Dental surface imaging using polarized fringe projection

Abstract

An intra-oral imaging apparatus having a fringe pattern generator energizable to emit a fringe pattern illumination having a predetermined spatial frequency, with light in the approximate 350-500 nm range. A polarizer in the path of the fringe pattern illumination has a first polarization transmission axis. A projection lens is disposed to direct the polarized fringe pattern illumination as incident illumination toward a tooth surface. An imaging lens is disposed to direct light reflected and scattered at the tooth surface along a detection path. An analyzer is disposed along the detection path, having a second polarization transmission axis. A detector disposed along the detection path obtains image data from the light provided through the analyzer. A control logic processor is responsive to programmed instructions and actuable to adjust the intensity over one or more portions of the fringe pattern illumination according to the image data obtained from the detector.

Description

FIELD OF THE INVENTION[0001]The invention relates generally to the field of diagnostic imaging using structured light and more particularly relates to a method for three-dimensional imaging of the surface of teeth and other structures using fringe projection.BACKGROUND OF THE INVENTION[0002]Fringe projection imaging uses patterned or structured light to obtain surface contour information for structures of various types. In fringe projection imaging, a pattern of lines of an interference fringe or grating is projected toward the surface of an object from a given direction. The projected pattern from the surface is then viewed from another direction as a contour image, taking advantage of triangulation in order to analyze surface information based on the appearance of contour lines. Phase shifting, in which the projected pattern is incrementally spatially shifted for obtaining additional measurements at the new locations, is typically applied as part of fringe projection imaging, used...

AI Technical Summary

Benefits of technology

[0012]An advantage offered by the apparatus and method of the present invention relates to improved imaging of tooth surfaces and at lower cost over conventional contour imaging methods. Unlike conventional methods, no powder or other opaque substance must be applied to the tooth as a preparatory step for contour imaging.

Problems solved by technology

However, a number of technical obstacles have prevented effective use of fringe projection imaging of the tooth.

One particular challenge with dental surface imaging relates to tooth translucency.

Translucent or semi-translucent materials in general are known to be particularly troublesome for fringe projection imaging.

Subsurface scattering in translucent structures can reduce the overall signal-to-noise (S / N) ratio and shift the light intensity, causing inaccurate height data.

Another problem relates to high levels of reflection for various tooth surfaces.

In fringe projection imaging overall, contrast is typically poor, with noise as a significant factor.

From an optics perspective, the structure of the tooth itself presents a number of additional challenges for fringe projection imaging.

Moreover, reflection from opaque features beneath the tooth surface can also occur, adding noise that degrades the sensed signal and thus further complicating the task of tooth surface analysis.

However, there are drawbacks to this type of approach.

The step of applying a coating powder or liquid adds cost and time to the tooth contour imaging process.

Because the thickness of the coating layer is often non-uniform over the entire tooth surface, measurement errors readily result.

More importantly, the applied coating, while it facilitates contour imaging, can tend to mask other problems with the tooth and can thus reduce the overall amount of information that can be obtained.

Even where a coating or other type of surface conditioning of the tooth is used, however, results can be disappointing due to the pronounced contours of the tooth surface.

It can be difficult to provide sufficient amounts of light onto, and sense light reflected back from, all of the tooth surfaces.

The different surfaces of the tooth can be oriented at 90 degrees relative to each other, making it difficult to direct enough light for accurately imaging all parts of the tooth.

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