By Dan Durkin—

Editor’s note: This is the eighth piece in a series previewing the 2015 Bears as the first training camp practice approaches July 30. You can find them in one spot here as they’re posted.

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(CBS) In 2013, the Bears opened the season with four new starters along their offensive line. They went on to join the Eagles and Redskins as the only teams in the league to have the same five starters for all 16 games. Continuity is crucial for line play, as it lends itself to clear communication and understanding of specific blocking assignments.

Last season, the Bears started the year with the same five starters but didn’t end with them.

Injuries decimated the group, forcing them to use nine different starting combinations. The results were anything but positive, and the offense never found a rhythm.

The pass protection didn’t hold up with the front five alone, which forced the team to use six-man lines and check releases for the running back, limiting the number of eligible receivers out in routes. The unit went from the second-least false starts in 2013 (nine) to the second-most (27) in 2014, highlighting a lack of concentration and discipline.

This season, the group is guaranteed at least one new starter at center and perhaps another should the team decide to move Kyle Long to right tackle. How the offensive line solidifies — or doesn’t — during camp will be one of the most crucial story lines to follow.

Likely starters:
Left tackle: Jermon Bushrod (30, ninth year)
Left guard: Matt Slauson (29, seventh year)
Center: Will Montgomery (32, 10th year)
Right guard: Kyle Long (26, third year)
Right tackle: Jordan Mills (24, third year)

Other competitors: Vladimir Ducasse (27, sixth year), Michael Ola (27, second year), Jason Weaver (26, first year), Ryan Groy (24, second year), Charles Leno (23, second year), Conor Boffeli (23, first year), Tayo Fabuluje (23, rookie), Cameron Jefferson (23, rookie), Chad Hamilton (23, rookie), and Hroniss Grasu (23, rookie)

Key contributor: Kyle Long

Long has emerged as a true cornerstone piece for the Bears. He’s established himself as one of the league’s top young offensive lineman, which is incredible considering he’s still green as a football player.

Long’s been entrenched at right guard for two seasons. His his length, power and lateral agility have helped him win gaps in the run game and wall off inside pass rushers to allow the quarterback to climb up in the pocket as the edges collapse.

In Adam Gase’s offense, guards are heavily relied upon on pulls, traps, leads and in the screen game. Thus, the staff may put a premium on Long’s fluid feet and ability to glide to the second level and pave lanes for running backs. However, considering the best pass rushers in the NFC North are on the outside, his length and ability to mirror pass rushers may prompt a move to tackle.

Whichever direction the coaching staff elects to go with Long, they can’t go wrong. In the short term, they’ll consider their alternatives at both guard and tackle to determine where he will benefit the group most. But if the long-term goal is to move him outside, why wait?

Potential breakthrough player: Matt Slauson

Slauson was brought to Chicago on a one-year, “prove-it” deal in 2013, which he outperformed and parlayed it into a four-year extension. Last season, he injured his ankle in the season opener, which cost him three starts, then went on to tear his pectoral muscle in Week 8 and was lost for the season.

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Slauson had offseason surgery to repair his pectoral and is a full go for training camp. His presence brings stability back to the line and provides some nastiness in the run game.

While not as nimble as Long, Slauson flows to the second level to seal an edge or create an alley. He’s powerful in confined spaces and rarely loses ground when anchored at the point of attack.

Final thoughts: Heading into camp, the Bears are one player short on the starting five and have paper-thin depth. With 89 players on the roster currently, it wouldn’t be surprising to see an offensive lineman signed before camp starts.

Jermon Bushrod will be the league’s ninth-highest paid left tackle, but will his performance match his pay grade? He’s stabilized what was a blind-side turnstile for years in Chicago, but he’s struggled with speed rushers. He’s trusted to play on an island without help but must find more consistency in his protection sets.

On the opposite side, Jordan Mills remains a weak link. His ability to start 16 games as a rookie overshadowed poor play, particularly in pass protection. His footwork was sloppy, his hand placement was erratic and he had multiple lapses in concentration. His struggles carried over into last season, as did the foot injury he suffered in the final game of the 2013 season (a fractured fifth metatarsal in his left foot), which cost him three starts.

If the Bears were to move Long outside, Mills might be a candidate to move inside, which aligns with my assessment of him heading into his rookie season.

At center, veteran Will Montgomery will battle rookie Hroniss Grasu. Given what’s required of a center on a play-by-play basis, it’s a tough position for rookies to come in and start immediately. Montgomery has the NFL experience, as well as an existing relationship with coach John Fox and offensive line coach Dave Magazu, whom he played for both in Carolina and Denver.

Grasu is clearly the future at the position. He’s an excellent leverage player with quick feet who was a four-year starter at Oregon. He’s accustomed to making line calls and checks in a complex, high-tempo offense, which will benefit him when he eventually takes over.

With Grasu a lock to make the roster and the team likely to carry only eight offensive linemen, that leaves a group of questionable reserves to battle for the remaining two spots.

Of the reserves, only Vladimir Ducasse has more than one year of NFL experience, a career that’s been a disappointment.

Michael Ola gained valuable experience last year, starting 11 games at four positions, all but center. Considering a team only dresses seven offensive linemen for games, Ola’s versatility is a boon, but he didn’t stand out in any role.

Ryan Groy made three starts at left guard at the end of the season but is an unproven prospect.

The Bears have one blue-chip player (Long), two above-average starters (Slauson and Bushrod), a likely stopgap at center (Montgomery) and one hole on the right side of the line. This unit will be well-coached, but their concerns are legitimate.

Position grade: B-minus.

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter @djdurkin.