Why should a soccer player take care for his teeths .. is there a relation between soccer injuries and dental health ?

Yes: The relationship though is between dental health and playing soccer. I've seen many teeth injured during soccer . The more serious concern is concussions. It has been shown that wearing a properly fitted mouthguard reduces the risk of injury and concussion dramatically.

Soccer: All people should take care of their teeth. The specific relation i see between soccer and tooth care is one common with any contact sport, protecting your teeth from trauma (as well as your jaw and mouth in general). Using your head, or having a fast moving object coming at your head could lead to trauma. Always wear a mouthguard, a custom one is better but a generic is better than nothing.

Avoid tooth injuries: Soccer being a rough sport has the potential for tooth injuries. It is advisable to wear a mouth guard to protect the teeth from trauma.

Trauma: Any dentist in practice more than a short time can tell you "war stories" about injuries to teeth, jaws, and brain from playing contact sports and not wearing mouth guard. Angular fractures of upper front teeth (sportsmen's fractures) are common, as are loose exfoliated, or displaced teeth. Mouth guards help prevent concussion and jaw fracture. Better a live chicken than a dead duck.