Temporary tooth remaining after eruption of permanent tooth, canines and incisors most commonly affected .
If not removed, affect direction of eruption of permanent tooth causing malocclusions and gingivitis.
Mandibular canines : permanent tooth erupts medial to temporary - retention of temporary mandibular canines forces permanent tooth to be lingually displaced causing pain on closure of mouth as tooth impinges on hard palate/gingivae/other teeth.
Maxillary canines : permanent tooth erupts rostral to temporary, retention of temporary maxillary canines forces permanent tooth into space for mandibular canine when mouth closed. May result in:
Impaction of mandibular or maxillary canine.
Maxillary lateral incisor and/or canine pushed laterally by mandibular canine (often with impaction of mandibular canine).
Mandibular canine pushed medial relative to maxillary canine impinging on hard palate.
Incisors : permanent tooth erupts caudal to temporary - retention may affect scissor bite resulting in local soft tissue trauma.
Extraction of temporary tooth . Take care not to disturb permanent tooth and not to fracture temporary tooth root.
Do not put elevator between temporary and permanent teeth but loosen temporary tooth on other 3 sides: do not use dental forceps: use sharp elevator, luxator, size 11/15 scalpel blade to cut periodontal ligament, be very patient.
If tooth root fractures; less damaging to remain in situ, monitor with radiograph after 2 months to assess situation (absorption).
Subsequent management
Monitoring
Check direction of eruption of permanent tooth; if deviating from normal encourage better direction of eruption by digital pressure <2 hours daily.
malocclusion 
Take care not to disturb permanent tooth and not to fracture temporary tooth root.