Reason for Deviation 

Q: To place an implant at #21 (narrow space), you advises me to trim the mesial surface of the tooth #20 (see the 1st attachment).  I did, but I do not know how much to trim.  As a matter of fact, deviation occurs (2nd attachment), although immediate restoration is just fine.   Ever time we need to make trimming, deviation occurs.  In the future, I have to trim before CT and impression.  Right?  What else can we do?   Thanks.

A: I see. I reviewed the case again and is it okay if I put another screenshot for you to show you how much to trim (same as the planning software, Fig.1). 

And the reason of implant deviation towards distal is not because of we planned to adjust the mesial contact of #20. Adjusting the contact is only for guide insertion. Due to insufficient space for narrow metal sleeve, adjusting the mesial contact of #20 was suggested. When you look at the inner part of the surgical guide, those inner parts of interproximal are holding the guide steady during the osteotomy (Fig.2). Again, adjusting the contact does not mean that the whole guide will be shifted to that side, but only for the path of insertion. 

I am guessing the reason of the deviation would be the slanted surface of the bone. And when you see the red marked site (Fig.3), that shows white color (which also means dense bone). If there was more space, we could've used a regular metal sleeve and plan for a bone trimmer prior to the initial drilling, but this case, we couldn't do that. Narrow metal sleeve was used with 12mm of max offset. So, in this kind of case, I am sorry to tell you but we might have to manually remove the excessive bone to flatten the bone surface for osteotomy before implant placement when the regular bone trimmer can not be used.

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Xin Wei, DDS, PhD, MS 1st edition 03/01/2021, last revision 03/01/2021