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A patient presents with bimaxillary protrusion. The upper and lower first bicuspids are extracted. If you encounter skeletal resistance during space closure, how do you close the extraction spaces?
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If you mean that the root of the canine is contacting the cortical plate (buccal?), one has to consider centering the root in the trough by changing the torque (or bracket) to a positive, say +7 degrees or so. This can be further enhanced by expanding the canine segment of the archwire to some extent to undo the contracted arch. Then you can continue space closure.
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Determine the canine root position in the mandible. If it is contacting either cortical plate, move the canine away from it. I use lingual root torque on all canines, as this is a common problem with buccal root torque. My appliance has a +7 in all canines for this reason, and the occlusion looks better to me. You also may be having trouble due to the extraction sockets being compressed at the extraction appointment, creating a knife-edge alveolus; then you must use very light force to close the space, <100g per side. Sentalloy springs can be activated at this level and work well, or Burstone springs can be fabricated and are very efficient.
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Changing the canine torque could help in centering the root of the canine in the alveolar bone, that is why MBT suggests having three different torques for the canine brackets. For the upper canine +7, 0 ,-7, and for the lower +6, 0 ,-6. Different torque is used for different situations according to the position of the canine root. With a suggestion to have zero torque brackets in extraction cases, thus maintain the canine root in cancellous bone, and making root tip control during retraction easier.
If the extraction sockets gets compressed , and a knife-edge alveolus (furrow) is created, it is very difficult to close this space fully. Therefore, I prefer to extract second premolars in most of the cases. Second premolars are easier to extract than first premolars due to their anatomy, and if furrow is created the space left is further in the back and does not show.
Lama Jarrah
Amman-Jordan
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