Learning: Ergonomics: Critical Range of Motion

Q. What is the best position for the operator to sit in when performing dentistry? A. There are a multitude of opinions about operator position and, as is commonly the case when there are differing opinions, that usually means that there is no single answer. However, we can give you some background and a method of deciding how to make positioning ideal for your style of practice. First, here's a bit of history. The quest for “ideal” operator positioning comes from the studies of industrial hygiene (factories not dentistry!) at the middle of the past century. The whole idea was to make man part of the machinery—a tool with a dental degree. Here's the problem: Our patients vary; we have obese patients and tiny patients and patients that can't lie flat. This isn't an assembly line. If you break the machine (the doctor) you can't just buy a new one! So we have to create an environment that is best for the “machine” not just for the task.Therefore, we need to split the process into basic principles and flexible options. Basic principles—these are the ones that you probably learned in school: • Back upright • Minimal head tilt • Thighs parallel to the floor (not really—more on this later) • Feet flat on the floor (which can't really happen because of the foot control) • Patient low to the legs (there are reasons why this is probably wrong too) These principles are easier to adhere to from the 10° to 12° position, but that doesn't mean much in reality. This brings us to a flexible view of posture and positioning. Spines get nourishment through motion. Motion is good! If you convert to a fixed focal length, for example with a microscope, you do so at great personal risk, especially if you perform long detailed procedures such as endo or crown and bridge. (There are solutions coming for this but they are still a ways off). If it is true that bodies are healthiest when in motion, the goal should be to comfortably accommodate the range of postures required to provide care, so that it is not a big deal when Mrs. “I-can't-lie-back-beyond-45°” comes in for endo on an upper molar. To accomplish this you need flexible equipment—and most equipment isn't very flexible.What are the requirements for equipment flexibility? Flexible Equipment: Allows the operator to sit, stand or sit-stand in function Allows the assistant and to a lesser extent the operator to sit, stand or sit-stand in function Permits work from 7° to 1° for right handed operators (11° to 5° for left handers) A flexible equipment layout should not place dynamic instruments to the side or rear of the operator or assistant except in very special situations (but please don't do it—you don't need to) Equipment flexibility is most easily accomplished with over-the-patient or over-the-head equipment.
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