In order (let's cut down the distracting verbiage),
- Three clinical trials were found that supported it.
is produced by the syntactic rule of Extraposition from NP out of
- Three clinical trials that supported it were found.
And that's what it means. Extraposition from NP moves a relative clause from the noun it modifies (usually the subject NP) to the end of the sentence. It's an optional rule that's invoked when not doing so would result in an overlight verb phrase like were found, resulting (in the original) in:
- Three controlled animal clinical trials that supported the use of decortication prior to performing GBR were found.
English likes the verb more forward in a long sentence.
Second, the to in
- The literature addressing the capacity of decortication to affect only grafting or wound healing also provided mixed results.
That to is required by capacity. The prepositional phrase of decortication that intervenes between capacity and its complement infinitive interrupts the parsing. The to is still required --
- ... addressing its capacity to affect only some organs
is grammatical, but
- *... addressing its capacity affect only some organs
But English has to put things somewhere, and the author of these sentences is apparently determined to get as much information in each sentence as they possibly can; like every period deducts money from their paycheck.