Abstract: A quasi-hyperbolic endodontic instrument having a cylindrical, elongated shaft with a radius that varies as a smooth, continuous curve along the length of the shaft and is larger near the distal portion of the file than near the proximal end of the file. The distal radius may be 10% or more larger than the proximal radius. This design provides a flexible file that minimizes the possibility of breaking, and ensures that if breakage does occur, it will occur near the handle, allowing the broken bit to be easily removed from the tooth canal. The instrument may further, or instead, have a metal cable connecting the cutting head to the handle to help reduce metal fatigue.

Abstract: A quasi-hyperbolic endodontic instrument having a cylindrical, elongated shaft with a radius that varies as a smooth, continuous curve along the length of the shaft and is larger near the distal portion of the file than near the proximal end of the file. The distal radius may be 10% or more larger than the proximal radius. This design provides a flexible file that minimizes the possibility of breaking, and ensures that if breakage does occur, it will occur near the handle, allowing the broken bit to be easily removed from the tooth canal. The instrument may further, or instead, have a metal cable connecting the cutting head to the handle to help reduce metal fatigue.

Abstract: An interferometer for measuring the flatness, variation of thickness and parallelism of large, thin transparent wafers held vertically and undistorted by gravitational forces. A sodium lamp provides monochromatic light that is diffusely reflected off a background screen towards the wafer. A reference flat surface is positioned sufficiently closely to the wafer that an interference fringe pattern is formed that is a measure of the air gap between the reference flat surface and the surface of the wafer being measured. The background screen is angled so that the fringe pattern, which is localized at the air gap can be viewed at an angle to a normal to the wafer. The background screen has trapezoidal markings that, when viewed at the angle required to see the fringes, appear as a grid. This allows counting of the number of fringes visible within a fixed distance to characterize the surface flatness.

Abstract: An interferometer for measuring the flatness, variation of thickness and parallelism of large, thin transparent wafers held vertically and undistorted by gravitational forces. A sodium lamp provides monochromatic light that is diffusely reflected off a background screen towards the wafer. A reference flat surface is positioned sufficiently closely to the wafer that an interference fringe pattern is formed that is a measure of the air gap between the reference flat surface and the surface of the wafer being measured. The background screen is angled so that the fringe pattern, which is localized at the air gap can be viewed at an angle to a normal to the wafer. The background screen has trapezoidal markings that, when viewed at the angle required to see the fringes, appear as a grid. This allows counting of the number of fringes visible within a fixed distance to characterize the surface flatness.