gf. The ANOVA test indicated that the decrease in magnetic attraction observed across both types of coating material and technique did not show significant differences. The thickness and type of coating material had no significant effect on magnetic attraction.

Ideal set-up angle between a pair of oval dental magnetic attachments for suppression of the loss in retentive force associated with horizontal displacement

Two oval sandwich type magnetic attachments set up in various angulations and spacing, then the pattern of retentive force against horizontal displacement studied. A measuring device and methodology that matches ISO 13017 was used. A pair of magnetic attachments fixed on the same plane at a specific distance on the measuring device and set in various angulations. Retentive force readings of magnetic attachments in various setup positions against the horizontal displacement along the major or minor axis directions were taken. The pattern of decline in retentive force as horizontal displacement increased was different across the various set-ups. It was found that the decrease in retentive forces associated with horizontal displacement can be suppressed when the angle between the major axis and the direction of movement is as small as possible. Formation of a 90° angle between major axes of any pair of magnetic attachments led to nullification of the decline in retentive forces associated with displacement in any direction. Therefore, 90° is the practical, ideal set-up angle between any pair of dental magnetic attachments critical for suppression of the loss in retentive force associated with horizontal gap.

Factors Affecting the Attractive Force of Dental Magnetic Attachment: A Literature Review for Guiding Dentists in Clinical Application.

Aim The aim of this review is to get a comprehensive description of the factors that may influence the attractive force of the dental magnetic attachment. Background Dental magnetic attachment is a term for a magnet used as an overdenture retainer. Magnets that are widely used are permanent magnets such as neodymium iron boron (NdFeB) and samarium cobalt (SmCo). Theoretically, the magnetic attractive force in a permanent magnet has a constant retentive force, and the magnitude of the force will not decrease over time. However, several studies revealed that the magnetic attractive force can be decreased, resulting in the failure of overdenture retention. Some of the factors of reduced magnetic attraction that have been studied are corrosion and temperature. There are no articles that specifically review the factors that can influence magnetic attraction. Review Results. A total of 25,880 articles were obtained during a search on 3 journal databases: PubMed (2,647), ScienceDirect (23,184), and Scopus (229). From those publications, 15 articles reported relevant outcome data that were then extracted. Magnetic attractive force can be influenced by temperature, corrosion, keeper surface morphology, type of magnet, keeper-assembly size combination, inclination, insertion-removal cycle, gliding/loading cycle, number of magnets, crosshead speed, and force direction. Conclusion Many factors can affect the magnetic attraction force of the dental magnetic attachment. Corrosion is the most likely factor to occur because the dental magnetic attachment is always in the oral environment which contains corrosive saliva and is susceptible to damage due to mastication forces.

The Effect of Acid Solution on Dental Magnetic Attachment

Dental magnetic attachments used as a retainer for overdentures are encapsulated with a corrosion resistant casing to prevent corrosion of magnets. However, some studies reported that the casing still has a risk of corrosion. This study aims to determine the effect of acid solutions on magnetic attractive force, dissolving metal ions and corrosion of magnetic attachment surfaces. The dental magnetic attachment material used is Magfit DX 600 (Aichi, Japan). It consists of assembly and keeper. The assembly and keeper immersed in acid solutions with a pH of 3.8 and 5.8 for 7 and 14 days. After immersion, the assembly and keeper were analyzed using SEM, universal testing machine, and the atomic absorption spectrophotometry to determine the surface corrosion, the magnetic attractive force, and dissolved metal ions, respectively. It is found that all assemblies showed signs of corrosion and reduction of magnetic attractive force after immersed in acid solutions with a pH of 3.8 and 5.8 for 7 and 14 days. A greater decrease in magnetic attraction was obtained at 14 days immersion in an acid solution with a pH of 3.8. Fe ion dissolution in the assembly and keeper was found to increase at 14 days of immersion. The lower the pH of the acid solution and the longer the immersion time, the signs of corrosion on the surface of dental magnetic attachment are clearly observed. The magnetic attraction force also decreased with decreasing the value of pH as well as the increase of the content of Fe ion in immersed solution.

A Study on Performance Evaluation of Magnetic Dental Attachments

This study measures retentive force as function of the diameter, the cross-head speed, and the number of detachments of dental magnetic attachments in a clinical environment, and analyzes the validity of the international standard method for testing them. In this study, tests 1, 2, and 3 were used to measure the retentive force as a function of the contact area of the magnetic attachment, and tests 2 and 4 as a function of the cross-head speed. Test 2 and 5 compared function of the retentive force as a function of repeated detachments Results showed that the retentive force increases as the sample surface increases, and decreases as the cross head speed increases. Additionally, after 1500 detachment cycles, the retentive force increased. Finally, the international standard test method was validated, because an objective method for testing magnetic attachments in clinical environment could not be found.

Artifact on MR imaging by a dental magnetic attachment keeper: Preliminary study on a new keeper removable phantom

AbstractAimsDental magnetic attachments with satisfactory retentive force and stability are now commercially available for dental treatment. The aim of this study was to investigate a new phantom for evaluation of the artifact on magnetic resonance (MR) imaging by a dental magnetic attachment keeper.Material and MethodsWe developed a new keeper removable phantom for evaluation of the artifact on MR imaging. A keeper was inserted in an acrylic pole in a PET bottle. The keeper from acrylic pole of the phantom was removable. The keeper with saline solution in the PET bottle with a head and neck coil underwent MR imaging at our university hospital. We measured the real size (unit: mm) of artifact of the phantom with the keeper using a DICOM viewer. Furthermore, the size of artifact of a patient's image with the same three keepers in the mouth was measured on the image using the DICOM viewer, too.ResultsIn MR images of the phantom with a keeper, the maximum size of artifact on axial T1‐weighted, T2‐weighted and STIR images were 78 mm, 85 mm, and 67 mm, respectively. Regarding MR images of the patient with three keepers, the maximum size of artifact on axial T1‐weighted, T2‐weighted and STIR images were 106 mm, 111 mm and 100 mm, respectively.ConclusionsWe investigated a new keeper removable phantom for evaluation of the artifact on MR imaging. The phantom can be used to evaluate the artifact on MR imaging by a dental magnetic attachment keeper.

Fabrikasyon ve Döküm Manyetik Ataşmanların Korozyon Dirençlerinin İncelenmesi

Amaç: Bu çalışmanın amacı, protetik tedavilerde kullanılan döküm ve fabrikasyon manyetik ataşman sistemlerinin, korozyona karşı dirençlerinin incelenmesidir. Gereç ve Yöntem: Korozyon testi için, ağırlıkça %39,5 platin, %59,75 demir ve %0,75 niobyum içeren döküm manyetik ataşmanlar ile neodmiyum, demir ve boron içeriğe sahip fabrikasyon Hilop manyetik ataşman sistemleri, %1’ lik laktik asit ve %0,9’ luk NaCl solüsyon içerisinde 14 gün boyunca bekletilmiş (n:8). Örneklerden solüsyonlar içerisine salınan demir, platin, neodimyum, bor ve niobyum iyonlarının miktarı indüktif olarak eşleşmiş plazma kütle spektroskopi (ICP-MS) yöntemiyle tayin edilmiştir. Bulgular: Her iki manyetik ataşman sisteminde de en fazla solüsyon içerisine salınan ve korozyona neden olan element demir olarak tespit edilmiştir. Ayrıca her iki ortamda da döküm manyetik ataşman sistemi korozyona karşı en dirençli sistem olarak tespit edilmiştir. Sonuç: Paslanmaz çelik ile kaplama fabrikasyon manyetik ataşman sistemlerini korozyona karşı korusada döküm mıknatısların içeriğindeki yüksek orandaki platin malzemeyi korozyona karşı daha dirençli hale getirmiştir.

A computer simulation of the metallic artifacts in MRI caused by dental magnetic attachments

Dental magnetic attachments, which are relatively simple to use and provide good retention and stability, have been increasingly used as dental prostheses. These attachments are composed of ferromagnetic stainless-steel keepers and magnetic assemblies embedded in the denture. The use of magnetic resonance imaging (MRI) to investigate lesions in the oral and maxillofacial areas is quite common. When a patient with a magnetic keeper undergoes MRI examination of the oral or maxillofacial area, however, the keeper is considered a metallic artifact (MA). Depending on the location of the lesion requiring diagnosis, the patient may be required to remove the keeper. The extent of the MA is known to be related to the hardware and pulse sequence parameters and the magnetic properties of the keeper. In this study, we propose a new method to estimate the extent of the MA in MR images caused by a keeper placed in the MRI, approximating the keeper with a magnetic dipole. This method should allow us to express the relationship among the hardware and pulse sequence parameters, the magnetic properties of the keeper and the extent of the MA in the MR image. To evaluate the validity of the method, we compare the MA in MR images produced by the proposed method with those in any experimental MR images taken in the existing study. Via our computer simulations, we show that the proposed method outperformed the existing approach and can estimate the extent of the MA based on the hardware and pulse sequence parameters and the magnetic properties of the keeper. By estimating the extent of the MA in the MR image by using our method before the MRI examination, depending on the location of the lesion requiring diagnosis, it may not be necessary to remove the keeper.

Cytotoxic and genotoxic effects on gingival fibroblasts from static magnetic fields produced by dental magnetic attachments.

To investigate cytotoxic and genotoxic effects of static magnetic field (SMF) produced by dental magnetic attachments on human gingival fibroblasts in vitro. Magnetic attachments have numerous roles in dental prosthesis fixation, but few reports evaluate possible biological effects of static magnetic field (SMF) on human gingival tissues, particular genotoxic effects. The Dyna (500-gr breakaway force) and Steco (173-gr breakaway force) dental magnetic attachments were embedded into autopolymerising acrylic resin in four different configurations each, including single and double magnets. Gingival biopsy was performed on 28 individuals during third molar extraction, and each sample was divided into two pieces for culture under SMF exposure or as a control. In total, seven test and seven control gingival fibroblast cultures were performed for each group resulting in 56 gingival fibroblast cultures. The test culture flasks were placed atop the magnet-embedded resin blocks. After cultures were terminated, mitotic index (MI) and micronucleus (MN) rates were analysed at a p=0.05 significance level by Wilcoxon's test; intergroup differences were analysed with a Kruskal-Wallis test. There was no significant difference in intragroup or intergroup MI rates. The double Dyna (p=0.023) and double Steco (p=0.016) groups had statistically significant intragroup differences in the MN rates. There were no statistically significant differences in MN rates in intergroup analyses. In particular, higher magnetic fields from dental magnetic attachments might be toxic genetically to human gingival fibroblasts. However, there is need for further investigations from different aspects to detect any genotoxicity.

Electrochemical evaluation of the corrosion resistance of cup-yoke-type dental magnetic attachments.

The corrosion resistance of different magnetic assemblies—Magfit DX800 (Aichi Steel), Gigauss D800 (GC), Hyper Slim 4013, and Hicorex Slim 4013 (Hitachi Metals)—were electrochemically evaluated using anodic polarization curves obtained in 0.9% NaCl solution at 37°C. Stainless steels (444, XM27, 447J1, and 316L) composing the magnetic assemblies were also examined as controls. This revealed that all of the magnetic assemblies break down at 0.6-1.1 V; however, their breakdown potentials were all still significantly higher (p<0.05) than that of 316L. The distribution of elements in the laser welding zone between the yoke and shield ring was analyzed using EPMA; except with Magfit DX800, where the Cr content of the shield ring weld was greater than that of 316L. These magnetic assemblies are expected to have good corrosion resistance in the oral cavity, as their breakdown potentials are sufficiently higher than the 316L commonly used as a surgical implant material.

Magnetic displacement force and torque on dental keepers in the static magnetic field of an MR scanner

To evaluate the effect of the static magnetic field of magnetic resonance (MR) scanners on keepers (ie, ferromagnetic stainless steel plate adhered to the abutment tooth of dental magnetic attachments). Magnetically induced displacement force and torque on keepers were measured using 1.5 Tesla (T) and 3.0 T MR scanners and a method outlined by American Society for Testing and Materials (ASTM). Changes in magnetic flux density before and after exposure to scanner static magnetic field were examined. The maximum magnetically induced displacement forces were calculated to be 10.3 × 10(-2) N at 1.5 T and 13.9 × 10(-2) N at 3.0 T on the cover surface. The maximum torques exerted on the keeper (4 mm in diameter) were 0.83 N × 4 mm at 1.5 T and 0.85 N × 4 mm at 3.0 T. These forces were considerably higher than the gravitational force (7.7 × 10(-4) N) of the keeper but considerably lower than the keeper-root cap proper adhesive force. The keepers' magnetic flux density remained less than that of the Earth. Magnetically induced displacement force and torque on the keeper in the MR scanner do not influence the keeper-root cap proper adhesive force.

Effect of corrosive environments and thermocycling on the attractive force of four types of dental magnetic attachments

Background/purposeOne of the problems that has limited magnets’ wide acceptance by clinicians is their low corrosion resistance. The purpose of this study was to determine the effect of corrosive environments and thermocycling on the attractive force of different types of new generation magnetic attachments. Materials and methodsWe measured the attractive forces of 60 magnetic attachment systems (Hyper slim, Hicorex slim, Dyna, and Steco) with a universal test machine. We then immersed 40 of the magnetic attachment systems in two media, namely, 1% lactic acid solution (pH 2.3), and 0.9% NaCl solution (pH 7.3). The remaining magnetic attachments were put through 10,000 thermal cycles (5 °C/55 °C). We measured the attractive forces of the magnetic attachment systems again after immersion and thermocycling to compare data. The data were statistically evaluated with one-way analysis of variance, paired samples t-test, and post hoc Tukey–Kramer multiple comparison tests (α = 0.05). ResultsWe found significant differences between the mean values before and after immersion in corrosive environments (P < 0.05). In contrast to the Dyna and Steco systems (P < 0.001), the differences between the attractive forces before and after thermocycling were not statistically significant for the Hicorex slim and Hyper slim systems (P > 0.05). ConclusionMagnetic attachments showed lower attractive force after immersion in corrosive environments compared to their initial retentive force. In addition, closed-field systems were not affected by the thermocycling procedures and were more resistant than open-field systems to thermal variations characteristic of the oral cavity.

Radiofrequency heating and magnetically induced displacement of dental magnetic attachments during 3.0 T MRI.

The aim of this study was to estimate the risk of injury from dental magnetic attachments due to their radiofrequency (RF) heating and magnetically induced displacement during 3.0 T MRI. To examine the magnetic attachments, we adopted the American Society for Testing and Materials F2182-02a and F2052-06 standards in two MRI systems (Achieva 3.0 T Nova Dual; Philips, Tokyo, Japan, and Signa HDxt 3.0 T; GE Healthcare, Milwaukee, WI). The temperature change was measured in a cylindrical keeper (GIGAUSS D600; GC, Tokyo, Japan) with coping of the casting alloy and a keeper with a dental implant at the maximum specific absorption rate (SAR) for 20 min. To measure the magnetically induced displacement force, three sizes of keepers (GIGAUSS D400, D600 and D1000) were used in deflection angle tests conducted at the point of the maximum magnetic field strength. Temperature elevations of both coping and implant were higher in the Signa system than in the Achieva system. The highest temperature changes in the keeper with implant and keeper with coping were 0.6 °C and 0.8 °C in the Signa system, respectively. The temperature increase did not exceed 1.0 °C at any location. The deflection angle (α) was not measurable because it exceeded 90°. GIGAUSS D400 required an extra 3.0 g load to constrain the deflection angle to less than 45°; GIGAUSS D600 and D1000 required 5.0 and 9.0 g loads, respectively. Dental magnetic attachments pose no risk due to RF heating and magnetically induced displacement at 3.0 T MRI. However, it is necessary to confirm that these keepers are securely attached to the prosthesis before imaging.

上顎および頬部皮膚欠損に対して磁性アタッチメントを利用した顎補綴症例

症例の概要：73歳の男性で，審美，発音および咀嚼機能障害を主訴に右側上顎および頬部皮膚欠損に対する補綴装置の再製を希望し来院した．そこで，磁性アタッチメントを用いた上顎補綴装置を製作し，オブチュレーターとエピテーゼの結合にも磁性アタッチメントを用いた．考察：上顎前歯部の歯軸傾斜を変更することで口唇閉鎖が可能となったこと，咽頭部後縁封鎖が可能となったこと，補綴装置の維持力が向上したことにより，審美，発音および咀嚼機能が改善されたと考えられる．結論：上顎および皮膚欠損を有する症例に磁性アタッチメントを応用することで補綴装置の維持力が増強し，非常に有用であることがわかった．

Dental Magnetic Attachment: Toward Third Generation Devices

Toward realizing the performance of functional and versatile dental magnetic attachments in the third generation required for individual prosthesis, it is important to control retentive characteristics of the attachments. For this purpose, three new types of magnetic attachment, i.e., split-pole type with a slant magnetization, modified split-pole type, and cylinder type, have been developed and evaluated in terms of the restoring force as well as the retentive force. The new attachments are designed to have high corrosion resistance, combining magnetic and nonmagnetic stainless steels and microlaser welding similar to the usual cup-yoke and sandwich-yoke types. It has been found that the two split-pole types have stronger restoring force and the cylinder type has weaker restoring force in comparison with the usual magnetic attachments. The attachments can be used properly and selectively according to individual requirement on abutment state and denture retention. As a result, the newly developed attachments may provide flexible retention performance useful for more effective and extensive applications of a magnetic attachment.

Effect of simulating static magnetic field of magnetic attachment on osteoblastic morphology and surface ultrastructure

To investigate effects of the static magnetic field (SMF) generated by dental magnetic attachment on osteoblastic morphology and surface ultrastructure. The in vitro cultured rat osteoblasts were exposed continuously to 12.5 mT, 125 mT, and 250 mT static magnetic fields for 1, 3, 5, and 7 days. After exposed in SMF, osteoblasts were observed under a phase contrast microscope, and then HE stained and observed under a light microscope. In addition, the cells were observed under a scanning electron microscope (SEM). By continuous exposure, the different intensities of SMF exposure did not change the vital osteoblast growth pattern or distribution. The SEM photos showed that there were certain changes in cellular microstructures for osteoblasts after exposed to 12.5 mT for 5 to 7 days, as well as 125 mT and 250 mT for 3 to 7 days. The more exposure time increased, the more microvesicles on the surfaces of cells were observed. Continuous SMF-stimulation could not affect the shape, distribution, and growth pattern of osteoblasts. The SMF of magnetic attachments could lead to certain changes in surface ultrastructures of osteoblasts in this study.

Galvanic Corrosion between Dental Precious Alloys and Magnetic Stainless Steels Used for Dental Magnetic Attachments

In this study, we examined the corrosion behavior of dental precious alloys and magnetic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, used for dental magnetic attachments. Their galvanic corrosion behavior was evaluated from the viewpoint of corrosion potentials when they were in contact with each other. Rest potentials of the precious alloys were constantly higher than those of magnetic stainless steels. Since most gold alloys raised the corrosion potential more significantly than silver alloys did, silver alloys seemed to be better suited than gold alloys for combination with magnetic stainless steels. However, all corrosion potential values were sufficiently lower than the breakdown potentials of the stainless steels and existed within their passive regions. Based on the findings of this study, SUS XM27 and SUS 447J1--which exhibited higher breakdown potentials than SUS 444--emerged as the preferred choices for combination with gold alloys.

Clinical Application of Magnetic Attachment for Retention and Connection of Maxillofacial Prostheses to an Intraoral Prosthesis

Patient: A 73-year-old male patient was introduced by his plastic surgeon to the Kyushu Dental College Hospital. Numerous surgical excisions resulted in a defect in the region of the right upper palate. He also had a skin defect on the right cheek due. Although he had worn a removable partial denture and a facial prosthese, he had been complaining of mastication, articulation, and esthetic problems. Seven inner crowns with keeper of magnetic attachment were fixed to the abutment teeth. Metal welding was done between the outer crowns and metal frame. Magnetic assemblies were fixed into the outer crowns. Four magnetic attachments were applied to connect the partial denture and the obtulator. Two magnetic attachments were also applied to connect the facial prosthese and the obtulator.Discussion: Although the new maxillofacial prosthese was heavier than the old one, the VAS score of the patient’s satisfaction was 100. An articulation, masticatory function, and mealtime were improved.Conclusion: This clinical report describes the fabrication method for a maxillofacial prosthese by applying dental magnetic attachments for retention and connection. The evaluation of mastication and articulation was done before and after wearing the new prosthese and his complaining improved.

Galvanic Corrosion of Ferritic Stainless Steels Used for Dental Magnetic Attachments in Contact with an Iron-platinum Magnet

This study was an examination of the galvanic corrosion of ferritic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, in contact with a Fe-Pt magnet. The surface area ratio of each stainless steel to the Fe-Pt magnet was set at 1/1 or 1/10. Galvanic corrosion between the stainless steels and the magnet was evaluated by the amount of released ions and the electrochemical properties in 0.9% NaCl solution. Although each stainless steel showed sufficient corrosion resistance for clinical use, the amount of ions released from each tended to increase when the stainless steel was in contact with the magnet. When the surface area ratio was reduced to 1/10, the amount of Fe ions released from the stainless steels increased significantly more than when there was no contact. Since contact with the magnet which possessed an extremely noble potential created a very corrosive environment for the stainless steels, 447J1 was thus the recommended choice against a corrosion exposure as such.

Magnetic fields of 10mT and 120mT change cell shape and structure of F-actins of periodontal ligament cells

Dental magnetic attachments, usually applied locally to oral cavities, produce stray fields (flux leakage) spreading in adjacent tissues. It has been found that human periodontal ligament (PDL) cells change their geometry and the structure of their cytoskeleton F-actins when the cell cultures are exposed to B-field strengths of B = 10mT and 120mT, respectively, which are similar to those generated by dental magnetic attachments. Analytically, after long-time exposures to B-fields for 12h, 36h and 60h, respectively, cytoskeleton F-actins are labeled with a fluorescent dye and observed under a laser scanning confocal microscope. The geometrical cell parameters of cell length and cell width and the fluorescence emission of labeled F-actins, respectively, were determined and subjected to an automatic image analysis using a special software. The results on cell shrinkage and filament reorganizations were statistically analyzed by the program ANOVA ( P < 0.05). It was found that only long-time (hours) exposure to high fields in the order of 0.1T may produce tissue irritations during long-time medical treatments using open- and closed-field dental magnetic attachments.