You can make perforation of root especially during resorption period

Well, I think the use of rotary files in primary teeth has several advantages when compared with manual K files.

Tissue and debris are more easily and quickly removed and therefore decrease working time, that helps maintain child cooperation by decreasing the potential for tiredness.

The shape of the root canal is more conical with rotary files, favoring a higher quality of the root canal filling, and increasing clinical success.

In addition, the perforations may occur with both (manual and rotary instrumentation), but we must not forget that the nickel-titanium files are flexible allowing easy access to all canals.

I do not find a reason to use rotary files in primary teeth. Reason one, they are already wide enough for the files to be manipulated in; hence reducing the chances of breakage during manual endo as opposed to permanent teeth. The roots are also much shorter, and can possibly lead to working beyong the root apex without realizing so. Then again, if the child is not sedated, he or she may react violently while the instrument is working its way around in the mouth, and such sudden movements can cause the child some injuries as well.

The apex of primary it's not already close it is so wide but it not necessary to use it . First the permanent that under can domage by rotary files. And second create a wide space in the apex

The use of rotary files in primary teeth has several advantages when compared with manual K files: the efficiency in both, preparation time and root canal shape. 1. A decreased working time, that helps maintain patient cooperation by diminishing the potential for tiredness. 2. The shape of the root canal is more conical, favoring a higher quality of the root canal filling, and increasing clinical success.

Reference :

J Clin Pediatr Dent. 2008 Summer;32(4):295-8.

Comparison between rotary and manual instrumentation in primary teeth.

Crespo S, Cortes O, Garcia C, Perez L.

Endodontic treatment of primary teeth is still one of the most contradictory issues in the field of pediatric dentistry.

Besides the discussion about manual or rotatory instrumentation, medication and intra-canal filling material are also issues that deserve a thorough discussion.

May I please play devils advocate?

How do you justify invasive root canal treatment in primary molars in todays days?

The protapers which are commercially available now were not designed for primary teeth. It was designed taking the permanent root canal size, shape and depth in mind; depending upon the end result of a proper BMP. But as a primary teeth is not a miniature version of a permanent teeth, it cannot be considered on any grounds.