Long term the crystals form into stones, can damage the bladder wall, and cause discomfort and of course urinary blockages which can be fatal. Crystals are simply small formations and stones are the large ones.
The treatment depends on the kind of crystals they are.
Some are formed by infections being present in the bladder and resolving the infection resolves the problem. The infection breaks down the urea in the urine and in series of chemical actions a matrix which the struvite crystals use to form an actual stone is created.
Some stones made of calcium oxalate are formed because the dog has a faulty gene and cannot inhibite the precipitation of the calcium in the urine. For that a special diet to limit the amount of mineral consumed may help.
Struvite requires an alkaline pH to form while oxalate requires an acid pH to form.
The minerals precipitate out of the urine and form crystals which then attract more of the mineral to them making a stone.
Newfoundlands have a special inherited disorder that is different called Cystinuria
http://vetprof.com/clientinfo/newf-cystinuria.html
Cystinuria in dogs is generally treated with compounds that bind cystine and prevent crystal formation. The two most common drugs of choice are 2-mercaptopropionylglycine (MPG)and D-penicillamine. Newfs may need a larger dose of MPG than other breeds to help resolve this problem.
Otherwise you are looking at repeat surgery to resolve continual stone formation.