Magnetic Attachment on the Proximal Surface of an Abutment Tooth: Second Report

R. Mutou, M. Abe, F. Tsuchida, T. Hosoi, Y. Maeda1, M. Yamaguchi¹, Y. Miyama¹, and Y. Mizuno¹

Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine

¹The Dental Technician Training Institute, Tsurumi University School of Dental Medicine

Introduction

Magnetic attachments have been used as stud attachments, primarily for pulpless teeth. However, the use of magnetic attachments with vital teeth often requires nonreversible invasive procedures such as abutment tooth preparation and pulpectomy. At the 4th International Conference on Magnetic Applications in Dentistry, we proposed a method that places a magnetic attachment onto the proximal surface of an abutment tooth to minimize invasiveness.¹

The advantages of the present method are: magnetic attachment can be placed with minimal tooth damage and minimal invasion to an abutment tooth; and with anterior teeth and premolars, esthetics are better than with clasps.

The disadvantages associated with the present method are: weak attractive force against external forces that cause the magnetic assembly and keeper to slide; and difficulties in embedding a magnetic assembly into a denture and adhering the keeper to an abutment tooth. In addition, because magnetic attachments only possess retention function, when using another attachment, it is necessary to design a denture to ensure proper support and brace functions.

In order to make up for these disadvantages, the laboratory procedure has been improved in the following three clinical cases.

Clinical techniques and the laboratory procedure

Case 1

Patient: 56-year-old woman.

Chief complaint: The patient wanted a denture that was esthetically pleasing.

History of present illness and present status: She was using a partial denture having mandibular right premolar and third molar as abutment teeth for a few years. However, the mandibular right first premolar needed to be extracted due to caries, and her previous dentist proposed the use of a wire clasp using a mandibular right canine as an abutment tooth. However, the patient did not like the idea due to esthetic concerns, and she was referred to the Tsurumi University School of Dental Medicine Hospital in June 2006.

The patient did not have any noteworthy past medical history. The remaining teeth were not carious, and gingivitis was absent. The patient did not have abnormalities in the temporomandibular joint (Fig. 1a,b).

Diagnosis: Poor esthetics of a clasp, and masticatory disturbance due to missing teeth, mandibular right first premolar, second premolar, first molar, second molar and left second premolar.

Treatment plan

Because the patient expressed her desire for minimal tooth damage, to address missing tooth mandibular left second premolar, a partial denture was designed to cover the missing teeth, not a bridge. In order to improve the poor esthetics caused by the clasp, a magnetic attachment was placed on the proximal surface of the mandibular right canine.

Treatment process

A preliminary impression was taken using alginate. Using a study cast, the location of a magnetic attachment keeper (Hyperslim 3513, NEOMAX.Co., Ltd.) was determined on the distal proximal surface of the mandibular right canine where it came in contact with the denture. The location of the 3.5 mm keeper was determined so that it could remain as hidden as possible and was within the undercut of the proximal surface of the abutment tooth adjacent to the denture (Fig. 2).A clear resin core, which was used to attach a keeper, was then prepared. First, the keeper was fixed to a predetermined location using paraffin wax (GC), and a wax-up including the contour of the abutment tooth was prepared (Fig. 3).

After marking the contour line of the core, a clear resin (GC) was brushed on to prepare a core with an overall thickness of 1.0 to 1.5 mm. To make handling of the core in the mouth easier, a 2.0 mm knob was placed on the top of the core. To remove excess resin, a fissure bur was used to form a 1.0 mm semicircular escape path on the buccolingual and distal sides (Fig. 4).

As an adhesive resin, Beautiful Flow (filling composite resin, Shofu) was used. The proximal surface of the abutment tooth was subjected to etching and bonding. The keeper was attached to the magnetic assembly embedded in the medial surface of the core, and in order to separate the core and resin, a separating agent (ESTENIA C & B CR SEP III, Kuraray) was applied to the medial surface of the core (Fig. 5a). After filling the core with resin (Fig. 5b), the core was placed with pressure onto the abutment tooth (Fig. 5c). The resin was hardened by photopolymerization, and after adhering the keeper, the core was removed from the abutment tooth (Fig. 5d).

A denture was then prepared according to conventional methods. Impression was taken; a working cast was prepared for maxillomandibular registration. For missing teeth, a titanium framework (T-Alloy H, GC) was made. To the area corresponding to artificial tooth, a space for the magnetic assembly was secured. According to conventional methods, artificial teeth were arranged, and a wax denture was prepared. The denture was completed by resin polymerization. The magnetic assembly was placed after the patient wore the new denture for some time and the denture was adjusted to ensure stability. Prosthetic treatment was completed in November 2006. The patient was satisfied with both esthetics and functionality (Fig. 6).

Case 2

Patient: 52 year-old women.

Chief complaint: The patient wanted a denture without any visible wire.

History of present illness: The patient used a partial denture for missing teeth, maxilla right first premolar, second premolar and left first molar but she visited the Tsurumi University School of Dental Medicine Hospital in March 2005 because she did not like the visible wire clasp for a maxilla right canine. The remaining teeth were not carious, and gingivitis was absent. The patient did not have any occlusal abnormalities.

Diagnosis: Poor esthetics of the abutment tooth, a maxilla right canine, due to a visible wire clasp. Her masticatory disturbance was missing teeth, maxilla right first premolar and second premolar.

Treatment plan

In order to improve the poor esthetics caused by the wire clasp, a magnetic attachment was placed in the maxilla right canine. As to missing tooth, maxillar left first molar, before a partial denture was prepared, a bridge was placed (Fig. 7a,b). A unilateral partial denture without an indirect retainer was designed.

A preliminary impression was taken. On a study cast, the location of a magnetic attachment keeper (MAGFIT EX400W, Aichi Steel Corporation) was determined so that the keeper could be placed on the distal surface of the maxilla right canine, and be hidden as much as possible within the undercut of the lateral surface of the abutment tooth adjacent to the denture. In this patient, the keeper was attached to the abutment tooth also using a core (Fig. 8).

A denture was then made according to conventional methods. A precise impression of the maxilla was taken. A working model was prepared for checking the occlusion. To missing teeth, a resin denture with a cobalt-chromium retainer was made (Fig. 9). Prosthetic treatment was completed in November 2003. The patient was satisfied with both esthetics and functionality (Fig. 10, 11). Three years after preparing the partial denture, there are no changes in appearance or no reduction in attractive force.

Case 3

Patient: 66 year-old man.

Chief complaint: His masticatory disturbance was a poorly fit denture.

History of present illness: At another hospital, a total of seven dentures were made, but none were usable. With masticatory disturbance, the patient visited the Tsurumi University School of Dental Medicine Hospital in July 2003.

The patient had only two remaining teeth, mandibular right and left canine, and marked gingival recession. The exposed root surface was discolored, but soft dentin and tooth mobility were absent. In addition, the left canine was markedly worn. The maxilla was edentulous, and the patient did not wear a denture (Fig. 12).

Diagnosis: His masticatory disturbance was poorly fit maxillary and mandibular dentures.

Treatment plan

Although one therapeutic option was to cut the crown of the remaining teeth, and design an overdenture with stud attachments, the patient strongly expressed his desire to save his teeth, and thus we decided to fabricate a mandibular denture with magnetic attachments on the proximal surfaces of the remaining teeth and a maxillary complete denture.

Treatment process

Using a core, four keepers of magnetic attachments were placed to the medial and distal surfaces of the remaining two teeth (Fig.13a, b). For the mesial surfaces, MAGFIT EX600W (Aichi Steel Corporatio) was used, and for the distal surfaces, original rectangular keepers were used (Fig. 13c).

Next, a denture was made according to conventional methods. Impressions were taken. A working cast was prepared for maxillomandibular registration. The maxillary complete denture was made of titanium to emphasize comfort and light-weight, and the mandibular partial denture was made of cobalt-chromium to emphasize strength (Fig. 14a, b). Prosthetic treatment was completed in September 2003. The patient was satisfied with both esthetics and functionality. Three years after denture preparation, although plaque control is poor, there is basically no damage to the abutment teeth due to the use of the magnetic attachments.

Discussion

Three years have past since the first report, and as more patients are treated, the advantages and disadvantages associated with magnetic attachments have become clarified. The biggest advantage is the high degree of esthetic satisfaction, as canines and premolars are used as abutment teeth without damaging natural teeth. One point of caution is that when placing a keeper, excess resin can fill the gingival pocket.

In the present patients, in order to eliminate excess resin, escape paths were formed in the distal and buccolingual sides near the gingival crevice, but we believe that flow of excess resin into the gingival crevice can be reduced by moving the paths towards the crown side.

With regard to the problems associated with placing a magnetic assembly, an improper procedure causes a gap between the magnetic assembly and keeper, thus making it impossible to maintain the expected level of attractive force. This problem can be resolved by placing a magnetic assembly inside the mouth after confirming the stability and fit of a new denture, or in other words, a magnetic assembly should not be placed onto a denture on a working model. At this stage, it is important to wait for resin to harden while applying occlusal force. However, it is necessary to keep in mind that if excess resin fills the undercut of remaining teeth, it becomes difficult to remove a denture. It is effective to use only the minimally required amount of autopolymerizing resin for adhesion and to form an escape path for excess resin toward the occlusal surface, not the neck, of artificial teeth. Through these measures, we are now able to correctly position the magnetic assembly and keeper without a gap.

Cases 2 and 3 have only been followed for 2 and 3 years, respectively, but the dentures are esthetically and functionally favorable, and the attractive force of the magnetic attachments has not decreased. These are the advantages of placing magnetic attachments to the proximal surface of abutment teeth. In Case 3, the lower denture was highly stable because four magnetic attachments were placed almost in parallel. Proper plaque control will be necessary to achieve favorable outcomes.

In the future, it will be helpful to develop special keepers suitable for the present method and to improve the techniques for attaching magnetic assemblies to dentures.

Conclusions

With the present method, a magnetic attachment keeper is directly adhered to the proximal surface of a natural abutment tooth, and it markedly improves denture esthetics and achieves high levels of patient satisfaction. Use of a core for keeper placement is a labor-saving measure that streamlines and simplifies the clinical procedures.

References

1. Tanaka R, Tsuchida F, Abe M et al., Magnetic Attachment on the Proximal Surface of an Abutment Tooth, J J Mag. Dent 13(2): 33-37,2004.

Discussion Board