|Year : 2013 | Volume
| Issue : 1 | Page : 43-46
Magnet retained mandibular overdenture: A multidisciplinary approach
Suma Janya1, Priyanka Gubrellay1, Anupam Purwar2, Shally Khanna2
1 Department of Prosthodontics and Maxillofacial Prosthetics, M. S. Ramaiah Dental College and Hospital, Bangalore, Karnataka, India
2 Department of Prosthodontics and Maxillofacial Prosthetics, Purvanchal Institute of Dental Sciences, Gorakhpur, Uttar Pradesh, India
|Date of Web Publication||25-Oct-2013|
Department of Prosthodontics and Maxillofacial Prosthetics, Purvanchal Institute of Dental Sciences, Gorakhpur, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Magnets have been used widely in the field of dentistry for many years with some success, as they can be manufactured in small dimensions as retentive devices in overdenture technique, maxillofacial prosthesis, and obturators. These magnets are attached with remaining root structure or osseointegrated implants which transfer the occlusal load to the bone through the periodontal ligament of the retained roots, thereby prevent resorption of remaining alveolar bone proper and inter-radicular bone present around the roots. In this article, the use of magnetic assembly in fabrication of mandibular overdenture on retained roots and a conventional maxillary removable partial denture is discussed. Magnetic assembly consists of magnet and coping with a keeper on the remaining tooth structure since magnetic attachments can provide support, stability, and retention.
Clinical Relevance to Interdisciplinary Dentistry
- The present article demonstrates the rehabilitation of partially edentulous patient with the help of magnetic assembly mandibular overdenture and maxillary conventional removable partial denture. Clinical presentation showed few remaining teeth in relation to the mandibular ridge. A multidisciplinary approach was adopted to retain the remaining teeth in the mandibular arch with the help of endodontic treatment (root canal treatment) followed by prosthetic rehabilitation.
Keywords: Magnet, micro-laser welding, overdenture
|How to cite this article:|
Janya S, Gubrellay P, Purwar A, Khanna S. Magnet retained mandibular overdenture: A multidisciplinary approach. J Interdiscip Dentistry 2013;3:43-6
|How to cite this URL:|
Janya S, Gubrellay P, Purwar A, Khanna S. Magnet retained mandibular overdenture: A multidisciplinary approach. J Interdiscip Dentistry [serial online] 2013 [cited 2019 Oct 13];3:43-6. Available from: http://www.jidonline.com/text.asp?2013/3/1/43/120530
| Introduction|| |
Dental magnetic attachment systems have been increasingly utilized in prosthodontics to improve the retention of overdenture. Recently developed hard magnetic substances such as samarium-cobalt , and iron-neodymium-boron magnets (Fe14Nd2B) , provide stronger magnetic force per unit size than the earlier open-field aluminum-nickle-cobalt magnets which are susceptible to corrosion by the saliva and provide weak retentive force. Conventional overdenture placement involves embedding the magnetic assembly in the denture base and inserting its corresponding keeper into the abutment root. The magnetic assembly holds the keeper with a retentive force. , This clinical report describes the fabrication of mandibular overdenture retained by closed field magnetic assembly and maxillary conventional removable partial denture to rehabilitate the patient.
| Case Report|| |
A 58-year-old man was referred to the Department of Prosthodontics at M. S. Ramaiah Dental College, Bangalore. Intraoral evaluation revealed partially edentulous maxillary and mandibular arch. Remaining teeth in the maxillary and mandibular arch were periodontally sound, with slight gingival recession in the maxillary arch [Figure 1]. Patient was made aware of the clinical condition and he was willing to preserve the remaining teeth as long as possible. In the mandibular arch, the remaining teeth (33 and 43) were vital and moderate resorption was recorded in relation to bilateral mandibular posterior ridge.
Endodontic treatment and abutment teeth preparation for mandibular teeth
Abutment teeth (33 and 43) were endodontically treated and prepared with diamond rotary instruments (Shofu, Kyoto, Japan), producing a chamfer margin and reduced slightly above the gingival margin (2 mm), followed by removal of two-thirds of the root canal filling material with a rotary drill instrument (Peasow reamer; Dentsply, York, Pennsylvania, USA) to prepare the post space to accommodate the post along with the keeper [Figure 2]a.
|Figure 2: (a) Mandibular abutment teeth preparation, post space preparation, and gingival retraction. (b) Polyvinyl siloxane impression of abutment teeth and posts space|
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Mandibular abutment teeth impression
Gingival retraction (Ultrapak cord#000, SKU: 137; Ultradent, South Jordon, UT, USA) followed by full arch impression with polyvinyl siloxane impression materials (Aquasil, Dentsply International Inc., USA) to record the margin area and root post was successfully made [Figure 2]b and definitive cast [Ultrarock, type IV dental stone; Kalabhai Karson Ltd, Vikhroli (W), Mumbai, India] was fabricated.
Indirect inlay wax (Kerr Co., Washington D.C., USA) was used to make impression of post space to fabricate the post and 0.5-mm inlay wax was kept for the placement of keepers on root teeth [Figure 3]a and b.
|Figure 3: (a) Keepers with wax-up for casting along with posts. (b) Keepers along with post are cemented with glass ionomer|
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The keeper has a flat shape with an attractive face on one side and a dimple face on the other place. Attractive side was kept facing up on the wax-up. All the keepers were placed parallel to the occlusal plane ensured by the surveying procedure. Cast bonded keeper method was used to attach the keepers (Root keeper; Aichi Steel Co., Aichi, Japan) on the root teeth. Sprue wax attached to the wax-up unit and casting was performed for all root caps.
Try-in, setting of root caps, and definite impression of mandibular arch
All root caps were cemented on the roots with glass ionomer cement [Figure 3]b (GC Co., Tokyo, Japan). After cementing the root caps, impression was made with polyvinyl siloxane impression materials [Figure 4]a (Reprosil, monophase; Dentsply International Inc., USA) and definitive cast (Ultrarock, type IV dental stone; Kalabhai Karson Ltd) was poured. Now occlusal rims were fabricated on definitive upper and lower cast. Jaw relation, teeth arrangement, and try-in were completed on the waxed denture [Figure 4]b and processed. All interceptive occlusal contacts were eliminated before fixing the magnetic assembly.
Placement of magnetic assembly (magnet and keeper)
All magnets (Magfit; Aichi Steel Corp.) were kept on the top of keeper [Figure 5]a so as to coincide with both central axes, and autopolymerizing cure resin (DPI-RR; Dental Product of India, Wallace Street, Mumbai, India) was filled into the space left for magnetic assembly in the impression surface of mandibular overdenture. Patient was asked to occlude till curing of the resin. Excess of resin was removed [Figure 5]b, the occlusion was checked to remove interceptive occlusal contacts, and the denture was inserted [Figure 6].
|Figure 5: (a) Magnets are placed on top of keeper. (b) Magnets are fixed in lower denture with the help of autopolymerizing resin in patient's mouth|
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|Figure 6: Postoperative upper partial denture and lower magnet retained overdenture|
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| Discussion|| |
Dental magnetic assembly of various types and sizes are commercially available. These systems, consisting of a magnet and a keeper, are used to retain removable partial dentures and maxillofacial prostheses. Magnetic system can also be used in an implant-supported overdenture, with magnets incorporated into the denture acting upon keepers attached to implant abutments.  Most commercially available magnetic attachments are composed of a magnet and yoke made from ferromagnetic material. ,, In this case report neodymium-boron-iron (NdBFe) magnets, stainless steel (AUM20) yoke, keeper, disk, and stainless steel keeper holder (SUS316) assembly have been used. In our article the MAGFIT DX (Magfit; Aichi Steel Corp.) type magnets were used. The heights of magnets were 1.0 mm and keepers' height and diameter were 0.5 mm and 3.0 mm, respectively, selected according to the cross section of the retained root. Since these rare-earth magnets are vulnerable to corrosion, especially in the oral environment, they are covered and sealed with a yoke cap. In the present case, the magnetic assembly utilized a stainless steel casing hermetically sealed by micro-laser welding which provided a corrosion-resistant environment in the oral cavity, and magnets need not be replaced often, which is a major advantage over other magnet systems.
The magnetic system used to retain dentures may be an open-field or a closed-field system. In closed-field systems, the external magnetic flux fields are eliminated by placing the magnetic components in a series, called an assembly. , Therefore, it is not surprising to find the greatest retention force occurring with the closed-field magnets at both speeds of separation. Their closed field nature also makes this system more biocompatible than the open-field system, as open-field uncoated magnets exhibit significant cytotoxic effects. , The magnetic system used in this case was closed-field system and magnetic field leakage at the gingival margin was substantially below the accepted United State safety standard of 0.02 T.
Various documented cases of implant-supported mandibular overdenture are found, where the implants are usually placed in the anterior atrophic mandible in the canine regions and retention and soft tissue support is gained by anterior abutment and posterior segments of mandible, respectively. , In this case, magnet-retained mandibular overdenture was fabricated on anterior abutment teeth, which is similar to the former clinical condition.
Advantages of intra-oral magnets include: Easy incorporation into a denture involving simple clinical and technical procedures, ease of cleaning, ease of placement for both dentist and patient (physically disabled or neuromuscular compromised), automatic reseating, and constant retention with number of cycles.  They are typically shorter than mechanical attachments, are particularly useful for patients with restricted interocclusal space and challenging esthetic demands, can also accommodate a moderate divergence of alignment between two or more abutments,  and dissipate lateral functional forces.  On the other hand, poor corrosive resistance of magnets within oral fluid requires encapsulation within a relatively inert alloy such as stainless steel or titanium.  They do not provide a positive locking device, thus the retention provided is generally less than with intra-radicular retention systems. 
| Conclusion|| |
Magnetic assembly used in this case is a new-generation magnetic attachment system which provides predictable retention, stability, support, and offers long-term durability. This system has successfully rehabilitated the patient when compared to overdenture with implants, when cost and time factors were considered. Magnet-retained overdenture preserving natural abutment teeth has better proprioception and satisfaction, and also is psychologically beneficial as the patient had not undergone extraction.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]