Mandibular impacted canine that crossed the lower midline
It is quite impressive that after doing maxillary expansion, tongue crib, braces on upper and lower front teeth, placing upper and lower holding arch, an orthodontist do not question himself why the lower right permanent canine has erupted and the lower left primary canine was retained.
I am speechless.
At this stage, the prognosis to bring the canine in its position is poor. Many orthodontist will recommend its extraction because it may take 2 to 3 years to bring it into the mouth. If this is an extraction case, then it would be logical to extracted the impacted caine, the primary canine and 3 other premolars to obtain symmetric class I occlusion.
If it is not an extraction case, one can try to do orthodontic traction. Chances are that the canine will finish transpose with the lower left lateral incisor. This is not a bad solution and I did to one patients many years ago and I am currently doing it to another patients.

This case came in my office in february 2016. I initiated orthodontic traction and the teeth moved. However, last month, it was quite obvious that I could not get the canine into its position. So I decided to treat it transposed. I am curently opening a space between the cental and the lateral incisor.
This is better than nothing and better than an implant.
You have to know that the treatment time may be 30 to 36 months for such a case and it is costly. But the solution is defenitive and no further cost will occur during the life time like crown replacement, implant replacement, bone graft.
I don't know if you can find an orthodontist in your area that would be willing to try such treatment.
Bonne chance.