2Division of Oral and Croniomaxillofacial Research , Dental research center ,Nihon University School of Dentistry
I. Prolusion
When attaching a magnet assembly to a denture base, use of a gypsum dummy to assure the specified space is recommended. In clinical practice, after forming a given space inside the denture base, we sometimes apply a method of attaching the magnet assembly by means of a low-temperature resin.
If the amount of packing resin exceeds the standard, the amount of polymerization contraction might increase and separate the magnet assembly from the keeper surface. However, no report has yet been prepared.
In this study, we compared each embrasure in attaching the magnet assembly.We especially noted retention power when changing the height to examine the influence of polymerization contraction on the vertical direction when attaching the magnet assembly.
We would like to report the result of this study.
II. Materials and methods
(1)Materials and measuring devices
We used GIGAUSS, which has the same height, but different diameter for the magnet assembly used in this experiment. We compared each embrasure for attachment of the magnet assembly and the retention power of each when changing the height with sheet wax.
(2)Experimental method
The experimental flow chart and the GIGAUSS schema are shown below. The diameters of the magnet assemblies increase in order of D4, D6 and D8. The height is the same for each at 1.3 mm.
The diameter of the gypsum dummy is 0.3 mm wider than that of magnet assembly, and the height is 0.3 mm higher than the top of the magnet assembly, having an embrasure to attach with the cold-curring resin.
Thus, in this study, we added sheet wax of the same thickness of the embrasure (0.3 mm) to the gypsum dummy to increase the embrasure on the upper surface of the magnet assembly, and made a spacer.
1)Adjustment of the spacer
First, we used the gypsum dummy without adding the sheet wax and made a spacer with the height of the embrasure (0.3 mm).
We specified this as a control (C group).
Next, we added 0.6 mm of sheet wax (two sheets) to the gypsum dummy,and fixed the spacer at 0.9 mm
which is three times as long as C group in terms of the height of the embrasure. This was called the 0.9 group.
After that, we added 1.2 mm of sheet wax (four sheets) to the gypsum dummy,
and fixed the spacer at 1.5 mm (five times as long as C group) and referred to this as the 1.5 group.
2)Preparation of resin block
We made a buried resin block (10 mm on a side) from the spacer adjusted by the above method using Orthofast Clear.
Next, we removed the spacer within the resin block and formed an escape path with a round bar No. 6 (φ1.6mm) as shown in the slide.
3)Attachment of the magnet assembly
Before attachment, we performed alumina sandblast processing on the surface of the magnet assembly and coated it with metal primer II.
Next, we mixed Unifast II at the standard ratio of powder and liquid (2 g/1 ml) for 10 seconds, packed the same amount into the spacer, and then attached it within 60 seconds from the start of mixing.
During attachment, we applied 150g of static loading and removed it two minutes and 30 seconds from the start of mixing, leaving it at room temperature.
4)Tension test
We used a traction device mounted with a digital force gauge (FGC-2B) for the measurement of retention power.
Next, we pulled the magnet assembly with an operational wheel to measure the point at which the magnet assembly was attracted to the keeper.
