What size of Implant: wider or narrow?

Rule of thumb: leave minimum 2 mm buccally and 2 mm lingually. What is width of ridge at its narrowest?

Ridge is sort of "mushroom" shaped. The widest point at top of ridge where platform would be is 8.2. Below that, the narrowest point is 7.2. Using a tapered implant of course.

3.7 seems like the better choice. you can always tilt the implant away from the concavity and correct with an angled or custom abutment. 3.2 seems like a small implant for posterior region. Consider if patient is a bruxer or clencher. GIven the thick bone, that may be a very real possibility.

This case looks well designed. I presume you will progress with a surgical guide. I would suggest the wider platform but possibly consider a 11-12 mm length implant (there seems to be plenty of room for them to be a little longer). I wonder if the anterior implant could be placed further mesially? If the ridge is a little narrow in that area, it might be worth considering the narrower implant and positioning it further forward. The reason I raise this point is that the emergence profile would be better and create less food trapping (and easier cleaning) if the abutment and crown was a little closer to the adjacent tooth. It may not be possible – just worth considering I think.

Give us a little more information about the patient. Is he or she a clencher? I would not put anything narrower that standard diameter implants in the posterior region. You have plenty of bone for the 3.7 implant. Vascularity may not be a problem.

There is no advantage to placing an implant that is longer than 8mm. Regarding width, use the widest implant that leaves sufficient bone all around, minimum 1.5-2 mm.

I agree that there is no benefit to using an implant longer than 8.5 mm in a healed site. Longer implants are sometimes needed to achieve initial stabilization for immediate placement in fresh extraction sites. I would place a 3.7 given the choice but I would also consider placement of a 4.0. I think your approach to use a cantilevered mesial pontic is a good plan.

Can some doctors comment on the use of cantilever on implants. What are the general rules for placing cantilever pontics on implants

No cantilever is a good cantilever. Try to avoid them at all cost. In the AO4 configuration 10mm or less when possible.

Over the past 38 years I have restored hundreds of missing second bicuspids with mesial cantilever pontics with only a first molar as the abutment. None of them have failed after more than 2 decades of observation. I have also restored many cases with cantelevers using implants. What "they" say about cantilevered pontics is simply not true. Next week I will be placing a 4 unit bridge placed on implant abutments in sites 28 and 30 with pontics in sites 29 and 31. I know it will service fine for decades.

Great comment!!

It seems like D1.5 type bone to me. Just make sure you cool down the drilling site in order to avoid heat necrosis. Especially when you use implant guide, D1 bone with narrow drilling guide can sometimes cause heat necrosis. I prefer to use wider diameter of implant in case of wider bone like this patient.