Protruding Teeth Correction with Invisalign?

I would have to agree with Dr Virk's assessment. A lateral cephalometric x-ray is the standared of the industry to assess whether or not teeth should be extracted. Measurements are made from the x-ray to determine the biological limits as to how much incisors can be moved anteriorly or posteriorly within the confines of the boney ridge (the alveolar process) in which they sit. Simply increasing intercuspal width can lead to recession on the cuspids and/or be a reason for orthodontic relapse.
I would certainly see a dental professional that can assess your individual situation with the tools that would necessitate making the correct decision. That professional would be a board certified or board eligible orthodontist.
Invisalign can correct the problem with or without extraction in the right situation.

I agree with Dr Estep. Invisalign can widen the arches, thus creating space to bring the teeth back substantially. Also, in combination with that, the enamel can be thinned between your teeth, allowing them to move closer to each other. These things are now being done rather than extracting 4 teeth. Extractions like that can be problematic in the future and is a very 1980's way of thinking.

I do a lot of Invisalign cases, and I have yet to recommend 4 bicuspids to be extracted. I believe that you should keep all of your teeth (except wisdom teeth) if you can. Invisalign does an excellent job widening your arch and allowing room to pull back those protruding front teeth. And you smile will look great!

Invisalign is just another tool to correct mal aligned and crowded teeth. The treatment protocol depends upon thorough evaluation of your dentistion and skeletal structure (jaw placements etc).
In general, when we have to bring teeth back fto correct protrution we need space. Space can be achieved by three ways.
A. Extraction of teeth
B. Expansion of the arch
C. Inter proximal reduction. A tiny bit of enamel is shaved off to create space. This depends on size of teeth.
Expansion has limits. If you over expand you will predispose yourself to periodontal issues e.g. gums recession etc. The other issue is stability. Beyond some limits expansion is unstable.
Extraction obvioulsy will give more space but you will have to loose teeth. Now it depends upon how much of the protrusion has to be corrected.