Abstracts of The 8th International Conference on
Magnetic Applications in Dentistry
March 2 - March 21, 2009Session 1
Chair: Shin-ichi Masumi (Kyushu Dental College)
[POSTER][DISCUSSION]
1. The Full Mouth Reconstruction using Magnetic AttachmentsNakamura Y., Shoji K., Ando A., Tanaka T., 1 Okada M.,1 Imaoka S.,Ohno Y. and Tanaka Y.
Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
1Department of Dental Laboratory, Aichi-Gakuin University Dental Hospital
A magnetic attachment is device using magnetic attractive force to provide and assist in the retention of dentures. Dentures using these special attachments have been well received by patients and treating dentists. The purpose of this report is the case presentation for a patient who presented with chief complaints of aesthetic dissatisfaction and inability to chew properly. This patient underwent full mouth reconstruction using magnetic attachments at the retaining elements. The following is a summary of treatment completed.
Clinical History
The patient was a 42-year-old female with chief complaints of aesthetic dissatisfaction and masticatory dysfunction. The patient had received implants on the right lower molar region in 1995, but they were failed after 3 years. The edentulous upper and lower molar regions were left untreated for many years, resulting in a distorted plane of the occlusion and a decrease in occlusal vertical dimension. Although the patient visited several general practitioners and municipal hospitals to seek aesthetic correction, she was dissatisfied with the treatment results, and then consulted with our department.
[POSTER][DISCUSSION]
2. Longitudinal Study on Metal Plate Denture with Magnetic Attachments
R. Ito, K. Hoshiai, N. Hasegawa, N. Muraji, T. Kawaguchi, K. Noda, K. Watanabe and Y. TanakaDepartment of Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
[POSTER][DISCUSSION]
3. Evaluation of Swallowing Movement by Posture Change using Magnet-Impedance Sensor
K.Tanida1, M.Akutagawa2, Y.Kinouchi2, T.Ichikawa3, S.Hongama31Graduate School of Advanced Technology and Science The Univ. of Tokushima
2Institute of Technology and Science The Univ. of Tokushima
3Institute of Health Biosciences The Univ. of Tokushima
The objective of this study is to develop a screening device for the swallowing difficulty using Magneto-Impedance (MI) sensor.
VideoFluorography (VF) and VideoEndoscopic (VE) are effective to the diagnosis of swallowing difficulty.
The Repetitive Saliva Swallowing Test (RSST) is also one of the effective screening methods.
In this study, we developed the screening device to automate the RSST using a MI sensor.
The screening device is consisted of a MI sensor and a magnet.
A magnet was attached on the larynx, and a MI sensor was attached on breastbone.
The movement of magnet, which movement of larynx according to swallowing, was detected with MI sensor as a change in the magnetic field.
In this time, we examined the influence of subjects’ posture on swallowing movement.
Measurement result was different respectively by subjects’ posture change at measurement.
We examined the posture that was appropriate for swallowing by analyzing measurement result.
As a result of the analysis, swallowing movement appeared remarkably when subjects’ posture was cervix part bent position.
However, the screening device seems to be hard to obtain enough result, because its body moves when swallowing.
For the future, it is necessary to make the device that body movement doesn’t influence
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Session 2
Chair: Masatake Akutgawa (The University of Tokushima)
[POSTER][DISCUSSION]
4. Influence of the heating on the attractive force of a magnetic attachment
-Part 2. Study of Denture Based Resin Curing-
Miyata T., Nakamura Y., Niimi J., Ando A., Shouji k., Imaoka S., Ohno Y., and Tanaka Y.
Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
A magnetic attachment has achieved excellent clinical results, and has been recognized as a useful tool with numerous advantages compared with a conventional mechanical retainers.A Neodymium (Nd) magnet, recently available on the market, has a reported characteristic the temperature-related of magnetic force loss at low relative temperatures. This is considered as one disadvantage of a Nd magnet use.
The clinical use conditions including the effect of temperature relationship and laboratory processing should be evaluated.
We investigated the influence of the difference in curing methods and thickness of denture-base resin on the attractive force of a magnetic attachment on the assumption that magnetic assemblies were incorporated into the work model during polymerization temperatures.
[POSTER][DISCUSSION]
5. Effects of Dental Alloys and Magnetic Keeper on MRI.
Part2 Relationship between Cast Crowns and Artifacts of Axial Plane Images
Masayuki Hideshima, Hiroshi Mizutani, Tomohiro Ando, Darline Destine, Shin Ishikawa, Shinya Matsuzaki, Hidetaka Sasaki, Akira Nishiyama, Daisuke Okusa, Aiichiro Ao, Kazuo Nakamura, Yoshimasa Igarashi.
Graduate School, Tokyo Medical and Dental University Section of Removable Prosthodontics
Objectives: MRI artifacts, generated by dental alloys caused some problems according to their magnetic characteristics depending on whether they are diamagnetic, ferromagnetic or paramagnetic substances. The aim of this study was to examine the artifacts area around the specimens by analyzing MRI dicom data with comparing the CV (Coefficient variance) values of signal intensity among dental alloys.
Materials and Methods: Four clinically used dental alloys (Pd alloy, Type 3 Au alloy, Type 4 Au alloy for porcelain bonding, CoCr alloy) were selected and cast into a similar lower first molar using same shell crowns. In addition, the same shell crown itself as a control and a magnetic attachment keeper were also tested. Five from each specimen were prepared and every specimen was fixed into a (150 x 150 x 150) mm acrylic phantom filled with agar. The phantom with one specimen was placed on the table of MRI apparatus (1.5T Magnetom Vision) and was imaged in T1 and T2 weighted methods. Signal intensity ( SI ) around the specimen in the region of interest ( ROI approximatly 2780pixels ) was calculated with a free software ImageJ and CV was compared for evaluation of the homogeneity of the SI. One Way ANOVA and Dunnett’t-test was used for statistical analysis (p<0.05).
Results and Discussion: Different magnitudes of artifacts were observed in each alloy. In the CV of Keeper and CoCr crown, there were significant differences compared with other crowns. Regarding T1 and T2 in each specimen, CV of T2 was comparatively larger than that of T1, though no significant difference was found.
Session 3
Chair: Kazumoto Hoshiai (Aichi-Gakuin University)
[POSTER][DISCUSSION]
6. Evaluation of Leakage Flux out of Foreign Dental Magnetic Attachments
M. Nishida1, Y. Tegawa2, Y. Kinouchi3, and M. Akutagawa3
1 Graduate School of Advanced Technology and Science, The University of Tokushima,
2 Institute of Health Sciences, Graduate School, The University of Tokushima,
3 Institute of Technology and Science, Graduate School, The University of Tokushima
The tissues in the mouth may be exposed to the magnetic flux leaking out of the magnetic attachments for a long time. Therefore, it is important to discuss biological effects of them. Objective of this study is to evaluate the effects to the human body of the leakage flux out of foreign-made dental magnetic attachments.
Their analytical models are based on data of internal structures published in the 7th International Conference on Magnetic Applications in Dentistry. Magnetization J of the magnet is assumed to be 1.3T. Saturation magnetic flux density Bs of the soft magnetic stainless steel is 1.6T. Leakage magnetic flux has been analyzed by the use of FEM(μ-MF, μ-TEC Co., LTD., Tokyo). The leakage magnetic flux is evaluated the guideline that is proposed by ICNIRP and WHO. According to the guideline, the limits of exposure to static magnetic flux for the general public in continuous is 40mT.
As a result, the leakage magnetic flux of Dyna System、Titanmagnetics、Microplant and Multipurpose Magnet System are more than 40mT at the position of the gum. The other three magnetic attachments are less than 40mT.
[POSTER][DISCUSSION]
7. Application of a Split-Type Obturator Retained by Magnetic Attachments.
K.Kanada, M.Onuki and T.HosoiDepartment of Removable Prosthodontics, Tsurumi University School of Dental Medicine（Japan）
Purpose: Since maxillary defect occurring after tumor excision is most often extensive, prosthetic appliance that are used to cover these dento-maxillary defects becomes extremely difficult. The reasons being that the retention of these dento-maxillary prostheses may not be readily achieved, and the placement and removal these of large-sized obturators are difficult. In order to solve these problems, in this study a split-type obturator was applied to a dento-maxillary prosthesis in a patient with an extensive maxillary defect, and a favorable treatment result was obtained.
Methods & Materials: Case: The patient was a 76-year-old male who complained of difficulty in mastication due to denture mobility. The patient underwent surgical excision for a carcinoma of the maxillary sinus at another hospital in 1988.The maxilla was completely edentulous, and no missing teeth were noted in the mandible. Impressions for a denture and an obturator were taken separately, and, after inter-occlusal recording and wax denture try-in, a dento-maxillary prosthesis was completed. The border of the denture and obturator was set near the denture basal surface, and four magnetic attachments were used as a retention for the appliance.
Results: The dento-maxillary prosthesis inserted in the patient showed sufficient retentive force, relieving denture dislodgement during eating, which was the patient’s chief complain. Further more, mastication and speech improved, along with achieving satisfactory esthetics. The patient could easily split, attach, and detach the dento-maxillary prosthesis, and denture cleaning could be completely performed. The new denture also showed marked functional improvement in comparison with the old one.
Conclusion: The cleanability of the internal side of the obturator, which is usually poor in dento-maxillary prostheses, showed marked improvement, since the patient himself could split it to clean, and its morphology was also simple. Furthermore, since a channel to achieve close adhesion was set along the entire circumference of the junction between the obturator and denture, the seepage of water into the internal side of the obturator was successfully prevented. Further evaluation of this split type obturators with regard to, the position of splitting and the degree of the retentive force of magnets are considered necessary.
Session 4
Chair: Tetsuo Ichikawa (The University of Tokushima)
[POSTER][DISCUSSION]
8. Effect of Crosshead Speed on Magnetic Retentive Force
Y. Ogawa1, Y. Umekawa1,2, T. Ishigami1,2, Y. Takeuchi1, N. Tsukimura1,2, K. Ohtani1,2 and S. Ohno11 Department of Partial Denture Prosthodontics, Nihon University School of Dentistry, Japan
2 Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry, Japan
There have been many reports regarding magnetic retentive force. However, in these reports, the crosshead speeds for which the magnetic retentive force has been measured are not the same. Therefore, this experiment was conducted in order to evaluate the influence of the crosshead speed on the magnetic retentive force. Five GIGAUSS D600 (GC) magnets were used as samples. The retentive force of the magnetic attachment was measured using a customized testing jig and a universal testing machine (EZ-Test, Shimadzu) for various crosshead speeds. The crosshead speed was set to 43 different levels in the range between 0.5 mm/min and 500 mm/min. Statistical analysis was performed using the Dunnett test. The strongest retentive force was observed when the speed was lowest, and it was found that the retentive force of the magnets decreased as the crosshead speed increased.
[POSTER][DISCUSSION]
9. The inclination angle on the axial surface of coping affects the stress distribution of the abutment tooth for overdenturesD.Yamanaka1，T. Ohyama1,2，Y. Katakura1，E. Nagai1,2，Y. Mitsuhashi1，S. Nakabayashi1 and T. Ishigami1,2
1 Department of Partial Denture Prosthodontics, Nihon University School of Dentistry2 Division of Clinical Research，Dental Research Center，Nihon University School of Dentistry
When a magnetic attachment is applied to the abutment tooth for overdentures, the shape of coping may affect the stress distribution of the abutment tooth and the circumference tissue. The interaction between the difference of the inclination angle on the axial surface and, the stress distribution and displacement direction on the abutment tooth under the vertical load was examined by using three-dimensional finite element method. Above the coping was setting on the right mandibular canine, the complete overdenture model was evaluated. Three kinds of the inclination angle (0, 30, 45 degrees) on the axial surface of the coping were designed. Ten occlusal stops at the intercuspal position and the upper part of the condyle bilaterally was completely restrained on the models, and the vertical load that was added to the quantity of muscular contraction at closing movement was determined under the load condition. As a result, there were no significant differences about both the stress distribution and displacement direction on three kinds of analysis models. The displacement was correlated the elevated inclination angle on the axial surface was increased slightly
[POSTER][DISCUSSION]
10. Hardening time of self-curing resin for installing magnets and removing denture
S. Endo1, T. Ishigami1,2, K. Miyata1, H. Toyoma1,2, T. Ono1, M. Tsuyumu1, and T. Azuhata1
1 Department of Partial Denture Prosthodontics, Nihon University School of Dentistry, Japan
2 Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry, Japan
The self-curing resin is widely used for installing a magnet into denture bases. In this study, we evaluated the sufficient time needed for installing magnets and removing the denture safely. Five samples of each size of magnetic attachments (GIGAUSS D400, D600 and D800, GC) were tested. The self-curing resin (UNIFAST III LIVEPINK, GC) and gypsum spacers were used for making a resin block, which was set on the test apparatus. By using the brushed-on technique, a magnet was installed into a resin block with its keeper by the self-curing resin, and then the keeper was vertically pulled. The time from the start of brushing on the resin until the time of installing the magnets and removal of the resin block with the magnets was determined and monitored. The optimal time for installing the three types of magnets tested was 50 seconds. The adequate timing required for removing the keeper from the magnets was 130 seconds for D400, 140 seconds for D600 and 160 seconds for D800. In the case of installing the magnets with strong attractive force, there is a tendency for the removal time to become longer.
Session 5
Chair: Hisashi Koshino (Health Sciences University of Hokkaido)
[POSTER][DISCUSSION]
11. The Effect of Abutment Tooth Connection with Extracoronal Attachment using the Three Dimensional Finite Element Method
- Part 2. The Construction of Finite Element Model from CT Data –Ando A., Nakamura Y., Kanbara R., Kumano H., Miyata T., Masuda T., Ohno Y. and Tanaka Y.
Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
An extracoronal magnetic attachment retainer design for partial denture prosthetic applications has been developed. Restorative limitations of space and physiologic function requirements may complicate esthetic placement of attachments in a partial denture design. Our previous reports have presented the advantages of a extracoronal magnetic attachment design for extracoronal applications with vital teeth. The traditional retainer design requirements satisfying retention and resistance form and while providing an applications that is esthetic has shown good patient feedback.
In a distal extension partially edentulous treatment, a patient may refuse to wear bilateral denture for several reasons, including esthetic concerns and satisfactory hard and soft tissue adaptation and fit.
In applications of distal extension and cantilever, an extracoronal attachment has potential to cause overload. The optimal and proper use of any remaining teeth adjacent to the edentulous area for use as an supporting abutments is of great concern. Any decision in the selection of abutment number or interconnected splinting of supporting abutment teeth is based on the best knowledge based upon comprehensive dental evaluation. However, there are clinical situations where minimal supporting information exists to appropriately render these decisions.
Finite Element Method (FEM) has been well applied in stress evaluations for prosthodontic dental studies. We have previously reported the use of two-dimensional models of prosthodontic treatment situations. This study utilized the application of three dimensional modeling to evaluate the applications and stress distribution patterns for extracoronal magnetic attachment retainers for partial dentures.
The aim of the present study was to fabricate three-dimensional finite element model from actual patient data. We investigated the effect of interconnected abutment number in case of unilateral use of extracoronal magnetic partial denture retainers using the FEM model
.
[POSTER][DISCUSSION]
12. The effect of Bracing Arm with Extracoronal Attachment use evaluated by Three Dimensional Finite Element Method
Kanbara R., Ando A., Nakamura Y., Kumano H., Miyata T., Masuda T., Ohno Y. and Tanaka Y.
Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
[POSTER][DISCUSSION]In unilateral extension partial denture treatment situations, magnetic attachments are often used as a hidden attachment retaining retentive elements providing improved aesthetics and comfort. When an extracoronal magnetic attachments is used for retention, the functional cantilever behavior effect of denture should be well understood.
Solutions to cantilever stress transfer concerns include the use of splinting abutments, use of lingual bracing arms and extracoronal attachments interlocks. However, we have not discovered any significant reports or evidence regarding the relative use and merits of these different design elements for improved treatment decision making purposes.
The aim of the present study was to investigate the effect of bracing arms and interlocks employed with extracoronal attachments in unilateral partial dentures using the three-dimensional finite element method (FEM), and to seek alternative designs and comparisons.
13. A case Report of the RPD with magnetic attachments applied to the partially edentulous patient without occlusal contact
M.Hideshima, M.Fukumoto, M,Toko, T.Andoh, H. Mizutani, Y. Igarashi
Section of Removable Prosthodontics, Graduate School, Tokyo Medical and Dental University
It is well known that partially edentulous cases without or less occlusal contacts are severe cases because remaining dentition, supporting tissue and residual ridge are apt to be damaged and prosthodontic devices are easy to be fractured. The authors applied magnetic attachments for preparatory treatment so as to decrease overloading on abutment teeth and increase retention and stability of the denture.
A 74-year-old male patient presented partial edentia of maxillary Kennedy class Ⅳand mandibular Kennedy class Ⅰcontacting only with upper and lower 1 teeth at the habitual occlusal position. The existing maxillary denture was repetitively fractured and right lower canine which was only contacting at the occlusal position was with marked mobility.
Clinical examination revealed to fabricate maxillary and mandibular denture separately in order to maintain the existing occlusal height and apply magnetic attachments to an extruded upper isolated molar and right lower canine with marked mobility.
Each denture was designed with acrylic resin, wrought wires and reinforced cast metal framework because of the limitation of social health insurance system.
The metal frameworks were delivered with T-shaped in cross section and cast embrasure hooks were attached along buccal wrought wire clasps for the reinforcement and stability of the dentures.
The authors present a case report of this severe less occlusal contacting case which resulted in clinical success at 3 years
Session 6
Chair: Hiroshi Mizutani (Tokyo Medical and Dental University)
[POSTER][DISCUSSION]
14. Development of a Measurement System for Jaw Movement
N.Ishihara1, M.Akutagawa2, Y.Kinouchi2
1Graduate School of Advanced Technology and Science, The Univ. of Tokushima
2Institute of Technology and Science, The Univ. of TokushimaIn the diagnosis of the temporomandibular arthrosis, it is assumed to be one of the fundamental factors to know the jaw movement. We try to measure the jaw movement by using a small magnet, MI sensors and the Neural Network(NN).
The small magnet is attached at the jaw in the measurement area (100mm x 100mm x 100mm), and 18 magnetic sensors arranged around the magnet measure the magnetic flux density. Outputs obtained from MI sensors are presented to the NN. And the position and the direction of the magnet are estimated. This experiment has been conducted by the computer simulation. According to results of the computer simulation, estimation errors are up to 10μm and 0.002 degrees.
In this study, A measurement system that adapts to the computer simulation was developed. In the measurement area, the magnet is put and the outputs of the MI sensors are obtained.
The magnet is put around the measurement area. The outputs obtained from MI sensors are presented to the NN. The position and the direction of the magnet are estimated by the error margin of about 4.5mm and 4 degree.
In the future, our method should work with further accuracy.
[POSTER][DISCUSSION]
15. Analysis of Characteristics of Attractive Force of a Magnetic Attachment Using Finite Element Method
Kumano H., Nakamura Y., Masuda T., Imaoka S., Tanaka S., Ohno Y. and Tanaka Y.
Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University
A Magnetic attachment is a retaining device that can be incorporated in to the retainer elements for a removable denture. The retaining effect is dependant upon the attractive force of a specially designed magnet. This device gained widespread clinical use since the first commercially available product was introduced in 1992. Two design types of a magnetic attachment assembly are available. These circuit designs are known as either the cup yoke or the sandwich type.
It is well known that attractive force of a magnetic attachment is significantly affected by any air gap between a magnetic assembly and a keeper.
Different magnetic attachment designs may have different clinical behaviors under function. While the effect of conventional partial denture retentive mechanisms have been well reported. The functional behavior of different partial denture designs using magnetic retaining elements has not been well reported. Nakamura has previously reported an analysis of a sandwich-type magnetic attachment with partial denture use. The “cup-yoke” type magnetic attachment has not been well reported upon.
We performed an analysis of the mechanical properties of a cup type magnetic attachment as a denture retainer using the Finite Element Method, and compared with that of a sandwich type magnetic attachment to comparatively evaluate the mechanical behavior of a denture with different magnetic attachments.
[POSTER][DISCUSSION]
16. An Application of Magnetic Attachment to Cast Clasp
- Development of Magnetic Rest Clasp -
Toshiaki Hasuike, Toshiyuki Kusano, Fumiko Okutsu, Takaaki Matsukawa, Mineyo Sone, Shuji Ohkawa
Division of Removable Prosthodontics, Department of Restorative & Biomaterials Sciences, Meikai University School of Dentistry
The increased emphasis on physical appearance in contemporary society has increased the demand for esthetic dental treatment.
The metallic color of the buccal clasps on premolars or canines is one of the common causes of patient rejection.
Although the RPD design with no buccal arm could offer a solution favorable to patients, but the retentive function of clasps eliminated buccal arms is extremely poor.
The appearance would be vastly improved if metal buccal clasps were eliminated. However, the retentive function of clasps eliminated buccal arms is extremely poor. We developed a new retainer of no buccal clasp arm with the magnetic attachment in the occlusal rest of clasps (Magnetic Rest Clasp).
This report describes the fabrication of a new retainer “Magnetic Rest Clasp” for lower premolars with a plastic jaw model having artificial teeth.