The magnetic attachments for dentures were developed and it was widely applied to the prosthetic dentistry clinic of dentures in the 1980s.
Although power of absorption bigger as a magnet approaches is demonstrated, if it separates, power of absorption will decrease rapidly and with little direction dependency, high power of absorption is demonstrated, but since abutment teeth is received from the feature that power of absorption declines rapidly when it distance, there is an advantage of many -- there is little damage.
Although many researches on power of absorption etc. have been done, there is little research on the damage of the root at the time of detachment.
Then, we research about the damage of the periodontal membrane by a path of insertion this time using the finite element method.
The software used by this research was Marc2003 (general-purpose finite-element-method software) and Mentat2003 (pre-post processor) made by MSC Software Company.
The computer used in the study was the personal computer Dimension8300 (Dell Computer Corp).
The model assumed a Japanese average lower jaw canie and 11mm of root length with keeper HYCOLEX hyper-slim 3015 diameters of 3 mm at coping of 45 taper angles of gold-and-silver palladium alloy nature, and 0.2 mm cortical bone of periodontal membrane is 2 mm uniformly were structured.
Although it assumed the model with a keeper and coping using resin cement, since it was 30 micro meter or less, and the thickness of a cement layer thought on calculation that it was not so important, and did not make a model but it had adhesiveness, the model thought that it could be assumed that it is continuum completely.
Numbers of nodes were 36,660 and of elements were 6, 991, and an element type were the quadrangle in this FEM model.
About the boundary conditions of a model, restrained the flexibility of all the nodes of the model apex side sponge bone basal surface.
The load was 400 gf at the surface of keepers as absorption power.
The direction of the load was assumed to be 90 degrees, 60 degrees, and 45 degrees.
The node on the surface of the keeper was loaded with the point load.
The material properties used were shown in upper fig..
These values determined the report of past Nakamura, Ishida, etc. as reference.
The main stress was displayed, and the result expanded and displayed it 2000 actual times, in order to make it intelligible about deformation.
When the amount of deformation was displayed about every result with base, it was the little which can hardly understand a difference.
The analysis result at the time of making it separate vertically was shown in upper fig.
The global image was shown in the upper left portion, and apex was shown in the fig’s left, the keeper circumference and a lower right part.
Concentration of the main stress was seen at the junction apex side of a keeper, junction axial side of coping, coping, and dentine.
Moreover, in the inside of periodontal membrane, it is large at the apex side and a value is 0.035kg/mm2.
When it was made to detach at the angle of 60 degrees, concentration of the main stress was looked at by the apex path-of-insertion part coping, the path-of-insertion opposite side of dentine junction axial plane, and inside periodontal membrane.
The maximum of the main stress within periodontal membrane was 0.071kg/mm2.
When it was made to detach at the angle of 45 degrees, concentration of the
main stress was looked at by the apex path-of-insertion part coping, the
path-of-insertion opposite side of dentine junction axial plane, and inside
periodontal membrane.
As compared with the case of 60 degrees, the main stress is distributed broadly.
The maximum of the main stress within periodontal membrane was 0.110kg/mm2.
From this result, the direction at the time of making it a magnetic attachment separate vertically was considered that the maximum of the main stress within periodontal membrane falls greatly.
In order that periodontal membrane might resist in a big area as this cause, it was thought that it was distributed equally.
When an angle was made to give and separate, since periodontal membrane was greatly pulled by apex, it was thought that big concentration of the main stress arose.
In this case, it was thought that the main stress generated, so that an angle becomes large became large.
Vertically detaching a magnetic attachment to the keeper is few damage to periodontal membrane from this research
It was thought that damage to periodontal membrane increased by growing of the angle of detach.
However, although it was thought that it hardly became a problem when applying to a healthy tooth etc., since the stress to generate is small enough, when applying to the bad tooth of a state, a possibility that a prognosis good in the long run would be obtained was able to be considered by coping with explaining the method of attachment and detachment to the patient who gives a keeper a taper etc.
From now on, we shall developed the model into the three dimensions, and other attachment (ball attachment etc.) also carried out the simulation with the viscoelasticity of periodontal membranes etc., and we shall carry out comparison examination and discusses that he wants to acquire the indicator about the design of removal dentures.