The Bruins lead the Atlantic Division by 4 points. The trade deadline is more than three months away. The Providence-to-Boston shuttle — or, in the case of David Warsofsky and Nick Johnson, a trip from Glens Falls, N.Y., to Ottawa via Providence — is filling in the holes that riddle the varsity lineup. Time and depth are on the Bruins’ side. They are in no rush to make a deal. But at least one will be coming. The Bruins, internally and via the trade market, will not find a replacement for Dennis Seidenberg. The No. 2 defenseman, ruled out for the year Saturday because of a demolished right knee (torn ACL and MCL), touches the game in every situation. In the playoffs, Seidenberg plays against top-line forwards. The left-shot defenseman switches to the right side. Seidenberg is paired with Zdeno Chara. Before their tanks ran dry in the Stanley Cup Final last season, they were the shutdown defensemen nobody wanted to face. But it is management’s imperative to acquire a veteran defenseman who can provide at least some of Seidenberg’s qualities. Assuming the Bruins’ run of ill health stops short by the playoffs, they should have another roster ready for a run at more rings. Tuukka Rask is a Vezina Trophy candidate. Chara is the NHL’s most feared shutdown defenseman. Their top line of Milan Lucic, David Krejci, and Jarome Iginla is the kind of heavy-duty, playoff-hockey unit that should be sponsored by Caterpillar. The Western Conference is loaded with Cup-worthy teams in Chicago, Anaheim, San Jose, Los Angeles, and St. Louis. The Bruins and Penguins, both racked by injuries, appear to be the only legitimate troublemakers in the East. But the current crew will need help. Matt Bartkowski, the left-shot defenseman most similar to Seidenberg, doesn’t have his mentor’s pedigree of consistency. Johnny Boychuk and Adam McQuaid are right-shot defensemen. Torey Krug is a lefty, but is a puck-moving, power-play specialist.