2. Longitudinal Study on Metal Plate Denture with Magnetic Attachments

 

R. Ito, K. Hoshiai, N. Hasegawa, N. Muraji, T. Kawaguchi, K. Noda, K. Watanabe and

Y. Tanaka

 

Introduction

 

At present, magnetic attachments have been applied clinically in various cases.

It’s useful to carry out postoperative investigations and to confirm results, as it shows the criterion of the clinical application. Thus, we can use magnetic attachments safely.

From this point of view, postoperative investigation on 252 magnetic attachments which were applied to 105 metal plates in Aichi-Gakuin University Dental Clinic over the 10 year period from 1993 to 2003, were carried out. The results of this investigation were reported in 2003.

In this study, a further 5 years were researched to compose a longitudinal study over approximately 15 years.

 

Methods and Results

 

Fig.1 shows the transition of the conditions of all abutment teeth over the 15 years　period 1993 to 2008.

The numbers of extracted teeth were 29, censored teeth were 117 and the remaining teeth were 106.

 

Fig.2 shows the survival probability of all abutment teeth using a Kaplan-Meier analysis.

After 10 years, the cumulative survival rate was 88% and after 15 years the cumulative survival rate fell to 77%.

 

Fig.3 shows the transition of abutment teeth by tooth classification, and classified the teeth as incisors, cuspids, premolars or molars. The inside of Fig.3a are the conditions when the research was started. The outside portion of the graph in Fig.3a was the transition.

Fig.3b was the rate of the remaining teeth by tooth classification. No large changes could be seen from the start of the study. 3 incisor teeth, 11 cuspid teeth, 11 premolar teeth, and 4 molar teeth were extracted.

 

Fig.4 shows the survival probability of the tooth classification. The survival rate of   incisor teeth was 67%, cuspid teeth was 78%, premolar teeth was 80% and molar teeth was 86%. But no significant differences were found (log-rank test : spss statistics 17.0).

 

Fig.5 shows transition of the condition using Kennedy’s classification. No large changes were found from the start of the study. The number of extracted teeth of Class�Twere 15, Class�Uwere 12, Class �V were 2 and Class �W were 0.

 

Fig.6 shows the survival probability of the Kennedy’s classification. The survival rate of Class�Twas 78%, Class�U was 71%, Class�V was 88% and Class �W was 100%. But no significant differences were found.

 

Fig.7 shows the transition of the condition by Eichner’s classification. The rate of remaining teeth of class B were looked to have increased for 15 years, because of a large number of Class C that were unsored. The number of extracted teeth of Class A were 0, Class B were 28, and Class C were 1. Extraction was concentrated in Class B which lost one part of the four occlusal supports.

 

Fig.8 shows the survival probability of the Eichner’s classification. The survival rate of Class A was 100%, Class B was 74%, and Class C was 98%. A significant difference was found between Classes B and C.

 

We also researched magnetic attachments which were applied to acrylic resin plates and compared these with those attached to metal plates. Magnetic attachments were applied to 1133 teeth and 111 of these teeth were chosen for this study.

 

Fig.9 shows the transition of the conditions of abutment teeth of resin plates.

The numbers of extracted teeth were 16, remaining teeth were 67, and censored teeth were 28.

 

Fig.10 shows a comparison of the survival rates between metal plates and resin plates.

After 7 years, the cumulative survival rate of resin plates was about 70% and after 10 year it fell to 53%. A significant difference between resin plates and metal plates was found.

 

Fig.11 shows a comparison by age groups when attachments were applied. We divided the case to 3 groups, the group of ~65, the group of 65~75 and the group of 75~. The rate of abutment teeth of the group of ~75 for metal plates was higher than that for resin plates.

The rate of censored teeth was high in the group of ~75 for metal plates. On the other hand, it was low in the group of ~75 for the resin plate.

 

Fig.12 shows the survival probability of the age classification. The survival rate of metal plates was 79% for the group of ~65, 76% for the group of 65~74, and 69% for the group of 75~. The survival rate of resin plates was 81％ for the group of ~65, 64% for the group of 65~74 , and 46% for the group of 75~. Significant differences were found between the 2 groups of metal plates for the groups under 75 and the 2 groups of resin plates for the groups over 65. This shows the survival rate is high for the group of ~75 of metal plates.

 

1.      The survival rate of abutment teeth of metal plates was 77% after 15 years and of resin plates was 53% after 10 years.

 

2.      There were many extractions of abutment teeth in Class 1 and 2 of Kennedy classification.   

On the other hand, there were few extractions in Class A and C of Eichner’s classification where no occlusal support or all occlusal support existed.

 

3.  No significant difference could be found between different plate materials of plate by age classifications. However, there were difference of the survival rate between the group of age over 65 of resin plates and the groups of age under 75 of metal plates. This shows the survival rate of metal plates for ages under 75 is high.

 

Discussion

 

A significant difference in the survival rate between metal plates and resin plates was found. One of the reasons is design of denture. Metal plates allow for great latitude in design and enable the design of an ideal partial denture. Another major reason for the survival rate of metal plates is that the major connectors are solid. 

The major connectors of resin plates can be strained by the occlusal force as abutment teeth are moved badly.

A significant difference was found between Class B and C of Eichner’s classification.

Even within class B, the survival rate of abutment teeth that have few occlusal supports is high . If the plate has many occlusal supports, strong occlusal force is added to the part with no occlusal support. As bearing of the abutment teeth increases it may cause periodontisis.

A significant difference could be found between the group of age under 75 with metal plates and the group of age over 75 with resin plates. This is the same reason of comparison of denture material. However, there are few cases in the group of age over 75,and it’s essential to look at further cases in future.