Complex sentence: Chris Poland, who played lead guitar on Megadeth's first two albums, was hired to contribute guitar solos to the new album; this was the first time he and Mustaine worked together since Poland's dismissal in the 1980s.
Split into simpler sentences: Chris Poland, who played lead guitar on Megadeth's first two albums, was hired to contribute guitar solos to the new album. This was the first time he and Mustaine worked together since Poland's dismissal in the 1980s.