Construction of tooth positioners with LTV vinyl silicone rubber and some case reports.
In the orthodontic field, attention has recently begun to center on active treatment with tooth positioners, appliances with elasticity made of rubber materials used for orthodontic force in place of conventional metal wires[1-7]. Tooth positioners were contrived by KESLING as retainers to be used after the use of metal wires in active treatment[8,9]. Nowadays, it is used for closing the spaces due to band removal after active treatment, for the minute regulation of the occlusal relationship and for aftercare as a retainer. Not only that, as it is possible to regulate malocclusion by moving teeth with rubberlike elasticity applied in place of metal wires or brackets, it is beginning to draw attention as a new active treatment appliance to be substituted for conventional metal wires. With regard to the materials for tooth positioners to be used as active treatment appliances, various kinds of materials have been applied since KESLING contrived them[10-12], but few materials satisfy the necessary conditions for tooth positioners[10]; 1) easy manipulability, 2) elasticity and hardness, 3) tastelessness and odorlessness in the oral cavity and 4) durability. Polyurethane rubber and heatvulcanized silicone (HTV) rubber which are tasteless, odorless and superior in elasticity, have recently been developed[1,4-7], but these materials require special mold materials and equipment in the preparation process which is also very complicated, so their use has not been widespread as yet. Therefore, for several years the authors have been studying their practical application and trying to develop a material that is easy to manipulate and superior in physical properties[2,3,13]. As a result, the authors have developed a clinically applicable method of tooth positioners with low temperature vulcanized (LTV) vinyl silicone rubber. The following is an outline of its physical properties, the method for its preparation and some case reports.
A new construction of tooth positioner by LTV vinyl silicone rubber.
The present material, having wide function area because of its excellent rubber-like elasticity, can afford to move teeth to a great degree, as compared with the conventional tooth positioner. Besides, its manipulability is preferable. So, wide application can be expected regarding the teeth movement.The preparing method by use of this material has merits as follows : 1) Silicone mixture can easily be filled into mould by disposable syringe.2) Manipulability is preferable, silicone mixture having 24-hour pot life at the room temperature.3) Curing finishes in a comparatively short time at low temperature.4) The set product is tasteless and odorless and shows preferable rubber-like elasticity.5) Preferable moulding products can be obtained by use of plaster moulds, without any special mould materials.6) Takeout of moulding products is easy, easily separated from the moulds.7) The surface of products is very lubricous.8) The products having very thin flash even in the split moulding case, have little effect on the height of bite.9) Its clinical application proves the effect of treatment to be extremely preferable.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow