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| May 2009 | Courtesy of BEGO USA |
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Axis of Rotation When designing partial denture frameworks, it is important to have a good understanding of the concept of the "axis of rotation". In the photo locate the red line drawn that intersects the two supporting rests in each quadrant. This line is the axis of rotation or sometimes referred to as the fulcrum line. As chewing forces are applied to the partial, the restoration will rotate around this line. Line "L" represents the load force or downward force applied to the restoration. The length of the line is measured from the axis line to the distal of the last tooth. Line "K" represents the counterforce or the upward force applied. This line is measured from the axis line to the furthest anterior clasp tip away from the line. The design should try to keep these two lines length the same, meaning there is equal working forces exerted on each side of the framework, the same concept as a teeter-totter. Notice in the photo that line "L" is longer than line "K". How would you improve this design? An answer could be to move the rest seat on the last molar to the distal side of the tooth. This would move the axis line back resulting in line "K" becoming longer and equaling out the forces. Another possibility could be to move the last denture tooth in the saddle out of occlusion, but moving the rest seat might be an easier fix. |
 The red line represents the "axis of rotation" while the "K" and "L" lines represent the forces applied to the restoration. When possible try to keep the two forces or lines equal.  | |||
 For more information, call your local dealer or BEGO USA, 1.800.342.2346 www.begousa.com | |
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