James Rael and Peter Reilly join Des Merrey in the front row, while Alan O'Connor, another new starter, will partner Iain Henderson in the second row.
Aaron Conneely and Josh van der Flier have been added to the back row alongside regular number 8 Jack Conan who will captain the team.
Mike Sherlock has been named at full-back with Conor Finn selected on the right wing and Peter Nelson moving from full-back to centre where he links up with his Dungannon club-mate Chris Farrell.
Luke McGrath and Jack Carty, who plays for Buccaneers like Finn, will combine at half-back, with the pair making their first starts of the Junior World Championship.
Commenting on the team selection, Ruddock said: "We have had two extremely physical battles against South Africa and England and we felt we needed to freshen the team up.
"A number of players are carrying bumps and bruises and it provides opportunities for other squad members to step up and take their chance."
This fixture has been moved from Danie Craven Stadium in Stellenbosch to Cape Town Stadium. TG4 will carry live coverage of the game on Tuesday afternoon.
IRELAND UNDER-20 Team & Replacements (v Italy Under-20s, IRB Junior World Championship Pool B, Cape Town Stadium, Cape Town, Tuesday, June 12, 2.45pm local time/1.45pm Irish time):
15. Mike Sherlock (Clontarf/Leinster)
14. Conor Finn (Buccaneers/Connacht)
13. Peter Nelson (Dungannon/Ulster)
12. Chris Farrell (Dungannon/Ulster)
11. Sam Coghlan Murray (UCD/Leinster)
10. Jack Carty (Buccaneers/Connacht)
9. Luke McGrath (UCD/Leinster)
1. Des Merrey (Clontarf/Leinster)
2. James Rael (Garryowen/Munster)
3. Peter Reilly (Lansdowne/Leinster)
4. Alan O'Connor (UCD/Leinster)
5. Iain Henderson (Queen's University/Ulster)
6. Aaron Conneely (Corinthians/Connacht)
7. Josh van der Flier (UCD/Leinster)
8. Jack Conan (Old Belvedere/Leinster) (capt)
16. Niall Scannell (Dolphin/Munster)
17. Tadhg Furlong (Clontarf/Leinster)
18. Jake Cawley (Old Belvedere/Leinster)
19. Tadhg Beirne (Lansdowne/Leinster)
20. Shane Buckley (Garryowen/Munster)
21. Kieran Marmion (Corinthians/Connacht)
22. Cathal Marsh (Dublin University/Leinster)
23. Stuart Olding (Belfast Harlequins/Ulster)
2012 IRB JUNIOR WORLD CHAMPIONSHIP -
POOL B RESULTS/FIXTURES:
All kick-off times are local -
Monday, June 4: England 64 Italy 5, University of Western Cape Stadium, Cape Town
Monday, June 4: South Africa 19 Ireland 23, Danie Craven Stadium, Stellenbosch
Friday, June 8: South Africa 52 Italy 3, University of Western Cape Stadium, Cape Town
Friday, June 8: England 20 Ireland 15, Danie Craven Stadium, Stellenbosch
Tuesday, June 12: Ireland v Italy, 2.45pm, Cape Town Stadium, Cape Town
Tuesday, June 12: South Africa v England, 6.45pm, Cape Town Stadium, Cape Town
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