Frank in 1966 was one of the first to describe the clinical methods using calcium hydroxide paste & camphorated monochlorophenol (CMCP),to stimulate root closure.
The procedure for Apexification is
The tooth is isolated with rubber dam, & access is gained into the pulp chamber.
1. Using large reamers & files, remove the debris from the coronal half of the pulp & establish the file length radiographically.
2. Clean the canal, irrigate it & then dry it with a paper point. Repeated gentle use of sodium hypochlorite assists debris removal.
3. Seal a pellet of CMCP in the pulp chamber with a provisional restorative material.
4. On recall, in 1 to 3 weeks, remove the restoration & clean the canal.
5. Take care to avoid any instrumentation of the walls of the dentin near the apex.
6. Mix a paste of calcium hydroxide & CMCP on a glass slab. Carry the paste to the canal & force it into the apex with a larger plugger or cone-shaped instrument. The objective is to fill the canal completely. Obtain a radiograph to check the accuracy of the root canal filling.
7. On a 6 month recall, you should see radiographic evidence of an apical closure.
8. When you have accomplished apical closure, the root canal filling is completed.
9. If apexification has not been completed, repeat the cleaning & insertion of a calcium hydroxide & CMCP paste.

Apexification pre-treatment showing open apex

Calcium hydroxide placed in the pulp chamber following removal of pulp

Check X-ray-Apical constriction formed by 12-13 months.

Post-treatment obturated with gutta percha
Treatment evaluations of Apexification
The first evaluation may be done after 3 months. Radiographs may show hard tissue deposition, but such evidence is not considered reliable. It is necessary to test the quality of apical barrier with a size 35 file.
If the 3 months radiograph shows little or no apical changes, reschedule the patient for another 3 months recall. There is no need to change the calcium hydroxide if it appears to occupy the root canal space adequately, & if the coronal temporary seal appears satisfactory.
The follow-up evaluation is repeated every 3 months until successful apical bridging has occurred. This may take as little as 3 months or as long as a year or more, depending on the degree of apical destruction & the ability of the apical tissue to repair.
Obturation of the root canal
Because the root canal wall does not change during apexification, the shape of the canal will remain the same after the apical barrier has formed, namely a reverse taper. These canals are probably best suited for obturation by a thermoplasticized technique.