Most important factor of Cvek pulpotomy in young permanent tooth according to latest AAPD guidelines:
Cvek pulpotomy or partial pulpotomy

Cvek has shown that, in exposures resulting from traumatic exposures, pulpal changes are characterized by a proliferative response, with inflammation extending only a few millimetres into the pulp. 
When the hyperplastic tissue is removed, healthy pulp is seen.
In cases with carious exposure, it might be necessary to remove tissue to a greater depth in order to reach non-inflamed pulp. 
Cutting of the tissue with a diamond bur using high speed with water cooling is the best method. 
After pulp amputation, saline is used for irrigation and the hemorrhage is controlled with cotton pellets.  
A dressing of calcium hydroxide is gently placed on the amputation site.  
Care should be taken not to push the material into the pulp. An entrance filling with GIC or composite is done. Recently MTA has been used to carry out these procedures.

Pediatric Dentistry, Principles and Practice / M.S. Muthu, N. Sivakumar - 2nd Ed pdf no. - 795
Type of medicament used
Extension of inflammation in pulp
Time gap between accident and treatment
Size of exposure