There is two school of thought for frenectomy such as

1. at mid orthodontic treatment i.e. immediately closure of the mid line diastema

2.after completion of orthodontics treatment .

we should not do frenectomy before the start of orthodontic treatment because the scar tissue formed, will be hamper the tooth movement and there is more chance of relapse.

Regards

Abhay

The midline diastema should be closed orthodontically  in order to compress an active  frenum prior to a frenectomy, thus minimizing the resultant scar formation, reducing the chances of re-opening of the diastema. De-rotation of incisors should also be completed simultaneously and consideration given to circumferential dento gingival fibre cuts at the same time as the frenectomy to further improve stability

As beautifully demonstrated by Bergstrom's 1973 article (The effect of superior labial frenectomy in cases with midline diastema, AJO 63 -6, pp.633-8), way more frenectomies are performed than are necessary. There should be appropriate diagnostic criteria to establish the need for this procedure: does normal function have a detrimental effect on the periodontium? Is there a non-union in the mid-palatine suture – one where soft tissue needs to be removed in order to provide a rigid status for the alveolus to support the incisors? What will be the long term impact on gingival height and interproximal papilla?

Once it is determined that the procedure is indicated, timing becomes the issue. If the procedure is done prior to closure (or near closure) of the diastema, the size of the scar will be larger; closing the space will involve an exaggerated amount of dense collagen (scar tissue) to bunch up making space closure more difficult. The optimal time for the frenectomy to be done is when you still have enough space to run a bone bur into the suture (if necessary) and yet when the space is very nearly closed. Also, the appliances should be in place so that immediate force application will close the space and hold it closed while healing takes place. In this way the “scarring” will help sustain the space closure, not prevent it. Finally, the procedure should be done with sufficient creativity that the incisive papilla is enhanced, not destroyed.

My answer though seem odd but i have abandoned frenectomy in majority of my cases with median diastema. i believe if the frenum is hindering space closure do frenectomy no matter you notice it in at initial of space closure or at final 1 mm . if you are able to close all the space with good incisive papilla support in between than give a fix  permanent retention. No need to do frenectomy.A good fix lingual retainer will no let the space to open . if its a fix permanant retainer at end than what is the fun of fibrotomy and frenectomy if all the space is closed . yes if someone give a 1 year of retention after frenectomy and fibrotomy than its advantageous to go for it but i think evidence only support permanant retention for these cases.

The problem with permanent fixed palatal retainers used to retain a closed  midline diastema due to a large  frenum,, whist efficient, on occasion dislodge and the diastema  re-occurs very quickly. A frenectomy and/or a fine septotomy in most cases will reduce this provided other  factors such as the shape and size of the incisors, the over jet and overbite have been considered.  It would appear that the optimum time for this minor surgery is after the upper canine teeth have erupted in the later stages of orthodontic treatment when the appliances will maintain the closure whist healing takes place.  Age is therefore an important consideration as midline diastemas mostly reduce in size between 8years  and young adulthood. Some cases require early intervention due to their unsightly appearance. In all  cases the gingival contours and papilla need to be respected 

Perhaps all of us should consider why there is little evidence to show that our direct ancestors had these problems. It has been suggested that enlarged frenums are related to lack of tongue to palate contact combined with poor lip function. Is that right or wrong? If it was a problem surely natural selection would have eliminated those who could not grind and swallow correctly. Prof John Mew.

Usually the frenectomies are performed after space closure in case of diastemas with fixed orthodontic treatment.