2. Prognosis for the Overdentures with Magnetic Attachment: Cases with the Reinforcement Structure
Toshiaki Hasuike, Shuji Ohkawa
Division of Removable Prosthodontics,Department of Restorative & Biomaterials Sciences,Meikai University School of Dentistry
Introduction
In recent years, overdentures with magnetic attachments are widely used in clinical practice because of their many advantages. However, a bending moment is likely to be generated in dentures having abutment teeth as fulcrums. When compared to conventional dentures, one of the disadvantages of overdentures with magnetic attachments is that an occlusal force would result in denture fracture. Especially, when the labial side of abutment teeth is kept open to improve patient comfort and enable self-cleaning around abutment teeth, the risk of fractures is higher. In this study, a reinforcement structure was prepared around the magnetic attachments in order to prevent denture fracture in patients and the dentures were reviewed.
Objective
The aim of this study was to evaluate the clinical long-term success of the reinforcement structure in the denture base around the magnetic assembly.
Materials and Methods
In 12 patients (5 men, 7 women, average: 62.3 ±9.1 years) at the Meikai University hospital wearing dentures with reinforcement structures around the magnetic attachments, the occurrence of denture base fracture was determined and 19 abutment teeth prepared by 1 operator were followed up. Table 1 shows the gender, age and edentulous areas of the subjects, and numbers marked in red indicate the abutment teeth with magnetic attachments. The abutment teeth included in the present study were upper central and lateral incisors and canine and lower central and lateral incisors, canine and first premolar.
These are schematic diagrams of the labiolingual cross-section of an anterior abutment tooth in a conventional denture and a denture that is open on the labial side. (Fig.1, 2) On the labial side of an anterior abutment tooth, an undercut area is likely to form in the direction of denture removal, and with the conventional design, the thickness of the denture base and block out result in a slightly protruded labial flange. When the labial side of the abutment tooth is open, protrusion of the labial side is avoided. The blue section in the Fig.2 represents the difference in the exterior design between the conventional and open-design dentures. Although the no labial flange denture has a anatomical form, the risk for denture fracture is higher. Therefore, a reinforcement structure was added around each magnetic attachment.
Cases
Case 2 with the reinforcement structure of metal frame around the magnetic assembly is shown in Fig.3-9.
To the abutment tooth on the working model (right lower canine), a plaster replica of the magnetic attachment was fixed, and a 24-gauge sheet wax was applied to the lateral and top sides of the plaster replica to take an impression for the duplicate cast. Then, from the framework, a reinforcement structure for preventing denture base fracture was made to cover about three quarters of the circumference of the magnetic attachment.
An opaque material was applied to the labial surface of the framework to cover the metallic color. The pink-colored opaque resin (Rosa, Heraeus Kulzer) was used.
The abutment tooth area in the lower right canine was made using a hard resin for facing (Solidex, Shofu). Because the labial side of the abutment tooth was open, the esthetics was much better when compared to dentures covering the gingiva of the same area. A crown-colored self-curing resin was used to make the base of the crown area that was prepared using hard resin, i.e., the space between the plaster replica and the reinforcement structure, and the area that was in contact with the abutment tooth. The primer (Contact Primer, Heraeus Kulzer) was used to adhere the facing hard resin to the self-curing resin.
The X-ray fluoroscopy images of the membrane side of the denture base before and after cementing the magnetic attachment are shown in Fig.7. About three quarters of the circumference of the magnetic attachment was covered by the framework. We can see the housing space (about 0.5mm) between magnetic assembly and metal framework (left). The magnetic assembly was cemented with self-curing adhesive resin, being positioned almost at the center of the skeleton reinforcement structure.
The lower right anterior teeth have no clasps and the labial side of the abutment tooth is open. Hence, the lip discomfort was low, and the patient was very satisfied.
The periodontal tissue around the abutment tooth is healthy.
Although the retainer was worn, no notable abnormality was seen in the periodontal tissues surrounding the abutment tooth.
Abnormalities such as denture base fractures were absent, and the prognosis was favorable. And favorable esthetic result with patient satisfaction was obtained.
Results and Considerations
Table 2 indicates the length of follow-up of the 19 abutment teeth in the 12 patients. The average length of follow-up for the 19 abutment teeth was 6 years and 10 months. The abutment tooth area of four dentures had smaller chipped, and that of five dentures was discolored. However, no denture base fracture was reported and none of the abutment teeth had been extracted in any of the 12 patients.
The above findings show that designing overdentures with magnetic attachments having an no flange design on either the labial or the buccal side of abutment teeth alleviates lip discomfort and enables self-cleaning around abutment teeth. Having a reinforcement structure as discussed above appears to be very effective in preventing denture base fractures.
Conclusions
It was suggested that the magnetically retained overdenture with the reinforcement structure of metal framework, designed no labial flange of denture base on the abutment, have a favorable clinical prognosis.