Ikuya Watanabe,¹, Yasuhiro Tanaka², Kunihiro Hisatsune², Mitsuru Atsuta², Khoi Nguyen¹, P. Andrew Benson¹, Jennifer Chang¹, Yvonne Chiu¹.
1 Department of Biomaterials Science, Baylor College of Dentistry,Texas A&M University System Health Science Center, Dallas, TX, USA
2 Department of Developmental and Reconstructive Medicine, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan

Abstract: This study investigated the joint properties of a cast Fe-Pt magnetic alloy (Fe-36at%Pt) laser-welded to three gold alloys. The gold alloys used were ADA Type II and Type IV gold alloys, and a Ag-based (Ag-Au) gold alloy. Cast plates (0.5 x 3.0 x 10 mm) were prepared for each alloy. After the cast Fe-Pt plates were heat-treated, they were butted against each of the three alloys and then laser-welded with Nd:YAG laser at 200V. Homogeneously welded specimens were also prepared for each alloy. Tensile testing was conducted at a crosshead speed of 1 mm/min. Failure load (Fl: N) and elongation (El: %) were recorded. The Fl values of the group of alloys welded homogeneously were ranked in the order of: Ag-Au alloy > Type IV alloy > Type II alloy > Fe-Pt alloy. The Type IV alloy welded to Fe-Pt alloy had the highest Fl value among the three alloys tested. The El results tended to follow a similar pattern. The results of this study indicated that Type IV gold alloy is a suitable alloy for metal frameworks to which cast Fe-Pt magnetic alloy is laser-welded.

Jie Liu¹, Ikuya Watanabe², Yasuhiro Tanaka¹, Kunihiro Hisatsune¹, Mitsuru Atsuta¹.
1 Department of Developmental and Reconstructive Medicine, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan
2 Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center, Dallas, TX, USA

Abstract: This study examined the laser penetration into cast Fe-Pt magnetic alloy and compared with that into Co-Cr alloy. Cast blocks (20 x 5 x 5 mm) were prepared using a custom made Fe-Pt alloy (Fe-36at%Pt) and a Co-Cr alloy (Cobaltan, Shofu Inc.). After the cast surfaces were air-abraded with 50 micron Al2O3, two cast blocks were butted against one another on the 20 x 5 mm surfaces. They were then perpendicularly laser-welded at their interface using Nd:YAG laser (Tanaka TLL7000) under the following parameters: current of 160 - 300 A (increments of 20 A), spot diameter of 0.4 - 1.6 mm (increments of 0.2 mm) and pulse duration of 1 - 13 ms (increments of 3 ms). After the welded blocks were mechanically separated, the penetration depth (n=3) of the laser into each alloy was measured using computer graphics. The laser penetration into Fe-Pt alloy was greater than that into Co-Cr alloy at any welding parameter, especially at higher current and smaller spot diameter in each pulse duration. The present study could show the basic data to laser-weld cast Fe-Pt metal frameworks to Co-Cr frameworks.

Naoki Baba¹, Ikuya Watanabe², Yasuhiro Tanaka¹, Kunihiro Hisatsune¹, Mitsuru Atsuta¹.
1 Department of Developmental and Reconstructive Medicine, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan
2 Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center, Dallas, TX, USA

Abstract: This study investigated the effect of argon shielding on joint strengths of cast Fe-Pt magnetic alloy laser-welded to Co-Cr alloy. Cast plates (0.5 x 3.0 x 10 mm) were prepared with a custom made Fe-Pt alloy (Fe-36at%Pt) and a Co-Cr alloy (Vitallium, Austenal). After the cast Fe-Pt plates were heat-treated, they were butted against cast Co-Cr plates and then bilaterally laser-welded using Nd:YAG laser at 200V (voltage), 10ms (pulse duration) and 1.0mm (spot diameter). Control (non-welded: 20 mm length) and homogeneously welded specimens were also prepared for each alloy. Laser welding was performed with and without argon shielding. Tensile testing was conducted and failure load (Fl: N) and elongation (El: %) were recorded. The Fl value of the welded Co-Cr without argon shielding was equivalent to its corresponding control (Co-Cr with argon was less than half as strong). There was no difference in Fl value between with and without argon for homogeneously welded Fe-Pt and Fe-Pt welded to Co-Cr. The Fl value of the welded Fe-Pt/Co-Cr fell into the middle of homogeneously welded Fe-Pt (lowest) and Co-Cr (highest) alloys. The El results tended to follow a similar pattern. These results indicated that the argon shielding has no effect on weld strength between Fe-Pt and Co-Cr alloys.

Hiroshi Mizutani¹, Darline Destine¹, Vygandas Rutkunas², Kazuo Nakamura³,Shin Ishikawa⁴.
1 Graduate School, Tokyo Medical and Dental University
2 Lithuania Vilnius University Institute of Odontology
3 International University of Health and Welfare
4 Ishikawa Dental Clinic

Abstract: Understanding of retentive properties during various dislodgement patterns will aid in proper use of overdenture attachments in particular clinical situation. The aims of the study were to 1) evaluate maximum retentive force and energy of different overdenture attachments during anterior, posterior and lateral dislodgments. and 2) compare retentive characteristics between different types of attachments and types of dislodgements. The types of attachments tested were: Magnedisk 500, Magfit EX 600W, Root keeper (domeshaped), Hyperslim 4013, Hyperslim 4513, O-P anchor, Root Locator (pink), Era Overdenture (white and orange). 12 specimens of each type of attachment were tested. 10 measurements of maximum retentive force and energy for each type of attachment were recorded by universal testing machine AGS-H and software interface Trapezium. Maximum retentive force and retentive energy measurements were made by universal testing machine AGS-H and software interface Trapezium. Measurements performed with cross head speed of 50 mm/min. 12 specimens of each attachment type were used and 10 measurements for each specimen were recorded. The results were as follows; only maximum retentive force cannot define retentive properties of attachment devices. Magnetic attachments owing low retentive energy inherently have comparatively small range of retention. Retentive energy represents energy transferred to abutment during dislodgement. However the exact value of load or energy tolerable by abutments is unknown and depends on multiple factors. Retentive characteristics strongly depend on pattern of dislodgement.

Shinya Nakabayashi¹, Hiroshi Takimoto^1,2, Tomohiko Ishigami^1,2, Tetsuo Ohyama^1,2, Hitoshi Toyoma^1,2, Eiichi Nagai^1,2.
1 Department of Removable Partial Denture Prosthodontics, Nihon University School of Dentistry
2 Division of Oral and Craniomaxillofacial Research, Dental Research Center, Nihon University School of Dentistry

Abstract: It is recommended to use a gypsum dummy to ensure specific space in attaching a magnet structure to a resin-based denture. In clinical use, we sometimes form an adequate space inside the denture and attach the magnet structure using cold-curring resin. In this case, too much resin has a bad effect on the amount of polymerization contraction, which may detach the magnet structure from the surface of the keeper. However, no reports have been observed.
Therefore, we made samples in which space amounts were changed with GIGAUS D400, D600, and D800 made by GC. We compared their suction power respectively to examine the influence of resin polymerization contraction in attaching the magnet structure. We would like to report the results of our examination.

M. Motonaga, F. Tsutida, M. Abe, T. Hosoi
First department of prosthetic dentistry, School of dental medicine, Tsurumi University

Abstract: The research on the load of the root of a tooth when detaching it is a little though a lot of researches on the absorption power etc. have been done for a dental magnetic attachment so far. Then, the load of the periodontal membrane by the direction of detaching was researched by using the finite element method this time. The software used Marc/Mentat2003 (MSC software). The model installs Coping that installs the keeper in a Japanese average lower jaw canie, assumes the one to have the periodontal membrane, the cortical bone, and the cancellous bone, and the scale is number 36,991 of 36,660 node number elements. The model restrained the degree of freedom of all nodes on the model base side. The load was assumed 400gf, and was loaded from the keeper to the angle of vertical and 60 degrees and 45 degrees. The material constant was decided referring to a past report. The result paid attention to a main stress. Because an interesting finding was obtained, it reports.

T. Fujimoto¹, T. Ishigami^1,2, N. Tsukimura^1,2, K. Ohtani^1,2, M. Sawano¹, A. Majima¹, A. Kurata¹.
1 Department of Removable Partial Denture Prosthodontics, Nihon University School of Dentistry
2 Division of Oral and Craniomaxillofacial Research, Dental Research Center, Nihon University School of Dentistry

Abstract: Metal plate dentures using magnetic attachments are difficult to remake in accordance with the denture when the root cap and keeper separate after preparing the denture. However, because of the recent widespread use of keeper trays, it has become possible to fix the keeper on the root cap in accordance with the magnetic assembly. I would like to report two cases. In one, I adjusted the keeper for the magnetic assembly within the oral cavity to remake the root cap. In the other, good results were achieved by using the keeper tray for the existing inner cap to improve it to magnotelescope against the decrease of retentive force of konuskronen teleskop.

Motonobu Miyao, Jiro Kishii, Akihiko Nigauri Yoshifumi Higashino and Masatoshi Iwahori
Department of Prosthodontics, Division of Oral Functional Sciences and Rehabilitation, Asahi University School of Dentistry

Abstract: Magnetic attachments have been used for more than 10 years. Magnet material was changed to NdFeB from Sm2Co17. Due to this change, the magnet power became stronger. On the other hand, new problems occurred. Those problems were erosion and abrasion of Magnetic attachments. The purpose of these clinical reports are to present a observation of the erosion and abrasion of Magnetic attachments with microscopic examination.

Nobuki Shoji¹, Shinn Kasahara¹, Osamu Okuno², and Kohei Kimura¹
1 Division of Fixed Prosthodontics, Department of Restoration Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan
2 Division of Dental Biomaterials, Department of Restoration Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan

Abstract: The removable prosthetic appliance makes plaque control easy, comparing with the fixed prosthetic. However, conventional retainer of removable prosthesis has problems declining of retention and lowering of esthetic. As a solution, the removable crown and bridge system assembled with the Fe-Pt magnet outer cap and the magnetic stainless steel (SUS447J1) inner cap has been investigated. Using the integral element method, the 3-dimensional magnetic field of the outer and inner cap model were analyzed to determine the optimal method for the design and magnetization of removable crown and bridge system made of the Fe-Pt magnet. The following matters were examined. It was thought that sectorial four-pole magnetization was the most suitable for magnetization of the Fe-Pt magnet.$B!!(BIn the thickness of upper surface of outer cap, the width of shoulder and the thickness of upper surface of inner cap, the thickness of upper surface of outer cap had the most influence on the attractive force. In case of that the thickness of upper surface of outer cap was 1.0mm, 1.5mm, the attractive force indicate optimum clinically.$B!!(B In this examination, the influence of material and length of axial surface about the attractive force was examined.$B!!(BAs a result, some findings were obtained.