For good exterior density keep them happy. The leaves on the inside age and die out regardless, you cannot do anything about that. But if you can see this inner bareness it means the outer shell has gaps - that is your problem.

. I have never pruned it and didn't know you could do this to pines to promote inner fullness.

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you cant bet on it

it wont... fill back in for sure ... though it might get fuzzier on the periphery .... there is no way to make it thicker inside...

all pines shed there needles within 1 to 3 years.. and interior needle loss is NORMAL ...

pruning of the new growth on pines is VERY TIME SPECIFIC .... its called 'candling' ...

they are conifers.. and there is a conifer forum should you wish opinion other than those here ...

but frankly.. w/o a pic ... we cant help very much ...

intro to conifers at link.. i THINK there is a pruning section

ken

Here is a link that might be useful: link .. look for 'candling'

Here are some photos...

One more photo

The main source of baldness at this point is probably shade from the pine right next to it. Most pines need full light, more so than arborvitaes or hemlocks which are climax species adapted to growing beneath, replacing other trees in the forest.