Objectives: This study assessed the retentive force of three attachments for root-supported overdentures.

Materials and Methods: Patrix of “O” ring post anchor (OPA) attachments (#2; Inoue attachments), magnetic attachments (MA) (3513, Neomax), and coping telescopes (CT) were cast with Ag-Au-Pd alloy (Castwell, GC). For OPA and MA, the “O” ring and magnet were placed on the post anchor and keeper, respectively. For CT, autopolymerized PMMA was used to connect the patrix coping and the matrix framework. The retentive force (n=5, N) was measured at a crosshead speed of 20 mm/min as the maximum load when the joined patrix and matrix of either the single or the double retainer (30 mm apart) were separated under the dry and wet conditions. The results were analyzed by ANOVA/Tukey's HSD test (a=0.05).

Results: For the single retainer, the retentive force of CT was significantly greater than for MA and OPA (p<0.05). Excluding MA, the retentive force under the wet conditions decreased compared to the dry conditions. For the double retainer, all the attachments had retentive force approximately two times greater than for the single retainer.

Conclusion: Although the greatest retention was found using CT, the retentive force of each CT specimen varied widely.

As the magnetic attachment (MA) is one of the most useful retainers to stabilize the natural root- and/or implant- supported overdenture, it is essential to fix magnetic assemblies into denture base and keepers into abutments firmly.Newly developed MAs are stronger in force and smaller in size compared with the old ones: that is to say new MAs are easily to be detached from the denture base or abutments. Therefore, it is very important to evaluate the adhesive strength of magnetic assembly to denture base whether or not the assembly has side slot, preliminary treatment of sand blast or adhesive resin coating. We examined the adhesive strength of magnetic assembly to denture base with the difference of these conditions and tried to define the standardization of dental magnetic attachment.

Purpose: It is recommended that the keeper surface of magnetic attachment be parallel to the occlusal plane. Therefore, an anterior tooth is tilted buccally, and the loading direction of the occlusal force is parallel to the axis of the abutment tooth; the keeper surface may incline away from the occlusal plane. The purpose of this study was to evaluate the retentive force of the magnetic attachment at various keeper angles.

Materials and Methods: The magnetic attachment that was tested consisted of a magnetic assembly and KB keeper of GIGAUSS C600 (GC). A tensile test was performed on a magnetic attachment at various keeper angles by using a testing jig. The retentive force of magnetic attachment at a keeper angle of 0° to 75° was measured, and statistical analysis was performed using ANOVA and Tukey's test.

Result: The retentive force of the magnetic attachment decreased from 5.6 N at 0° to 1.6 N at 75°.

Conclusion: The limitation of this study was that the retentive force of GIGAUSS C600 reduced when the setting angle of magnetic attachment was increased. No significant difference was indicated in the retentive force for keeper angles between 30° and 45°. In this study, the experimental testing jig was useful in reducing the slippage of the magnetic attachment.

The structure of the attractive force is slightly complicated. This is due to the complicated gradient of the magnetic distribution affecting the shape of the magnetic assembly and keeper, and mutual relationship between them. Various mechanical actual measurements and theoretical analyses based on the finite element method have been performed regarding attractive force of a magnetic attachment.

In measurement of the attractive force of a magnetic attachment, the maximum value should be measured accurately as an indicator of the rational characteristics. To achieve this, it is important to pull in the vertical direction to the adsorption surface of magnetic assembly and keeper. However, it was difficult to obtain a reliable value by the conventional method since the sideslip which is one of the characteristics of a magnetic attachment made measurement procedures complicated. Therefore, we devised exclusive JIG and die which designate the direction to solve this problem, and measured attractive force of a magnetic attachment. These devices enabled to designate the pulling direction easily. We report reproducible results obtained in the present study.

Magnetic attachment for practical use was developed in Japan in 1992. Since then, dentures using magnetic attachment have been providing tremendous benefits both to patients and dentists over the last 14 years, and there are high expectations from various fields for the future.

However, in clinical practice, we have been experiencing problems including the loss of magnetic assembly detached from the denture, and the weakening of the magnetic force due to the damage of magnetic assembly. In such case, it is desirable to use a magnetic assembly of the same kind for restoration. However, it is often difficult to obtain the same kind of assembly due to the rapid alternation of generations of magnet attachments.

In the present study, we measured the attractive force between a magnetic attachment keeper and a magnetic assembly from different manufacturers using a device developed in our department, and obtained interesting findings.

The dental magnetic attachments are a device used in the mouth to retain a denture. The tissues in the mouth are exposed to the magnetic fields leaking out of the magnetic attachments for a long time. It may therefore be important to discuss biological effects of the leakage magnetic fields. It is required at first to evaluate the strength of the leakage magnetic fields. As an example, a cup yoke type of magnetic attachment is focused here for evaluating the leakage magnetic fields because the attachment is used most generally. Strength of the leakage magnetic fields is analyzed by changing magnetic structure parameters using a finite element method, and is discussed in relation with the optimum structure giving the maximum magnetic attraction.

The objective of this study is to develop a screening device for the dysphagia using the Magneto-Impedance (MI) sensor. The Repetitive Saliva Swallowing Test (RSST) [1] is used for screening of the dysphagia. Currently, particular training for doctors is required for the RSST. We developed a screening device to automate the RSST for operating for operating the test without training. The screening device is simply consisted of a MI sensor and a neodymium magnet. The MI sensor can sense the movement of the magnet as the change of magnetic field. The magnet will be attached on larynx of a patient and the waveform from the MI sensor represents the movement of larynx by swallowing. Experimentations are performed to evaluate the availability of the device for two healthy subject. The device can measure the movement of larynx and count the number of swallowing.

Introduction: MI sensor aided to Magneto-inductive effect in amorphous wires is able to recognize 0.1mG. Motion control sensor (AMI601, Aichiseikou) constructed with a geomagnetism-sensor and an acceleration-sensor can measure the posture angles of pitching, yawing and rolling of the object as all directional angle analysis of the three dimensions. This sensor may be expected a useful equipment as a clinical tester.

Objective: The purpose of this study was to report a summary of this system and to assess the possibility of applications of prosthetic treatment.

Material and methods: This system constructed with the detecting elements and the sensor of IC. The detecting element had an USB connecter, so the measured date could be handled on PC. We developed the software (α version) for this system and assessed that for prosthetic treatment by Navigation of the preparation of abutment tooth and the formation of implant fossa, Evaluation of the occlusal plane and Evaluation of the occlusal plane.

Results: This system facilitated to evaluate more easily and objectively.

Conclusions This study suggested that MI sensor-aided motion control system might be an effective system for requiring the evaluations of the angles through the treatment in prosthetic dentistry.

Gigauss C600 EC Keeper Tray released last autumn has been applied to the pulpless tooth. This tray was developed as a ready-made plastic pattern for extracoronal attachments. It is required to provide enough strength in an extracoronal attachment, especially in the neck region. The general prosthetic technology providing the strength is to set high corner R to distribute stress. However, corner R needs to be minimal to place components into the limited space in clinical practice. We confirmed the difference in corner R in the neck region using finite element method to investigate the shape meeting this contradictory requirement. In addition, we performed a breaking test of a casting based on a prototype with different corner R in the neck region, and compared the fracture surface with the analysis result. This report summarizes findings obtained by the present study useful for the future deign guide.

A conventional magnetic attachment is an abutment generally introduced on a pulpless tooth. An extracoronal attachment developed in recent years utilizes the space of missing teeth, and therefore can be applied to a vital tooth. The introduction of an extracoronal magnetic attachment markedly expanded the clinical application range of a magnetic attachment. However, extracoronal attachment required complicated laboratory works due to the complex shape of the abutment.

The introduction of a ready-made plastic pattern, “GIGAUSS C600EC keeper tray” enabled standardization and simplification of laboratory works. However, minor changes of the attachment shape are frequently needed in consideration of neighboring alveolar ridge shape and opposing relations in clinical practice. In the present study, we performed stress analysis of extracoronal magnetic attachment by changing the shape in parts of a ready-made pattern. The present paper reports the summary of the analysis results.

Dental magnetic attachments are usually composed of ferritic and austenitic stainless steels such as SUS444, SUSXM27, SUS447J1 and SUS316L. In this study, corrosion behavior of the stainless steels was examined with a focus on electrochemical properties and released ions. Galvanic corrosion of these stainless steels was also considered using electrochemical properties when they contact with dental precious alloys used for a root cap.

The stainless steels mainly released Fe ions after immersion for 168 hours in 0.9% NaCl and 1% lactic acid solutions at 37°C, and SUS447J1 released the smallest amount of Fe ions among them in both solutions.(n=5) Anodic and cathodic polarization curves in 0.9% NaCl solution showed that corrosion potentials on each stainless steel maintained within passive region even when they contacted with the precious alloys.(n=3) Though the pitting potential on SUS316L was lowest at 0.35V of those on the stainless steels, it was higher than that of its corrosion potential in contact with the precious alloys. These findings indicate that the ferritic stainless steels composing dental magnetic attachments have superior corrosion resistance to SUS316L and that they can be safely used as magnetic yokes or keepers in an oral cavity even in contact with the precious alloys.

Sterilization and disinfection are important in dental treatment. While magnetic attachments have been used in clinical dentistry for about ten years, there have not been many studies on sterilization and disinfection. Sterilization and disinfection can alter the surface properties of magnetic surfaces or lower attractive force because heating can weaken magnetic assemblies and keepers, and chemicals can corrode metals. There is a need to develop sterilization and disinfection methods that are suitable for magnetic attachments.

To optimize and standardize sterilization and disinfection methods for magnetic attachments, the present study subjected magnetic attachments to conventional dental sterilization and disinfection and then measured the surface properties and attractive force of magnetic attachments. Surface roughness was measured using a non-contact three-dimensional measurement equipment, and attractive force using a digital force gauge.

The results showed that EOG sterilization and STERIHYDE are suitable for sterilizing and disinfecting magnetic attachments, but NaOCl is unsuitable.

Magnetic attachment is a clinical tool retaining a denture to abutment tooth using attractive force of a permanent magnet. In recent years, the clinical use of dentures using magnetic attachment has been increasing due to its benefits. However, transformation and abrasion develop at the contact surface of magnetic assembly and keeper due to the long-term functional burden placed on magnetic attachment in the mouth, resulting in the destruction of magnetic attachment and decrease in the attractive force. In the present study, repeated loads (10 kgf, 100,000 times) were applied to the magnetic assembly and adsorption site of the keeper using repeated duster examination machine. We measured the durability of magnetic assembly and keeper, surface morphology of the adsorption site, and attractive force of the magnetic attachment, and investigated the mechanical strength required for the magnetic attachment.

We have already showed that the technique of the magnetic attachment on the proximal surface of an abutment tooth at the 16th JSMAD meeting. The clinical report of the case was published in the Volume 13, Number 2, 2004, JSMAD. That magnetic attachment is little damage to the abutment tooth, and it can be superior to cosmetics as the circumferential clasp is used. There is a weak point in the method, and that means it is difficult to set the keeper on the proximal surface of the abutment tooth. Therefore we improved the technique, we used a clear resin core which we originally designed, and that we improved the technique of the keeper adhesion. As a result, we were able to get improvement in cosmetics. Through three clinical cases showed clearly that resins were into the cervical margin with the keeper adhesion, it is difficult to polish of the abutment tooth after the adhesion. It was thought that the improvement of technique was necessary continuously.

Objectives: To evaluete and compare incorporating technique with spill-way (WS)and without spill-way (WOS) for incorporating the magnetic assembly into overdenture base.Material and methods: Fife specimens of magnetic attachment (MAGFIT(R)DX 600, Aichi SteelCorporation, Japan) were used. Denture base was substituted with Resin-cap fabricated by heat curing resin ( Acron, GC Corporation, Tokyo, Japan). Each specimen was measured 10 times for without resin caps (control), after incorporation WS and WOS by universal testing machine AGS-H and software interface Trapezium 2.24. Resin-cap was loaded by 25N, while each incorporation. Between measurements samples were cleaned by Chloroform. Stastistical analysis: One-way ANOVA and Tukey HSD Pst Hoc Tests(P<0.05). Results: After WS attractive force decreased by16.87 % and after WOS by 9.38%. Conclusion: After incorporation WS reduction of the attractive force was bigger than WOS.That reduction was statistically significant. Incorporation technique WOS more reliable.