My new four unit porcelain bridge broke while eating sandwich. the crown's still there. my dentist's appointment is after two day, on monday. would i get an infection?

No: The underlying tooth is still protected by the underling metal.

Depends: If the porcelain chipped due to a defect, then the metal will still protect the underlying tooth (if the bridge is constructed with porcelain to metal) but -- if the porcelain broke due to tooth fracture / decay, then the tooth could become sensitive and infected, possibly requiring root canal treatment.

Unlikely: If it is just a stuctural failure of the ceramic, the tooth is still protected by the underlying metal.

Unrelated issues: If only the porcelain broke, it's just a cosmetic problem. If the solder joint broke in between the crowns, it's more of a structural problem. In any case, whether or not you get an infection would be unrelated to the bridge breaking. That is not to say that you might have other problems in the bone or gums, but would be totally independent of what just happened. I wouldn't worry.