Int Poster J Dent Oral Med 2013, Vol 15 No 1, Poster 631
Using magnets to increase retention of lower dentures - case report
Assist. Prof. Dr. Alexandru-Titus Farcasiu, Lecturer Oana-Cella Andrei, Prof. Emilian Hutu,
Removable Prosthetic Department, University of Medicine and Pharmacy Carol Davila, Bucharest, Romania
April 28th-May 1st 2011
16th Congress of Balkan Stomatological Society
Oral diseases and the patient's history of dental treatments can compromise important jawbone characteristics. If possible, extractions should be avoided for all patients (1) who already suffered extensive bone loss because of the reduced stability and retention of the future denture, especially the lower one. Implants are a good solution but a healthy root system of teeth deteriorated above the gum line always surpasses the value of the artificial root due to the presence of periodontal ligament which enable the transmission of axial forces towards the alveolar bone.
The axial forces are essential in maintaining the height of alveolar bone. The magnetic attachment consists of the magnetic assembly and the keeper. The magnetic assembly is the main part of the magnetic attachment and consists of the magnet and its coating. The keeper is a metal part casted on the root cap which is attracted to the magnetic assembly.
It has to be noticed that magnets increase retention of partial or complete dentures and overdentures regardless of the path of insertion. Magnets are easy to use alone or together with any type of retainers. The most important aspect to be cleared is the influence of magnetism to human body. Modern magnets were tested in many aspects (cell toxicity, cell growth, allergic response) and the results meet international standards. The magnetic field leakage is extremely weak compared to daily use magnetic appliances. For a long time the saliva corrosion of rare-earth magnets was the reason which determined the decrease of magnetic attractive force. The problem was solved through the enclosure of magnets in anticorrosive steel with a small percentage of iron.
Patient A.S., female, 62 years-old, came to the dental office for a complete rehabilitation complaining of chewing inefficiency and inestheticappearance. She has a pathological history of osteoporosis and diabetes. The patient presented at the upper jaw two metalo-acrylic bridges (fig. 1, 2). The central incisors presented severe coronary destruction. Both fixed partial dentures presented mobility. The lower jaw presents only the frontal group of teeth united by a metalo-acrylic cantilever bridge with a two teeth distal extension only on the right side. Periodontal disease is extended and associated with labial and lingual gingival retraction at teeth 4.1, 3.1 and 3.2.
Material and Methods
The only tooth excepted from extraction was the left canine (3.3) because of its good implantation and stability. The surgical phase was executed and a 30-days period elapsed before the primary impression was made. During this period the endodontic treatment of 3.3 was completed. After the root canal treatment, this tooth was used for a cap-type magnetic appliance (Magfit, Aichi Steel Corporation, Japan) on the occlusal surface of the root cap. The preparation involves placing chamfered margin at the level of marginal gingivaand creating slightly divergent walls of root canal and slightly convergent for the axial walls (around 15°). Due to low lateral forces transferred to abutments, the dowel post can be shorter – about 5 mm or less. Also ferrule effect is useful in protection of abutments. Root cap embeds the keeper, which should be surrounded by proper thickness of metal; otherwise the possibility of casting defects will be high. The wax pattern cast with the bonded keeper is the critical laboratory phase; it is necessary to have at least 0,3 mm thick wax for a proper casting (fig. 3, 4).
Two complete overdentureswere fabricated and the patient's esthetic appearance and chewing efficiency improved. The magnet's position is parallel with the occlusion plan in order to obtain better retention for the lower denture (fig. 5). Thepatient was instructed how to clean the denture in the area where the magnet is located (fig. 6). Placing the magnet on the lower caninedid not disturb the esthetic appearance (fig. 7). The massive bone loss that began following extractions will be prevented around the kept canine (fig. 8).
Rutkunasand Mizutanipresent the experimental superiority of studs regarding stabilization but underline that constant retentive properties of magnetic attachments assist abutment preservation. Decreased dexterity and multiple abutments could indicate the use of magnetic devices. Mizutaniand al. compared the retentive force of magnetic (including Magfit) and mechanical attachments, concluding that magnetic attachments have adequate retentive force. Ono et al. support the use of magnets even when the bone supporting tooth is insufficient, the preservation becoming possible by reducing crown/root ratio. Chung et al. found a 18% decrease of retentive ability for Magnedisksystem after 100 loadings but underline the ease of magnet replacing which can solve these situations.
- Minoru A, Yuh-Yuan S. New magnetic applications in clinical dentistry. Quintessence publishing, 2004.
- Rutkunas V, MizutaniH. Retentive and Stabilizing Properties of Stud and Magnetic Attachments Retaining Mandibular Overdenture. An in vitro study. Stomatologija, Baltic Dental and Maxillofacial Journal, 6:85-90, 2004.
- Mizutani H, RutkunasV, Takahashi K, Destine D. Comparison of Retentive Characteristics between Mechanical and Magnetic OverdentureAttachments. Stomatologija. 2005;7(4):115-20.
- Ono T, ToyomaH, IsigamiT, OhyamaT, Shigeru O, Nakabayashi S, MitsuhashiY, Nakajima R. Immediateoverdenturewith magnetic attachment. The 6thInternational conference on magnetic applications in dentistry, 1-20 March, 2007, http://wwwsoc.nii.ac.jp/jmd/index-e.shtml.
- Chung KH, Fletcher-Stark M, Anderson M, Johnson G, WatahaJ, Duh JG. Retention Characteristics of Magnetic OverdentureAttachments After Cyclic Loading. The IADR 86th General Session, 1-5 July, Toronto, Ontario
This Poster was submitted by Assist. Prof. Dr. Alexandru-Titus Farcasiu.
Assist. Prof. Dr. Alexandru-Titus Farcasiu
Removable Prosthetic Department, University of Medicine and Pharmacy Carol Davila
Str. Serghei Rahmaninov nr. 76-80