The assignee for this patent, patent number 8506294, is 3M
Reporters obtained the following quote from the background information supplied by the inventors: "Tooth replacement parts, such as crowns, bridges or implants, and other dental workpieces are normally produced by the desired shape of the workpiece being optically or mechanically scanned from a corresponding model, and by the data thus obtained being used to generate milling tracks. Based on these milling tracks, the dental workpiece is then produced from a blank in a milling tool or other suitable machine tool.
"EP 0 759 728 B1 discloses a device in which the blank intended for production of a dental prosthesis is embedded in a ring of metal, ceramic or hard plastic. For cost reasons, the blank is dimensioned so that as little as possible of the expensive material of the blank is wasted during the machining. The generally cylindrical blank is embedded in the ring by means of a dental adhesive applied all around it and, together with the ring, it is inserted into a support body which in turn is clamped into the machine tool.
"Particularly in the case of fairly large blanks for production of bridges, it has been found that adhesive applied on all sides leads to stress cracks during milling, which stress cracks are not easily discernible in the blank. These cracks can run through the entire blank, transverse to the longitudinal axis, and can thus make the workpiece unusable.
"The effect becomes apparent when, after milling of the top side, the underside is exposed and these two planes meet one another. Since the strength of the material normally used is only about 20 to 30 MPa in the raw state, and since that of the epoxy adhesives generally used lies in the same range, a blank which is surrounded all round by adhesive is subjected to forces in a biaxial stress field, which forces can amount to several 100 N depending on the adhesive surface. The notch effects which occur during milling intensify this effect, with the result that the strength of the material of the blank is exceeded and the latter fractures transverse to the longitudinal direction.
"A further difficulty in the known device is that, in the case of adhesive-bonding, the adhesive inevitably runs on the mutually parallel cylinder faces of blank and ring and reaches those surface parts of the blank which are to be machined, and thus also reaches the milling head. As a result of this, the milling head is soiled, and the precision of the milling is adversely affected.
"These difficulties also exist in the device which is known from DE 298 15 486 U1, in that the blank in said document is inserted into the central opening of the plate-shaped support body with adhesive applied all around it.
"An object of the invention is to make available a device for producing dental workpieces which permits better machining of the blank.
Most Popular Stories
- American Airlines, US Airways Complete Merger
- ACA Delay Stresses Small Businesses
- Questions Remain in Jenni Rivera's Death
- Unemployed Wait as Lawmakers Debate
- Harley Issues Motorcycle Recall
- General Dynamics Plans 200 New Jobs in N.M.
- Auto Dealer Builds Big Solar Project
- Entrepreneurs' Next Creation May Be New Laws
- Saab Gets Back into the Game; U.S. Auto Sales Soar
- Dell Offers Undisclosed Number of Employee Buyouts