The revolutionary system for precision in dentistry

Quality of dentistry performed depends on the ability of the operator to control the hand held instrument in three dimensional settings.

 It requires manual dexterity, particularly in the form of fine motor skills, spatial technique and hand-eye co-ordination. The improvement of the ability to control the instrument depends on feedback the operator receives while performing this procedure.

  As an example of tactile feedback in dentistry let’s consider the ability to control the amount of pressure applied on the file in root canal treatment. Rotating the file inside canals requires skilled control on the amount of pressure and direction. Too much effort can break the file or force the file to penetrate the dentine of the root. So the operator working with the file in the canal must learn to apply the appropriate amount of pressure to perform the task successfully perceiving the resistance of the root canal walls to pressure of the file.

  Another learning experience is using pressure feedback in extracting teeth. After an operator secures the pliers on the tooth he(she) starts to apply a little bit of pressure in different directions seeking the path of least resistance and then applies additional pressure in that direction to loosen the tooth out of the socket. Too much force or pulling in the wrong direction will cause the tooth to crack and break.

    The same can be said about an operator cutting the skin with a scalpel. The operator should learn to apply controlled pressure to cut the tissue to a predictable depth.

    It is also important to learn to control the amount of pressure applied on the handpiece during tooth preparation.

    Unfortunately an operator does not have the opportunity to learn to control the angular position of a handpiece in space with the help of feedback and has to rely on visual control only. In order to realize the limitations of visual observation versus perception, it is important to understand how human eyes and the human brain provide us with depth perception.

    “To understand this, and many other issues in geometrical optics, we need to first understand how we perceive the distance to a point source. The light from a point source reaches the retina of our two eyes at different positions. The brain notices this ``disparity'' and uses it to estimate the distance to the source. To a lesser extent this can works for one eye however the resolution is much worse. Even the resolution of distance to a point source using the disparity in two eyes does not give high resolution. Our eyes provide excellent depth resolution when the landscape has many features. The brain uses all of these features as landmarks in forming an overall perception of the scene. Depth resolution is much worse when those features are absent, for example a point source of light on a dark night. Disparity is due to diverging rays of light. By tracing these rays back to their source we perceive depth. Subconsciously our brain carries out this process all the time. Now we have to do it consciously. The focus of our analysis is thus to find points from which light appears to emanate. These points are perceived by our brains as an ``object''. If they are not a true object or source of the original light, we call them an image. “ http://www.pa.msu.edu/~duxbury/courses/phy294H/lectures/lecture40/lecture40.html

      In depth disparity the eye's focusing mechanism separates objects at different distances. If the eye focuses on one object, others nearby will be slightly out of focus. The eye-brain control system continually uses the focusing property to scan a scene, focusing at different distances to intensify the depth perception. "Depth disparity is an essential element to our perception of 3-D, but it is not recorded in stereoscopic images because they are essentially flat images located in one plane in space," Dolgoff explained. "So, you cannot change your focus when looking at those images due to the fact that everything is always in the same plane.

      Dolgoff's work centered on a set of visual-accommodation techniques, used in real life to sense the depth disparity that is missing in most 3-D systems. "When one focuses on objects close up, background objects blur and vice versa, so the eyes continually focus and refocus on near and far objects," he said. "Basically, the eyes change focus when examining a scene, and depending on where the eyes concentrate objects shift from clear to blurry or from blurry to clear, and the scene is in constant flux between sharp and blurred images."

      In addition, as the brain shifts its attention from near or far objects, images at a given depth converge to form single images, while objects at other depths appear as double images. "Basically, we see one plane in space as a single sharp image and all other planes as blurry double images," he said. " We found that 98 percent of what we see in real life is a blurry double image." ; not paradoxically the brain could not process the totality of information presenting itself.

      The nature of perception is rather to provide a useful description of objects in the outside world instead of being an accurate mirror image of the physical world.

 http://coe.sdsu.edu/eet/articles/visualperc2/start.htm

      It is very difficult to control the distance to the object using direct vision. It is much more difficult to control angular position of the instrument. It is almost impossible to control the angular positioning of a hand-held instrument using the mirror image of the operating field.

      Let’s say an operator, looking at a tooth finds an optimal direction of the preparation of the tooth for a laminate, a crown or a bridge. In order to control the direction of a preparation, he (she) places a first groove at a surface of the tooth that corresponds to the right direction of the preparation. Then the operator shifts the direction of his (her) eyes to the other surface of the same tooth or even to the other tooth trying to work in direction parallel to the first groove. In this situation the first grove goes to 98% of the invisible field and control over the angulations is lost.

      Even more disastrous is trying to control the angulations of the hand-held instrument looking at the mirror images of the operating field; the operator does not even have control of the distances, more so not to say of angulations.

      Our vision from either eye is two-dimensional. The brain infers and creates the third dimension (depth) by clues in the image (such as perspective) and by interpolating the differences between the images from each eye.

      Make a simple experiment: look at yourself in a mirror, you saw nothing new until now; now looking at your face with this new knowledge, you can appreciate that we as humans have a limitation of not being able to see our face in direct vision. To verify this fact look at your hands directly, now look at them in the mirror. See the difference? Chances are you’ve realized the difference for the first time in your life. It might have the different levels of significance from philosophical to psychological, but we are going to discuss the practical significance from the point of view of a dentist.

      Using the mirror image of the operating field does not really make much difference: to control the removal of decay, finding the root canal opening or tartar on the surface of the root. We do not have to depend on depth perception, but it makes a dramatic difference in controlling the correct angulations of the hand-held instrument. That is why preparations for the crowns and bridges are far from perfect.

      The fact that the operator in dentistry has to rely on mirror image of the operating field greatly reduces the ability to control the desired angulations of the instrument. Perception is the same as working with one eye closed using the direct view. It is practically impossible to have a predictable control of the angulations of hand-held instrument looking at the mirrored image of the operating field while managing instrument in it.

      That is probably why we sometimes have a problem of acceptance of cosmetic dentistry by our patients when they look at it in the mirror. Perhaps it’s a good idea to invite relatives to interpret the success of the procedure.

      To appreciate the difference between Direct Vision and Mirror Reflection Perception in a practical sense, make an experiment; try to trim the eye brows on some one else and then try to do the same on yourself looking at the mirror image of your face. Isn’t it much more difficult to perform it using a mirror reflecting perception than Direct Vision?

      An operator having the opportunity to verify the exact position of the hand-held instrument does not even realize or at best fully realize the limitations of controlling the angulations of a hand-held instrument. Working with the AcuHand System I’ve encountered the situation that when I try to place parallel groves on the upper central incisor it was easy to accomplish on the front and proximal surfaces but when I tried to do it on lingual surface looking in the mirror it was much more difficult, not to mention working with the mirror on the more distant teeth. It have been taken me years of working with AcuHand System to realize the perceptional difference between using direct vision and looking at the mirror.