It is well known that the overdenture is an efficient treatment option for the edentulous jaw with some remaining teeth. The implant is used as the anchor for overdenture which improves her or his quality of life, even in the fully edentulous patient. However, the planning of it should be classified from the view point of biomechanics. The fundamental considerations in overdenture treatment are described in this article.
This paper is a summary of a lecture at the 17th Annual Meeting of the Japanese Society of Magnetic Application in Dentistry, which was held in Tokyo Medical and Dental University on November 17th, 2007.
The interaction mechanisms of magnetic fields with matter are briefly reviewed to address the significance of magnetic field effects. Biological effects of magnetic fields are then summarized based on the recent reviews developed by scientific organizations consisting of reputable scientists. The critical, established effects are vertigo and nausea observed when human head moves rapidly in a field more than 2 Tesla, due to the disturbance of vestibular function by induced current in the central nervous systems. There is little evidence of other effects including carcinogenesis, though experimental data are still sparse.
Current guidelines for limiting exposure to static magnetic field were developed by International Commission on Non-ionizing Radiation Protection in 1994. The scientific basis for the limit values is not fundamentally different from the current consensus of experts in spite of a lot of studies that have been conducted thereafter.
Recent topics in the risk management of human exposure to electric and magnetic fields are also reviewed. Exposures to electric and magnetic fields are regulated in many countries in order to protect humans from excessive exposure. There is a problem of conflict between beneficial use and worker protection from exposure in the application of magnetic field, especially for medical magnetic resonance imaging.
The guideline for static magnetic field is now in the process of revision.
The revised guideline will be issued soon. The role of guideline should
be not only limiting use of electromagnetic energy but also promoting beneficial
use of this energy within the limitation of safety.
The purpose of this study was to compare through in vitro analysis the load transfer characteristics of different magnetic attachment systems retained by two implants.
Three kinds of magnetic attachments (flat, dome and reverse-dome type) were prepared. Two implants were placed in canine regions of the mandibular edentulous model. Four strain gauges were attached to the mesiodistal and buccolingual sides around implant. A load cell transducer was embedded beneath the bilateral molar ridges. A static load of 98 N was applied. The loading sites were three points: A: first premolar region, B: first molar region, C: second molar region. Comparisons were performed using the Kruskal Wallis test.
The site applied with the load became more posterior, and the measured stress at the molar ridge became higher. No significant difference was found among three attachments. With regard to the measured strains around the implant, strain in the reverse-dome type was significantly higher than those of other types.
As the load was applied more posterior, less strain around the implants
and more stress at the molar ridge were found. Magnet-retained overdenture,
in particular, the reverse-dome type, would result in stress concentration
around the implant.
We devised a new application to place magnetic attachments on the proximal surfaces of the abutment teeth of removable partial dentures and have applied this method clinically. The purpose of the present study was to assess the efficacy of placing magnetic attachments on the proximal surfaces by measuring retentive force using abutment tooth models.
The PHYSIO MAGNET 35 (Nissin, Kyoto,Japan)was used in this study. Abutment tooth models of the mandibular left first premolar were made of acrylic resin.
Experimental conditions were as follows:
1. Effects of 4 placement angles; 0°, 2°, 4° and 6?.
2. Magnetic attachment was compared to a proximal plate having no attractive force under 3 conditions.
Under the 12 possible experimental conditions, retentive force was measured using a digital force gauge (FGC-1; NIDEK-SHINPO, Kyoto,Japan). For each condition, retentive force was measured 10 times to calculate mean value and standard deviation.
When the magnetic attachments were placed on the mesial and distal proximal surfaces, retentive force tended to decrease as placement angle increased from 0° to 6?. The retentive force obtained by proximal surface application was about 15-20% when compared to the conventional application.
The Magnetic leakage fields out of a sandwich type of magnetic attachment are evaluated by a FEM analysis. The leakage field is analyzed not for the attachment in normal use but for that in the special states that a magnetic assembly is moved vertically and horizontally from the normal position for a keeper. The magnetic field distribution is not an axis symmetry as a cup type of a magnetic attachment. As a whole, the value of the leakage magnetic field of a sandwich type is larger, and the distribution of the leakage magnetic field of a sandwich type is wider than that of a cup type. Under some condition, the leakage magnetic field exceed the guideline value. But, the magnetic leakage field of the normal use is about 11[mT] at the position of the gum. This value is less than 40[mT], the guideline by ICNIRP(International Commission on Non-Ionizing Radiation Protection) and WHO(World Health Organization). Therefore, the leakage magnetic field of sandwich type of magnetic attachment in normal use is considered to be the safe from a viewpoint of biological effects of static magnetic fields.
Key words: Magnetic attachment, Sandwich type, Leakage magnetic field, Guideline on biological effects of static magnetic fields
In generally, Denture was made a spillway for fix the magnetic assembly, using a self-curing resin. In clinical practice, we often notice cracks and discolorations surrounding the spillway of the denture. In this study, it was examined the influence of a surface treatment method after push out a self-curing resin from a spillway. These methods were applying a light-cured glazing and coating material (NANOCOAT Lab?(GC)) on the push out a self-curing resin , and not applying it the coloration and surface texture using thermal cycling. We made two groups of specimens using the polymerizing method surrounding the spillway. These were Non-Pressed cure Group (NPG) and Pressed cure Group (PG). Ten specimens were made with NANOCOAT processing to NPG and ten to PG respectively. It was made four types of specimens (NPG-NANOCOAT, NPG-NonNANOCOAT, PG-NANOCOAT, PG-NonNANOCOAT), each made up ten of samples.
The result of this study shows
1. When the magnetic assembly was fixed, it was a validity method to use a light-cured glazing and coating material for the self-curing resin surface surrounding the spillway.
2. The magnetic assembly was fixed with a self-curing resin under pressure, where it was possible to fix the assembly without making a significant gap.
Key words: Magnetic assembly, Spillway, Light-cured glazing and coating material, Coloration, Thermal cycling
There are many female patients who refuse to apply removable partial denture from their aesthetic problem, even though fixed bridge is poor convalescence from the prosthodontic standpoint.
In this case report, we fabricated a removable bridge for the patient who didn’t want to wear a removable partial denture because of an aesthetic problem.
A 54-years-old female patient had missing teeth of #11, #12, #13, and #14. Five inner crowns with keeper of magnetic attachment were fixed to the abutment teeth of #15, #16, #17, #21, and #22．The inner and outer crowns were made with an Au-Ag- Pd alloy. Magnetic assemblies were fixed into the outer crowns and then one-piece removable bridge from #22 to #17 was set.
A magnotelescopic crown is useful for not only removable partial denture, but also removable bridge prosthese. Both patient and us were satisfied with the prosthese.
Key words: Magnotelescopic crown, Removable bridge, Magnetic attachment
The overdentures with magnetic attachment are susceptible to fracture as compared with the conventional denture, because the abutment becomes the fulcrum. Especially the overdentures, designed no labial flange of denture base over the abutment, have stronger possibility of fracture. 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.
Twelve patients received 19 magnetic attachments prepared by 1 operator. Twelve dentures and 19 abutments were followed up for between 5 years 10 months and 7 years 10 months (average period: 6 years 10 months) with inspection. A few clinical problems occurred, including quite small chipping and color change of the denture base on the abutment. However, no tooth was extracted, and no denture was fractured.
It could be asserted that this reinforcement structure in the denture base around the magnetic assembly, designed no labial flange of denture base over the abutment, have a favorable clinical prognosis.
Key words: Magnetic attachment, Prognosis, Reinforcement structure
The aim of prosthetic treatment is to restore damaged morphology and function. But cosmetic disturbance frequently results from prosthetic devices, particularly removable partial denture.
The patient (51-years-old, female) complained aesthetic clasps. In order to avoid cosmetic disturbance, the magnetic attachment was applied as direct retainer, with creating ferrule effect to strengthen abutment. The patient was satisfied with denture retention and sensuousness.
Seven years after the denture setting, the patient addressed the clinic
with complaint of brokenrtificial tooth. The increased occlusal loads and
insufficaient thickness of acrylic resin due to space limitation were the
main reason of failure. To increase resistance of artificial tooth, an
acrylic faced metal cast crown enable to contain the magnetic assembly
were employed. As a result, the partial overdenture was advantage for sensuousness
and strength was achieved.
Key words: Cosmetic disturbance, Magnetic attachment, Removable denture